HBL-14-008, Enclosure 9: Technical Report TR-HBIP-2002-01, Seismic Hazard Assessment for the Humboldt Bay ISFSI Project. Appendix 9A-42 to End. Enclosures 10 & 11: Humboldt Bay Power Plant Tritium Evaluation and DECON-POS-HOS-H011, Groundwater Invest

Enclosure 9: Technical Report TR-HBIP-2002-01, Seismic Hazard Assessment for the Humboldt Bay ISFSI Project. Appendix 9A-42 to End. Enclosures 10 & 11: Humboldt Bay Power Plant Tritium Evaluation and DECON-POS-HOS-H011, Groundwater Investig

ML14045A395
Person / Time
Site:	Humboldt Bay
Issue date:	12/27/2002
From:	Swan F Pacific Gas & Electric Co
To:	Document Control Desk, NRC/FSME
Shared Package
ML14045A387	List: HBL-14-008, Enclosure 9: Technical Report TR-HBIP-2002-01, Seismic Hazard Assessment for the Humboldt Bay ISFSI Project. Appendix 9A-42 to End. Enclosures 10 & 11: Humboldt Bay Power Plant Tritium Evaluation and DECON-POS-HOS-H011, Groundwater Invest
References
HBL-14-008 DECON-POS-H011, TR-HBIP-2002-01
Download: ML14045A395 (104)

Text

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Figure 4. 1992 Mw 7.7 Nicaragua earthquake and tsunami runup. Source area is indicated by the rectangle; solid dots are aftershocks and shaded areas represent regions of high moment release. Mechanism of earthquake in lower left comer. Arrow indicate$ Cocos-Can'bbean relative plate motion. The highest tsunami runup shows a general correlation with offshore areas of highest moment release. [From Geist ( 1998)].

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Enclosure 10 PG&E Letter HBL-14-008 Enclosure 10 ENERCON Services, Inc.:

"Humboldt Bay Power Plant Tritium Evaluation" September 7, 2006 Pages 1 to 30

HUMBOLDTBAYPOWERPLANT TRITIUM EVALUATION Prepared For:

Pacific Gas & Electric Humboldt Bay Power Plant 1000 King Salmon Avenue Eureka, CA 95503 Prepared By:

ENERCON Services, Inc.

4499 Old William Penn Highway Murrysville, PA 15668 September 7, 2006 001

TABLE OF CONTENTS PAGE 1.0 Purpose Statement .................................................................................................................... 1 2.0 NEI Initiative Action Plan Development. ................................................................................. 3 3.0 Site Background ....................................................................................................................... 5 3.1 Unit 3 Description .................................................................................................................... 5 3.2 Previous Site Investigations ..................................................................................................... 6 3.3 Prior Significant Radiological Releases ................................................................................... 6 3.4 Other Potential Tritium Source Contributors ........................................................................... 8 4.0 DSAR and ISFSI Design Report Assessments of Groundwater Contamination ...................... 9 5.0 Geologic and Hydrologic Site Characterization ..................................................................... 10 5.1 Site Stratigraphy ..................................................................................................................... 10 5.2 Aquifers in the Area ............................................................................................................... 11 6.0 HBPP Groundwater Monitoring Program Evaluation ............................................................ 15 6.1 Description of the Existing Program ...................................................................................... 15 6.2 Assessment of Data from Existing Program ........................................................................... 15 6.3 Identification of Potential Transport Pathways ...................................................................... 18 6.4 Identification of Optimum Monitoring Positions ................................................................... 19 6.5 System Component Evaluation .............................................................................................. 20 7.0 Tritium Monitoring Impact on HBPP Licensing .................................................................... 21 8.0 Conclusions ............................................................................................................................ 23 9.0 Recommendations and Suggestions ....................................................................................... 24 10.0 Report Limitations ................................................................................................................ 25 11.0 References ............................................................................................................................ 26 Attachment Attachment 1 Map-- Suggested Locations Proposed New Monitoring Wells 002

Tritium Evaluation Humboldt Bay Power Plant 1.0 Purpose Statement The purpose of this report is to provide a review of the existing groundwater monitoring program at Humboldt Bay Power Plant (HBPP). The objectives of this review include:

• Identify sources that may cause inadvertent radiological releases to the groundwater

• Identify migration pathways for inadvertent radiological releases to move offsite

• Identify unmonitored pathways that may allow undetected radiological releases offsite

• Recommend actions to address those unmonitored pathways This report was prepared by ENERCON Services, Inc. (ENERCON) to address the objectives described above, and present options to HBPP for a path forward to achieve those objectives if needed. The tasks associated with this effort are outlined below.

Task 1 - Operational Engineering Review Review HBPP documentation to identify previous releases and thus identify potential sources of tritium that may be released from the site.

Task 2 - Hydrogeology Review Review site hydrogeology information to assess the technical and regulatory completeness of the existing information.

Task 3 -Data Gap Analysis After completing Tasks 1 and 2, identify data gaps that may require additional or prudent groundwater hydrogeology work including but not limited to:

• Expansion of existing environmental monitoring program at HBPP to fill data gaps.

• Collection of additional hydrogeology data at the site to fill data gaps.

• Addition of new monitoring programs at the site to fill data gaps.

Task 4- Groundwater Monitoring Recommendations After completing Tasks 1 through 3, recommend actions to effectively implement a groundwater monitoring program. Key elements of these recommendations may include:

003

Tritium Evaluation Humboldt Bay Power Plant

• Identification of system(s) and/or previous release locations likely to require future monitoring.

• Identification of additional data that can be collected during normal site operation and maintenance activities.

• Identification of new sampling and analysis efforts at existing site water collection points.

• Identification of new monitoring well and piezometer locations on site.

• General description of additional monitoring programs, if appropriate.

In support of this effort, ENERCON participated in a recent Nuclear Energy Institute (NEI) industry-wide workshop focused on (1) lessons learned from recent tritium release sites and (2) developing an industry initiative Action Plan. The industry initiative Action Plan should anticipate and prevent inadvertent or otherwise uncontrolled releases of radionuclides, specifically tritium, into the environment that could lead to groundwater contamination and eventual transport offsite.

2 004

Tritium Evaluation Humboldt Bay Power Plant 2.0 NEI Initiative Action Plan Development NEI along with the Nuclear Power Generation Industry has made a commitment to an Industry Initiative course of action supported by the industries chief nuclear officers. The Industry Initiative is binding on all companies operating or decommissioning a nuclear power plant. The objectives of this tritium in groundwater initiative include:

• Improve management processes to identify inadvertent radiological releases to the groundwater

• Prevent migration of licensed radioactive materials offsite

• Quantify impacts on decommissioning nuclear plants

• Enhance trust and confidence of local communities, States, and the Nuclear Regulatory Commission (NRC) in the industry The first requirement associated with this commitment involves developing and implementing a site-specific Action Plan with a target date of July 31, 2006. To support this effort among its members, the NEI committed to provide an industry standard Action Plan Outline that contains the minimum recommended content categories. The Industry Initiative recognizes the importance of maintaining the flexibility to adequately address site-specific conditions. Each plant's Action Plan should address how that site will approach or develop an approach to a number of issues.

The basic components of an Action Plan were discussed at the NEI workshop on June 9, 2006.

The proposed NEI Action Plan outline will be finalized and provided to its members at a later date.

Developing an Action Plan to meet the Industry Initiative is a plant-specific action. Engineering, hydrogeology, and environmental efforts are necessary to develop a site-specific Action Plan that meets NEI requirements. Key parts of the Action Plan are outlined below along with our assessment of the plant's current status.

• System Component Evaluation - The system component evaluation will be developed by ENERCON in conjunction with and supported by HBPP plant staff.

3 005

Tritium Evaluation Humboldt Bay Power Plant

• Hydrogeology Characterization - The hydrogeology evaluation will be prepared by ENERCON for this report.

• Historical Site Assessment - Review and evaluation of the documentation provided to ENERCON addresses this point.

• Voluntary Data Collection Plan - voluntary data collection efforts cannot be implemented without first evaluating the existing data collection program and identifying specific gaps.

The evaluation of the existing groundwater monitoring program addresses this point.

• Selection of Optimum Monitoring Positions - data compiled as part of a voluntary data collection plan under the industry initiative may impact the need for additional monitoring wells if the existing program does not fully address the NEI objectives. ENERCON believes that no additional monitoring should be initiated until the industry initiative is better defined.

4 006

Tritium Evaluation Humboldt Bay Power Plant 3.0 Site Background Humboldt Bay's nuclear unit, HBPP Unit 3, is a 65 megawatt (nominal, electric) natural circulation boiling water reactor, which has been shut down since July 1976. Background information on the Unit and prior site investigations are provided in this chapter.

3.1 Unit 3 Description Unit 3 consists of a General Electric natural circulation, single cycle boiling water reactor, the associated turbine-generator, and necessary support and auxiliary systems. The reactor vessel is a 10 feet diameter, 40.5 feet long pressure vessel that is suspended in a drywell containment vessel.

The reactor primary containment is located entirely below grade. It is comprised of the centrally located drywell vessel, which is connected to a suppression chamber concentrically surrounding most (300 degrees) of the drywell vessel. The suppression chamber is a space about 12 feet wide by 49 feet high with exterior and interior reinforced concrete walls about four feet thick. Most of the chamber (except for a partition wall between chambers) is lined with steel. During operation, the chamber was partially filled with water, into which the vent piping from the drywell was partially immersed. Collectively, the drywell, the suppression chamber, the water, and the vent piping comprised a pressure suppression containment system.

The drywell and suppression chamber are located inside a reinforced concrete caisson which, in the vicinity of the reactor, is 59.5 feet in diameter and extends to an inside depth of78 feet below grade. A caisson access shaft extends from the top of the caisson to the space beneath the drywell. The access shaft contains the reactor auxiliary systems. The refueling building encloses the space above the caisson. In addition to the reactor caisson, the refueling building contains the spent fuel storage pool and the new fuel storage vault.

The caisson above elevation (-14 feet up to grade at elevation +12 feet) is rectangular (about 49 feet wide by 75 feet long) and serves as the structural foundation for the refueling building and former stack projection. The drywell vessel and biological shield continue up to grade and serve as a central support pier for the floors at elevations (-14 feet), (-2 feet), and +12 feet. The base of the caisson was sealed with tremie concrete underneath the drywell and suppression chamber at elevation -66 feet, and under the two levels of the spent fuel pool (SFP) floor at elevation (-14 5

007

Tritium Evaluation Humboldt Bay Power Plant and -24 feet). A 6-inch pervious gravel blanket on the tremie and below the 6-inch floor slab was designed to collect seepage and to prevent any pressure buildup. Seepage into the areas below the drywell and suppression chamber is collected in a tank called the caisson sump. Seepage into the areas below the floor of the SFP is collected in a space called the French drain. Groundwater is also routinely collected from the reactor caisson sump. Water from both systems is sampled, analyzed, and treated prior to discharge.

3.2 Previous Site Investigations PG&E performed a background and site radiological characterization survey at HBPP in 1997.

The radiological characterization consisted of three separate surveys:

• survey of facility structures

• survey of soils and sediments within HBPP properties

• survey of soils, sediments and construction materials in the vicinity of HBPP to assess background levels of radioactivity.

The process through which the HBPP radionuclide analytical data were evaluated consisted of 1) elevated measurement comparisons, 2) update of survey unit boundaries, and 3) statistical analysis of the data. Elevated measurements comparisons consisted of identifying individual sample results that exceeded 1 pCi/g. Cs-137 and Co-60 were the only reactor-generated radionuclides that significantly exceeded this level.

3.3 Prior Significant Radiological Releases As constructed, the SFP was a Carboline coated concrete structure, to be filled with demineralized water. Upon initial use, the water had undesirable levels of chlorides postulated to be either from the concrete or from groundwater in-leakage. To eliminate the potential for in-leakage, a stainless-steel liner was installed in the SFP in 1963.

After the refueling outage in the fall of 1965, the SFP water contamination of primarily Zn-65 increased significantly, and the SFP water level was observed to decrease due to evaporation from the water heated by the freshly discharged fuel. In March 1966, it was discovered that a leak in the SFP liner had developed, changing the water loss from about 0.23 inch per day to about 0.42 inch per day, or nominally between 75 to 130 gallons per day.

6 008

Tritium Evaluation Humboldt Bay Power Plant Investigations were conducted to determine the magnitude of any groundwater contamination that could have occurred. Samples of groundwater from the two plant domestic water wells and the reactor caisson sump did not reveal signs of contamination. About early April 1966, a sample well (consisting of a pipe water-washed into the soil) was installed north of the spent fuel storage pool (between the pool and the bay) and it revealed evidence of contamination, but the levels were a factor of 100 below allowable drinking water limits. Two more similar sample wells were installed in May of 1966 to the east and south of the spent fuel storage building. Neither well showed any signs of contamination. Samples of water and sediment from the SFP liner and from the French drain showed Zn-65 levels comparable to the SFP water.

Operating procedures were developed to minimize leakage by maintaining the water level in the gap between the liner and the SFP about 30 to 50 inches below groundwater level. The subsequent water influx resulted in approximately 12 gallons of slightly contaminated water being pumped every 5 to 7 days for processing in the low level water (LL W) treatment system.

The French drain under the SFP (initially referred to as the "blotter" drain) was presumably designed to be continuously drained, to prevent any pressure buildup under the floor of the SFP.

However, at some point subsequent to filling the SFP, the drain valve for this system was routinely kept closed, and opened only to collect water samples. After a chart recorder was added to the SFP liner gap water level monitoring system for SAFSTOR, in 1984, it was noted that the liner gap water level dropped upon sampling the French drain water. It was surmised that the French drain influenced more by the liner gap water than groundwater. At that time, the French drain sample station was modified to take continuous sample at a rate low enough (via a peristaltic pump) not to disturb the desired hydraulic gradient from groundwater to French drain to SFP liner.

In the period from 1981 to 1984, concentrations of Cs-13 7 and Co-60 from the French drain were evaluated and shown to have similar ratios of these radionuclides to samples from the liner gap and the SFP. The significantly lower concentration of these radionuclides from water collected from the liner gap suggested that infiltrating groundwater was the major contributor of water to the liner gap. Analysis of the volumes of water and the concentrations indicated that the SFP leakage was on the order of about 2 gallons per day.

7 009

Tritium Evaluation Humboldt Bay Power Plant 3.4 Other Potential Tritium Source Contributors Historical releases have occurred that may have been contributors to previously detected tritium in groundwater. Documented releases to the ground surface have occurred from condensate and liquid radwaste spills.

Other potential sources were leakage from near surface underground piping such as the original liquid radwaste discharge piping, a clay drain line from the radwaste tankage area, and contaminated electric conduit/pull boxes. The precise contribution of these potential sources if any to the previously measured tritium levels in groundwater cannot be determined.

In addition, a potential source of the tritium observed in MW-11 is from the radwaste discharge.

Between 1976 and 1984 the radwaste discharge was to the Unit 3 circulating water discharge tube. However, during this time period there was no circulating water flow, and the only dispersion mechanism was tidal dilution. It is possible that tritium in the liquid radwaste may have diffused into the soil surrounding the discharge tube.

8 010

Tritium Evaluation Humboldt Bay Power Plant 4.0 DSAR and ISFSI Design Report Assessments of Groundwater Contamination Evaluation of groundwater contamination in the Defueled Safety Analysis Report (DSAR) assumed the complete release of the SFP water volume and concluded the following:

"ground water could be contaminated by the SFP water, but the contamination would be very slight. Resulting concentrations of the three significant isotopes in ground water would approximate 1.2E-7 ,uCi/ml 137Cs, 7 .SE-9 ,uCi/ml 134 Cs, and 2.5E-1 0 ,uCi/ml 6°Co. This estimate is conservative since the water volume released from the pool would reach equilibrium with the very high water table in the site soil strata, resulting in less release than the entire pool volume."

The DSAR stated that data from the site indicated that the flow of groundwater in the vicinity of the spent fuel storage pool is towards Humboldt Bay. Flow measurements made by Bechtel in 1984 indicated that the groundwater flow direction is affected by the tidal cycles in Humboldt Bay. During the summer months, and during flood tides, groundwater flow is generally inland.

During ebb tides, groundwater flows towards the bay. During winter months groundwater flow is affected by tidal actions but not as much as in the summer. During the winter, the controlling flow is always toward Humboldt Bay even though during flood tides there may be a minor temporary flow reversal.

As an integral component of the Independent Spent Fuel Storage Installation (ISFSI) Design, a detailed evaluation of the geologic strata was completed. This assessment reported that HBPP lies in the Eureka Plain Sub-basin of the North Coast Basin. The Eureka plain drainage basin is within the hydrologic unit defined as the Redwood Creek-Mad River-Humboldt Bay Unit. With respect to the site, the watersheds of Humboldt Bay and the bay itself are the most relevant surface water bodies. The four major creeks that drain into Humboldt Bay are Freshwater Creek, Elk River, Salmon Creek, and Jacoby Creek. Several smaller tributaries also drain into the Bay.

Salmon Creek and Elk River are the nearest streams to the site, within a mile south and north of the site respectively. Salmon Creek and Elk River are used for watering livestock, but are not used as a potable water supply.

9 011

Tritium Evaluation Humboldt Bay Power Plant 5.0 Geologic and Hydrologic Site Characterization Groundwater level and flow direction at the HBPP is influenced by several factors, including topography, proximity to Humboldt Bay, and stratigraphy. The site stratigraphy and underlying groundwater conditions are described in the following sections.

5.1 Site Stratigraphy The geology in the region is presented and discussed in Section 2.6.3 of the ISFSI Design Report.

The geology and aquifer characteristics that are important to understanding the groundwater at and near the site are summarized in this section. The main geologic formation in this area is the Pleistocene Hookton Formation that is about 1,100 feet thick beneath the site. Its sediments hold several of the important groundwater aquifers in the site area. The Hookton Formation unconformably overlies the Pleistocene Scotia Bluffs Formation. The Pleistocene marine terrace deposits that cap the Hookton are generally included as part of the formation. The Hookton Formation locally is overlain by Holocene Bay deposits of Humboldt Bay and by Holocene alluvial deposits along the streams in the region.

Surface soils at the site are described to consist of firm to stiff clay and silt of the Upper Hookton formation to a depth of 15 to 35 feet. These fine-grained soils are predominately a sand and gravel unit to a depth of about 110 feet. The generalized stratigraphic description of the Hookton Formation is described below.

5.1.1 Hookton Formation The Hookton Formation consists of interbedded shallow-water marine, estuarine, and fluvial deposits of sand, silty sand, chert-rich gravel, and clay that is about 1,100 feet thick below the site. The formation is divided into Upper and Lower Hookton. The upper unit is 60 to 80 feet thick and consists of laterally discontinuous beds of clay and silt, and sand and gravel that change laterally with interfingering, cut-and-fill, and gradational facies changes. The clay beds that are ancient bay sediments have more lateral persistence than interbedded sandy and silty layers. The Hookton strata beneath Buhne Point Hill have been tectonically tilted to the east a few degrees toward the intake and discharge canals. The Discharge Canal fault has displaced the Hookton Formation, the south side up-thrown compared to the north side.

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Tritium Evaluation Humboldt Bay Power Plant 5.1.2 Lower Hookton Formation The Lower Hookton Formation consists of laterally persistent beds of alternating sand, silty sand, gravel, gravely sand, silty clay, and clay. The upper 26 to 150 feet consists of sand and gravel that overlies the Unit F clay. The Unit F clay, which is about 50 feet thick, is a distinctive marker bed with relatively low permeability that functions as a regional aquitard. Beneath the Unit F clay are alternating layers of clean, well-sorted sand and clay that extend from 200 to about 1,100 feet deep.

5.1.3 Upper Hookton Formation The Upper Hookton Formation in the general site area can be divided into two informal lithologic units: the Upper Hookton silt and clay beds and the Upper Hookton sand beds. The Upper Hookton sand beds overlie a discontinuous clay bed (the 'second bay clay') that underlies the Unit 3 power plant area and the waste disposal ponds where it is 8 to 13 feet thick and is present in much of the site area. The Upper Hookton sand beds are 25 to 40 feet thick and consist of sand and gravel layers with lesser silt and clay beds.

Under Buhne Point Hill the Upper Hookton sand beds are overlain by the Upper Hookton silt, clay and silty sand beds, which extend from the surface to a depth of about 30 feet. Included in the upper part of this unit are late Pleistocene estuarine/marine terrace deposits that consist of silty sand and silt beds with lenses of sand. The lower part consists of clay and silt beds referred to as the 'first bay clay' that is present in the subsurface across beneath Buhne Point Hill.

5.2 Aquifers in the Area The groundwater in the HBPP area was investigated over a several year period by PG&E. The results of these studies are reported in Bechtel Inter-office memorandum, dated July 31, 1984 (Reference 2); PG&E Department of Engineering Research (DER) Report No. 402.331-85.11, 1985 (Reference 3), Woodward-Clyde Consultants (WCC), dated November 1985 (Reference 4),

and PG&E Department of Technical and Ecological Services (TES) Reports, dated January 1987, November 1988 and December 1989 (References 5, 6, and 7). Two areas have been investigated in detail, one near the Unit 3 Power Plant and one near the former wastewater pond site that is east (PG&E east) of Unit 3. Table 2.5-1 of the ISFSI Design Report summarizes the basic information about the 67 borings and monitoring wells used to measure the piezometric levels 11 013

Tritium Evaluation Humboldt Bay Power Plant taken on May 6, 1999. Of these, only the five Bechtel wells have been left open. The others were closed in September 1999.

Based on the information from these borings and analysis of the stratigraphy and aquifer characteristics, several aquifers and zones of perched groundwater are evident. The interpretation of the groundwater aquifers and zones in the ISFSI Design Report was described as varying significantly from earlier interpretations because the strata within the Hookton Formation was better understood. Also, in the earlier interpretations the Holocene bay deposits were lumped with the Hookton, but in later interpretations were separated and shown to unconformably overlie the Upper Hookton Formation.

The identified aquifers and groundwater zones are listed below. For reference, the earlier interpretations are noted in parentheses as well as illustrated on the generalized model of aquifers.

The zones are described in the following sections are from deeper to shallower.

(1) 'Lower Hookton aquifer' - The lower Hookton aquifer is the freshwater aquifer in the sands and gravels below the Unit F clay in the lower Hookton Formation (second aquifer of Bower, 1988; in TES, 1988, Reference 6). The lower Hookton aquifer lies below the 50ft thick, regional aquitard known as the Unit F clay. Beneath this impermeable layer, the aquifer is defined as the freshwater bearing zone of clean, sorted sands that are deeper than about 50 feet below mean sea level (MSL).

(2) 'Aquifer between Unit F and 2nd bay clays' - The sand and gravel beds of lower Hookton Formation above the Unit F Clay and below the 2nd bay clay are probably also an aquifer that connects hydraulically to the Upper Hookton aquifer. However, little was known of this aquifer and it was not discussed further in the ISFSI Design Report.

(3) 'Upper Hookton aquifer' - The Upper Hookton aquifer is the brackish water aquifer in the Upper Hookton sand beds above the 2nd bay clay and below the overlying silt and clay beds of the Upper Hookton Formation. (This aquifer is the zone C and D of the semi-unconfined second water bearing zone of Bower, 1988; in TES, 1988, Reference 6; Upper sand zone of Dames and Moore as reported in WCC, Reference 4. Above the Unit F clay aquitard and below the Upper Hookton silt and clay beds (comprising permeable beds in both the lower and Upper Hookton Formation) is the shallow, brackish-water aquifer that was called for convenience in the ISFSI Design Report the Upper Hookton aquifer. The aquifer, which is over 100 feet thick, is semiconfined by the upper silt and clay bed aquitard. The unit is comprised of sand and gravel lenses, including some clean sand strata. A clay bed of varying thickness and extent is about 20 feet below the top of the aquifer. This clay bed was shown as the second bay clay in the geologic sections and had been referred to as a site-wide aquitard (clay layer of Bower, 1988; in TES, 1998, Reference 6). As discussed in the ISFSI Design Report, however, it is discontinuous. The character of the Upper Hookton aquifer is known from several piezometers and monitoring wells in the 12 014

Tritium Evaluation Humboldt Bay Power Plant wastewater pond area and in the Unit 3 area. The monitoring wells were screened at two intervals: the C-level monitoring wells were screened in the upper portion of the aquifer and the D-level monitoring wells were screened at a deeper level in the aquifer but above the second bay clay "aquitard." Several other wells also record the piezometric surface of the Upper Hookton aquifer on Buhne Point Hill. The piezometric surface in May 1999 from the Upper Hookton aquifer is shown in Figures 2.5-5 to 2.5-8 and as contours in Figure 2.5-9of the ISFSI Design Report. The Upper Hookton aquifer is confined by the Upper Hookton silt and clay beds in the Unit 3 and wastewater ponds area, but is unconfined beneath the higher part of Buhne Point Hill, making it a semi-confined aquifer.

The tides have a strong influence on the Upper Hookton piezometric surfaces. The piezometric surface lags the tidal changes by a few hours and has up to about a 3 feet elevation change during a tidal cycle. This indicates that water in Humboldt Bay and in this aquifer is connected in the outcrops below the bay.

(4) 'Zone of perched groundwater in the Upper Hookton silt and daybeds' - The zone of perched groundwater in the Upper Hookton silt and clay beds includes several perched water tables in the Upper Hookton fine-grained deposits. The upper part of this zone consists of sandy silt, silt and clay beds, and the lower part consists of silt and clay beds (zones A and B of first water bearing zone of Bower, 1988; in TES, 1988, Reference 6).

The zone of perched groundwater in the Upper Hookton deposits is in the silt and clay beds between the surface and the Upper Hookton aquifer. These silt and clay beds are approximately 30 feet thick. The groundwater in this zone occurs as discontinuous zones of perched water tables. The piezometers were placed in the upper and lower parts of this zone, indicated as A and B respectively, and these show somewhat different piezometric levels. Analysis shows that the piezometric surface in the lower part (B) of the groundwater zone slopes to the north south of Unit 3 (where the wells are). The upper part (A) of the zone of perched groundwater in the Upper Hookton silt and clay beds shows a perched table at Boring MW-8 (BEC84-8) on Buhne Point Hill north of Unit 3 that is at elevation 17.92 feet, only 6 feet below the surface. South of Unit 3 a different perched surface is near horizontal at about 8.5 feet, as evident in five wells, 1 to 3 feet above the piezometric surface of the B zone.

(5) 'Zone of perched groundwater in the Holocene bay silts and clays' -The zone of perched groundwater in the Holocene bay silt and clay deposit is the unconfined groundwater zone (Zones A and B of first water bearing zone of Bower, 1988; in TES, 1988, Reference 6).

The zone of perched groundwater in the Holocene bay silt and clay beds is in the tidal marsh deposits and bay mud that underlie the former wastewater pond site and is believed to be similar to other locations in bay deposits. This groundwater zone is in unconsolidated silt and clay beds that unconformably overlie the Upper Hookton sand beds that are 23 to 26 feet below the surface. Monitoring wells in the Holocene bay silt and clay beds at the pond site help characterize the water table and piezometric surfaces in this unit. The A-level monitoring wells were screened to bracket the surface of the water table and the B-level monitoring wells were screened in the middle and lower portions of the deposit. The general piezometric surface for the B part of the zone ranges between the 6 and 10 feet elevation, a foot or two below the water table in the A part of the zone. Contours on the B part of the zone show a northwest trending trough to the northwest of the ponds site with highs on either side, indicating that flow directions are toward Humboldt Bay and away from the bay toward the marsh to the southeast. The B piezometric surface in the Holocene bay deposits is separate from the B piezometric surface in the Upper Hookton groundwater 13 015

Tritium Evaluation Humboldt Bay Power Plant zone by the unconformity between them. The A part of the zone appears to record a perched water table or various localized water tables. The surface indicates that the A part of the groundwater flows to the northwest toward the discharge canal and southeast toward the marsh. The piezometric surfaces for the A part of the zone at the pond site fluctuates about 3 feet seasonally. The tides have almost no influence on any of the A orB perched water tables in the Holocene bay deposits.

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Tritium Evaluation Humboldt Bay Power Plant 6.0 HBPP Groundwater Monitoring Program Evaluation 6.1 Description of the Existing Program The existing HBPP groundwater monitoring program utilizes 5 existing wells. These wells, identified as MW1, MW-2, MW-4, MW-6, and MW-11, are described below.

• MW-1 was originally installed as BEC 84-1 in 1984. The well is located near the southwest comer of the Unit 3 refueling building, approximately 10 feet from the building. The screened interval of the well is across the elevation range of (-28) to -32) feet below mean lower low water (MLL W). The geologic unit monitored by the screened zone is the Upper Hookton aquifer.

• MW-2 was originally installed as BEC 84-2A in 1984. The well is north-northeast of the north side of the Unit 3 refueling building, approximately 30 feet from the building. The screened interval of the well is across the elevation range of (-28) to (-38) feet below MLLW.

The geologic unit monitored by the screened zone is the Upper Hookton aquifer.

• MW-4 was originally installed as BEC 84-4 in 1984. The well is along the east side of the Unit 3 building and is generally northeast of the refueling building. The screened interval of the well is across the elevation range of (-28) to (-38) feet below MLLW. The geologic unit monitored by the screened zone is the Upper Hookton aquifer. The bottom of the screened interval of this monitoring well is an estimated 34 feet above the reactor building caisson bottom.

• MW-6 was originally installed as BEC 84-6 in 1984. The well is northeast of the north side of the Unit 3 refueling building, approximately 55 to 60 from the building. The screened interval of the well is across the elevation range of (-32) to (-36) feet below MLLW. The geologic unit monitored by the screened zone is the Upper Hookton aquifer.

• MW-11 was originally installed as BEC 84-11 in 1984. The well is southeast of the Unit 3 building, approximately 90 feet from the refueling building. The screened interval of the well is across the elevation range of (-23) to (-32) feet below MLLW. The geologic unit monitored by the screened zone is the Upper Hookton aquifer.

6.2 Assessment of Data from Existing Program To assist our assessment of the performance of the existing groundwater monitoring program, HBPP provided time-trend plots of laboratory data obtained from the existing groundwater monitoring program. ENERCON has reviewed this data and is providing the following observations:

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Tritium Evaluation Humboldt Bay Power Plant 6.2.1 Data from Monitoring Well No.1 Tritium data from MW -1 plotted on a time-trend chart from 1993 through December 2005 shows predominately no detectable tritium. During a period from mid-1997 through mid-1998, tritium was detected at levels below 1,000 pCi/1. Levels of tritium in this range were also detected in a single sampling event in mid-1999 and mid-2000, twice in mid-200 1, and again as a single event in mid-2002. For comparison, the warning limit established by HBPP is 2,000 pCi/1, the administrative limit is 15,000 pCi/1, and the regulatory limit is 30,000 pCi/1. Until June of 2001, the level of detection for all samples was 500 pCi/1, and it has subsequently been lowered to 400 pCi/1.

Based on evaluation of the groundwater flow direction, this monitoring well is located 10 feet upgradient from the Unit 3 refueling building and the SFP. In our opinion, the tritium detected in this well during this time was likely due the historical releases from Unit 3, discussed in Section 3.3. Because this monitoring well is in such a close proximity to Unit 3 (source area), it is susceptible to the periodic groundwater flow variations or the tidal influences that are known to impact groundwater flow direction at the site.

6.2.3 Data from Monitoring Well No.2 Tritium data from MW-2 plotted on a time-trend chart from 1993 through December 2005 shows no detectable tritium. Based on evaluation of the groundwater flow direction, this monitoring well is located down gradient from the Unit 3 refueling building and the SFP. The lack of tritium detection at this down gradient well indicates that the historical releases discussed in Section 3.3 have not impacted the Upper Hookton Aquifer downgradient of the Unit 3 Refueling building.

6.2.4 Data from Monitoring Well No.4 Tritium data from MW-4 plotted on a time-trend chart from 1993 through December 2005 shows no detectable tritium. Based on evaluation of the groundwater flow direction, this monitoring well is located down gradient from the Unit 3 refueling building and the SFP. The lack of tritium detection at this down gradient well indicates the historical releases discussed in Section 3.3 have not impacted the Upper Hookton Aquifer downgradient of the Unit 3 Refueling building.

6.2.5 Data from Monitoring Well No.6 16 018

Tritium Evaluation Humboldt Bay Power Plant Tritium data from MW-6 plotted on a time-trend chart from 1993 through December 2005 shows no detectable tritium. Based on evaluation of the groundwater flow direction, this monitoring well is located down gradient from the Unit 3 refueling building and the SFP. The lack of tritium detection at this down gradient well indicates the historical release discussed in Section 3.3 have not impacted the Upper Hookton Aquifer downgradient of the Unit 3 Refueling building.

6.2.6 Data from Monitoring Well No. 11 Tritium data from MW-11 plotted on a time-trend chart from 1993 through December 2005 shows no detectable tritium since 1998. During the period from 1993 through 1998, tritium was detected at continuously decreasing levels until, starting in 1998, no further detection occurred.

The initial tritium level detected in 1993 was about 1,500 pCi/1, with levels decreasing until early 1998 when tritium detection at this well ceased. For comparison, the warning limit established by HBPP is 2,000 pCi/1, the administrative limit is 15,000 pCi/1, and the regulatory limit is 30,000 pCi/1. (Additionally, the site staff investigated and discovered tritium contamination in the French drain under the old abandoned railroad tracks near MW-11. The staff pumped out the drain (which was sealed on the outfall end by clay, such that it could not drain) processed the water in radwaste and since that time, there has been no detectable contamination in MW-11 ).

Based on evaluation of the groundwater flow direction, this monitoring well is located on a lateral gradient from the Unit 3 refueling building and the SFP. During the time period of the tritium detection described above, tritium was not detected in downgradient monitoring wells. In our opinion, the tritium detected in this well during this time was most likely due to the periodic groundwater flow variations or the tidal influences that are known to impact groundwater flow direction at the site. It is also feasible that a preferential pathway such as transport along a buried underground line or within the gravel bedding for an underground system could have assisted groundwater transport to this monitoring well.

6.2. 7 Data from Other Monitored Locations Three additional locations provide routine water and groundwater sampling locations for HBPP.

These three locations are as follows:

• SFP liner. Water samples are collected quarterly from the gap between the stainless steel SFP liner and the concrete reactor caisson. Water samples are analyzed for Cs-137 and Co-60. Leakage from the SFP into this gap has routinely occurred for a number of years.

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Tritium Evaluation Humboldt Bay Power Plant Time-trend plots of the data by HBPP show radionuclide levels that have continually decreased since 1993. Radionuclide levels have remained relatively consistent for about 6 years.

• French Drain. Water samples are collected quarterly from the French drain underlying the SFP. Water samples are analyzed for Cs-137 and Co-60. Time-trend plots of the data by HBPP show that radionuclide levels of Co-60 have remained relatively consistent at low detectable levels for about 6 years. Time-trend plots of the data by HBPP show that radionuclide levels of Cs-137 were detected at low levels and have generally decreased since 1993. One anomalous high spike in 1996 was attributed to failure of a sampling pump that caused the introduction of non-filtered soils into the water sample.

• Caisson sump. Groundwater samples are collected quarterly from the reactor caisson sump.

Groundwater from the subsurface area adjacent to the reactor caisson structure can seep from the Upper Hookton formation through the concrete and be sampled at this location.

Groundwater samples are analyzed for Co-60, Cs-137, and tritium. Time-trend plots of the data by HBPP show that all radionuclides have remained detectable at low levels from 1993 through 2005.

6.3 Identification of Potential Transport Pathways Based on the configuration of geologic units and the subsurface structures at HBPP, the primary geologic unit that should be monitored by any groundwater monitoring program is the Upper Hookton formation groundwater. As discussed above, the groundwater flow direction is generally toward the bay. However, tidal variations have been shown to impact the groundwater flow direction. At times, the groundwater flow direction has been observed to flow inland.

Therefore, potential groundwater contamination could be transported in any direction, as shown in the tritium detections observed in MW-1.

In addition, tritium was detected in a lateral gradient monitoring well (MW-11) which is located approximately 90 feet southeast of the Unit 3 refueling building. At the time of these tritium detections in MW-11, tritium was not detected in either MW-2 or MW-4 which are located within 30 feet of the Unit 3 refueling building in the downgradient direction. Since tritium was not detected in the closer downgradient wells, it is unlikely that the tritium observed in MW-11 was the result of contaminant migration in the secondary flow direction caused by tidal influences.

Rather, these elevated tritium concentrations could be the result of a preferential pathway from the SFP or from the yard areas southeast of the refueling building which have been subject to condensate spills. There are a number of candidates for preferential pathways nearby to MW-11 such as bedding material associated with an underground line or backfill after construction of subsurface structures. Specifically, Well MW-11 is adjacent to 18 020

Tritium Evaluation Humboldt Bay Power Plant

• the Unit 3 circulating water discharge tube (buried in a trench connecting to the plant structure),

• a buried terracotta drain line (known to have been contaminated) from the radwaste area to the outfall canal,

• a connection point for the original liquid radwaste discharge to the circulating water tube, and

• a buried drain pipe installed in the original drain trench along the rail spur to the refueling building.

A secondary aquifer of concern is the aquifer between the Unit F clay and the 2nd Bay Clay. This aquifer is considered the uppermost water-bearing zone of the Lower Hookton Formation and is referenced to in this section as Zone E. The 2nd Bay Clay is a laterally discontinuous aquitard that is located at an elevation of approximately -50.00 feet below MSL in the vicinity of the Unit 3 reactor. Due to the discontinuous nature of the clay unit, there is substantial communication between the underlying aquifer (Zone E) and the Upper Hookton Aquifer (Zone D).

At the depth of the reactor caisson (approximately .,.66.00 feet MSL), the discontinuous nature of the 2nd Bay Clay is not clearly understood. Thus groundwater and tritium transport near the base of the reactor caisson can not be accurately assessed with the existing groundwater monitoring system of wells. Releases that may have in the past or could in the future reach the Zone E aquifer can not evaluated for impact on the environment.

6.4 Identification of Optimum Monitoring Positions All five current monitoring wells are constructed to communicate with Upper Hookton Aquifer.

The monitoring wells are located upgradient (MW-1 ), side gradient (MW-11 ), and downgradient directly in the path of groundwater flow (MW-4, MW-6, and MW-8). The monitored zone depths range approximately from (-28 feet MLL W) to (-50 feet MLL W). Since the focus of the groundwater monitoring program would be leakage from the SFP (bottom elevation approximately (-24 feet) MLL W) and the potential impacts to the Upper Hookton Formation, it is our opinion that monitoring of the existing wells should continue. Additional supporting data from the sampling and analysis of groundwater from the french drain and reactor caisson sump should continue.

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Tritium Evaluation Humboldt Bay Power Plant However, an additional Upper Hookton Aquifer monitoring well should be installed downgradient of the radwaste handling building north of Unit 3. Additional monitoring well should also be installed west and northwest of the Unit 3 refueling building to assess the potential for tritium migration associated with the variable groundwater flow directions caused by tidal changes. Provided in Attachment 1 is a map with the suggested locations of these two proposed new monitoring wells. These wells should be installed as part of PG&E commitment to participate in the NEI groundwater monitoring initiative because they close a gap in the existing monitoring well network.

The aquifer (herein referred to as Zone E) between the Unit F Clay and the second Bay Clay may be in direct communication with the base of the reactor caisson which is at an elevation of approximately (-66 feet) MSL. Since no monitoring wells existing to evaluate and monitor this aquifer, new monitoring wells should be installed in this aquifer at a depth of a least the bottom of the reactor caisson sump. A minimum of five new monitoring wells are recommended for installation in a radial pattern around Unit 3. This monitoring well network should provide sufficient data to evaluate groundwater flow patterns of this regional aquifer for which there is little information.

6.5 System Component Evaluation Based on our evaluation of the existing groundwater monitoring program in relation to the HBPP system components, the radwaste treatment building was identified as the only structure or system that may potentially impact groundwater with tritium without likely detection by the existing program. The radwaste treatment building is at a hydrologic downgradient location from all of the wells in the existing groundwater monitoring program.

Used to process liquid wastes, the radwaste treatment building is located in an excavated portion of an earthen embankment north of the refueling building. This building contains two concentrated liquid radioactive waste storage tanks and the resin disposal tank. It is constructed such that three sides of the structure are subgrade. A steel building encloses the entire liquid radwaste treatment area. North of the radwaste building are three high-level solid radioactive waste storage vaults, a low-level waste storage building, and a low-level waste handling building.

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Tritium Evaluation Humboldt Bay Power Plant 7.0 Tritium Monitoring Impact on HBPP Licensing As part of the license renewal regulatory process for licensed plants, NRC has developed a Generic Environmental Impact Statement (GElS) that identified groundwater use and quality was a Category 1 issue. An overview of the Category 1 and 2 designations is provided below. NRC established its standard of significance using the Council on Environmental Quality terminology for "significantly" (40CFR1508.27) for assessing environmental issues in the GElS. Using the Council on Environmental Quality guidelines, the NRC established three levels of significance:

• SMALL: Environmental effects are not detectable or are so minor that they will neither destabilize nor noticeably alter any important attribute of the resource.

• MODERATE: Environmental effects are sufficient to alter noticeably, but not to destabilize, important attributes of the resource.

• LARGE: Environmental effects are clearly noticeable and are sufficient to destabilize important attributes of the resource.

The GElS assigned a Category level to each environmental issue. In assigning these levels, it was assumed that ongoing mitigation measures would continue. The GElS included a determination of whether the analysis of the environmental issue could be applied to all plants and whether additional mitigation measures would be warranted. Issues were then assigned a Category 1 or a Category 2 designation. As set forth in the GElS, Category 1 issues are those that meet all of the following criteria:

• The environmental impacts associated with the issue were determined to apply either to all plants or, for some issues, to plants having a specific type of cooling system or other specified plant or site characteristics.

• A single significance level (i.e., SMALL, MODERATE, or LARGE) was assigned to the impacts (except for collective offsite radiological impacts from the fuel cycle and from high-level waste and spent fuel disposal).

• Mitigation of adverse impacts associated with the issue was considered in the analysis, and it was determined that additional plant-specific mitigation measures are not likely to be sufficiently beneficial to warrant implementation.

For issues that meet the three Category 1 criteria, no additional plant-specific analysis is required unless new and significant information is identified. Category 2 issues are those that do not meet 21 023

Tritium Evaluation Humboldt Bay Power Plant one or more of the criteria of Category 1, and, therefore, additional plant-specific review for these issues is required. In the specific case of groundwater use and quality, NRC identified this as a Category 1 issue with small significance.

However, NRC staff has recently identified tritium in groundwater as a new and significant information issue for nuclear plants currently in the license renewal process. This approach represents an obvious shift from the position of NRC relating to groundwater issues, and may in fact signal an eventual shift from groundwater use and quality from a Category 1 to a Category 2 issue for plants in the license renewal process.

Currently, HBPP is licensed as a SAFSTOR unit until 2015. It is our opinion that the current regulatory approach regarding tritium being utilized by NRC will not impact the existing HBPP licensing. Since decommissioning is being considered in the near future for HBPP and license extension under SAFSTOR by HBPP is unlikely, ENERCON has concluded that the HBPP licensing basis DSAR is unlikely to be impacted by this program.

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Tritium Evaluation Humboldt Bay Power Plant 8.0 Conclusions ENERCON's conclusions of our evaluation of the existing groundwater monitoring program are as follows:

• The Upper Hookton formation is the primary geologic unit that would be impacted by leaks from the HBPP SFP and radwaste treatment building.

• The existing groundwater monitoring program adequately monitors the Upper Hookton formation at locations that are up gradient and down gradient of the Unit 3 refueling building and the SFP. Lateral gradient monitoring is sufficient east of the Unit 3 building; however, there are no monitoring wells west of Unit 3 to assess the potential for lateral contaminant migration to the west that may be caused by the variable tidal influenced groundwater flow directions.

• Historical leaks at HBPP did slightly impact the groundwater.

• Down gradient Monitoring Wells Nos. 2, 4, and 6 have had no tritium detection since 1993.

Lateral gradient Monitoring Well No. 11 has had no tritium detection since 1997. Upgradient Monitoring Well No. 1 has had no tritium detection since 2001 (at a lower level of detection of 400 pCi/1).

• Levels of radionuclides detected from the french drain have trended down continuously since 1993.

• Levels of radionuclides detected from the reactor caisson sump have maintained at low detectable levels since 1993.

• The radwaste treatment building handles contaminated water at a hydrologic down gradient location from the existing monitoring wells.

• The base of the reactor caisson may be in direct communication with the aquifer (referred to as Zone E) between the Unit F clay and the 2nd Bay clay.

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Tritium Evaluation Humboldt Bay Power Plant 9.0 Recommendations ENERCON has evaluated the existing groundwater monitoring program and offers the following recommendation to meet the programmatic objectives of the tritium monitoring initiative by NRC and the NEI.

• The existing groundwater monitoring program adequately monitors the Upper Hookton formation at locations that are upgradient and down gradient of the Unit 3 building and the SFP. It is our recommendation that the existing groundwater monitoring program continue.

• Lateral gradient monitoring is sufficient east of the Unit 3 building. However, there are no monitoring wells west of Unit 3 to assess the potential for lateral contaminant migration that may be caused by the variable tidal influenced groundwater flow directions. Due to the variability of the groundwater flow direction, one additional monitoring well should be installed northwest of the Unit 3 refueling building to better assess the lateral groundwater conditions. Attachment 1 provides the general location of this well. The exact location can be adjusted based on the existence of plant systems and field conditions encountered when drilling.

• One new groundwater monitoring well should be installed downgradient of the radwaste handling building within the Upper Hookton Aquifer. Attachment 1 provides the general location of this well. The exact location can be adjusted based on the existence of plant systems and field conditions encountered when drilling.

• A monitoring network should be installed to assess the potential for groundwater contamination and movement at the base of the reactor caisson. This network of monitoring wells is recommended to consist of a minimum of five wells to provide sufficient hydrogeologic data surrounding Unit 3 at this depth to assess the groundwater flow direction associated with this regional aquifer. Attachment 1 provides the general location of these wells. The exact location can be adjusted based on the existence of plant systems and field conditions encountered when drilling.

We are aware of the pending construction of an ISFSI at HBPP that should start in less than one year. The existing wells as well as any additional wells that may be considered by HBPP may potentially be damaged or destroyed by the transport operation of the .spent fuel casks to the ISFSI. No new groundwater monitoring wells should be installed without verification that the location(s) is not be damaged by the transport operation. Additionally, it is possible that existing wells may also be damaged or destroyed during the transport operations. Therefore, it is advisable assess the impact of these actions on the existing groundwater monitoring wells and the locations of any new wells.

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Tritium Evaluation Humboldt Bay Power Plant 10.0 Report Limitations This report was prepared at the request of HBPP for their exclusive use. Conclusions and recommendations were limited to the information available to support this effort, and the time available to complete this task. Both parties understand that additional work may be required to more fully develop these opinions that are based upon information at the time of the report preparation, and our best professional judgement. In the event that additional information becomes available after the date of this report, ENERCON retains the right and may request the opportunity to re-evaluate that additional information and modify, if warranted, the conclusions and recommendations presented in this report.

Efforts by NEI to establish an Industry Initiative for monitoring tritium in groundwater at operating nuclear plants is an ongoing effort. In the event that NEI positions and recommendations change after the date of this report, ENERCON retains the right and may request the opportunity to re-evaluate that additional information and modify, if warranted, the conclusions and recommendations presented in this report 25 027

Tritium Evaluation Humboldt Bay Power Plant 11.0 References The documents below were reviewed and evaluated to support the HBPP tritium initiative review in preparation of this report:

• Final Safety Analysis Report, Humboldt Bay Independent Spent Fuel Storage Installation Report, January 2006

• Defueled Safety Analysis Report, Humboldt Bay Power Plant, Unit 3

• Humboldt Bay Procedure ODCM, SAFSTOR Off-Site Dose Calculation Manual, December 29,2005

• HBPP Data Time-Trend Plots for Monitoring Wells 1, 2, 4, 6, and 11

• Environmental Radiological Survey Report, April 1998

• HBPP Procedure HBAP D-500, Documenting Site Radioactive Contamination During SAFSTOR, May 11, 2006

• Nuclear Energy Institute Industry Initiative on Groundwater Protection, NRC Public Meeting, May 9, 2006 26 028

ATTACHMENT 1 029

Legend :

• Potential location of monitoring well to be down gradient of the rad waste building e Potential location of monitoring well to be laterally gradient of the Unit 3 refueling building

• Potential location of monitoring wells to be radially around the Unit 3 refueling building 030

Enclosure 11 PG&E Letter HBL-14-008 Enclosure 11 PG&E: "DECON-POS-H011:

Groundwater Investigation History, Control, and Management, Revision B" May 2009 Pages 1 to 59 1

PACIFIC GAS AND ELECTRIC COMPANY GROUNDWATER INVESTIGATION HISTORY, CONTROL, AND MANAGEMENT DECON-POS-H011 Revision B May 2009 001

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT STUDY REVISION PAGE Position Paper: DECON-POS-H011 Groundwater Investigation History, Control, and Management for Humboldt

Title:

Bay Power Plant Decommissioning Revision Signatures Ted N. Ferrando Ker~ Rod Prepared by Date Approved by Date Rev.

Status Date Prepared By Pages Description of Changes No.

Final 0 11/25/08 Randall Lantz 31 Original Issue B 03/05/09 Ted Ferrando 31 Comment resolutions 002

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT TABLE OF CONTENTS 1.0 EXECUTIVE

SUMMARY

.................................................................................................1 1.1 Objective ................................................................................................................ 1 1.2 Overview of Approach ............................................................................................ 1 1.3 Conclusions ............................................................................................................ 1

2.0 INTRODUCTION

.............................................................................................................3 2.1 Background ............................................................................................................3 2.2 Definitions, Acronyms and Abbreviations ............................................................... .4 3.0 ASSUMPTIONS AND BASES ........................................................................................6 3.1 Present Technology and Regulatory Changes ........................................................ 6 3.2 Future Risks ...........................................................................................................8 4.0 TECHNICAL DISCUSSION ........................................................................................... 10 4.1 Technicallssues ................................................................................................... 10 4.2 Financial Risks Associated With Technicallssues ................................................ 18 5.0 INVESTIGATION ..........................................................................................................20 5.1 Industry Reports and Studies ................................................................................ 20 5.2 Use and Application of Industry Reports and Studies ........................................... 21 6.0 ANALYSIS OF RESULTS .............................................................................................24 6.1 Overview of Results ..............................................................................................24 6.2 Discussion of Results ........................................................................................... 24

7.0 CONCLUSION

S AND RECOMMENDATIONS ............................................................. 26 7.1 Conclusions ..........................................................................................................26 7.2 Recommendations ................................................................................................26

8.0 REFERENCES

..............................................................................................................28 9.0 ATTACHMENTS ...........................................................................................................30 Attachment A - Conceptual Groundwater Model Attachment 8- Calculation of HBPP Unit 3 Dewatering Radius of Influence Attachment C - Personnel Contact Log ii 003

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT 1.0 EXECUTIVE

SUMMARY

1.1 Objective The objective of this position paper is to describe the groundwater issues, describe the strategy to address groundwater control during decommissioning activities, and to identify cost drivers for these issues that vary from the current Humboldt Bay Power Plant (HBPP) baseline cost study (Reference 1). To identify the strategy that will be implemented.

This position paper provides a summary description of the processes necessary to develop a reasonable hydrogeologic site conceptual model, and processes to identify and define potential sources of impact related to historic site operations, storage, or disposal practices. The paper describes the technical factors to characterize groundwater impact, define applicable regulations associated with potential impacts to human health and the environment, and outlines the process to meet cleanup standards and objectives for groundwater at HBPP.

1.2 Overview of Approach This position paper provides a summary description of the processes necessary to develop a reasonable hydrogeologic site conceptual model, and processes to identify and define potential sources of impact related to historic site operations, storage, or disposal practices. The paper describes the technical factors to characterize groundwater impact, define applicable regulations associated with potential impacts to human health and the environment, and outlines the process to meet cleanup standards and objectives for groundwater at HBPP.

The TLG estimate had no explicit cost to monitor or control groundwater. This position paper estimates the level of effort to monitor and control groundwater for the baseline demolition to a nominal three feet below ground surface to be approximately $1 ,425,000; which is an overall increase of $1,425,000. The TLG estimate does estimate a Sr-90 Groundwater Program.

To support decommission activities, groundwater controls for deep excavations will require some form of control to allow sufficient dewatering during sub-grade structure removal. Shallow excavations may require some groundwater controls; however, due to the limited extent of groundwater bearing formations within the shallow surficial soil, this will be a minor issue during shallow excavations. Cost to remove, control, contain, and dispose of groundwater from site excavations is included in DECON-POS-H009, "Removal of Sub-grade Structures".

Groundwater monitoring will be required to assess potential impacts from decommissioning activities. To achieve this, it will be required to remove and install groundwater monitoring wells in the vicinity of Unit 3 as decommissioning activities disturb monitoring well locations. Following removal of source areas, the monitoring wells can be abandoned.

1.3 Conclusions In regards to groundwater control, each decommissioning site will be unique and will pose special challenges due to the site specific nature of the subsurface systems. Site-specific solutions are used at each decommissioning site; therefore, groundwater control must also be designed for the site-specific conditions at HBPP.

Page 1 of 31 004

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 8 MANAGEMENT Based on results from previous Radiological Environmental Monitoring Program (REMP) monitoring well sampling, groundwater contamination is either not present beneath Unit 3 or the concentration is low and not migrating. Demolition activities could change that and there is no provision in the current baseline for groundwater monitoring.

This paper concludes that the baseline report does not address the level of groundwater monitoring effort that will be required and the cost of those efforts.

This paper has evaluated the level of effort to monitor groundwater during remediation and concluded that an increased level of effort will be required. This conclusion is based on field observations and evaluations detailed in this paper.

The baseline report had no explicit cost to monitor or control groundwater. The level of effort estimated to monitor and control groundwater for decommissioning is estimated to be approximately $1,425,000, which is an overall increase of $1,425,000.

DECON-POS-H009, "Removal of Sub-grade Structures", recommends removal of the spent fuel pool and the surrounding impacted soil. Groundwater controls are reasonably determined to be required during this operation. Costs for those controls are addressed and included in that position paper. Those costs are not included in the estimate stated above.

Page 2 of 31 005

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT

2.0 INTRODUCTION

2.1 Background Since commencement of operations and final shutdown in 1976, multiple groundwater investigations have been conducted on the HBPP site. The most significant of these studies are referenced in this report and include an assessment of tidal effects on groundwater flow in 1987 (Reference 7), the decommissioning Safety Evaluation Report in 1987 (Reference 16), a hydrologic characterization of the former wastewater treatment system impoundments in 1988 (Reference 5), the Final Safety Analysis Report (FSAR) update for the ISFSI installation in 2006 (Reference 8), and additional site characterization for the HBPP repowering project in 2008 Reference (Reference 6).

Information obtained from these reports and studies were used to develop the site groundwater conceptual model and assess groundwater related operations for the decommissioning activities.

Groundwater control will be required during the decommissioning activities to minimize the impact of existing groundwater contamination and prevent future contamination from site activities that could mobilize contaminants from uncontaminated areas during structure removal. A Conceptual Groundwater Model has been included as Attachment A with estimated groundwater dewatering calculations in Attachment B.

The current baseline does not assess groundwater management or their costs in any direct integrated fashion. Groundwater is not a factor in removal of sub-grade structures within 3ft below ground surface (bgs). The recognized at-grade elevation of HBPP is 12ft mean sea level (msl). Therefore, the baseline presumes that all sub-grade structures at an elevation of 9ft msl and below are targeted for decontamination, survey, and release in-situ after the decommissioning is completed. Based on the findings of the groundwater model, groundwater control and management within the area of HBPP Unit 3 will not be an issue until excavations reach depths of approximately-10ft msl which is the bottom of the 1st Bay Clay confining unit.

• Groundwater level readings and groundwater well sampling activities can be performed by PG&E personnel or approved environmental subcontractors. Installation of additional monitoring wells requires using a California licensed monitoring well installation company, overseen by PG&E personnel or approved subcontractors.

2.1.1 Contentions Elsewhere in the Industry Other decommissioned nuclear plants (i.e. Maine Yankee, Rancho Seco, SONGS-1, and Yankee Rowe) and Federal radiological remediation sites (i.e. Hanford) used several methods of groundwater control including slurry wall and sheet pile installations to minimize groundwater migration into excavations. Groundwater removed from the excavations normally utilizes settling ponds and/or tanks to capture and treat dewatering effluents prior to disposal.

In regards to groundwater control, each site will be unique and will pose special challenges due to the site specific nature of the subsurface systems. If available, other sites with similar subsurface conditions can be reviewed to provide an example of how procedures and problems were addressed. For example, due to a shallow water table, the Maine Yankee decommissioning project utilized temporary holding ponds and tanks in conjunction with skid mounted water processing systems for dewatering and filtering Page 3 of 31 006

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. B MANAGEMENT effluents during decommissioning. Rancho Seco is located in an area with very deep (approximately 140ft bgs) groundwater with no radiological impact; and no dewatering was required for excavations. Site-specific solutions are used at each decommissioning site; therefore, groundwater control must also be designed for the site-specific conditions at HBPP.

2.2 Definitions, Acronyms and Abbreviations Acronyms used within this paper are listed below:

AEC -Atomic Energy Commission Am -Americium bgs - below ground surface CaiARP -California Accidental Release Program Cm/sec - centimeters per second COC - Contaminant of Concern Co-Cobalt CUPA- Certified Unified Program Agency CWT- Concentrated Waste Tank Cs-Cesium DCGL- Derived Concentration Guideline Level DP- Decommissioning Plan DPR- Demonstration Power Reactor DSAR - Defueled Safety Analysis Report DTSC - Department of Toxic Substances Control Fe-lron FSAR - Final Safety Analysis Report Gpd - gallons per day Gpm- gallons per minute HSA- Historical Site Assessment HBPP- Humboldt Bay Power Plant HCDEH- Humboldt County Division of Environmental Health HOPE- High Density Polyethylene HOPS- High Density Polystyrene ISFSI-Independent Spent Fuel Storage Installation LOP - Local Oversight Program MARSSIM- Multi-Agency Radiation Survey and Site Investigation Manual MEPP- Mobile Emergency Power Plants Page 4 of 31 007

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT Mg/L- milligrams per liter

!Jg/L- Micrograms per liter

!Jmhos/cm- Micromhos per centimeter (aquifer conductivity) msl - mean sea level MWe - megawatt NCRWQCB - North Coast Regional Water Quality Control Board NEI- Nuclear Energy Institute Ni- Nickel NPDES- National Pollutant Discharge Elimination System NRC- Nuclear Regulatory Commission NUREG- Nuclear Regulatory Commission publications, reports, or brochures on regulatory decisions, results of research, results of incident investigations, and other technical and administrative information.

NWP - Northwestern Pacific OWS- Oil/water separator PG&E- Pacific Gas and Electric Company PSDAR- Post Shutdown Safety Analysis Report Pu- Plutonium RCA - Radiologically Controlled Area REMP - Radiological Environmental Monitoring Program SAFSTOR- one of several NRC-defined closure strategies for nuclear power facilities SCE- Southern California Edison SFP -Spent Fuel Pool SPCC - Spill Prevention Control and Countermeasures Sr- Strontium SWMU- Solid Waste Management Unit SWRCB- State Water Resources Control Board TUc- Toxic unit chronic= 100/noec, where noec is no observed effect concentration UST- Underground Storage Tank Page 5 of 31 008

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. B MANAGEMENT 3.0 ASSUMPTIONS AND BASES This position paper has been developed using numerous assumptions to support the technical evaluation. Each assumption and its basis are listed below.

3.1 Option #1 is targeted removal of Spent Fuel Pool (SFP) structures. This excavation option includes deep excavations to approximately-30ft msl to remove the SFP and underlying contaminated soil and foundations. Other near-surface areas will be excavated to approximately-10ft bgs which is above the first aquifer. All remaining subsurface structures will be cleaned to clearance levels and remain in place. This assumption follows the baseline intent to decontaminate, release, and abandon large underground structures in place.

3.2 Option #2 is targeted removal of the caisson structure and underlying tremie concrete.

This excavation option includes scope from option # 1 above plus deeper excavation to approximately-80ft msl to remove the entire Unit 3 caisson structure. This assumption is a bounding evaluation of worst-case excavation and its potential impacts on groundwater.

3.3 Deep excavations beyond-10ft msl (Option #1 and Option #2) will require extensive dewatering operations or installation of a groundwater control or prevention system to maintain a dewatered excavation. These dewatering options are discussed in position paper DECON-POS-009, "Removal of Sub-grade Structures". The basis is the location and extent of the Upper Hookton Aquifer interface with the 1st Bay Clay geologic formation.

3.4 Excavations from 10-20 ft bgs will produce only localized pore volume water drainage and no significant excavation groundwater. The basis is the location and extent of the 1st Bay Clay geologic formation.

3.5 Groundwater monitoring will be required during decommissioning to ensure decommissioning activities do not have a negative effect on groundwater quality.

3.6 Groundwater monitoring operations will be required until license termination.

3.7 Present Technology and Regulatory Changes The following topics are excluded from discussion in this position paper.

• Costs associated with excavation barrier technologies (i.e. ground freezing, sheet pile, slurry wall) and associated groundwater/excavation water systems. These costs are discussed in position paper DECON-POS-009, "Removal of Sub-grade Structures".

• Non-radiological waste water management and disposal (hazardous or non-hazardous) issues not associated with the operation of HBPP Unit 3.

Technical This paper uses current and historical site investigations as the basis for the subsurface groundwater conditions potentially encountered during various decommissioning activity options.

Page 6 of 31 009

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT Regulatory Currently, the NRC follows the guidance and reporting requirements of the NEI Groundwater Protection Initiative for radiological releases to groundwater. Groundwater quality can be ensured by development of a sampling program for the monitoring wells surrounding Unit 3. There are currently 12 groundwater monitoring wells in the vicinity of Unit 3. Five wells have been sampled in conjunction with the site Radiological Environmental Monitoring Program (REMP). Seven additional wells were added in 2008 to monitor areas not covered by the REMP wells and to satisfy NEIInitiative 07-07 which is described later. Additional wells may need to be installed to further assess potential contamination beneath the SFP and Unit 3 caisson.

Additional wells will also improve the site management ability to respond to instances where the inadvertent release of radioactive substances may result in low (but detectable) levels of plant-related materials in subsurface soils and waters. These program requirement levels are well below the currently established NRC limits for the protection of public health and safety.

The NEI-07-07 groundwater protection initiative includes the following items:

• Implement a company/site specific action plan(s) to detect and mitigate inadvertent radiological releases in groundwater by:

• Performing a site assessment of the groundwater pathways that could adversely affect a drinking water source.

• Installing monitoring wells to evaluate and monitor for leakage from the reactor plant.

• Perform voluntary reporting on requirements beyond the existing minimums in the REMP.

Based on review of the HBPP REMP reports and discussions with PG&E radiological personnel, these requirements have been adopted and are in progress. The site assessment has been completed and additional groundwater monitoring wells were installed. According to PG&E personnel, plans are in preparation for sampling soil and groundwater beneath the SFP and Unit 3 caisson. Currently, no data exists regarding the extent of impacts from previously identified radiological releases near the SFP and caisson. As decommissioning progresses, evaluation of groundwater monitoring points may require additional assessment to ensure excavations and site activities are properly monitored for radiological releases and to confirm what level of threat, if any, these activities pose to the local groundwater systems.

Hazardous Constituents Groundwater at the HBPP is not expected to generate commingled hazardous waste as part of the radioactive decommissioning activities. No objective evidence of hazardous chemical impacted groundwater was reported at the HBPP associated with the operation of Unit 3. If groundwater is found to be threatened or impacted by a non-radiological hazardous substance release, the California Department of Toxic Substances Control (DTSC) provides technical oversight for the characterization and remediation of soil and groundwater contamination. The DTSC and the North Coast Regional Water Quality Control Board (NCRWQCB) would coordinate regulatory oversight of groundwater remediation.

Page 7 of 31 010

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT Locally, the Hazardous Materials Program of the Humboldt County Division of Environmental Health (HCDEH) is the Certified Unified Program Agency (CUPA) charged with conducting compliance inspections in Humboldt County. The CUPA program elements include:

• Hazardous Materials Release Response Plans, and Inventory (Business Plans)

• California Accidental Release Program (CaiARP)

• Underground Storage Tanks (UST)

• Aboveground Petroleum Storage Spill Prevention Control and Countermeasures SPCC)

• Hazardous Waste Generation and Onsite Treatment Under the Hazardous Material Program, the Local Oversight Program (LOP) is in contract with the State Water Resources Control Board (SWRCB) to oversee the cleanup of sites where underground petroleum storage tanks have leaked. The LOP works with responsible parties and consultants to assure that the UST Corrective Action Requirements are met. Compliance with these requirements allows cleanup costs to be reimbursed by the state's Underground Storage Tank Cleanup Fund to the maximum extent possible. In addition to working with SWRCB, consultants and responsible parties, the LOP works closely with the NCRWQCB staff on a site-specific basis.

Regulation of cleanup efforts for non-radiological, hazardous material releases will be conducted through the required federal, state, and local programs; however, if a radiological component is present in the hazardous waste, it is considered a mixed waste and is regulated by the Resource Conservation and Recovery Act (RCRA), and overseen by the EPA and the NRC. Waste characterization, treatment, storage, and disposal issues will require coordination and compliance with requirements from both programs.

3.8 Future Risks Future risks are related to contamination generated during the decommissioning activities (accidental spills), areas of historic contamination not previously identified, and mobilization of contaminated groundwater to areas previously uncontaminated due to dewatering efforts.

Groundwater contamination generated during the decommissioning can be minimized by following standard work and best management practices during site activities.

Historic contamination should be a minimal risk given the extent of site investigation, spill control, and sampling activities; however, unknown areas may be identified during sub-grade soil excavation and structures removal. These will need to be assessed and controlled. Costs may be handled by contingency planning in anticipation of finding unknown areas.

Mobilization of contaminated groundwater to areas previously uncontaminated due to dewatering efforts can be minimized by planning efforts and assessment of potential problems prior to commencement of the site activities. Planning may include assessment of groundwater flowpaths in the area of excavations, analysis of the radius of influence intersecting known contaminated areas, and possible installation and testing of monitoring wells to provide advance warning of contamination migration prior to it Page 8 of 31 011

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT entering construction areas. Also to be considered are engineered groundwater control systems to minimize dewatering required during deep excavations (such as sheet pilings, freezing, pumping) or to block/limit flow of contaminated perched groundwater in shallow excavations.

Page 9 of 31 012

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT 4.0 TECHNICAL DISCUSSION 4.1 Technicallssues The Conceptual Groundwater Model (Attachment A) was developed from the review of previous geologic and hydrologic studies as well as present subsurface investigation activities being conducted in the vicinity of HBPP Unit 3. Summary pictures from this model for the HBPP site aquifers and clay layers are represented below:

Ground Surface Hookton Silts and Clays

____ _'La.r.iable_dJlpt.b _

1st Bay Clay 30 ft b s Confined Groundwater A) Excavation does not encounter a perched zone or exceed the base of the 1 st Bay Clay Ground Surface Unconfined.Percbed Groundw er

':;;;_:**::_**::_ _ __ ~**:.:: *::: *:::*::: *::: *:.:: *:.::*::. Groundwater in Hookton Silts

- - - -- - - - - - - - - - - ~ excavation equal to Confined Groundwater and Clays

-*- *-*-*- -*-*-*-*-*- *-*- * *am-ountlri-p*erchea * *-*POtentfometrTc.ceve1-*-*-*-*-*-*-*-

_ _ _ __ __ __ __ _ __ _ _ _ _ _ _ zone _________________\La.r.iable_d_ept.b_

1st Bay Clay 30 ft b s Confined Groundwater B) Excavation encounters a perched zone but does not exceed the base of the 1 st Bay Clay Ground Surface Hookton Silts and Clays C) Excavation exceeds the base of the 1st Bay Clay Excavation Groundwater Model A description of previous groundwater assessments provided by PG&E is included in the conceptual model and discussed below. Review of the various subsurface studies and conclusions regarding the overall groundwater characteristics are also described in the model.

Page 10 of 31 013

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT The previous studies included investigation and characterization of the underlying geologic formations and associated groundwater aquifers. The development of the site conceptual model and its use at the HBPP site during decommissioning is based on recent experience in the definition, setup, and use of a site conceptual model for NRC licensed sites. The site model was developed based on the review of the previous and current groundwater investigation projects at the HBPP. Any areas not having sufficient information to provide a conservative analysis were identified as "data gaps" with recommendations for further investigation.

The HBPP currently performs quarterly groundwater sampling at five (5) monitoring wells surrounding the Unit 3 caisson and SFP for the REMP. These wells are located within the assumed flow path of groundwater and are monitored for radiological releases from the facility. These previous reports show some residual radiological impacts were present at the HBPP. However, due to remediation efforts and radioactive decay, the most recent sampling data report no detectable groundwater impact migrating from the Unit 3 area at the HBPP (with the exception of minor concentrations <23 pCi/L of beta-activity that may have come from background sources). Additional sampling data of the discharge canal effluent show no detectable concentrations of Co-60, Cs-137, or tritium since 2004.

The REMP report also included tritium sampling data from the Unit 3 caisson sump.

Values of tritium in the caisson sump are well below the regulatory screening level

(<30,000 pCi/L). Historic sampling of water in the sump reported a maximum tritium concentration of 1,310 pCi/L in 2004 and 1,270 pCi/L in 2007. A maximum concentration of 4,025 pCi/L was reported in June 2005; however, this value was an anomalously high outlier since the remainder of the year was consistent with the normal concentrations between 300 pCi/L and 1,100 pCi/L. Tritium concentration was the only analyte reported from water samples taken from the caisson sump.

Separate from the REMP sampling, PG&E radiological monitoring personnel noted that water collected from the caisson sump has also been evaluated for Sr-90.

Concentrations of Sr-90 are approximately 180 pCi/L. This has been reported as approximately the same concentration as found in the SFP and SFP French Drain, suggesting a leakage pathway from the SFP to the Unit 3 caisson.

This scenario of contaminated water leaving the SFP, entering groundwater, and then leaking into the reactor caisson with the same concentration of Sr-90 is considered to be an unlikely situation. Any contaminated water leaving the SFP would have to travel approximately 50 feet with the groundwater saturated soils along the outer caisson wall before reaching any potential in-leakage pathways to enter the caisson and be collected in the caisson sump. The Upper Hookton sands are highly permeable and groundwater saturated within this entire interval and has a general movement towards the bay, thus causing significant dilution of any SFP water released into the groundwater. The amount of leakage required from the SFP to saturate and bring the groundwater concentration into equilibrium with the SFP for the entire 50 foot length with result in a complete loss of water in the SFP in a very short amount of time. For example, if the leakage path was isolated to a one foot square area over the entire length of the caisson (1 ft x 1 ft x 50ft),

the volume of groundwater within this path would be approximately 112 gallons (50 fe x 7.48 gal!fe x 0.30 formation porosity). Leakage from groundwater and the SFP into the SFP liner gap was measured in 1987 to assess leakage rates. Water leakage from the SFP into the liner gap was measured at 0.12 gpd. Leakage from groundwater into the Page 11 of 31 014

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. B MANAGEMENT SFP liner gap was measured at 2.5 gpd (Reference 16); therefore, due to dilution effects and low amount of measured leakage from the SFP, it is considered unlikely that leakage from the SFP could migrate undiluted from the SFP to the Reactor caisson.

Although the direct pathway appears unlikely, previous leakage has been reported from the SFP. Evaluation of the soils and groundwater beneath the SFP and Unit 3 caisson is needed to determine if there is a groundwater pathway for the suspected leakage. All five REMP wells and seven monitoring wells surrounding Unit 3 show no detectable Sr-90 in the Upper Hookton Aquifer in the vicinity of Unit 3.

4.1.1 Groundwater Monitoring Groundwater is not reported to be impacted above regulatory limits at the HBPP; however, site activities involving disturbance of the sub-grade structures, removal and remediation of impacted surficial soil, and potential contamination released from site decommissioning activities dictate that groundwater monitoring should continue through termination of the site license and completion of decommissioning activities.

Currently, twelve (12) groundwater monitoring wells are installed within the vicinity Unit

3. Ten (1 0) of these wells are within close proximity to planned site traffic patterns and soil/structure excavations. Therefore, it is anticipated that these ten (1 0) wells are likely to become abandoned to support decommissioning site activities. To allow for additional conservatism and monitoring of both upper (level of SFP) and lower portions (level of the Unit No. 3 caisson) of the Upper Hookton aquifer, it is anticipated that these ten (1 0) wells will need reinstallation in areas that will not be disturbed by site activities yet will continue to monitor groundwater pathways for potential impacts from decommissioning activities.

4.1.2 Location of Known and Potential Subsurface Contamination This section addresses locations of known and potential subsurface contamination that have, or may have, impacted groundwater. This assessment is based upon previous and ongoing site characterization activities and reports at the HBPP.

Previous investigations, and the current REMP sampling, report there is no current groundwater contamination issue within the Upper Hookton Aquifer. Localized radiologic contamination may exist in areas directly adjacent and underneath the Unit 3 caisson and SFP; however, sample results for current site investigation of these areas have not been completed. No currently known, non-radiological impacts have been reported within the RCA footprint.

The location of potential soil contamination at the HBPP is discussed in position paper DECON-POS-010, "Excavation and Removal of Subsurface Soil". Groundwater wells located within the potential soil contamination zone do not show any impact to the underlying groundwater, most likely due to the 1st Bay Clay acting as a migration boundary. Although the discharge canal sediments are potentially impacted with radionuclides, sampling data of the effluent water within the discharge canal has not reported any detectable activity; therefore, it is expected that leaching of the sediments will not impact the subsurface groundwater near the discharge canal.

4.1.3 Sub-grade Structure Removal Excavation Dewatering Excavations at the HBPP may require dewatering dependent on the location and depth of the excavation. Most buildings on the site are of a limited depth and do not exceed Page 12 of 31 015

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. B MANAGEMENT the depth of the surficial aquitard, the 1st Bay Clay. The notable exception is the Unit 3 caisson (approximately -80 foot elevation) and the Spent Fuel Pool (approximately

-30 foot elevation). The expected base of the 1st Bay Clay is depicted in Attachment A, Figure A-1-3. Excavations exceeding this depth (approximately 16-20 feet bgs at the Unit 3 location) will produce significant amounts of brackish groundwater that will require possible treatment and disposal. Methods available to control the volume of groundwater produced, as well as temporary storage and disposal of dewatering effluents are discussed in position paper DECON-POS-009, "Removal of Sub-grade Structures".

4.1.4 Groundwater Monitoring Requirements During Decommissioning A groundwater monitoring plan must be developed and implemented prior to site decommissioning activities. This monitoring plan will be a function of the specific decommissioning activity (i.e. excavation depth, volume of soil/groundwater removed, and contaminants encountered) and may change as site characterization and decommissioning activities progress. The goal of the groundwater monitoring plan is to identify contaminant types (i.e. radiological, hazardous, and mixed) for potential waste characterization and disposal options and to prevent/minimize impacts to the groundwater beneath HBPP during decommissioning. The groundwater monitoring plan must consider local, state and Federal regulatory requirements for each waste stream/contaminant encountered.

Sampling and monitoring of the on-site monitoring wells should continue through license termination, currently scheduled for 2015. Sampling the wells should remain consistent with quarterly sampling per the existing REMP. Sampling should be conducted quarterly until all subsurface sources of potential radiological contaminants are removed (soils, sediments, SFP and caisson removed or decontaminated to final end-use status) and for four quarters following. If residual contaminates in excess of regulatory limits are reported during the final four quarters of groundwater sampling, then the sores of the contaminants should be investigated and corrected, then sampling continued until four quarters of sampling are reported at concentration below the appropriate regulatory limits. Following completion of the final quarterly sampling and license termination, these monitoring wells are no longer required and should be abandoned.

4.1.5 Potential for Migration Using Cone-Of-Influence Considerations As discussed in the conceptual groundwater model of the HBPP site, groundwater production from the perched groundwater zones will influence only those areas connected to the perched groundwater formation. Drainage of these layers is reported to be rapid and short term; therefore, the radius of influence is limited and will limit migration of other contaminants into the excavation.

If the excavation exceeds the depth of the 1st Bay Clay, dewatering operations will affect the entire site. The radius-of-influence will potentially draw existing on-site groundwater contamination within the Upper Hookton Aquifer into the excavation. Previous investigations and the current REMP sampling report indicate that there is no current groundwater contamination issue within the Upper Hookton Aquifer. Localized radiologic contamination may exist in areas directly adjacent and underneath the Unit 3 caisson and SFP; however, sample results for current site investigation of these areas have not been completed.

Page 13 of 31 016

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT Groundwater issues for three optional sub-grade structure removal options are summarized below:

• Baseline: Removal of all structures to a depth of 3 ft bgs. This option will require the least amount of groundwater control as no structures will be disturbed below the 1st Bay Clay and 3 ft bgs does not appear to impact any of the known perched groundwater zones. Structures will be abandoned in place and current groundwater monitoring wells will be sufficient to provide long term monitoring. Due to decommissioning activities, the present monitoring wells may have to be abandoned and replaced during removal of structures and to allow heavy equipment traffic movement.

• Option #1: This is the option that PG&E will implement. Baseline scope plus removal of the SFP. Due to depth of the bottom of the SFP at-30ft msl, this option will breach the bottom of the 1st Bay Clay and require significant amounts of excavation dewatering unless engineered groundwater controls are installed. Calculations of groundwater dewatering (Attachment B) suggest minimum dewatering rates of thousands of gallons per day to maintain the excavation drained if no groundwater controls are implemented. The Unit 3 caisson will remain and be abandoned in place. Current groundwater monitoring wells are sufficient to provide long-term monitoring; however, dewatering activities will require additional wells of different types surrounding the excavation to monitor groundwater flow (for contaminant migration) and dewatering effectiveness. Due to decommissioning activities, excavations, and heavy equipment traffic patterns, most of the current monitoring wells will need to be abandoned and replaced.

• Option #2: Removal per Option #1 plus removal of the Unit 3 caisson. Due to depth of the bottom of the SFP (-30ft bgs) and depth of the Unit 3 caisson (-80ft bgs), this option will breach the bottom of the 1st Bay Clay and require significant amounts of excavation dewatering unless engineered groundwater controls are installed.

Calculations of groundwater dewatering suggest minimum dewatering rates in excess of 200,000 to 300,000 gallons per day to maintain the excavation drained.

Current results from groundwater monitoring wells surrounding Unit 3 show that radiological concentrations are not above detectable levels in the Upper Hookton Aquifer. The wells are sufficient to provide long term monitoring, however, dewatering activities will require additional wells surrounding the excavation to assess groundwater flow for contaminant migration and dewatering effectiveness.

4.1.6 Dewatering Effluent Segregation Groundwater effluents produced from the dewatering of excavations and trenches will require some form of disposal based on the quality of the effluent. The amount of groundwater produced will depend on the location and size (depth and area) of the excavation. Stormwater accumulation within the excavation will also need to be removed; however, the storage and possible treatment of stormwater dewatering effluent will be handled in the same method as effluent groundwater and is discussed in position paper DECON-POS-009, "Removal of Sub-grade Structures".

Due to no reported groundwater contamination above regulatory requirements, it is currently expected that dewatering and stormwater effluents will be temporary stored in dedicated containers, sampled, then discharged via a permitted outflow without treatment, other than sediment settling prior to discharge.

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT Three potential scenarios and controls required are discussed below:

Radiologically impacted groundwater Decommissioning and groundwater controls will be conducted to prevent or minimize the amount of mixed waste that is generated. If dewatering will draw non-radiological contaminants into a radiologically contaminated groundwater zone, then prevention measures (slurry wall, sheet piles, freezing) should be considered prior to initiation of dewatering. Groundwater wells should be installed between the contaminated zones to monitor for migration between impacted areas to prevent the generation of mixed waste.

Groundwater pumped from the excavation, or from dewatering wells installed in the impacted zone, will be stored in appropriately sized containers, sampled and analyzed for appropriate contaminants of concern (COC) prior to processing and discharge.

Dewatering effluents can be temporarily placed in dedicated above ground storage tanks, containers, or holding ponds prior to treatment.

Disposal options (on-site processing/off-site shipping)

• NPDES Permit CA0005622 allows for discharges of liquid low-level radioactive waste from Unit 3 of up to 7,500 gallons per day through the combined cooling water discharge (outfall 001, discharge canal). This waste stream is described as treated, filtered, and stored liquids from Unit 3 (outfall 001 E) and infiltrating groundwater removed from the Unit 3 caisson sump (outfall 001 G). No high-level radioactive waste discharge is allowed (Reference 13).

• After the decommissioning of Units No. 1 and 2, the combined cooling water discharge will no longer be available for radiological discharges. Alternate methods will be required for discharge of treated low-level liquid waste, including discharge via permit to the municipal sewer system or other approved on-site discharge location. Off-site shipping for disposal is not recommended for low-level liquid wastes.

Hazardous (non-radiological) impacted groundwater

1. Prior to dewatering the groundwater, within the excavation, or from monitoring wells installed in the impacted zone, will be sampled and analyzed for appropriate COC prior to pumping.

2. Dewatering effluents can be temporarily placed in dedicated above-ground storage tanks, containers, or holding ponds prior to treatment. Storage locations shall be appropriately sized for the amount of liquid generated and be constructed of the appropriate material (i.e. steel, HOPE) as required for the contaminants within the groundwater.

3. Disposal options (on site processing/offsite shipping)

• National Pollutant Discharge Elimination System (NPDES) Permit CA0005622 does not specifically address groundwater disposal from excavation dewatering activities (Reference 13). Alternate methods will be required for discharge of treated groundwater, including discharge via permit to the municipal sewer system or other approved on-site discharge location.

• Current NPDES effluent limitations are as follows:

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT Constituent Units Daily Maximum 30-Day Average Chronic Toxicity TUc 6.06 (single unit) N/A 7.06 (dual unit)

Suspended Solids mg/L 100 30 Grease and Oil mg/L 20 15 Iron mg/L 1.0 1.0 Copper mg/L 1.0 1.0 Constituent Units 1-Hour Average 4-Day Average Dissolved Copper 1-Lg/L 4.8 3.1 Non-impacted (clean) groundwater

1. Prior to dewatering, the groundwater within the excavation or from monitoring wells installed in the impacted zone will be sampled and analyzed to confirm the groundwater meets all requirements for discharge to the site prior to pumping.

2. NPDES requirements for discharge to the site NPDES Permit CA0005622 does not specifically address groundwater disposal from excavation dewatering activities (Reference 13). Alternate methods will be required for discharge of treated groundwater, including discharge via permit to the municipal sewer system or other approved onsite discharge location.

4.1. 7 Groundwater Remediation Groundwater is not reported to be impacted above regulatory limits at the HBPP; however, this conclusion is based on minimal information. The quality of the groundwater beneath the SFP and Unit 3 caisson is unknown and has been identified to PG&E in earlier correspondence as a data gap that requires further evaluation.

If groundwater contamination is discovered during site decommissioning activities, several options are available for groundwater remediation to control the impacts on groundwater:

Avoidance: Based on the low concentrations and accessible subsurface contamination, one option is to leave certain contaminants in place with no disturbance. A risk assessment is conducted, per NRC and State of California Regulations, as applicable, to determine if the remaining contamination will migrate to a location where the public health will be endangered or there will be an unacceptable environmental impact. If the contamination is isolated so that no pathway poses a hazardous condition to the public or environment, the contamination can be left in place to decay naturally. A groundwater assessment and monitoring program will be required to determine the horizontal and vertical extent of the contaminated zone and to monitor the control and degradation or spread of the contaminant plume in the groundwater. Avoidance would be the least Page 16 of 31 019

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 8 MANAGEMENT costly of all options. Based on the current assessments, groundwater at the HBPP site is not radiologically impacted; however, data gaps exist in complete delineation of the groundwater systems at the site. In particular, additional data is needed for areas below the Unit 3 caisson and SFP, beneath the Liquid Radioactive Waste Treatment building, and in areas of suspected deeper soil contamination.

Remediation: Common methods of groundwater remediation to remove contaminants include:

Pump and Treat: This method removes the contaminated groundwater and utilizes a process to reduce the contaminants below regulatory limits for release to the environment. Processes could include aeration (strips air soluble, volatile, or dissolved gaseous components) and filtration (mechanically removes solid material and/or adsorbs dissolved compounds). These are the most common remediation options. The treated groundwater is then discharged to an acceptable surface location or can be re-injected to the subsurface.

Sequestration: This in-situ method involves injection of a substance that captures and "traps" the contaminant of concern. The most common use is the removal of strontium-go (Sr-90) by injection of the mineral apatite (Cas(P0 4)3(F,CI,OH)) into the groundwater bearing formation down gradient of the contamination plume. As the groundwater moves through the permeable reactive barrier or apatite wall, the Sr-90 is captured (high affinity for Sr) and bound to the apatite. This prevents further migration in the groundwater to a receptor. The radionuclide remains bound to decay naturally.

Redox manipulation: This in-situ method is most useful for metal and metal ion contamination. A chemical wall is injected into the groundwater bearing formation down gradient of the contamination plume. As the groundwater moves through the "wall" the contaminant is converted from a harmful valence state (such as chromium VI) into a less harmful form (chromium Ill).

Disposal: The excavation dewatering effluents produced at the HBPP will require disposal. The following options are available for disposition of the groundwater:

On-site disposal without treatment: Groundwater is stored in temporary containers pending sampling. After confirmation of concentrations less than permitted levels (via sampling) is obtained, non-impacted groundwater (or concentration less than NPDES limits) can be discharged to the site. Groundwater can be discharged on-site via ground application, discharge canal or temporary settling pond overflow, or to the municipal sewer system, via permit.

On-site Treatment: Groundwater is stored in temporary containers pending sampling and treatment. Following treatment (such as filtration, aeration) to reduce or eliminate contamination, and confirmation of concentrations less than permitted levels (via sampling), groundwater can be discharged on-site via methods discussed above.

Treatment system byproducts (such as filters, settling pond silts) would be sent to an off-site disposal facility. Treatment systems would be operated to avoid producing Class 8/C radioactive waste.

Off-site disposal without treatment: Shipment of untreated radioactive groundwater to an off-site processor or disposal facility requires evaluation of containers, treatment, transport, and disposal issues. The preference is to treat and recycle water at the point-Page 17 of 31 020

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 8 MANAGEMENT of-generation, but direct solidification and disposal is a cost-effective approach for highly-impacted water.

4.2 Financial Risks Associated With Technical Issues Cost for treatment of groundwater removed from excavations at HBPP is included in position paper DECON-POS-009, "Removal of Sub-grade Structures".

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT 5.0 INVESTIGATION 5.1 Industry Reports and Studies This paper reviewed numerous industry reports/studies, conference proceedings, lessons-learned, and technologies/systems from vendors that were used at various commercial nuclear facilities and Federal cleanup projects. Staff personnel were interviewed and site visits were made to discuss and identify potential groundwater management techniques that can help assure proper and safe management of groundwater for the protection of workers and prevent the spread of potential groundwater contamination (Attachment C). A summary of these efforts is discussed below.

5.1.1 Lessons Learned From Other Decommissioned Facilities Eight other decommissioned and remediation sites were contacted or reviewed to determine how their experience with groundwater control and management might guide decommissioning operations at HBPP. These reviews are included as follows:

1. Big Rock Point, Michigan: Big Rock Point utilized a slurry wall system to about 20 ft bgs to reduce groundwater intrusion into the excavations. Groundwater was temporarily stored in tanks to settle solids, sampled, and then discharged via normal discharge pathways.

2. Yankee Nuclear Power Station, Massachusetts: Yankee Rowe utilized a slurry wall system to reduce groundwater introduction to the excavations.

3. San Onofre Nuclear Generating Station (SONGS) Unit 1, California: During remediation activities inside containment, a breach of the containment vessel allowed water from the pedestal area to enter the environment. When sampled, the water had elevated concentrations of tritium. As part of the NEI ground water initiative related to tritium in ground water at other reactor facilities, Southern California Edison (SCE) installed several monitoring wells around the Unit 1 structures. Some concentrations above background were measured, but all were far below the EPA drinking water limits, and in non-potable saline water. Extraction wells were used to remediate all tritium that was above background. SCE has elected to leave the below-grade portions of the turbine building in place after grouting the expansion joints and embedded pipes. Because SCE has not submitted an LTP for this unit, it is not known if the surveys performed on these areas prior to grouting will meet NRC requirements for final status surveys at the time of request for license termination. The PSDAR states all equipment and structures from Unit 1 will be removed from the site at the time of license termination, but SCE has stated it may reconsider this later, and possibly leave some of the below-grade structures in place (Reference 14).

4. DOE Hanford Site, Washington: The Hanford site is in the process of remediating several contamination plumes, both radiological and non-radiological. Multiple methods are in use including pump and treat systems, apatite sequestration, and redox manipulation. Groundwater is very deep with both confined and unconfined zones.

5. DOE Feed Materials Production Center, Ohio: The Fernald site experienced extensive uranium contamination of the Great Miami Aquifer, which is an EPA-Page 20 of 31 023

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT designated sole source aquifer. Groundwater is being remediated using an advanced pump and treat system with processed groundwater returned to the ground. In 2005, 1.6 billion gallons of groundwater had been treated, recovering over 600 lbs. of uranium.

6. NASA-Plum Brook Reactor Facility (PBRF}, Ohio: Structures demolished to 3 feet below grade. No further monitoring is anticipated.

7. Maine Yankee, Maine: Groundwater produced during decommissioning activities was stored in temporary holding ponds and tanks. Skid mounted water processing systems were used prior to discharge on site.

8. Rancho Seco, California: This facility is located in an area with very deep (approximately 183 feet bgs) groundwater with no radiological impact and no dewatering required for excavations.

5.1.2 NRC Lessons Learned From NRC Regulatory Issue Summary 2002-02 Lessons Learned Related to Recently Submitted Decommissioning Plans and License Termination Plans, January 16, 2002 (Reference 10):

"Groundwater- Operational environmental monitoring of groundwater, although adequate for its intended purpose, may not be adequate for site characterization and to support dose assessments. As noted in NUREG-1727, "NMSS Decommissioning Standard Review Plan," Section 4.6, Groundwater, states "The information supplied by the licensee should be sufficient to allow the staff to fully understand the types and movement of radioactive material contamination in groundwater at the facility, as well as the extent of this contamination." The actual number, location, and design of monitoring wells depend on the size of the contaminated area, the type and extent of contamination, the background quality, hydrogeologic system, and the objectives of the monitoring program. For example, if the objective of monitoring is only to indicate the presence of groundwater contamination, relatively few downgradient and upgradient monitoring wells are needed. In contrast, if the objective is to develop a detailed characterization of the distribution of constituents within a complex aquifer as the design basis for a corrective action program, a large number of suitably designed and installed monitoring wells may be necessary. Power reactors normally have groundwater monitoring programs as part of their radiological environmental monitoring programs (REMP). Although data derived from a REMP may provide useful information, the data still tend to be insufficient to allow the staff to fully understand the types and the movement of radioactive material contamination in groundwater at the facility, as well as the extent of this contamination.

Therefore, a licensee may need to gather additional data to understand the types and movement of radioactive material contamination in groundwater at the facility, as well as the extent of this contamination."

5.2 Use and Application of Industry Reports and Studies Many of the reports/studies, lessons-learned, and technologies/systems noted above as used at commercial nuclear facilities and Federal cleanup projects have application to HBPP. A key challenge at HBPP is to sequence incremental closure of different plant areas in an efficient fashion. Those areas and the lessons-learned below will be useful at HBPP to help assure proper safe groundwater control and remediation.

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. B MANAGEMENT Quarterly groundwater sampling per REMP is currently in progress for the site. Current subsurface investigations are in progress in the vicinity of HBPP Unit 3 to characterize potential groundwater contamination produced by known leakage from the SFP.

Comparison of the groundwater model to the other decommissioning sites indicates the HBPP has a unique situation that would directly affect the ability to dewater deeper excavations. Sites that utilize slurry wall technologies either had limited groundwater infiltration (1-3 gpm in the groundwater zones at Connecticut Yankee) or had deeper groundwater (Rancho Seco, Hanford) not requiring groundwater control. Groundwater at HBPP is unique since a productive aquifer is shallow (approx 20ft bgs) and confined beneath a sealing clay layer; therefore, excavation to the clay will not produce significant groundwater. If the clay is breached, the high hydraulic conductivity of the aquifer will produce significant amounts of water. Finally, no other near-surface sealing layer is available; since the top of the Unit F Clay is deep at 150ft bgs.

Comparison of the various options for groundwater control are discussed in position paper DECON-POS-009, "Removal of Sub-grade Structures".

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT 6.0 ANALYSIS OF RESULTS 6.1 Overview of Results The baseline cost study did not include scope or cost for groundwater control and management based on the limited excavation depth to about 3ft bgs and all deeper structures remaining in place. If this excavation depth is maintained, groundwater would be a minor factor since excavations will not exceed the existing static perched groundwater level or penetrate below the 1st Bay Clay aquitard.

The current baseline does not contain any explicit groundwater monitoring costs during decommissioning activities. Due to demolition activities, approximately ten (10) wells will require abandonment and reinstallation in different locations. The cost is approximately

$5,000 per well to abandon and $10,000 per well to install; which results in an estimated cost of $150,000 to change well locations. Following license termination and completion of quarterly sampling, the remaining wells on site should be abandoned, resulting in an estimated cost of $50,000. Groundwater monitoring must be maintained and PG&E budgets approximately $175,000 per year to implement the REMP monitoring.

Maintaining this program from 2009 through 2015 will cost approximately $1,225,000.

The incremental cost of these groundwater monitoring changes is approximately

$1,425,000.

6.2 Discussion of Results Radiologically impacted soils have been identified in various locations throughout the site. These areas are discussed in position paper DECON-POS-01 0, "Excavation and Removal of Subsurface Soil". Impacted soil may cause localized contamination of the perched groundwater zones on site; however, due to the continuous nature and very low vertical hydraulic conductivity of the 1st Bay Clay, no impact from surficial soil contamination is expected to affect the Upper Hookton Aquifer.

Based on monitoring well sampling data obtained during the HBPP REMP, groundwater in the Upper Hookton Aquifer shows no detectable radiological impacts.

6.2.1 Decommissioning Strategy Action Plan - Summary Actions The ENERCON Decommissioning Strategy Action Plan, May 2008, (Reference 15) includes the following items regarding soil and groundwater characterization:

1. Assess and integrate currently known groundwater sampling data into characterization: This position paper discusses the current status of radiological sampling data to characterize the groundwater quality. Current sampling operations are in progress in the vicinity of Unit 3 for impacts from the oil/water separator; however, sample results are not completed at this time.

2. Collect directional drilled soil samples under the SFP and analyze water samples beneath the SFP when soil samples are collected: This has been identified as a data gap and has not been performed.

3. Utilize soil sample data collected during tritium and water sampling data to refine final deep soil sampling efforts around the caisson.

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT

4. Use the information above to support the remediation cost estimate below: No current radiological groundwater contamination has been identified. Treatment costs associated with removal and treatment of potentially contaminated perched groundwater is addressed in position paper DECON-POS-01 0, "Excavation and Removal of Subsurface Soil". Data gaps include additional sampling beneath the caisson and the SFP.

5. Evaluate groundwater knowledge impact on DCGLs. The groundwater DCGLs for HBPP have not been determined, however, contaminant concentration limits are based on the selection of an industrial use end-state that does not include any use of groundwater. As stated previously, no current radiological groundwater contamination is reported for the HBPP in the vicinity of Unit 3.

6. Consider a deep water well in a clean portion of the site: Deep groundwater, below the Unit F Clay, is located well below the potentially impacted portions of the site.

The top of the Unit F Clay is approximately 150ft bgs (50 feet thick) and overlaid by saturated sands of the Upper Hookton Aquifer. Current sampling shows no radiological impact to the overlying Upper Hookton Aquifer. Based on the lack of impact to the overlying aquifer, and the thickness and regional persistence of the Unit F Clay aquitard, it is unlikely that operations at the HBPP have impacted the Lower Hookton Aquifer below the Unit F Clay; therefore, a deep well should not be required.

7. Collect additional soil/water samples as data support: Data gaps have been identified and additional sampling data, for both soil and groundwater are required. Costs associated with additional sampling, as required by unknown site conditions, may be handled by contingency measures.

8. Determine a strategy to manage tidal flow and seasonal rain: This will be evaluated in position paper DECON-POS-009, "Removal of Sub-grade Structures".

Excavations will be constructed to prevent or minimize surface stormwater flow from entering the excavation. Seasonal rain within the excavation will be removed from the excavation and contained and treated in the same manner as for groundwater.

9. Clearly identify areas with hazardous materials: Potential radiologically impacted areas are discussed in position paper DECON-POS-01 0, "Excavation and Removal of Subsurface Soil". Delineation of current non-radiological impacts has not been completed and is not included in this position paper.

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. B MANAGEMENT

7.0 CONCLUSION

S AND RECOMMENDATIONS 7.1 Conclusions In regards to groundwater control, each decommissioning site will be unique and will pose special challenges due to the site specific nature of the subsurface systems. Site-specific solutions are used at each decommissioning site; therefore, groundwater control must also be designed for the site-specific conditions at HBPP.

Based on results from previous REMP monitoring well sampling, groundwater contamination is either not present beneath Unit 3 or the concentration is low and not migrating. Demolition activities could change that and there is no provision in the current baseline for groundwater monitoring.

This plan concludes that the baseline report does not address the level of groundwater monitoring effort that will be required and the cost of those efforts.

This plan has evaluated the level of effort to monitor groundwater during remediation and concluded that an increased level of effort will be required. This conclusion is based on field observations and evaluations detailed in this paper.

The baseline report had no explicit cost to monitor or control groundwater. The level of effort estimated to monitor and control groundwater for decommissioning is estimated to be approximately $1,425,000, which is an overall increase of $1,425,000.

DECON-POS-H009, "Removal of Sub-grade Structures", recommends removal of the spent fuel pool and the surrounding impacted soil. Groundwater controls are reasonably determined to be required during this operation. Costs for those controls are addressed and included in that position paper. Those costs are not included in the estimate stated above.

7.2 Recommendations This position paper has identified strategies and actions that can enhance the overall completeness, accuracy, and reliability of the decommissioning planning process.

Specific recommendations for PG&E's consideration are as follows:

Note: Recommendations for excavation dewatering to protect groundwater are included in position paper DECON-POS-009, "Removal of Sub-grade Structures".

1. Continue sampling on-site monitoring wells through license termination. Sampling the wells should remain consistent with quarterly sampling per the existing REMP.

2. PG&E should plan to replace and reinstall approximately ten (1 0) wells that will likely be abandoned in different locations due to decommissioning activities affecting their physical integrity and function. Wells will require abandonment following license termination and completion of quarterly sampling.

3. A data gap exists regarding the nature and extent of suspect contamination beneath the Spent Fuel Pool, SFP French Drain, Liquid Radwaste Building, and Reactor Caisson Sump. Sampling and evaluation of the soil and groundwater beneath these structures is needed to determine if there is a pathway for this suspected leakage to affect the groundwater integrity.

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 8 MANAGEMENT

4. Additional information regarding groundwater gradients to delineate groundwater movement in the vicinity of Unit 3 is required. Although some information is available in the former waste pond area, limited groundwater gauging information is available in the Unit 3 area. PG&E personnel commenced sampling in June 2008. It is recommended that monthly gauging continue for approximately one year until seasonal variations in groundwater flow are better assessed and understood. This gauging program should be developed to account for these variations, such as timing the gauging event to correspond to the daily high and/or low tide.

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8.0 REFERENCES

1. TLG Decommissioning Cost Study for the Humboldt Bay Power Plant Unit 3 SAFSTOR 2009, October 2005 (Baseline)

2. HBPP NRC License #DPR-7

3. State of California, Department of Water Resources, California's Groundwater, Bulletin 118, October 2003

4. County of Humboldt Department of Health and Human Services, Public Health Branch, Hazardous Materials Unit, Website, http://co.humboldt.ca.us/HHS/PHB/

EnvironmentaiHealth/HazardousMaterialsUnit.asp, accessed August 29, 2008

5. Pacific Gas and Electric Company, Humboldt Bay Power Plant Wastewater Treatment System Impoundments Hydrologic Characterization Study, November, 1988

6. Arcadis, Additional Site Characterization and Limited Remedial Action Report, Humboldt Bay Repowering Project, May 2008

7. Pacific Gas and Electric Company, Effects of Tides on Groundwater Flow at Humboldt Bay Power Plant, January 21, 1987

8. Pacific Gas and Electric Company, Humboldt Bay Independent Spent Fuel Storage Installation, Final Safety Analysis Report Update, Revision 0, January 2006

9. US DOE, Hanford Groundwater Management Plan: Accelerated Cleanup and Protection, March 2003

10. Nuclear Regulatory Commission, NRC Regulatory Issue Summary 2002-02 Lessons Learned Related to Recently Submitted Decommissioning Plans and License Termination Plans, January 16, 2002, Website, http://www.nrc.gov/reading-rm/doc-collections/gen-comm/reg-issues/2002/ri02002.html

11. Department of Energy, 2005 Site Environmental Report, Fernald Closure Project, June 2006, Website, http://www.lm.doe.gov/land/sites/oh/fernald _orig/Cieanup/

Environmentai_Monitoring/ 2005%201SER/20051SER.htm

12. Electric Power Research Institute (EPRI), EPRI Guidelines for Groundwater Protection, Technical Presentation 1015118, January 21,2007

13. California Regional Water Quality Control Board-North Coast Region, Waste Discharge Requirements for Pacific Gas and Electric Company Humboldt Bay Power Plant, Order No. R1-2001-45, NPDES Permit No. CA 0005622, February 28, 2001

14. Nuclear Regulatory Commission, San Onofre- Unit 1, Website, http://www.nrc.gov/info-finder/decommissioning/power-reactor/san-onofre-unit-1.html, accessed October 17, 2008

15. Decommissioning Strategy Action Plan, ENERCON, May 2008

16. Pacific Gas and Electric, Safety Evaluation Report, Humboldt Bay Power Plant Unit No. 3 Decommissioning, April, 1987 Page 28 of 31 031

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT 9.0 ATTACHMENTS Attachment A: Conceptual Groundwater Model Attachment B: Calculation of HBPP Unit 3 Dewatering Radius of Influence Attachment C: Personnel Contact Log Page 30 of 31 033

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GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT Attachment A Page 1 of 10 035

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT Groundwater Model Discussion 1.0 Introduction The purpose of this conceptual model of the groundwater system at the Humboldt Bay' Power Plant (HBPP) is to quantify and predict groundwater issues arising from excavation dewatering and remediation of existing groundwater impacts due to the former operations of HBPP Unit 3. This model is based on previous groundwater investigations performed at the site and current investigations in progress to determine the extent of radionuclide impact in the vicinity of Unit 3.

This model will focus on the known geologic and groundwater characteristics to determine the most likely groundwater flow direction and velocities and estimate the radius of influence from excavation dewatering operations. This information is needed when planning the excavation for dewatering to determine the amount of groundwater that will be produced in the excavation and if the radius of influence will draw contaminated groundwater from nearby impacted zones into the excavation.

2.0 Discussion 2.1 Geology HBPP lies in the Northern California Coast Ranges geomorphic province. This province consists of a system of longitudinal mountain ranges (2,000 to 4,000 foot elevations with occasional6,000 feet peaks) and valleys (Reference A1).

The immediate vicinity of the site (Figure A-1-1) consists of sands, silts, clays, and alluvial soil of the Pleistocene-age Hookton sedimentary formations. These formations are primarily consolidated sands, gravels, clays and conglomerates. The HBPP buildings have their foundations in these strata (Reference A 1). In addition to the above mentioned formations, the northeast portion of the site, northeast of the discharge canal, consists of Holocene-age bay deposits. The former waste settling ponds were constructed in these deposits as well as the former asbestos disposal area. A site geologic map is included as FigureA-1-1.

In the vicinity of HBPP, the Hookton Formation is divided into a lower and an upper unit.

The Upper Hookton Formation deposits consist primarily of silt and clay alternating with thinner sand and gravel lenses approximately 70 feet thick. The Lower Hookton Formation deposits consist of alternating sand, silty sand, gravelly sand, silty clay, and clay over 1,000 feet thick (Figure A-1-2).

2.1.1 Upper Hookton Formation The Upper Hookton consists of surficial silt and clay terrace deposits overlying a local clay layer named the 1st Bay Clay. The 1st Bay Clay appears to be continuous across the site, with possible exception near the shoreline. Figure A-1-3 illustrates the estimated elevation of the bottom of the 1st Bay Clay in the vicinity of Unit 3.

Beneath the 1st Bay Clay is a groundwater saturated sand and gravel layer overlying a discontinuous clay layer named the 2nd Bay Clay. The 2nd Bay Clay is approximately 10 feet thick and is more persistent in the eastern portions of the site. Recent borings in September 2008 near the Unit 3 caisson did not encounter this clay layer. Where present, the base of the 2nd Bay Clay marks the top of the Lower Hookton formation.

Attachment A Page 2 of 10 036

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT 2.1.2 Lower Hookton Formation The Lower Hookton consists of alternating layers of sand, sand and gravel, and silt/clay beds (Figure A-1-2). The top of the Lower Hookton consists of an 80 feet thick layer of sand and gravel overlying a regionally persistent aquitard clay layer named the Unit F Clay. It is continuous across the site and is approximately 50 feet thick.

Beneath the Unit F Clay aquitard are alternating sand, silty sand, gravelly sand, silty clay, and clay layers down to approximately 1,100 feet below ground surface (bgs). Due to the depth, confining nature, and regional persistence of the Unit F Clay, it is not anticipated that site decommissioning activities will affect the groundwater below this layer. Therefore, groundwater discussions will not include analysis of these formations.

2.2 Local Aquifers Hydrogeology at the site is complex due to influences from tides, seasonal groundwater flow variability, heterogeneity in soil stratigraphy, and constructed features that effect groundwater at the site. Groundwater is found in multiple sand and gravel layers separated by clay aquitards.

The 50 foot thick regional Unit F Clay aquitard underlies the site at approximately 100-150 ft bgs. It forms a barrier for groundwater contaminant migration; therefore, this discussion will be limited to the aquifers above the Unit F Clay since these will be the most susceptible to impact. The deeper water-bearing zones, below the Unit F Clay called the Lower Hookton Aquifer, is the main groundwater supply source near the HBPP and is the most productive aquifer in the local area.

Four distinct aquifers are described within the strata above the Unit F Clay:

• Perched groundwater zones within the Upper Hookton silt and clay deposits (west of the discharge canal)

• Perched groundwater zones within the Holocene Bay Deposits (east of the discharge canal)

• Upper Hookton Aquifer (between the 1st Bay Clay and 2nd Bay Clay)

• Aquifer between Unit F Clay and 2nd Bay Clay (bottom of Lower Hookton Formation) 2.2.1 Perched Groundwater Zones- Upper Hookton Formation The zone of perched groundwater in the Upper Hookton deposits is in the silt and clay beds between the surface and the Upper Hookton aquifer. These silt and clay beds are approximately 30ft thick in the HBPP site area (Figure A-1-4). The groundwater in this zone occurs as discontinuous zones of perched water tables. Previous studies showed that piezometers placed in the upper (A) and lower (B) portions of this zone produced different piezometric levels. These zones of perched water were not found to be continuous across the site and exhibited unconfined aquifer characteristics, consistent with water trapped in thin sand lenses within the surficial deposits and the 1st Bay Clay.

It is interpreted that these groundwater zones will produce limited amounts of groundwater, further proven by former trenching activities at the site. It was observed that where the trenches were excavated at the site, groundwater flowed into the trench for a few hours from local groundwater zones, but had stopped by the next day (Reference AS).

Attachment A Page 3 of 10 037

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT 2.2.2 Perched Groundwater Zones - Holocene Bay Deposits The zone of perched groundwater in the Holocene bay silt and clay beds is in the tidal marsh deposits and bay mud that underlie the former wastewater ponds. This groundwater zone is in unconsolidated silt and clay beds that unconformably overlie the upper Hookton sand beds that are 23 to 26ft below the surface (Figure A-1-5).

The Holocene Bay Deposits appear to have larger and thicker sequences of sand and potential water bearing strata, within the silt and clay above the Upper Hookton Aquifer sand bed, than in the Upper Hookton sands and silts (Reference A3). This, combined with possible interconnection with piping fill material (preferential pathways) may contribute to higher groundwater availability and more distinct perched water-bearing zones in the bay deposits than in Upper Hookton silts and clays. The effective porosity of the formation was estimated as 0.30 (Reference A3).

Horizontal hydraulic conductivities of this layer were estimated to range from 2x1 o-6 to 8x10-4 centimeters per second (em/sec). Vertical hydraulic conductivities in this layer are generally about an order of magnitude lower, resulting in predominantly horizontal groundwater flow. Based on an assumed saturated thickness of 20 feet, the range of transmissivity values for the Holocene Bay Deposits is between 1x10-3 to 5x10- 1 cm 2/sec (Reference A3).

2.2.3 Upper Hookton Aquifer Above the Unit F clay aquitard and below the upper Hookton silt and clay beds (comprising permeable beds in both the lower and upper Hookton Formation) is the shallow, brackish-water aquifer referred to as the Upper Hookton aquifer. This aquifer, which is up to 100ft thick in the region and is 25ft to 40ft thick at HBPP Unit 3, is confined to semi-confined by the upper silt and clay bed aquitard. The unit is comprised of sand and gravel lenses, including some clean sand strata. The 2nd Bay Clay, a clay bed of varying thickness and extent, is located about 20 ft below the top of the aquifer; however, analyses show that it is discontinuous with extensive communication across the clay layer. The 2nd Bay Clay is present beneath the ISFSI site, former settling ponds, and in areas south of Unit 3, but does not seem to be present in the immediate vicinity of Unit 3, at the base of the caisson (Figure A-1-4).

As evident on the cross sections, the Upper Hookton aquifer is confined by the Upper Hookton silt and clay beds in the Unit 3 and wastewater ponds area, but is unconfined beneath the higher part of Buhne Point Hill, making it a semi-confined aquifer. The effective porosity of the formation was estimated as 0.30 (Reference A3).

Horizontal hydraulic conductivities of this layer are estimated,to range from 7x1 o-s to 2x1 o-3 em/sec. Vertical hydraulic conductivities in this layer are estimated to range from 1x1o-s to 4x1 o-4 em/sec. The transmissivity values ranged from 0.4 to 1.21 cm 2/sec (Reference A3).

2.2.4 Aquifer between Unit F Clay and 2nd Bay Clays The uppermost layers of the Lower Hookton Formation consist of sand and gravel beds above the Unit F Clay and below the 2nd Bay Clay. Where the 2nd Bay Clay is continuous, this portion of the Upper Hookton Aquifer may be considered a separate, confined water bearing zone. However, due to the discontinuous nature of the 2nd Bay Clay at the HBPP site, this aquifer is assumed to be hydraulically connected with the Upper Hookton Aquifer above the 2nd Bay Clay at the HBPP. Little testing has been Attachment A Page 4 of 10 038

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT performed on this aquifer; however, due to the lithologic similarity to the Upper Hookton formation, it is assumed that the hydraulic properties will be similar.

2.2.5 Aquifers below the Unit F Clay The Lower Hookton Aquifer lies below the 50 ft thick, regional aquitard known as the Unit F clay. Beneath this impermeable layer, the aquifer is defined as confined, freshwater bearing formations of clean, sorted sands deeper than about 200 ft bgs. The sand layers extend deeper and are utilized in water wells greater than 450ft depth with reported artesian flow. The conductivity of the aquifer ranges from 140 to 200 11mhos/cm which supports its isolation from the overlying, brackish Upper Hookton Aquifer (Reference AS).

Due to its depth and isolation from the overlying aquifers, the Lower Hookton aquifer is not considered to be a potential impacted groundwater source and will not require further investigation.

2.3 Groundwater Flow Direction Groundwater studies performed by PG&E show considerable complexity in the groundwater systems at the site. A general model of the groundwater flow directions is depicted in Figure A-1-6 (Reference AS).

2.3.1 Perched Groundwater Zones- Upper Hookton Formation Information on the flow direction of the perched groundwater zones of the Upper Hookton silts and clays was limited to areas south of Unit 3 near the Oil/Water Separator (OWS) with none found in the immediate vicinity of Unit 3.

During a study of tidal effects on groundwater at the HBPP in 1986 (Reference A2),

seasonal groundwater elevation measurements were performed (Figure A-1-2). Shallow wells installed in the perched groundwater zones showed a westerly groundwater flow direction. Groundwater piezometric surface elevation ranged between 7.27 and 9.07 feet above mean sea level (msl) with the exception of two anomalously low readings reported at approximately 6 ft msl. Tidal variations were reported as very small between the daily high and low tides. Some seasonal variation in flow direction was noted; however, due to reported heavy rains, which resulted in increased surface infiltration, the results were noted as inconclusive and subject to error.

During a subsequent assessment in 1999 (Reference AS), two potential perched groundwater zones were identified in the vicinity of the OWS (Figure A-1-8). The surface of the first (A) zone was identified as fairly flat-lying (no discernable gradient direction) at an approximate elevation of 8.5 feet msl. The second (B) zone exhibited a northerly groundwater flow direction with the piezometric surface between 5.17 and 8.32 feet msl. This assessment is based on a single gauging event on May 6, 1999 with no seasonal trends discussed.

2.3.2 Perched Groundwater Zones- Holocene Bay Deposits Information on the flow direction of the perched groundwater zones of the Upper Bay Deposits was limited to areas surrounding the former wastewater ponds.

During a study of tidal effects on groundwater at the HBPP (Reference A2), seasonal groundwater elevation measurements were performed in 1985 and 1986 (Figure A-1-9).

Shallow wells installed in the perched groundwater zones generally showed a westerly groundwater flow direction, toward the discharge canal, during both the end-of-dry Attachment A Page 5 of 10 039

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT season (October-November) and wet season (February-March) gauging events. A southerly gradient was depicted in areas closer to the bay (north of the former ponds) during the wet season. This is possibly due to higher infiltration rates from precipitation in the unpaved areas close to the bay, resulting in higher groundwater surface elevations in the perched zone. Groundwater piezometric surface elevation ranged between 7.33 and 8.38 feet msl during the dry season and between 8.80 and 11.9S feet msl during the wet season. Tidal variations were also reported as small between the daily high and low tides with possible connections to the Upper Hookton Aquifer from piping fill interactions surrounding the discharge canal.

During a subsequent assessment in 1999 (Reference AS), two potential perched groundwater zones were depicted in the vicinity of the former wastewater ponds (Figure A-1-1 0). The surface of the first (A) zone was identified as having two maximum groundwater points, one north of the wastewater ponds, at approximately 12 feet msl, and one south of the wastewater ponds, at approximately 11 feet msl. The piezometric surface then slopes toward the discharge canal to the west and toward the marsh to the east. The two high groundwater points were attributed to higher infiltration rates in areas outside the lined ponds. Groundwater potentiometric surfaces ranged between 8. 74 and 12.07 feet msl. The second (B) zone exhibited multiple groundwater flow directions, both toward Humboldt Bay and the eastern marsh, and from the discharge canal and Humboldt Bay. Flow directions from the discharge canal may indicate possible recharge from the discharge canal into the perched zone; however, the flow direction from Humboldt Bay may indicate increased precipitation infiltration from areas north of the former wastewater ponds. Piezometric surface elevations ranged between 7.09 and 10.24 feet msl. This assessment is based on a single gauging event on May 6, 1999 with no seasonal trends discussed.

2.3.3 Upper Hookton Aquifer During a study of tidal effects on groundwater at the HBPP, seasonal groundwater elevation measurements were performed in 198S and 1986 (Figure A-1-11) on deep piezometers installed in the Upper Hookton Aquifer (Reference A2). These wells were screened in different intervals, some near the top of the aquifer sands, and some in the lower portions of the aquifer, above the 2nd Bay Clay (where present). Analysis of the data shows that the piezometric levels for both the upper and lower zones are essentially identical, indicating good vertical communication in the aquifer above the 2nd Bay Clay bed (Reference A4).

Piezometric surfaces show significant tidal effects with good communication between the Upper Hookton Aquifer and Humboldt Bay, further proven by the high chloride concentrations reported in samples taken from the Upper Hookton Aquifer (Reference AS). In general, water levels in the wells showed an easterly (inland) groundwater flow direction during high tides, and westerly, toward the onsite canals and Humboldt Bay, during low tides. This trend was persistent during both the end-of-dry season (October-November) and wet season (February-March) gauging events (Reference A2). When an average was taken across three tidal cycles, the wet season average gradient showed overall annualized groundwater movement towards the site water bodies (discharge canal, marsh, and Humboldt Bay). Dry season gradients depicted groundwater movement toward the marsh and east of the former wastewater ponds. In general, although groundwater recharge from Humboldt Bay and the on-site canal appears to occur during high tides, the overall gradient for groundwater flow is towards the bay and onsite surface water bodies. Groundwater piezometric surfaces were reported as Attachment A Page 6 of 10 040

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT averaging approximately 5.5 feet msl with approximately 3 feet of tidal variation during the tidal cycle.

Several other wells also record the piezometric surface of the upper Hookton aquifer on Buhne Point Hill (Figure A-1-12). The piezometric surface beneath Buhne Point Hill is nearly horizontal, and slopes gradually to the north toward Humboldt Bay. North of the Discharge Canal fault the piezometric surface slopes northwest. The difference in the amount and direction of slope of the piezometric surface on either side of the fault indicates that the fault is an aquitard, with higher water levels on the north side than the south (Reference A4). This assessment is based on a single gauging event on May 6, 1999 with no seasonal trends discussed.

2.4 Radius of Influence Assessment Dewatering of a subsurface groundwater zone will produce a cone of depression in the groundwater potentiometric surface. Within this cone of depression, groundwater, and any contaminants within those zones, will be drawn towards the dewatering center. The outer edge where dewatering would influence the groundwater flow direction, is termed the "radius of influence." Evaluation of this radius of influence allows planning for groundwater control measures which will be required to prevent mobilization of contaminants from a known contaminated location into a "clean" (uncontaminated) zone.

This will also help control remediation costs by avoiding the spreading of a plume and minimizing additional problems and disposal costs of the dewatering effluent.

2.4.1 Perched Groundwater Zones Due to the unconfined nature and apparent limited extent of the perched water zones, the radius of influence would be limited to the particular water-bearing portion of the formation. Due to the unpredictable nature of the individual water-bearing perched zones, assessment of the radius of influence for dewatering these zones would not be possible without additional data. As these deposits drain rapidly (Reference AS) and are of limited extent, it is considered that the radius of influence would not be a significant concern and therefore would not require further evaluation.

2.4.2 Upper Hookton Aquifer The Upper Hookton Aquifer is a highly transmissive, confined aquifer underlying the entire site. Based on the studies of tidal effects (Reference A3), pressure changes due to rising and falling seawater levels in Humboldt Bay are felt across the site within a matter of hours, resulting in rapid changes in monitoring well water levels. The radius of influence has not been measured at the site; however, due to the confined nature of the aquifer, it most likely extends across the entire site. The radius of influence for a confined aquifer is significantly greater than for an unconfined aquifer with similar properties. Highly transmissive confined formations may have a radius of influence up to several miles.

The radius of influence can be estimated in an unconfined aquifer using methods developed for similar formations (Reference A4). To place a minimum value on the influence of excavations at the site, calculations (Attachment B) were made for the estimated radius of influence assuming unconfined conditions in the Upper Hookton Aquifer. As shown, the unconfined radius of influence for a 30 foot deep excavation would be at least 290 feet laterally. These results are depicted on Figure A-1-13. If the excavation was deepened to 80 feet, the radius of influence would increase to approximately 750 feet laterally, effectively covering the entire site and continuously Attachment A Page 7 of 10 041

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT drawing water from Humboldt Bay. This assessment assumes unconfined conditions; therefore, the actual confined nature of the Upper Hookton Aquifer would result in a much larger radius of influence on groundwater flow and contaminant migration from excavations below the 1st Bay Clay.

2.5 Groundwater Volume Characterization Disposition options for groundwater from excavations are dependent on the amount and required pumping rate needed to maintain the excavation dry. In perched groundwater-bearing formations groundwater is usually sporadic and limited; however, the areal extent and thickness of the water-bearing portion of the formation is usually difficult to quantify. The following discussion is based on limited existing information, and assumptions will be used to place a conservative estimate on the amount of groundwater produced during excavations at the HBPP.

2.5.1 Perched Groundwater Zones- Upper Hookton Formation As discussed in Subsection 2.3.1, perched groundwater occurs in the Upper Hookton Formation silts and clays above the 1st Bay Clay. The thickness of the Upper Hookton Formation silts and clays is reported to be approximately 30 feet thick, although in the vicinity of Unit 3, the formation appears to be approximately 20 feet thick from the surface to the bottom of the 1st Bay Clay. The 1st Bay Clay is described as a site wide clay unit approximately 10 feet thick; therefore, the potential water bearing strata would be 10 feet thick. Perched piezometric surfaces within the formation are reported at approximately 5 feet below ground surface where present; therefore, it is assumed the strata where groundwater-bearing layers are present will be approximately 5 feet thick.

For the purpose of this assessment, it is assumed the entire 5 foot thick layer will be saturated.

The full areal extent of the perched water-bearing zones has not been established and would be difficult to delineate due to their random nature and the practical limitations of drilling operations, identification of the exact water bearing formation, and potential for multiple small perched zones appearing to be a single unit. Perched groundwater has been described in borings and former groundwater wells near both the ISFSI and the oil/water separator; however, based on preliminary information from monitoring well installations, the formation above the 1st Bay Clay in the vicinity of Unit 3 appears to have been replaced by consolidated fill material with little observed perched, water-bearing strata. Therefore, for purposes of this assessment, the perched zones in this area are presumed to be discontinuous and do not provide a significant amount of groundwater in the vicinity of Unit 3.

The perched zones beneath the ISFSI area are assumed to cover an areal extent of approximately 131,000 ff Based on the above assumptions, the saturated formation total volume would be 6.5x1 05 fe. With the effective porosity of the saturated portions of the silts and clays as 0.30, the initial volume of groundwater within the perched formation would be 200,000 fe (or 1.5 million gallons).

The perched zones beneath the oil/water separator area are assumed to cover an areal extent of approximately 65,000 te. Based on the above assumptions, the saturated formation total volume would be 3.3x1 05 fe. Given the assumed effective porosity of the saturated portions of the silts and clays, reported as 0.30, the initial volume of groundwater within the perched formation would be 97,500 fe, or approximately 730,000 gallons.

Attachment A Page 8 of 10 042

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. B MANAGEMENT These are considered to be highly conservative estimates and the anticipated volume of water is considered to be much less.

2.5.2 Perched Groundwater Zones- Holocene Bay Deposits As discussed in Subsection 2.3.2, perched groundwater occurs in the Holocene Bay Deposits above the Upper Hookton aquifer sands. The thickness of the water bearing portions of the Holocene Bay Deposits is reported to be approximately 20 feet thick. For the purpose of this assessment, it will be assumed the entire 20 foot thick layer will be saturated.

The full areal extent of the perched water-bearing zones has not been established and would be difficult to establish due to limitations of drilling operations, identification of the exact water bearing formation, and the potential for multiple small perched zones appearing to be a single unit. Two prominent perched groundwater zones have been described from borings and former groundwater well data used in evaluation of the former wastewater treatment ponds. Previous reports also describe the potential for recharge into the perched zones from the discharge canal (via piping fill material) and from the underlying Upper Hookton aquifer (via leakage through the lower clay layers).

The perched zones beneath the ISFSI area are assumed to cover an areal extent of approximately 59,000 te. Based on the above assumptions, the saturated formation total volume would be 1.8x1 06 fe. Given the assumed effective porosity of the saturated portions of the silts and clays is reported as 0.30, the initial volume of groundwater within the perched formation would be 354,000 fe, or approximately 2.6 million gallons. Due to the reported recharge pathways, it is unlikely that this perched zone would be drained and ongoing dewatering would be required.

2.5.3 Upper Hookton Aquifer With the exception of excavations which encounter the above-mentioned perched groundwater zones, groundwater from the Upper Hookton Aquifer would not pose a concern unless the excavation exceeded the base depth of the 1st Bay Clay (or base of the Bay Deposits in the former wastewater treatment area). After the surface of the Upper Hookton Aquifer is breached, groundwater would have a pre-existing, nominal 10 foot hydraulic head due to the confined nature of the Upper Hookton Aquifer.

To bound the minimum pumping rate required for dewatering, calculations in Attachment B for groundwater production from an unconfined aquifer with similar characteristics to the HBPP were performed. Calculations show a 20 foot deep excavation under unconfined aquifer characteristics would require a minimum of 30 gpm (43,200 gpd) to maintain a 25 foot radius excavation dewatered. Pumping rates increase rapidly with depth and excavation radius (Reference A4).

For example, a 60 foot diameter excavation, 30 feet deep would require dewatering at 71 gpm (1 02,240 gpd); whereas a 60 foot diameter excavation, 80 feet deep would require 89 gpm (128, 160 gpd). However, based on the fact that the Upper Hookton Aquifer is confined beneath the 1st Bay Clay, dewatering rates could be significantly higher.

3.0 Conclusion The groundwater system beneath the HBPP, in the various aquifers present beneath the site, represents a complex system of groundwater flow pathways. Groundwater studies show considerable complexity in the groundwater systems at the site with perched, Attachment A Page 9 of 10 043

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT unconfined surficial aquifers overlying a highly transmissive, confined brackish aquifer in good connection with the adjoining Humboldt Bay, as evident by the tidal effects on groundwater wells and the brackish quality of the groundwater.

Additional confined water-bearing layers of sand and gravel are found deeper in the Hookton Formation; however, due to a thick, regional clay aquitard, these formations are considered to be at minimal risk of contamination from surficial operations at HBPP.

Groundwater gradients within the surficial perched zones range from nearly static (level) gradients to minor flows towards the discharge canal and adjacent marshes. In general, groundwater flow direction in the Upper Hookton Aquifer show an easterly (inland) groundwater flow direction during high tides, and westerly, towards the canals and Humboldt Bay, during low tides; however, net movement of groundwater is towards Humboldt Bay.

Dewatering of excavations within the upper perched water zones will require disposition of groundwater; however, this groundwater will be of limited quantity and should be within the capability of standard dewatering and treatment methods. Excavations broaching the surface of the Upper Hookton Aquifer will require extensive dewatering to maintain the excavation drained and will produce large volumes of dewatering effluents.

Data Gaps Groundwater flow directions have been established during various site investigations; however, most investigations concentrated efforts on the former waste pond area, to the east of the discharge canal. Some information is available south of Unit 3, but the information is dated (1985/1998) and only addresses a short term or single gauging event. Current groundwater information is needed to assess groundwater flow directions and tidal effects in the vicinity of the Unit 3 . This data should cover a seasonal range of time (wet-dry periods) to assess potential seasonal flow directions and potential contaminant transport during decommissioning activities.

4.0 References A 1. Pacific Gas and Electric Company, Humboldt Bay Power Plant Historic Site Assessment, January, 2007 A2. Pacific Gas and Electric Company, Effects of Tides on Groundwater Flow at Humboldt Bay Power Plant, January, 1987 A3. Pacific Gas and Electric Company, Humboldt Bay Power Plant Wastewater Treatment Impoundments Hydrogeologic Characterization Study, November, 1988 A4. Broward County EPD, Pollution, Prevention, and Remediation Division, EAR Section Standard Operating Procedure for Dewatering, Exhibit Ill, Website, http://www.broward.org/pprd/cs_dewatering.htm, Revision 2, August 2008 AS. Pacific Gas and Electric Company, Humboldt Bay Independent Spent Fuel Storage Installation, Final Safety Analysis Report Update, Revision 0, January 2006 Attachment A Page 10 of 10 044

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. B MANAGEMENT Attachment 8 Calculation of HBPP Unit 3 Dewatering Radius of Influence 045

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV.B MANAGEMENT 046

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT

.:d ENERCON Excellence- Every project. Evuy day

~E ERCO CALC. NO. HBPP-TC-008 l .l ct:flence- -[ve r>* projeu E.-e1y dCiy. CALCULATION COVER SHEET REV. 0 PAGE NO. 1

Title:

Calculation of HBPP Unit 3 Dewatering Radius of Client: Pacific Gas & Electric Influence and Pumping Rate Estimate for LTP and Decommissioning Planning Project: PG&E067 TASK 017C Item Cover Sheet Items Yes No

~-~ *- - --

1 Does this calculation contain any open assumptions that require confirmation? (If YES, D ~

Identify the assumptions) 2 Does this calculation serve as an "Alternate Calculation"? (If YES, Identify the design D ~

verified calculation.)

Design Verified Calculation No.

3 Does this calculation Supersede an existing Calculation? (If YES, identify the D ~

superseded calculation.)

Superseded Calculation No.

Scope of Revision:

Revision Impact on Results:

Study Calculation D Final Calculation D Safety-Related D Non-Safety Related ~

(Print Name and Sign)

/

Originator: Randall N. Lantz, P.G.

~ Date: 10/29/2008 Design Verifier: Darren D. Lovvorn, P.G. C__] _c:;r__) Date: 10/29/2008 Approver: Gerald E. Williams

~-/u_~r;)C {_~

~

Date:

l o{z..yf2o7::.-f" I

047 Attachment B Page 1 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT CALC. NO. HBPP-TC-008 CALCULATION REVISION STATUS SHEET REV. 0 PAGE NO. 2 CALCULATION REVISION STATUS REVISION DESCRIPTION PAGE REVISION STATUS PAGE NO. REVISION PAGE NO. REVISION APPENDIX REVISION STATUS APPENDIX NO. PAGE NO. REVISION NO. APPENDIX NO. PAGE NO. REVISION NO.

1 1 0 048 Attachment B Page 2 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT CALC. NO. HBPP-TCM008 CALCULATION DESIGN VERIFICATION REV. 0 PLAN AND

SUMMARY

SHEET PAGE NO. 3 l;aiCUI<atlc*n Design Verification Plan:

design verification was performed by reviewing references to verify input values. Then the spreadsheet entries formulas were checked to verify that the outputs were being calculated correctly.

for Approval- mark uNIA" if not required)

Approver: Gerald E. Williams Date:

Calculation Design Verification Summary:

The calculation design verification was completed and the calculation was verified as acceptable.

10/29/2008 049 Attachment B Page 3 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT ENERCON Excellence- Every project. E ery doy r.* ENERCON CALCULATION CALC. NO. HBPP-TC-008

[xceflence-f*:ery pro,ecr, [very doy.

DESIGN VERIFICATION REV. 0 CHECKLIST PAGE NO. 4 Item CHECKLIST ITEMS Yes No N/A 1 Design Inputs- Were the design inputs correctly selected, referenced (latest revision), consistent with the design basis and incorporated in the D D ~

calculation?

2 Assumptions -Were the assumptions reasonable and adequately described, justified and/or verified, and documented?

~ D D 3 Quality Assurance -Were the appropriate QA classification and requirements assigned to the calculation? D D ~

4 Codes, Standards and Regulatory Requirements- Were the applicable codes, standards and regulatory requirements, including issue and D D ~

addenda, properly identified and' their requirements satisfied?

5 Construction and Operating Experience - Have applicable construction and operating experience been considered? D D ~

6 Interfaces- Have the design interface requirements been satisfied, including interactions with other calculations? D D ~

7 Methods- Was the calculation methodology appropriate and properly applied to satisfy the calculation objective? ~ D D 8 Design Outputs- Was the conclusion of the calculation clearly stated, did it correspond directly with the objectives and are the results reasonable ~ D D compared to the inputs?

9 Radiation Exposure - Has the calculation properly considered radiation exposure to the public and plant personnel? D D ~

10 Acceptance Criteria -Are the acceptance criteria incorporated in the calculation sufficient to allow verification that the design requirements have ~ D D been satisfactorily accomplished?

11 Computer Software- Is a computer program or software used, and if so, are the requirements of CSP 3.02 met?

0 0 ~

COMMENTS:

~tN~Sign)

Design Verifier: Darren D. Lovvorn, P.G. G_l_(/j_J Date: 10/29/2008 Others: Date:

050 Attachment B Page 4 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT

[xcellr:net>-Fvery project. Every doy CALC. NO. HBPP-TC-008 CALCULATION CONTROL SHEET REV. 0 PAGE NO. 5 Table of Contents 1.0 Purpose And Scope To estimate the groundwater radius of influence and dewatering rates for excavations involving removal of the Unit No. 3 caisson and/or Spent Fuel Pool (SFP) with no groundwater controls. This calculation is performed as an estimation of the minimum values as the actual radius of influence will be much larger due to the confined nature of the Upper Hookton Aquifer.

2.0 Summary Of Results And Conclusions Dewatering of deep excavations with no groundwater controls will require extensive dewatering due to the shallow surface soils overlying a highly transmissive, confined sand and gravel aquifer. The dewatering of the deep excavations surrounding the Unit No. 3 caisson and the SFP will produce very high dewatering rates and a groundwater radius of influence extending site wide and into Humboldt Bay, thus requiring some form of groundwater control.

3.0 References

1. Broward County EPD, Pollution, Prevention, and Remediation Division, EAR Section Standard Operating Procedure for Dewatering, Exhibit Ill, Website, tlttp://www.broward.org/pprd/cs dewaterinq.htm, Revision 2, August 2008

2. Pacific Gas and Electric Company, Humboldt Bay Independent Spent Fuel Storage Installation, Final Safety Analysis Report Update, Revision 0, January 2006 4.0 Assumptions

1. The calculation is performed using estimation methods from a comparable sand and gravel aquifer location (Reference 1).

2. Equations are calculated using a radial geometry and vertical excavation walls. No compensation has been included for non-circular excavations or side sloping for excavation stability.

3. Due to lack of in-situ testing data on the confined Upper Hookton aquifer at the HBPP site, the calculations contained herein are performed using unconfined conditions to place a lower bound on actual radius of influence distances. Due to the large radius of influence for unconfined conditions, this lower bound is sufficient to show groundwater control methods will be required for deep excavation dewatering.

4. Design inputs are from client provided references based on previous site evaluations (Reference 2);

however, there is no information that suggests the historic data may have changed between the time of acquisition and the present and is therefore assumed valid.

5.0 Design Inputs Hydraulic conductivity (Kh) for the Upper Hookton Aquifer was reported as 1.00x1 o- em/sec 3

1.

(Reference 2).

2. Variable excavation radii and depths were calculated in an Excel matrix spreadsheet. The radii and depth were chosen to bound the radius and depth of the Unit No.3 caisson and SFP.

3. For the purpose of this calculation, the base of the 151 Bay Clay was considered as the top of the aquifer hydraulic head (unconfined assumption), approximately 10 feet below ground surface. The 051 Attachment B Page 5 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT Exceilence-E,lety project. Every day actual piezometric surface of the Upper Hookton aquifer is above the bottom of the 1st Bay Clay due to confined conditions of the aquifer. Groundwater will not be encountered in excavations terminated above the base of the 1st Bay Clay.

4. For the purpose of this calculation, the base of the Unit No. 3 caisson was considered as the bottom of the saturated portion of the formation. The actual base of the Upper Hookton aquifer is the top of the Unit F Clay, approximately 150 feet below ground surface (bgs) in the vicinity of Unit No. 3.

6.0 Methodology Calculations are based on dewatering estimate procedures for the Biscayne Aquifer in Broward County, Florida (Reference 1), a sand and gravel aquifer with similar hydraulic properties to the Upper Hookton aquifer at the HBPP. Input values are based on reported hydraulic conductivity values and subsurface formation characteristics reported from previous site assessments at HBPP (References 2 and 3).

Radius of Influence:

Equation 6.1 R, = 3000( H - h )..[if; (Reference 1)

Where: Ro = radius of influence (m)

H =total head of water in the aquifer (m)

(elevation of the groundwater surface- elevation of the aquifer base) h head of dewatered aquifer (m)

(elevation of the depressed groundwater surface- elevation of the aquifer base)

Kh =formation hydraulic conductivity (m/s)

Equation 6.1 (Sichardt's equation) is used to determine the radius of influence (groundwater flows towards the excavation) for pumping wells surrounding a cylindrical excavation. The general process followed is:

1. Obtain data for hydraulic conductivity from Reference 2.

2. Determine bounding depth and radius of the potential excavation (bounding limits).

3. Determine aquifer thickness information from Reference 2.

4. Determine the radius of influence using Equation 6.1.

Dewatering Rate:

The dewatering flow rate is estimated by the following equation:

(H 2 -h 2 )=_!!3__(lnR -Jnr) (Reference 1)

JrKII o "

Where: nq =total pumping flow rate from all wells to dewater the excavation (m 3/sec)

Kh =formation hydraulic conductivity (m/s)

H =total head of water in the aquifer (m)

(elevation of the groundwater surface- elevation of the aquifer base) h = head of dewatered aquifer (m)

(elevation of the depressed groundwater surface- elevation of the aquifer base)

Ro = radius of influence (m) re =effective radius of dewatering (m)

Solving for nq yields the following:

052 Attachment B Page 6 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT Fxcelienre-F.;ery project F:very day Equation 6.2 Equation 6.2 is used to determine pumping rate required to maintain the excavation dry. The general process followed is:

1. Determine the dewatering radius of influence using Equation 6.1.

2. Determine bounding depth and radius of the potential excavation (bounding limits).

3. Obtain data for hydraulic conductivity from Reference 2.

4. Determine aquifer thickness information from Reference 2.

5. Determine the pumping rate from all wells using Equation 6.2.

7.0 Calculations Calculations were performed using an Excel spreadsheet and various excavation dimensions, both radius and depth, to bound the size of the excavations required at the HBPP. The spreadsheet performed the calculation using metric units (m, m3/s) then converted the final result into english units (ft., gpm) using standard conversion factors.

The excel spreadsheet displays rounded values in the displayed cells and printout. The actual calculation may use more significant digits than are displayed thus resulting in rounding errors if rounded numbers from the attached printout are used for additional calculations.

Table 1 presents the radius of influence (R 0 ) for various excavation depths for the assumed unconfined conditions. Actual site radius of influences will be much greater than listed below due to the confined nature of the Upper Hookton aquifer at the HBPP site.

Table 1 Radius of Influence (in ft)

Table 2 presents the dewatering rate (nq) for various excavation radii (re) and excavation depths for the assumed unconfined conditions. Actual site dewatering rates will be much greater than listed below due to the confined nature of the Upper Hookton aquifer at the HBPP site and should be considered rninirnurn values.

Table 2 Dewatering Rate (in gpm)

Excavation Depth (ft) r., (ft) 20 25 30 35 40 45 50 55 60 65 70 75 80 30 33 42 49 55 60 64 67 69 71 72 72 71 70 40 39 49 57 63 68 72 75 77 78 79 79 78 77 50 45 56 64 70 75 79 82 84 86 86 86 85 83 60 52 63 71 78 83 87 89 91 93 93 92 91 89 70 60 71 79 85 90 94 97 98 99 99 99 97 95 80 70 80 87 93 98 102 104 105 106 106 105 103 101 90 81 90 96 102 106 109 111 113 113 112 111 109 106 100 94 100 106 111 114 117 119 120 120 119 117 115 112 053 Attachment B Page 7 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT The output from the calculations are in matrix format based on excavation depth vs. excavation radius.

Gallons of groundwater produced per day for dewatering the excavation is estimated by multiplying the value for the radius and depth of interest (in gpm) by 1440 minutes per day.

For example:

Given an excavation with a 60 foot radius to a depth of 30 feet, dewatering rates would be approximately 71 gpm from all wells. The daily dewatering rate would be 71 gpm x 1440 minutes per day, or 102,204 gallons per day of dewatering effluent to maintain the excavation dry. As stated previously, this is a minimum estimate based on calculations using unconfined conditions. The actual dewatering rate with no groundwater controls is expected to be much higher due to the confined conditions of the Upper Hookton Aquifer in the vicinity of Unit No. 3.

A printout from the calculation spreadsheet is provided in Appendix 1.

8.0 Appendices Appendix 1: Excel calculation sheet, Excel file "HBPP Excavation Dewater Estimate.xls" 054 Attachment B Page 8 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT Excellence-f,;ery project. Every day.

Appendix 1 055 Attachment B Page 9 of 12

Estimated Excavation Dewatering Rate (gpm)

(Unconfined Aquifer)

Excavation Depth (ft) m 6.10 7.62 9.14 10.67 12.19 13.72 15.24 16.76 18.29 19.81 21.34 22.86 24.38 ft 20 25 30 35 40 45 50 55 60 65 70 75 80 7.62 25 30 39 46 51 56 60 63 65 67 67 68 67 66 9.14 30 33 42 49 55 60 64 67 69 71 72 72 71 70 10.67 35 36 45 53 59 64 68 71 73 75 75 75 75 74 g 12.19 40 39 49 57 63 68 72 75 77 78 79 79 78 77 tn 13.72 45 42 52 60 67 72 76 79 81 82 83 82 82 80

s

0 15.24 50 45 56 64 70 75 79 82 84 86 86 86 85 83

<<< 16.76 55 49 59 68 74 79 83 86 88 89 89 89 88 86 a:

s:: 18.29 60 52 63 71 78 83 87 89 91 93 93 92 91 89 G)

.2 19.81 65 56 67 75 82 87 90 93 95 96 96 94 92 96 ;a i<<< 21.34 70 60 71 79 85 90 94 97 98 99 99 99 97 95 Io

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22.86 75 65 75 83 89 94 98 100 102 103 103 102 100 98 -C w

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24.38 25.91 80 85 70 75 80 85 87 92 93 98 98 102 102 105 104 108 105 109 106 109 106 109 105 108 103 106 101 104 wz

-to 27.43 28.96 90 95 81 87 90 95 96 101 102 106 106 110 109 113 111 115 113 116 113 116 112 116 111 114 109 112 106 109 s:~~

)>-<-t 30.48 100 94 100 106 111 114 117 119 120 120 119 117 115 112 z_ m

)>O;a Ro ft 189.74 237.17 284.60 332.04 379.47 426.91 474.34 521.78 569.21 616.64 664.08 711.51 758.95 ~O m 57.83 72.29 86.75 101.21 115.66 130.12 144.58 159.04 173.50 187.95 202.41 216.87 231.33 S:~~

m:::am WT Depress ft 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00 zow

-lr-t m 3.05 4.57 6.10 7.62 9.14 10.67 12.19 13.72 15.24 16.76 18.29 19.81 21.34

)>G5 Calculation parameters (metric units) z)>

H m 21.34 21.34 21.34 21.34 21.34 21.34 21.34 21.34 21.34 21.34 21.34 21.34 21.34 o:::!

h m 18.29 16.76 15.24 13.72 12.19 10.67 9.14 7.62 6.10 4.57 3.05 1.52 0.00 0 H-h m 3.05 4.57 6.10 7.62 9.14 10.67 12.19 13.72 15.24 16.76 18.29 19.81 21.34 z H2-h2 m2 120.8 174.2 223.0 267.1 306.6 341.4 371.6 397.2 418.1 434.3 445.9 452.9 455.2 In function 0.6405 0.8636 1.0459 1.2001 1.3336 1.4514 1.5568 1.6521 1.7391 1.8191 1.8932 1.9622 2.0268 m/d cm/s m/s Hydraulic Conductivity (Kh) 0.864 1.00E-03 1.00E-05 ft m 0 Hd - Depth to Aquitard 80 24.38 m

()

Hs - Depth to Groundwater 10 3.05 "U)> 0 Q)

(.Q H - Saturated Thickness (Hd-Hs) 70 21.34 zI CD ~ 3 Conversion m /s to gpm 15850.32 "U

~:Y 0 o3 Conversion ft to m 0.3048 ;acp 0 CD mi

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Attachment 8 Page 12 of 12

GROUNDWATER INVESTIGATION DECON-POS-H011 HISTORY, CONTROL, AND REV. 0 MANAGEMENT Attachment C - Personnel Contact Log company Name 1 Quoted? Nuclear Facility Date Group Contact Name I Number (yes/no) Discussion Topic (5 words) Name 8/29/2008 Humboldt County, Bob Stone, CHMM no State/Local and County HBPP Division of Hazardous Materials Groundwater Regulations Environmental Health Specialist 707/268-2239 9/22/2008 PG&E Joe Davis no Status of monitoring well testing HBPP 707/496-4745 9/26/2008 PG&E Andrew Cordone no Groundwater gauging of REMP HBPP Sr. Project Manager wells 10/2/2008 NASA Keath M. Peecook no Concrete rubble placed below PBRF keith.m.peecook@nasa.gov grade 10/15/2008 PG&E John Albers no Status of compliance with NEI HBPP Initiative, SFP/caisson leakage Attachment C p Page 1 of 1 059