Text

Technology Evaluation of the Pilot Permeable Treatment Wall and Recommended Path Forward
	ML11214A189
Person / Time
Site:	West Valley Demonstration Project, P00M-032
Issue date:	08/02/2011
From:	; West Valley Nuclear Services Co
To:	; NRC/FSME
References
	Download: ML11214A189 (234)
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TECHNOLOGY EVALUATION OF THE PILOT PERMEABLE TREATMENT WALL AND RECOMMENDED PATH FORWARD Prepared by:

West Valley Nuclear Services West Valley Demonstration Project

TABLE OF CONTENTS Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii 1.0 Introduction - Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.0 Technical Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1 Reactive Barrier Technology Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.2 Technology Application at WVDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.3 General Conceptual Hydrogeologic and Sr-90 Distribution Model of the North Plateau . 5 3.0 Construction Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1 PTW Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 As-Built Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.0 Hydraulic Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1 Hydrogeologic Conditions at the North Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2 Distribution of Hydraulic Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.3 Pre-Construction Groundwater Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.4 Post-Construction Groundwater Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.5 PTW Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.6 Post-Construction Distribution of Sr-90 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.7 Hydrogeologic and Hydraulic Conditions Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.0 Performance Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.1 Smearing of PTW Sidewalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.2 Consolidation of Clinoptilolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.3 Crushing of Clinoptilolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.4 Clinoptilolite Plugging Void Spaces in Roundstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.5 Fines Movement as PTW Filled with Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.6 Groundwater Flow Under PTW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.7 Potential Surface Influences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 5.8 Summary of Performance Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.0 Lessons Learned . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.0 Proposed Data Collection and Options for Pilot PTW Modifications . . . . . . . . . . . . . . . . . . . . . 28 7.1 Data Collection and Modeling Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 7.2 Modification Options and Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 7.2.1 Option 1 - No Modifications of the Pilot PTW . . . . . . . . . . . . . . . . . . . . . . . . . . 30 7.2.2 Option 2 - Install Lateral Hydraulic Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 7.2.3 Option 3 - Install Extension to PTW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 7.2.4 Option 4 - Install a New Pilot PTW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 i

TABLE OF CONTENTS (continued) 8.0 Proposed Path Forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 8.1 Pilot PTW Path Forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 8.2 Full-Scale PTW Path Forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 9.0 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 LIST OF FIGURES Figure 1. WVDP Site Basemap Showing Major Facilities Figure 2. Site-Wide Gross Beta Distribution Map and Sr-90 Distribution Near the North Plateau Remediation Area Figure 3. Geologic Boundaries on the North Plateau of the WVDP Figure 4. North Plateau Groundwater Remediation Facilities: Monitoring Locations, Topography and Groundwater Elevations Figure 5. Regional Groundwater Elevations Figure 6. Monitoring Locations Near the Permeable Treatment Wall Figure 7. Drawdown Distribution from the January 2000 Pumping of WP-25 Figure 8. Drawdown Distribution from the January 2001 One-week Development Program LIST OF APPENDICES Appendix 1 - Groundwater Elevation Data Appendix 2 - Groundwater Sampling Results Appendix 3 - Well WP-25 Pumping Test Data Appendix 4 - PTW Development Data, Data & Graphs From PTW Development Activities Appendix 5 hour5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months PTW Pumping Test Data Appendix 6 hour6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months PTW Pumping Test Data Appendix 7 week PTW Pumping Test Data Appendix 8 - PTW Water Level Hydrographs Showing Cap Infiltration Characteristics Appendix 9 - PTW Development Results Summary Data Appendix 10- Geomatrix Report: Pilot Permeable Treatment Wall Hydraulic Evaluation Report Appendix 11 - Geomatrix Report: Pilot Permeable Treatment Wall Hydraulic Engineering Report Appendix 12 - Geomatrix Report: Pilot Permeable Treatment Wall Modification Options Report Appendix 13 - Cost Estimate for Focused Data Collection and Analysis Program Appendix 14 - Path Forward Project Schedule ii

Pilot PTW Evaluation Report Executive Summary The purpose of this technology evaluation report is to evaluate and recommend a path forward for the Pilot Permeable Treatment Wall (PTW) located on the North Plateau at the West Valley Demonstration Project (WVDP). A pilot scale PTW was installed on the 2nd lobe of a Sr-90 plume under the North Plateau in the Fall of 1999. The 30 ft. pilot PTW was deployed at a location on the North Plateau where the Sr-90 plume narrows near its leading edge.

A fairly simple design configuration was used to install the pilot PTW using a sheet pile cofferdam setup and conventional construction equipment and methods. The cofferdam design would allow internal soil to be excavated and the void backfilled with the reactive media, clinoptilolite, after which the cofferdam would be removed and the PTW become operational.

Hydraulic monitoring of the pilot PTW is performed using a series of well points, monitoring wells, and piezometers, most of which were installed after PTW construction. Post-PTW monitoring indicates that unique hydraulic conditions may be preventing groundwater flow through the PTW and associated treatment of contaminated groundwater. The conclusion regarding the hydraulic conditions may be related to the complex hydrogeology and the design and construction at the pilot PTW. Possible explanation as follows:

Sheet pile extraction during PTW construction produced commingled clinoptilolite and roundstone and a zone of fine clinoptilolite particles around the north and east edges causing a discontinuous skin of fine zeolitic material and diverted groundwater flow.

Hydraulic conductivity of the clinoptilolite media following construction may be up to two or three orders of magnitude less than that for the clinoptilolite prior to placement, thus causing flow path diversion.

The PTW does not appear to be fully penetrating through the upper water bearing zone causing possible underflow in its central and eastern portions.

A highly heterogeneous and anisotropic aquifer of fine and course sediments may be causing diverted flow.

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Pilot PTW Evaluation Report Lessons learned were evaluated and focused on the engineering detail of the PTW design and installation.

These lessons learned will assist in the eventual development of engineering alternatives to enhance the performance of the pilot PTW and future deployments of PTW technology. Lessons learned are discussed in detail in Section 6.0.

Four options for modification are presented in Section 7.2; no modification, two engineering modifications (Installation of lateral barriers or installation of an extension to the PTW), and one option that comprises of a complete rebuild of the pilot PTW.

Based on the evaluation of information prepared by WVNS and Geomatrix Consultants, WVNS is recommending Option 2, Installation of Lateral Hydraulic Barriers. However, prior to implementing this option or any others, it will be very important to collect additional characterization data to integrate into the development of a three-dimensional flow model in order to optimize and ensure the effectiveness of the proposed modifications. Therefore as a first step further characterization and assessment of the local geology and hydrogeology near the pilot PTW, is needed to decrease the degree of uncertainty with the pilot PTW performance issues and to increase the potential to select and implement an effective engineering solution.

Secondly, it is recommended that 1st lobe preliminary design proceed. FY2001 preliminary design activities begin with selection of wall location then proceed with design and implementation of a comprehensive soil and groundwater characterization program. Activities will continue with evaluation of geological and hydrogeological data. Once the data is throughly analyzed, a conceptual design may commence. At completion of conceptual design, a decision will be made as to whether full-scale deployment is feasible on the 1st lobe.

By completion of the planned path forward, there will be increased confidence both that a reliable solution to the pilots performance can be selected and further PTW design and installations can be successfully applied at the WVDP.

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Pilot PTW Evaluation Report 1.0 Introduction - Summary The West Valley Demonstration Project (WVDP) site is a 220-acre parcel located in a rural area within the Allegheny section of the Appalachian Plateau. The site is bordered on the north, south, and east by two creeks that generally divide it into two upland subareas referred to as the north plateau and south plateau (Fig. 1). The north plateau contains a 1960's-era commercially unviable spent nuclear fuel reprocessing plant that is now governed under the control of the United States Department of Energy (DOE) pursuant to the 1980 West Valley Demonstration Project Act.

Radioactive contamination that leaked from a main plant system in the late 1960's produced a strontium-90 (Sr-90) contaminated groundwater plume that now extends north-northeasterly from beneath the former reprocessing plant across the north plateau. An extensive subsurface investigation conducted in 1994 identified the primary source of Sr-90 activity and defined the horizontal and vertical extent of contamination in the soil and groundwater. Sampling results also showed that the Sr-90 migrates via preferential pathways governed by coarse textured sedimentary layers or zones. Data from subsurface sampling programs in 1995, 1997, and 1998 as well as more recent data from the quarterly groundwater monitoring program and north plateau operational locations all indicate that the Sr-90 plume is migrating toward a drainage ditch north of the CDDL and the main CDDL area (Fig. 2).

A groundwater recovery and ion exchange treatment system was installed as an initial mitigative effort in November 1995 across a preferential pathway near the western or 1st lobe of the plumes leading edge (Fig. 4). The continuous tracking and evaluation of groundwater levels and chemical data during system operation indicates it effectively mitigates Sr-90 transport to the surface near this location. However, maintaining optimum capture is both challenging and resource intensive.

The subsurface investigations that were conducted in 1994 and 1997 further characterized the lateral and vertical distribution of radiological contamination near the leading edge of the 1st lobe and the eastern or 2nd lobe of the plume. The resulting geologic and geochemical data analyses underwent an external technical peer review (Berkey [1997]) in order to evaluate mitigation technologies for Sr-90 on the north plateau. Recommendations developed by the two review teams stated that future tasks should focus on evaluating low maintenance and low cost groundwater remediation technologies to optimize Sr-90 mitigation. Following these recommendations, extensive research into alternative technologies indicated that an in-situ permeable reactive barrier (herein referred to as a permeable treatment wall or PTW) would best suit site needs for long-term, low-cost, low-maintenance remediation of transportive subsurface contamination.

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Pilot PTW Evaluation Report 2.0 Technical Evaluation 2.1 Reactive Barrier Technology Evaluation Pump and treat systems and permeable reactive barriers were evaluated as innovative technology because of their extensive use at groundwater cleanup projects and as a passive, low-cost way to reduce contamination. Conceptual engineering designs for a PTW and a pump and treat system on the north plateau were performed in 1994 to determine which could be carried out quickly at a reasonable cost. The PTW designs were technically feasible but the initial costs were high as compared to a pump and treat system.

Consequently, a pump and treat system known as the North Plateau Groundwater Recovery System (NPGRS) was installed at the leading edge of the 1st Lobe and has been operational since November 1995 (Fig. 4).

Since the NPGRS was considered a temporary effort, a subsequent feasibility study was initiated to identify and evaluate long-term groundwater remediation programs. Studies at Brookhaven National Laboratories (BNL) (Aloysius, D. L. [1995]) used groundwater and soils from the north plateau to identify geochemical factors that influence Sr-90 sorption to various sorbent media that may be used in a subsurface barrier.

The geochemical studies and modeling indicated that clinoptilolite should be evaluated via bench scale testing and additional computer modeling. Subsequent testing results showed that clinoptilolite could reduce Sr-90 concentrations on the north plateau to 1,000 pCi/L in about ten years using a three-foot thick barrier. However the 1995-era time and cost limitations indicated that pump and treat technology still remained the preferred interim mitigative technology for the north plateau.

The 1997 Technical Peer Review (Berkey [1997]) determined that pump and treat technology was a valuable interim measure for plume control but further investigations indicated that a permeable reactive barrier would be an efficient alternative application at the WVDP.

Beginning in April 1998, several evaluations were conducted to support PTW implementation including additional geochemical analyses, potential conceptual designs, and suitable wall locations (Berkey [1999]). The geochemical analyses indicated that additional laboratory studies would significantly enhance the confidence associated with predictions of barrier performance.

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Pilot PTW Evaluation Report 2.2 Technology Application at WVDP Batch and column tests performed by the State University of New York at Buffalo (UB) in April 1999 positively quantified Sr sorption by clinoptilolite (CH 14 x 50). Preliminary results suggested that a barrier life of about 36 years could be achieved with a barrier of clinoptilolite (Kd of 2,350 ml/g) using a cofferdam installation design. These geochemical data and additional recommendations from a second Technical Peer Review (Berkey

[1999]) indicated that a pilot-scale wall in the 2nd lobe should be installed. The conceptual PTW design involved the construction of a simple cofferdam within the 2nd lobe of the plume at a location with high Sr-90 concentrations and easy access (e.g., no adjacent buildings, obstructions, underground power lines, etc.)

The chosen reactive media, clinoptilolite, is a zeolite mineral with a solid solution formula of [(Ca, Mg, Na2, K2)(Al2Si10O24.8H20)] (Warner, 1986), which has been shown to passively and effectively reduce the concentration of Sr-90 in groundwater. This alternative remediation technology and reactive media is capable of effectively mitigating further migration of Sr-90 in groundwater over a large portion of the north plateau.

The intent of the pilot PTW installation was to assess a small-scale field version of a full-scale remedy and to define those design parameters that must be quantified to ensure successful and cost-effective implementation of an innovative full-scale remedy of a Sr-90 adsorbing zeolite in a complex hydrogeologic environment. The full-scale deployment of this technology requires a step-wise approach to determine the nature and extent of technical, regulatory, and stakeholder issues associated with deployment.

Although PTW technology has been tested at more than 40 sites in North America, it remains an innovative technology when applied to complex hydrogeologic conditions, radioactive contaminants, variable groundwater chemistry, available construction methods, and especially with clinoptilolite as the reactive medium. The PTW must be both chemically successful at remediating contaminated groundwater and function properly from a hydraulic perspective. This pilot PTW provides site-specific information imperative to developing a competent full-scale system that meets its design objectives with the greatest certainty.

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Pilot PTW Evaluation Report The testing and monitoring program for the pilot PTW was designed to determine if the data quality objectives (DQOs) prepared to evaluate pilot PTW operation (WVDP-350) were being met. The primary criteria for assessing wall operation were to establish groundwater flow through the wall and sufficient reduction in Sr-90 activities by the clinoptilolite treatment medium. Specific assessment goals were to:

1) Determine if groundwater flows through the PTW and is not backed up or diverted around the PTW;

2) Determine if Sr-90 activity in groundwater is reduced as the groundwater passes through the PTW; and

3) Compare Sr-90 activities up gradient and downgradient of the PTW. (Sr-90 activities immediately downgradient of the pilot PTW can be expected to decrease over time.)

An initial six-month assessment used water level data from WPs 16, 25, 26 and 27 and monitoring well 8603 before and during construction, and then water levels, Sr-90, and inorganic analyte data from an additional 13 post-construction well points. These data are graphically presented in Appendix 1 and 2.

Data from the initial assessment was again technical peer reviewed to evaluate plume mitigation and confirm initial assessment results. Common opinions reached by these reviewers include the following:

C There are sufficient positive indications that the clinoptilolite is effective in removing the Sr-90;

Placement of a PTW into a natural groundwater flow system can easily disrupt the flow system;

Problems related to the hydraulic performance of PTWs are common but under-reported;

The PTW monitoring system was well planned and allows for a detailed evaluation of the flow regime in the immediate vicinity of the pilot PTW; 4 of 34

Pilot PTW Evaluation Report

Other PTW installations have identified possible zones of reduced permeability, thus it is likely that a skin effect may be present around the pilot wall; and

Early performance of the wall indicates that there is some hydraulic connectivity between all monitoring points, suggesting that the skin effect may be more permeable at some locations or not present on all sides of the treatment wall.

2.3 General Conceptual Hydrogeologic and Sr-90 Distribution Model of the North Plateau The unconfined and semi-confined groundwater flow conditions in the PTW area prior to construction were influenced by both laterally and vertically varying hydraulic conductivity and undulations in the surface of the underlying low permeability sediments, which act as a basal hydraulic barrier to the flow system. The regional groundwater flow direction was toward the north-northeast, as determined by WVDP groundwater monitoring program data (Fig. 5).

The leading edge of the Sr-90 plume bifurcates around a topographically significant erosional remnant of lower conductivity clay and silt that is identified in the borings logs for well 0115 and B-94-13; this bifurcation is exhibited in Figure 2 where the <1,000 pCi/L zone separates the plume. The thin section of sand and gravel that overlies this remnant thickens to the west and east, thereby providing flow paths of least resistance around the clay and silt unit into thicker water-bearing zones, where the Sr-90 becomes more highly concentrated in discrete (preferred) zones of locally higher hydraulic conductivity. (See Figures 2.1 and 2.2 in Appendix 10.) Although potentiometric surfaces do not show evidence of mounding that would bifurcate the plume, the hydrograph for well 116 has a low fluctuation and thus lower local recharge, which is indicative of a hydraulically tighter media at well 116.

The pilot PTW was installed at the western edge of the eastern lobe of Sr-90 near the 10,000 pCi/L contour, which was verified by data from pre-construction well points WP-25, WP-26, and WP-27; Sr-90 varied from 500 pCi/L in the west at WP-25 to a high value of 40,000 pCi/L in the east at WP-26. These well points are all screened between 7 and 22 feet below ground surface (bgs) and traverse the hydrostratigraphic layers near the PTW.

Previous Geoprobe boring data and field gamma scans of soil collected during the installation of the PTW dewatering wells suggest that the higher activity groundwater exists in the lower half (i.e., depths greater than about 15 feet bgs) of this shallow water bearing system.

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Pilot PTW Evaluation Report 3.0 Construction Methodology 3.1 PTW Design The pilot PTW was designed as a passive groundwater treatment system that does not rely on collecting, diverting, channeling, or pumping groundwater to a media bed during operation. This guideline led to a simple continuous reactive barrier design configuration that could be installed safely and easily at the identified location in the 2nd lobe of the Sr-90 plume. The cofferdam construction design would allow internal soil to be excavated and the void backfilled with the reactive clinoptilolite, after which the cofferdam would be removed and the PTW become operational. Features and design specifications for the pilot PTW are as follows:

C Rectangular cofferdam: The cofferdam was designed as a rectangular 30.5 ft long (east to west), 7-ft wide (north to south), 26-ft deep cofferdam.

C Cofferdam construction materials: 42 Arbed AZ48 sheet piles; Adeka Ultraseal

50A (for application to sheet pile interlock); two W36 x 182 wales, two W18 x 86 wales; four pumps, 2-inch polyethylene pipe, 1000-gallon hold tank and sump pump for dewatering, treatment and discharge; piping for drain-line and riser-pump assembly.

C Basic installation method: Dewatering wells and monitoring well points pre-installed in excavation area; piles driven around excavation area using vibratory hammer to approximate contact with Lavery till at 28-ft below original ground surface/1356-ft above mean sea level (msl), to be driven an additional 10-feet into the till (1346 msl) or to a lesser depth if difficulty encountered, cutting off the top of sheet piles to uniform height as needed; cofferdam support provided by a single layer of external bracing formed by placing longer wales along cofferdam length with restraint brackets mounted on 7'7" centers and shorter wales along cofferdam width so that wales are installed horizontally around outer perimeter of cofferdam at 1384-ft msl, (horizontal axis at 1382-ft msl.)

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Pilot PTW Evaluation Report C Excavation and backfill method: After structural elements are set in place, soil inside cofferdam dewatered using pumps installed in wells, placed at equal intervals directly beneath alignment of PTW; groundwater pumped from wells through 2-inch pipe to hold tank for treatment (pumps activated by pressure switch designed to engage when groundwater level in well 12-inches above pump); sump used to discharge water from hold tank to Lagoon 2; soils excavated and cofferdam subsequently backfilled with 5.5-ft of unmixed 100% clinoptilolite (CH 14 x 50) and 1.5-ft with pea gravel placed in an area separated by moveable partition at south face of excavated area; horizontal drain-line placed along bottom of gravel section and connected to vertical riser-pump assembly.

C Surface completion method: After sheet piles extracted, surface area to be created over PTW with 1.4-ft to 1.9-ft thickness of clay fill as needed to match existing grades at the edge of the excavation (1384.6 msl), mounding fill about 6-inches higher in the middle of the excavation (1385.1 msl), with 3.5-inch diameter bumper posts placed at four corners of the PTW for demarcation/protection.

See Appendix 12 for a full description of construction methods.

3.2 As-Built Construction The following as-built analysis of the cofferdam construction, excavation, backfilling, and surface completion relied on the following as-built construction drawings:

C North Plateau Permeable Treatment Wall, Drawing no. 900D-7867, sheets 1 through 8 of 8, C North Plateau Treatment Wall Cofferdam, Drawing no. 900D-7857, sheets 1 through 4 of 4, and C Site, North Plateau Area, Topography and Underground Piping, Drawing no.

900D-6743, sheet 1 of 1.

The pilot PTW installed on the north plateau is an approximate 100 ft by 100 ft area and northwest of Lagoons 4 and 5, where the ground surface generally slopes downward at about 3 percent from south to north (Fig. 4).

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Pilot PTW Evaluation Report C Construction preparation: 100-ft by 100-ft area around PTW prepared as work surface (hardstand) by laying down 7-inch thick layer of crush stone over geotextile; dewatering wells installed and piped to hold tank; two inclinometers placed about 8-ft from where sheet piles were to be driven on north and south sides of the cofferdam to monitor movement during excavation and backfilling; electrical line installed in conduit run through trench about 2-ft wide by 2-ft deep to support pumping operations; hardstand layer scraped and geotextile cutback to allow for sheet pile installation.

C Cofferdam construction: Cofferdam laid-out and sheet piles driven with vibratory hammer to approximate top of till at 1358 msl; sheet piles driven into till with impact hammer (12-ft); hardstand and native soil excavated around outside of sheet piles and geotextile cut back to allow for installation of external wale system; internal soils excavated and dewatered to about 15-ft below ground surface using well pumping system; sump pumps dropped into area to continue dewatering during excavation as dewatering pumps were removed; divider system installed within cofferdam to maintain separation between clinoptilolite and 1-inch roundstone (pea gravel); 6-inch diameter perforated PVC pipe placed along abase of excavation within roundstone for drainage with 10-inch PVC riser pipe attached at lower east end of drainage pipe with both pipes wrapped in geotextile; cofferdam backfilled by emptying supersacks of clinoptilolite into dry excavation from surface; 1-inch roundstone placed in 1.5-ft separated area using PVC elephant trunk; distance between clinoptilolite and roundstone backfill maintained at 1-ft maximum during backfilling by observation, backfilling to approximately 1382 msl before removing divider system; clinoptilolite and roundstone brought to design elevation of 1383.2 msl and wales removed; zone outside cofferdam once occupied by wales backfilled with previously excavated material.

C Sheet pile removal and surface completion: Geotextile underneath hardstand cut back until excavation sidewalls visible; starting from west end of cofferdam, sheet piles were withdrawn from ground using vibratory hammer, scraping off any material stuck to sheet piles as needed; settling of clinoptilolite recorded at about 4-ft after last sheet pile removed, with inclinometers indicating lateral movement into the excavation of about 7-inches on the south side, 3 inches on the north side; clinoptilolite added to existing material to bring it to grade at 1383.2 msl, with fill mounded in the middle to 1384.6 msl; 1-inch thick layer of granular bentonite (Volclay CG-50) placed over excavated area; hardstand stone raked over filled area around the PTW to provide working surface; four 7-ft by 3.5-ft round bumper posts 8 of 34

Pilot PTW Evaluation Report placed at each corner of PTW perimeter (moving each post from position where it was originally placed during backfilling).

See Appendix 12 for a more detailed discussion of as-built construction.

4.0 Hydraulic Evaluation This section describes observations regarding the ground water hydraulics and hydrogeologic conditions near the pilot PTW. Additional details associated with this evaluation are presented in Appendix 11, Pilot Permeable Treatment Wall Hydraulic Evaluation Report, by Geomatrix Consultants.

Hydraulic monitoring of the pilot PTW is performed using a series of well points, monitoring wells, and piezometers, most of which were installed after PTW construction (Fig. 6).

Construction details of these monitoring locations are listed in Table 2 of Appendix 11.

Groundwater elevation contour maps representing conditions during various stages of the pilot test are shown in Figure 3.3 in Appendix 11. Hydrographs for select monitoring points in the PTW area are shown in Appendix 1 and are discussed in the following sections.

4.1 Hydrogeologic Conditions at the North Plateau Post-PTW-installation monitoring indicates that a unique hydraulic condition may be preventing groundwater flow through the PTW and associated treatment of contaminated groundwater. Several PTW development (pumping) efforts and expert review of the hydrogeologic and Sr-90 data determined potential causes of this flow restriction, which are discussed presently and in Section 5.0.

The interpretation of regional hydrostratigraphy and groundwater flow conditions was derived from borehole data collected during various characterization activities performed over the last several years including geotechnical data collected during the PTW design activities, and assessment data collected after PTW installation. These data are presented on a Sr-90 distribution map, a potentiometric surface map, and in the hydrostratigraphic cross-sections shown in Figures 2 and 4, and in Appendix 11, Figures 2.1, 2.2, 2.3, 2.4, and 3.3.

Two distinct hydrostratigraphic units exist beneath the north plateau:

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Pilot PTW Evaluation Report C The Shallow Water-Bearing Zone (SWBZ), consisting of alluvial sand and gravel (AS&G), and the Slackwater Sequence (SWS); and C A basal confining aquitard (or low permeability zone) consisting of lacustrine clay and silt, and Lavery Till.

The SWBZ is a heterogeneous and anisotropic unit consisting of the both laterally continuous and discontinuous layers in both the AS&G and the SWS. The cross-section in Figure 2.2 of Appendix 11 shows unconfined conditions generally appear to exist in the upper portion of the SWBZ within the AS&G. The layers of clay to silty clay and silty gravel present within the SWS likely produce semi-confined conditions within the lower portion of the SWBZ.

The SWBZ near the NPGRS is composed only of the coarse-grained, unconfined deposits that extend from grade to the basal confining unit. The thickness of the AS&G unit in this area varies from 5 to 15 feet, depending on the topography of the basal layer; the water table is approximately five feet below grade.

The cross-section A-A in Figure 2.2 of Appendix 11 traverses the PTW and NPGRS areas.

It shows the lower-most basal unit to be the topographically variable Lavery Till, which is a laterally continuous, stiff, and unsorted sequence of silty clay to clayey silt and a hydraulic conductivity of less than 1x10-7cm/s.

A thin sequence of lacustrine clay with silt apparently overlies the Lavery Till in the study area; this unit is thickest in the boring log for well 0115 and boring B-94-11, where it was previously interpreted as Lavery Till. However, the alternating sequence of clayey silt and silty clay is indicative of a lacustrine depositional environment. The hydraulic conductivity of the clay with silt unit was found to be 4x10-8 cm/s by slug testing performed on well 0115, which is screened entirely in the unit. Since the Lavery Till is a silty clay that likely was derived from proglacial lacustrine deposits, such actual lacustrine layers could have been easily mistaken as Lavery Till, especially in field samples.

In the PTW area, the lacustrine clay with silt unit is overlain by the SWS, a thick sequence of water-lain deposits of alternating thin, well-sorted beds of loose silty gravel and fine sandy silt that fills a wide, channel-like depression as shown on Figure 3. Cross-section C-C in Figure 2.4 of Appendix 11 shows how the interbeds of coarse and fine-grained sediments may cause confining groundwater conditions to exist within the water-bearing deposits of the SWS. Variations in the stratigraphy (i.e., thickness and lateral continuity of 10 of 34

Pilot PTW Evaluation Report water-bearing deposits) may significantly change the local hydraulic gradient and flow directions, which cannot be accounted for on site-wide maps.

The SWS near the PTW is overlain by the AS&G unit that exhibits a finer sequence of silt and sand with less gravel and less stratification than the underlying SWS. The AS&G coarsens to the west towards the NPGRS, showing lesser fine-grained material, and is described as an alluvial gravel and fine sand on cross-section A-A (Fig. 2.2 in Appendix 11).

The uppermost stratigraphic unit near the PTW is a silty clay fill that overlies the locally finer grained AS&G. Data on cross-sections A-A and C-C indicate that the fill is consistently 2 to 3 feet thick and may serve as a confining layer to the underlying water-bearing units. Such semi-confined conditions are likely to be spatially and temporally variable.

The eastern lobe of the Sr-90 plume is apparently subjected to a steeper apparent hydraulic gradient toward well 0105, causing a slightly eastward dispersion of the lobe. The steep hydraulic gradient between wells 8603 and WP-11 (illustrated in Fig. 5) may be coincident with the transition between the semi-confined and unconfined conditions. An evaluation of hydrographs and precipitation data did not reveal consistent characteristics of a confined system, so a confident surface delineation of this clay fill is not possible with current data.

In addition, stratigraphic data forming cross-section D-D indicates that the central and eastern ends of the pilot PTW may not penetrate to the Lavery Till, but may hang in the SWS above the top of the Lavery Till. Additional details regarding the hydrostratigraphy near the pilot PTW can be found in Appendix 11.

4.2 Distribution of Hydraulic Conductivity The variable hydrostratigraphy and soil texture in the SWBZ produces hydraulic conductivity values in the 10-3 cm/s magnitude in the western lobe of the plume near the NPGRS where the AS&G is coarser-grained. As the grain size composition of the AS&G becomes finer in an eastward direction toward the PTW, conductivity values in the AS&G decrease. Well 0116 is screened within this finer facies and yields a slug-test-based hydraulic conductivity value of 6x10-5 cm/s.

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Pilot PTW Evaluation Report Near the PTW, the SWBZ consists of a finer AS&G and the alternating SWS that produces hydraulic conductivity values between 1x10-3 to 1x10-4 cm/s. The fully penetrating wells and piezometers installed near the PTW yield average hydraulic conductivity values. Thus, higher conductivity is possible in discrete, continuous sand and gravel layers associated with the SWS, which may mask the lower hydraulic conductivity in the locally finer AS&G. Since the AS&G near the PTW may have a lower hydraulic conductivity than the underlying SWS, the AS&G may also act as a confining bed over the SWS.

The hydraulic conductivity values obtained from the slug testing of wells in and near the PTW are shown in Figure 3.10 of Appendix 11. Slug tests commonly are less reliable for engineering-scale quantitative assessments because the results may be highly dependent on well construction (i.e. sand pack, drilling skin, and development effort). However, the resulting hydraulic conductivity data still can provide qualitative information useful for assessing approximate conditions. Slug test results outside the pilot PTW range from 6.6x10-5 cm/s to 6.0x10-3 cm/s. Hydraulic conductivity measured within the roundstone of the PTW ranged from 1.5x10-4 cm/s to 2x10-2 cm/s. This difference may be based on well point construction and/or variability of hydraulic conductivity in the roundstone. All slug test results obtained within the clinoptilolite portion of the PTW are in the 1x10-3 cm/s range.

4.3 Pre-Construction Groundwater Conditions The regional groundwater flow patterns in the SWBZ prior to PTW installation were evaluated under a period of low groundwater elevation (August 1998) and high groundwater elevation (February 1997).

The groundwater flow pattern in August 1998 (Fig. 2.6 in Appendix 11) indicated that groundwater flows from southwest of the vitrification test facility generally towards the north-northeast. A uniform hydraulic gradient existed throughout much of the NPGRS/PTW area. The August 1998 groundwater distribution suggests that the groundwater flow direction before construction of the PTW was virtually perpendicular to the current long-axis of the PTW.

The groundwater flow pattern in February 1997 (Fig. 2.7 in Appendix 11) generally resembles that of the low groundwater flow pattern. The groundwater flow direction was nearly perpendicular to the current PTW during this high groundwater condition.

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Pilot PTW Evaluation Report Pre-construction (July 1999) groundwater levels near the PTW from well points WP-25, WP-26 and WP-27 generally indicate that the groundwater was approximately 6.5 to 6.7 feet bgs and had a fairly flat gradient with a slight eastward groundwater flow component near the PTW. This departs from the regional northeastward groundwater flow direction for that area (Fig. 3.3 in Appendix 11). The absence of lithologic information from these monitoring locations limits the ability to determine if the groundwater measurements represent the same flow or a subflow zone.

4.4 Post-Construction Groundwater Conditions The regional groundwater flow pattern after PTW construction is generally similar to historical patterns except immediately near the PTW, where the flow geometry changed and groundwater now mounds south and west of the wall and within the wall, with an apparent flattening of the horizontal hydraulic gradient to the northeast of the PTW. Unlike pre-PTW-construction flow conditions, the overall flow direction is now due eastward near the PTW, generally parallel to its long axis. (See Figures 2.8 and 2.9 in Appendix 11.)

Post-construction groundwater data from twenty-six well points (WP-25 through WP-40 and PZ-01 through PZ-10) allow detailed local analysis of the flow regime. A comparison of the pre- and post-construction hydraulic head data (Fig. 3.3 in Appendix 11) and hydrographs from July 1999 to February 2001 (Appendix 1) indicate the following observations:

C Water levels measured from wells located in the PTW are consistently higher than measurements from well points screened in the native sediments with the exception of water levels measured in WP-25; C The groundwater elevations measured from well points located inside the PTW are practically identical, indicating a near zero horizontal hydraulic gradient; Additional detailed observations are presented in Appendix 11.

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Pilot PTW Evaluation Report 4.5 PTW Development The 6-inch lateral pipe and connected 10-inch riser in the roundstone zone were subjected to pumping in July, August, and September 2000 and January 2001. The development efforts were intended to: reduce groundwater mounding in the PTW; minimize preferential pathways around, rather than through the wall; mobilize and remove any low permeability skin that may have developed due to PTW emplacement activities; to qualitatively evaluate hydraulic response in the PTW area during longer duration pumping and; to increase the hydraulic conductivity of the zeolite, roundstone, and adjacent soil; This development has decreased the horizontal hydraulic gradient between the PTW and native soil, but has not eliminated the mounding of groundwater in and around the wall.

Prior to PTW development, several mini-pump tests were performed at WP-25 in January and April 2000 to generate a hydraulic pressure response that could be used to evaluate the presence of a lower hydraulic conductivity skin along the interface of the PTW with the native aquifer. Figure 7 shows the final drawdown distribution produced by pumping WP-25 in January 2000. Hydrographs in Appendix 3 show the delayed drawdown response in WP-29 located inside the PTW, which strongly indicates the importance of storage (drainage from specific yield) in the unconfined or less confined PTW. WP-27 on the opposite side of the PTW had the lowest response to pumping, indicating that PTW storage and the low hydraulic conductivity boundary at the PTW-native soil interface is minimizing hydraulic connection.

Figure 8 shows the final drawdown values for the January 2001 development effort, which is considered to be a comprehensive effect of the seven efforts, which are graphically presented in Appendices 4 through 7 and 9.

The drawdown of about 5 ft at WP-29 indicates that the PTW riser pipe and the PTW media is in good hydraulic connection (i.e., the PTW responds like a large rectangular well with uniform drawdown). The drawdown responses indicate that the PTW is best connected to the ambient soil at the western end of the PTW and apparently also moderately connected to the soil in the eastern third, but not at the eastern end, which appears to be a boundary. The drawdown data suggest that lower hydraulic conductivity zones especially exist at the PTW-soil boundary along the east end and north edge, as well as in the western third of the PTW. The possibility that a singular transmissive zone is responsible for a large amount of inflow to the PTW is also possible. The decrease in degree of confinement between the native sediments and the PTW may partially account for the mounded head observed in the PTW during periods of transient head fluctuation.

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Pilot PTW Evaluation Report The February 2000 and 2001 hydrographs and precipitation data plot presented in Appendix 8 indicate that surface-source inflow to the PTW is subdued by the installation of the surface drain in 2001; WP-29 heads that did not exceed WP-25 heads, which had occurred in February 2000. However, the head increases within the PTW are still greater than outside the PTW, suggesting that: (1) surface water infiltration still influences water levels within the PTW and/or (2) pressure response differences between the semi-confined aquifer system and the unconfined PTW system give rise to temporal mounding. These data suggest that both the PTW development and the surface water drain have been effective in reducing, but not completely eliminating hydraulic mounding caused by surface infiltration into the PTW.

The difference in groundwater elevations between well point WP-29 inside the PTW and other external well points both before and after the PTW development and after the surface water drain was installed is shown as follows:

Groundwater Elevation Differences (feet)

North South East West WP-29-WP-30 WP-29-WP-34 WP-29-WP-40 WP-29WP-28 WP-29WP-36 WP-29-WP-27 WP-29-WP-25 Before Development 1.44 1.53 1.41 0.72 1.20 1.99 -0.57 After Development, 0.85 0.83 0.85 -0.03 0.41 1.18 -0.84 Before Drain Installation After Development and 0.83 0.81 0.83 -0.02 0.37 1.14 -0.81 Drain Installation Although the groundwater elevation inside the PTW remains consistently higher than ambient elevations (except for the west end), the decreases in head differences caused by development and the surface drain installation indicates hydraulic connection is improving.

Appendix 9 provides comparative data generally indicating that the hydraulic response of the ambient system to PTW development is improving with each successive effort.

4.6 Post-Construction Distribution of Sr-90 The spatial and temporal variability in the distribution of Sr-90 following installation of the pilot PTW is presented in Figures 3.6 and 3.7 of Appendix 11 and Figure 4. The pre- and post-PTW installation distribution of Sr-90 verifies that the pilot PTW is located within the western fringe of the 2nd lobe and confirms a regional north-northeast migration pattern.

Review of the Sr-90 data leads to the following observations:

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Pilot PTW Evaluation Report C Sr-90 in groundwater sampled from within the clinoptilolite of the PTW is low to negligible indicating both removal of Sr-90 due to ion exchange processes and perhaps the influence of lower activity source water (area around WP-25);

C Elevated Sr-90 migration towards the PTW from the south-southwest is reduced in WP-28 and WP-36, located about 5 feet north and south of the west end of the PTW, due to possible treatment with the PTW. This suggests a short southerly flow vector towards WP-28 caused by the minor mounding in the wall.

C The high Sr-90 at PZ-09, which is located within the roundstone, may represent direct influx to the PTW and the absence of zeolitic fines capable of removing Sr-90 from the groundwater within this portion of the gravel section.

C Sr-90 activity in WP-27 at the east end of the PTW increased from about 10,000 pCi/L to 15,000 pCi/L after the sheet piles were installed and then to 40,000 pCi/L immediately after removal of the sheets.

The Sr-90 trends at wells downgradient of the PTW indicate the following trends depending on their proximity to the PTW:

C Low Sr-90 at WP-30 (<5,000 pCi/L) is partially due to the inflow of lower activity groundwater from the west and by the local outflow of low-activity (i.e., treated) water from the PTW; C Sr-90 at WP-34 located approximately five feet north of the PTW has steadily increased to over 30,000 pCi/L in the past 12 months, which is contrary to a three-month long decreasing trend that followed the removal of the sheet piles. The current increasing trend may be related to the possible underflow of Sr-90 below the central and eastern portions of the pilot PTW. The general Sr-90 trend at WP-34 is consistent with the Sr-90 trend at up gradient well point WP-26 suggesting that both wells may be along a similar flow path even though they are on opposite sides of the pilot PTW.

C Sr-90 at WP-35 located approximately 20 feet north of the PTW also shows a similar rate of increase as WP-34 indicating continued migration of the Sr-90 lobe to the north-northeast.

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Pilot PTW Evaluation Report C After an initial increase, Sr-90 at WP-40 has significantly decreased since November 2000. The decrease may be caused by slowly migrating low activity (i.e., treated) groundwater emanating from the northeastern end of the PTW toward this well location.

4.7 Hydrogeologic and Hydraulic Conditions Summary The hydrogeologic description of PTW conditions discussed in sections 4.0 through 4.6 is not without some uncertainty but it can be used to evaluate engineering solutions to either restore the intended hydraulic performance of the system, or modify the design to promote the treatment of Sr-90 contaminated groundwater.

The hydrogeologic description may be used to further develop a conceptual model that will provide input to a groundwater flow model. The overall hydraulic performance of the pilot PTW likely is controlled by the following conditions that should be accounted for in the setup of a model to ensure probable site conditions are simulated:

C a predominantly more eastward groundwater flow direction than initially anticipated (the PTW was oriented for predominantly northward flow and did not include lateral hydraulic controls to direct flow into the PTW);

C a highly heterogeneous and anisotropic aquifer sequence of fine and coarse sediments; C a relatively narrow zone of high activity Sr-90 water that exists topographically low in the aquifer and increases in concentration from the west end of the PTW to the east end; this flow path is partially diverted around the east end of the PTW; C a hanging central and eastern portion of the pilot PTW likely allows some underflow of high Sr-90 activity groundwater; C a discontinuous skin of fine zeolitic material at the contact with the zeolite/roundstone backfill and native aquifer material resulting from installation activities; 17 of 34

Pilot PTW Evaluation Report C slow discharge of dilute, low Sr-90 activity water from portions of the PTW, which is evident in some wells located close to the PTW; and, C continuing, although reduced, direct surface water infiltration into the PTW.

Though not a specific physical condition, the scale of the test also influences the observed performance because it is a relatively small-scale test that cannot absorb the influences from the high degree of heterogeneity and complexity (in aquifer material and the direction of the hydraulic gradient) associated with the local system. Large-scale implementation of a PTW would counteract such small-scale conditions by preventing flow adjustments and generally forcing the flow system to employ the wall in a steady-state flow net.

Although current conditions at the pilot PTW indicate that the system is not performing from a hydraulic perspective as intended, this pilot test successfully identified specific technical issues that can be addressed and designed for prior to deploying an effective full-scale system. Prior to designing such a full-scale system, the identified technical issues that likely limit the hydraulic performance of the pilot PTW should be further evaluated so that proper remedies to these issues can be appropriately engineered. To support this, a focused data collection program is proposed as described in Section 7.1.

5.0 Performance Assessment Section 4.0 indicates that groundwater from the south and expected regional up-gradient direction likely is flowing around the PTW to the east, with groundwater from the west entering the PTW.

This section discusses potential causes of limited flow through the PTW that could have resulted from the design and construction of the PTW.

5.1 Smearing of PTW Sidewalls The driving and extraction of sheet piles likely smeared some fine-grained materials along the interface between the sheet piles and the native soil, possibly creating a skin of lower permeability material around the PTW. The interlayered fine-grained and coarse-grained units of the SWS are more susceptible to this smearing and resulting hydraulic conductivity reduction. This smearing would only marginally affect thicker, coarser-grained water bearing zones, but greatly affect thinner water bearing zones, which may normally act as outflow pathways from the PTW. If hydraulic heads are higher in these coarser units and smearing is prevalent in select smaller outflow zones, then higher 18 of 34

Pilot PTW Evaluation Report water levels would be observed in the PTW than are observed in well-points and piezometers outside the PTW because the wells would be better developed.

The magnitude of smearing caused by driving and extracting the sheet piles, and its effect on the local hydraulic conductivity of native materials has not been extensively studied.

The magnitude of this effect depends on soil strength and plasticity, the thickness of the coarse- and fine-grained units, the thickness of the sheet piles, and the length of time the sheet piles are in the ground. The installation of monitoring wells screened strictly in the interlayered SWS near the PTW will indicate whether piezometric water levels are higher in this unit than in the overlying finer-grained AS&G. If water levels in these wells are similar to water levels measured in the PTW, then smearing of smaller outflow layers could be the sole cause of the observed hydraulic regime.

5.2 Consolidation of Clinoptilolite The surface of the clinoptilolite and roundstone settled about 4 feet as the sheet piles were withdrawn, which equals about 1,000 cubic feet. The inclinometers to the north and south of the PTW showed approximately 3 and 7 inches of movement into the excavation, respectively, or an estimated excavation volume loss of about 85 cubic feet to the north and 113 cubic feet to the south due to soil decompression and movement into the PTW.

(See Appendix 10 for inclinometer data.) A resulting backfill volume loss estimate of 1,200 cubic feet after sheet pile removal probably resulted from four mechanisms: the volume of the extracted sheet piles (200 cf), consolidation of the clinoptilolite (150 cf),

crushing of the clinoptilolite (200 cf), and movement of the clinoptilolite into the roundstone zone (530 cf). The sheet-pile volume of 200 cubic feet was estimated via a cross-sectional area of 0.192 square feet per sheet pile multiplied by 40 sheet piles inserted to an average depth of 26 feet.

The approximate 15% to 20% consolidation of clinoptilolite may affect the hydraulic performance of the PTW as shown in previous laboratory tests (Rabideau, 2000), where loose samples of clinoptilolite had a hydraulic conductivity of about 1.2x10-1 cm/sec and consolidated samples a hydraulic conductivity of 4.0x10-2 cm/s. Consequently, the consolidation of the material without crushing the grains (see below) would not sufficiently reduce hydraulic conductivity to prevent groundwater flow through the PTW.

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Pilot PTW Evaluation Report 5.3 Crushing of Clinoptilolite The clinoptilolite used in the PTW was manufactured as a 14x50 mesh size, but can be easily crushed by mechanical disturbance, which will reduce its hydraulic conductivity.

However, material testing performed at UB still produced a relatively high hydraulic conductivity of 4x10-3 cm/sec for compacted clinoptilolite. Mechanical disturbance of the clinoptilolite would have occurred at least three times during construction of the PTW:

transportation, placing clinoptilolite in the PTW, and extraction of the sheet piles.

Manufacturer quality assurance testing of the clinoptilolite before delivery showed less than 4 percent fines in the material. The design did not prescribe any specific procedures for transportation, storage, handling or inspection of the clinoptilolite at the site prior to placement in the PTW.

The clinoptilolite was delivered by truck to WVNS from Oregon in supersacks that were susceptible to jostling and vibration, which may have caused grain breakage. Although a grain size analysis of delivered clinoptilolite was not performed as a quality assurance check, the limited amount of fines generated would not have a significant impact on the hydraulic conductivity of the material.

The clinoptilolite may have also been crushed by its placement in the PTW; the zeolite was simply dropped into the cofferdam from up to 30 feet at the beginning, which probably generated fines from crushed and abraided clinoptilolite grains. However this effect cannot be easily quantified.

In addition, the clinoptilolite nearest the cofferdam sheet piles was intensely disturbed and almost certainly crushed when the sheet piles were withdrawn with a vibratory hammer.

The clinoptilolite grains greater than 2 feet from the sheet piles along the west, north, and east lengths likely suffered only minor breakage, with the roundstone along the south side of the PTW buffering the clinoptilolite grains from breakage. The clinoptilolite near the bottom of the PTW would also be subject to severe crushing because of burial stresses. The addition of water to the PTW prior to sheet pile extraction would have absorbed some of the vibratory energy and provided pore pressure to reduce burial stress and thus reduced grain crushing near the sheet piles and base. The crushed clinoptilolite grains and associated fines present within about 2 feet of the north, east, and west sides of the PTW and near the base of the PTW were likely transported around the PTW as groundwater entered from the west end and affected this crushed grain distribution.

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Pilot PTW Evaluation Report Consequently, the total volume loss due to grain crushing may be about 200 cubic feet, or about 6 to 7 percent of the estimated clinoptilolite volume of 4,875 cubic feet, which corresponds to the volume reduction noted by Rabideau (2000) in compacting clinoptilolite, where the porosity reduced from 0.51 to 0.48, or a volume reduction of 6 percent.

5.4 Clinoptilolite Plugging Void Spaces in Roundstone The grain size of the roundstone was 90-100% smaller than 0.5 inches, and 0-15% smaller than 0.25 inches, while the grain size of the clinoptilolite varied between 0.055 and 0.017 inches, which is about one tenth that of the roundstone. Consequently, the clinoptilolite could easily penetrate the void spaces within the roundstone as could some of the adjacent soils. Inclinometer data show the compression of the southern wall into the PTW, which promulgated clinoptilolite grains to penetrate into the roundstone and subsequently flow into PVC riser pipe at the base of the roundstone zone.

The presence of clinoptilolite within the voids of the roundstone likely reduced the hydraulic conductivity of the roundstone. If the clinoptilolite filled all of the voids of the roundstone (assuming 30 percent porosity) about 530 cubic feet of clinoptilolite would be moved into the roundstone.

5.5 Fines Movement as PTW Filled with Groundwater The PTW was not filled with water before the cofferdam was removed, thus upon sheet-pile extraction the inflow from approximately 20 feet of hydraulic head difference (from PTW base to the exterior potentiometric surface) would have turbulently transported clinoptilolite fines to the edges of the PTW as the water filled the PTW. As the first sheet piles were removed at the west end of the PTW, groundwater under an assumed average linear flow velocity of 0.2 feet per second flowed into the cofferdam. This rate likely varied due to clinoptilolite heterogeneities from the bottom of the cofferdam (compacted) to the top (loose). Inflow would have transported fines to the edges of the PTW, eventually ceasing when the water level reached equilibrium with adjacent groundwater levels. The approximately 10,000 gallon void space of the dry PTW likely was filled on the order of tens of hours, or within one to two days.

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Pilot PTW Evaluation Report Since the sheet piles were first extracted at the west side of the PTW near WP-25 (a high-head area), any fines along this side would have been flushed into the PTW towards the non-contributing edges (south, east, and north sides). Additional fines generated when extracting sheet piles along the south, east and north sides of the PTW would then contribute to this fine-grained zeolitic skin.

Since this was a transient effect that occurred when the sheet piles were withdrawn, the mechanism cannot easily be replicated, and other data that could be collected to support it may prove inconclusive. The hydraulic testing (pump tests) that were performed on the PTW indicate a less conductive skin is present.

5.6 Groundwater Flow Under PTW As-built information suggests that the PTW was not excavated to the top of the Lavery Till, which is possibly allowing groundwater and Sr-90 to flow under the central and eastern portions of the PTW, as indicated by the following data.

C Sr-90 trends in several WPs north and south of the PTW are somewhat similar and are most notable in the Feb. 2001 data when all PTW WPs and PZs were sampled.

(See Appendix 2) In addition, increasing in Sr-90 at downgradient WPs 34 and 35 may be coincident with the highest activity observed in the 1997 data, which indicate that a preferred flow zone in a possible finger-shaped lens may extend south to WP-26 and PZ-01, north to WP-16, and further north to GP-16-97. This finger may also be a zone of higher permeability based on soil samples from GP-20-97 (WVDP 1998).

C Head south of the PTW has been . 0.5 ft higher than north of the PTW, which would provide sufficient gradient for groundwater flow and plume transport, if the soil beneath the PTW is not influenced by higher heads within the wall.

C Since Sr-90 is apparently bypassing the wall, the high head within the PTW does not appear to have significantly raised the head in soils beneath the wall, which indicates that the low permeability skin may occur at the base of the PTW as well as the sides.

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Pilot PTW Evaluation Report 5.7 Potential Surface Influences Permeable Cap Over PTW: The cap over the PTW was designed to have a low hydraulic conductivity to prevent infiltration of surface water into the PTW. The 1-inch thick Volclay CG-50 bentonite layer that was placed over the clinoptilolite and roundstone zone has a grain size that is 99 percent smaller than 0.008 inches and 15 percent less than 0.0003 inches, or about one tenth that of the clinoptilolite, and one hundredth that of the roundstone. Since this material could easily fall into the void spaces of the PTW materials, the 1-inch thickness is likely inconsistent due to lateral movement during soil capping and alluviation into the PTW materials, thus compromising its intent on being a low permeability layer. Although this may be an entry point for surface water to the PTW, WVNS believes it to be a minor to negligible factor on overall PTW performance.

The overlying clay capping soil is borrowed Lavery Till that has a hydraulic conductivity of about 1x10-7 cm/sec when compacted. However the clay was not compacted when placed over the PTW for fear of crushing the clinoptilolite. Thus potential flow paths through this uncompacted clay allow surface infiltration to enter the PTW. While the cap limits direct infiltration from above, bypass occurs because well hydrographs that show the magnitude of water-level increases within the PTW were greater than increases in the native aquifer during and after rainfall and snow events. These discrepancies became less pronounced, although not eliminated, after the installation of the surface drain to the south (up gradient).

Surface Water Inflow: Hydrographs of PTW-area wells show that water levels within the PTW rise sharply during rainfall and snow events, thus indicating a hydraulic connection between surface water and groundwater within the PTW. Surface water may enter the PTW via the hardstand surface layer that is present about the PTW, especially since the hardstand slopes slightly to the north and allows runoff to flow towards the PTW. A surface drain that was constructed in October 2000 to divert surface water around the southern side of the PTW has reduced the sharp post-precipitation water-level rises within the PTW. Although the volume of flow into the PTW has been reduced by the surface drain, water-level data still indicate that the hardstand layer is somewhat hydraulically connected to the PTW. Although this is an entry point for surface water to the PTW, it is minor to negligible, because of the outward slope of the PTW cap.

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Pilot PTW Evaluation Report 5.8 Summary of Performance Assessment The engineering design relied on traditional construction methods that have been used successfully at other sites. Evaluation of the hydraulics in and around the PTW indicate that hydraulic heads in the PTW are higher than the surrounding aquifer, thereby limiting groundwater flow through the PTW. Consequently, the conclusions regarding the design and construction at the pilot PTW are as follows:

C Sheet pile extraction and mobilization of fines during PTW construction produced a comingled clinoptilolite and roundstone zone and a zone of crushed clinoptilolite particles around the north and east edges.

C The hydraulic conductivity of the crushed material may be up to two or three orders of magnitude less than that for uncrushed clinoptilolite.

C The hardstand is hydraulically connected to the PTW and numerous potential flow paths have been identified through the cap and other surface features.

C The PTW does not appear to be fully penetrating through the upper water bearing zone and likely hangs in its central and eastern portions above the top of the Lavery Till potentially allowing underflow.

6.0 Lessons Learned The previous section has focused on the engineering detail of the PTW design and installation and will assist in the eventual development of engineering alternatives to enhancing the performance of the PTW. Based on the conclusions of the previous sections and the hydraulic evaluation section, several important lessons learned are identified and will help create a better future PTW design at the WVDP:

Site characterization for PTW design purposes must focus on the location of the proposed installation and cannot rely solely on regional information

PTW design work must include temporal and spatial data on the three-dimensional distribution of target contaminants in the proposed location 24 of 34

Pilot PTW Evaluation Report

Hydraulic head information should focus locally and include a sufficiently wide area to account for potential spatial (both lateral and vertical) and temporal changes to the direction and magnitude of the hydraulic gradient. This information should be collected before and after PTW construction so that the effect of the PTW on the local hydraulic regime can be understood.

Stratigraphic information must be sufficiently detailed in the vicinity of the proposed location to accurately design the PTW for proper vertical coverage, and/or penetration of the affected water bearing zone. This stratigraphic information must also be considered in the engineering designing of the excavation support for the PTW.

Generally, the use of sheet piles to support the excavation for a PTW will modify the local stratigraphy and may affect discrete flow paths. Removal of sheet piles will consolidate any loose or uncompacted material in the PTW, and will allow materials with dissimilar grain sizes to co-mingle. Sheet pile removal may also generate high dynamic stresses within the PTW materials that can break fragile particles of the reactive material within the PTW.

The hydraulic head within a PTW excavation should be maintained at the top of the emplaced material when the excavation support system is removed to reduce the potential for rapid inflow of water that may mobilize fines or other materials within the PTW during removal of the excavation support.

The performance of a PTW can be affected by numerous external factors, such as surface water infiltration, utility trenches, etc., that must be addressed during the detailed engineering design. Given the high cost of installation, monitoring and correcting any performance problems, the engineering design should be conservative in addressing site-specific issues that could affect PTW performance. For example, an HDPE liner placed over the PTW treatment materials and appropriately keyed into the surrounding native material would be a more effective cap than the granular bentonite and uncompacted clay cap that was installed.

The PTW deployment approach must take greater care to avoid potential skin effects and pulverization of treatment material, and creation of fines.

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Pilot PTW Evaluation Report

PTWs that hang, or do not completely penetrate an underlying low hydraulic conductivity unit, over all or part of their alignment, generally have greater potential for unintended performance than fully-penetrating PTW designs.

Continuous wall PTW designs (similar to the WVDP pilot) typically are less complicated to design and build than funnel and gate designs, but must fully capture the affected groundwater, including during variations in the direction of the lateral hydraulic gradient.

If the PTW does not perform as-designed, accurate and well-documented as-built information is critical in understanding the problem and developing suitable remedies.

When constructing a pilot PTW to evaluate the technology, this information is even more important.

The conditions and issues that have reduced the intended performance of the pilot PTW also have been problematic for other sites that have deployed PTW technology over the past 10 years.

Generally, the remedial effectiveness of PTW technology from a chemical standpoint (e.g.,

destruction of organic compounds, immobilization of inorganic compounds, and buffering of low pH conditions) has been demonstrated and is fairly well understood as per documentation from the Remediation Technology Development Forum (e.g., see http://www.rtdf.org). Examples and lessons learned from specific sites are summarized in Appendix 11. No reports of full-scale PTW failures due to chemical treatment inadequacies are apparent although laboratory bench-tests have shown limitations to various chemical treatment processes. Issues regarding plugging or fouling of a PTW from chemical processes are being studied and monitored at both research and full-scale commercial sites; these processes are anticipated and have apparently not yet diminished the effectiveness of a PTW for a given site.

As is the case for the pilot PTW, most difficulties with permeable reactive barriers generally are due to unintended hydraulic performance resulting in:

incomplete capture of the affected groundwater (e.g., flow around or below, the PTW).

design groundwater velocity not being achieved.

non-uniform flow conditions within the PTW.

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Pilot PTW Evaluation Report Consequently, this PTW assessment had led to the following list of considerations in design and construction of future permeable reactive barrier (PRB) installations at the WVDP:

Sheet pile cofferdams are probably the most effective means of constructing the PRB, but driving and extraction of the sheet piles will affect local hydraulic conductivity. Thus a factor of safety should be included in the intended Sr-90 capture zone.

Wing walls should be considered in design to create a remedy that will direct the flow of water through the PRB. Suitable dimensions of the wing wall sections can be developed from careful hydraulic modeling of all anticipated groundwater conditions.

Geotechnical design should minimize sheet pile penetration of the Lavery Till to reduce the energy required to extract the sheet piles.

A conservative cap design, using HDPE liners or other impermeable materials should be used to prevent surface water infiltration.

All possible sources of surface water should be diverted away from the area of the PRB.

More delicate placement techniques can be developed to place the clinoptilolite.

The excavation should be filled with water before the sheet piles are removed.

The divider system between the clinoptilolite and any gravel zones should be removed after the sheet piles are removed.

Considerations for future designs also should consider using a coarser grain size distribution for the zeolite treatment media, or an aggregate that is less susceptible to grain breakage during construction of the PRB and post-construction movement of soil towards the PRB.

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Pilot PTW Evaluation Report 7.0 Proposed Data Collection and Options for Pilot PTW Modifications The unique hydraulic conditions at the WVDP PTW can be characterized by a small-scale investigation designed to specifically fill data gaps that currently lead to some uncertainty regarding hydraulic conditions near the PTW. (See Figure 1.5 in Appendix 13.) The investigation will target the potential for vertical head distributions, groundwater flow below the PTW, and the source of high head to the west. The data collection program is discussed below:

7.1 Data Collection and Modeling Program Additional field data will both strengthen the current conceptual model and support development of a three-dimensional numerical groundwater model that can be used to confidently assess an engineering solution to either modify the existing PTW, alter its orientation, or design a new PTW under the unique site specific conditions in the same or different portions of the north plateau. Although the current hydraulic conditions have been well explained, there remains enough uncertainty that a supplemental and cost-efficient field investigation would be beneficial to decrease the degree of uncertainty and increase the potential that an effective engineering solution can be developed and implemented.

Therefore, the following recommendations are presented by WVNS:

1. Install two new wells via hollow-stem auger method and collect continuous stratigraphic information in the vicinity of WP-25 (west-end) and WP-27 (east end) to confirm the water level conditions that appear to provide major control on the assumed groundwater flow directions in the vicinity of the PTW.

2. Drill at least three additional soil borings each adjacent to the north, south, and eastern face of the PTW that are continuously logged for stratigraphic detail to confirm whether the pilot PTW penetrates the underlying till or is hanging within the SWBZ. One additional soil boring for stratigraphy should be drilled toward the western end of the PTW, and one additional boring should be drilled near the south face of the PTW. The seven total borings should be converted to 2-inch monitoring wells with vertically distinct screened intervals in order to facilitate focused aquifer testing.

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Pilot PTW Evaluation Report

3. Perform a long-term (72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to one week) aquifer testing program consisting of a series of step-test periods, a constant-discharge period, and recovery period. The test could be performed using the vertical riser drainpipe installed within the up gradient gravel section of the pilot PTW with observation wells monitored using downhole pressure transducers. Short-term (i.e., 4 to 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months ) step-tests also should be performed in the new wells recommended in No. 1 and 2 above.

4. Perform a series of aquifer tests on several of the proposed wells to better understand the vertical separation of hydrostratigraphy near the PTW.

The hydraulic and hydrostratigraphic data collected from the supplemental well installations and testing should be integrated into the development of a three-dimensional numerical flow model to better assess and predict the observed hydraulic conditions. The modeling would greatly improve the ability to develop an engineering solution that achieves the level of operational success required by the project stakeholders. This model would also be expanded to include other areas of the north plateau as the PTW program is implemented on a full-scale schedule.

7.2 Modification Options and Recommendation Four options for modification for the pilot PTW program are presented in this section as follows:

Option 1 No Modifications of Pilot PTW Option 2 Install Lateral Hydraulic Barriers Option 3 Install Pilot PTW Extension Option 4 Install New Pilot PTW The basic criteria for selecting each option were as follows:

C The Basis for Selection C Assumptions C Cost Estimate C Assessment of Future Performance C Waste Generation 29 of 34

Pilot PTW Evaluation Report C Ease of Implementation C Likelihood of Success The four options are summarized in the following section. A more detailed description of each option can be found in Appendix 12.

7.2.1 Option 1 - No Modifications of the Pilot PTW This option consists of completing the assessment of the pilot PTW program and moving forward with making the decision of whether or not to design the full-scale PTW for the site. This option would strictly be used as a lessons-learned that assists in development of information necessary for designing and deploying the full-scale PTW. This option would have zero costs associated with the pilot PTW program.

7.2.2 Option 2 - Install Lateral Hydraulic Barriers This option consists of installing flow barriers at the west and, possibly, east ends of and perpendicular to the PTW, as shown in Appendix 12, Figure 2.1. The purpose of the flow barriers is to hydraulically isolate the PTW from higher water levels at WP-25, and to redirect the flow of groundwater through the PTW. The length of the barrier walls necessary to cerate the required groundwater flow conditions would be determined from analytical modeling and detailed design. For cost purposes it was assumed a 60 foot barrier would be needed and would cost approximately $80,000 for one end and $130,000 for both ends.

7.2.3 Option 3 - Install Extension to PTW This option consists of installing an extension on the east side of the existing PTW, as shown in Appendix 12, Figure 2.2. The purpose of the PTW extension is to capture the flow of groundwater that appears to be flowing around the eastern end of the existing PTW. The conceptual design of this alternative assumes an extension of approximately equal length (approximately 30 feet) and width of the existing pilot PTW. The conceptual design of this alternative assumes an extension of approximately equal length (approximately 30 feet) and width of the existing pilot PTW. Again it will be important to use a groundwater flow model to design 30 of 34

Pilot PTW Evaluation Report the final geometry and alignment of this option. This option would be installed using lessons-learned from the original pilot installation and is estimated to cost approximately $400,000.

7.2.4 Option 4 - Install a New Pilot PTW This option consists of installing a new pilot PTW at a suitable location, either up or down gradient of the existing PTW. Additional soil and groundwater investigation would be performed to locate and design the new pilot PTW, and the new PTW would be constructed in a manner that incorporates the lessons learned from the design, construction and monitoring of the existing PTW. The new pilot would have similar dimensions and construction as the existing pilot PTW. The general cost estimate for this option is $720,000.

The main point of these examples is that designing for hydraulic performance is critical to any PTW application. Comprehensive site characterization is key, and will more likely result in a reliable PTW design that becomes a cost-effective remedy for a given site.

8.0 Proposed Path Forward 8.1 Pilot PTW Path Forward Based on the evaluation of information prepared by WVNS and Geomatrix Consultants, WVNS is recommending Option 2, Installation of Lateral Hydraulic Barriers. By installing the lateral hydraulic barriers on the western end, it is expected to hydraulically isolate the PTW from higher water level conditions in WP-25 and to redirect the flow of groundwater through the PTW. The eastern sheet pile barrier wall will also isolate the PTW from any anomalous conditions that may be present at the eastern end of the PTW.

The flow barriers will consist of sheet piles driven approximately 1 foot into the Lavery Till. The sheet piles will be driven in interlock to provide a continuous barrier. The length of the barrier walls necessary to create the required groundwater flow conditions will be determined in detailed design after the development of a three-dimensional flow model.

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Pilot PTW Evaluation Report Prior to implementation of this modification option or any other, it will be very important to collect additional characterization data to integrate into the development of the three-dimensional flow model. The following is the proposed recommended path forward for both the pilot PTW and future deployment of PTW technology at the WVDP.

As a first step, further characterization and assessment of the local geology and hydrogeology near the pilot PTW, to decrease the degree of uncertainty with pilot PTW performance issues and increase the potential to select and implement an effective engineering solution is recommended. This effort will include the installation of at least seven continuously sampled boreholes that will be completed with a 2-inch diameter groundwater monitoring well. Four of the boring wells will be located along the western, southern, and eastern sides of the pilot PTW and completed with a 15-foot well screen. The additional three wells will be completed with 5-foot well screens, installed at various depths (Fig. 3.1 in Appendix 12). Water levels and groundwater sampling for these new wells would be integrated into the operational monitoring program to provide vertical gradient information. A hydraulic testing program will also be conducted to confirm the influence and distribution of skin at locations around the pilot PTW and to better assess the distribution of hydraulic conductivity in and around the pilot PTW. Cost estimates for this data collection program are listed in Appendix 13.

8.2 Full-Scale PTW Path Forward Secondly, it is recommended that the1st lobe preliminary design proceed. FY2001 preliminary design activities begin with selection of wall location then proceed with design and implementation of a comprehensive soil and groundwater characterization program.

This will be carried out on a local scale and include the collection of hydrogeologic data through the installation of boreholes and conventional 2-inch wells, and conducting seasonal pumping tests to thoroughly understand the local hydrogeology.

Activities will continue with evaluation of geological and hydrogeological data. Once the data is thoroughly analyzed, a conceptual design may commence. At completion of conceptual design a decision will be made as to whether full-scale deployment is feasible on the 1st lobe. A project schedule can be found in Appendix 14.

By the completion of the aforementioned steps, there will be increased confidence that both a reliable solution to the pilots performance can be selected and further PTW design and installations can be successfully applied at the WVDP.

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Pilot PTW Evaluation Report 9.0 References Aloysius, D. L., 1995. Sorbent Material Testing and Evaluation for Passive Filter Wall Design, Dames and Moore, Orchard Park, NY Berkey, E., 1997. Technical Peer Review - North Plateau Groundwater Plume, West Valley Demonstration Project, November 14.

Berkey, E., 1999. Review of North Plateau Groundwater Remediation Effort, West Valley Demonstration Project, July 8.

Berkey, E., 2000. Review of Preliminary Operational Assessment Report for the Pilot Permeable Treatment Wall (Draft), West Valley Demonstration Project, May 5.

Geomatrix Consultants, Inc. 2000a. Pilot Permeable Treatment Wall Hydraulic Evaluation Report, prepared for West Valley Nuclear Services, LLC, West Valley, New York, March.

Geomatrix Consultants, Inc. 2000b. Pilot Permeable Treatment Wall Engineering Evaluation Report (Draft), prepared for West Valley Nuclear Services, LLC, West Valley, New York, March.

Geomatrix Consultants, Inc. 2000c. Pilot Permeable Treatment Wall Modifications Options Report, prepared for West Valley Nuclear Services, LLC, West Valley, New York, April.

Hemann, M., B. Fallon, and C.L. Repp, 1998, 1997 Geoprobe Investigation of the North Plateau at the West Valley Demonstration Project, West Valley Nuclear Services Company, Inc., West Valley, New York.

Moylan, J., 2000, Technical peer review/evaluation of the West Valley Pilot Permeable Treatment Wall, URS, October 11.

Rabideau, A.J., I. Jankovic, and V. Raghaven, 2001, Flow Modeling of the WVDP Treatment Wall: Preliminary Results DRAFT, Department of Civil, Structural, and Environmental Engineering, State University of New York at Buffalo.

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Pilot PTW Evaluation Report Rabideau, A.J., J. Van Benschoten, C. Huang, and A. Patel, 1999, Bench Testing of Zeolite Barrier Materials, State University of New York at Buffalo.

Rabideau, A.J. and J.E. Van Benschoten, 2000, North Plateau Groundwater Remediation: Progress Report, University of Buffalo.

Warner, S.D., 1986, Modeling the aqueous geochemical evolution of ground water within the Grande Ronda Basalt, Columbia Plateau, Washington. M.S. Thesis, Indiana University, Bloomington, Indiana.

West Valley Nuclear Services, LLC. (WVNS), 1995, 1994 Subsurface Probing Investigation on the North Plateau at the West Valley Demonstration Project, WVDP-220, May.

WVNS, 1999, 1998 Geoprobe Investigation in the Core Area of the North Plateau Groundwater Plume, WVDP-346, June.

WVNS, 1999, Data Quality Objectives for the Pilot Scale Permeable Treatment Wall Operational Assessment Program, WVDP-350, June.

WVNS, 2000, Preliminary Operational Assessment for the Pilot Permeable Treatment Wall, May, 12.

WVNS, 2001, Summary Information from PTW Evaluation and Assessment Activities, February.

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Pilot PTW Evaluation Report FIGURES

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Pilot PTW Evaluation Report APPENDIX 1 GROUNDWATER ELEVATION DATA

PTW WP Groundwater Levels - Initial WPs and Background Wells 1 3 8 1 .0 0 1 3 8 0 .5 0 1 3 8 0 .0 0 1 3 7 9 .5 0 1 3 7 9 .0 0 1 3 7 8 .5 0 1 3 7 8 .0 0 1 3 7 7 .5 0 1 3 7 7 .0 0 1 3 7 6 .5 0 1 3 7 6 .0 0 WP-25 WP-26 WP-27 WP-16 8603

PTW WP Groundwater Levels - Initial WP Installations 1 3 8 1 .0 0 1 3 8 0 .5 0 1 3 8 0 .0 0 1 3 7 9 .5 0 1 3 7 9 .0 0 1 3 7 8 .5 0 1 3 7 8 .0 0 1 3 7 7 .5 0 1 3 7 7 .0 0 1 3 7 6 .5 0 1 3 7 6 .0 0 WP-25 WP-26 WP-27

PTW WP Groundwater Levels - Four Sides of PTW and Inner PTW 1381.00 1380.50 1380.00 1379.50 1379.00 1378.50 1378.00 1377.50 1377.00 1376.50 WP-25 WP-27 w p-29 w p-26 w p-34

PTW WP Groundwater Levels - Western PTW - Upgradient to Inner PTW 1380.00 1379.50 1379.00 1378.50 1378.00 1377.50 WP-28 PZ-08 w p-29

PTW WP Groundwater Levels - Central PTW - Upgradient to Inner PTW 1380.00 1379.50 1379.00 1378.50 1378.00 1377.50 WP-26 PZ-09 w p-31

PTW WP Groundwater Levels - Eastern PTW - Upgradient to Inner PTW 1 3 8 0 .0 0 1 3 7 9 .5 0 1 3 7 9 .0 0 1 3 7 8 .5 0 1 3 7 8 .0 0 1 3 7 7 .5 0 WP-36 w p-37

Pilot PTW Evaluation Report APPENDIX 2 GROUNDWATER SAMPLING RESULTS

45000 Sr-90 Sr-90 50000 40000 35000 45000 40000 35000 Sr-90 30000 25000 30000 25000 20000 15000 20000 15000 10000 10000 5000 5000 0

0 Jun-99 Jun-99 0 5000 10000 15000 20000 25000 30000 Jul-99 Jul-99 Jun-99 Aug-99 Aug-99 Jul-99 Sep-99 Sep-99 Aug-99 Oct-99 Oct-99 Sep-99 Nov-99 Oct-99 Nov-99 Dec-99 Nov-99 Dec-99 Jan-00 Dec-99 Jan-00 Feb-00 Jan-00 Feb-00 WP-25 WP-26 Mar-00 Feb-00 Mar-00 WP-16 Apr-00 Mar-00 Apr-00 May-00 Apr-00 May-00 May-00 May-00 Upgradient Wells May-00 WP-26 WP-28 Jun-00 8603 May-00 Jun-00 Jul-00 Jun-00 Pre-Installation Wells Jul-00 Aug-00 Jul-00 Aug-00 WP-27 Sep-00 Aug-00 Sep-00 Sep-00 WP-36 Oct-00 PTWRP Oct-00 Trends for the PTW Monitoring Program Nov-00 Oct-00 Trends for the PTW Monitoring Program Trends for the PTW Monitoring Program Nov-00 Dec-00 Nov-00 Dec-00 Jan-01 Dec-00 Jan-01 Feb-01 Jan-01 Feb-01 Feb-01 Local Background Wells and PTW Riser Mar-01 Mar-01 Apr-01 Mar-01 Apr-01 May-01 Apr-01 May-01 May-01 9

8 7

6 Sr-90 5

4 3

2 1 16 14 12 10 8

Sr-90 Sr-90 0 6 4

2 0

Dec-99 Dec-99 Dec-99 Jan-00 0 5000 10000 15000 20000 25000 30000 35000 Jan-00 Jan-00 Dec-99 Feb-00 Feb-00 Feb-00 Jan-00 Mar-00 Mar-00 Mar-00 Feb-00 Apr-00 Apr-00 Apr-00 Mar-00 May-00 May-00 WP-30 May-00 Apr-00 Jun-00 Jun-00 Jun-00 May-00 Jun-00 WP-29 Jul-00 Jul-00 Jun-00 Jul-00 WP-34 WP-37 Aug-00 Aug-00 Jul-00 Aug-00 Sep-00 Sep-00 Aug-00 WP-31 Wells Inside PTW Wells Inside PTW Sep-00 Downgradient Wells Oct-00 Oct-00 Sep-00 Oct-00 Nov-00 Nov-00 WP-35 Oct-00 WP-38 Nov-00 WP-32 Nov-00 Dec-00 Nov-00 Dec-00 Trends for the PTW Monitoring Program Dec-00 Trends for the PTW Monitoring Program Dec-00 Jan-01 Jan-01 Jan-01 Feb-01 Jan-01 WP-33 WP-40 WP-39 Feb-01 Trends for the PTW Monitoring Program Feb-01 Mar-01 Feb-01 Mar-01 Mar-01 Mar-01 Apr-01 Apr-01 Apr-01 Apr-01 May-01 May-01 May-01 May-01

P T W M o n i t o r i n g S h o w i n g B y- P a s s o r U n de r f l o w F r o m U p g r a d i e n t ( W P - 2 6 )

t o D ow n g r a d i e n t ( W P - 3 4 a n d WP - 3 5 ) W h e r e W P - 4 0 Sh o w s T r e a t m e n t T r e n d 45000 40000 35000 30000 25000 Sr-90 20000 15000 10000 5000 0

WP-26 WP-34 WP-35 WP-40

pH pH 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 pH 6.6 6.8 7.0 7.2 7.4 7.6 6/1/99 6/1/99 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 2/1/99 7/1/99 7/1/99 3/3/99 8/1/99 8/1/99 4/3/99 9/1/99 9/1/99 5/4/99 10/1/99 6/3/99 10/1/99 7/4/99 11/1/99 11/1/99 8/4/99 12/2/99 12/2/99 9/3/99 1/1/00 1/1/00 10/4/99 2/1/00 2/1/00 11/4/99 3/3/00 3/3/00 12/5/99 8603 1/4/00 4/3/00 4/3/00 2/4/00 WP-26 5/3/00 5/3/00 WP-25 3/6/00 Upgradient Wells Background Wells 6/3/00 6/3/00 WP-02 4/5/00 Pre-Installation Wells 7/4/00 7/4/00 5/6/00 WP-28 8/3/00 WP-26 8/3/00 6/6/00 9/3/00 9/3/00 7/6/00 WP-05 8/6/00 10/4/00 10/4/00 9/6/00 WP-36 11/3/00 WP-27 11/3/00 10/7/00 12/4/00 12/4/00 WP-16 11/6/00 1/4/01 1/4/01 12/7/00 2/4/01 2/4/01 1/7/01 2/6/01 3/6/01 3/6/01 Groundwater Trends for the PTW Monitoring Program 3/9/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 4/6/01 4/6/01 4/9/01 5/7/01 5/7/01 5/9/01 6/6/01 6/6/01 6/9/01 7/7/01 7/7/01 7/10/01 pH pH 6.5 7.0 7.5 8.0 8.5 6.6 6.7 6.8 6.9 7.0 7.1 7.2 7.3 7.4 7.5 6/1/99 6/1/99 7/1/99 7/1/99 8/1/99 8/1/99 WP-29 9/1/99 9/1/99 10/1/99 10/1/99 11/1/99 11/1/99 12/2/99 12/2/99 WP-31 1/1/00 1/1/00 2/1/00 2/1/00 3/3/00 3/3/00 WP-30 WP-32 4/3/00 4/3/00 5/3/00 5/3/00 6/3/00 6/3/00 7/4/00 WP-34 7/4/00 WP-33 8/3/00 8/3/00 Wells Inside PTW 9/3/00 9/3/00 Downgradient Wells 10/4/00 10/4/00 WP-35 WP-37 11/3/00 11/3/00 12/4/00 12/4/00 1/4/01 1/4/01 WP-38 2/4/01 WP-40 2/4/01 3/6/01 3/6/01 4/6/01 4/6/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 5/7/01 5/7/01 WP-39 6/6/01 6/6/01 7/7/01 7/7/01

Conductivity umhos/cm Conductivity umhos/cm Conductivity umhos/cm 0 500 1000 1500 2000 2500 0 200 400 600 800 1000 1200 1400 1600 1800 2000 6/1/99 0 500 1000 1500 2000 2500 6/1/99 2/1/99 7/1/99 7/1/99 3/3/99 8/1/99 8/1/99 4/3/99 9/1/99 5/4/99 9/1/99 10/1/99 10/1/99 6/3/99 11/1/99 7/4/99 11/1/99 8/4/99 12/2/99 12/2/99 9/3/99 1/1/00 1/1/00 10/4/99 2/1/00 2/1/00 8603 11/4/99 3/3/00 3/3/00 12/5/99 WP-26 4/3/00 1/4/00 WP-25 4/3/00 2/4/00 5/3/00 5/3/00 WP-02 3/6/00 6/3/00 6/3/00 4/5/00 7/4/00 7/4/00 5/6/00 WP-28 8/3/00 WP-26 6/6/00 8/3/00 9/3/00 9/3/00 7/6/00 Upgradient Wells WP-05 Background Wells 8/6/00 10/4/00 10/4/00 9/6/00 Pre-Installation Wells WP-36 11/3/00 11/3/00 WP-27 10/7/00 12/4/00 12/4/00 11/6/00 WP-16 1/4/01 1/4/01 12/7/00 2/4/01 2/4/01 1/7/01 2/6/01 3/6/01 3/6/01 3/9/01 4/6/01 4/6/01 4/9/01 5/7/01 5/7/01 5/9/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 6/6/01 6/6/01 6/9/01 7/7/01 7/7/01 7/10/01 Conductivity umhos/cm Conductivity umhos/cm 0 200 400 600 800 1000 1200 1400 1600 1800 0 200 400 600 800 1000 1200 1400 1600 1800 2000 6/1/99 6/1/99 WP-29 7/1/99 7/1/99 8/1/99 8/1/99 9/1/99 9/1/99 10/1/99 10/1/99 WP-31 11/1/99 11/1/99 12/2/99 12/2/99 1/1/00 1/1/00 WP-32 2/1/00 2/1/00 WP-30 3/3/00 3/3/00 4/3/00 4/3/00 5/3/00 5/3/00 WP-33 6/3/00 WP-34 6/3/00 7/4/00 7/4/00 8/3/00 8/3/00 Wells Inside PTW WP-37 9/3/00 9/3/00 Downgradient Wells 10/4/00 WP-35 10/4/00 11/3/00 11/3/00 12/4/00 12/4/00 WP-38 1/4/01 1/4/01 WP-40 2/4/01 2/4/01 3/6/01 3/6/01 WP-39 4/6/01 4/6/01 5/7/01 Groundwater Trends for the PTW Monitoring Program 5/7/01 Groundwater Trends for the PTW Monitoring Program 6/6/01 6/6/01 7/7/01 7/7/01

Total nonrad Sr (ppb)

Total nonrad Sr (ppb) 0 100 200 300 400 500 600 700 Total nonrad Sr (ppb) 6/1/99 0 100 200 300 400 500 600 700 6/1/99 0 50 100 150 200 250 300 350 400 450 7/1/99 2/1/99 7/1/99 8/1/99 3/3/99 8/1/99 4/3/99 9/1/99 9/1/99 5/4/99 10/1/99 10/1/99 6/3/99 11/1/99 7/4/99 11/1/99 12/2/99 8/4/99 12/2/99 1/1/00 9/3/99 1/1/00 10/4/99 2/1/00 2/1/00 8603 11/4/99 3/3/00 WP-26 3/3/00 12/5/99 4/3/00 1/4/00 WP-25 4/3/00 5/3/00 2/4/00 5/3/00 6/3/00 WP-02 3/6/00 6/3/00 4/5/00 WP-28 7/4/00 7/4/00 5/6/00 WP-26 8/3/00 8/3/00 6/6/00 9/3/00 9/3/00 7/6/00 Upgradient Wells WP-05 Background Wells 10/4/00 8/6/00 WP-36 10/4/00 9/6/00 Pre-Installation Wells 11/3/00 WP-27 11/3/00 10/7/00 12/4/00 12/4/00 11/6/00 WP-16 1/4/01 1/4/01 12/7/00 2/4/01 2/4/01 1/7/01 3/6/01 3/6/01 2/6/01 3/9/01 4/6/01 4/6/01 Groundwater Trends for the PTW Monitoring Program 4/9/01 5/7/01 5/7/01 Groundwater Trends for the PTW Monitoring Program 5/9/01 Groundwater Trends for the PTW Monitoring Program 6/6/01 6/6/01 6/9/01 7/7/01 7/7/01 7/10/01 Total nonrad Sr (ppb)

Total nonrad Sr (ppb) 0 100 200 300 400 500 600 700 800 900 0 50 100 150 200 250 300 350 6/1/99 6/1/99 WP-29 7/1/99 7/1/99 8/1/99 8/1/99 9/1/99 9/1/99 10/1/99 WP-31 10/1/99 11/1/99 11/1/99 12/2/99 12/2/99 1/1/00 1/1/00 WP-32 2/1/00 2/1/00 WP-30 3/3/00 3/3/00 4/3/00 4/3/00 5/3/00 5/3/00 WP-33 6/3/00 WP-34 6/3/00 7/4/00 7/4/00 8/3/00 8/3/00 Wells Inside PTW WP-37 9/3/00 9/3/00 Downgradient Wells WP-35 10/4/00 10/4/00 11/3/00 11/3/00 12/4/00 12/4/00 WP-38 1/4/01 WP-40 1/4/01 2/4/01 2/4/01 3/6/01 3/6/01 WP-39 4/6/01 4/6/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 5/7/01 5/7/01 6/6/01 6/6/01 7/7/01 7/7/01

Total Sodium (ppb) Total Sodium (ppb) Total Sodium (ppb) 50000 0

20000 40000 60000 80000 0

100000 120000 140000 160000 100000 150000 200000 250000 20000 40000 60000 80000 0

100000 120000 140000 160000 6/1/99 6/1/99 6/1/99 7/1/99 7/1/99 7/1/99 8/1/99 8/1/99 8/1/99 9/1/99 9/1/99 9/1/99 10/1/99 10/1/99 10/1/99 11/1/99 11/1/99 11/1/99 12/2/99 12/2/99 12/2/99 1/1/00 8603 1/1/00 1/1/00 2/1/00 2/1/00 2/1/00 3/3/00 3/3/00 3/3/00 WP-26 4/3/00 4/3/00 WP-25 4/3/00 WP-02 5/3/00 5/3/00 5/3/00 6/3/00 6/3/00 6/3/00 7/4/00 7/4/00 7/4/00 WP-28 WP-26 8/3/00 8/3/00 8/3/00 WP-05 9/3/00 Upgradient Wells 9/3/00 9/3/00 Background Wells 10/4/00 10/4/00 10/4/00 Pre-Installation Wells WP-36 11/3/00 11/3/00 11/3/00 WP-27 WP-16 12/4/00 12/4/00 12/4/00 1/4/01 1/4/01 1/4/01 2/4/01 2/4/01 2/4/01 3/6/01 3/6/01 3/6/01 4/6/01 4/6/01 4/6/01 Groundwater Trends for the PTW Monitoring Program 5/7/01 Groundwater Trends for the PTW Monitoring Program 5/7/01 5/7/01 Groundwater Trends for the PTW Monitoring Program 6/6/01 6/6/01 6/6/01 7/7/01 7/7/01 7/7/01 Total Sodium (ppb)

Total Sodium (ppb) 0 100000 200000 300000 400000 500000 600000 700000 800000 900000 1000000 100000 150000 200000 250000 0

50000 6/1/99 6/1/99 WP-29 7/1/99 7/1/99 8/1/99 8/1/99 9/1/99 9/1/99 WP-31 10/1/99 10/1/99 11/1/99 11/1/99 12/2/99 12/2/99 1/1/00 1/1/00 WP-32 WP-30 2/1/00 2/1/00 3/3/00 3/3/00 4/3/00 4/3/00 WP-33 5/3/00 WP-34 5/3/00 6/3/00 6/3/00 7/4/00 7/4/00 8/3/00 8/3/00 Wells Inside PTW WP-37 9/3/00 WP-35 Downgradient Wells 9/3/00 10/4/00 10/4/00 11/3/00 11/3/00 12/4/00 12/4/00 WP-38 WP-40 1/4/01 1/4/01 2/4/01 2/4/01 3/6/01 3/6/01 WP-39 4/6/01 4/6/01 5/7/01 5/7/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 6/6/01 6/6/01 7/7/01 7/7/01

Total Potassium (ppb) Total Potassium (ppb)

Total Potassium (ppb) 0 5000 10000 15000 20000 25000 5000 0

10000 15000 20000 25000 0 1000 2000 3000 4000 5000 6000 6/1/99 6/1/99 6/1/99 7/1/99 7/1/99 7/1/99 8/1/99 8/1/99 8/1/99 9/1/99 9/1/99 9/1/99 10/1/99 10/1/99 10/1/99 11/1/99 11/1/99 11/1/99 12/2/99 12/2/99 12/2/99 1/1/00 1/1/00 1/1/00 2/1/00 2/1/00 8603 2/1/00 WP-26 3/3/00 3/3/00 3/3/00 4/3/00 WP-25 4/3/00 4/3/00 5/3/00 5/3/00 5/3/00 WP-02 6/3/00 6/3/00 6/3/00 WP-28 7/4/00 7/4/00 7/4/00 WP-26 8/3/00 8/3/00 8/3/00 9/3/00 9/3/00 Upgradient Wells WP-05 9/3/00 Background Wells 10/4/00 10/4/00 10/4/00 Pre-Installation Wells WP-36 11/3/00 WP-27 11/3/00 11/3/00 12/4/00 12/4/00 12/4/00 WP-16 1/4/01 1/4/01 1/4/01 2/4/01 2/4/01 2/4/01 3/6/01 3/6/01 3/6/01 4/6/01 4/6/01 4/6/01 5/7/01 5/7/01 5/7/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 6/6/01 6/6/01 6/6/01 7/7/01 7/7/01 7/7/01 Total Potassium (ppb)

Total Potassium (ppb) 0 10000 20000 30000 40000 50000 60000 70000 80000 10000 15000 20000 25000 30000 0 5000 6/1/99 6/1/99 WP-29 7/1/99 7/1/99 8/1/99 8/1/99 9/1/99 9/1/99 WP-31 10/1/99 10/1/99 11/1/99 11/1/99 12/2/99 12/2/99 1/1/00 1/1/00 WP-32 2/1/00 WP-30 2/1/00 3/3/00 3/3/00 4/3/00 4/3/00 WP-33 5/3/00 5/3/00 6/3/00 WP-34 6/3/00 7/4/00 7/4/00 8/3/00 8/3/00 Wells Inside PTW WP-37 9/3/00 9/3/00 Downgradient Wells WP-35 10/4/00 10/4/00 11/3/00 11/3/00 WP-38 12/4/00 12/4/00 1/4/01 WP-40 1/4/01 2/4/01 2/4/01 3/6/01 3/6/01 WP-39 4/6/01 4/6/01 5/7/01 5/7/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 6/6/01 6/6/01 7/7/01 7/7/01

Total Magenesium (ppb) Total Magenesium (ppb)

Total Magenesium (ppb) 100000 120000 0

20000 40000 60000 80000 100000 120000 0

20000 40000 60000 80000 6/1/99 6/1/99 0 5000 10000 15000 20000 25000 30000 35000 7/1/99 7/1/99 2/2/99 8/1/99 8/1/99 3/4/99 9/1/99 4/4/99 9/1/99 10/1/99 5/5/99 10/1/99 6/4/99 11/1/99 11/1/99 7/5/99 12/2/99 12/2/99 8/5/99 1/1/00 9/4/99 1/1/00 2/1/00 8603 10/5/99 2/1/00 3/3/00 11/5/99 WP-25 3/3/00 WP-26 12/6/99 4/3/00 4/3/00 1/5/00 5/3/00 2/5/00 5/3/00 WP-02 6/3/00 3/7/00 6/3/00 7/4/00 WP-26 4/6/00 WP-28 7/4/00 5/7/00 8/3/00 8/3/00 6/7/00 9/3/00 Upgradient Wells 9/3/00 WP-05 7/7/00 Background Wells 10/4/00 10/4/00 8/7/00 Pre-Installation Wells WP-27 WP-36 11/3/00 9/7/00 11/3/00 12/4/00 10/8/00 12/4/00 WP-16 11/7/00 1/4/01 1/4/01 12/8/00 2/4/01 2/4/01 1/8/01 3/6/01 3/6/01 2/7/01 4/6/01 3/10/01 4/6/01 4/10/01 5/7/01 5/7/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 5/10/01 6/6/01 6/6/01 6/10/01 Groundwater Trends for the PTW Monitoring Program 7/7/01 7/7/01 7/11/01 Total Magenesium (ppb)

Total Magenesium (ppb) 0 5000 10000 15000 20000 25000 30000 WP-29 6/1/99 10000 15000 20000 25000 30000 35000 7/1/99 0 5000 6/1/99 8/1/99 7/1/99 9/1/99 8/1/99 WP-31 10/1/99 9/1/99 11/1/99 10/1/99 12/2/99 11/1/99 WP-32 1/1/00 12/2/99 2/1/00 WP-30 1/1/00 3/3/00 2/1/00 4/3/00 3/3/00 WP-33 5/3/00 4/3/00 6/3/00 WP-34 5/3/00 7/4/00 6/3/00 8/3/00 7/4/00 Wells Inside PTW WP-37 8/3/00 9/3/00 Downgradient Wells WP-35 9/3/00 10/4/00 10/4/00 11/3/00 11/3/00 WP-38 12/4/00 12/4/00 1/4/01 WP-40 1/4/01 2/4/01 2/4/01 3/6/01 WP-39 3/6/01 4/6/01 4/6/01 5/7/01 5/7/01 Groundwater Trends for the PTW Monitoring Program 6/6/01 6/6/01 Groundwater Trends for the PTW Monitoring Program 7/7/01 7/7/01

Total Calcium (ppb) Total Calcium (ppb) Total Calcium (ppb) 0 100000 150000 200000 250000 300000 350000 400000 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000 0

50000 100000 150000 200000 250000 300000 350000 400000 0

50000 6/1/99 2/2/99 6/1/99 3/4/99 7/1/99 7/1/99 4/4/99 8/1/99 8/1/99 5/5/99 9/1/99 9/1/99 6/4/99 10/1/99 7/5/99 10/1/99 11/1/99 8/5/99 11/1/99 12/2/99 9/4/99 12/2/99 1/1/00 10/5/99 1/1/00 8603 11/5/99 2/1/00 2/1/00 12/6/99 3/3/00 3/3/00 1/5/00 WP-26 4/3/00 4/3/00 WP-25 2/5/00 5/3/00 5/3/00 WP-02 3/7/00 6/3/00 6/3/00 4/6/00 7/4/00 5/7/00 WP-28 7/4/00 6/7/00 8/3/00 WP-26 8/3/00 WP-05 7/7/00 9/3/00 Upgradient Wells 9/3/00 Background Wells 8/7/00 10/4/00 10/4/00 9/7/00 Pre-Installation Wells WP-36 11/3/00 11/3/00 10/8/00 WP-27 12/4/00 12/4/00 WP-16 11/7/00 1/4/01 1/4/01 12/8/00 2/4/01 1/8/01 2/4/01 2/7/01 3/6/01 3/6/01 3/10/01 Groundwater Trends for the PTW Monitoring Program Groundwater Trends for the PTW Monitoring Program 4/6/01 4/6/01 4/10/01 Groundwater Trends for the PTW Monitoring Program 5/7/01 5/7/01 5/10/01 6/6/01 6/6/01 6/10/01 7/7/01 7/7/01 7/11/01 Total Calcium (ppb) Total Calcium (ppb) 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000 0

10000 20000 30000 40000 50000 60000 70000 80000 90000 0 100000 6/1/99 6/1/99 7/1/99 7/1/99 WP-29 8/1/99 8/1/99 9/1/99 9/1/99 10/1/99 10/1/99 11/1/99 11/1/99 WP-31 12/2/99 12/2/99 1/1/00 1/1/00 2/1/00 WP-30 2/1/00 WP-32 3/3/00 3/3/00 4/3/00 4/3/00 5/3/00 5/3/00 6/3/00 WP-34 6/3/00 WP-33 7/4/00 7/4/00 8/3/00 8/3/00 Wells Inside PTW 9/3/00 9/3/00 Downgradient Wells WP-35 10/4/00 WP-37 10/4/00 11/3/00 11/3/00 12/4/00 12/4/00 1/4/01 WP-40 1/4/01 WP-38 2/4/01 2/4/01 3/6/01 3/6/01 4/6/01 4/6/01 Groundwater Trends for the PTW Monitoring Program 5/7/01 Groundwater Trends for the PTW Monitoring Program WP-39 5/7/01 6/6/01 6/6/01 7/7/01 7/7/01

Pilot PTW Evaluation Report APPENDIX 3 WELL WP-25 PUMPING TEST DATA

WP-25 Pumping & Recovery (1/31/00) 0.00 0.10 0.20 0.30 Drawdown (ft) 0.40 0.50 0.60 Pump Off 0.70 0.80 0.90 1.00 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Pumping Time (min) w p-25 w p-29 w p-28 w p-26 w p-27 w p-30

WP-25 Pumping (1/31/00) 0.00 0.01 0.02 0.03 Drawdown (ft) 0.04 0.05 0.06 0.07 0.08 0.09 Pump Off 0.10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Pumping Time (min) w p-29 w p-28 w p-26 w p-27 w p-30

WP-25 Pump Test Recovery (1/31/00) 0 0.01 0.02 0.03 Drawdown (ft) 0.04 0.05 0.06 0.07 0.08 0.09 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Approx. Recovery Time (min) w p-29 w p-25 w p-26 w p-27 w p-28 w p-30

Hand Measured Water Level Data from WP-25 Mini-Pump Test 1/31/2000 Time Since WP-31 WP-31 WP-32 WP-32 WP-33 WP-33 WP-34 WP-34 PZ-03 PZ-03 PZ-06 PZ-06 Start of Water Water Water Water Water Water Pumping Level Drawdown Level Drawdown Level Drawdown Level Drawdown Level Drawdown Level Drawdown (min) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) 0 9.87 0.00 9.98 0.00 9.95 0.00 11.28 0.00 9.78 0.00 9.39 0.00 5 9.79 0.01 9.47 0.08 35 9.96 0.01 9.83 0.05 9.57 0.18 60 9.92 0.05 9.99 0.01 9.97 0.02 11.32 0.04 9.85 0.07 9.60 0.21 120 9.94 0.07 10.03 0.05 10.01 0.06 11.32 0.04 9.84 0.06 9.53 0.14 Distance from wp-25 (ft) 22.20 22.20 22.00 22.30 16.10 18.40 WP-25 WP-26 WP-27 WP-28 WP-29 WP-30 Distance from wp-25 (ft) 0.00 23.80 43.00 16.70 14.50 15.20 Shut off pump at 100 mins

WP-25 Pumping (4/19/00) 0 0.1 0.2 0.3 Drawdown (ft) 0.4 0.5 0.6 0.7 0.8 0 10 20 30 40 50 60 70 80 90 100 110 120 Pumping Time (min) w p-25 w p-29 w p-28 w p-26 w p-27 PZ-06

WP-25 Pumping and Recovery (4/19 and 4/20/00) 0 0.1 0.2 Drawdown (ft) 0.3 0.4 0.5 0.6 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 Time (min) w p-29 w p-28 w p-26 w p-27 PZ-06

Pilot PTW Evaluation Report APPENDIX 4 PTW DEVELOPMENT DATA, DATA & GRAPHS FROM PTW DEVELOPMENT ACTIVITIES

Drawdown In PTW Riser versus Time for Each PTW Developm e nt Program 0

2 4

6 8

10 12 14 16 18 20 0 50 100 150 200 250 300 350 400 Pump ing Time (min) 7/24/00 7/25/00 7/31/00 8/30/2000

Discharge From PTW Riser for Each PTW Development Program 35 30 25 20 15 10 5

0 0 50 100 150 200 250 300 350 400 Pump ing Time (min) 7/18/00 7/24/00 7/25/00 7/31/00 8/30/2000

Pilot PTW Evaluation Report APPENDIX 5 22-HOUR PTW PUMPING TEST DATA

Drawdown In PTW Riser versus Time for 9/07/00 -- 9/08/00 PTW Development Program 0

2 4

6 8

10 12 14 16 18 0 1 00 200 300 400 500 600 700 800 900 1 000 1 1 00 1 200 1 300 1 400 Pumpi ng T i me (mi n)

Groundwater Elevation during 9/07/00 -- 9/08/00 PTW Development 1380.00 1379.00 1378.00 Elevation (ft) 1377.00 1376.00 1375.00 1374.00 1373.00 1372.00 0 120 240 360 480 600 720 840 960 1080 1200 Time since start of pumping (min) wp-25 wp-29 wp-34 wp-26 wp-27 wp-37

Drawdown during 9/07/00 -- 9/08/00 PTW Development 0

1 2

Drawdown (ft) 3 4

5 6

0 120 240 360 480 600 720 840 960 1080 1200 Time since start of pumping (min) wp-25 wp-29 wp-34 wp-26 wp-27 wp-37

Groundwater Elevation during 9/08/00 -- 9/09/00 PTW Recovery 1380.00 1379.00 1378.00 1377.00 Elevation (ft) 1376.00 1375.00 1374.00 1373.00 1372.00 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1680 1800 1920 2040 2160 2280 Time since end of pumping (min) wp-25 wp-29 wp-34 wp-26 wp-27 wp-37

Recovery during 9/08/00 -- 9/09/00 PTW Development 7

6 5

Recovery (ft) 4 3

2 1

0 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1680 1800 1920 2040 2160 2280 Time since end of pumping (min) wp-25 wp-29 wp-34 wp-26 wp-27 wp-37

Pilot PTW Evaluation Report APPENDIX 6 2-HOUR PTW PUMPING TEST DATA

Pumping Rate During the 1/19/01 Two Hour Pump Test Clock Pumping Elapsed Pump Gallons Flow Time Duration Time Reading Pumped Rate (minutes) (minutes) (gallons) (gal/min) 9:45 AM 0 870 10:00 AM 15 15 1055 185 12.3 10:10 AM 25 10 1228 173 17.3 10:20 AM 35 10 1390 162 16.2 10:30 AM 45 10 1557 167 16.7 10:40 AM 55 10 1727 170 17.0 10:50 AM 65 10 1897 170 17.0 11:00 AM 75 10 1998 101 10.1 11:10 AM 85 10 2100 102 10.2 11:20 AM 95 10 2193 93 9.3 11:30 AM 105 10 2285 92 9.2 11:40 AM 115 10 2375 90 9.0 11:50 AM 125 10 2454 79 7.9 12:00 PM 135 10 2538 84 8.4 Pump Test Flow Rate Data 30 25 Discharge (gpm) 20 15 10 5

0 9:30 10:00 10:30 11:00 11:31 12:01 Time Pump Test Flow Rate Data 20 15 Discharge (gpm) 10 5

0 0 15 30 45 60 75 90 105 120 135 150 Pumping Duration (min)

Hand Measured Groundwater Elevations during 2-Hour Pumping Hand Measured Groundwater Elevations during 2-Hour Pumping 1380 1379 1380 WP-29 1379 1378 PZ-01 WP-31 1378 Elevation (ft) Elevation (ft)

PZ-02 1377 WP-32 1377 PZ-04 1376 WP-33 1376 PZ-08 1375 1375 1374 1374 1373 1373 Initial 30 M in. 60 M in. 90 M in. 120 M in.

Initial 30 M in. 60 M in. 90 M in. 120 M in. Ela p s e d Time Ela p s e d Time Hand Measured Groundwater Elevations during 2-Hour Pumping Hand Measured Groundwater Elevations during 2-Hour Pumping 1387 1386 1380 WP-37 1385 1379 WP-38 Elevation (ft) 1378 1384 8604 WP-39 Elevation (ft) 1377 104 PZ-09 1383 1376 1382 1375 1374 1381 1373 1380 Initial 30 M in. 60 M in. 90 M in. 120 M in. Initial 30 Min. 60 Min. 90 Min. 120 Min.

Ela p s e d Time Ela p s e d Time Hand Measured Groundwater Elevations during 2-Hour Pumping Hand Measured Groundwater Elevations during 2-Hour Pumping 1380 1379 1380 8603 WP-16 1378 1379 105 Elevation (ft)

WP-17 Elevation (ft) 1378 1377 1377 WP-18 1376 1376 1375 1375 1374 1374 1373 1373 Initial 30 Min. 60 Min. 90 Min. 120 Min. Initial 30 Min. 60 Min. 90 Min. 120 Min.

Elapsed Time Ela p s e d Time

Hand Measured Groundwater Elevations during 2-Hour Pumping Hand Measured Groundwater Elevations during 2-Hour Pumping 1380 1380 PZ-03 1379 PZ-06 W P -28 1379 1378 W P -35 Elevation (ft) 1378 W P -26 Elevation (ft) 1377 PZ-07 1377 W P -36 1376 1376 1375 1375 1374 1374 1373 1373 Initial 30 M in. 60 M in. 90 M in. 120 M in.

Initial 30 M in. 60 M in. 90 M in. 120 M in.

Elapsed Time Elapsed Time Hand Measured Groundwater Elevations during 2-Hour Pumping Hand Measured Groundwater Elevations during 2-Hour Pumping 1380 1379 1379 WP-30 1378 1378 WP-34 W P -27 Elevation (ft) 1377 Elevation (ft) 1377 WP-40 1376 PZ-05 1376 1375 1375 1374 1374 1373 1373 1372 Initial 30 M in. 60 M in. 90 M in. 120 M in.

Initial 3 0 Min. 6 0 Min. 9 0 Min. 1 2 0 Min.

Elapsed Time Elap sed T ime Hand Measured Groundwater Elevations during 2-Hour Pumping 1380 1379 1378 Elevation (ft) 1377 1376 1375 1374 WP-25 1373 Initial 30 M in. 60 M in. 90 M in. 120 M in.

PZ-10 Elapsed Time

Pilot PTW Evaluation Report APPENDIX 7 1-WEEK PTW PUMPING TEST DATA

ONE WEEK PUMP TEST DATA DATE & TIME ELAPSED PUMP GALLONS PUMP RATE TIME (min) READING PUMPED (gal/min) 1/24/01 10:15 2538 1/24/01 15:45 330 3960 1422 4.31 1/25/01 8:30 1005 8507 4547 4.52 1/25/01 12:11 221 9750 1243 5.62 1/25/01 14:15 124 10360 610 4.92 1/25/01 15:50 95 10820 460 4.84 1/26/01 9:35 1065 15548 4728 4.44 1/26/01 10:00 25 15654 106 4.24 1/26/01 11:22 82 16060 406 4.95 1/26/01 14:50 208 17048 988 4.75 1/27/01 8:05 1035 21793 4745 4.58 1/28/01 14:15 1810 29145 7352 4.06 1/29/01 8:00 1065 31320 2175 2.04 1/29/01 10:23 143 31985 665 4.65 1/29/01 12:46 143 32725 740 5.17 1/29/01 14:42 116 33300 575 4.96 1/29/01 16:00 78 33680 380 4.87 1/30/01 8:35 995 38035 4355 4.38 1/30/01 11:15 160 38780 745 4.66 1/30/01 13:45 150 39360 580 3.87 1/30/01 16:12 147 40040 680 4.63 1/31/01 8:00 948 43300 3260 3.44 1/31/01 9:48 108 43850 550 5.09 1/31/01 11:52 124 44070 220 1.77 1/31/01 13:55 123 44970 900 7.32 1/31/01 15:02 67 45264.1 294.1 4.39 Average discharge = 4.12 gpm One Week Pump Test Flow Rate 8.0 7.0 6.0 5.0 gal/min 4.0 3.0 2.0 1.0 0.0 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan 01-Feb Day

P TW Pumping Test Measurements (One-W e e k Test) P TW Pumping Test Measurements (One-W e e k Test) 1380 1380 1379 1379 PZ-01 1378 1378 PZ-02 Elevat ion (ft)

Elevation (ft) 1377 1377 PZ-04 1376 WP-29 1376 1375 WP-31 1375 1374 WP-32 1374 1373 WP-33 1373 1372 PZ-08 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan Elap s ed T ime Ela p s e d Time P T W Pumping T est Measurements (One-Week T est) P TW Pumping Test Measurements (One-W e e k Test) 1387 1380 WP-37 1386 1379 WP-38 1378 1385 8604 WP-39 Elevation (ft) Elevat ion (ft) 1377 1384 104 PZ-09 1376 116 1383 1375 1374 1382 1373 1381 1372 1380 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan Ela p s e d Time Elap s ed T ime P TW Pumping Test Measurements (One-W e e k Test) P TW Pumping Test Measurements (One-W e e k Test) 1380 1380 1379 1379 1378 W P-16 Elevation (ft) 1378 Elevat ion (ft) 1377 1377 W P-17 1376 8603 1376 W P-18 1375 1375 105 1374 1374 1373 1373 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan 1372 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan Elapsed Time Elap s ed T ime

P T W Pumping Test Measurements (One-Week Test) P T W Pumping Test Measurements (One-Week Test) 1380 1380 1379 1379 PZ-06 1378 1378 PZ-03 Elevation (ft)

W P -35 Elevation (ft) 1377 1377 W P -28 PZ-07 1376 1376 W P -26 1375 1375 W P -36 1374 1374 1373 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan 1373 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan Elap s e d Time Elapsed Time P T W Pumping Test Measurements (One-Week Test) P T W Pumping Test Measurements (One-Week Test) 1380 1379 1379 1378 1378 WP-30 1377 Elevation (ft) Elevation (ft) 1377 WP-34 1376 W P -27 1376 WP-40 1375 PZ-05 1375 1374 1374 1373 1373 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan 1372 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan Elapsed Time Elapsed Time P TW Pumping Test Measurements (One-Week Test) 1380 1379 1378 Elevation (ft) 1377 WP-25 1376 PZ-10 1375 1374 1373 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan Elapsed Time

Pilot PTW Evaluation Report APPENDIX 8 PTW WATER LEVEL HYDROGRAPHS SHOWING CAP INFILTRATION CHARACTERISTICS

PTW Water Table Flucutations in February 2001 1381.0 1380.0 Period of 1379.0 Elevation (ft)

Recovery from PTW Pumping

<============>

1378.0 1377.0 1376.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 1 2 February 2001 Dates WP-27 w p-29 w p-25 w p-26 w p-34

PTW Water Table Flucutations in February 2000 1383.0 Rainfall and/or Snowmelt 1382.0 1381.0 Water Table Elevation (ft) 1380.0 w p-25 1379.0 w p-29 (inside ptw )

1378.0 w p-26 1377.0 w p-27 1376.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 February 2000 Dates WP-27 w p-29 w p-25 w p-26

Pilot PTW Evaluation Report APPENDIX 9 PTW DEVELOPMENT RESULTS

SUMMARY

DATA

Maximum Hand-Measured Drawdown During Seven PTW Development Efforts Drawdown in Feet at Measurement Location:

Date/Time Standpipe WP-16 WP-25 WP-26 WP-27 WP-28 WP-29 WP-30 WP-31 WP-32 WP-33 WP-34 WP-35 WP-36 WP-37 WP-38 07/17/00 11.69 1.09 1.87 1.27 0.77 1.5 1.05 3.93 3.16 3.7 0.99 1 0.92 3.9 3.76 07/24/00 15.12 2.03 2.9 2.48 1.35 2.59 4.84 2.08 5.15 5.17 5.02 1.99 1.99 2.29 5.17 5 07/25/00 17.2 2.2 3.34 2.67 1.69 2.82 5.16 2.25 5.5 5.56 5.43 2.21 2.17 2.55 5.56 5.39 07/31/00 22.65 2.08 3.05 2.51 1.56 2.67 5.15 2.10 5.42 5.54 5.29 2.07 1.99 2.48 5.51 5.27 08/30/00 9.15 1.7 3.22 2.09 1.34 2.12 4.72 1.72 5.04 5.11 4.99 1.7 1.58 2.9 5.21 5.02 09/08/00 15.33 2.37 3.31 2.8 2.65 2.86 5.63 2.43 5.83 6.02 5.84 2.42 2.32 3.43 6.03 5.79 01/19/01 11.51 1.32 2.05 1.57 0.87 1.74 4.79 1.24 4.54 4.79 4.64 1.31 1.2 2.43 4.98 5.62 Date/Time WP-39 WP-40 105 8603 8604 PZ-01 PZ-02 PZ-03 PZ-04 PZ-05 PZ-06 PZ-07 PZ-08 PZ-09 PZ-10 07/17/00 3.3 1.05 0.04 1.14 0.74 1.54 1.51 1.44 1.15 0.44 1.35 1.04 07/24/00 5.06 2.06 0.02 2.05 1.34 2.69 2.73 2.6 2.21 1.26 2.36 2.07 07/25/00 5.46 2.24 0.13 2.23 1.42 2.87 2.89 2.75 2.32 1.48 2.62 2.25 07/31/00 5.35 2.11 0.04 2.07 1.34 2.72 2.87 2.64 2.14 1.10 2.39 2.10 08/30/00 5.09 1.73 0.01 1.73 1.11 2.35 2.29 2.75 1.71 1.23 2.07 1.73 4.39 4.69 09/08/00 5.93 7.35 0.22 2.4 1.55 2.96 3.02 2.88 2.46 2.2 2.58 2.41 5.48 5.5 01/19/01 4.71 1.34 0.16 1.28 0.89 1.95 1.26 1.77 1.13 0.49 1.94 1.21 4.77 4.74 1.33

Maximum Hand-Measured Drawdown During Seven PTW Development Efforts Percentage of PTW-Riser Drawdown in Feet at Measurement Location:

Date/Time Standpipe WP-16 WP-25 WP-26 WP-27 WP-28 WP-29 WP-30 WP-31 WP-32 WP-33 WP-34 WP-35 WP-36 WP-37 WP-38 07/17/00 100.0 9.3 16.0 10.9 6.6 12.8 9.0 33.6 27.0 31.7 8.5 8.6 7.9 33.4 32.2 07/24/00 100.0 13.4 19.2 16.4 8.9 17.1 32.0 13.8 34.1 34.2 33.2 13.2 13.2 15.1 34.2 33.1 07/25/00 100.0 12.8 19.4 15.5 9.8 16.4 30.0 13.1 32.0 32.3 31.6 12.8 12.6 14.8 32.3 31.3 07/31/00 100.0 9.2 13.5 11.1 6.9 11.8 22.7 9.3 23.9 24.5 23.4 9.1 8.8 10.9 24.3 23.3 08/30/00 100.0 18.6 35.2 22.8 14.6 23.2 51.6 18.8 55.1 55.8 54.5 18.6 17.3 31.7 56.9 54.9 09/08/00 100.0 15.5 21.6 18.3 17.3 18.7 36.7 15.9 38.0 39.3 38.1 15.8 15.1 22.4 39.3 37.8 01/19/01 100.0 11.5 17.8 13.6 7.6 15.1 41.6 10.8 39.4 41.6 40.3 11.4 10.4 21.1 43.3 48.8 Date/Time WP-39 WP-40 105 8603 8604 PZ-01 PZ-02 PZ-03 PZ-04 PZ-05 PZ-06 PZ-07 PZ-08 PZ-09 PZ-10 07/17/00 28.2 9.0 0.3 9.8 6.3 13.2 12.9 12.3 9.8 3.8 11.5 8.9 07/24/00 33.5 13.6 0.1 13.6 8.9 17.8 18.1 17.2 14.6 8.3 15.6 13.7 07/25/00 31.7 13.0 0.8 13.0 8.3 16.7 16.8 16.0 13.5 8.6 15.2 13.1 07/31/00 23.6 9.3 0.2 9.1 5.9 12.0 12.7 11.7 9.4 4.9 10.6 9.3 08/30/00 55.6 18.9 0.1 18.9 12.1 25.7 25.0 30.1 18.7 13.4 22.6 18.9 48.0 51.3 09/08/00 38.7 47.9 1.4 15.7 10.1 19.3 19.7 18.8 16.0 14.4 16.8 15.7 35.7 35.9 01/19/01 40.9 11.6 1.4 11.1 7.7 16.9 10.9 15.4 9.8 4.3 16.9 10.5 41.4 41.2 11.6

Maximum Drawdown Data From PTW Development Programs 25 20 Drawdown (ft) 15 10 01/19/01 09/08/00 5 08/30/00 07/31/00 Event Date 07/25/00 07/24/00 07/24/00 0

Measurement Location 07/24/00 07/24/00 07/25/00 07/31/00 08/30/00 09/08/00 01/19/01

Percentage of PTW-Riser Drawdown From PTW Development Programs 100.0 90.0 Percentage of 80.0 70.0 60.0 01/ 19/ 0 1 50.0 09/ 08/ 0 0 PTW-Riser Drawdown 40.0 08/ 30/ 0 0 30.0 07/ 31/ 0 0 Event Date 07/ 25/ 0 0 20.0 07/ 24/ 0 0 10.0 07/ 17/ 0 0 0.0 Measurement Location 07/17/00 07/24/00 07/25/00 07/31/00 08/30/00 09/08/00 01/19/01

Pilot PTW Evaluation Report APPENDIX 10 GEOMATRIX REPORT: PILOT PERMEABLE TREATMENT WALL HYDRAULIC EVALUATION REPORT

TABLE OF CONTENTS Page

1.0 INTRODUCTION

AND SCOPEOF REPORT............................................................... 1 1.1 APPROACHOFASSESSMENT AND ORGANIZATION OFFINDINGS............................. 3

1.2 DESCRIPTION

OFTHEPILOTPTW........................................................................... 4 1.3 SLJMMARYOFPREVIOUSPTW TECHNICALPERFORMANCE ASSESSMENT REPORTS ........................................................................................... 5 2.0 HYDROGEOLOGICCONDITIONSAT THE NORTH PLATEAU.............................. 7 2.1 SITEHYDROSTRATIGRAPHY ................................................................................... 7 2.2 DISTRIBUTIONOFHYDRAULICCONDUCTIVITY...................................................... 9 2.3 REGIONALGROLJNDWATER CONDITIONS .............................................................. 10 2.4 REGIONALDISIWBUTION0F SmomuM-90....................................................... 12 2.5 CONCEPTUAL HYDROGEOLOGIC MODEL OFTHENORTHPLATEAU..................... .13 3.0 HYDRAULIC CONDITIONSIN PROXIMITY TO THE PILOT PTW....................... 14 3.1 HYDROSTRATIG&APHY PROXIMALTO THEPILOTPTW........................................ 14 3.2 GROLJNDWATER ELEVATIONCONDITIONS.. .......................................................... 15 3.2.1 Pre-Construction GroundwaterElevations.............................................. 15 3.2.2 Post-Construction Groundwater Elevations............................................ 15 3.3 DISTRIBUTIONOF SR-90 ....................................................................................... 17 3.3.1 Pre-Construction Distributionof Sr-90.................................................. .17 3.3.2 Post-Construction Distributionof Sr-90 .................................................. 18 3.4 ASSESSMENT OFPTW DEVELOPMENT AND HYDRAULICTESTING...................... .20 3.4.1 QualitativePumpingTestAnalysis........................................................ .21 3.4.2 Reviewof SlugTestAnalyses................................................................. 22 3.5 CONCEPTUAL MODEL OF THE PILOT PTW HYDRAULIC PERFORMANCE.. ............ .23 4.0 RECOMMENDATIONS................................................................................................ 26

5.0 REFERENCES

28 TABLES Table1 Chronologyof Activities Relatedto the PTW Pilot Test Table2 MonitoringPoint Construction R:WELENE\ptweval\geomatrix\Hydraul_Rpt-Final

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TABLE OF CONTENTS (Continued)

FIGURES Figure1.1 SiteLocation Figure1.2 PTW DesignDrawing Figure2.1 SitePlanandCross-Section Location Figure2.2 Hydrostratigraphic Cross-SectionsA-A Figure2.3 Hydrostratigraphic Cross-SectionsB-B Figure2.4 Hydrostratigraphic Cross-SectionsC-C Figure2.5 Aerial Extentof SlackWaterSequence Figure2.6 RegionalGroundwater Elevations- High WaterLevel Figure2.7 RegionalGroundwater Elevations- Low WaterLevel Figure2.8 RegionalGroundwater Elevations- PostConstruction,Pre-Development Figure2.9 RegionalGroundwater Elevations- PostConstruction,Post-Development Figure3.1 PTW Area andCross-Section D-D Location Figure3.2 PTW AreaCross-Section D-D Figure3.3 Groundwater ElevationsPre-andPost-Construction Figure3.4 Hydrographs- July 1999to February2001 Figure3.5 Hydrographs- February2001 Figure3.6 Strontium-90Distribution Figure3.7 Strontium-90Concentration vs. Time Figure3.8 SelectedPTW StandpipePumpingTestResponses Figure3.9 WP-25PumpingTestResponses Figure3.10 SlugTestResults R:\HELENE\ptweval\geomatrix\Hydraul_Rpt-Foal

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PILOT PERMEABLE TREATMENT WALL HYDRAULIC EVALUATION REPORT West Valley Nuclear Services,LLC West Valley, New York

1.0 INTRODUCTION

AND SCOPE OF REPORT ThisPilot PermeableTreatmentWallHydra&c EvaluationReportwaspreparedby Geomatrix Consultants, Inc. at the requestof WestValleyNuclearServices,LLC (WVNS). The report wascommissioned by WVNS (Project19-098745~C-JK) to assistin assessing the hydraulic performance of a pilot permeable treatmentwall (PTW)designedto remediategroundwater affectedby Strontium-90(Sr-90)beneatha portionof the WestValley Demonstration Project (WVDP)locatedin westernNew York State(Figure1.1). A secondevaluationreportprepared by Geomatrixfor WVNS,the Pilot Permeable TreatmentWall EngineeringEvaluationReport, is preparedunderseparate cover. Both this hydraulicevaluationreportandthe companion engineeringevaluationreportsupportpreparationof the Pilot Permeable TreatmentWall ModificationReport,to be submittedto WVNS by April 25,2001.

A pilot PTW,composed of the mineralclinoptilolite,a zeolitewhosegeneralsolid solution formulais [(Ca,Mg, Na2,K2)(Al$Sit0024.8H20)] (Warner,1986),wasdeployedby WVNS at WVDP in the Fall of 1999to assess the ability of PTW technologyto passivelyandeffectively reducethe concentration of Sr-go-affected groundwater.Thepilot PTW wasinstalledto treata portionof what is referredto asthe 2nd lobe of the Sr-90plumebeneaththe North Plateauof the site. Initial mitigationof the 1st lobe of the Sr-90plumelocatedbeneaththe western portionof the North Plateaucurrentlyis beingaddressed by a groundwater recoveryand aboveground ion exchange treatmentsystem(pump-and-treat)whichwasinstalledin 1995.

While the pump-and-treat remedyhasbeenreportedby WVNS to reducelocalmigrationof the Sr-90plume,it is considered by WVNS not to be capableof completelycapturingand remediatingthe affectedgroundwater beneaththeNorth Plateau.Thusa reviewof alternative remediationtechnologies wasconductedby WVNS,andPTW technologywasidentifiedasa methodpotentiallycapableof effectivelymitigatingfurthermigrationof Sr-go-affected groundwaterover a largeportionof theNorth Plateau.

The generalpurposeof this reportis to assess the hydraulicperformance of the pilot PTW throughits first approximately15monthsof operation.This hydraulicperformanceevaluation wascommissioned becausemonitoringinformationfrom the initial assessment of the testas R:WELENE\phveval\geomatrkAHydraul_Rpt-Final

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performedby WVNS indicatesthat Sr-90-affected groundwater from south,or the presumed hydraulicdowngradientside,of the pilot PTW maynot be flowing throughthe pilot PTW as intended.

WVNS hasidentifiedseveralobjectives,which areto be addressed for the pilot PTW assessment to moveforward. Meetingtheseobjectivesareimportantif the potential effectiveness of this remedialapproachasa final remedyto this andotherportionsof the North Plateauis to be accuratelyevaluated.The objectivesinclude:

l Evaluatethe groundwater hydraulicsin the pilot PTW area.

l Evaluateperformance of the pilot PTW.

l Collectapplicablelessons-learned.

l DevelopandcomparePTW modificationoptions.

l Providea recommendation for modifyingthe pilot PTW.

Thebasicpremisefor conductinga pilot testof an innovativeapproachto groundwater remediationis to assess a small-scale field versionof a potentialfull-scaleremedyso asto refinethosedesignparameters thatmustbe metto assuresuccessful, andcost-effective implementation of the full-scaleremedy.Theapproachtakenby WVNS to first assess a smaller-scale versionof the PTW is valid dueto the innovativenatureof the remedy(PTW composed of a zeolite)in a complexhydrogeologicenvironment.AlthoughPTW technology (oftenreferredto aspermeable reactivebarriertechnology)hasbeentestedat morethan40 sitesin North America,it remainsan innovativetechnologywith a limited database for usein characterizing its potentialuseoverthe wide varietyof hydrogeologic conditionsthatexistat affectedgroundwatersites.Very few of thosesitesusethe clinoptiloliteasreactivemedium.

We alsoknow thatperhapsmorelimiting to the success of a PTW thanits ability to chemically remediatea contaminant in groundwater, is its ability to functionproperlyfrom a hydraulic perspective.Pilot testingcanprovideadditionaldetailandinformationimperativeto developinga full-scalesystemthatmeetsits designobjectives.We believethatthe pilot PTW testhasmet thoseobjectivesandthatinformationfrom this pilot providesgreatercertaintythat a full-scalesystem,or deploymentof the PTW technologyin otherareasof theNorth Plateau, canbe effectivelydesignedandimplemented.

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1.1 APPROACH OF ASSESSMENTAND ORGANIZATION OF FINDINGS The goalsof this reportareto assessthe hydraulicperformanceof the pilot PTW. Specifically, the objectivesof the reportareto providethe following:

l A descriptionof the currentperformanceof the pilot PTW from a hydraulic perspective.

l A discussionof conditionsthat may becontributingto the currentperformance includinglocal andregionalhydrostratigraphic andtopographicalfeatures,zonesof lower or higherpermeability,andpreferentialflow paths l A discussionof key factorsthat mustbe overcomeor modifiedto establish appropriategroundwaterflow throughthe PTW l Identificationof datagapsor otherneedsessentialto understanding andrestoring the hydraulicsaroundthe pilot PTW.

The activitiesundertakento meettheseobjectivesincluded:(1) initially meetingwith WVNS staff andstakeholders to discussthe testprogram;(2) reviewingdataandreportsmade availableby WVNS; (3) requestingadditionaldata,or clarificationof information,from WVNS staff; (4) reviewinganddiscussingthe resultsof hydraulicmodelingeffortswith researchers at the StateUniversityof New York at Buffalo (LIB)who havebeencommissioned by WVNS to developa hydraulicmodelof the pilot PTW; and(5) preparingthis report.

We understand thatthe designof the pilot PTW wasbasedon a basicreviewof regional hydrogeologicconditions,supplemented with additionalcharacterization of the location selectedfor the pilot PTW test. Becausethe hydrogeologicconditionsat thepilot PTW, and its performance, areintimatelyrelatedto the regionalhydrogeologiccharacteristics of the North Plateau,our generalapproachto this studyhasfocusedon integratingour interpretationof regionalconditionsto the local behaviorin andaroundthe PTW. Also, althougha detailed engineeringevaluationof the pilot PTW is containedin a separate report,we haveintegrated certainaspectsof the installationmethodsandas-builtconditionsthat mayhaveaffectedthe hydraulicperfornx-uxe.We alsohavebeenin regularcommunication with UB researchers as they continueto developa groundwatermodelof the pilot PTW area. We haveintegrated aspectsof the UB work in this report;however,we do not presentspecificresultsfrom that work. The resultsof our assessment, however,may be consideredimportantto continuing modeldevelopment by UB or others,andwe includeconceptualrecommendations for such work.

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Asidefrom our recommendation to WVNS to samplefour piezometers southof the pilot PTW (whichwasperformedby WVNS in lateFebruary2001)for which Sr-90activitydatawasnot available,we havenot performedfield work, nor haverequested additionalfield work be performedfor this assessment. However,basedon our interpretationof the current information,we providerecommendations for additionalfieldworkthatwe considerimportant for developingan approachto modify the pilot PTW andassuringsuccess of future deployments.

Followingthis introductorysection,which includesa generaldescriptionof the pilot PTW and a summaryof previouslypublishedtechnicalevaluationsof the pilot PTW performance, this reportconsistsof the following Sections:

l Section2.0 - HydrogeologicConditionsat theNorth Plateau(includingdiscussions of sitehydrostratigraphy, regionalgroundwater conditions,distributionof hydraulic conductivity,distributionof Sr-90,the conceptualhydrogeologic modelof the North Plateau).

l Section3.0 - HydrogeologicConditionsin Proximityto the Pilot PTW (including discussions of localhydrostratigraphy, potentiometicconditionspre- andpost-PTW construction;distributionof Sr-90pre- andpost-PTWconstruction;assessment of hydraulictestingin andnearthe PTW; andthe conceptual modelof thepilot PTW performance includingan assessment of numericalmodelingexercisesconductedby UB).

l Section4.0 - Recommendations (includingidentificationof datagapsand recommendations for collectingadditionalinformation).

l Section5.0 - References

1.2 DESCRIPTION

OFTHEPILOT PTW A detailedengineeringdescriptionof the constructionof the pilot PTW is providedin the companionEngineeringReport,however,a generaldescriptionof the system,basedon existingreportsprovidedby WVNS, is asfollows. Thepilot PTW wasinstalledasan approximately30-footlong by 26-footdeepby 7-footthick continuousPTW (i.e.,lateral hydraulicbarrierswerenot installedto directgroundwater flow into the PTW) in an area characterized asthe leadingedgeof the 2ndlobeof the Sr-90plume. A generalcross-section of the pilot PTW is providedasFigure1-2. ThePTW wasconstructed usingconventional trench andfill techniques wherethe PTW trenchwasstabilizedusingsealedsheetpilesto createa cofferdam-type structureprior to excavatingnativesoil from the interiorof the sheets.The sheetpiles wereinstalledto a depthof approximately 36 feetbelowgroundsurface(bgs)or R:WEL!ZNE\ptweval\geomatrbAHydraul_Rpt-Final

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approximately10 to 12 feetbelowthe anticipatedcontactbetweenthe upperwater-bearing materialandthe underlyinglow permeabilitytill. Thenativematerialwithin the cofferdam wasdewatered prior to excavationusing8-inchdewateringwells installedprior to the excavation,andwaskeptdry duringplacementof the treatmentmaterial.Unmixedzeolitic material(i.e., 100percentclinoptiloliteasdelivered)wasplacedto fill the cofferdamto near groundsurfacewith the exceptionof an approximately1.5foot zoneof gravel(l-inch roundstone)thatwasplacedat the upgradientfront (south)of the pilot PTW. A horizontal drainpipewasplacedat the bottomof the gravelsection;the connectingriserpipe with pump assemblyis locatedat the easternendof the gravelsection.Oncethe excavationwasfilled, the sealedsheetpileswereremovedstartingat the westendof the pilot PTW. The sheetpileswere installedin August1999andremovedin November1999.

Settlementof approximatelyfour feetwithin the PTW materialwasreportedby WVNS to have occurredfollowing removalof the sheetpiles. Followingtopping off with additionalzeolite material,an approximately2-footthick low permeabilityclay capwasplacedon top of the PTW to aid in preventingsurfacewaterinfiltrationto the system.A hardstandareawasplaced aroundthe PTW to providea workingsurfacefor heavyequipmentduringthe PTW installation.A surfacewatercutoff drainwas installedat groundsurfacein mid-October2000, approximately10 monthsfollowing installationof the PTW,to limit the potentialfor surface waterrunoff (partiallyvia the hardstandconfiguration)to infiltrateinto the PTW.

Thehydraulicmonitoringsystemof the pilot PTW locally consistsof a seriesof well points, monitoringwells, andpiezometers locatedaroundandwithin the PTW; mostof thesedevices wereinstalledafterthe PTW construction.Locationsandconstructiondetails(depthand screenintervals)of thesewaterlevel monitoringpointsarediscussed in greaterdetailin Section3.

1.3

SUMMARY

OF PREVIOUS PTW TECHNICAL PERFORMANCEASSESSMENT REPORTS As part of this assessment, we havereviewedandconsidered opinionsrenderedin previously publishedtechnicaldocumentson the pilot PTW performance.Specifically,the reviewed assessment documents include:

0 SummaryInformationfrom PTW EvaluationandAssessment Activities, dated February6,2001, preparedby WVNS.

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0 Technical PeerReview/Evaluation of the WestValley Pilot Permeable Treatment Wall, datedOctober11,2000,preparedby J. Moylan,URS Corporation.

l Preliminary OperationalAssessment for the Pilot Permeable TreatmentWall, datedMay 12,2000,preparedby WVNS.

l Review of PreliminaryOperationalAssessment Reportfor the Pilot Permeable TreatmentWall (Draft), WestValley Demonstration Project,datedMay 5,2000, preparedby E. Berkey,Ph.D.

Althoughthe purposeof this report(andsection)is not to reiteratethe detailedopinionsand commentsof eachof the abovedocuments, somecommonopinionsincludethe following:

1. Uncertaintyexistsasto the directionof the local lateralhydraulicgradientprior to construction(theregionaldirectionwasgenerallyobservedto be towardthe north; thoughsomedataindicateda northeasterly direction).

2. Waterlevelsin well WP-25controlthe interpretationof the local groundwater gradientdirection;waterlevelsincreasedfollowing sheetpile installationand remainhigh. The directionof groundwaterflow appearsto flow directlyeastward throughthe PTW basedin part on well WP-25data.

3. Surfacewaterinfiltration wasconsidered to stronglycontributeto hydraulic moundingwithin the PTW. .

4. Uncertaintyexistsasto the natureandlocationof a skin effectandits influence on hydraulicconnections betweenthe PTW andthe nativeaquifer;thoughresults from long-termpumpingdoesindicatereasonable hydraulicconnectionthat appeared to improvefollowing long-termpumpingfrom within the PTW.

5. Thereis considerable variabilityin the distributionof hydraulicconductivityin the upperwater-bearing unit.

6. Slugtestresultsmay not fully representactualhydraulicconditions.

7. The activity of Sr-90in groundwatersampledfrom within the PTW is very low.

Activity of Sr-90in groundwatersampledfrom westof the PTW is low; activity of Sr-90in groundwatersoutheast, east,andnorthof the PTW is high andappearsto haveincreasedin severallocationssinceinstallationof the PTW.

Fromthe previousassessments, multipleopinionsexistasto whatthe mostappropriate modificationto the PTW consistsof (e.g.,additionaldevelopment, installationof wing or lateralhydraulicbarriersto routegroundwaterthroughthe PTW, etc.). Generally,however, certaindatagapsexistwhich specificadditionalfield characterization activitiesshould R:\HELENE\phveval\geomatrix\Hydraul_Rpt-Final

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adequately addressandresultin developingan engineeringsolutionwith high potentialfor success.

2.0 HYDROGEOLOGIC CONDITIONS AT THE NORTH PLATEAU This sectionprovidesan interpretationof regionalhydrogeologicconditionsof the North Plateau.Emphasisis placedon interpretingthe generalhydrostratigraphic sequence and groundwaterflow conditionsregionallyto assistin understanding the local conditionsin and nearthe pilot PTW that contributeto the currenthydraulicperformance.Informationthat supportsthe following interpretationwasobtainedfrom existingreportsfor the sitepublished between1995andthe present,includingWVNS (1995),Hemann,et al. (1998),andWVNS (2000),andunpublishedinformationprovidedby WVNS. A mapillustratingfeaturesof the siteandshowingthe alignmentof hydrostratigraphic cross-section, aswell as showingthe regionaldistributionof Sr-90in groundwater is providedasFigure2.1.

Theunderlyingstratigraphyof theNorth Plateauwasevaluatedthroughexaminationof boreholelogscollectedduringcharacterization activitiesperformedin 1993,1994,1995and 1997,aswell asdatacollectedduringthe PTW designactivities. The comprehensive recordof boringsyieldsinsightinto the varyingspatialandcompositionaldistributionof geologic materialsbeneaththeNorth Plateau.

Hydraulicheaddatafrom 1992to the presentwereprovidedby WVNS for this assessment.

Our analysisfocusedon four separate measurementdatesto providesomerepresentation of temporalandspatialvariabilityin groundwaterconditionsacrossthe plateau.

Datafrom the 1997Geoprobesamplingevent(Hemann,et al., 1998)werereviewedand integratedwith stratigraphiccross-sections developedfor this assessment to betterinterpretthe verticaldistributionof Sr-90andidentifypreferentialflow pathsimportantto understanding the chemicalmigrationpathwayin the vicinity of the pilot PTW. Concentration datafrom more recentgroundwatersamplingeventsalsowerereviewedin this assessment.

Detailsof our findingsof the regionalconditionsareprovidedin the following subsections.

2.1 SITE HYDROSTRATIGRAPHY Two distincthydrostratigraphic unitsareinterpretedto existbeneaththe North Plateau:

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l A basalconfiningaquitard(or low permeabilityzone)consisting of lacustrineclay andsilt, andLaveryTill; l TheShallowW a ter-Bearing Zone(SWBZ),consisting of alluvialsandandgravel (AS&G),andthe Slackwater Sequence (SWS).

TheSWBZmaybe furthercharacterized asa heterogeneous unit representing a composite of thebothlaterallycontinuous anddiscontinuous layersrepresentative of boththe AS&G andthe SWSasdescribed in furtherdetailhenceforth the SW B Z existsapproximately five feetbelow groundsurfacein the vicinity of theP T W ,andextendsdownwardto thebasalconfiningunit.

Unconfinedconditionsgenerallyappearto existin theupperportionof the SWBZwithin the AS&G, however,logsfor Geoprobe@ andsoil boringdatashowseverallayersof clayandsilty claypresentwithin the SWSandlikely contributeto thedevelopment of semi-confined conditionsto developwithin the lowerportionof the SWBZ.

In thewesternportionof the studyarea,the SWBZis composed only of the coarse,unconfined depositsof the overlyingAS&G unit, whichextendsfrom the groundsurfacedownwardto the basalconfiningunit. Thethickness of theAS&G unit in thewesternportionof the studyarea variesfrom 5 to 15feet,depending on thetopography of the basalconfining.Thewatertablein AS&G unit is approximately five feetbelowgroundsurface.

Threecross-sections asshownon Figure2.1 illustratethehydrostratigraphy beneaththe site (Figures2.2,2.3,and2.4). CrosssectionA-A (Figure2.2)crosses bothlobesof the Sr-90 plumefrom northeast of theP T Wto southwest of the groundwater recoverysysteminstalledin thewesternlobeof theplume. Thelower-mostunit encountered in theboringlogsalongA-A is the LaveryTill, definedin borelogsasa laterallycontinuous stiff, unsortedsequence of sand,silt, clayandgravel.Thehydraulicconductivityof theLaverytill is reportedto be low (lessthan 1x1O-c m/s)producinga basalunit with variableelevationbeneath the shallowwater-bearingzonein the areaof interestaroundthe Sr-90plume.

A sequence of lacustrineclaywith silt overliestheLaveryTill acrossmuchof the studyarea, with the exceptionof the extremenortheast corner,whereit is replacedwith a fine sandandsilt unit, identifiedin theboringfor well #8603.Thethicknessof theclaywith silt unit varies considerably from eastto west,with thethickestsectiondescribed in the boringlog for well

0115andboringB-94-l 1. Thisthick clayandsilt unit hasbeeninterpreted asthe LaveryTill in previousborings,howeverbasedon the evidence of an alternatingsequence of clayeysilt andsilty clayin theborelogs,it is probablethat it is theresultof a lacustrinedepositional R:lHELENE\ptweval\geomatrix~ydraul_Rpt-Final

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environment.Thehydraulicconductivityof the clay with silt unit wasfoundto be 4x 1Ow8 cm/s by hydraulictestingperformedon well #0115,which is screened entirelyin the unit.

Thelacustrineclay with silt unit is overlainby a thick sequence of water-laindeposits composingthe SWS. Sediments associated with the SWSarecomprisedof thin, well-sorted bedsof gravel,fine sandandsilt andfills a wide,channel-likedepression in the easternhalf of the studyarea(Figure2.5). Locally,significantvariationsof the grainsizeof geologic materialscomprisingthe SWSexist.Theborelogforwell #8604on cross-section C-C (Figure 2.4) identifiesa two-feetthick silty clay lenswithin thesurroundinggravelandfine sand.The interbedded natureof coarseandfine-graineddepositscausesconfininggroundwaterconditions to existwithin the water-bearing depositsof the SWS, Variationsin the stratigraphy (i.e.,thicknessandlateralcontinuityof water-bearing deposits)may significantlychangethe localhydraulicgradientandflow directions,which cannotbe accountedfor on site-widemaps.

The SWSis overlainby alluvial sandandgravel(AS&G) in the northernhalf of the studyarea.

This unit is distinguished from the SWSby a finer sequence of silt andsand,with lessgravel andlessstratificationthanthe underlyingunit. The unit coarsens to the west,with the disappearance of muchof the finest-grained material,andis describedas alluvial graveland fine sand(CrosssectionA-A) .

Theuppermoststratigraphicunit in theNorth Plateauis a silty clay unit, which overliesthe finer grainedalluvial silt andsandwith gravellayer. Bore-logsalongcross-sectionsA-A and C-C indicatethatthe silty clay is consistently2 to 3 feetthick acrossthe northernhalf of the studyarea.This unit may serveas a confininglayerto the underlyingwater-bearing units,and may limit verticalrechargefrom surfaceinfiltrationby precipitationwhereit is continuous.

2.2 DISTRIBUTION OF HYDRAULIC CONDUCTIVITY Thevariabilityof geologicmaterialsacrosstheNorth Plateaustudy-area contributesto variable hydraulicconductivity.Thehighesthydraulicconductivityvaluesreportedfor the SWBZ exist in the westernlobeof contamination nearthe groundwaterextractionsystem(GWES)(3x1Oq3 cm/s;WVNS, verbalcommunication). As the grainsizecompositionof the AS&G becomes finer in an eastwarddirectiontowardthe PTW, conductivityvaluesdecrease to 1x1OS5 cm/s within the AS&G.

Well #0116is screened westof the facieschangein the AS&G unit westof the SWS,and yieldsa hydraulicconductivityvalueof 6x1Om5 cm/s. Therecoverywells (RW-01throughRW-R:WELENE\ptweval\geomatriAHydraul_Rpt-Final

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03) associated with the GWESin the westernlobeof contamination arescreened in the coarser gravelandfine sandof the AS&G. Hydraulictestingassociated with thesewells yieldsa significantlyhigheraveragehydraulicconductivityvalueof 3x10-cm/s.

Furtherto the east,in the vicinity of the PTW wherethe SWBZconsistsof boththe AS&G and the SWS,hydraulicconductivityvaluesarereportedto be in the rangeof 1x10 to 1~10~~ cm/s.

Thefully penetratingnatureof wells andpiezometers installedin the SWBZ yieldsaverage hydraulicconductivityvalues,andhigherconductivityis possiblein discrete,continuoussand andgravellayersassociated with the SWS. Alternatingsilt andclay layerswith sandand gravellayerscontributesto anisotropicconditionsin the SWBZandlocalizedconfined conditionsmay developwithin the sequence asa resultof the decreasedverticalhydraulic conductivityproducedby the clay andsilt layers.

2.3 REGIONALGROUNDWATERCONDITIONS Theregionalgroundwaterflow patternsin the SWBZwereevaluatedfor four separate groundwaterflow conditionsat the North Plateau.Thefirst two scenarios wereconstructed to definethe ambientregionalgroundwater flow patternsunderperiodof low groundwater elevation(August1998)andhighergroundwater elevation(February1997)andprior to any constructionactivitiesassociated with the PTW. Potentiometric mapswereconstructed to showthe site-wideheaddistributionbeforeandaftershorttermpumping(i.e.,hydraulic development) of the PTW.

Low GroundwaterElevationFlow Pattern(August1998): The groundwater flow patternin the vicinity of the Sr-90impactedzonewasevaluatedfor a low-groundwater elevationcondition thatexistedin August1998(Figure2.6). Thehighestgroundwater elevationwasfound southwestof the vitrificationtestfacility, leadingto a generalgroundwater flow directionto the north-northeast. A uniformhydraulicgradientexistedthroughoutmuchof the studyarea,with the exceptionof the northeastcorner,in the vicinity of wells #0105and#8603wherethe gradientincreased, alongwith a changein flow directiondirectlyeastwardtowardwell #105.

Superposition of the August1998groundwater conditionsurfaceontocurrentsitemaps suggests thatthe groundwater flow directionbeforeconstructionof the PTW wasvirtually perpendicular to the currentlong-axisof the PTW.

High GroundwaterFlow Pattern(February1997): Thegeometryof ambientgroundwater flow patternfor the high watertableconditionsin February1997is illustratedin Figure2.7.

Thepotentiometricsurfaceundertheseconditionscloselyresembles thatof the low R:\HELENE\prweval\geomatrix\Hydraul_Rpt-Fink

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groundwaterflow pattern.The generalflow directiontowardthe north-northeast, however, becamemoreeastwardin the vicinity of wells #105and#8603.Thehydraulicgradientbetween wells #105and#8603is interpretedto be higherthanthat associated with the lower watertable conditions.Theanomalously high headvaluein well #8603,which directlyinfluencedthe magnitudeanddirectionof groundwaterflow in the northeastquadrantof the studyarea,may be explainedby a semi-confined conditionfor the water-bearingzonein the vicinity of well

8603. The groundwaterflow directionwasnearlyperpendicular to the currentPTW during the high groundwatercondition.

PostConstructionPre-Development GroundwaterFlow Pattern(May2000): The groundwater flow patternfor the conditionsafterconstructionof the PTW wasalsoevaluated(Figure2.8).

Theoverallsite-wideflow patternwassimilarto historicalpatterns,however,the flow field wasperturbedin the immediatevicinity of the PTW. Emplacement of the PTW caused groundwater moundingsouthandwestof the wall, aswell aswithin the wall, changingthe flow geometry.Furthermore, an apparentflatteningof the horizontalhydraulicgradientis observedto the northeastof the PTW. Unlike pre-PTW-construction flow conditions,the overallflow directionwasdueeastwardin the vicinity of the PTW, andparaZleE to the long axis of the PTW (Figure2.8).Thehorizontalhydraulicgradientis steeperanddirected eastwardin the vicinity of well # 105.

PostConstructionPostDevelopment GroundwaterFlow Pattern( November2000): The PTW was subjectedto pumpingin July,AugustandSeptember 2000in orderto increasethe hydraulicconductivityin the materialboth in andadjacentto the wall. Prior to development, groundwaterwasmoundedin andaroundthe PTW, leadingto preferentialpathwaysaround, ratherthanthroughthe wall itself. Developmentof the PTW hasdecreased, but not eliminated the moundingof groundwater in andaroundthe wall. Thepresenceof the apparentvery low lateralhydraulicgradientdowngradient of the PTW (Figure2.9),persistingafterdevelopment, indicatesthat conductivityof someof the materialwithin or aroundthe PTW may be comparativelylowerthanthe surroundingnativedeposits.Thegeneralgroundwaterflow directionin the vicinity of the PTW is obliquefrom the southwest, but changesto directly eastwardat the faceof the wall. At this scale,groundwater flow appearsto flow parallelto, anddirectlythroughthe long axis of the PTW. On a smallerscale,however,flow nearthe westernportionof the wall mayhavea shortsoutherlyflow vectorfrom the wall into the SWBZ,causedby minor moundingwithin the wall. Substantialreductionin Sr-90activity in WP-28supportsthe identificationof this flow path.

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2.4 REGI~NALDISTR~UTION~F STR~N~JN~-~O Sr-90with a radioactivehalf-life of approximately 28 yearsis a commonproductof the fission of Uranium-235andhasa generalchemistrysimilarto that of calcium. Solubilityof Sr in naturalgroundwater typically is controlledby Sr carbonate andsulfatemineralssuchas strontioniteandcelestite,respectively, with strontionitelesssolublethancelestite.The ambient concentration of Sr in naturalwatersat nearneutralpH is typicallymuchlessthansolubility andnormallylessthanabout0.15milligramsper liter. This suggests that Sr canbe considered relativelyconservative andnot likely to be significantlyincorporated into secondary mineralizationunless,similarto calcium,hydrochemical conditions(suchasa changein pH) altermineralsolubility. However,strontiumcanreplacecalciumin like minerals(similarto the objectiveof usingthe zeoliteclinoptilolitein promotingan ion exchange reactionwithin the pilot PTW);thusthe presence of nativecalcium-based carbonates andothermineralsin the geologicmaterialbeneaththeNorth Plateaucanpromotelocal limitednaturalmitigationof the Sr-90plume.

Thedistributionof the two lobesof the Sr-90plumeasinterpretedfrom datacollectedin December1999andJanuary2000(Figure2.1) areconsistentwith the distributionof higher hydraulicallyconductivematerialsacrosstheNorth Plateau.Thezonesof higherconductivity associated with the SWSin the easternlobeandthe AS&G unit in the westernlobecontainthe highestconcentrations of Sr-90in the studyarea.Theapparentbifurcationof the Sr-90plume canbestbe attributedto the existenceof the largelowerconductivityclay andsilt unit identifiedin the boringlogsfor well #0115andB-94-13.A thin sectionof the AS&G sequence overliesthe thick clay andsilt unit, howeverthepathof leastresistance for groundwater is aroundthe clay andsilt unit into the thickerwater-bearing zonesassociated with the SWSand the AS&G.

Theverticaldistributionof Sr-90follows the zonesof highesthydraulicconductivityin the subsurface.Thehighestconcentrations of Sr-90in the easternlobe(12,200pCi/L, 1997 GeoprobeBdata)arefoundin the lowerportionsof the SWS(Figure2.2). ThehighestSr-90 concentrations associated with the westernlobeof the plumearefoundin the coarsedeposits associated with the AS&G deposits.Sr-90concentrations areoftenhigherin the lowerportions of the AS&G unit, nearits contactwith the clay with silt unit.

ThemostrecentSr-90samplingdata(February28,200l) hasyieldeddatapromptinga revised interpretationof the locationof the 10,000pCi/L isoconcentration line. Basedon concentration datafrom monitoringwells PZ-04(41,100pCi/L) andPZ-02(3,650pCi/L), the width of the R:\HELENE\ptweval\geomatrix\Hydraul_Rpt-Final

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>lO,OOO pCi/L zonemay be morenarrowthanthat shownon the plot of the 1997GeoprobeB samplingdata.Implicationsof the new datafrom PZ-01throughPZ-04arefurtherdiscussed in Section3.3.It is possiblehoweverthatthe low Sr-90activitymeasured in PZ-02in February 2001illustratesa local conditionthat is not laterallyextensive.Strontium-90activities measured in well #8603prior to the installationof the PTW wereactuallyhigherthan 10,000 pCi/L. Additionalcharacterization in this areawould be beneficialto assessthe distributionof Sr-90southof the pilot PTW.

2.5 CONCEPTUALHYDROGEOLOGICMODELOFTHENORTHPLATEAU The groundwaterflow conditionsthat existedprior to anyconstructionactivitiesassociated with the PTW wereprimarily influencedby spatiallyvaryinghydraulicconductivityacrossthe siteas well asundulationsin the surfaceof the underlyingtill. Thegeneralgroundwaterflow directionwastowardthe north-northeast. Groundwater movementoccursprimarily within the SWBZ,with the low conductivitytill andclay with silt layeractingas a basalhydraulicbarrier to the flow system.On the easternportionof the moundedaquitardunit nearboring#0116,a northeasterly flow componentdeveloped,potentiallydirectinggroundwaterinto the higher conductivity,stratigraphically lower SWSbelowthe easternlobeof Sr-90contamination.

The largeareaof low-conductivityclay with silt hadno recognizable effecton waterlevelsin the surroundingwells (whenviewedon a regionalscale),but appearsto separate the Sr-90 plumeinto two parts. This is bestexplainedby the existenceof thicker,moreconductiveunits eastandwestof the clay with silt low conductivityzone. Preferentialpathwayswithin these units causedSr-90to becomemorehighly concentrated in discretezoneslower in the sequence wherehydraulicconductivitymay be locally higher. The easternlobeof the Sr-90plumeis subjectedto a steeperapparenthydraulicgradienttowardwell #0105,causinga slightly eastwardextensionof part of the lobe. Theoverallgroundwaterflow directionat the current locationof the pilot PTW is thereforeinterpretedto be nearlyparallel(eastto east-northeast) to the long axis of the pilot PTW.

Theflow systemin the easternlobe of the Sr-go-impacted areamaybecomesemi-confined wherethe thick silt andclay unit capsthe SWBZ. The steephydraulicgradientbetweenwell

8603andWP-11(illustratedin Figure2.6) maybe coincidentwith a transitionbetweensemi-confinedandunconfinedconditions.

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3.0 HYDRAULIC CONDITIONS IN PROXIMITY TO THE PILOT PTW This sectionpresentsan assessment of hydrogeologicconditionsandhydraulicperformance within andspecificto the vicinity of the pilot PTW. Existingdatahasbeenreviewedandan interpretationof the local hydrostratigraphy, groundwater headconditions,distributionof Sr-90 from bothpre andpost-construction periods,andPTW hydraulicdevelopment activitiesis provided.A conceptualmodelof the PTW with respectto its hydraulicperformance is presented at the conclusionof this section.

3.1 HYDROSTFUTIGRAPHYPROXIMALTOTHE PILOTPTW Figure3.1 showsthe locationsof borings,monitoringpointsandthe locationof cross-section D-D in the pilot PTW area.Thelocal stratigraphyis shownon Figure3.2. Geologiclogsare availablefrom boringsGP597, GP2197, GP497, GP2097, GP397, GP1997, andGP297, advancedduringthe 1997Geoprobeinvestigation.Thecenterlineof the PTW is located approximately8 feetto the southof the soil boringsalignment.

Consistentwith the regionalhydrostratigraphy describedin Section2.1,the glaciolacustrine depositsencountered in the PTW areaconsistpredominantly of silty clay (groundsurfaceto approximately6 feetbgs),silt andgravel(approximately 6 to 11feetbgs),alternatinglayersof fine to coarsesandwith gravelandsilty clay with gravelcharacteristic of the SWS (approximately11to 25 and30 feetbgs). The SWSis highlyheterogeneous with layersof sandandgravelalternatingwith clay andsilt layersapproximately every6 inchesbasedon boringlog reports.Thelateralextentof eachinterbedappears to be highly variable.This alluvial sequence overliesthe Laverytill which is encountered at depthsof approximately 25 to 30 feetbgs. Thetop of the Laverytill unit is variableandappearsto undulatein the vicinity of the pilot PTW.

Our reviewof stratigraphicdetailfrom boringlogsalongcrosssectionD-D (Figure3.1) in the vicinity of the PTW suggests thatthe centralandeasternendsof the pilot PTW maynot penetrate the LaveryTill. Figure3.2 illustratesthe interpretedsettingof the PTW in the local stratigraphicsequence,Thatportionof the PTW that lies abovethe top of the LaveryTill is considered to be a hanging PTW.

The SWSconstitutesmostof the shallowwater-bearing zonein the vicinity of the PTW. The presence of the silty clay unit andthe alternatingbedsof silt andclay within the SWS contributeto the development of semi-confined or confinedgroundwater flow conditions.

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3.2 GROUNDWATERELEVATION CONDITIONS Figure3.3 presentsgroundwater elevationcontourmapsrepresenting conditionsprior to the PTW construction,afterconstructionbut beforethe PTW drainandriserpipe werepumped (referredto asthe PTW development),andafterPTW development. Figure3.4 shows hydrographs for selectmonitoringpointsin the PTW Area.

3.2.1 Pre-ConstructionGroundwaterElevations Pre-construction groundwaterelevationsareavailablefrom well pointsWP-25,WP-26and WP-27startingin July 1999(Table2). Well pointsinstalledin the PTW areagenerallyconsist of 1-inchPVC casingperforatedfrom 7 to 22 feetbgsor approximately1363to 1378feetasl, wells PZ-08,-09 and-10 aremadeof 1.25-inchgalvanizedsteelandhave3-footlong screens; this depthintervalplacesmostof the well screenscompletelywithin the SWSsediments (Figure3.2) but penetratingboththe silt andgravel(6 to 11 ft bgs)andlower alternatingsand andgravelandsilty clay sequence.Depthto groundwater prior to constructionis approximately6.5 to 6.7 feetbgs. Groundwater elevationdataavailablefor the monthof July 1999(Figure3.3) indicatethat WP-25,locatedto the westof the PTW hasslightly higher groundwater elevationsthanWP-26andWP-27,locatedto the southandeastof the PTW, respectively.Thesedatasuggesta fairly flat gradientbut exhibitsan eastwardgroundwater flow componentin the PTW area,which departsfrom the regionalnorthwardgroundwaterflow directioninterpretationfor the North Plateau(Figures2.6 and2.7). The absenceof lithologic informationfrom monitoringpointslimits our ability to interpretwhetherthe measurements madefrom thesepointsarerepresentative of the sameflow, or subflow,zone.It is likely that stratigraphicheterogeneities affectthe local flow directions.

3.2.2 Post-ConstructionGroundwaterElevations Post-construction groundwaterelevationsareavailablefrom a greaternumberof well points (WP-25throughWP-40andPZ-01throughPZ-10)thanduringthe pre-construction period.

Well pointsWP-28throughWP-40andPZ-01throughPZ-07,screened between7 and22 feet bgs,wereinstalledby December1999. Well pointsPZ-08 (screened between15 and 18 feet bgs)andPZ-09(screened between15.5and 18 feetbgs),wereinstalledon August24,2000, andPZ-10,screened between9 and 12 feetbgs,wasinstalledon October30,200O.

The groundwaterelevationcontourmap,hydrographs from July 1999to February2001,and hydrographs for February2001(Figures3.3,3.4 and3.5) showthe following observations:

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l Groundwater elevationin WP-25roseby approximately 2 feetabovebackground (well #8603)afterinstallingthe sheetpilesandremainedelevated.

l W a terlevelsmeasured from wells locatedin theP T W areconsistently higherthan measurements from well pointsscreened in thenativesediments with the exception of waterlevelsmeasured in WP-25; l The groundwater elevations measured from well pointslocatedinsidetheP T W are practicallyidentical,indicatinga nearzerohorizontalhydraulicgradient; l Groundwater elevationcontoursindicatethat groundwater is flowing towardsthe eastnortheast throughtheP T Wandradiatesawayfrom theP T W on the south,east, andnorthfacesindicatinghydraulicmoundingconditions; l ThehorizontalhydraulicgradientbetweentheP T W andthe nativematerial decreased followingP T W development; l Groundwater elevations fluctuationsdueto precipitationor snowmeltaregenerally similarin all well pointsinsideor outsidethe P T W ;well pointslocatedinsidethe P T Whavegreaterfluctuations; l Groundwater elevations insidetheP T W arehigherthanoutside,exceptfor elevations measured at well WP-25.

Thecurrentmonitoringnetworkdoesnot allowthe quantitative evaluationof verticalhydraulic gradients.Theclosestwell pair is WP-25andPZ-10andgroundwater elevations measured showanupwardgradient.

Thedifferencein groundwater elevations betweenwell pointWP-29(insidethePTW)and otherwell pointslocatedoutsidetheP T Wat times:(1) beforetheP T W development (December 1999to June2000);(2) aftertheP T Wdevelopment but beforethe surfacewater draininstallation(September to M id-October2000),and(3) aftersurfacewaterdrain installationis shownbelow:

GroundwaterElevationDifferences(feet)

North South East West WP-29-WP-30WP-29-WP-34WP-29-WP-40WP-29-WP-28 WP-29-WP-36WP-29-WP-27 WP-29-WP-25 BeforeDevelopment 1.44 1.53 1.41 0.72 1.20 1.99 -0.57 After Development, BeforeDrainInstallationI 0.85 0.83 0.85 ) -0.03 0.41 ) 1.18 ] -0.84 I I 8 I After Development and DrainInstallation 0.83 0.81 0.83 -0.02 0.37 1.14 -0.81 R:~LE~\ptweval\geomatrix\Hydraulppt-Final

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The elevationdifferencecalculationsindicatethatthe elevationinsidethe PTW is consistently higherthanthe surroundings, exceptwhencomparedto well point WP-25,which is between 0.2 to 1.2feethigherthaninsidethe PTW. The averagegroundwaterelevationdifferences calculatedafterthe installationof the surfacedrainindicatesthatthe drainhasslightly impacted groundwaterelevationsby furtherdecreasing the elevationdifference.

Figure3.5 showshydrographsandprecipitationfor February2000and2001.Comparisonof the two seriesof hydrographs showthat the PTW development andthe additionof the surface waterdrainhashelpedattenuate the horizontalhydraulicgradientacrossthe PTW area.Ground waterlevel increases within the wall in February2001areslightly largerthanin well points outsidethe PTW but the increaseis muchsmallerthanduringFebruary2000precipitation events.Groundwaterelevationsin WP-29did not exceedthe elevationmeasuredin WP-25,as observedin February2000. In both February2000andFebruary2001,however,the magnitudeof the rise in headwasgreaterwithin the PTW thanoutsidethe PTW. This suggests that: (1) surfacewaterinfiltration still influenceswaterlevelswithin the PTW thoughlessthan beforeinstallationof the surfacedrain;(2) pressureresponse differencesbetweenthe semi-confinedaquifersystemandthe unconfinedPTW systemgive riseto temporalmounding; and/or(3) both surfacewaterdrainageandpressuredifferentialsinfluencethe headresponse.

Thesedatasuggestthat boththe PTW development andthe surfacewaterdrainhavebeen effectivein reducing,but not completelyeliminatingsurfaceinfiltration into the PTW.

3.3 DISTRIBUTION 0~ M-90 Assessment of the spatialandtemporalvariationin Sr-90distributionin groundwater nearand within the PTW providesinsighttowardunderstanding the influenceof the constructedsystem on the ambientflow field. Definedmetrics(WVDP-350,June1999)for assessing the performance of the pilot PTW include:(1) the ability of the PTWs treatmentmatrixto remove Sr-90from affectedgroundwater, and(2) the changein activity/concentration of Sr-90 downgradient of the pilot PTW. Therefore,the effectof the pilot PTW on the Sr-90 distributionis critical to assessing the performance of the pilot PTW.

3.3.1 Pre-ConstructionDistribution of Sr-90 Theregionaldistributionof Sr-90prior to constructionof the pilot PTW wassummarized in Section2.4 andis indicatedon Figure2.1. Thepilot PTW wasinstalledin an areawherethe distributionof Sr-90wasrepresented by the leadingedgeof a lobeof Sr-90with an activity of approximately10,000pCi/L asinterpretedfrom a coarsenetworkof Geoprobeandwell installationinformation.A relativelysteepactivity gradientfrom greaterthan 10,000pCi/L to R:\HELENE\ptweval\geomatrix\Hydraul_Rpt-Final

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lessthan 1,000pCi/L was apparentfrom the centralportionof this lobe(or the approximate centralpoint of the thenproposedPTW alignment)westwardtowardwell #115andthe defined regionof low hydraulicconductivitywithin theNorth Plateau.

Installationandsamplingfrom new well points,WP-25locatedon the westsideof the proposedPTW alignment,WP-26locatedon the south,andpresumed hydraulicupgradientside of the proposedPTW, andWP-27,locatedimmediatelyeastof the proposedPTW,confirmed the locationof the westernedgeof Zndlobeof the Sr-90regionalplume. Analysisof groundwatersamplesfrom thesewell pointsalsoindicatedthat Sr-90activitiesashigh as 40,000pCiL existedimmediatelysouth,or presumedupgradient,from the proposedPTW alignment(WP-26)while the activityof Sr-90waslessthan500pCi/L,immediatelyadjacentto the westernendof the PTW alignment(WP-25). Eachof the well pointshavesimilarscreen intervals(7 to 22 feetbgs)that cut acrossthe alternatingsequence of low andhigh hydraulic conductivityzonesin the vicinity of the PTW. Inferencefrom regionalGeoprobedataas describedpreviously,aswell asthe resultsof a scanof Betaactivityin soil collectedfrom the pre-emplacement PTW dewateringwell boringssuggestthatthe higheractivitygroundwater hasa greaterlikelihoodof existingin the lowerhalf (i.e.depthsgreaterthanabout15feetbgs) of this shallowwaterbearingsystem.

3.3.2 Post-ConstructionDistribution of Sr-90 Figures3.6 and3.7 illustratethe spatialandtemporalvariabilityin the distributionof Sr-90 following installationof the pilot PTW. Figure3.6 depictsthe currentdistribution (January/February 2001)of Sr-90activity in groundwaterinterpretedfrom samplescollectedin the threeinitial well points(WP-25,WP-26,andWP-27)andthe additionalwell pointsand piezometers installedfollowing constructionof thepilot PTW. Trendsin Sr-90activityover time sinceinstallationof thepilot PTW alsoareshownon theFigure. Figure3.7 compares the historicaltrendsin Sr-90activityfor samplescollectedfrom wells representing areasadjacent to eachsideof the pilot PTW: WP-25on the westside,WP-26on the southside,WP-27on the eastside,andWP-30on the northside. Historicaltrendsprior to February2001for Sr-90 activity in samplescollectedfrom PZ-01, PZ-02,PZ-03,andPZ-04locatedsouthof the pilot PTW arenot availableasthesepointsweresampledonly in February2001.

Certainsimilaritiesin the distributionof Sr-90activityexistbetweenthe currentconditionand the interpretedconditionprior to deploymentof the PTW: Sr-90activitywestof the PTW remainslow; the greatestSr-90activityoccursalongthe easterntow-thirdsof the southand northfaces,andat the easternendof the alignment.This confirmsspeculation thatwhile the R:MELENE\phvewl\geomatrix~ydraul~Rpt-Final

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pilot PTW may havebeenlocatedcloseto a leadingdowngradient front of the 2ndlobe (as designed),it alsowasplacedat the westernfringe of the lobewherethe Sr-90activity increases greatlyovera shortlateraldistanceandalongthe lengthof the pilot PTW. The general distributiontendsto confirma regionalnorth-northeast migrationpattern.However,other significantobservations of the Sr-90activity distributionandtrendsareimportantto assessing the effectof the PTW on the local migrationpathway:

l Sr-90activitiesin groundwatersamplescollectedfrom within the zeoliticmaterial of the pilot PTW arelow to negligibleindicatinga combinationof nearcomplete treatmentof affectedgroundwater(removalof Sr-90dueto ion exchangeprocesses) andthe influenceof lower activity sourcewater(areaaroundWP-25);

0 Thehigh Sr-90activity sourcewateris locatedto the south-southwest of the PTW basedon regionaldataandrecentanalysisof groundwatersamplescollectedfrom PZ-01,PZ-03,andPZ-04(the Sr-90activity in the samplecollectedfrom PZ-02 waslower). A recentincreasingtrendin the activity of groundwatersamples collectedfrom WP-26couldindicateflux of a higheractivity upgradientsource movingtowardthe PTW. The lower Sr-90activity in samplesfrom WP-28and WP-36,locatedwithin approximately5 feetof the southsideof the PTW, could indicatethe flux of low activity [possiblytreated]wateroutwardfrom the PTW, or for the caseof WP-28,the effectof lower activity groundwaterfrom the west. The high Sr-90activity in groundwatersamplesfrom PZ-09locatedwithin the upgradientgravelsectionmay representdirectinflux to the PTW. The activity level in samplesfrom PZ-09alsosuggests thatzeoliticfinescapableof removingSr-90 from the groundwater havenot mixed significantlyinto this portionof the gravel sectionalthoughthe shortscreenintervalof PZ-09may not be indicativeof the full verticalthicknessof the gravelsection.

l Activity in WP-27(immediatelyeastof the PTW) increased moderately(50 percent)from its baselineof about10,000pCi/L afterthe sheetpileswereinstalled andprior to their removal,andincreased morethan400percentaboveits baseline activityimmediatelyafterremovalof the sheets.The activityhasremained consistentat or about40,000pCi/L sincethe sheetswereremovedin November 1999. Thetrendsindicatethat the installationandremovalof the sheetshad profoundaffectson the flow system.While the sheetswerein place,flow of slightly higherthanbaseline(10,000pCiL) activitywaterwasdivertedto the WP-27 locationfrom the southwest;following sheetremoval,oneexplanationfor the immediate300percentincreasein activitymight havebeenthe hydrodynamic pressureeffectson the flow systemassociated with sheetremovalactivities; however,the sustained high activity at WP-27suggests an alteredflow pattern, comparedto pre-sheetemplacement, that is connectedto a high activity sourcearea.

Theexactphysicalcauseof this conditionis not fully explainedandremainsunder consideration. r R:\HELENE\phveval\geomatrixWydraulppt-Final

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l Trendsin activitylevelsin groundwater samples collectedfrom wellslocatednorth of theP T W show,variabilitydepending on proximityto thepilot P T W :

1. Sr-90activityin groundwater samples from WP-30is consistently low (~5,000 pCi/L) relativeto otherwells. Thismaybe dueto bothto its locationwithin a pathof loweractivitygroundwater from thewestandby the flux of low-activity (possiblytreated)wateroutwardfrom theP T W ;

2. Sr-90activityin groundwater samples collectedfrom WP-34locatedwithin approximately five feetof thenorthfaceof theP T Wgenerallyhasincreased at an average rateof approximately 70 pCi/dayduringthepast12monthsto greaterthan30,000pCi/L. Thisincreasing trendfollowsan approximately three-month periodbeginningwith removalof the sheetpileswherethe activity Sr-90in groundwater samples decreased from approximately 15,000pCi/L to about6,000pCi/L. Thecauseof the initial decreasing Sr-90activitytrend followedby theincreasing activitytrendis unknown.W ith respectto the initial decreasing trend,theremaybe a relationbetweenan initial flushingof dilute low activitywaterthroughthis areafollowingsheetpile removalandlocal m itigationof Sr-90waterby ion exchange with zeolitefinesthatcouldhave enteredthe formationnearWP-35.Theincreasing trend,whichappears to be consistent with a generalsite-wideincrease in Sr-90activityin groundwater, maybe relatedto thepossibleunderflowof high Sr-90activityin thecentraland easternportionsof thepilot P T W . Theapproximately onefoot headdifference betweenwells WP-26locatedimmediately southof thepilot P T W andwell WP-34 locatedimmediately northof thepilot P T W suggests thepresence of a northwardlateralhydraulicgradientthatmaybe indicativeof continued groundwater flow beneaththepilot P T W . Thestartof the increasing trendin Sr-90activityat WP-34seemsconsistent with the startof an increasingtrendin Sr-90activityat WP-26suggesting thatbothwellsmaybe alonga similarflow patheventhoughtheyareon oppositesidesof thepilot P T W .

3. Sr-90activitiesin WP-35locatedapproximately 20 feetnorthof theP T W has showna similarrateof activityincrease asWP-34indicatingm igrationof the Sr-90lobeto thenorth-northeast.

4. Sr-90activitiesin groundwater samples collectedfrom WP-40,afterfirst increasing from approximately 10,000pCi/L to approximately 22,000pCi/L has decreased by abouttwo timessinceNovember2000. Thedecrease mayindicate influencefrom a front of slowlym igratinglow activity(possiblytreated) groundwater emanating from thenortheastern endof theP T Wtowardthewell location..

3.4 ASSESSMENTOF P T W DEVELOPMENTAND HYDRAULIC TESTING Selected datacollectedduringdevelopment andhydraulictestingof theP T W wereusedfor qualitativeanalysisof hydraulicconditionsaroundtheP T W .P T Wdevelopment wasconducted R:USELENE\phveval\geomatrixWydrau~~Rpt-Final

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evaluationby WVNS in July,August,September 2000,andJanuary2001.Hydraulictesting wasperformedby WVNS andconsistedof mini-pump testsat WP-25in JanuaryandApril 2000,slugtestsin severalwell pointsperformedin April and October2000(Table1). Figures 3.8 through3.10illustratethe resultsof selectedtestanalyses. The main objectiveof our review is to discernwhetherthe observedhydraulicpressureresponse dueto the testingindicates whethera lowerhydraulicconductivityskin existsalongthe interfaceof the PTW with the nativeaquifer.

3.4.1 Qualitative PumpingTest Analysis Figure3.8 showsthe drawdownresponse in selectedwell pointsto pumpingthe PTW riserpipe duringdevelopment activitiesin January2001. The datais providedfor the following well points:WP-29locatedinsidethe PTW, WP-34locatedto the north,PZ-06locatedto the northwest,WP-26locatedto the south,WP-27locatedto the east,andWP-25locatedto the westof the PTW. As reportedby WVNS,the purposeof the development wasto attemptto mobilizeandremoveany low permeabilityskin thatmay havedevelopeddueto PTW emplacement activities,andto qualitativelyevaluatehydraulicresponse in the PTW area duringlongerdurationpumping.As notedby WVNS duringthe initial development eventin July 2000,severalfeetof fine sedimentresemblingzeoliticmaterialwasobservedwithin the PTW riserpipe.

Qualitativeobservationindicatesthat thereis goodhydraulicconnectionbetweenthe PTW riserpipe andwell WP-29,asindicatedby the drawdownresponseof approximately6 feetin WP-29. Thenext bestresponse is encounteredat well WP-25,followedcloselyby PZ-06and WP-26(drawdownof approximately3 feet). The drawdownresponsefrom wells WP-34 (northof PTW) andWP-27 (eastof the PTW) is approximately2.5 feet. The drawdown responses indicatebetterhydraulicconnectionbetweenthe PTW andthe westernendof the PTW as seenat WP-25andPZ-06,which arelocatedfarthestfrom PTW riserpipe,than betweenthe easternendas seenat WP-27,which is closestto the PTW riserpipe.Theseresults suggestthatzonesof lowerhydraulicconductivityexistbetweenthe PTW andthe east,south, andnorthedgesof the PTW.

Figure3.9 showsthe drawdownresponse to pumpingfrom well point WP-25in January2000.

Whatis mostnoticeablefrom the drawdownresponses is the delayedresponsein WP-29 locatedinsidethe PTW. This observationstronglyindicatesthe importanceof storage (drainage)at WP-29suggesting that unconfined,or lessconfininggroundwaterflow conditions existwithin the PTW. Qualitativeobservations indicatesimilarbehaviorasnotedabovewith RMELElE\ptweval\geomat5xWydraul_Rpt-Final

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the lowestdrawdownresponse observedin WP-27. Thedecrease in degreeof confinement betweenthe nativesediments andthe PTW maypartiallyaccountfor the highergroundwater elevationdistributionobservedin the PTW duringperiodsof transientheadfluctuation.It is possiblethatthe response to rechargein the PTW mayresultin an apparentmoundingdueto hysteresisof the drainageandimbibitionprocessof the unconfinedsystem,or dueto a transient contrastin pressureresponse betweenthe confinednativesediments andthe unconfinedPTW.

Themagnitudeof influencefrom theseeffectsrequiresfurtherevaluationusinga numerical model.

3.4.2 Reviewof Slug Test Analyses Figure3.10showsthe hydraulicconductivityvaluesobtainedfrom slugtesting.Generally,slug testresultsarenot considered reliablefor the quantitativeassessment of hydraulicconductivity asthe resultsmaybe highly dependent on well construction(i.e. sandpack.skin,and development) but they still canprovidequalitativeinformationusefulfor assessing approximateconditions.Reportedresultsfrom the slugtestsrangefrom 1x 1Om5 cm/sin well point PZ-05locatedto the eastof the PTW to 2~10~~ cm/sin well point PZ-08locatedwithin the roundstonesectionof the PTW.All slugtestresultsobtainedwithin the clinoptilolite portionof the PTW arein the 1~10~cm/srange.Hydraulicconductivitymeasured in PZ-09, the secondwell point screened in the gravelroundstone portionof the PTW, is 1.5x1OAcm/s, which is muchlowerthanin PZ-08.It shouldbe notedthatthe constructionof well pointsPZ-8, PZ-9,andPZ-10is lessconduciveto slugtestingthanthe otherPTW well pointsand piezometers asthe screensaremuchshorter(2.5to 3 feet).

The slugtestresultsappearconsistentwith the resultsof permeameter testson the zeolite materialperformedat UB (Rabideau, et al, 1999).Thereportedresultsfrom the permeameter testingindicateda hydraulicconductivityfor the uncompacted looseclinoptiloliteto be 1.2x10-r cm/s. Whencompacted, the hydraulicconductivityreducedto 4~10~~ cm/s,which is within the generalrangeof the slugtestresults.However,theseresultsarebasedon laboratory conditionsandalthoughstronglycompacted, do not accountfor the likely sorting,andhigh degreeof pulverizingandcreationof finesthat mayhaveoccurredduringthe PTW emplacement.

Reviewof the hydraulicresponses andhydraulicconductivityvaluesobtainedfrom various typesof hydraulictestsindicatesthatthe PTW areais highly heterogeneous. Theresultsof pumpingtestanalysissuggestthatthe hydraulicconductivityof the PTW maybe lowerthan first anticipated.A systematic programof step,constant-rate, andrecoverytestingis R:\HELENE\ptweval\geomatrix\HydrauL_Rpt-Final

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recommended to obtainrepresentative hydraulicinformationthat canbe usedfor engineering design/modification activities.

3.5 CONCEPTUALMODELOFTHEPILOTPTWHYDRAULICPERFORMANCE A conceptualmodelwith respectto hydraulicperformance of the pilot PTW is presentedin this section.The conceptualmodelprovidesinsightinto possiblescenariosandinfluencesthat have leadto currentconditions.The conceptualmodelis not withoutuncertainty,andis to be used asa tool by which to testcertainhypotheses,The goalof the conceptualmodelis to provide directionby which to developengineeringsolutionsto eitherrestorethe intendedhydraulic performance of the system,or modify the designto promotethe desiredtreatmentof affected groundwaterin the sitevicinity.

As part of the assessment of hydraulicconditionsanddevelopment of this conceptualmodel, we havecoordinatedwith Dr. Alan Rabideauandstaff at UB who havebeencommissioned by WVNS to developa modelof hydraulicconditionsin the vicinity of the PTW. The model beingdevelopedby UB is basedon an analyticalapproachthat approximates two-dimensional groundwaterflow conditions(Rabideau,2000,200l). The analyticalmodeldoesnot account for verticalflow, or differencesin hydraulicpressureregimesthat,from a reviewof model resultsandsitehydrogeologicconditions,may be importantfor developingthe detailfor engineeringdesignpurposes.The following descriptionof the conceptualmodel,however, considerspreliminaryresultsfrom the UB modelingbut doesnot detailthoseresults. Separate reportshavebeenandarebeingpreparedby UB to documentthe analyticalmodel development.

Theconceptualmodelof the flow systemin the vicinity of the pilot PTW consistsof the following components, which aregenerallydescribedin Figure3.2:

1. A shallow,generallyunconfinedto semi-confined groundwatersystemthat consists of a heterogeneous sequence of silty clay, silt andgravel,andalternatinglayersof fine to coarsesandwith gravel,overlyinga low permeabilitytill. The contact betweenthe till andthe overlyingwater-bearing sediments undulatesacrossthe projectarea.

2. Hydraulicconductivityof the aquifersystemin a bulk senseis approximately1OAto lo cm/sthoughindividuallayerscanrangeup or downby an additionaloneto two ordersof magnitude.The bulk hydraulicconductivityof the underlyingtill is believedto be approximately3 to 4 ordersof magnitudelower.

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3. Theregionaldirectionof the lateralhydraulicgradientgenerallyis northto northeastwith a magnitudeof 0.03to 0.05ft/ft; however,the directionof the ambient(i.e.,pre-construction) lateralhydraulicgradientappearsto be relativelyflat locally with a shift towarda moreeasterlydirectionin the vicinity of the PTW, possiblyin response to the low permeabilityclay with silt sequence located immediatelywestof the PTW. Thewestendof the PTW may abuta portionof this low permeabilityzone. The interpretationof the moreeasterlygradientdirectionis controlled,in part,by measured waterlevelsat wells WP-25andWP-27. A review of limited headdatasuggests that an east-northeasterly directionexistedprior to constructionof the pilot PTW.

4. The activity of Sr-90is greatestin the lowerportionsof the SWS,andexistsasa narrow,but concentrated zonethatmigratesnortheasterly throughthe locationof the PTW; the activitygenerallyincreases from westto eastin the local vicinity.

5. Thepilot PTW straddlesthe westernedgeor fringeof the 2ndlobeof Sr-90.The pilot PTW may not fully penetratethe SWBZdownto the underlyingLaveryTill in its centralandeasternportion. This hanging PTW may allow underflowof high Sr-90activity groundwater assuggested by increasingconcentrations of Sr-90along portionsof the northsideof the PTW.

6. Thehigh stressof sheetpile installationlikely modifiedhydrostratigraphic pathways nearthe sheetpile alignment;majorflow conditionchangesareobservedat wells WP-25andWP-27,bothlocatedwithin approximately 5 feetof the pilot PTW. A discontinuous skin of fine zeoliticmateriallikely existsat the contactbetweenthe zeoliteandthe nativeaquiferon the eastandnorthsidesof the PTW. The skin may havedevelopeddueto the creationof finesduringemplacement andsheetpile movement,andmay havemigratedpartiallythroughthe morepermeable zeolite materialto the interfacewith the nativeaquiferduringsheetpile removalandthe relativelyquick flooding of the PTW by groundwater.The skin effectalongthe southsidelikely is a resultof finesmigratinginto the gravelasa resultof PTW development activitiesandsmearingof fine aquifermaterialacrossmorepermeable zonesadjacentto the sheetpile alignment.The interiorof the PTW likely is more heterogeneous thandesigneddueto the creationof finesandsortingof the zeolite from installationactivities.

7. Thehydraulicconductivityinsidethe PTW appearsto be highly variableandis likely controlledby the distributionof fine zeoliticmaterialsin the peripheryof the PTW (i.e.,skin) andwithin the PTW.

8. Hydraulictestinganddevelopment activitiessuggestthatthe entirehydraulic systembothwithin andoutsidethe pilot PTW is connected.However,hydraulic connectiondoesnot necessarily indicateSr-90migrationpathways.Local heterogeneity is moreresponsible for the Sr-90migrationpathway;somedegreeof anisotropybetweenthe directionof transportandthe directionof the hydraulic gradientlikely exists.

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9. The flow systemchangefrom a semi-confined nativeaquiferto an unconfined permeable treatmentzonelikely contributesto hydraulicmoundingwithin the pilot PTW dueto a contrastingtransientresponse to rechargeeventsbetweenthe native aquiferandthe PTW. Themagnitudeof this effectcouldfurtherbe assuredusinga numericalmodel.

10. Surfacewaterinfiltration into the PTW, althoughreducedby constructionof an upgradientdrainagesystem,continuesto contributeto headfluctuatingwithin the PTW.

To summarize, the overallhydraulicperformance of the pilot PTW likely is controlledby the following conditions:

l a predominantlymoreeastwardgroundwaterflow directionthaninitially anticipated (thePTW wasorientedfor predominantlynorthwardflow anddid not includelateral hydrauliccontrolsto directflow into the PTW);

0 a highly heterogeneous aquifersequence of fine andcoarsesediments; l a relativelynarrowflow zoneof high activity Sr-90waterthat existslow in the aquiferandthat is low at the westendof the PTW andhigh at the eastend;this flow pathis partiallydivertedaroundthe eastendof the PTW; l a hangingcentralandeasternportionof the pilot PTW which allowssome underflowof high Sr-90activity groundwater; l a discontinuous skin of fine zeoliticmaterialat the contactwith the nativeaquifer materialandheterogeneity with the PTW treatmentmaterialresultingfrom installationactivities; l slow dischargeof dilute,low Sr-90activitywaterfrom portionsof the PTW; this waterappearsto dilutehigherSr-90activity in somewells locatedcloseto the PTW; and, l continuing,althoughreduced,directsurfacewaterinfiltration into the PTW.

Thoughnot a specificphysicalcondition,the scaleof the testalsoinfluencesthe outcomeand contributesto the observedperformance of this pilot test. Thepilot PTW systemis a relatively small-scaletestandcannotabsorbthe influencesof complexityassociated with a high degree of heterogeneity (in aquifermaterialandthe directionof the hydraulicgradient)that characterizes the local system.Additionalaspectsof the effectof scaleon development of the engineered solutionareaddressed in the complimentaryengineeringassessment report.

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4.0 RECOMMENDATIONS Althoughcurrentconditionsat the pilot PTW indicatethatthe systemis not performingfrom a hydraulicperspectiveasintended,this pilot testsuccessfully identifiedspecifictechnicalissues that canbe addressed anddesignedfor prior to deployingan effectivefull-scalesystemat this and/orotherlocationsat theNorth Plateau.Priorto designingsucha full-scalesystem,the identifiedtechnicalissuesthat likely limit the hydraulicperformance of the pilot PTW should be furtherevaluatedso thatproperremediesto theseissuescanbe appropriately engineered.

Specifically,we recommend a follow-upphaseto this assessment that integrates the gathering of additionalspecificfield datawith the development of a three-dimensional numerical groundwater model. Thedevelopment of an engineering solutionto eithermodify the existing PTW, alterits orientation,or designa new PTW underthe uniquesite specificconditionsin the sameor differentportionsof the North Plateau,relieson the ability to appropriately represent currentconditions.Althoughwe havedevelopedhypotheses asto how the currenthydraulic conditionsdeveloped, thereremainssignificantuncertaintyfor which performinga supplemental andcost-efficientfield investigationwouldbe beneficialto decrease the degreeof uncertaintyandincreasethe potentialthat an effectiveengineering solutioncanbe developed andimplemented.

We thereforerecommend the following (in orderof importance):

1. Installtwo new wells andcollectstratigraphicinformationin the vicinity of WP-25 (westend)andWP-27(eastend)to confirmthe waterlevel conditionsthat appearto providemajorcontrolon the assumed groundwater flow directionsin the vicinity of the PTW. We recommend thatthesewells be installedby conventionaldrilling methodsandnot direct-pushmethods.

2. Drill at leastthreeadditionalsoil boringseachadjacentto the north,south,and easternfaceof the PTW that areloggedfor stratigraphic detailto confirmwhether the pilot PTW penetrates the underlyingtill or is hanging within the SWBZ. One additionalsoil boringfor stratigraphyshouldbe drilledtowardthe westernendof the PTW, andoneadditionalboringshouldbe drilled nearthe southfaceof the PTW. Theseboringsshouldbe convertedto 2-inchmonitoringwells to facilitate focusedaquifertesting(seeRecommendation No. 4).

3. Performa long-term(72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months sto oneweek)aquifertestingprogramconsistingof a seriesof step-testperiods,a constant-discharge period,andrecoveryperiod. The testcouldbe performedusingthe verticalriserdrainpipeinstalledwithin the upgradientgravelsectionof the pilot PTW with observation wellsmonitoredusing R:WLENE\ptweval\geomatrix\HydrauI~Rpt-Final

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downholepressuretransducers.Short-term(i.e.,4 to 8 hour9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months )step-tests alsoshould be performedin the new wells recommended in No. 2 above.

4. Performoneor moretracerteststo providefield evidenceof the flow field that predominates in vicinity of the pilot PTW.

Otherfield measures that couldprovideadditionalinsightinto the performance of the PTW (includingcoringanddetermination of Sr-90activityin zeolitecoresat variouslocationsin the PTW; andassessing the ion exchangeratio betweenSr-90andcalciumconcentrations in water samples)areavailablebut arenot considered to be asof high valuefor the taskof developing an engineeringsolutionto the PTW performance, The datacollectedfrom the supplemental investigationshouldbe integratedinto the development of a three-dimensional numericalflow modelto betterassess andpredictthe observedhydraulicconditions.Themodelingwould be performedby UB with consultation from GeomatrixandWVNS.

We believethatthe collectionandassessment of the supplemental data,alongwith development of the three-dimensional modelwill greatlyimprovethe ability to developan engineeringsolutionthat achievesthe level of operationalsuccessrequiredby the project stakeholders.

We believethatthe pilot PTW testis successfully meetingits objectivesto provideinformation critical to designinganddeployinga full-scalePTW at WVDP.

Additionalassessment andan initial surveyof possibleengineeringsolutionswill be provided in the complimentary engineeringassessment reportandthe PTW modificationsreport.

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5.0 REFERENCES

Berkey,E., 2000,Reviewof PreliminaryOperationalAssessment Reportfor the Pilot Permeable TreatmentWall (Draft),WestValley Demonstration Project,May 5.

Hemann,M., B. Fallon,andC.L. Repp,1998,1997GeoprobeInvestigationof theNorth Plateauat the WestValley Demonstration Project,WestValleyNuclearServices Company,Inc., WestValley,New York.

Moylan,J., 2000,Technicalpeerreview/evaluation of the WestValley Pilot Permeable TreatmentWall, URS,October11.

Rabideau,A.J., I. Jankovic,andV. Raghaven, 2001, Flow Modelingof the WVDP Treatment Wall: PreliminaryResultsDRAFT,Departmentof Civil, Structural,andEnvironmental Engineering,StateUniversityof New York at Buffalo.

Rabideau,A.J., J. Van Benschoten, C. Huang,andA. Patel,1999,BenchTestingof Zeolite BarrierMaterials,StateUniversityof New York at Buffalo.

Rabideau,A.J. andJ.E.Van Benschoten, 2000,North PlateauGroundwater Remediation:

ProgressReport,Universityof Buffalo.

Warner,S.D., 1986,Modelingthe aqueousgeochemical evolutionof groundwaterwithin the GrandeRondaBasalt,ColumbiaPlateau,Washington.M.S. Thesis,IndianaUniversity, Bloomington,Indiana.

WestValley NuclearServices,LLC. (WVNS), 1995,Subsurface ProbingInvestigationon the North Plateauat the WestValley Demonstration Project,WVDP-220,April.

WVNS, 1999,WVDP-350,DataQualityObjectivesfor the Pilot ScalePermeable Treatment Wall OperationalAssessment Program,June17.

WVNS,2000,PreliminaryOperationalAssessment for the Pilot PermeableTreatmentWall, May, 12.

WVNS, 2001,SummaryInformationfrom PTW EvaluationandAssessment Activities, February6.

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GEOMATRIX TABLE 1 CHRONOLOGY OF ACTIVITIES RELATED TO THE PTW PILOT TEST West Valley Nuclear Services West Valley, New York Year l Installationof WP-25,-26, -27 July

% l PTW sheetpiles installed : August Q) r l PTW sheetpiles pulled November8 - 12

. Installationof WP-28throughWP-40andPZ-1 throughPZ-7 CompletedDecember13

. First mini pumpingtest from WP-25 January3 1

. Secondmini pumpingtest from WP-25 April 19 l Slugtestingof selectedPTW WPs andPZs April l Peerreview of PTW PreliminaryOp. Assess.Report May 5 l PreliminaryOperationalAssessment Report May 19 l PTW development July, August,and September 8-9 l Installationof gravelzonePZs (PZ-08andPZ-09) August24 00 l URS (@ WVDP) review andevaluationof PTW conditions September15 - 18 z

l Slug testingof PTW WPs andPZsnot previouslytested September26 - October10 & 17 l Headchangesin PZ-01,-04, -05, -06 September 25 - October2 l Moylan peerreview/evaluation andreport October9 - 11 and3 1 l URS simplified groundwatermodelingof PTW area October17 - 27; December6 - 11 l Completionof surfacewaterdrainaroundPTW mid-October l Installationof PZ-10 October30 l WVNS management briefing on Pilot PTW path forward November29 l Temporarypumpingof PTW riser hourtest andrecovery January19

- l-week pumpingandrecovery January24 - 3 1 February5 - 19 weekpumpingandrecovery l SUNY Buffalo groundwatermodeling

- Startof modelingeffort January5 r; February2 1

- Preliminaryreport s March 9

- Final report l GeomatrixPTW evaluation

- Kickoff meeting February6 - 7

- PTW chapterreports(draft andfinal) March andApril

- Final report April 25 l WVNS Reportsubmittedto DOE June I:\Doc~Safe\7000s\7061Wydraulic Rpt\TABLE I.dcc

GEOMATRIX TABLE 2 MONITORING POINT CONSTRUCTION West Valley Nuclear Services West Valley, New York Monitoring Monitoring Top of Screen Bottom Point ID Point Diameter (feet bgs) of Screen PZ-01 1%-inch ! 7 22 PZ-02 1%-inch 7 22 PZ-03 1%-inch 7 22 PZ-04 1%-inch 7 22 PZ-05 1%-inch 7 22 PZ-06 1% -inch 7 22 PZ-07 1%-inch 7 22 I l%inch 1 PZ-09 1%-inch 15.5 18 PZ-10 1Vi-inch 9 12 WP-25 I WP-26 l-inch 7 22 WP-27 l-inch 7 22 WP-28 1-inch 7 22 WP-29 I WP-30 1-inch 7 22 WP-31 1-inch 7 22 WP-32 1-inch 7 22 WP-33 1-inch 7 22 WP-34 1-inch 7 22 WP-35 1-inch 7 22 WP-36 1-inch 7 22 WP-37 1-inch 7 22 WP-38 1-inch 7 22 WP-39 I 1-inch 7 22 WP-40 1-inch 7 22 1:U)oc~Safc\7000s\7061\Hydraulic Rpt\TABLE 2.dcc

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TABLE OF CONTENTS Page

1.0 INTRODUCTION

AND SCOPEOF REPORT............................................................... 1 1.1 ORGANIZATION OFREPORT .2 1.3

SUMMARY

OFHYDRAULICEVALUATION REPORT.. .2 1.3.1 Summaryof PreviousReports................................................................... 2 1.3.2 Site Hydrostratigraphy.. .4 1.3.3 Pre- and Post-Construction GroundwaterElevations............................... .4 1.3.4 HydraulicTestingin and nearPTW ......................................................... .5 1.3.5 Conclusions.............................................................................................. .5 1.3.6 Recommendations for CollectingAdditional Data................................... 6 2.0 PILOT PTW CONSTRUCTIONAND INSTALLATION METHODS ......................... .6 2.1 ENGINEERING DESIGNOFPILOTPTW ................................................................... .6 2.1.1 PlacementandAssemblyof Cofferdam................................................... .7 2.1.2 Excavationof Soil andPlacementof the TreatmentMedia..................... .8 2.2 AS-BUILTCONSTRUCTION OFPILOTPTW ............................................................ .9 3.0 POTENTIAL CAUSESOF LIMITED GROUNDWATERFLOW THROUGH THE PILOT PTW ................................................................................................................................ 12 3.1 HIGHGROUNDWATER LEVEL.............................................................................. .12 3.2 SMEARING OFPTW SIDEWALLS 12 3.2.1 Descriptionof Mechanism..................................................................... .12 3.2.2 CollectingData to SupportMechanism................................................. .13 3.3 CONSOLIDATION OFCLINOPTILOLITE.. .13 3.3.1 Descriptionof Mechanism...................................................................... 13 3.4 CRUSHING OFCLINOPTILOLITE.. .14 3.4.1 Descriptionof Mechanism...................................................................... 14 3.4.2 CollectingDatato SupportMechanism................................................. .16 3.5 CLINOPTILOLITE PLUGGING VOID SPACES IN ROUNDSTONE.. ..............................16 3.5.1 Descriptionof Mechanism..................................................................... .16 3.5.2 CollectingDatato SupportMechanism.................................................. 17 3.6 FINESMOVEMENTASPTW FILLEDWITHGROUNDWATER.. ................................17 3.6.1 Descriptionof Mechanism...................................................................... 17 3.6.2 CollectingData to SupportMechanism 18 3.7 GROUNDWATER FLOWUNDERPTW ................................................................... .18 3.7.1 Descriptionof Mechanism..................................................................... .18 3.7.2 CollectingDatato SupportMechanism................................................. .18 4.0 POTENTLALCAUSESOF HIGHER HYDRAULIC HEAD MEASURED IN THE PILOT PTW ............................................................................................................................... .18 4.1 POTENTIAL CONDUITS INTOTHEPTW ................................................................ .19 4.1.1 Descriptionof potentialconduits.. .19 4.2 PERMEABLE CAPOVERPTW.. .............................................................................. 19 I:\Project\7000s\706l~eports\Engineerinevised Engineering Report-fs-sdw.doc 1

TABLE OF CONTENTS (Continued)

5.0 CONCLUSION

S............................................................................................................

.20 6.0 RECOMMENDATIONS...............................................................................................

.23 7.0 LESSONSLEARNED ...................................................................................................

.24 FIGURES Figure1.1 SiteLocation Figure1.2 SitePlan Figure1.3 PTWAreaandCross-Section Location Figure1.4 PTW Area Cross-Section D-D Figure4.1 PotentialSourcesof SurfaceWaterInflow into PTW I:\Project\7000s\706luleports\Engincc~ng~evised Engineering Report-fs-sdw.doc ii

PILOT PERMEABLE TREATMENT WALL ENGINEERING EVALUATION REPORT WestValley NuclearServices,LLC WestValley,New York

1.0 INTRODUCTION

AND SCOPE OF REPORT This Pilot PermeableTreatmentWall,EngineeringEvaluationReport was preparedby GeomatrixConsultants,Inc. (Geomatrix)at the requestof West Valley Nuclear Services,LLC (WVNS). The report was commissionedby WVNS (Project 19-098745-C-JK)to assistin assessing the performanceof a pilot permeabletreatmentwall (PTW) designedto remediate groundwateraffectedby radioactiveStrontium-90(Sr-90) beneatha portion of the West Valley DemonstrationProject(WVDP) locatedin westernNew York state(Figure 1.l). A companion report,the Pilot PermeableTreatmentWall Hydraulic EvaluationReport,(the Hydraulic EvaluationReport)was alsopreparedby Geomatzixfor WVNS. Both of thesereportssupport preparationof the Pilot PermeableTreatmentWall Modzjkation Report,to be submittedto WVNS by April 25,200l.

A pilot PTW was installedby WVNS at the WVDP in Fall 1999to assessthe ability of the technologyto passivelyand effectivelyreducethe concentrationof Sr-90affectedgroundwater.

The pilot PTW was installedto treata portion of the 2nd lobe of the Sr-90plume beneaththe North Plateauof the site (Figure 1.2). The lSt lobe of the Sr-90plume to the west currentlyis being remediatedby a groundwaterrecoveryand abovegroundion exchangetreatmentsystem (pump-and-treat) that was installedin 1995. While the pump-and-treatremedyreportedly reduceslocal migrationof the Sr-90plume,WVNS doesnot considerit capableof completely capturingand remediatingthe affectedgroundwaterbeneaththe North Plateau. Thus WVNS identified PTW technologyas a methodpotentiallycapableof effectivelymitigating further migration of Sr-90affectedgroundwater.

Monitoring datacollectedby WVNS indicatesthat the PTW may not be functioningas designed,specificallygroundwaterfrom south,andpresumedup hydraulic gradientside of the PTW may not be flowing northwardthroughthe PTW. The generalpurposeof this report is to evaluatethe engineeringdesignand constructionof the pilot PTW and,in conjunctionwith the I:\Projcct\7000s\706i~cpons\Engince~ng~cvised Engineering Report-fs-sdw.doc 1

companionHydraulicEvaluationReport,to betterunderstandthe monitoringdatacollectedto date.

This engineeringevaluationhas focussedon four tasks:

l A descriptionof the designof the PTW l A narrativeof the constructionof the PTW l Potentialcausesof limited or no flow throughthe PTW l Potentialcausesof raisedwater levelsmeasuredin the PTW relativeto surrounding water levels.

A brief discussionof lessonslearnedfrom PTW installationsat other sites,and how such lessonsrelateto the Pilot PTW at WVDP also is presented.

1.1 ORGANIZATIONOFREPORT The organizationof this report follows the approachwe havetakenin this evaluation.

Following this introductorysectionthis reportsconsistsof the following Sections:

l Section2.0 Pilot PTW Constructionand InstallationMethods(including discussionsof engineeringdesignof the PTW, and reportedas-builtconstructionof the PTW).

l Section3.0 PotentialCausesof InferredLimited or No GroundwaterFlow Throughthe Pilot PTW (includingdatagapsfor the causes) l Section4.0 PotentialCausesof Higher HydraulicHeadMeasuredin the Pilot PTW (includingdatagapsfor the causes).

0 Section5.0 Conclusions l Section6.0 Recommendations l Section7.0 LessonsLearned 1.3 SIJMMARYOFHYDRAULICEVALUATIONREPORT 1.3.1 Summaryof PreviousReports The Hydraulic EvaluationReportsummarizedpertinentresultsfrom previousevaluation reportson the PTW performance,specifically:

I:\Projcct\7000s\706l\Reports\Engincc~ng~cviscd Engineering Report-fs-sdw.doc 2

l SummaryInformationfrom P T W EvaluationandAssessment Activities, dated February6,2001,preparedby WVNS.

0 TechnicalPeerReview/Evaluation of the WestValley Pilot Permeable Treatment W a ll, datedOctober11,2000,preparedby J. Moylan,URS Corporation.

0 Preliminary OperationalAssessment for the Pilot Permeable TreatmentW a ll, datedMay 12,2000,preparedby WVNS.

l Review of PreliminaryOperationalAssessment Reportfor the Pilot Permeable TreatmentW a ll (Draft), WestValley Demonstration Project,datedMay 5,2000, preparedby E. Berkey,Ph.D.

Commonopinionsfrom thesereportsinclude:

1. Uncertaintyexistsasto the directionof the local horizontalhydraulicgradientprior to P T W construction (theregionaldirectionwas generallyobservedto be towardthe north,thoughsomedataindicateda northeasterly direction).

2. W a terlevelsin well WP-25,directlywestof the PTW, andwell WP-27,directly eastof the PTW, controlthe interpretation of the local groundwater gradient direction;waterlevelsincreased in well WP-25anddecreased slightlyin well WP-27 following sheetpile installation.The directionof groundwater flow appearsto flow directlyeastwardthroughthe P T W basedin part on well WP-25andwell WP-27 data. W a terlevelsalsoaregenerallyhigheron the southsideof the P T W compared to the northsideof the PTW.

3. Surfacewaterinfiltration was considered to be a significantcontributingfactorto hydraulicmoundingwithin the PTW.

4. Thereis potentiallya skin aroundthe subsurface P T W causedby the construction method.Uncertaintyexistsasto the natureandlocationof the skin andits influenceon the hydraulicconnectionbetweenthe P T W andthe aquifer,although waterlevel dataindicatesthat the hydraulicconnection appeared to improve following long-termpumpingfrom within the PTW.

5. The activityof Sr-90in groundwater sampledfrom within the P T W is very low.

Activity of Sr-90in groundwater sampledfrom westof the P T W is low; activity of Sr-90in groundwater southeast, east,andnorthof the P T W is high andappears to haveincreased in severallocationssinceinstallationof the PTW.

6. From the previousassessments, multipleopinionsexistasto what the most appropriate modificationto the P T W consistsof (e.g.,additionalpumpingand development, installationof wing or lateralhydraulicbarriersto route groundwater throughthe PTW, etc.).

I:\Project\7000s\7061\Rcports\Engineering\Xevised Engineering Report-fs-sdw.doc 3

1.3.2 Site Hydrostratigraphy The following informationon site hydrostratigraphy generallyis summarizedfrom the companionHydraulicsReport.

Two distincthydrostratigraphic units are interpretedto exist beneaththe North Plateau:

l A basalconfiningaquitard(or low permeabilityzone)consistingof lacustrineclay and silt, and Lavery Till l The ShallowWater-BearingZone,consistingof alluvial sandandgravel,and the SlackwaterSequence Figure 1.3 showsthe borings,well-pointsandpiezometersin the vicinity of the PTW. Cross-sectionD-D (Figure1.4)showsthe stratigraphythroughthe PTW indicatedby the boring logs.

(Cross-sections A-A, B-B, and C-C areprovidedin the companionHydraulicsReportbut are not repeatedin this report). In the vicinity of the PTW, the ShallowWater-BearingZone generallyconsistsof silty clay (groundsurfaceto approximately6 feet bgs), silt and gravel (approximately6 to 11 feet bgs), andalternatinglayersof fine to coarsesandwith graveland silty clay with gravelcharacteristicof the SlackwaterSequence(approximately11 to 25 and 30 feet bgs). The ShallowWater-BearingZone overliesthe Lavery till which is encountered at depthsof approximately25 to 30 feet bgs. The top of the Lavery till unit is variableand appearsto undulatein the vicinity of the pilot PTW.

1.3.3 Pre- and Post-ConstructionGroundwater Elevations Threewell-points(WP-25,WP-26 andWP-27)were installedin July 1999,prior to construction.Twenty-threeadditionalwell-pointsand piezometerswere installedin and aroundthe PTW following construction.Comparisonof the pre-andpost-construction dataand review of post-construction dataindicatedthe following:

l Water levelsmeasuredfrom wells locatedin the PTW are consistentlyhigher than measurements from well points screenedin the native sedimentswith the exception of waterlevelsmeasuredin WP-25; l Following installationof the sheetpiles,waterlevelsin well WP-25 increasedabove ambientconditionsandhaveremainedhigh; following removalof the sheetpiles, waterlevelsin WP-27 decreased slightly; l The groundwaterelevationsmeasuredfrom well pointslocatedinsidethe PTW are practicallyidentical,indicatinga nearzero horizontalhydraulicgradient; I:\Project\7000r\706l\Rcports\EnginccringUleviscd Engineming Report-fs-sdw.doc 4

l Groundwater elevationcontoursindicatethat groundwater is flowing towardsthe eastthroughthe P T W andradiatesawayfrom the P T W on the south,east,andnorth facesindicatinghydraulicmoundingconditions;however,waterlevelson the south arealsogenerallyhigherthanwaterlevelsto the north andeastsidesof the PTW; l The horizontalhydraulicgradientbetweenthe P T W andthe nativematerial decreased following P T W development (assuggested by waterlevelsmeasured in wells WP-29andWP-26,respectively, andshownin Figure3.4 of the Hydraulic EvaluationReport);

l Groundwater elevationfluctuationsdueto precipitationor snowmelt are generally similarin all well pointsinsideor outsidethe PTW; well pointslocatedinsidethe P T W havegreaterfluctuations; l Groundwater elevationsinsidethe P T W are alwayshigherthanthosemeasured outsidethe PTW, , exceptduringprecipitationandsnowmeltwhenelevations measured in WP-25arehigher; l Constructionof the surfacewaterdrainin October2000hasbeeneffectivein reducingsurfacewaterinfiltration into the PTW.

1.3.4 Hydraulic Testingin and near P T W In summer2000,the P T W wasdevelopedby pumpingwaterout of the drainpipe in the roundstone zoneof the PTW. Thepurposeof the development wasto attemptto mobilizeand removeany low permeabilityskin that may havebeenpresentaroundthe PTW. Severalfeet of fine sediment,presumablyclinoptilolite,wasreportedlyobservedwithin the lo-inch riser pipe within the roundstone zone.

W a terlevelswereobservedin a numberof well-pointsandpiezometers in andaroundthe P T W duringpumping.W a terlevelsindicatedtherewas somehydraulicconnectionbetweenthe P T W andthe surroundingaquifer. Evaluationof the waterlevelsindicatedthat zonesof lower hydraulicconductivitymay existat the east,northandsouthsidesof the PTW.

1.3.5 Conclusions The HydraulicEvaluationconcludedthat the performance of the P T W is probablycontrolled by:

l a moreeastwardgroundwater flow directionthaninitially anticipated(the P T W was orientedfor northwardflow);

l a highly heterogeneous aquifersequence of fine andcoarsesediments; I:\Projcct\7000s\706l~e~~~ngin~~ng~eviscd Engineering Report-fs-sdw.doc 5

l a narrowflow zoneof high activity Sr-90waternearthe baseof the aquiferandthat is lower in activity at the westendandhigherin activity at the eastendof the PTW; this flow appearsto be partiallydivertedaroundthe eastendof the PTW; l the P T W may not havefully penetrated the aquifer,andthe hanging centraland easternportionof the P T W may allow underflowof high Sr-90activity groundwater; l a discontinuous skin of lower permeabilitymaterialat the contactof the P T W materialswith the nativeaquifermaterialandheterogeneity within the P T W treatmentmaterialresultingfrom installationactivities;and, l slow discharge of treatedlow Sr-90activitywaterfrom portionsof the PTW; this waterappears to reduceSr-90activity in somewells locatedcloseto the PTW.

1.3.6 Recommendations for CollectingAdditional Data The HydraulicEvaluationReportrecommended the following datacollectionactivitiesto assess the possiblecausesof poor P T W performance:

1. Install two or morenew wells andcollectstratigraphicinformationin the vicinity of WP-25(westend)andWP-27(eastend)to confirmthe waterlevel conditionsthat appearto providemajor controlon the assumed groundwater flow directionsin the vicinity of the PTW.

2. Drill at leastthreeadditionalsoil boringsaroundthe easternendof the pilot P T W (oneeachadjacentto the north,south,andeasternface)that areloggedfor stratigraphicdetailto confirmwhetherthe pilot P T W penetrates the underlyingtill or is hanging within the aquifer. Oneadditionalsoil boringfor stratigraphy shouldbe drilled towardthe westernendof the PTW, andoneadditionalboring shouldbe drilled nearthe southfaceof the PTW. Theseboringsshouldbe convertedto 2-inchmonitoringwells for subsequent aquifertesting.

3. Performoneor moretracerteststo providefield evidenceof the flow field that has beeninterpretedfrom waterlevelsin the vicinity of the pilot PTW.

4. Performa long-termaquifertestconsistingof a seriesof step-testperiods,a constant-discharge period,andrecoveryperiod,to provideadditionaldataon the hydraulicconnectionof the P T W to the surroundingaquifer.

2.0 PILOT P T W CONSTRUCTION AND INSTALLATION METHODS 2.1 ENGINEERING DESIGNOFPILOTP T W The engineering designof the P T W was evaluatedfrom the designdrawingssuppliedto Geomatrix.Thesedrawingswere:

I:\Projcct\7000s\706I\Rcports\Enginccring\Reviscd Engineering Report-fs-sdw.doc 6

l North PlateauPermeable TreatmentW a ll, Drawingno. 900D-7867,sheets1 through8 of 8.

l North PlateauPermeable TreatmentW a ll Cofferdam,Drawingno. 900D-7857, sheet1 through4 of 4, and l Site,North PlateauArea,TopographyandUnderground Piping,Drawingno. 900D-6743,sheet1 of 1.

The following presentsa narrativeof the designof the PTW.

2.1.1 Placementand Assemblyof Cofferdam The P T W wasdesignedasa rectangular cofferdam,measuring7 feetwide by 30.5feet long.

The designspecified42 sheetsof ArbedAZ48 sheetpiles to be drivenwith a vibratoryhammer to the approximate contactwith the LaveryTill at 28 feetbelow originalgroundsurfacealong the alignmentof the treatmentwall. The designdepthis shownas 1356feet abovemeansea level (msl) on CAD drawing#900D-7857sheet1. The designthenspecifiedthe sheetpilesbe drivenan additionalten feet (to 1346msl) into the LaveryTill with an impacthammer.The designalsospecifieda contingency plan,allowingthe contractorto drive the sheetpilesto a lesserdepthandcut off the topsto a uniformheight,shouldpenetrationof the Till be difficult.

Prior to driving,AdekaUltraseal#50A was to be appliedto eachsheetpile interlock,to m inimizeleakageof groundwater into the excavationduringconstruction.

The designrequiredthe cofferdamto be supported by a singlelevel of externalbracingthat consistedof 2-W36x182waleswith restraintbracketsmountedon 77 centersalongthe length of the cofferdam, andof two W18x86walesalongthe width. The waleswereto be installed horizontallyaroundthe outerperimeterof the cofferdambeneaththe existinggroundsurface (1384feetmsl), with the horizontalaxisat 1382feetmsl. On the southsideof the cofferdam, flowablefill wasto be placedunderthe wale systemto providesupportfor equipment.

After completionof the structuralelementsof the cofferdam,the volumeof soil within the cofferdamwasto be dewatered with four dedicated pumps(DW -I, -2, -3, -4) installedat equal intervalsdirectlybeneaththe alignmentof the PTW. Eachdewateringwell wasto be activated by a pressureswitchdesigned to engagethe pumpwheneverthe groundwater risesin the well 12 inchesaboveeachindividualpump. Groundwater pumpedfrom thesewells wasto be pumpedto the surface,conveyedin 2-inchpolyethylene pipe anddischarged to a 1000gallon holdingtank. From the tank,the treatedwaterwasto be pumpedby a sumppump,activatedby a float switch,to Lagoon#2.

I:\Projeci\7000s\7061\Reports\Engince~ng~cviscd Engineering Report-fs-sdw.doc 7

2.1.2 Excavation of Soil and Placementof the Treatment Media The soil within the cofferdamwas to be excavatedto 1356feet msl or approximately28 feet below original groundsurface(bgs). The drawingsdo not indicateany slopeof the bottom of the PTW. Prior to any backfilling, the drawingsspecifyplacementof a 6 inch perforatedPVC pipe, wrappedin non-wovengeotextileor a sock-typegeosyntheticpipe sleeve,attachedto a 10 inch diameterperforatedPVC standpipeto be placedin the eastend of the roundstonezoneof the PTW.

A divider system,consistingof a long steelplate,suspended by cablesfrom the surface,was to be constructedand installedto maintainphysicalseparationof a 18-inchwide vertical layer of

l stone(roundstone)adjacentto a 66-inchwide vertical layer of clinoptilolite,the zeolitic treatmentmedia. The separatorplatewas to be raisedstepwisein incrementsof 2.75 feet alwaysleavinga minimumof 8 inchesof the plateburiedbetweenthe stoneand the clinoptilolite. This buffer would be maintainedby visual inspection.The roundstonewas to be pouredin 12 inch lifts on the southwestside of the divider systeminto a 42x42 inch hopper with a flexible 8 inch PVC elephanttrunk attachedto its dischargeport. The purposeof the flexible hosewas to channelandcontrolthe flow of the roundstone,as the hopper,free to roll on steelI-beamrails at the surface,was guidedforwardandbackwarddispensingthe stonein a uniform fashion. Otherthan the 12-inchlift limitation, alternatingwith lifts of stone,the methodof clinoptiloliteplacementwas not specified.

Following placementof the roundstoneand clinoptilolite backfill to within 2 feet of finished gradeof elevation1383.2,the walesandbackfilling systemwere to be removed. The area behindthe sheetpiles wherethe waleswere locatedto be filled with previouslyexcavated,non-contaminatedmaterial,andthe clinoptilolite androundstonewere to be broughtup to elevation 1383.2. The designcalledfor a one inch layer of granularsodiummontmorillonite(Volclay CG50Bentonite)to be placedover the roundstone,clinoptilolite, andbackfill placedaroundthe outsideof the sheetpiles,moundedto 6 incheshigh on the insideand outsideof the sheetpiles.

We understandthat this layer of bentonitemay havebeenplacedafterthe sheetpiles were extracted,althoughthis conflictswith the as-builtdrawings. The sheetpiles then were extractedandthe surfacecompletioninstalled.

The surfacecompletionwas to consistof clay fill approximately1.4to 1.9 feet thick constructedover the PTW. The clay fill was to matchexistinggrades(El. 1384.6)at the edge of the excavationandbe mounded6-incheshigherin the middle of the PTW (El. 1385.1).

Protective3.5-inchdiameterbumperpostswereto be placedaroundthe perimeterof the PTW I:\Project\7000s\7061\Reports\Enginee~ng~cviscdEnginceFing Report-fs-sdw.doc 8

at eachof the four comers. No compactionrequirementsor selectbackfill specificationsare indicatedby the drawings.

We understandthat quality assurance testingof the clinoptildlite beforedelivery showedless than4 percentfines in the material. Thedesigndid not prescribeany specificproceduresfor transportation,storage,handlingor inspectionof the clinoptilolite at the site prior to placement in the PTW.

2.2 As-BUILTCONSTRUCTION OFPILOTPTW The as-builtconstructionof the PTW was describedin the as-builtconstructiondrawingsand in WVNSs responseto questionssubmittedby Geomatrixon February14,2001, Jim Woodworth,the CognizantEngineerfor the PTW work, and Mark Hemannof WVNS provided responses to Geomatrixs questions.The following narrativewas developedfrom their answers andreview of the as-builtdrawings.

The pilot PTW was installedto treata portion of the rc2nd lobe of the Sr-90plume beneaththe North Plateauof the site (Figure 1.2). The approximately100feet by 100feet areaof the PTW is locatedto the north westof LagoonsNo. 4 and No. 5. The groundsurfacegenerallyslopes down at about3 percentfrom southto north in the areaof the PTW.

The 100 feet by 100feet areaaroundthe PTW was first preparedby laying down a working surfaceconsistingof a 7-inch thick layer of crushedstoneplacedon geotextile(the hardstand). The PTW dewateringsystemof four wells was then installed,andthe well dischargepipedto the lOOO-gallon holding tank then to Lagoon#2. The electricalline to the wells was installedin a conduitthat wasplacedin a trenchabout2 feet wide and2 feet deep.

In the areaof the PTW, the hardstandlayer was scrapedback andthe geotextilecut to allow installationof the sheetpiles. The PTW cofferdamwas then laid out andthe sheetpiles driven to createthe structure.The sheetpiles were driven on the weekof August23, 1999.

The sheetpiles were drivenwith a vibratoryhammerto approximatelyelevation1358msl, which is approximatelythe top of the Lavery Till; the sheetpiles thenwere driven to grade with an impacthammer. The top of the Till was encountered at approximatelyelevation1358 insteadof the designelevationof 1356. The sheetpiles thuswere driven 12 feet into the Till, insteadof the designed10 feet penetration.The hardstandandnative soil were excavated aroundthe outsideof the sheetpiles andthe geotextilewas cut back to provideroom to place I:\Project\7000s\706l~eports\Enginee~ng~eviscd Engineering Report-fs-sdw.doc 9

the externalwale system. Two inclinometerswere installedat the sametime as the four dewateringwells about8 feet from the sheetpiles on the north and southsidesof the cofferdam;theseinclinometerswere monitoredduring excavationand backfilling of the PTW, includingextractionof the sheetpiles.

The interior of the PTW was dewateredby pumpingthe 4 wells within the cofferdam.

Excavationbeganto removethe materialinsidethe cofferdam. The excavationwas dewatered by the 4 wells until the excavationreachedabout 15 feet bgs. Below this depthsumppumps were droppedinto the excavationto dewaterthe top of the excavationas it proceeded,and the dedicateddewateringwells were removedby the excavation.The sheetpiles had Adeka sealanton the interlocksto reduceseepageinto the cofferdamexcavation.This sealantis designedto swell in contactwith waterandplug the spacein the interlock. Howeversome water continuedto flow into the excavation;this waterwas removedby the sumppumps.

The baseof the excavationwas at approximatelyelevation1358 msl at the eastend, slopingup to approximately1358msl at the west end. A baseelevationof1356msl was depictedon the designdrawings. The baseof the excavationslopedfrom eastto west, andthe west endwas about 1 foot higherthan the east. Basedon pre-excavation boring data,portionsof the excavationdid not extendto the top of the Till (seeFigure 1.4). The inclinometersindicateda maximumof about 1 inch of movementof the top of the excavationafter it was complete.

A divider systemwas installedwithin the cofferdamto keepthe clinoptilolite androundstone separateduringbackfilling. A 6-inch diameterperforatedPVC pipe was placedalongthe base of the excavationwithin the roundstonebackfill area,with a IO-inchPVC riser pipe attachedto the lower eastend of the drainagepipe. The cofferdamwas backfilledby emptyingsupersacks of clinoptilolite into the excavationfrom the surface,andplacingroundstonethrougha PVC elephanttrunk. Lift thicknesses were approximately1 foot. The level of the clinoptilolite androundstonebackfills were maintaineda maximum1foot apartduring backfilling by observation.Backfill was placedin a dry excavation.This methodof backfilling the excavationwas reportedlyvery effective.

The cofferdamwas backfilled with clinoptilolite androundstoneto approximatelyelevation 1382when the divider systemwas removed. The clinoptilolite and roundstonewas then broughtup to designelevationof 1383.2.By this time the waleshad beenremoved,andthe zoneoutsidethe cofferdamwherethe waleshad beenwas backfilledwith previouslyexcavated material. The geotextileunderneaththe hardstandwas cut back to whereit daylightedinto the I:\Project\7000s\706I\Reports\Enginee~ng~eviscd Engineering Report-fs-sdw.doc 10

excavationsidewalls. The as-builtdrawingsindicatethat the l-inch thick layer of Volclay CG-50 (a granularbentonitewith a grain sizesimilar to a sand)was placedover the excavationat 1383.2,with additionalmoundsof CG-50placedon both sidesof the sheetpiles; howeverwe understandthat no bentonitewas placeduntil the sheetpiles were extracted.The purposeof the CG-50was to sealthe surfaceof the treatmentzone.

From November8 through12, 1999the sheetpiles werewithdrawnfrom the ground. The sheetpiles were removedwith a vibratoryhammer,startingat the west side of the cofferdam nearWP-25. Any materialstuckto the sheetpiles was scrapedoff; reportedlythis material amountedto lessthan 2 wheelbarrowloadsper sheetpile. As the sheetpiles werewithdrawn, the surfaceof the clinoptilolite settled;onceall of the sheetpiles hadbeenwithdrawn,the surfaceof the clinoptilolitehad settledapproximately4 feet. The inclinometersindicated lateralmovementinto the excavationof about7 incheson the southside,and 3 incheson the north side. Well WP-26 directly southof the cofferdamsettledabout 0.36 feet.

Additional clinoptilolitewas addedto the existingmaterialto bring it backup to gradeat 1383.2.A one-inchlayer of CG-50was placedover the roundstoneand clinoptilolite surface, and clay fill was placedin the excavationto bring the surfaceup to final elevationof 1384.6, moundedto 1385.1in the middle of the PTW. The clay fill was not compactedso that further settlingof the clinoptilolite would not occur. Hardstandstonewas then reportedlyrakedover the filled areato providea goodworking surface.

Four bumperpostswereplacednearthe comersof the PTW. The bumperpostswere initially installedas the cofferdamwas backfilled,but they werein the wrong locationso they were removedandreinstalled.The bumperpostsare 7 feet long, and about3.5 feet of eachpost is embeddedin the ground. The postswere installedby rotatingthem into the ground.A helical screwat the baseof eachpost securesit into the ground. Basedon the as-builtlocationof the bumperpostsandthe PTW, it appearsthat the at leastone andpossiblytwo of the postswere installeddirectly over the clinoptilolite or roundstonezone;the othertwo postsarewithin 6-inchesof the clinoptilolite and roundstonezone. The top of the filled areawas at elevation 1384.6to 1385.1,so the helical screwis at 1381.1to 1381.6,or about 1.5to 2 feet below the top of the clinoptilolite androundstone.

A surfacewaterdrain was installedin October2000. This drain consistedof a l-foot deep ditch lined with HDPE on the baseand downstreamside andfilled with surgestone. The drain was installedabout 12 feet southand slightly uphill from the PTW, and it directedflow north I:\Projcct\7000s\7061\Reports\EnginccringIRevised Engineering Report-fs-sdw.doc 11

andaway from the PTW area. Flow hasbeenobservedin the drain, andthe sharpwater level increaseswithin the PTW that were observedfollowing rain or snowmelthavenot been observedsincethe drain was installed.

3.0 POTENTIAL CAUSES OF LIMITED GROUNDWATER FLOW THROUGH THE PILOT PTW Water levelsweremeasuredin well pointsand piezometersinstalledin and aroundthe PTW beforeand after constructionof the PTW. Interpretationof thesewater levelsindicatesthat groundwaterfrom the southand expectedregionalupgradientdirectionlikely is flowing around the PTW to the east;with groundwaterfrom the west enteringthe PTW. This sectiondiscusses potentialcausesof limited flow throughthe PTW that could haveresultedfrom the designand constructionof the PTW.

3.1 HIGHGROUNDWATERLEVEL Measuredwaterlevelswithin the PTW are higherthan waterlevelson the outsideexceptat WP-25. Higher waterlevelswithin the PTW would preventthe Sr-90plume to the southfrom flowing throughthe PTW, andno othereffectsarenecessaryto explainthe observedhydraulic condition.. Potentialcausesof higherwater levelswithin the PTW are discussedin Section4 of this report.

3.2 SMEARINGOF PTW SIDEWALLS 3.2.1 Description of Mechanism Driving and extractionof sheetpiles will smear materialsalongthe interfacebetweenthe sheetpiles andthe nativesoil, creatinga skin of lower permeabilitymaterialaroundthe PTW.

As describedin the HydraulicEvaluationreport,the SlackwaterSequence penetratedby the PTW consistsof interlayeredfine-grainedand coarse-grained units, and this sequenceis probablythe most susceptibleto smearingas the finer-grainedunits are smearedacrossthe coarse-grained waterbearingunits. Portionsof the PTW sidewallsare probablysmeared, reducingflow throughtheseportionsof the aquifer.

However,someflow was observedcomingin to the excavationthroughthe sealedsheetpiles as the PTW was constructed.This indicatesthat groundwaterflow throughportionsof the aquiferwas probablynot affectedby smearing,at leastwhen the sheetpiles were installed. In addition,an hydraulicconnectionbetweenthe PTW andthe surroundingaquiferhasbeen observedin variouspumpingtestsin the area.

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We believethat smearingmay havecut off someof the thinnerwaterbearingzones,but has only marginallyaffectedthicker,coarser-grained waterbearingzones. If hydraulicheadsare higherin thesecoarserunits,then higherwater levelswould be observedin the PTW than are observedin well-pointsandpiezometersoutsidethe PTW that are screenedacrossboth coarse-grainedand fine-grainedwaterbearingunits, Smearingmay alsoreducethe effect of underflowbeneaththe PTW, althoughthis cannotbe quantifiedwith availabledata.

The magnitudeof smearingcausedby driving and extractingthe sheetpiles, and its effect on the local hydraulicconductivityof nativematerialshasnot beenextensivelystudied,to our knowledge.We expectthat the magnitudeof this effect dependson soil strengthandplasticity, the thicknessof the coarse-and tine-grainedunits, the thicknessof the sheetpiles and the lengthof time the sheetpiles are in the ground.

3.2.2 Collecting Data to Support Mechanism Carefulinstallationof monitoringwells screenedonly in candidatecoarse-grained units near the PTW can indicatewhetherpiezometic waterlevelsare higher in theseunits than in fmer-grainedunits. Thesemonitoringwells shouldbe installedin additionto thoserecommended in the HydraulicEvaluationreport. If water levelsin thesewells are similar to water levels measuredin the PTW, then smearingcould be the sole causeof the observedhydraulicregime.

Additional monitoringwells could alsobe installedthroughthe PTW and screenedin the potentialunderflowzoneto evaluategroundwaterflow underthe PTW.

3.3 CONSOLIDATIONOFCLINOPTILOLITE 3.3.1 Description of Mechanism As the sheetpiles were withdrawn,the surfaceof the clinoptilolite settledabout4 feet, indicatingsignificantconsolidationanddensificationof the material;for a 30 feet long and 8.5 feet wide PTW, we estimatea volumelossof about1000cubic feet. In addition,the inclinometersshowedup between2 and 6 inches of movementinto the excavation;we estimatethis volumelossto be about85 cubic feet to the north and 113cubic feet to the south of the PTW. We thereforeestimatethat therewas a loss of volume of about 1200cubic feet during sheetpile extraction. This volume lossprobablyresultedfrom four mechanisms;the volumeof the extractedsheetpiles, consolidationof the clinoptilolite,crushingof the clinoptilolite,and movementof the clinoptiloliteinto the roundstonezone. The volume of the extractedsheetpiles was approximately200 cubic feet (crosssectionalareaof 0.192 square feet per sheetpile, 40 sheetpiles and an averagedepthof about26 feet).Thus about 1000cubic

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feet of volumelossprobablyoccurreddue to consolidation,crushingor movementof the clinoptilolite. We believethat about80 to 90 percentof this volumelossoccurredbecauseof crushingof the clinoptilolite andmovementof the clinoptilolite into the roundstonezone(see following sectionsof this report). Thuswe estimatethat approximately100to 200 cubic feet of lost volumeresultedfrom consolidationof the clinoptilolite.

Laboratorytestsconductedby the Universityof Buffalo (UB) (Rabideau,2000) on loose samplesof clinoptilolite indicatea hydraulicconductivityof about 1.2~10~centimetersper second(cm/set). We believethat consolidationof the materialwithout crushingthe grains(see below) would not sufficientlyreducehydraulicconductivityto preventgroundwaterflow throughthe PTW.

3.4 CRUSHING OFCLINOPTILOLITE 3.4.1 Descriptionof Mechanism Althoughthe clinoptilolite was manufacturedas a 14x50meshsize,clinoptilolite can be crushedto dustby finger pressure.Materialtestingperformedat UB showedan hydraulic conductivityof 1.2x10 cm/set for looseclinoptilolite,and an hydraulicconductivityof 4~10~~

cm/set for compactedclinoptilolite. Clearly any significantmechanicaldisturbanceof the clinoptilolitewill crushsomeof the grainsandreducethe hydraulicconductivityof the material. Mechanicaldisturbanceof the clinoptilolite would haveoccurredat leastthreetimes during constructionof the PTW: transportation, placingclinoptilolite in the PTW, and extractionof the sheetpiles.

The clinoptilolite was deliveredto WVNS in supersacks that were transportedby truck from the sourcein Oregon. Jostlingandvibrationduringtransportationand deliveryprobably resultedin somegrain breakage,but we expectthat the limited amountof fmesgenerated would not havea significantimpacton the hydraulicconductivityof the material. Grain size analysisof deliveredclinoptilolitewould havebeena usefulquality assurance check.

The clinoptilolite was droppedinto the excavationto backfill it. The high drop probably crushedmore clinoptilolitegrains,resultingin more fines generation.We cannotquantifythe effect of this placementmethodon the grain sizeof the clinoptilolite.

The clinoptilolite was subjectedto the most intensedisturbancewhen the sheetpiles were withdrawnwith a vibratoryhammer. The clinoptilolite next to the sheetpiles would havebeen most affected,with many of thesegrainsalmostcertainlycrushed.The clinoptilolite nearthe I:\Project\7000s\7061\Reports\Engineering~eviscd Engineering Report~fs~sdw.doc 14

bottomof the PTW would be subjectto the most severecrushingbecausethis materialis subjectto additionalstressesfrom the depthof burial. Crushingof the clinoptilolite grains probablydissipateswith lateraldistancefrom the sheetpiles, and we estimatethat clinoptilolite grainsmorethan about2 feet away sufferedonly minor breakage.Along the southside of the PTW, the roundstonewas adjacentto the sheetpiles, so we would not expectmuch grain breakagein the clinoptilolitezone2 feet away from the sheetpiles. In addition,if water levels within the PTW rose significantlyduring sheetpile extraction,someof the vibratory energy would be dissipatedinto the waterandthe amountof grain crushingwould be lessin areas wherethe sheetpiles werewithdrawnafter water levelsrose. If this modelis correct,crushed clinoptilolite grainswerepresentwithin about2 feet of the north, eastandwest sidesof the PTW, and the grainswere more severelycrushedat the baseof the PTW. Inflow of water during andpossiblyafter the sheetpiles were withdrawnmay havetransportedfines aroundthe PTW and affectedthis distribution.

As discussedabove,we estimatedthe total volumeloss of the clinoptilolitezoneto be about 1000cubic feet. We estimatedvolumelossdueto consolidationof about 150cubic feet, and that dueto movementinto the roundstoneof about530 cubic feet (seebelow). Thuswe estimatethe volumeloss dueto grain crushingto be about320 cubic feet, or about6 to 7 percentof the estimatedclinoptilolite volumeof 4875 cubic feet. We note that this corresponds very closelyto the volumereductionnotedby Rabideau(2000)in compactingclinoptilolite, wherethe porosityreducedfrom 0.51 to 0.48,or a volumereductionof 6 percent.

The inclinometerreadingsindicatedthat the north side of the excavationmovedinward about2 inchesafter the sheetpiles werepulled,while the southside,adjacentto the roundstonezone, movedinward about6inches.Becausethe roundstoneprobablycompactslessthan the clinoptilolite,and it would not be subjectto grain breakage,the greaterinward movementon the southside indicatesthat the roundstone/clinoptilolite interfacewas probablymore unstable than the clinoptilolite on the north sideduring sheetpile extraction. Becausewe do not expect much grain breakagealongthe roundstone/clinoptilolite interface,this would indicatethat the clinoptilolite penetratedinto voids within the roundstone.This conclusionis also supportedby the clinoptilolite fines that were found in the PVC riser pipe in the roundstonezone.

In conclusionwe believethat the clinoptilolitenext to the sheetpiles on the north, east,and west sidesof the PTW, and at the baseof the PTW, probablysufferedsignificantgrain breakageandinter-grainabrasionas the sheetpiles were extracted.Along the north side,the clinoptilolite sufferedmuch lessgrain breakage,but the sidesof the excavationmovedmore as I:Vrojcct\7000s\706l\Reports\Engineering\Revised Engineering Report-fs-sdw.doc 15

the clinoptilolite penetratedvoids within the 2-feetthick roundstonezone,as discussedin the next sectionof the report.

3.4.2 Collecting Data to Support Mechanism Slug test resultsdiscussedin the Hydraulic EvaluationReportindicatea hydraulicconductivity of about1~10~~ cm/set throughoutthe clinoptilolite zone. It appearsthat the in situ hydraulic conductivityof the clinoptilolite is significantlylessthan 1.2x10-tcm/set determinedfor loose clinoptilolite,and is in the rangeof 4x10m3 cm/set that was determinedin laboratorytestson compactedclinoptilolitein which fines were generatedwithin the clinoptiloliteby the compactioneffort (Rabideau,2000).Reviewof the hydraulicresponsesand distributionof hydraulicconductivityvaluesfrom varioustypesof hydraulictestsin and aroundthe PTW (see the HydraulicEvaluationReport,Section3.4.2)indicates that the hydraulicconductivitylikely is highly variablewithin the PTW.

Collectingsamplesof clinoptilolite alongthe north, east,andwest sidesof the PTW and performinggrain sizeanalyseson thesesamplesmay provideadditionalsupportfor the grain-crushinghypothesis.HoweverRabideaunotedonly 23 percentfines (passingno. 200 sieve)in the compactedclinoptilolite (comparedto 2 percentfines in the uncompactedclinoptilolite),

which was sufficientto reducethe hydraulicconductivityby two ordersof magnitude. The processusedto samplethe clinoptilolite may also generateenoughfines to maskthosealready presentand makeevaluationof in situ fines difficult. Thereforewe do not recommendthis courseof actionbecausethe additionaldatamay be misleading.

3.5 CLINOPTILOLITE PLUGGING VOID SPACESIN ROUNDSTONE 3.51 Description of Mechanism The grain sizeof the roundstonewas 90-100%smallerthan 0.5 inches,and O-15%smallerthan 0.25 inches,while the grain sizeof the clinoptilolitewas betweenabout0.055and 0.017inches.

With an averagegrain sizeof aboutonetenththat of the roundstone,the clinoptilolite could easilypenetratethe void spaceswithin the roundstone.As describedin Section3.4, interpretationof inclinometerdataindicatethat the clinoptilolite penetratedinto voids within the roundstoneon the south sideof the PTW. This conclusionis alsosupportedby the clinoptilolite fines that were found in the PVC riser pipe in the roundstonezone.

The presenceof clinoptilolite within the voids of the roundstonereducesthe hydraulic conductivityof the roundstone.As discussedin the HydraulicEvaluationreport,resultsof slug test in the two piezometers(PZ-08and PZ-09)in the roundstonezoneof the PTW indicate I:\Project\7000s\706l\Reports\Engineering\Rcviscd Engineering Report-fs-sdw.doc 16

hydraulicconductivitiesof 2x10m2 and 1.5~10~~ cm/set. Althoughtheseslug testresultsmay be biasedfrom the directpushinstallationand constructionof the piezometers,thesedataindicate variablehydraulicconductivityin the roundstone,with areasof reducedhydraulicconductivity dueto the presenceof clinoptiloliteparticlesand fines.If the clinoptilolite filled all of the voids of the roundstone(estimatedto be 30 percentvoids in a volume30 feet long, by 26 feet deepby 2.25 feet wide), we estimatethat this accountsfor about530 cubic feet of volumeloss in the clinoptilolite.

3.5.2 Collecting Data to Support Mechanism It is very likely that clinoptiloliteenteredthe roundstonezone. We do not think thereis any merit in obtainingadditionaldatato supportthis hypothesis.

3.6 FINESMOVEMENT ASPTW FILLEDWITHGROUNDWATER 3.6.1 Description of Mechanism The PTW was not filled with waterbeforethe cofferdamwas removed.Thus groundwater flowed into the PTW as the sheetpiles were extracted.At the baseof the excavationtherewas approximately20 feet of hydraulicheadforcing the groundwaterinto the PTW. Significant amountsof clinoptilolite fines could havebeentransportedthroughthe PTW as the turbulent flow of waterenteredthe PTW and filled it. Assuminga headpotentialof approximately20 feet betweenthe interior of the dry cofferdamandthe ambientpotentiometricsurface,a hydraulicconductivityof 1 x 10s2cm/set(or 3 x 10 ftLsec)basedon estimatesfor the uncompactedlooseclinoptilolite,and a porosityof 0.3, the initial velocity of waterflowing into the cofferdamas the first sheetpiles were removed,accordingto the equation:

v=Ki/n

where, v = velocity (IVsec),K = hydraulicconductivity(ft/sec),i. = gradient(ft/ft) andn = porosity would be approximately0.2 feet per second.This shouldbe consideredan upperbound approximateestimate;the actualinflow rate likely was somewhatlessas the clinoptilolite at the bottomof the cofferdamwould havebeensomewhatcompactedfrom the weight of the overlyingclinoptilolite . As the PTW filled with water,the flow ratewould havereducedand eventuallyceasedwhen the water level reachedequilibriumwith adjacentgroundwaterlevels.

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The approximately10,000gallon void spaceof the dry PTW likely was on the orderof tensof hours,or aboutoneto two days.

Sheetpiles were first extractedat the west sideof the PTW, nearWP-25 whereelevated groundwaterelevationsare almostthe sameas currentgroundwaterelevationsin the PTW.

Any tines in this areawould havebeenflushedto the south,eastandnorth sidesof the PTW as the groundwaterflowed in. We cannotcalculatehow fast the PTW would fill up with groundwater(the distributionof hydraulicconductivityis not well definedin the PTW), nor do we know exactlyhow long it took to removethe sheetpiles. However,it seemslikely that the major portion of the inflow occurredas the sheetpiles at the west end of the PTW were removed. Thus,fines generatedin this areafrom sheetpile extractioncould havebeenflushed into the PTW, and could conceivablycontributeto the skin of low permeabilitymaterialthat is thoughtto be presentaroundthe PTW. Additional fines generatedwhen extractingsheet piles alongthe south,eastandnorth sidesof the PTW would then contributeto this skin.

3.6.2 Collecting Data to Support Mechanism This was a transienteffect that occurredwhen the sheetpiles were withdrawn. The mechanism cannoteasilybe replicated,and otherdatathat could be collectedto supportit may prove inconclusive.

3.7 GROUNDWATER FLOW UNDERPTW 3.7.1 Description of Mechanism As describedin the HydraulicEvaluationreport,as-builtinformationindicatesthat the PTW was not excavatedto the top of the Lavery Till, and groundwatermay be flowing underthe east sideof the PTW.

3.7.2 Collecting Data to Support Mechanism The HydraulicEvaluationReportrecommended drilling at leastthreeadditionalsoil boringsto confirm whetherthe pilot PTW penetratesthe underlyingtill or is hanging within the aquifer.

4.0 POTENTIAL CAUSESOF HIGHER HYDRAULIC HEAD MEASURED IN THE PILOT PTW This sectiondiscusses potentialcausesof higherhydraulicheadmeasuredin the PTW. This discussiondoesnot addresspotentialcausesassociated with site stratigraphyor hydrogeology; theseissuesare discussedin the HydraulicEvaluationreport.This sectiondescribespotential I:\Projcct\7000s\7061\Rcports~\Enginccring\Revised Engineering Report-fs-sdw.doc 18

conduitsfor surfacewaterto infiltrate into the PTW. Eachof the potentialconduitsdescribed below is illustratedin Figure4.1 4.1 POTENTIAL CONDUITS INTOTHEPTW 4.1.1 Descriptionof potentialconduits Waterlevel dataindicatethat waterlevelswithin the PTW rise during rainfall and snowevents.

Thus thereappearsto be a hydraulicconnectionbetweensurfacewaterand groundwaterwithin the PTW.

A potentialsourceof surfacewaterthat could enterthe PTW is the hardstandsurfacelayer that is presentover the areaof the PTW, as notedin previousevaluationreports. The 7-inch thick layer over the 100by 100feet areaof the PTW could hold up to 13,000gallonsof waterwhen fully saturated.Surfacegradesover this areaslopedown to the north, so watercan flow to the PTW. A surfacedrainwas constructedin October2000to divert surfacewateraroundthe southernside of the PTW. Sinceinstallationof the drain,sharprisesin waterlevelswithin the PTW havenot beenobservedduring rainfall and snowevents. Thereforethe volume of flow into the PTW hasbeenreducedby the constructionof the surfacedrain.However,the datastill indicatethat the hardstandlayer is hydraulicallyconnectedto the PTW.

Drawing 900D-7867sheet1 showstwo buriedconduitsthat enterthe areaof the PTW from the west (the areaof elevatedgroundwateraroundWP-25). The trenchesin which theseconduits are buried could divert surfacewater into the PTW. The cross-sectionof the trenchesin which the conduitsare buriedis reportedly2-feet deepand 2 feet wide andprobablyfilled with granularmaterial.

The as-builtlocationsof someof the bumperpostsare on top of the PTW. The locationsof the remainingbumperpostsare almostcertainlyon top the cap over the PTW. We do not know wherethe bumperswere first installedbeforethey weremovedto their currentposition,but someof theselocationsmay alsohavebeenover the PTW. The bumperpostsare screwed3.5 feet into the ground,which would penetratethe cap over the PTW. Thesebumperstherefore also providean entry point for surfacewaterto enterthe PTW.

4.2 PERMEABLE CAPOVERPTW The cap over the PTW was designedto havea low hydraulicconductivityto preventinfiltration of surfacewater into the PTW. Thereare issueswith both the designand the constructionof the cap that haveprobablyrenderedit ineffectivein preventingsurfacewater infiltration. The I:Wroject\7000s\7061\Reports\Engineering~evised Engineering Report-fs-sdw.doc 19

l-inch thick bentonitelayer placedover the clinoptilolite and roundstonezonewas Volclay CG-50which hasa grain sizeof 99 percentsmallerthan 0.008inchesand 15 percentlessthan 0.0003inches,or aboutonetenththat of the clinoptilolite,and onehundredththat of the roundstone.This materialcould easilyfall into the void spacesof the PTW materials.We also suggestthat it would be very difficult to maintainthe l-inch thicknessduringplacementof the overlyingclay material,and that the bentonitecould easilyhavebeendisplacedeitherlaterally or into the PTW materialsas the clay fill was placed,thuscompromisingthe integrity of the low permeabilitylayer.

We understandthat the clay fill hasa hydraulicconductivityof about 1~10~~ cm/set when compacted.Howeverthe clay was not compactedwhen placedover the PTW for fear of further crushingthe clinoptilolite. Thereare almostcertainlyflow pathsthroughthis uncompactedclay that would allow surfaceinfiltration to enterthe PTW. While the cap limits the volume of surfacewaterthat directly entersthe PTW from above,somebypasslikely does occur. Hydrographsshownas Figures3.4.and3.5 of the Hydraulic EvaluationReportindicate that the magnitudeof waterlevel increaseswithin the PTW is greaterthan the water level rise in the nativeaquiferduring and afterrainfall and snowevents. This responseappearedto becomelesspronounced,althoughnot eliminated,after the installationof an upgradientsurface drain.

The constructiondetail of how the clay cap is tied into the adjacenthardstandlayer is critical in evaluatingwhetherwaterin the hardstandcan enterthe PTW. No detailswere shownin the set of constructiondrawingswe reviewed. Accordingto Woodworth,the connectionconsistedof sprinklingbentoniteover the exposednativesoil surfacesthenplacing the clay cap over the PTW; onceat grade,the hardstandstonewas rakedover the clay to providea good walking/workingsurface.Thereis a high probabilitythat surfacewater can leak throughthis connection.

5.0 CONCLUSION

S The pilot PTW hasyieldedsignificantinformationthat canbe usedin the designof full-scale permeablereactivebarriersat the WVDP site. The conceptualdesignof the PTW wasbased on a soundevaluationof the clinoptilolite to treat Sr-go-affected water anda reasonablygood understanding of geologicandhydrogeologicconditionsin the areaof the installation. The engineeringdesignrelied on traditionalconstructionmethodsthat havebeenusedsuccessfully 1:Wrojcct\7000s\7061RcportsEnginccring\Reviscd Engineering Report-fs-sdw.doc 20

at othersites.Evaluationof the hydraulicsin andaroundthe PTW containedin the Hydraulic EvaluationReportindicatesthat the hydraulicheadmeasuredin the PTW is higherthan the surroundingaquifer,andtheremay be only limited groundwaterflow throughthe PTW. This EngineeringEvaluationReporthas assessed the designand constructionof the PTW and has postulatedpotentialcausesof the observedhydraulicconditionsin and aroundthe PTW. The following conclusionsare drawnfrom this assessment:

1. The sidesof the PTW may havea lower than expectedhydraulicconductivity becausethe native soilsmay havebeen smearedduringpile driving and extraction. However,water flow throughthe sheetpile joints during excavationof the PTW indicatesthat smearingprobablydid not eliminateor significantlyreduce waterflow acrossthe entireinterface. Smearingwas most likely in the interlayered SlackWater Sequence, wherethin layersof fine-grainedmaterialsmearedacross thin layersof coarsegrainedmaterial,

2. During sheetpile extraction,the volumeof the PTW reducedby about 18 percent.

We believethis volumelossresultedfrom the volume of the sheetpiles, consolidationandparticlebreakageof the clinoptilolite,andmovementof the clinoptilolite into the roundstonezone. We estimatethat the clinoptilolite lost about 7 percentof its volumedueto particlebreakage,which is a similar volume reductionnotedby Rabideau(2000)when samplesof clinoptilolite were compacted.

Slug testsindicatea hydraulicconductivityof about 1x10-3cm/setthroughoutthe clinoptilolite. Slug testsresultsfor piezometerswithin the roundstonemay be biasedbecauseof the piezometerinstallationmethods,however,the hydraulic conductivityin this zonelikely is variableand lower in a bulk sensedue to clinoptiloliteand tines infilling pore spacesin the gravel. The field valuesare close to the hydraulicconductivityof 4~10~~ cm/setmeasuredby Rabideaufor compacted clinoptilolite,and are at leasttwo ordersof magnitudelower than the hydraulic conductivityof 1.2x10-lcm/set measuredfor uncompactedclinoptilolite.

3. The PTW was not filled with waterprior to extractingthe sheetpiles. The groundwaterwould havebeenunderapproximately20 feet of headas the first sheet was extracted.Significantamountsof fines,if present,could havebeenflushed(at a flow velocity initially severalordersof magnitudegreaterthan likely ambientflow velocity) to the sidesof the PTW as it filled up. The first sheetswerepulled at the west end of the PTW, so the tines would havebeenflushedto the north, southand eastsides. However,we expectthat only a limited amountof fines would be present(the tines that were in the deliveredproduct,andthe fines generatedas the clinoptilolitewas dumpedin the PTW) as the first.sheetpile was extracted,so it is unclearwhat contributionthis mechanismhad on the formationof a skin around the threesidesof the PTW.

4. Comparisonof reportedas-builtconditionsand Geoprobeboringsperformedbefore PTW constructionindicatethat the PTW may not extendto the top of the Lavery I:\Project\7000s\706l~cportr\Engince~ng~evised Engineering Report-fs-sdw.doc 21

Till at the eastsideof the PTW. Groundwatermay be flowing underthe PTW in this area.

5. The hardstandsurfacelayer hasbeenrecognizedas a potentialreservoirof surface waterthat is availableto flow into the PTW if a suitableflow path exists.

Constructionof a surfacedrain in October2000upgradientof the PTW reducedthe hydraulicresponseto rain and snowmelt,indicatingthat the hardstandis connected hydraulicallyto the PTW.

6. Potentialflow pathsexist linking the hardstandsurfacelayer with the PTW. These includean existingconduittrench,the uncompactedclay cap,the connectionof the cap to the sidesof the PTW excavationandto the PTW materials,andthe installationof bumpersthroughthe surfacecap into the PTW. Any or all of these flow pathsmay be contributingto the higherwater levelsobservedin the PTW than in the surroundingaquifer.

This reportthereforeconcludesthat the clinoptilolite androundstonezoneswithin the PTW wereprobablytransformedduring sheetpile extraction. The resultingPTW probablycontains a comingledzoneof roundstoneand clinoptilolite,and zonesof clinoptilolite aroundthe north and eastedgesthat containa significantamountof crushedclinoptilolite particles. The hydraulicconductivityof the materialis two or threeordersof magnitudelessthan that for uncrushedclinoptilolite. The hardstandis hydraulicallyconnectedto the PTW, and numerous potentialflow pathshavebeenidentifiedthroughthe cap andother surfacefeatures.The PTW doesnot appearto be fully penetratingthroughthe upperwaterbearingzoneand likely hangs in its centraland easternportionsabovethe top of the Lavery Till potentiallyallowing underflow.

Futurepermeablereactivebarrier(PRE3)installationsat the WVDP in similar nativesoils shouldincludeconsiderationof thesefactorsin designand construction.

l Sheetpile cofferdamsareprobablythe most effectivemeansof constructingthe PRB, but driving and extractionof the sheetpiles will affect local hydraulicconductivity.

l Wing walls shouldbe consideredin designto createa remedythat will direct the flow of waterthroughthe PRE3.Suitabledimensionsof the wing wall sectionscanbe developed from carefulhydraulicmodelingof all anticipatedgroundwaterconditions.

l Geotechnicaldesignshouldminimize sheetpile penetrationof the Lavery Till to reducethe energyrequiredto extractthe sheetpiles.

~:Vrojcct\7000s\706l~eports\Enginee~ng~evised Engineering Report-fs-sdw.doc 22

l A conservative capdesign,usingHDPE linersor otherimpermeable materialsshouldbe usedto preventsurfacewaterinfiltration.

0 All possiblesourcesof surfacewatershouldbe divertedawayfrom the areaof the PRB.

l More delicateplacementtechniques canbe developed to placethe clinoptilolite.

l The excavationshouldbe filled with waterbeforethe sheetpiles areremoved.

l The dividersystembetweenthe clinoptiloliteandany gravelzonesshouldbe removedafter the sheetpiles areremoved.

l Considerations for futuredesignsalsoshouldconsiderusinga coarsergrain size distributionfor the zeolitetreatmentmedia,or an aggregate that is lesssusceptibleto grain breakageduringconstructionof the PREL 6.0 RECOMMENDATIONS If clinoptilolitefineshaveloweredthe in situ hydraulicconductivityof the P T W materials,a systematic programto furtherdevelopthe P T W by aggressive pumpingfrom the PVC riser pipecouldbe designed.However,we understand pumpingratesarelim ited by the apparent pluggingof the geotextilearoundthe PVC riserpipe.

Methodscouldbe developed to attemptto removeor penetratethe skin of lower permeability materialaroundthe PTW. This zoneof materialcouldbe removedby augering,or a piping systemandmanifoldcouldbe constructed within the clinoptilolitezoneto removewatermore effectively. Otherinnovativemethodsthat arebeingdeveloped by practitionersin the field includein situ sonificationand in situ fluidizationwhich may merit consideration.However, both of thesemethodshavesignificantlim itations(sonificationmay createmorefines; fluidizationwould requirea methodto collectthe fluidizedfines,suchasa horizontalwell installednearthe top of the saturated zonewithin the PTW) andunpredictable results.W e believethat manyof these techniques will alsogenerateadditionaltines,makingevaluationof the modifiedP T W evenmorecomplex.

I:\Project\7000s\706l\Reports\Enginccdng\Revised Engineering Report-fs-sdw.doc 23

Onepassivemethodthat could induceflow throughthe treatmentmediaof the PTWwouldbe to lower the headwithin the PTW using a siphonby connectinga new well installedin the centerof PTW to a lower headreservoir,suchas a downgradientlower elevationditch. This method,while hypotheticallypossible,may not be practicalconsideringsite logistics.

The potentialflow pathsconnectingthe hardstandlayer and the PTW can be testedto see which is contributingto the higherwaterlevelswithin the PTW. While monitoringwells within andnearthe PTW, freshwatercan be introducedinto the potentialflow paths,suchas onto the hardstanddirectly upgradientfrom the PTW, or into the conduittrenchwest of the PTW, or aroundthe bumperposts,or directly onto the cappedsurface.Throughcontrolled applicationof waterand carefulmonitoringof water levels in the wells, the specificflow path or pathscan be identified. Recommendations can then be developedto addressthe identitied flow paths.

Alternatively,the surfacecompletionover the PTW canbe replacedwith a carefullydesigned low permeabilitycap comprisedof a suitablehigh-densitypolyethylene(HDPE) liner keyed into the adjacentsurfaceclay layer,with sealedpenetrationsthroughthe liner for the wells and PVC riser pipe. Bumperpostswould be movedawayfrom the PTW zone. A carefully designedand constructedcap shouldeliminateflow pathsfrom the hardstandto the PTW.

Subsurfaceconditionsthat could resultin higherwater levelswithin the PTW are addressed in the HydraulicEvaluationreport.

7.0 LESSONSLEARNED This reporthasfocusedon the engineeringdetail of the PTW designand installation. The conclusionsof this reportwill assistin the eventualdevelopmentof engineeringalternativesto enhancingthe performanceof the PTW. Basedon the conclusionsof this report and the companionHydraulicEvaluationreport,severallessonslearnedare identifiedthat we believe are importantto future PTW designwork at the WVDP:

l Site characterization for PTW designpurposesmust focuson the locationof the proposedinstallationand cannotrely solely on regionalinformation l PTW designwork must includetemporaland spatialdataon the three-dimensional distributionof targetcontaminantsin the proposedlocation l Hydraulicheadinformationshouldfocuslocally and includea sufficientlywide areato accountfor potentialspatial(both lateralandvertical) andtemporalchanges to the directionandmagnitudeof the hydraulicgradient. This informationshould I:\Project\7000s\706IUlepom\Enginecring\Reviscd Engineming Report-fs-sdw.doc 24

be collectedbeforeand afterPTW constructionso that the effect of the PTW on the local hydraulicregimecan be understood.

l Stratigraphicinformationmust be sufficientlydetailedin the vicinity of the proposedlocationto accuratelydesignthe PTW for propervertical coverage,and/or penetrationof the affectedwaterbearingzone. This stratigraphicinformationmust alsobe consideredin the engineeringdesigningof the excavationsupportfor the PTW.

l Generally,the use of sheetpiles to supportthe excavationfor a PTW will modify the local stratigraphyandmay affect discreteflow paths. Removalof sheetpiles will consolidateany looseor uncompacted materialin the PTW, and will allow materialswith dissimilargrain sizesto co-mingle. Sheetpile removalmay also generatehigh dynamicstresseswithin the PTW materialsthat can breakfragile particleswithin the PTW.

l The hydraulicheadwithin a PTW excavationshouldbe maintainedat the top of the emplacedmaterialwhen the excavationsupportsystemis removedto reducethe potentialfor rapid inflow of waterandturbulentflow conditions. Theseconditions may mob&e fines or othermaterialswithin the PTW during removalof the excavationsupport.

l The performanceof a PTW canbe affectedby numerousexternalfactors,suchas surfacewater infiltration, utility trenches,etc.,that mustbe addressed during the detailedengineeringdesign. Given the high cost of installation,monitoringand correctingany performanceproblems,the engineeringdesignshouldbe conservativein addressingsite-specificissuesthat could affect PTW performance.

For example,an HDPE liner placedover the PTW treatmentmaterialsand appropriatelykeyedinto the surroundingnativematerialwould be a moreeffective cap than the granularbentoniteanduncompactedclay cap that was installed.

l If the PTW doesnot performas-designed, accurateand well-documentedas-built informationis critical in understanding the problemand developingsuitable remedies.When constructinga pilot PTW to evaluatethe technology,this informationis evenmore important.

The conditionsand issuesthat havereducedthe intendedperformanceof the pilot PTW also havebeenproblematicfor other sitesthat havedeployedPTW technologyover the past 10 years. Generally,the remedialeffectivenessof PTW technology,from a chemicalstandpoint, that is, destructionof organiccompounds,immobilizationof inorganiccompounds,buffering of low pH conditions,hasbeendemonstrated and is fairly well understoodthanksto the thousandsof laboratory-scale, hundredsof pilot tests,and nearly 50 full-scalePTW implementations that havebeenreportedby groupssuchas the RemediationTechnology DevelopmentForum(e.g.,seehttp://www.rtdf.ora).We havenot seenany reportsof full-scale I:\Project\7000s\706I\Reports\Engineerinevised Engineering Report-fs-sdw.doc 25

PTW failuresdueto chemicaltreatmentinadequacies althoughlaboratorybench-testshave shownlimitationsto variouschemicaltreatmentprocesses.Issuesregardingplugging or fouling of a PTW from chemicalprocessesarebeing studiedand monitoredat both research and full-scalecommercialsites;however,theseprocesses are anticipatedand haveapparently not yet diminishedthe effectiveness of a PTW for a given site.

As is the casefor the pilot PTW at WVDP, most diffkulties with PTW operationto-date generallyare due to unintendedhydraulicperformancewith the specificperformance inadequacies resultingin:

l incompletecaptureof the affectedgroundwater(e.g.,flow aroundor below, the PTW).

l designgroundwatervelocity not being achieved.

l non-uniformflow conditionswithin the PTW.

From our experiencewith PTW designand assessment, our participationin the RTDF and developmentof the U.S. EnvironmentalProtectionAgencytraining courseon PTW technology,andour generalreview of the state-of-thepractices,we havedevelopedthe following list of lessonslearned:

l A comprehensive site characterization programthat providesdetailedstratigraphic informationalongand in the vicinity of the proposedPTW alignmentis critical to developinga reliablehydraulicand geotechnicalPTW design. Incompletesite characterization is the primary causeof hydraulicfailure in existingPTW sites.

Informationon the depthand locationof primary, and discretegroundwaterflow paths,temporaland spatialvariability in three-dimensional hydraulichead information,and reliabledetail on the expectedrangeof hydraulicconductivity valuesmustbe collected.

l A three-dimensional groundwaterflow modelthat can reliably interpretthe spatial and temporalvariability in site conditionsis critical to designinga reliablePTW.

Temporaland spatial variability in hydraulichead,directionandmagnitude of hydrauhcgradients,and contaminantfIowpathscan be addressed by a representative model l The PTW deploymentapproachmust take greatercareto avoid potentialskin effectsand pulverizationof treatmentmaterial,and creationof fines. Many conventionalimplementationmethods(e.g.,sheetpiled excavationand fill; trenchingmachine)havethe potentialfor creatinga skin acrosspreferentialflow paths. Integrationof the site characterization, which shouldidentify the degreeof heterogeneitywith the aquifersystemandpotentialfor smearingdueto clay and silt I:\Project\7000s\7061\Rcports\Enginee~ng~evisedEngineeringReport_fs~sdw.doc 26

seamsin the subsurface,with the engineeringdesigncan help reducethe potential for a skin to developand controlthe hydraulicperformanceof the PTW. Different deploymentscenarios,includingmodificationsof geometry,orientation,and grain sizedistributionof the treatmentmaterialwith a PTW canbe considered.

l PTWsthat hang,or do not completelypenetratean underlyinglow hydraulic conductivityunit, over all or part of their alignment,generally havegreaterpotential for unintendedperformancethan fully-penetratingPTW designs.

l Continuouswall PTW designs(similar to the WVDP pilot) typically are less complicatedto designandbuild than funnel and gate designs;however,the continuouswall must fully capturethe affectedgroundwater,includingduring variationsin the directionof the lateralhydraulicgradient. Assessingthe performanceof a continuouswall designis scaledependent;that is, shortwalls that do not fully coverthe width of a plumemay not be able to handlethe inherent heterogeneityof an aquifersystemandprovide adequatetreatment.Also, because any emplacedengineeringstructuresuchas a PTW changesthe ambientflow field, shorterwalls may havea tendencyto result in greaterrelativechangesto the flow field than longerwalls.

l Trenchand fill type PTWs alwayscreateunconfinedheadconditions;this mustbe takeninto accountin any PTW designas the creationof a unconfinedtrenchin a semi-or completelyconfinedaquifercan affect the hydraulicconditionsand flow field within and aroundthe PTW.

Examplesand lessonslearnedfrom reportson specificsitesare summarizedin the following paragraphs.Generally,thesesummariescan be found courtesyof the Remediation TechnologiesDevelopmentForum,PermeableBarriersAction Teamwebsite(of which Geomatrixis a member),http://www.rtdf.org/public/permbarr/prbsumms/default.cfm U.S. Department of Energy, KansasCity Plant, Kansas City, MO (information source RTDF) (hvdraulic head redistribution and diversion ofgroundwater flow)

A PTW was installedin April 1998at the U.S. Departmentof Energys KansasCity Plantin KansasCity, MO. Contaminantsof concerninclude 1,2-dichloroethylene (1,ZDCE) andvinyl chloride(VC). Maximuminitial concentrations encountered at the site were 1,377pg/L of 1,2-DCE and291 pgL of VC. The PTW was constructedas a continuoustrenchmeasuring130 tI long. Sheetpiles were driven into bedrockto supportthe sidewalls. The resultingexcavation was 6 ft wide. The first 6 A of the trenchabovebedrockwas filled with 100%zero-valentiron.

The remainderof the trenchwas filled with 2 ft of zero-valentiron and4 ft of sand.These differing thicknesses were usedto compensate for the increasedflow-throughthickness requiredfor the basalgravelunit. Data evaluationindicatedthat flow aroundthe walls south endwas causedby headredistribution.The wall actssomewhatlike an equalizationtank redistributingheads.Flow gradientinto the north end of the wall is approximatelyfour times I:\Project\7000s\706lWcports\Engincering\Rcvised Engineering Report-fs-sdw.doc 27

higherthan at the southend.Thereforesomeof the groundwaterflow at the southend is redistributedaroundthe wall. Potentialremediesto treatflow aroundthe walls southend include: 1) a cut-off wall acrossthe permeablebarrierto preventheadredistribution,2) a cut-off wall or permeablebarrier at the southendto direct groundwaterflow back into the wall, or

3) extensionof the iron treatmentwall to the south.Lessonlearned:Installationof the continuouspermeablebarriercan causea redistributionof headsand a partial changein plume direction.

Former Manufacturing Facilitv, Sunny-vale,California (information source,Geomatrix)

A PTW was installedin November1994at a former semi-conductor manufacturingsite in northernCalifornia. The PTW, composedof zero-valentiron sandwichedbetweenup and downgradientpeagravelsections,is successfullytreatingchlorinatedVOCs. The site replaced a formerpump andtreatremedy. The systemincludesa 38 foot long by 22 foot deepby 8 foot wide PTW cell, with laterallow permeabilitybarriersextendingupgradientmore than 250 feet on eitherside of the PTW to direct groundwaterflow andreduceaffectsfrom changing hydraulicgradientdirections.A short(20 foot) downgradientsheetpile on one sideof the PTW reducespotentialnon-uniformflow conditionsassociatedwith the variableambientflow direction. Hydraulicmoundinghas occurredfollowing extendedprecipitationevents;the moundingis temporaland dissipatesfollowing the rainy season.Transientresponseto regional and local precipitationandpressureheadchangesbetweenthe ambientsemi-confinedaquifer and the constructedunconfinedPTW are believedto contributeto theseconditions. Because theseconditionsare temporaland dissipate,modificationsto the systemare not currently required.

U.S. Coast Guard Support Center, Elizabeth City, NC (information source:RTDF and U.S. EPA National Risk Monitoring Laboratorv, Ada, Oklahoma A full-scaledemonstration of a PTW to remediategroundwater contaminatedwith chromium and chlorinatedorganiccompoundswas initiatedat the U.S. CoastGuardSupportCentersite in ElizabethCity, NC, in 1995.The primary contaminantsof concernarehexavalentchromium (Cr%) andtrichloroethylene(TCE). Initial maximumconcentrations were more than 4,320 ug/L for TCE andmore than 3,430ug/L for (Cr*). The contaminantplume was estimatedto covera 34,000-It2area.The plume is adjacentto a former electroplatingshopthat operatedfor more than 30 yearsprior to 1984when operationsceased.Groundwaterbeginsapproximately 6 ft below groundsurface,and a highly conductivezoneis located16-20ft below the surface.

This layer coincideswith the highestaqueousconcentrations of chromiumand chlorinated organiccompoundsfound on the site.A low-conductivitylayer+layey, fine sandto silty clay-is locatedat a depthof about22 ft. This layer actsas an aquitardto the contaminants locatedimmediatelyabove. A continuouswall composedof 100%zero-valentiron (Fe) was installedin June1996using a trencherthat was capableof installingthe granulariron to a depthof 24 ft. The continuoustrenchingequipmentusedfor the installationhasa large cutting chainexcavatorsystemto removenativesoil combinedwith a trenchbox and loadinghopper to emplacethe iron. The PTW is approximately2 ft thick and about 150ft long. Researchers I:\Project\7000s\7061\Reports\Engineering\Revised Engineering Report-fs-sdw.doc 28

are investigatingthe possibilitythat the TCE plume hasdippedlower in the aquiferafter the wall was installedand is now movingunderthe wall. A significantamountof recharge occurredinto the reactionzonefollowing installationdue to removalof the concreteparking lot coveringthe site.This rechargemay havedriven the plume deeperthan had previouslybeen observedallowing someof the plume to move underthe wall. Smearingat the interface betweenthe PTW and the nativematerialmay haveoccurredduring construction,however, thereis little indicationat this time that suchsmearing,if it doesoccur,hassignificantly affectedperformanceof the PTW U.S. Department of Energy, Frv Canyon Site, UT (source: RTDF and U.S. Geological Survevj A field-scaledemonstration of a PTW systemis underwayat an abandoned uraniumupgrader site in Fry Canyon,UT. The U.S. EnvironmentalProtectionAgency (EPA) is the lead agency on the site.The ultimategoal of the demonstrations is to determinethe technologicaland economicfeasibility of using permeablechemicalor biological obstacles,placedin the flow path, for removingdissolvedmetalsand radionuclidesfrom contaminatedgroundwater.This projectis testingthe performanceof threepermeablereactivebarriersat the Fry Canyonsite.

Anticipatedresultsof the researchfor eachof the PTW testedwill includelong-termremoval efficienciesfor uraniumand an evaluationof the commercialization potentialfor each.Specific objectivesof the field demonstration projectinclude:(1) hydrologicand geochemical characterization of the site prior to emplacementof barriers;(2) design,installation,and operationof threePRBs;and (3) evaluationof barrier(s)performanceand commercialization potential.At the Fry Canyonsite,the watertable is locatedapproximately8 ft to 9 ft below groundsurface,and the underlyingaquiferrangesfrom 1 ft to 6 ft deep.Estimatedhydrologic propertiesand measuredhydraulicgradientsindicatethat groundwater in the alluvial aquifer movesat a rate of about 1.5 B/daynearlyparallelto the directionof streamflow.

The systemhassuccessfullyshownthe removalefficacyof severalreactivemedia. The following performanceissuesalso arebeing assessed:

1) In a low-gradientsystemlike Fry Canyon,it is difficult to estimatemassof treatedwater and,at times,whetherthereis evenflow gettingthroughsomeof the gatestructures.This presentsan unknownto regulatorsin estimatingtotal massof contaminantthat will be cleaned up per unit of time sincePTW deployment.

2) Seasonalchangesare apparentin the PTWsefficiencyin removinguranium.The processes causingthesechangesneedto be identifiedin orderto effectivelydeterminelong-termclean-up goals.

3) Pubs that areplacedadjacentto ephemeralchannelscould be destroyedor havetheir long-term function significantlycompromisedduring intensethunderstormeventsin the Fry Creek drainagebasinwithout propererosioncontrolmeasures.

4) Groundsettlingcould compromisethe lack of visual impactthat PRBshavein future remediationapplicationsand could impactmonitoringwells.

Othersites,includinga pilot test of a landfill in the northeastU.S. and FederalFacility in I:~roject\7000s\7061\Reports\Engineering~cviscd Engineering Report-fs-sdw.doc 29

Colorado,haveobservedhydrauliceffectsdue to the presenceof skin (referencedreportsnot available). In eachcase,(onea pilot caissoninstallation,one a full-scalesheet-pilereactive gateinstallation)skin was speculatedto divert flow or createmounding. The skin effect for the pilot testwas apparentlynot remedied.A remedyfor the full-scalereactivegatethat involved siphoningwater from the interior of the PTW reactivezonearoundthe skin was apparently designed;the skin, in this case,was not removed.

The main point of theseexamplesis that designingfor hydraulicperformanceis critical to any PTW application. Comprehensive site characterization is key, andwill more likely resultin a reliablePTW designthat becomesa cost-effectiveremedyfor a given site.

I:Vroject\7000s\7061\Repolts\Engineering\Revised Engineering Report-fs-sdw.doc 30

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Pilot PTW Evaluation Report APPENDIX 12 GEOMATRIX REPORT: PILOT PERMEABLE TREATMENT WALL MODIFICATION OPTIONS REPORT

GEBMATRIX Pilot Permeable Treatment Wall Modification Options Report West Valley Nuclear Services, LLC West Valley, New York Prepared for:

West Valley Nuclear Services, LLC 10282 Rock Springs Road West Valley, New York 14171-9799 Prepared by:

Geomatrix Consultants, Inc.

2101 Webster Street, 12th Floor Oakland, California 94612 April 2001 Project No. 7061.000

GEOMATRIX TABLE OF CONTENTS Page

1.0 INTRODUCTION

.. ........................................................................................................... I 1.1 PILOTTESTOBJECTIVES AND ASSESSMENT.. ......................................................... .2 1.2 ORGANIZATION O FREPORT.. ................................................................................... 4 1.3 PERTINENT ASPECTSO FTHEHYDRAULICEVALUATIONREPORT.......................... .4 1.4 PERTINENT ASPECTSO FTHEENGINEERING EVALUATIONREPORT.. ...................... .5 1.5 ADDITIONALDATA NEEDS..................................................................................... .

1.5.1 Description ............................................................................................... .7 Component 1: Borehole drilling, well installation, and water le\rel monitoring program ...................................................... 7 Component2: Focusedhydraulic testing program ................................. .8 Component3: Tracer testing program.. .................................................. .9 2.0 PILOT PTW MODIFICATION OPTIONS .................................................................... 10 2.1 CRITERIAFORSELECTING PILOTPTW MODIFICATIONOPTIONS......................... 1 1 2.2 ALTERNATIVE1 - No MODIFICATION O FTHEPILOTPTW .................................. .12

. 2.2.1 Description ............................................................................................. .12 2.3.1 Basis for Selection.................................................................................. .12 2.3.2 Assumptions........................................................................................... .13 2.3.4 General Cost Estimate............................................................................ .14 2.3.5 Waste Generation................................................................................... .14 2.3.6 Easeof Implementation.......................................................................... .14 2.3.7 Likelihood of Success.. ........................................................................... .14 2.3 ALTERNATIVE2 - INSTALLLATERALHYDRAULICBARRIERS............................. .I4 2.3.1 Description ............................................................................................. .14 2.3.2 Basis for Selection................................................................................... 14 2.3.3 Assumptions........................................................................................... .16 2.3.4 General Cost Estimate............................................................................ .16 2.3.5 Waste Generation.................................................................................... 16 2.3.6 Easeof Implementation........................................................................... 16 2.3.7 Likelihood of Success.. ........................................................................... .I7 2.4 ALTERKATI~E3 - INSTALLEXTENSION T O PTW ...._............................................. 17 2.4.1 Description .............................................................................................. 17 2.4.2 Basis for Selection................................................................................... 17 2.4.3 Assumptions........................................................................................... .18 2.4.4 General Cost Estimate............................................................................. 18 2.4.5 Waste Generation....... ............................................................................ .19 2.4.6 Easeof Implementation........................................................................... 19 2.5.7 Likelihood of Success.. ........................................................................... .1-9 2.5 ALTERNATIVE4 - INSTALLA NEW PILOTPTW ................................................... .19 2.5.1 Description ............................................................................................. .I9 2.5.2 Basis for Selection................................................................................... 19 1:\Doc_S~fe\7000~:706I~ lodi~carionOptions Rpl:Mod-Rpt-Fin3l.doc i

GEOMATRIX TABLE OF CONTENTS (Continued)

Page 2.5.3 Assumptions............................................ ...................... ........................ ..-70 2.5.4 General Cost Estimate.......................................................... ...................2 1 2.5.5 Waste Generation............. ........................................ ...............................21 2.5.6 Easeof Implementation................................. ........................................ ..-1 25.7 Likelihood of Success .................... .............................. ............................2 1

3.0 CONCLUSION

S AND RECOMENDATIONS ..... ........................................................22 3.1 PREFERRED ALTERNATIVE. ... . . ... . . ... . . .. .. . .. . . .. . . ... . . .. . . ..~., .. . . . . . .. . . ... . .. .. ... . . ... . . ... . . ... . ..22 3.2 RECOMMENDED COURSEO FACTION.. . .. . . .. . . ... . . .. . . ... . . .. . . .. . . .. . . . .. . .. . . ... . . ... . . .. . . ... . . ... .22

4.0 REFERENCES

....... ......... ....................... ..... ................. ............. .................................... ..~ 33 TABLES Table 1 EstimatedCost ConceptualAlternative 2 Table 2 EstimatedCost ConceptualAlternative 3 Table 3 EstimatedCost ConceptualAlternative 4 FIGURES Figure 1.1 Site Location Figure I .2 Site Plan Figure 1.3 PTW Area and Cross-SectionLocation Figure 1.4 PTW Area Cross-SectionD-D Figure 1.5 Pilot PTW Modification - ProposedBorings for Data Collection Figure 2.1 Pilot PTW Modifications ConceptualAlternative 2 Figure 2.2 Pilot PTW Modifications ConceptualAlternative 3 I:~.Doc_Safe\7OOOs~ i06I\Modificat~on Opttons RptM od-Rpt-Final.doc ii

GEOMATRIX I

PIL~TPERMEABLE~REATMENTWALL MODIFICATIONOPTIONSREPORT West Valley Nuclear Services,LLC West Valley, New York

1.0 INTRODUCTION

This Pilot PermeableTreatmentWall,Mod$cation OptionsReportwas preparedby Geomatrix Consultants,Inc. (Geomatrix) at the requestof West ValIey Nuclear Services,LLC (WVNS). The report was commissionedby WVNS (Project 19-098745~C-JK)to assistin recommendingoptions for assessingand enhancingthe performanceof a piIot permeable treatmentwall (PTW) designedto remediategroundwateraffected by radioactive Strontium-90 (Sr-90) beneatha portion of the West VaIley DemonstrationProject (WVDP) locatedin westernNew York state(Figure 1.1). Two supportingreports, the Pilot PermeableTreatment Wall Hydra&c EvahationReport,(Geomatrix, 2001a) (the Hydraulic Evaluation Report) and the Pilot PermeableTreatmentWall EngineeringEvaluationReport(Geomatrix,2001b) (the Engineering Evaluation Report) also were preparedby Geomatrix and previously submittedto LWNS.

Each of thesereports,and the opinions and recommendationsprovided within, are basedon our review and evaluationof data and other relevant documentationon the pilot PTW program at provided by WVNS, as well as technical discussionsheld with WVNS staff and their contractors.

A pilot PTW was installed by WVNS at WVDP in Fall 1999 to assessthe ability of the technologyto passivelyand effectively reducethe concentrationof Sr-90 affected groundwater.

The pilot PTW was installed to treat a portion of the 2nd lobe of the Sr-90 plume beneaththe North Plateauof the site (Figure 1.2). Figures 1.3 and 1.4 show the monitoring well network and a cross-sectionof the PTW area. The 1st lobe of the Sr-90 plume to the west currently is being remediatedby a groundwaterrecovery and abovegroundion exchangetreatment system (pump-and-treat) that was installed in 1995. While the pump-and-treatremedy reportedly reduceslocal migration of the Sr-90 plume, WVNS doesnot considerit capableof completely capturing and remediatingthe affected groundwaterbeneaththe North Plateau. Thus, WVNS identified PTW technologyas a method potentially capableof effectively mitigating further migration of Sr-90 affected groundwater.

,s fi:deptdata\Doc_Safe~,7OOOs\706l~oditcattonOptions RpPMod-Rpt-Finahdoc 1

GEOMATRIX Monitoring data collected and analyzedby WVNS indicatesthat the pilot PTW may not be functioning as designed;specifically affected groundwaterfrom south,and presumeddown hydraulic gradient side of the PTW may not be flowing through the pilot PTW. The Hydraulic Evaluation and EngineeringEvaluation Reports assessedthe hydrauhcperformanceand constructionmethodsof the pilot PTW using data and relevant information provided by WVNS. The analysesconsideredpreliminary resultsof groundwatermodeling of the system being performed by researchersat the StateUniversity of New York at Buffalo (UB). The reports also provided possibleexplanationsfor the observedperformanceof the pilot PTW as well as recommendationsfor collecting additional data to both confirm the explanationsand provide information for developing an engineeringsolution.

1.1 PILOTTESTOBJECTIVES ANDASSESSMENT We understandthat the purposeof the PTW pilot test program at WVDP is to assessthe feasibility and practicality of mitigating Sr-90 affected groundwaterusing PTW technology.

Pilot tests are typically performed for proving the efficacy of a remediationmethod under field conditions if: (1) the technologyrelies on innovative treatmentmethodswhere performance data isn ot readily available for a wide variety of sites; (2) the installation methodsproposed have not been testedelsewhere;and (3) unique field conditions require a pilot test for developing additional data designingthe full-scale application. We believe that performing the pilot test at WVDP was well founded basedon theseconsiderationsbecauseno other full-scale PTW systemshave been deployed,to our knowledge, to mitigate Sr-90 affected groundwater, although laboratory studieshave beenperformed by severalorganizations,and at least one other pilot test is being performed in North America.

Data Quality Objectives(DQOs) were developedby WVNS (Report WVDP-350) in June 1999 for assessingthe performanceof the pilot PTW. TheseDQOs included: (1) establishing groundwaterflow through the pilot PTW; and (2) providing treatmentof the Sr-90 affected groundwaterby the pilot PTW clinoptilolite (zeolite) treatmentmedia. The specific criteria for assessingthe performanceof the pilot PTW basedon the DQOs, therefore,include:

1. Determining if groundwaterflows through the PTW and is not backedup or diverted around the pilot PTW.

2. Determining if Sr-90 activity in groundwateris reducedas the groundwaterpasses through the pilot PTW.

~:s~\deptdata~ oc~Safe\7000s:7061~Modifica~ion Options RpvMod-Rpt-Final.doc 2

GEOMATRIX

3. Comparing Sr-90 activities up and downgradientof the PTW to assessthe potential for mitigation of downgradientgroundwater(this activity was identified as possibly continuing beyond the initial pilot test performanceprogram).

To assesstheseDQOs, specific criteria were developedby WVNS including:

l Contouring groundwaterhead data to evaluatethe direction of groundwaterflow near and within the pilot PTW l Identifying whether Sr-90 activity in groundwaterwithin the PTW is reducedto less than 1000 to 1500 picocuriesper liter (&i/L).

The evaluationsperformedby WVNS and others to-date indicate that only DQO #2 abovemay have been met, althoughthere is no confirmation that the low Sr-90 activity groundwater sampledwithin the pilot PTW is the result of treating previously high Sr-90 activity groundwaterfrom upgradientsources.

Beyond the DQOs specifiedby W V NS for the pilot PTW project, a pilot program also provides other useful information for designing and deploying a full-scale system,including:

l effects of constructionactivities on the native hydraulic system; l details of the local hydrostratigraphiccharacteristics; l geotechnicalinformation; 0 effectsof rechargeon hydraulic performance.

It is important to note that theperformanceof apilot testdoesnot needto beperfectfor it to provideusefill informationfor either making a go/no-go decision on future deployment,or for designing a successfulfull-scale systemas long as the test: (1) identifies the specific and unique site and engineeringcharacteristicsthat affect systemperformance,and (2) provides information useful for overcomingperformancedeficiencies.

DQO #l-hydraulic efficacy-is the most important metric that appearsnot to have been met by the pilot PTW thus far. From our analysisof the hydraulic and engineeringinformation provided by the pilot PTW (as detailed in Geomatrix 2001a and 2001b and summarizedin Sections 1.4 and 1.5 of this report), we concludethat the unintendedhydraulic performanceof the pilot PTW may be due to specific design and constructionfactors, including:

1. a short, continuouswall PTW that: (a) may not be oriented perpendicularto the local lateral hydraulic gradient direction, (b) has no lateral hydraulic control; and

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GEOMATRIX (c) may not fully penetratethe completethicknessof the affected aquifer (i.e.. the PTW may hang abovethe underlying till in its central and easternportions);

2. rechargeof surfacewater directly into the pilot PTW;

3. a discontinuousskin effect that preventsefficient groundwaterflow through the PTW and may have developeddue to specific constructionactivities.

Wedo not believethat a technically feasibleand cost-effective methodor approachexiststhat cancompletel)eiiminatethesefactorsfrom the existingpilot PTK We also do not believe that all shortcomingsor potential causesof the poor PTW performancemust be correctedto render the pilot test successful.However, we have developedrecommendationsfor providing additional data and engineeredmodification alternativesto both confirm and enhancethe hydraulic performanceof the pilot PTW.

1.2 ORGANIZATIOtiOFREPORT Following this introductory section,which also includes summariesof pertinent information from the Hydraulic Evaluation and Engineering Evaluation Reports,this report consistsof the following Sections:

l Section2.0 Pilot PTW Modification Options (including a descriptionof the alternative;the basis for selection,assumptions,rough cost estimate,assessment of future performance,waste generation,easeof implementation,and likelihood of success).

l Section 3.0 Conclusionsand Recommendations(of the preferred alternative,and the recommendedcourseof action).

1.3 PERTINENTASPECTSOFTHEHYDRAULICEVALUATIONREPORT This sectionsummarizespertinent aspectsof the Hydraulic Evaluation Report that are important for selectingan appropriatepath forward in the pilot test program. The Hydraulic Evaluation concludedthat the performanceof the PTW likely is controlled by:

l a more eastwardgroundwaterflow direction than initially anticipated(the PTW was oriented for northward flow);

l a highly heterogeneousaquifer sequenceof fine and coarsesediments; l a narrower than anticipatedfi ow zone of high activity Sr-90 water near the baseof the aquifer, with generally lower activity groundwaterat the west end and higher

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GEOMATRIX activity groundwaterat the east end of the PTW; this flow appearsto be partially diverted around the eastend of the PTW; l the PTW may not have fully penetratedthe aquifer, and the hanging central and easternportion of the PTW may allow underflow of high Sr-90 activity groundwater; l a discontinuousskin of material at the contactwith the native aquifer material and heterogeneitywithin the PTW treatmentmaterial resulting from fines createdduring installation activities; and, l reduced,though continuing (primarily during precipitation or runoff events),direct surfacewater infiltration into the pilot PTW.

1.4 PERTINENTASPECTSOFTHEENGINEERINGEVALUATIONREPORT This sectionsummarizespertinent aspectsof the EngineeringEvaluation Report that are important for selectingan appropriatepath forward in the pilot test program. The Engineering Evaluation Report concludedthat the following construction-relatedactivities and methods likely contributedto the observedperformanceof the pilot:

l the zeolite and roundstonezoneswithin the pilot PTW were likely transformed during the constructionactivities to a more homogeneousmixture of roundstoneand fine (somecrushed)zeolite particles which lowered the effective hydraulic conductivity along the south face of the pilot PTW; l the PTW doesnot appearto be fully penetratingthrough the upper water bearing zone and likely hangs in its central and easternportions abovethe top of the Lavery Till potentially allowing underflow; l the installation and removal of the sheetpiles likely altered local but significant hydrostratigraphiczonesand flow pathsadjacentto the pilot PTW that control the migration of Sr-90 within the upper water bearing zone; l both the orientation (at an angle to the local lateral hydraulic gradient) and the relatively short length of this continuous wall pilot PTW contribute to the unintendedapparentdeflection of groundwateraround the system; l the creation of a confined permeabletrench within an otherwisesemi-confined systemmay contribute to unintendedtransienthydraulic effects (including minor mounding) within the pilot PTW; and, l the surfacehardstandis hydraulically connectedto the pilot PTW, and numerous potential flow paths have been identified through the cap and other surfacefeatures.

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GEOMATRIX 1.5 ADDITIONALDATA NEEDS The Hydraulic Evaluation and EngineeringEvaluation Reportsrecommendedthe collection of additional datathat would: (1) addressthe possiblecausesof the unintendedperformanceof the pilot PTW and (2) be usedto assistin designing a successfulengineeringsolution for the pilot PTW. We emphasizethe importanceof collecting additional information to assessand confirm both the hydraulic performanceof the pilot PTW, and to support the selectionof an engineering alternative.

The following data collection activities were recommendedin the Hydraulic Evaluation and EngineeringEvaluation Reports.

1. Install two or more new wells and collect stratigraphicinformation in the vicinity of WP-25 (west end) and WP-27 (eastend) to confirm the water level conditions that appearto provide major control on the assumedgroundwaterflow directions in the vicinity of the PTW.

2. Drill at least three additional soil borings around the easternend of the pilot PTW (one eachadjacentto the north, south, and easternface) that are logged for stratigraphicdetail to confirm whether the pilot PTW penetratesthe underlying till or is hanging within the aquifer. One additional soil boring for stratigraphy should be drilled toward the westernend of the PTW, and one additional boring should be drilled near the south face of the PTW. Theseborings should be convertedto 2-inch monitoring wells for subsequentaquifer testing.

3. Perform a long-term aquifer test consistingof a seriesof step-testperiods, a constant-dischargeperiod, and recoveryperiod, to provide additional data on the hydraulic connectionof the PTW to the surroundingaquifer.

4. Perform one or more tracer teststo provide field evidenceof the flow field that has been interpretedfrom water levels in the vicinity of the pilot PTW.

5. Develop a comprehensivethree-dimensionalnumerical model that can best assess and predict the observedhydraulic conditions, and can thus be integratedinto design activities for developing the engineeringmodification or alternative,and eventually, the full-scale design.

Prior to selectingand subsequentlydesigning an engineeredmodification alternative,we recommendperforming a focuseddata collection and analysisprogram. The basis for such a program is describedin the following paragraphs.

Note that completion of the focuseddata collection program may show that the hydraulic communicationis better than previously indicated. In this case,the overall pilot program may Y&3\deptdata~Doc~Safe\7OOOs\706lWodification Options RptM od-Rpl-Finakdoc 6

GEOM~TRIX be sufficient to move to a full-scale design program without implementing an engineering solution to enhancethe performanceof the pilot PTW. If the resultsof the data collection program confirms that hydraulic communication is insufficient for making decisionsregarding the feasibility of a full-scale system,an engineeringalternativemay be justified.

1.51 Description The focuseddata collection and analysisprogram would be designedto: (1) confirm the hydraulic conditions in and adjacentto the pilot PTW; and (2) collect key hydrostratigraphic and hydraulic information necessaryfor determining the hydraulic effectivenessof the pilot PTW and for use in selecting,designing,and assessingthe performanceof engineering modifications. A specific objective of this program is to confirm the high head potential measuredat well WP-25 and to determinewhether groundwaterflow from south of the pilot PTW is occurring. A secondobjective will be to confirm the elevationof the top of the Lavery Till to determinewhether the pilot PTW is hanging in its central and easternportions.

The componentsof this program include:

1. Borehole drilling and logging, monitoring well installation, and water level monitoring.

2. Systematicand focusedhydraulic testing program.

3. Tracer test program.

Details of the componentsare provided in the following paragraphs.

Component I: Borehole drilling, well installation, and water level monitoring program This componentwill consistof a program to develop additional hydrostratigraphicinformation and to confirm water level and hydraulic gradient (lateral and vertical) conditions adjacentto the pilot PTW. Figure 1.5 indicatesthe approximatelocationsof the sevenrecommended borings. Detailed hydrostratigraphicboring logs will be producedfor eachboring, and the cross-sectionsdevelopedfor the Hydraulic Evaluation Report will be updated Although the specific drilling and well completion method would be specified in a work plan developedprior to conductingthe field work, we recommendusing coring for developingrepresentativeand detailed stratigraphiclogs and we recommendcompleting the borings as 2-inch (or greater) diameterwells to assurereliable hydraulic communicationwith the native hydraulic system during water level monitoring and hydraulic testing. As a narrow diameter (i.e., 1 inch-diameter)well commonly is installed using direct push methods,the potential for

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GEOMATRIX compromising hydraulic communication with the native system is greaterthan for larger diameter wells due to a propensity for smearingof the narrow-diameterwell screenand well damage.

Four of the boring/wells will be located along the western, southernand easternsidesof the pilot PTW. Thesewells (WV-l, WV-2, WV-4, and WV-5) will be completedsimilarly to other borings with approximately 15-foot well screenswithin the saturatedzone. The three additional borings will be completedas shorter-screenedwells (WV-3A, WV-3B, and WV-6)

(5foot well screen)and would be installed at various depths (WV-3A screened8-13 ft bgs, WV-3B and WV-6 screened17-22 fi bgs) as well pairs to provide vertical gradient information.

Water levels and groundwatersampling for thesenew wells would be integratedinto the network-wide monitoring program. We recommenda monthly water level and sampling program for a three-month period.

Component 2: Focused hydraulic testing program This componentwill consist of a focusedhydraulic testing program with two primary objectives: (1) to confirm the influence and distribution of skin at locations around the pilot PTW; and (2) to better assessthe distribution of hydraulic conductivity in and around the pilot PTW. The testing will consist of a seriesof step-ratepumping tests and a longer constantrate test. Step-ratepumping tests are performed by pumping from a well at three successfully greater flow rates for relatively short durations (approximately 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months each); a water level recovery phaseensuesimmediately following the last step. Water levels are monitored in the pumping well and nearby observationwells. The step test, which provides specific capacity information, can provide empirical estimatesof hydraulic conductivity and can stressthe systemin such a way that boundary effects may be observable. The step testing also provides information for selectingan appropriatepumping rate for the ensuingconstant-ratetest. The short duration of the testing (we recommendtesting one well per day) allows broad coverage.

We recommendperforming step testing in 2-inch diameter wells and at the location of wells WP-25, WP-28, WP-27 and WP-34 (or the new wells installed during ComponentNo. 1).

A longer duration constantrate test, basedin part on results from the step-testing,is recommendedto provide critical information to assessingthe presenceof skin and boundary conditions in and near the pilot PTW. We recommendperforming two constantrate tests lasting approximately 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months each followed by a 12 hour1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months recovery period; one at the location of well WP-28, and one at the location of well WP-34.

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GEOMATRIX We recommendinstrumentationof nearby monitoring wells both inside and outsidethe pilot PTW with pressuretransducersto continually monitor water level responsesto pumping. We assumethat up to 10 wells would be instrumented. Details for instrumentingthe wells. and the sequenceof the testing would be detailed in a workplan developedprior to implementing this program. A report detailing the testing and analysiswould be developedfollowing the field program.

Component3: Tracer testingprogram A limited tracer testing program will provide direct evidenceof the flow pathwaysin and around the pilot PTW. We recommendintroducing tracer into three wells simultaneouslyand monitoring observationwells using available field equipment,including ion specific meters.

The existing wells that should be consideredfor the testing program include WP-25 (west end);

WP-28, south side, and WP-36, south side. Newly installed wells under ComponentNo. 1 may also be consideredfor testing.

Tracer solutions that are conservativewith respectto the Pilot PTW should be applied.

Becausethe clinoptilolite material within the pilot PTW has a slightly negativechargeand thus is prone to ion exchangereactionswith positively chargedions, the tracer should consistof a solution that is anionic (such as bromide or chloride). Dyes may be consideredas well, however, additional information as to their potential retardation within the zeolite media is required and can be included in a work plan developedfor the testing program.

Assuming bromide and a dye are usedas tracers,the tracer program would involve injecting a bromide tracer solution in Well WP-25 and well WP-26, and a dye in well WP-28. Field equipment,including ion specific electrodesand calorimeterswould be usedto analyze samplescollected from a seriesof wells (we assumeIO) in and around the pilot PTW on a regular schedule. Specificsof the testing program would be provided in a test workplan preparedin advanceof commencingthis program.

Analysis would consistof developingbreakthroughcurvesfor eachof the observationwells to assessthe travel path and migration rates of the tracer in the system. A report documentingthe test would be developedfollowing the program.

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GEOMATRIX The results of this program could provide information to definitively determinethe communicationconditions betweenthe pilot PTW and the native aquifer material, as well as indicating the areaslikely affected by skin.

This focuseddata gatheringprogram is recommendedbecauseof the importanceof gathering data that can be used to confirm: (1) the high head at well WP-25 adjacentto the western portion of the pilot PTW; (2) whether the PTW is hanging near its central and eastern sections;(3) the hydraulic efficacy of the pilot PTW in its current statewithout deploying invasive engineeringactivities. We also understand,basedon recent discussionswith researchersat UB, a calibratedhydraulic model of the pilot PTW systemhas not yet been completeddue in part to difficulty in accountingfor apparentdata inconsistencies.Therefore, this field testing and data gatheringprogram would be critical to developing a representative model that could be used for further evaluating and selectingengineeredpilot PTW modification alternatives,as well as being useful for designing a full-scale PTW system.

2.0 PILOT PTW MODIFICATION OPTIONS Four alternativesfor the pilot PTW program are presentedin this section;one no additional work alternative,two engineeringmodification alternatives,and one alternativethat comprises a completerebuild of the pilot PTW. We emphasizethat the objective of the two engineering modification alternativesis to modify the PTW so that sufficient information can be obtained from the installation to allow designof a full-scale PTW at WVDP. The objective is not to createa perfectly functioning pilot PTW.

We do not recommendattemptingto removethe postulatedlow-permeability zone around two or more sidesof the PTW (the skin), or to prevent potential underflow beneaththe PTW in areaswhere the PTW may not extendto the underlying Lavery Till. WVNS has already attemptedto dislodge the skin through aggressivepumping of water within the PTW, with limited success.Other, more invasive methods,such as disturbing the skin areawith drilling or other tools, will crush additional clinoptilolite, generatingmore fines that will only add to the skin. Methods that involve excavationof the clinoptilolite below the water table (such as a passivepiping and manifold systemto move water through the skin-zone)require shoring that will again generatemore fines as the sheetpiles are driven and extracted.Similarly, any invasivemethodsthat could reducepotential underflow, such as grouting, would require drilling or penetrationthrough the clinoptilolite zone, creating more fines. We suggestthat thesemethodswill introduceadditional complicating variablesto an already complex system, st3 deptdataDoc_Safe\7000s\7061UlodificatlonOptions Rpt,Mod-Rpt-FinaLdoc 10

GEOMATRIX and therefore we recommendimplementing simple solutions that allow sufficient information to be obtainedto completea full-scale PTW design.

Each alternative is presentedaccordingto the requirementsof the scopeof work containedin the Geomatrix contract. A descriptionof the alternative is first presented,followed by the basis for selectingthe alternative. Assumptionsmade in developing the alternative and the associatedcost estimateare then described. A generalcost estimatebasedon REM IV guidelines is developedfor eachalternative; thesecost estimatesshould be consideredorder of magnitude estimatesbecausewe are not familiar with WVNS contractingand procurement proceduresfor civil constructionwork. Any waste materialsthat may be generatedare described,(though costsfor managingpotentially radioactive spoil material are not included) along with the relative easeof implementing the alternative. Finally the likelihood of successis evaluated.

2.1 CRITERIAFORSELECTING PILOT PTW MODIFICATIONOPTIONS The criteria we have usedin selectingpotential alternativesfor meeting the goals of the pilot PTW test are basedon simple, relatively low cost strategiesthat can be usedto provide the information necessaryto assessthe feasibility of a full-scale PTW at the site.

The basic criteria usedfor identifying each alternative are listed below.

l Does the alternativeaddressand mitigate the possiblehigh head potential at the west end of the pilot PTW?

l Does the alternativehave a high likelihood of restoring sufficient hydraulic performanceto the pilot PTW?

l W ill the alternativebe of sufficiently low invasivenessso as not to createmore fines within the pilot PTW, or negatively divert ambient groundwaterflow from the pilot PTW l Is the alternativetechnically feasible?

l Is the alternativecost-effective(for this case,we have assumedthat a cost-effective alternativeis approximately20 percentor lessof the estimatedcost of the design, installation, and assessment of the current pilot PTW system)

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. GEOMATRIX The four alternativesidentified for considerationinclude:

Alternative 1 No Modification of Pilot PTW Alternative 2 Install Lateral Hydraulic Barriers Alternative 3 Install Pilot PTW Extension Alternative 4 Install New Pilot PTW Each of the alternativeslisted in the following sectionsgenerally meet most or all of the above criteria in our professionaljudgement. As discussedpreviously, other technically feasible alternatives,such as invasive programsthat attempt to remove or reducepotential skin effects, or that are not seento be cost-effective at this time (such as deploying a completely new pilot PTW) are not consideredhere.

2.2 ALTERNATIVE1 - No MODIFICATIONOFTHE PILOT PTW 2.2.1 Description This alternative consistsof completing the assessmentof the pilot PTW program and moving forward with making the decision of whether or not to design the full-scale PTW for the site.

The purposeof pilot testing a remedial method is to collect field data necessaryto design a full-scale system. We believe that the data collected and evaluatedas part of the PTW pilot study, including the laboratory data evaluatedby UB that assessesthe ability of the zeolite treatment material to provide ion exchange-basedmitigation of the Sr-90 in groundwater,provides data sufficient to develop a program for designing a full-scale remedy at WVDP. Figures 1.2 and 1.3 indicate the current geometry of the existing pilot PTW and, thus, this alternative.

2.3.1 Basisfor Selection This alternative is evaluatedaccording to the selection criteria describedin Section2.1:

l Doesthe alternativeaddressand mitigatethepossiblehigh headpotentialat the westend of thepilot PTW?

This alternative does not attempt to further assessthe high head potential at the west end of the pilot PTW. Additional data collection performed as recommendedin Section 1.5 would provide further data. However?we believe that modifying the pilot PTW is not necessaryto implement a program to design a full-scale PTW at the site. A full-scale PTW, if deployed in this samearea,would be designedto accommodatethe field conditions.

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GEOMATRIX l Doesthe alternativehavea high likeiihoodof restoringsufjcient hydraulicperformanceto thepilot PTW?

Basedon experienceand information collected during the pilot PTW program, a full-scale systemcould be designedto provide appropriatehydraulic performance.

l W ill the alternativebe of sufficientlylow invasiveness so as not to createmorejnes within thepilot PTW or negativelydivertambientgroundwaterflowj?om thepilot PTW Basedon experienceand information collected during the pilot PTW program, a full-scale systemcould be designedto reducethe potential for a significant amount of fines to either be created,or to significantly impair the required hydraulic performanceof the PTW system.

a Is the alternativetechnicallyfeasible?

Basedon existing data from the pilot PTW program, including laboratory chemical treatability tests,and knowledge of site conditions in other portions of the site, designing a full-scale PTW systemis potentially feasiblewithout first modifying the pilot PTW program. We assumethat as part of a full-scale designprogram, comprehensivehydraulic, hydrostratigraphicand geotechnicalinformation would be collected in the vicinity and along the proposedalignment of a fill-scale PTW.

l Is the alternativecost-effective Cforthis case,we haveassumed that a cost-ef,ctive alternativeis approximately 20percentor lessof the estimatedcostof the design, installation,and assessment of thepilot PTWsystem)?

This alternativewould have zero costsassociatedwith the pilot PTW program. No costshave been estimatedfor a full-scale systembecausethis cost is dependenton field conditions along the proposed(unknown) alignment, which has not been determinedand is beyond the scopeof this work.

2.3.2 Assumptions The purposeof a pilot program is to develop information necessaryfor designing and deploying a full-scale system. The pilot PTW program at WVDP, including previously conductedlaboratory treatability testing, provided information, including hydraulic, hydrostratigraphic,and engineeringdata that can be used to successfuliydesign a full-scale

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GEOMATRIX systemat the site. Designing and applying engineeringsolutions to make the pilot PTW function perfectly are not considerednecessaryto successfullydesign a full-scale PTW.

2.3.4 General Cost Estimate Zero future costsare associatedwith the pilot PTW program under this alternative. Costsfor a full-scale systemare beyond the scopeof this report.

2.3.5 Waste Generation No wastewill be generatedby this alternative.

2.3.6 Ease of Implementation An evaluationof the pilot PTW has been performed. Thus, this alternativehas been implemented.

2.3.7 Likelihood of Success The pilot PTW program has successfullyprovided local hydrostrigraphic,hydraulic, and engineeringinformation. This information forms a basis for implementing a full-scale PTW designprogram without completely modifying the pilot PTW for enhancedperformance.

2.3 ALTERNATIVES-INSTALLLATERALHYDRAULICBARRIERS 2.3.1 Description This alternativeconsistsof installing flow barriers at the west and, possibly, eastendsof and perpendicularto the PTW, as shown on Figure 2.1. The purposeof the flow barriers is to hydraulically isolate the PTW from higher water levels at WP-2.5,and to redirect the flow of groundwaterthrough the PTW.

If hydraulic mounding remainsafter deploying the lateral barriers,pumping from one or more nearby downgradientwells may be implementedto attempt to stimulate flow through the northern side of the pilot PTW. Pumping could be conductedfrom one or more of the proposed 2-inch (or larger) diameterwells recommendedfor the focusedadditional data collection program.

2.3.2 Basis for Selection This alternativeis evaluatedaccordingto the selectioncriteria describedin Section2.1:

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GEOMATRIX l Doesthe alternativeaddressand m itigatethepossiblehigh headpotentialat the westend of thepilot PTW?

The westernsheetpile barrier wall is expectedaddressthe anomalouslyhigh water level in WP-25 that has beenpresentsince constructionof the pilot PTW started.

l Doesthe alternativehavea high IikeIihoodof restoringsuf$cienthydraulicperformanceto thepilot PTW?

If the mounded groundwaterin the PTW results from high hydraulic head or other hydrogeologic conditionsnear WP-25, then this solution will removethe influence of these local conditions on the hydraulic performanceof the PTW. The easternsheetpile barrier wall will also isolate the PTW from any anomalousconditions that may be presentat the easternend of the PTW. The two lateral hydraulic barrier walls will createan approximatelytwo-dimensional flow regime where groundwaterfI ow is orthogonal to the orientation of the PTW, allowing much easierinterpretationof groundwaterflow conditions through the PTW. Flow through the PTW will then be determinedby the presenceof the skin on the sidesof the PTW.

l W ill the alternativebe of suf$cientIylow invasiveness so as not to createmore$neswithin thepilot PTW or negativelydivertambientgroundwaterflowfrom thepilot PTW The sheetpiles will be driven through the clinoptilolite zone, and so will createmore fines.

However, thesefines should only be presentnear the sheetpile barrier and will only influence flow near the barrier. The groundwaterflow regime away from the barrierswill not be affected, exceptto the extentthat the barriersredirect groundwaterflow.

l Is the alternativetechnically feasible?

Sheetpiles were driven at WINS to constructthe PTW, so constructionof the barriers is technically feasible.

l Is the alternativecost-effective Cforthis case,we haveassumed that a cost-effective alternativeis approximately 20percentor lessof the estimatedcostof the design.

installation,and assessment of thepilot PTWsystem)?

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GEOMATRIX As describedbelow, the estimatedcost for this alternativeis $80,000 for installing just the westernlateral hydraulic barrier, which we understandis lessthan 10 percentof the cost of the original installation.

2.3.3 Assumptions The flow barrierswill consist of sheetpiles driven approximately 1 foot into the Lavery Till.

The sheetpiles will be driven in interlock to provide a continuousbarrier; we do not recommendusing sealablesheetpiles for this application becausethe head differencesacross the sheetpiles will be very low. The length of the barrier walls necessaryto createthe required groundwaterflow conditions will be determinedin detailed design; for the purposesof preparing a cost estimate,we assumeda length of 60 feet for both barrier walls.

2.3.4 General Cost Estimate Table 1 providesgeneralcost information for this alternative, including erigineeringdesign, constructionoversightand bid and scopecontingencies.WVNS purchasedthe sheetpiles used to constructthe PTW; thesesheetpiles can be reusedto install the flow barriers. Costsare basedon conventionalactivities, and do not include special circumstances,procedures,or handling of materialsat the WVDP. Costs for managing spoils and other investigationderived waste is not included in this estimate.This cost doesnot include evaluationof the successor failure of this alternativeto provide the necessaryinformation to design a full-scale PTW.

The generalcost estimatefor this alternative is $80,000. If this alternativeis implementedin phases,the additional cost will be about $50,000.

2.3.5 Waste Generation Minimal wastewill be generatedfrom driving the sheetpiles.

2.3.6 Ease of Implementation The design of the sheetpile walls will require determinationof the length and depth of the walls, the type of sheetpiles, and the equipmentusedto drive the sheets.The sheetpiles will be thosethat WVNS purchasedto install the PTW, and the pile driving equipmentwill probably also be the same. The length of the sheetpile barrier walls will be determinedform analytical modeling, probably using the model already developedat UB. The depth of the walls can be determinedfrom existing subsurfacedata. Once the dimensionsare specified.the walls can quickly be installed.

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GEOMATRIX 2.3.7 Likelihood of Success The two sheetpile barrier walls will effectively eliminate the influence of hydraulic conditions eastand west of the PTW. Evaluation of monitoring data will be greatly simplified becausethe systemwill be a quasi-two dimensionalflow systemwith groundwaterflow throughout the PTW. Low permeability zoneswithin the PTW, such as the skin, will retard the flow of water through the PTW, we anticipatethat some affected groundwaterwill flow through. Thus the effectivenessof the PTW technologycan be evaluatedbasedon the monitoring data.

2.4 ALTERNATIVE%INSTALLEXTENSIONTO PTW 2.4.1 Description .

This alternativeconsistsof installing an extensionon the eastside of the existing PTW, as shown on Figure 2.2. The purposeof the PTW extensionis to capturethe flow of groundwater that appearsto be flowing aroundthe easternend of the existing PTW. The conceptualdesign of this alternativeassumesan extensionof approximately equal length (approximately30 feet) and width to the existing pilot PTW. However, we strongly recommendusing a groundwater flow model to design the final geometryand alignment of this alternative.

2.4.2 Basis for Selection This alternativeis evaluatedaccordingto the selectioncriteria describedin Section2.1:

l Doesthealternativeaddressand m itigatethepossiblehigh headpotentialat the westend of thepilot PTW?

The easternextensionof the PTW will not directly mitigate the high head potential at the west end of the existing PTW. By capturing additional flow that currently flows around the eastern end of the PTW, the effect of this high head may be reduced.

l Doesthealternativehavea high likelihoodof restoringsufjcient hydraulicperformanceto thepilot PTW?

The easternextensionof the PTW will be installed using constructiontechniquesthat have been modified basedon the lessonslearnedfrom the original pilot PTW installation. Thus less fines and a less significant skin will be presentin and around the easternextensionof the PTW.

It is thereforeanticipatedthat groundwatercurrently flowing aroundthe PTW will flow through the PTW extension,providing much better hydraulic performance.

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GEOMATRIX l W ill the alternativebe of sufficientlylow invasiveness so as not to createmore-fineswithin thepilot PTW or negativelydivertambientgroundwaterjloM1 from thepilot PTW The PTW extensionwill be installed using refined techniques,so fines generationwill be much lower than in the original installation. Minimal fines may be createdwithin the existing PTW in the areawhere the PTW extensionconnectsto it, becausesheetpile driven into the PTW will createfines locally. Thesefines are not expectedto adverselyaffect the performanceof the extendedPTW.

l Is the alternativetechnically feasible?

Constructionwill be similar to the original PTW installation, so constructionis technically feasible.

l Is the alternativecost-effective G forthis case,we haveassumed that a cost-effective alternativeis approximately 20percentor lessof the estimatedcostof the design, installation,and assessment of thepilot PTWsystem)?

As describedbelow, the estimatedcost for this alternativeis about $400zOO0, which we understandis about 30 percentof the cost of the original installation. This alternativetherefore doesnot meet the criteria for cost-effectiveness.

2.4.3 Assumptions The PTW extensionwill be installed within a cofferdam similar to the constructionof the original PTW. Bracing designwill probably differ, allowing lesssheetpile penetrationof the Lavery Till and therefore lessdisruption during sheetpile extraction. The cofferdam will be flooded prior to removing the sheetpiles to prevent fines being redistributedwithin the PTW.

A comprehensivecap will also be installed over the PTW.

2.4.4 General Cost Estimate Table 2 provides generalcost information for this alternative,including engineeringdesign, constructionoversightand scopecontingencies.WVNS purchasedthe sheetpiles usedto constructthe original PTW; thesesheetpiles can be reusedto install the PTW extension.

Costsare basedon conventionalactivities, and do not include special circumstances, procedures,or handling of materials at the WVDP. Costsfor managingspoils and other

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GEOMATRIX investigationderived waste is not included in this estimate.This cost doesnot include evaluationof the successor failure of this alternativeto provide the necessaryinformation to design a full-scale PTW The generalcost estimatefor this alternative is $395,000.

2.4.5 Waste Generation Significant wastewill be generatedfrom constructionof the PTW extension,similar to that generatedfrom the constructionof the original PTW. Dewatering the cofferdam will generate significant quantitiesof water containing Sr-90, and excavationwill generatesignificant quantities of spoils. Handling of thesewastesis not included in the cost estimatefor this alternative.

2.4.6 Ease of Implementation Constructionwill be similar to constructionof the original PTW, and should be easierbasedon lessonslearnedfrom that experience. The design of the PTW extensionwill be slightly different to accommodatelessonslearnedfrom the performanceof the PTW.

2.5.7 Likelihood of Success The PTW extensionshould captureflow that is currently going aroundthe existing PTW if designedbasedon the current knowledge of site hydrogeologic conditions in the vicinity of the pilot PTW. However, evaluating this alternativewith a groundwaterflow model is necessary for finalizing the design.

2.5 ALTERNATIVE 4 ~NSTALLANEWPILOT PTW 2.51 Description This alternativeconsistsof installing a new pilot PTW at a suitable location at WVDP.

Additional soil and groundwaterinvestigationwill be performed to locate and design the new pilot PTW, and the new PTW will be constructedin a manner that incorporatesthe lessons learnedfrom the design,constructionand monitoring of the existing PTW. A representative groundwatermodel is necessaryfor designingthis alternative.

2.5.2 Basis for Selection This alternativeis evaluatedaccordingto the selectioncriteria describedin Section 2.1:

~.sfi\deptdata~ ~ac_Safe 7000s~ 7061Woditicatvx1 Options Rpt>Mod-Rpt-Final.doc 19

GEOMATRIX l Doesthe alternativeaddressand m itigatethepossiblehigh headpotentialat the westend of thepilot PTW?

This alternativemitigates this by installing a new pilot PTW.

l Doesthe alternativehavea high likelihoodof restoringsufjcient hydraulicperformanceto thepilot PTW?

No, this alternativerelies on an adequatedesign, installation and monitoring of a new pilot PTW that has sufficient hydraulic performanceso that the effectivenessof the PTW technology can be evaluated.

l W ill the alternativebe of suf$cientlylow invasiveness so as not to createmorefines within thepilot PTW,or negativelydivertambientgroundwater flow from thepilot PTW No, this alternativerelies on an adequatedesign, installation and monitoring of a new pilot PTW that has sufficient hydraulic performanceso that the effectivenessof the PTW technology can be evaluated.

l Is the alternativetechnicallyfeasible?

Installation of the new pilot PTW will use design,constructionand monitoring techniques similar to those employedfor the original pilot PTW, so the alternativeis technically feasible.

l Is the alternativecost-effective Cforthis case,we haveassumed that a cost-effective alternativeis approximately 20percentor lessof the estimatedcostof the design, installation,and assessment of thepilot PTWsystem)?

As describedbelow, the estimatedcost for this alternativeis about $720,000,which we understandis about 50 percentof the cost of the original installation. Thereforethis alternative doesnot meet the criteria for cost-effectiveness.

2.5.3 Assumptions The new pilot PTW will have similar dimensionsto the existing pilot PTW, and will be installed using a similar cofferdam design,exceptthat the bracing will be designedto allow less sheetpile penetrationof the Lavery Till. WVNS will be able to reusethe sheetpiles that were purchasedto install the original pilot PTW.

sf3:deptdat~0x~Safe\7000s\7061U4oditicatm Optmns Rpl Mod-Rpt-Final.doc 20

GEOMATRIX 2.5.4 General Cost Estimate Table 3 provides generalcost information for this alternative,including engineeringdesign, constructionoversight and scopecontingencies. WVNS purchasedthe sheetpiles usedto constructthe PTW; thesesheetpiles can be reusedto install the new pilot PTW.

This cost estimatealso includes soil and groundwaterinvestigation and an engineeringdesign for the PTW. All costsare basedon conventionalactivities, and do not include special circumstances,procedures,or handling of materialsat the WVDP. Costsfor managing spoils and other investigation derived waste is not included in this estimate.This cost doesnot include evaluation of the successor failure of this alternativeto provide the necessaryinformation to design a full-scale PTW.

The generalcost estimatefor this alternative is $720,000.

2.5.5 Waste Generation Significant waste will be generatedfrom constructionof the new pilot PTW, similar to that generatedfrom the constructionof the original PTW. Dewatering the cofferdam will generate significant quantities of water containing Sr-90, and excavationwill generatesignificant quantities of spoils. Handling of thesewastesis not included in the cost estimatefor this alternative.

2.5.6 Ease of Implementation A suitable location for the new pilot PTW at WVDP will need to be identified, and a comprehensivesoil and groundwaterinvestigation completedin the area. A new PTW design will be completedto incorporatethis investigation data and the lessonslearnedfrom constructionof the original pilot PTW. Constructionwill be similar to constructionof the original PTW, and should be easierbasedon lessonslearnedfrom that experience.

2.5.7 Likelihood of Success The successof the new pilot PTW will dependon the adequacyof the additional soil and groundwaterinvestigation and the new engineeringdesign, including groundwatermodeling.

Site-specificparameterswill need to be evaluatedand carefully consideredin the implementation of the new pilot PTW.

. ~s~~deptdata\Doc~Safe\7OOOs\7OGl~~fodi~cation Optlons RptM od-Rpt-Final.doc 21

GEOMATRIX

3.0 CONCLUSION

S AND RECOMENDATIONS This sectionprovides our recommendationsfor the preferred alternative and courseof action.

3.1 PREFERREDALTERNATIVE The final engineeringmodification alternative is dependenton testing the selectedalternates with the groundwatermodeling tool currently being developedby UB. However, basedon the generalobjectives for performing a pilot test of a remedial technology, and the data collected during the WVDP pilot PTW and feasibility testing program, we recommendthat Alternative 1 be formally implemented,that the pilot PTW program be concluded,and that the full-scale PTW design program begin. The full-scale PTW designprogram might include methods describedin focusedadditional data collection program describedin Section 1.5, but would not necessarilyinclude the specific data collection activities recommendedfor assessing performanceof the existing pilot PTW.

3.2 RECOMMENDEDCOURSEOFACTION If an engineeredmodification alternative is selected, we recommendand emphasizethe importance of completing Components1 and 2 of the focused additional data collection program describedin Section 1.5, and completing the modeling study by UB (the results from the focused additional data collection program may be critical for developing a representative groundwatermodel). These actions will increasethe confidencethat a reliable solution to the pilot PTWs current performancecan be selected,designed,and implemented and can be designedwith a high probability of success.

M3\deptdataD oc_Safe~7OOOs~iO6lWodification Options RptMod-Rpr-Finakdoc 22

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GEOMATRIX 4 .0 REFERENCES G e o m a trixConsultants,Inc., 2 0 0 0 a P , ilot P e r m e a b lTreatment e W a ll HydraulicE v a l u a tio n R e p o r t,p r e p a r e dfor W e s tV a l l e y N u c l e a rServices,L L C , W e s tValley, N e w York, M a r c h .

G e o m a trixConsultants,Inc., 2 0 0 0 a P , ilot P e r m e a b lTreatment e W a ll E n g i n e e r i n gE v a l u a tio n R e p o r t,p r e p a r e dfor W e s tV a l l e y N u c l e a rServices,L L C , W e s tValley, N e w York, M a r c h .

. s i3\deptdataDoc~Safe~.7OOOs\706lWodification Opttons Rpt*Mod-Rpt-Ftnal.doc 23

GEOMATRIX TABLES

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Pilot PTW Evaluation Report APPENDIX 13 COST ESTIMATE FOR FOCUSED DATA COLLECTION AND ANALYSIS PROGRAM

Pilot PTW Evaluation Report APPENDIX 13 COST ESTIMATE FOR FOCUSED DATA COLLECTION AND ANALYSIS PROGRAM This appendix / attachment presents a cost estimate for implementing Components 1-3 of the focused data collection and analysis program presented in section 1.5.1 of the report by Geomatrix Consultants, Inc.

titled Pilot Permeable Treatment Wall Modification Options Report, dated April 2001.

Component 1: Borehole drilling, well installation, and water level monitoring program Mobilization / demobilization for drilling rig and 2-person crew, including radiological worker training:

- training $5,000

- mobilization $3,000

- demobilization $3,000 Total for Mobilization / Demobilization $11,000 Complete 4 test borings to a depth of 30-feet each using hollow-stem augers with continuous split-spoon sampling at 2-foot intervals, complete 2 similar test borings to a depth of 22-feet each, and complete 1 similar test boring to a depth of 13-feet (plus 15% contingency).

200 feet at $30/foot = $6,000 Install 4 monitoring wells to a depth of 30-feet each, install 2 wells to a depth of 22-feet each, and install 1 well to a depth of 13-feet. Wells will be constructed of 2-inch ID PVC screen and riser pipe, with a filter sand pack adjacent to the screen, bentonite seal above the sand pack, and cement grout backfill up to ground surface (plus 15% contingency).

200 feet at $30/foot = $6,000 Installation of protective well casings for each well.

7 protective casings at $500/each = $3,500 Decontamination time for drilling rig and crew.

Estimate 20 hours2.314815e-4 days 0.00556 hours 3.306878e-5 weeks 7.61e-6 months at $150/hour = $3,000 Subtotal for Component 1 = $29,500

Pilot PTW Evaluation Report Component 2: Focused hydraulic testing program Purchase or rent equipment for groundwater pumping tests including, but not limited to:

- pumps

- pump controllers

- pipe

- valves

- hoses

- pressure transducers Estimate $6,000 Subtotal for Component 2 = $6,000 Component 3: Tracer testing program Purchase or rent equipment for tracer tests including, but not limited to:

- tracer solutions

- tracer dyes

- ion specific electrodes

- colorimeters Estimate $6,000 Subtotal for Component 3 = $6,000 Total Estimate for Components 1-3 = $41,500

Pilot PTW Evaluation Report APPENDIX 14 PATH FORWARD PROJECT SCHEDULE

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ML11214A189

Contents

Text

SUMMARY

1.0 INTRODUCTION

1.2 DESCRIPTION

5.0 REFERENCES

1.0 INTRODUCTION

1.2 DESCRIPTION

SUMMARY

5.0 REFERENCES

1.0 INTRODUCTION

SUMMARY

5.0 CONCLUSION

1.0 INTRODUCTION

5.0 CONCLUSION

1.0 INTRODUCTION

3.0 CONCLUSION

4.0 REFERENCES

1.0 INTRODUCTION

3.0 CONCLUSION

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ML11214A189

Text

SUMMARY

1.0 INTRODUCTION

1.2 DESCRIPTION

5.0 REFERENCES

1.0 INTRODUCTION

1.2 DESCRIPTION

SUMMARY

5.0 REFERENCES

1.0 INTRODUCTION

SUMMARY

5.0 CONCLUSION

1.0 INTRODUCTION

5.0 CONCLUSION

1.0 INTRODUCTION

3.0 CONCLUSION

4.0 REFERENCES

1.0 INTRODUCTION

3.0 CONCLUSION

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