ML071510137

Yankee Atomic Electric Company, Final Groundwater Condition Report for the Yankee Nuclear Power Station

ML071510137
Person / Time
Site:	Yankee Rowe
Issue date:	02/15/2007
From:	Gerard van Noordennen Yankee Atomic Electric Co
To:	Document Control Desk, NRC/FSME
References
Download: ML071510137 (131)

Text

Final Groundwater Condition Report Yankee Nuclear Power Station Rowe, Massachusetts February 15, 2007

Table of Contents Final Groundwater Condition Report List of Tables........................................................................................ii List of Figures ...................................................................................... 11i List of Appendices ................................................................................ vi Executive Summary ............................................................................... I 1.0 Introduction........................................... ...... ***...*"**...... ..... 4 1.1 Groundwater Monitoring Program Overview and Site Setting ................... 4 1.2 Groundwater Monitoring Program Plans and Procedures ......................... 5 2.0 Site Geology and Hydrogeology......................................................... 6 2.1 Background ............................................................................. 6

2. 1.1 Geology and 1-ydrogeological Conceptual Model............................ 7 2.1 .2 Work Completed Since 2006 Interim Groundwater Report ................. 8 2.2 Groundwater Elevation and Flow Direction......................................... 8 2.2.1 Site Measurements of Groundwater Elevation................................ 8 2.2.2 Groundwater Contour Maps ................................................... 10 2.2.4 Groundwater Influences ........................................................ 11 2.3 Groundwater Influences During and After Demolition........................... 15 3.0 Groundwater Sampling and Analysis.................................................. 16

3. 1 Description of Field Measurements................................................. 17 3.2 Summary of FieldMeasurements................................................... 17 3.3 Sample Locations ..................................................................... 17 3.4 Laboratory Analysis .................................................................. 17 4.0 Laboratory Analytical Results.......................................................... 19

4. 1 Tritium ................................................................................. 19 4.2 Boron................................................................................... 20 4.3 Other Radionuclides in Groundwater............................................... 21 4.4 General Geochemistry ............................................................... 22 5.0 Spatial Trend Analysis .................................................................. 23 5.1 Spatial Distribution of Tritium Third and Fourth Quarters 2006................ 24 5.1.1 Spatial Distribution of Tritium from Third Quarter 2006................... 24 5.1.2 Spatial Distribution of Tritium from Fourth Quarter 2006 ................. 26 5.2 General Geochemistry of Site Groundwater ....................................... 26 5.3 Trend Analysis of Tritium ........................................................... 27 5.4 Fate and Transport of Tritium ....................................................... 28 6.0 Groundwater Model ..................................................................... 31 6.1 Introduction .................................................................. ,.........

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6. 1.1 Scope and Objectives........... ................................................... 31 6.1 .2 Modeling Software.............................................................. 33 6.1.3 Base Map Preparation and Spatial Location of Data........................ 33

6. 1.4 Rockworks Database and Surfer used for Geologic Data and Layer Elevations.................................................................................... 34

6.2 Model Discretization .................................................................................... 34 6.3 Boundary Condition Specification ................................................................ 35 6.4 Hydraulic Conductivity and Recharge Parameterization .............................. 36 6.5 Transient and Solute Transport Parameters .................. ............................... 39 6.6 Model Calibration and Verification .............................................................. 39 6.6.1 Single Head Calibration ....................................................................... 41 6.6.2 Vertical Gradient Calibration ................................................................ 41 6.6.3 Verification Data Set Calibration ........................ ................................. 42 6.6.4 Discussion of Sensitivity Analyses ........................................................ 42 6.7 Discussion of Various Model Test Runs ..................................................... 44 6.7.1 MW - 107C Pumping Test Simulation ................................................... 44 6.7.2 Simulating the Effect of Plant W ell Pumping ...................................... 45 6.7.3 Simulating the Effect of Tailwater Elevation Fluctuation on MW-i 13C. 46 6.7.4 Effect of rise and fall of Sherman Reservoir ........................................ 46 6.7.5 Response to heavy rainfall events ........................................................ 46 6.8 Groundwater Head Distributions, pre- and post-Demo Conditions .............. 47 6.9 Specific Fate and Transport Simulations ..................................................... 48 6.9.1 Reverse Particle Tracking from Sherman Spring ................................. 48 6.9.2 Simulation of the IXP Leak of 1963 ..................................................... 49 6.9.3 Simulation of Tritium Concentrations in M W -107C in 2006 ............... 50 6.9.4 The "Resident Farmer W ell" Scenario ................................................ 51 6 .10 S u m m a ry ........................................................................................................... 52 7.0 Conclusions and Recommendations ................................................................ 54 7.1 Groundwater Quality Status: ...................................................................... 54 7.2 Evaluation of LTP Closure Criteria .............................................................. 54 7.3 Subsequent Sampling Recommendations ..................................................... 56 8 .0 A c ro n y m s .............................................................................................................. 57 9 .0 R e fere n c e s ............................................................................................................. 59 L ist o f Ta b le s ..................................................................................................................... iii L ist o f F ig u re s .................................................................................................................... iii L ist o f A pp en d ic e s ............................................................................................................. vi ii

List of Tables Table 1-1 ........................................................... Sum mary of M onitoring W ell Completion Details Table 1-2 ........................................................ History of Surveyed Locations of M onitoring W ells Table 2-1 ......... Inventory of Long-Term Pressure Transducer Records in Rowe Monitoring Wells Table 2-2 .................................................................... History of Hand-M easured Water Elevations T able 2-3 ....................................................................................... Plant Well W eekly W ater U sage Table 2-4 ............................................... Summary of Influences on Monitoring Well Water Levels Table 3-1 ......................... Summary of Laboratory Analysis for Quarterly Groundwater Sampling Table 3-2 .......................... Summary of Groundwater Laboratory Analytical Program for Q4 2006 Table 4-1 ................................................................... Sum m ary of 2006 Tritium A nalytical Results Table 4-2 ................................................ Tritium Results for 2006 Replacement Monitoring Wells Table 4-3 ................................. Summary of Q2 2006 Boron and Cation-Anion Analytical Results Table 5-1 .... Summary of Trend Analysis for Monitoring Wells Included in LTP Monitoring Plan Table 6-1 ........................................................ Conceptual M odel Design in Vertical Cross Section Table 6-2 ................................................... Pre-Demo Model Hydraulic Conductivity Zone Values Table 6-3 ....................................................... Pre-Demo Model Average Annual Precipitation Rate Table 6-4 ........................ Model Specific Storage, Specific Yield, and Porosity Zone Descriptions Table 6-5 ............................................. Pre-Demo Model Average Annual Recharge Mass Balance Table 6-6 ................. Model Chemical Mass Balance for IXP Tritium Leak Simulation 1965-1985 Table 6-7 .................................. Pre-Demo Model Calibration Statistics for Steady-State Recharge Table 6-8 ................................................ Pre-Demo Model Vertical Gradient Calibration Statistics for Average Annual Recharge Table 6-9 ....................... ;.............................. Pre-Demo Verification Data Set Calibration Statistics Table 6-10 ...................... Calculation of Weighted Tritium Concentration in Resident Farmer Well List of Figures Figure 1-1 ...................................................................... Location of Y ankee Nuclear Pow er Station Property Boundaries and Regional Context on the Deerfield River Figure 1-2 ............................................................. Current 10 CFR Part 50 Licensed Site Boundary F igure 1-3 ....................................................................................................... YN P S P lant S ite M ap Figure 1-4 ................................................................... Locations of Groundw ater M onitoring Wells Figure 2-1 .......................................... 9/11/06 Glaciofluvial Groundwater Contour and Data Points Figure 2-2 ........................................ 9/11/06 Groundwater Elevation in Upper Till and Data Points iii

Figure 2-3 ........ 9/11/06 Groundwater Elevation in Lower Till & Glaciolacustrine and Data Points Figure 2-4 ........................................... 9/11/06 Groundwater Elevation in Bedrock and Data Points Figure 2-5 ........................................ 12/4/06 Glaciofluvial Groundwater Contours and Data Points Figure 2-6 ........................................ 12/4/06 Groundwater Elevation in Upper Till and Data Points Figure 2-7 ........ 12/4/06 Groundwater Elevation in Lower Till & Glaciolacustrine and Data Points Figure 2-8 ........................................... 12/4/06 Groundwater Elevation in Bedrock and Data Points Figure 2-9 .......................................................................... Am bient A ir Tem perature at YN PS Site Figure 2-10 .............. Deep Excavations for Utility and Soil Removal and Locations of Temporary Stormwater Basins During 2006 Figure 2-11 ............... Concrete Slabs, Foundation Walls, and Underground Utilities Left in Place, Post Demolition Figure 2-12 ............................................... Final Site Ground Surface Contours in Post-Demo State Figure 5-1 .................................................. Tritium in Downgradient Monitoring Wells 2004-2006 Figure 5-2 ...................... Distribution of Tritium in Groundwater in Glaciofluvial Unit, Sept. 2006 Figure 5-3 .......................... Distribution of Tritium in Groundwater in Upper Till Unit, Sept. 2006 Figure 5-4 .............................................................................. Locations of G eologic Cross Sections Figure 5-5 ................... Cross Section A-A' Showing Isocons of Tritium on Sept. 6, 2006 in pCi/L Figure 5-6 .................... Cross Section B-B' Showing Isocons of Tritium on Sept. 6, 2006 in pCi/L Figure 5-7 .................... Cross Section C-C' Showing Isocons of Tritium on Sept. 6, 2006 in pCi/L Figure 5-8 ................... Cross Section D-D' Showing Isocons of Tritium on Sept. 6, 2006 in pCi/L Figure 5-9 .................... Cross Section E-E' Showing Isocons of Tritium on Sept. 6, 2006 in pCi/L Figure 5-10 ..................... Distribution of Tritium in Groundwater in Glaciofluvial Unit, Dec. 2006 Figure 5-11 ......................... Distribution of Tritium in Groundwater in Upper Till Unit, Dec. 2006 Figure 5-12 .................. Cross Section A-A' Showing Isocons of Tritium on Dec. 6, 2006 in pCi/L Figure 5-13 ................... Cross Section B-B' Showing Isocons of Tritium on Dec. 6, 2006 in pCi/L Figure 5-14 ................... Cross Section C-C' Showing Isocons of Tritium on Dec. 6, 2006 in pCi/L Figure 5-15 .................. Cross Section D-D' Showing Isocons of Tritium on Dec. 6, 2006 in pCi/L Figure 5-16 ................... Cross Section E-E' Showing Isocons of Tritium on Dec. 6, 2006 in pCi/L Figure 5-17 .................................................................... Tritium in M W -105B Q 1 through Q4 2006 Figure 5-18 ........................................ Tritium in Down Trending Monitoring Wells 2006, Group 1 Figure 5-19 ........................................ Tritium in Down Trending Monitoring Wells 2006, Group 2 Figure 5-20 ................................................................................. U pw ard Tritium Trend M W -1 1OC Figure 5-21 ................................................................................... Tritium in M W -107C 2003-2006 F igure 5-22 .................................................................................................. T ritium in C FW -6 2006 Figure 5-23 ............................. FSS Tritium Soil Concentrations in Concrete Rubble Storage Area Figure 6-1 ........................................................................... Location of K now n Bedrock Elevations Figure 6-2 ..................................................................... Location of Borings and M onitoring W ells Figure 6-3 ..................................................................... Groundw ater M odel Finite-D ifference Grid Figure 6-4 ...................................................... Pre-demo Groundwater Model Boundary Conditions Figure 6-5 ............................................................................... Elevation of Top of B edrock Surface Figure 6-6 ................................................................... Layer 1 Hydraulic Conductivity D istribution Figure 6-6A ....................................... Cross Section along Center of Row 22 of the Model Showing Layering and Horizontal Hydraulic Conductivity iv

Figure 6-6B ............. Cross Section along Center of Column 48 of the Model Showing Layering and Horizontal Hydraulic Conductivity Figure 6-7 ................................................................... Layer 2 Hydraulic Conductivity D istribution Figure 6-8 ................................................................... Layer 3 Hydraulic Conductivity D istribution Figure 6-9 ................................................................... Layer 4 Hydraulic Conductivity D istribution Figure 6-10 ................................................................. Layer 5 Hydraulic Conductivity D istribution Figure 6-11 ................................................................. Layer 6 Hydraulic Conductivity D istribution Figure 6-12 ................................................................. Layer 7 Hydraulic Conductivity D istribution Figure 6-13 .......................................... Layers 8, 9, 11 and 13 Hydraulic Conductivity Distribution Figure 6-14 ............................................................... Layer 10 Hydraulic Conductivity D istribution Figure 6-15 ............................................................... Layer 12 Hydraulic Conductivity D istribution Figure 6-16 ........... ................... ............................. Layer 14 Hydraulic Conductivity Distribution Figure 6-17 ............................................................... Layer 15 Hydraulic Conductivity D istribution Figure 6-18 ...... Average Annual Recharge Rates During Operational History of the Nuclear Plant Figure 6-19 ....................... Model Layer 1 Property Zones for Specific Storage and Specific Yield Figure 6-20........... Model Layers 2, 3 & 4 Property Zones for Specific Storage and Specific Yield Figure 6-21 ....... Model Layers 5, 6, 7 & 8 Property Zones for Specific Storage and Specific Yield Figure 6-22 ........... Model Layer 9 Property Zones for Specific Storage and Specific Yield Figure 6-23 ............................................................... M odel Layers 10, 11, 12 & 13 Property Zones for Specific Storage and Specific Yield Figure 6-24 ..................... Model Layer 14 Property Zones for Specific Storage and Specific Yield Figure 6-25 ..................... Model Layer 15 Property Zones for Specific Storage and Specific Yield Figure 6-26 ........................................................................... Cum ulative Precipitation at Row e M A Figure 6-27 ................................................. Observed vs. Computed Average Annual Head Values F igure 6-28 ................................................................................................... O bserv ed vs. R esiduals Figure 6-29 .................................................. Observed vs. Computed Values for Vertical Gradients Figure 6-30 .................................................. M odel Residuals for Verification Calibration Data Set Figure 6-31 ........................................................................... M odel Param eter Sensitivity A nalyses Figure 6-32 ............. Comparison of MW-I07C Pumping Test Measured v. Simulated Drawdowns Figure 6-33 ................................... Phreatic Surface Groundwater Contours during Plant Operation Figure 6-34 ................. Model Layer 3 Groundwater Contours during Plant Operation Figure 6-35 ..................................... Model Layer 5 Groundwater Contours during Plant Operation Figure 6-36 ..................................... Model Layer 7 Groundwater Contours during Plant Operation Figure 6-37 ....... ......... Model Layer 10 Groundwater Contours during Plant Operation Figure 6-38 .................................. Model Layer 12 Groundwater Contours during Plant Operation Figure 6-39 ................................... Model Layer 14 Groundwater Contours during Plant Operation Figure 6-40 ................................... Model Layer 15 Groundwater Contours during Plant Operation Figure 6-41 ................................. Layer I Hydraulic Conductivity Distribution in Post-Demo State Figure 6-42 ................................. Layer 2 Hydraulic Conductivity Distribution in Post-Demo State Figure 6-43 ....................................... Simulated Change in Groundwater Elevation, Model Layer 2 in Post-Demo State, Average Annual Steady-state Recharge Figure 6-43A .............. Phreatic Surface Contours in Post-Demo State, Average Annual Recharge, and Particle Track from Top Model Layer at MW-107 Figure 6-44 ........................ Reverse Particle Track from Sherman Spring for 760 day Travel Time Figure 6-45 .... Comparison of Measured vs. Simulated Tritium Concentrations in Sherman Spring Figure 6-46 .................... Model-simulated Tritium Distribution in Layer 1 from IXP Leak in 1963 v

Figure 6-47 .................... Model-simulated Tritium Distribution in Layer 3 from IXP Leak in 1963 Figure 6-48 .................... Model-simulated Tritium Distribution in Layer 7 from IXP Leak in 1963 Figure 6-49 .................. Model-simulated Tritium Distribution in Layer 14 from IXP Leak in 1963 Figure 6-50 .................. Model-simulated Tritium Distribution in Layer 15 from IXP Leak in 1963 Figure 6-51 .......................................................................... Concentration of Tritium in M W -107C Figure 6-52 ..................... Tritium Conc. vs. Time at Resident Farmer Well at MW-107C Location List of Appendices Appendix A Boring Logs and Monitoring Well Installation Diagrams for Fall 2006 Well Installation Appendix B-I 2004-2005 Hydrographs Appendix B-2 Winter 2006 Hydrographs Appendix B-3 Stacked Hydrographs at Multi-Well Clusters Appendix B-4 Hydrographs from Pressure Transient Testing Appendix C 2006 Field Parameters Appendix D 2006 Radionuclide Analytical Results for YNPS Monitoring Wells Appendix E Tritium Trend Analysis vi

Executive Summary Quarterly groundwater sampling at YNPS was conducted during 2006 to support NRC License Termination. Groundwater samples were taken all four quarters during 2006 and were analyzed for both routine parameters (gross alpha, gross beta, tritium, gamma emitting radionuclides, and Sr-90) and Hard-To-Detect radionuclides (alpha, beta and X-ray emitting, fission and activation product radionuclides). Boron and general geochemistry parameters (alkalinity, sulfate, chloride, calcium, sodium, potassium, and magnesium) were analyzed in all groundwater samples in the second quarter 2006 only.

Previous studies have provided a Conceptual Site Model that includes four hydrogeologic units at the site:

• a water table aquifer that occurs in stratified drift (glaciofluvial deposits),

• a glacial till unit with multiple water-bearing sand lenses;

• a glaciolacustrine unit with multiple water-bearing sand lenses; and

• a bedrock aquifer.

In these four hydrogeologic units, groundwater occurs under unconfined, semi-confined, and confined conditions. The previous studies have also identified the former spent fuel pit/ion exchange pit as the significant source area for tritium at the YNPS site. This source area was remediated via soil removal in summer and fall 2005.

In summary, tritium was the only radionuclide detected in site groundwater. Tritium concentrations ranged from non-detect values to values in excess of 40,000 pCi/L, and generally exhibited decreasing concentrations through the 2006 quarterly sampling program, The groundwater sampling results were used to develop plan-view plume maps of the glaciofluvial and glacial till aquifers and cross-sections illustrating the vertical distribution of tritium. A plume of tritium-contaminated groundwater occurs within the glaciofluvial aquifer, and is mapped from the former spent fuel pit/ion exchange pit source area across the YNPS site towards the Deerfield River. Tritium concentrations in the plume within the glaciofluvial aquifer range from about 10,000 pCi/L near the source area to values less than 1,000 pCi/L near the Deerfield River.

A deeper plume within sand lenses in the glacial till is also identified. The deeper plume has less aerial extent relative to the plume in the glaciofluvial aquifer, but has tritium concentrations up to 30,000 pCi/L. Migration of tritium in the glacial till is minimized due to the lower hydraulic conductivity measured for the glacial till rdlative to the glaciofluvial aquifer. The tritium-contoured cross sections demonstrate that tritium has migrated into the deeper portion of the glacial till beneath the former spent fuel pit/ion exchange pit area, but tritium has not moved a significant distance downgradient of the source area in the deeper portions of the till. In contrast, tritium has migrated from the

spent fuel pit/ion exchange pit source area downgradient to the Deerfield River within the glaciofluvial unit.

An evaluation of tritium trends was conducted in all monitoring wells included in the LTP monitoring program. A total of 43 monitoring wells had no discernable trends and are characterized as stable, while 10 monitoring locations had statistically-determined downward trends for tritium. One monitoring well had an upward trend, but the tritium concentrations were an order of magnitude below the USEPA MCL of 20,000 pCi/L.

The groundwater laboratory results for radionuclides were non-detect for all radionuclides except for tritium, and as such were below all threshold levels developed in License Amendment No. 158.

A three-dimensional flow and transport groundwater model has been developed to support the decommissioning of the Yankee Nuclear Power Station in Rowe, MA. The modeling work began in July 2006. This model covers a large area on both sides of the Deerfield River so that the model boundaries are naturally located on streams and groundwater divides far from the nuclear plant site. The finite-difference grid cells are discretized with variable spacing from 25 feet near the center of the plant site to as far apart as 400 feet near the outer limits of the model. The model consists of 15 layers: 13 soil layers and two bedrock layers. The model extends 500 feet into bedrock.

The model was used to verify the direction and time of travel from the ion exchange pit to Sherman Spring and then to simulate the May 1963 leak from the ion exchange pit and compare measured Sherman Spring tritium concentrations over time with the simulated results. These results are in good agreement. The model has also been used to simulate the change in tritium concentration from April 2006 through December 2006 at MW-107C, again, with good agreement.

The model reproduces the magnitude of pressure transient responses to the MW-107C pumping tests and a variety of other pressure transient events. Although groundwater gradients between the bedrock and the next higher monitoring wells at several locations were not faithfully reproduced as to direction, most gradient directions were preserved among the 54 pairs tested.

The model was used to evaluate the potential attenuation of tritium in MW-107C, which has been identified as the only portion of the site even close to exceeding LTP dose standards or EPA MCLs. Because the thin sand zone in which MW-107C is located is incapable of supplying the needs of the hypothetical resident farmer well as specified in the LTP, other soil units above and below MW-107C were tried in various combinations that would produce the required well yield, but at the highest dose. This resulted in combining other soil units with lower tritium concentrations but higher flow rates, such that the well concentration would be 8150 pCi/L in April 2007, decreasing to 5100 pCi/L in April 2009.

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Based on the model results, a randomly located resident farmer's well at the site would produce water at less than LTP dose limits or EPA MCLs. The model also suggests that the highest point concentrations of tritium (in the glacial till above and below MW-107C) will decrease below the EPA MCL of 20,000 pCi/L about April of 2009. However, the tritium concentration in MW-107C may decrease below the MCL concentration as soon as June 2007 based on the current trend of sampling results.

Based on the results for the 2006 quarterly groundwater sampling, tritium trend analysis, and groundwater modeling, we believe that groundwater at the YNPS site meets the closure requirements specified in the LTP. While one monitoring well exceeds the USEPA MCL of 20,000 pCi/L (as of the fourth quarter sampling results), the modeling results demonstrate that tritium concentration in the resident farmer well will be below the MCL value.

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1.0 Introduction This report documents the groundwater monitoring activities conducted at Yankee Nuclear Power Station (YNPS) for the four quarters of 2006. The purpose of the groundwater monitoring program is to verify that groundwater quality conditions at Yankee Nuclear Power Station (YNPS) meet the closure requirements as defined in the License Termination Plan (LTP) and Nuclear Regulatory Commission (NRC) License Amendment No. 158 (Reference 1-1). The LTP specifies quarterly groundwater sampling for tritium and other radionuclides as appropriate, and that groundwater monitoring be conducted after decommissioning is completed but before license termination. The groundwater monitoring program was designed to determine the extent and range of radionuclide groundwater contamination, and to support final status survey (FSS). Figure 1-1 shows the location of YNPS and the surrounding area, and Figure 1-2 shows the current 10 CFR part 50 Licensed Site Boundary.

This report summarizes the site geology and hydrogeology in Section 2 and groundwater sampling and analysis activities and laboratory analytical results are described in Section 3 and 4, respectively. Spatial and trend analysis of tritium are presented in Section 5 and results of groundwater modeling are provided in Section 6. Conclusion and recommendations for the groundwater monitoring program are provided in Section 7.

1.1 Groundwater Monitoring Program Overview and Site Setting The Yankee Nuclear Power Station (YNPS) terminated power operation in 1991 and completed physical decommissioning work in the fall of 2006 under an approved Nuclear Regulatory Commission (NRC) license termination plan (LTP) (Reference 1-1) As of September 2006, all structures, systems and components planned for removal have been removed; site soils have been surveyed for radiological contamination; impacted soils in the unsaturated zone have been excavated and removed; and imported fill has been placed to achieve the final site grade. Accordingly, all potential primary sources of groundwater contamination have been removed from the site. A site map showing all former site structures and key site features is provided in Figure 1-3.

A groundwater monitoring program was initiated in support of decommissioning during the spring of 1993, with installation of ten monitoring wells. Seventy-one additional monitoring wells have been installed since 1993 as part of seven drilling campaigns, the most recent of which was completed summer 2006. A summary of the monitoring well completion details for the monitoring program and a history of surveyed well locations are included in Tables 1-1 and 1-2. Monitoring well locations included in the LTP monitoring program are shown in Figure 1-4. The results of previous groundwater investigations are documented in References 1-2, 1-3,1-4, and 1-5. Reference 1-6, Groundwater Compliance Plan for License Termination for Yankee Nuclear Power Station, details the ongoing groundwater monitoring that was completed in 2006 to demonstrate compliance with the criteria for license termination.

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The early monitoring programs in the late 1990s identified a plume of tritium in shallow groundwater, with maximum concentrations of about 5,000 picocuries per liter (pCi/L).

A more rigorous investigation began in 2003 and identified a second plume within a deeper, semi-confined geologic formation, with tritium concentrations up to 48,000 pCi/L. Follow-up drilling campaigns were completed in 2004 and again in 2006, to further investigate and bound the groundwater impacts identified by earlier investigations. No plant-related radionuclides other than tritium have been identified in the groundwater. YNPS has completed dose assessments for the existing on-site groundwater in accordance with the LTP and found a dose contribution of less than one millirem per year associated with groundwater at the MCL concentration of 20,000 pCi/L (Reference 1-1).

Prior to 2003, groundwater samples had been collected from all site monitoring wells generally three or four times per year, although not on a routine schedule. These samples were analyzed for tritium and gamma-emitting radionuclides. Two sample rounds (November 1997 and February 1998) included analysis for strontium. Beginning in August 2003, groundwater samples were collected from available monitoring wells on a quarterly basis and analyzed for a wider range of radionuclides, including ten gamma emitters, tritium, gross alpha, gross beta, and eleven hard-to-detect nuclides (Reference 1-3 and 1-4). Decommissioning activities made safe access to several wells impossible and groundwater sampling was suspended for the second and third quarters of 2005. The quarterly schedule of sampling resumed in the final quarter of 2005 and has continued through 2007. One additional quarterly sampling round is scheduled for spring 2007, and will be used to verify and confirm the trends established through 2006.

1.2 Groundwater Monitoring Program Plans and Procedures The 2006 groundwater sampling and analysis was conducted in accordance with the Groundwater Compliance Plan for License Termination for Yankee Nuclear Power Station (Reference 1-6) and following specific guidance under applicable YNPS procedures. The YNPS procedures utilized for the groundwater monitoring activities include: 1) YNPS Site Characterization and Site Release Quality Assurance Program Plan AP-9601; 2) Ground and Well Water Monitoring Program for YNPS Site AP-8601; and, 3) Groundwater Level Measurement and Sample Collection in Observation Wells DP-9745 (References 1-7, 1-8, and 1-9).

A sample event plan was prepared in accordance with AP-8601 and DP-9745 for each quarterly and monthly groundwater sampling round conducted at YNPS (References 1-8 and 1-9). The sample event plan specifies the number and type of containers to be filled with sample groundwater from each well, preservation and handling requirements for samples, and analyses to beperformed on samples from each well.

The methodology for representative sample collection and field measurements, including groundwater levels, is described in Groundwater Level Measurement and Sample Collection in Observation Wells (DP-9745) (Reference 1-9).

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2.0 Site Geology and Hydrogeology 2.1 Background The YNPS site geology has been investigated at intervals throughout the plant design period and operational life. Site hydrogeology was not studied in detail until decommissioning was underway. The most intensive studies have occurred from 2003 to present, culminating in the development of a groundwater fate and transport model that has helped to refine the hydrogeological conceptual site model.

The pre-design exploration of the site consisted of a few borings and some seismic refraction analysis in 1956 (Reference 2-1). A somewhat more elaborate investigation was performed as part of the NRC Systematic Evaluation Program (SEP) studies performed in 1979 through 1981 at the site (References 2-2 and 2-3). With the decommissioning of the plant, monitoring wells were installed and sampled. In 2003, Framatome (Reference 2-4) conducted a review of all prior investigations and groundwater studies. At this point, Radiation Safety and Control Services (RSCS) took charge of site hydrogeologic investigations relating to the Nuclear Regulatory Commission (NRC) License Termination Plan (LTP) (Reference 1-1).

On a parallel track, ERM, acting as the Licensed Site Professional (LSP) under the Massachusetts Contingency Plan, 310 CMR 40.0000, began site investigations in 2000 to evaluate the presence of oil and hazardous materials. ERM submitted a series of reports to the Massachusetts Department of Environmental Protection (MADEP) beginning in 2001 continuing to the present that document the presence and remediation of various non-radiological substances on the site. Separate borings were installed, and soil and water sampling were conducted by RSCS and ERM to satisfy the respective requirements of the NRC and the MADEP.

In 2006, Yankee Atomic Electric Company (YAEC) retained Stratex, LLC, to review the existing radiological groundwater investigation program, to model the groundwater at the site, and to predict the fate and transport of radionuclides at the site following license termination. During 2006 a pumping test was conducted on MW-107C, the location of the highest groundwater concentration of tritium at the site. Numerous other short-term drawdown tests (called "pressure transient" tests) were conducted at various monitoring wells with pressure transducers located in surrounding wells in an effort to identify the hydraulic continuity of various sand seams identified in drilling that contained significant tritium concentrations. Also in 2006, all of the previously acquired monitoring well water level data captured by continuously recording dataloggers since 2004 were processed and put into graphs and correlated with various possible influences.

Since 2003, YAEC has provided a series of periodic reports to the NRC documenting new hydrogeologic investigations as they were completed, and provided updates on monitoring well radionuclide concentrations from sampling episodes spread through the decommissioning period. The most recent report, Reference 1-5, provided a thorough review of the hydrogeologic conceptual site model and the pumping tests and transient 6

pressure tests done to evaluate the continuity of sand layers within the glacial till and glaciolacustrine units.

2.1.1 Geology and Hydrogeological Conceptual Model The stratigraphy and hydraulic relationships beneath YNPS comprise a complex, multi-unit groundwater flow system. A hydrogeologic conceptual site model (CSM) has been developed for YNPS based on both the regional geologic setting and on the hydrogeologic and chemical data collected at the site since the first monitoring wells were drilled in 1993 to support decommissioning. Four hydrogeologic units have been identified at the site:

1) a water table aquifer that occurs in stratified drift (glaciofluvial deposits),

2) a glacial till unit with multiple water-bearing sand lenses;

3) a glaciolacustrine unit with multiple water-bearing sand lenses; and

4) a bedrock aquifer.

In these four hydrogeologic units, groundwater occurs under unconfined, semi-confined, and confined conditions. Section 6-4 of this report summarizes the geology of the site and how it has been conceptualized into a layer structure that can be modeled.

The former reactor site lies relatively low in the Deerfield River valley, which has a great degree of vertical relief with steep sideslopes. The upper slopes of the valley walls are primarily exposed bedrock and thin glacial till. One exception to this is the thick glacial till section extending southward from the former reactor site. The till is over 200 feet thick near the valley floor level and extends up the slope about 700 feet in elevation above the Sherman Reservoir level. Small springs and streams drain the upland area, which sheds most of its precipitation to the local streams and the glaciofluvial terrace deposits. Recharge entering the upland areas seeps deep into the rock and moves laterally toward the Deerfield River, rising in the bottom of the River valley.

At the YNPS site the layered glacial geology is complex. The primary flow path within the glaciofluvial deposits from the Spent Fuel Pool and Ion Exchange Pit (SFP/IXP) was initially north, and then bifurcated to produce a westward path. In the downstream side of Sherman Dam where the dam meets the original land, the glaciofluvial deposit thins and Sherman Spring was created where the phreatic surface daylights. Although most of the leaked tritium from the SFP/IXP flowed northward toward Sherman Reservoir and westward toward the Deerfield River below the dam within the upper glaciofluvial deposits, some of the leaked tritium seeped deeper into the upper glacial till. Within the glacial till there are thin sand seams within which the tritium would collect and be captured in monitoring wells. Beneath some areas of till lies a glaciolacustrine layer with thin sand seams. Almost all the tritium that seeped beneath the glaciofluvial unit was contained within the glacial till and did not enter the glaciolacustrine unit. Earlier versions of the CSM held that the low permeability glacial till was unsaturated between saturated sand layers. However the MW-I 07C pumping test and pressure transient tests 7

showed that the till layers that vertically separated the sand seams were saturated and transmitted water pressure transients. The water pressure transient tests showed that the sand seams were limited in lateral extent to about 150 feet for the most extensive layers.

Because of the relatively short distance between the former reactor site and the Deerfield River, the contamination did not go deep and only minor tritium contamination occurred in the bedrock near the MW- 107 area where bedrock was shallower than to the north and west.

2.1.2 Work Completed Since 2006 Interim Groundwater Report Although the main purpose of this report is to summarize the final status of the groundwater flow system and its radiological content at the YNPS site, a secondary purpose is to complete the documentation of all that has been done to study the groundwater regime at the site. Since the Interim Groundwater Report (Reference 1-5),

the final site grading has been completed. Final borings have been completed and the logs of borings currently in use on the site that have never been submitted before are included in Appendix A. These logs include CB-3R, CW-5R, MW-6R, MW-104D, and MW-1 12A. The monitoring well hydrographs for both the long-term records and the short-term pressure transient hydrographs have been finalized and analyzed. The 2006 third quarter and 2006 fourth quarter groundwater sampling events have been completed.

The groundwater modeling has been completed and the future fate and transport has been simulated. A tritium trend analysis has been completed on each well. Finally, the status of the site is compared with the criteria of the LTP. This documentation is presented and summarized in this report along with its significance.

2.2 Groundwater Elevation and Flow Direction 2.2.1 Site Measurements of Groundwater Elevation Table 1-1 contains a summary of the details pertaining to all of the monitoring wells used in the 2006 monitoring program. Table 1-2 contains a history of the surveyed location and reference elevations of the monitoring wells used since 1993. Because some wells were destroyed and then replaced during demolition, or fill was added around certain wells, the reference elevations changed with time and the depth-to-water measurements have to be related to the specific well reference elevation that existed at the time of the measurement.

Many wells had continuous water level recordings made with the use of in-situ pressure transducers and dataloggers. Table 2-1 shows the period of record for each well for which a credible hydrograph could be obtained from the datalogger record. Appendix B contains the hydrographs developed from these records, along with some additional hydrographs that will be explained in more detail below.

Some of the data quality issues that had to be resolved in processing the raw transducer data were the following:

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1) Relating the pressure recorded by the transducer to a reference elevation. Some of the transducer cables were vented, but some were not. The latter transducer records had to be corrected by a software program that removed site barometric pressure variations (which were continuously recorded on the site). Some records were not calibrated with any hand measurements and the graphs in Appendix B note this on each graph for which no calibration to a reference elevation was available. In other situations, a graph would show a sharp jump in elevation at a point in time and there was only one reference elevation calibration point. A decision had to be made in each case as to how to deal with these sharp jumps. In most cases, the non-calibrated side of the jump was shifted across the board to match the elevation on both sides of the jump. Where multiple readings where taken within the time span of one continuous record, the graph was initially pinned at one elevation, then the differences between the other reference elevations in time and the respective time graph predictions were averaged. Transducer drift, where the error between measured and predicted elevation seems to become larger with time, was only corrected for the monitoring wells involved with the MW-107C pumping test where many hand measurements were taken on each monitoring well used as part of the test.

2) Relating the pressure recorded to a common time standard. An effort was made to bring all measured data that were related to the water level variations of each well to the common time standard of Eastern Standard Time. This meant that the record of Sherman Reservoir elevation fluctuations and flow releases from Sherman Dam had to be corrected in some instances from Daylight Savings Time. Some, but not all, records of MW-I107B, MW- 107E, and MW-II OB had to be corrected for a 4-hour time shift for which no verifiable explanation could be developed.

3) Switching of Well IDs. It became apparent in the course of detailed study of the graphs that certain graphs did not represent the record of the wells they purported to represent. On further examination it was found that some were indeed switched and the records were revised accordingly.

4) Large drops or jumps in data values. Most wells show large drops and/or jumps on days when hand measurements of water levels were made or water quality sampling occurred, due to displacement and/or drawdown by measurement and sampling devices.

When pressure transient testing was performed with a submersible pump, the heat of the pump also caused large temporary increases in temperature in the well water as measured by the transducer.

Many hand-measured water levels were recorded over time for the monitoring wells as part of synoptic water level measurements or prior to water sampling. Table 2-2 summarizes all of the hand-measured data with the exception of a few miscellaneous data that were used to set the reference elevations of the pressure transducers and the hand-measured data taken during the MW-107C pumping test. The miscellaneous reference elevation measurements were used in tying the datum to the respective hydrograph records as recorded by the pressure transducers. The MW-107C data are included in Appendix B of Reference 1-5.

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2.2.1.1 Vertical Groundwater Gradients All of the MW-100-series wells except for MW- 112 consist of clusters of closely-spaced individual wells with the screened zones separated vertically from one another to sample discrete geologic units. Most, but not all, of these well clusters had a well located in the top of bedrock. CFW-3 and CFW-4 also constituted a well cluster within the fill and underlying assumed glaciofluvial deposits of the Southeast Construction Fill Area (SCFA). For those well clusters for which simultaneous datalogging of pressure transducers was done in multiple wells, the hydrographs have been combined on the same graphs in Appendix B-3. For purposes of comparing modeled vertical groundwater elevation differences with measured groundwater elevation differences, Table 6-8 in the groundwater modeling section lists the head differences within each well cluster. In addition, Table 2-4 has a column indicating general direction of the vertical groundwater gradient.

All of the wells in the upper soil section have downward gradients. Near the bedrock surface, MW- 101, MW- 102, MW- 106, MW- 107, MW- 109, and MW-I 10 showed upward gradients from the bedrock. MW-104D at 40 to 45 feet in a sand layer in glacial till showed an upward gradient compared to the shallow well at MW-104A in the glaciofluvial deposit.

The upward gradients at or near the bedrock surface suggest, based on the modeling as discussed below, that there are relatively permeable zones in the bedrock or just above the bedrock surface that permit this upward flow at these points. In the case of MW-104D, this is probably being driven by seepage through a permeable layer within the till in the south abutment of Sherman Dam.

2.2.2 Groundwater Contour Maps Contour maps of synoptic hand-measured water elevations have been presented in previous reports submitted to the NRC since 2003. The 2006 Interim Groundwater Report (Reference 1-5) contained groundwater contour maps for the main hydrogeologic units for the spring and summer 2006 sampling quarters.

2.2.2.1 Fall Quarter 2006 Groundwater Flow Maps Figure 2-1 shows the groundwater contours on the surface of the upper sandy phreatic aquifer, the glaciofluvial unit, for September 11, 2006. The contours are relatively evenly-spaced and the inferred flow direction, perpendicular to the contours, is similar to past maps. Figure 2-2 shows the contour map of the groundwater heads in the "upper till" (identified as "UT" in some tables and figures) soil unit. The contours suggest a general westward flow. The contours are farther apart near the flatter land near the reservoir, then the contours become closer together westward of the axis of the dam, leading down to the River. The gradient westward of the dam is steeper in the upper till than in the glaciofluvial deposit. Figure 2-3 shows the contours in the lower glacial till and glaciolacustrine unit (identified as "LT-GL"). Because the glaciolacustrine unit is 10

not present everywhere under the YNPS site, it is combined with the somewhat arbitrarily demarcated lower till to represent the lower soil above the bedrock. The gradient is about equal to that in the glaciofluvial layer and the direction of flow is approximately the same. Figure 2-4 shows the September 2006 groundwater contours in the shallow bedrock under the site. The implied flow pattern is somewhat more complex than the other patterns. Although the overall flow direction is to the west, there is a small divide coming off the rock knob to the east of the former reactor site. The gradient is flatter next to the reservoir than to the west of a line between MW-108 and MW-109, where it is steeper than any of the overlying horizontal gradients.

2.2.2.2 Winter Quarter 2006 Groundwater Flow Maps Figures 2-5, 2-6, 2-7 and 2-8 represent the same groundwater flow maps as shown in the previous section except that these latter figures are for the groundwater sampling time of December 4, 2006. Implied flow patterns are identical between the September and December sampling periods. Groundwater elevations are slightly higher in December than September, but otherwise the maps are nearly identical between the two sampling periods.

2.2.4 Groundwater Influences Detailed analysis and cross correlation among the various hydrographs and various forces that can change water levels have yielded an understanding of the factors affecting the various monitoring well water levels. These are discussed in more detail below. Table 2-4 summarizes the relative strength of the various influences and provides other important data derived from the hydrographs relating to each well.

2.2.4.1 Precipitation All of the hydrographs after August 1,2004, presented in Appendix B-1 and B-2 have precipitation superimposed on the right-hand Y-axis, in inches per day. The site had a recording precipitation gauge with a tipping bucket that recorded each 0.01 inches with a date and time stamp. This gauge operated from August 1, 2004, through July 2006.

Unfortunately, the site data for the period January 1, 2006, through May 31, 2006, were lost and data from Amherst, MA, were used in its place. The daily and cumulative precipitation at the site over the period is discussed in Section 6 (see Figure 6-26).

Most wells at the site show a response to rainfall, although the rise of elevation per inch of rainfall varies among the wells and the delay between the time of rainfall and the occurrence of water rise varies. An example of a quick and large response is a 2.2-foot rise in water level in shallow well CB-I (Appendix B-i) on September 18, 2004, in response to a 3. 1-inch rainfall. Most of the bedrock monitoring wells also rose rapidly and with large responses to rainfall. It is the low-yield wells deep in the till or glaciolacustrine deposits that had small and delayed responses such as in MW-1O1C (Appendix B-2) and MW-104C (Appendix B-1). Section 6.6.4.3 contains more information on the response of site wells to precipitation recharge.

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2.2.4.2 Recession Recession is the decline in groundwater elevation following a recharge event. This decline is visually evident on most hydrographs. In low-yielding wells such as MW-103C (Appendix B-l) the rise and fall of the well can only be seen in a seasonal context and not in response to particular precipitation events. In the analysis of the MW-107C pumping test, the recession that was occurring in each well during the test was calculated and added back to neutralize the differing rates of recession on the calculation of drawdown.

2.2.4.3 Barometric Atmospheric pressure variations cause variations in water well levels. An increase in barometric pressure causes a depression in water level. A decrease in barometric pressure causes an increase in water elevation. The effect on phreatic water levels is very small; it has a larger effect on confined aquifers. The measure of how much barometric pressure variations affect well water levels is called barometric efficiency, which is the ratio of water level change in a well, in, for example, feet, divided by the barometric pressure change, in equivalent feet of water. In the evaluation of the MW-107C pumping test, the barometric efficiencies were calculated for each well in which pressure transducers were installed, and the effects neutralized so that small variations in actual drawdown could be detected. The typical range of barometric efficiency for the wells on this site is 10 to 60%. MW-107B has a barometric efficiency of about 50%, as shown in Appendix B, the "107Bsamplecorr" graph in Reference 1-5.

2.2.4.4 Earthtides Just as the motion of the sun and moon relative to the earth cause ocean tides, they also cause earthtides where the water is compressed in confined aquifers as the earth changes shape ever so slightly in response to expansions and contractions of the crust in response to the changes in gravitational pull of the moon and sun as the earth rotates. As explained in Section 5.1 of Reference 1-5, there appear to be two separate earthtide components in the datalogger records at the site. Figure 5-4 of Reference 1-5 shows a typical breakdown of the earthtide for MW-107B, as programmed with the theoretical parameters for components M2 and 01. Each component has its own repeating frequency and amplitude that changes with the moon phase. When added together, they produce a characteristic signature with an amplitude of about 0.15 feet in MW-107B.

The amplitude and frequency of each earthtide component was estimated for each well fitted with pressure transducers during the MW-I 07C pumping test, then inverted and added back to the record to neutralize the effect of earthtides on the drawdown measurements. The typical range of earthtide effects in water levels on the site is 0.05 feet to 0.2 feet of total amplitude.

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2.2.4.5 On-site Water Supply Well Through the analysis of the various well hydrographs it became apparent that there was an occasional source of drawdown that affected some of the wells on the site, particularly the bedrock monitoring wells in the vicinity of the former reactor. The only water well known within a large radius of the site is the well that supplies the site with water, identified as "Plant Well" on Figure 1-4. This well was drilled in July 1999 and had a reported yield of 60 gallons per minute at 21 feet below the top of bedrock. Based on the location of site bedrock monitoring wells that appear to respond to the use of the well, this high yield zone appears to extend north from the plant well through the former reactor area (see more discussion in Section 6.7.2). There is a water meter somewhere in the site water supply system that is read once per week. Table 2-3 records the weekly water use on the site between December 2005 and July 2007. Water use has decreased over this time period as site construction activities decreased. There is a large storage tank that is part of the water system, so the well is not used every day.

The response in monitoring wells from plant well use is most prominent in the bedrock wells, but other wells in till, such as MW-107D, also respond. It is hypothesized that some of the deeper soil monitoring wells in the former reactor area respond to the plant well through the pressure being transmitted from areas where sand seams in which the monitoring wells are located are in contact with the rising bedrock to the east of the former reactor site. The magnitude of response in monitoring wells would be affected by a number of site hydrogeologic parameters in addition to the pumping rate and the length of the pumping period. The installed pump is rated as 5 gallons per minute and the drawdown in the pumping well would not be great if the yield is 60 gallons per minute.

The typical magnitude of drawdown for wells that respond in a significant way to the plant water well is a few feet.

2.2.4.6 Reservoir and Tailwater Elevations Sherman Reservoir elevation is manipulated daily as part of a hydropower production system. The typical range of fluctuation across a day is about two feet. A typical pattern of Reservoir elevation change is shown in Appendix B, the "107Bsamplecorr" graph, in Reference 1-5. As shown in Table 2-4, not many wells responded to the rise and fall of the Reservoir. Some of the best responses are wells in bedrock, particularly CW-10, which is located close to the edge of the Reservoir. CW- 10 has a directly linked response, but other monitoring wells respond in different ways, as described in Table 2-4. MW-108A, another well located close to the Reservoir, shows small responses to the daily rise and fall of the Reservoir, but when the Reservoir tends to rise in average level over a week, that rise in average level is more directly translated to the well. In some of the more distant bedrock wells that respond, the effects are delayed, are diffuse, or are more related to the level of the average position of the reservoir over a period of days. More detail on the response to Reservoir levels is included in Section 6.7.4.

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While evaluating the shorter hydrograph records for MW-i 13C, a periodic drawdown and recovery effect was noticed that could not be tied to either the Reservoir fluctuation, the onsite well, nor any other offsite well. After further investigation and comparison of flow releases from Sherman Dam, a good correlation was found between Dam discharge rates and changes in level in MW-1 13C. This effect was first described in the 2006 Interim Groundwater Report (Reference 1-5). The analysis of this effect was refined some as part of the groundwater model development as described in Section 6.7.3. The 5-day graph of MW-1 13C presented in Appendix B-4 of this report is slightly revised from that provided in Reference 1-5, as the graph in the earlier report did not correct the times of discharge for the fact they were recorded on a Daylight Savings Time basis, whereas the well hydrograph is on Eastern Standard Time. Notice that maximum range of change due to release rate fluctuation is about one foot. It is interesting to note that MW- I13C is located about 130 feet below ground surface in the second significant sand seam in glacial till at that location; the River elevation next to the well is 1025 feet, and the average water elevation in MW-I 13C is 1031 feet. The only other wells that show a tailwater elevation response are MW-106B, C, &D, which are located close to the tailwater area, but do not show the magnitude of response seen in MW-I 13C. The hypothesis is that the sand seams in which the deeper soil wells reside may butt up against the bedrock wall that forms the northwest side of the Deerfield River in this area.

2.2.4.7 Freeze-Thaw and Snow Melt Although the winter of 2006 did not have much snow, the winter of 2005 did and a large snow melt event is recorded near the end of March when temperatures warmed above freezing (Figure 2-9) and many wells such as CB-2 (Appendix B-i) rose on the order of 5 feet or more. As shown in Table 2-4, only a few wells (deep ones) do not respond to a snow melt event. One low-yield well, MW-103C, showed a peculiar pressure spike when temperatures rose above freezing on March 7, 2006.

2.2.4.8 Stormwater Basin Management To control sediment discharge on the site during major earthwork in the spring and summer of 2006, a series of stormwater basins were created in the ground that provided both for temporary holding of precipitation runoff and for ground infiltration of runoff.

Figure 2-10 shows the location of the temporary stormwater basins and an area on the rock knob east of the former reactor site where stormwater was pumped to discharge on the ground there. The three identified East Side Stormwater Basins were sometimes pumped in series from the north to the south, and then up to the discharge area on the side of the rock knob.

The effect of filling these basins became apparent during the analysis of the MW-107C pumping tests (Reference 1-5). During the recovery period of the 24-hour test, many monitoring well water elevations rose significantly above elevations at which they began.

Field notes indicate that stormwater was being moved around the site and basins near MW-107C were being filled by pumping from other areas. The PAB Alleyway Basin 14

and the East Side Basin both had portions of the basins that are near areas of shallow bedrock. The hypothesis is that infiltration from the basins moved down the soil/bedrock interface and moved laterally through sand lenses in the till that butted up against the rock.

2.3 Groundwater Influences During and After Demolition During plant operations, the main restricted area of the site was primarily covered with buildings or asphalt and had a stormwater management system with catch basins and underground stormwater piping that removed potential groundwater recharge from the plant area. Site grading activities related to decommissioning are now complete.

Stormwater catch basins have been removed and underground stormwater piping has been removed or abandoned in place. All runoff is now controlled by site grading and surface swales and ditches. Some concrete slabs, foundation walls, and piping have been left in place and they are shown on Figure 2-11. The final site grading is shown on Figure 2-12. Figure 2-10 shows the locations of the major excavations that were completed on the site, either for soil remediation or for creation of temporary stormwater basins. The surface precipitation infiltration capacity of the site has been changed significantly from what it was in the operational state, as impervious surfaces have been removed and excavations in a sandy glaciofluvial deposit have been filled with more silty, till-like material. The changes in effective recharge rate as a consequence of adding the fill and removing impervious surfaces are discussed in Section 6.4.

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3.0 Groundwater Sampling and Analysis This groundwater condition report includes the laboratory analytical results for four quarterly groundwater-sampling events QI through Q4 2006 and several monthly sampling events. The monthly sampling activities were conducted in the same fashion as the quarterly sampling.

The first quarter (2006 Q 1) sampling event occurred between April 18 and May 3, 2006.

The second quarter (2006 Q2) sampling event occurred between June 26 and July 12, 2006. The third (2006 Q3) and fourth (2006 Q4) quarter sampling events occurred between September 12 and September 21, 2006 and December 4 and December 14, 2006, respectively. The analytical results from Q1 2006 and Q2 2006 and monthly results for January, February and May were presented previously (Reference 1-5). Results for Q3 and Q4 2006 and monthly sampling results for August, October and November 2006 are discussed in Sections 4 and 5.

The groundwater samples were forwarded to an offsite laboratory for radiochemical and inorganic analyses. The sample results for each quarter and monthly sampling event were assessed and validated, and a Data Assessment Report was developed for each sampling episode (References 3-1 through 3-7).

Measurements of field parameters were included as components of the groundwater sampling and are discussed in Section 3.1 and Section 3.2.

Groundwater samples were collected by low-flow sampling methodology utilizing either a peristaltic pump or a bladder pump with dedicated polyethylene tubing. Peristaltic pumps were typically utilized in shallow monitoring wells screened in the glaciofluvial aquifer, while the bladder pumps were used in deeper monitoring wells.

Prior to Q2 2006 groundwater samples at YNPS were typically filtered before analysis.

The groundwater sampling procedure required that all groundwater samples with turbidity greater than five (5) NTU be filtered. The 5-NTU criterion typically was exceeded, and filtering was conducted at the analytical laboratory following preservation in the field.

Beginning with Q2 2006, groundwater samples were not filtered. Using a non-filtered approach minimizes any potential bias associated with filtering. For comparison to the filtered Q1 2006 samples and previous groundwater samples that were filtered, a subset of the analyses conducted in Q2 2006 was analyzed using both filtered and unfiltered aliquots of samples. Filtered and unfiltered aliquots were analyzed for gamma-emitting radionuclides (Cs- 134, Cs-137, Co-60, Nb-94, Sb-125, Eu- 152, Eu- 154, Eu- 155, and Ag-108), tritium, and Sr-90.

No gamma-emitting radionuclides or Sr-90 were detected in either filtered or unfiltered groundwater samples, as all values were below detection (Reference 3-5). Accordingly, 16

the filtered and unfiltered results demonstrate no statistically significant differences for these radionuclides (Reference 3-5).

3.1 Description of Field Measurements Several types of field measurements were recorded in each well prior to sampling. Data obtained from these measurements included groundwater levels, the presence or absence of separate-phase fluid, and water quality parameters. These field measurements are essential components for the evaluation of water quality and hydrogeologic conditions at YNPS.

Depth-to-water measurements were determined using an electronic water level meter with a 0.01 -foot resolution. Water quality parameters recorded included specific conductance, pH, dissolved oxygen, temperature, oxidation-reduction potential and turbidity. These parameters are continuously measured prior to the sampling of each well until they meet the stability requirements of the low flow sampling methodology promulgated by EPA. This procedure is performed to confirm that well conditions have stabilized during the low-flow purging step, indicating enough water has been removed from the well so that a representative groundwater sample can be collected. These parameters were measured using a multi-parameter meter, with sensors arrayed within a flow-through cell. The field parameter data sheets summarizing these measurements are included in Appendix C.

3.2 Summary of Field Measurements The water quality parameter field measurements for the Q I through Q4 2006 sampling events are included in groundwater field sampling logs. The field sampling logs are field notes that document the sampling of each well, and are provided in Appendix C. As recorded in the field logs, the field parameters typically stabilized within an acceptable range.

3.3 Sample Locations The horizontal and vertical coordinates of each monitoring well were surveyed. The horizontal location of each well is referenced to the Massachusetts Mainland State Plane Coordinate System (NAD 83 in feet) and its vertical elevation is referenced to the 1988 North American Vertical Datum (NAVD) in feet. A summary of the coordinates and elevations for all monitoring wells is provided in Table 1-2. Monitoring well locations for wells included in the YNPS monitoring plan are shown in Figure 1-4.

3.4 Laboratory Analysis Groundwater samples for QI through Q3 2006 were analyzed for both routine parameters (gross alpha, gross beta, tritium, gamma emitting radionuclides, and Sr-90) and Hard-To-Detect (HTD) radionuclides (alpha, beta and X-ray emitting, fission and activation 17

product radionuclides). Boron and general geochemistry parameters (alkalinity, sulfate, chloride, calcium, sodium, potassium, and magnesium) were analyzed in all groundwater samples in Q2 2006 only. The analytical program for YNPS groundwater samples is summarized in Table 3-1.

The complete suite of radionuclides included in Table 3-1 was analyzed for all groundwater samples in Ql, Q2, and Q3 2006. As anticipated in theGroundwater Compliance Plan (Reference 1-6), tritium continued to be the only plant-related radionuclide identified in groundwater through Q3. Based on the tritium-only detections through 2006, Yankee proposed a reduced set of analyses for the Q4 2006 sampling campaign. Based on the results through Q3, YAEC proposed to discontinue gross alpha and gross beta analyses and to select radionuclides for which analyses are to be performed, based on the following graded approach:

• Wells that have consistently shown tritium levels below 5,000 pCi/l would undergo analysis for tritium only;

• Wells that have shown tritium levels above 5,000 pCi/I but less than 10,000 pCi/I would undergo tritium analysis, gamma spec analysis, and analysis for C-14, Sr-90, and Tc-99; and

" Wells that have shown tritium levels consistently greater than 10,000 pCi/1 would undergo tritium analysis, gamma spec analysis, and analysis for C-14, Sr-90, Tc-99, Am-241, Pu-238, Pu-239/240, Pu-241, Cm-242, and Cm-243/244.

A summary of the groundwater sampling program for Q4 2006 is included in Table 3-2.

Several monitoring wells were sampled for the complete suite of radionuclides even though the recent results did not fall into the full suite category due to either being a replacement well (CB-3) or a relatively recent monitoring well in the YNPS groundwater monitoring program (MW- 102D, MW- 104D, and MW- 107E) (Table 3-2).

The laboratory analytical results are discussed in Section 4.0.

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4.0 Laboratory Analytical Results A total of 53 monitoring wells and Sherman Spring are included in the YNPS monitoring program (the remaining wells have been abandoned in place by backfilling with grout, consistent with MADEP guidelines). The 53 monitoring wells were sampled each quarter during 2006, with minor exceptions. Monitoring well MW- 101C was obstructed during the first two quarters and was only sampled in Q3 and Q4. Several monitoring wells (MW-104D, MW-107E, MW-107F, MW-I 13A, and MW-i 13C) were installed during 2006, and were included in the sampling program as they were completed.

Quarterly groundwater samples were taken from all available monitoring wells during 2006, and selected monitoring wells were analyzed monthly. A complete suite of radionuclides was analyzed in groundwater samples taken in Q1, Q2, and Q3 2006 sampling rounds, while only tritium was analyzed in the monthly samples. As discussed in Section 3.4, radionuclides other than tritium were analyzed in selected monitoring wells for Q4 2006 groundwater analyses (Table 3-2).

A total of 49 monitoring wells and Sherman Spring were sampled in Q1 2006. The laboratory program included three field duplicates and three matrix/matrix spike duplicate (MS/MSD) samples in support of the quality control/quality assurance (QA/QC) program.

The Q2 sampling included 52 monitoring wells and Sherman Spring, three field duplicate samples and three MS samples. A total of 51 monitoring wells and Sherman Spring were sampled in Q3, and QA/QC samples included four duplicates and four MS samples. The Q4 sampling included 53 monitoring wells and Sherman Spring, and QA/QC for Q4 was supported by three duplicate and three MS samples. Complete laboratory analytical results for all four quarters are included as Appendix D.

In addition to the four quarterly sampling rounds conducted in 2006, monthly sampling for tritium was conducted on selected monitoring wells. The monthly sampling criteria included evaluation of significant changes in tritium concentrations in a monitoring well(s) and additional samples from newly installed and replacement monitoring wells.

The complete laboratory results for the monthly samples are included in Appendix D. A summary of the laboratory results is provided in the following sections.

4.1 Tritium During the first quarter 2006 sampling event, tritium was detected in 18 of the 49 wells sampled at concentrations greater than the sample MDCs. The highest concentration of tritium (41,300 pCi/L) was detected at monitoring well MW-107C which is screened in a sandy zone of the upper till. Tritium results for QI 2006 sampling event are summarized in Table 4-1.

Tritium was detected in 22 of the 53 groundwater samples during the second quarter 2006 sampling event at concentrations greater than the sample MDC. The highest tritium 19

concentration was again measured in well MW-107C at a concentration of 36,000 pCi/L.

Tritium results for the second quarter 2006 sampling event are summarized in Table 4-1.

Tritium concentrations ranged from non-detect to 32,500 pCi/L during Q3 2006, and the greatest concentration was present in MW-107C. Tritium was detected in 31 of 52 samples in Q3 and laboratory results are summarized in Table 4-1.

During the Q4 2006 sampling event, tritium was detected in 27 of 54 groundwater samples. Similar to the first three quarters, the highest tritium concentration was reported in MW- 107C. Tritium results for the fourth quarter 2006 sampling event are summarized in Table 4-1.

The results for the monthly tritium samples are also included in Table 4-1. The total number of tritium samples in the monthly sampling efforts ranged from three samples in October to 18 samples in May. The tritium concentrations detected in the monthly samples are generally consistent with that observed in the quarterly samples (Table 4-1)

Two monitoring wells were replaced during 2006 (CB-3 and CW-10) and the replacement monitoring wells (CB-3R and CW-IOR) were sampled and analyzed for tritium. The tritium results for both original and replacement monitoring wells are summarized in Table 4-2, and demonstrate that the results for the replacement wells are consistent with the previous results for the original monitoring wells.

All tritium results are below the US Environmental Protection Agency (EPA) maximum contaminant level (MCL) of 20,000 pCi/L except at MW- 107C. Monitoring well MW-107C has consistently had tritium concentrations above 30,000 pCi/L, with historic levels in excess of 40,000 pCi/L (References 1-3 and 1-4). In general during 2006, tritium concentrations have decreased from Q1 through Q4. Many monitoring wells have had significant decreases including MW-107C (41,300 pCi/L to 29,100 pCi/L) and MW-101A (16,900 pCi/L to 3,880 pCi/L) in the upgradient portion of the site, and MW-106A (10,300 pCi/L to 3,010 pCi/L) and CB-6 (7,680 pCi/L to 869 pCi/L) in the downgradient portion of the site. The consistent decreases in both the upgradient and downgradient portions of the site suggest that the source concentration is decreasing at the site.

4.2 Boron Boron was used as a neutron moderator in the primary cooling water during plant operation, and when detected above background levels in environmental samples at YNPS is a potential indication of plant-related contamination. Boron, like tritium, is conservative and does not partition significantly to soil or bedrock and may also be an effective tracer of potentially contaminated groundwater.

Boron was analyzed in all groundwater samples collected during Q2 2006. The boron results are summarized in Table 4-3. Boron concentrations ranged from not detectable at 4 micrograms per liter (ýig/L) to 258 ýtg/L in monitoring well CW-10. The highest boron concentrations are generally associated with monitoring wells located in the former SFP/IXP source area that are screened within the upper sand lenses in the till (i.e., MW-107C (214 tg/L) and MW-107D (168 ýig/L)) and glaciofluvial aquifers (i.e., MW-102D 20

(134 ýtg/L) and MW-i 07A (116 .tg/L)), similar to the location of the highest tritium concentrations (Tables 4-1 and 4-3). Lower boron concentrations are observed in the glaciofluvial, till, glaciolacustrine, and bedrock aquifers downgradient of the SFP/IXP source area.

The distribution of boron in the glaciofluvial aquifer is presented in the 2006 Interim Groundwater report (Reference 1-5). The boron plume in the glaciofluvial aquifer is very similar to the tritium plumes mapped there for QI and Q2 2006 (Reference 1-5, Figures 7-3, 7-4, and 7-12). The highest boron concentrations are located in the former SFP/IXP source area, with decreasing concentrations observed in the downgradient monitoring wells. Similar to the tritium plumes for QI and Q2, the boron distribution is also consistent with groundwater contours and flow directions mapped for the glaciofluvial aquifer (Reference 1-5, Figures 6-4 and 7-12). The elevated boron concentrations and the similarity of the tritium and boron plumes indicate a plant-related source for the boron. Since the fate and transport properties for boron and tritium are relatively similar, as both contaminants are minimally retarded in the aquifer, the similarity of the boron and tritium plumes further indicates that the plume distribution at YNPS is well characterized.

There are no state or EPA standards for boron. All boron concentrations currently and historically identified at the site are well below I mg/L. Boron in groundwater was evaluated at the site in 2003 and 2004 and detected concentrations ranged up to 490 ýtg/L.

The laboratory detection limits were higher then (100 Vtg/L), and many groundwater samples had boron concentrations in excess of 100 Vtg/L (Reference 4-1). The historic results indicate that the boron plume is slowly decreasing due to natural attenuation.

4.3 Other Radionuclides in Groundwater Groundwater samples from each of the existing monitoring wells have now been analyzed during at least three quarterly rounds for the full suite of 10 gamma-emitting radionuclides, tritium, gross alpha, gross beta and 11 hard-to-detect radionuclides. The results of these analyses are included in Appendix D, and show that no gamma-emitting or hard-to-detect radionuclides have been detected in any well. Low levels of a few radionuclides have been reported sporadically at concentrations near the critical level (1.645 times the standard deviation of the total counts), but these values fall within the statistically expected five percent of false positive values at the 95% confidence level.

The wells in which these values above the critical values are observed are evenly distributed among the wells and radionuclides. That is, there is no common plant-related radionuclide consistently identified in a single well (except for tritium).

The absence of radionuclides other than tritium in groundwater samples is consistent with soil-water partition coefficients (Kds) determined for these radionuclides (Reference 4-2). The partition coefficients control the distribution of radionuclides in groundwater, as compounds with low Kd values are strongly partitioned to groundwater relative to soil, concrete and geologic material, while compounds with higher Kd values are more readily partitioned to the solid phase. Tritium has an effective Kd value of approximately zero, 21

and Sr-90, Cs-137, and Co-60 typically have increasingly larger Kd values (Reference 4-2). Thus, the presence of tritium and absence of other radionuclides in site groundwater is consistent with the Kd values for these radionuclides. Although use of a linear isotherm to represent partitioning is usually modeled as a reversible process, many radionuclides including Cs-137 and Co-60 are partitioned to soil as an irreversible process (Reference 4-2).

4.4 General Geochemistry As part of the general groundwater characterization at Yankee Rowe, all monitoring wells listed in the NRC Groundwater Compliance Plan (Reference 1-6) were sampled and analyzed for anions and cations during the Q2 2006 groundwater sampling round.

Anions included in the laboratory analysis were sulfate, chloride and bicarbonate/carbonate. The cation analysis included magnesium, calcium, potassium, and sodium. The laboratory results for both anions and cations are summarized in Table 4-3.

Calcium and magnesium concentrations ranged from 2.32 to 223 milligrams per liter (mg/L) and 0.085 to 68.4 mg/L, respectively, while sodium and potassium concentrations varied from 1.85 to 184 mg/L and 1.31 to 25.2 mg/L, respectively. Sulfate concentrations (0.63 to 102 mg/L) were the lowest of the anions, with generally greater values for chloride (0.46 to 780 mg/L), bicarbonate (3.1 to 320 mg/L), and carbonate (non-detect to 234 mg/L). Carbonate was typically much lower relative to bicarbonate, as bicarbonate is the dominant carbonate species when pH is below 9.0 (Reference 1-7, Table 7-3). The two monitoring wells with pH values in excess of 11 (MW-107A and MW-I IOA) contained elevated carbonate concentrations (66 and 234 mg/L, respectively), and groundwater in that area is probably impacted by concrete in the nearby subsurface.

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5.0 Spatial Trend Analysis The spatial distribution of tritium has been mapped for the glaciofluvial, till, and bedrock aquifers for all four quarters of 2006. Plume maps and discussion of the tritium distribution for QI and Q2 2006 are included in Reference 1-5. A summary of the conceptual site model developed for YNPS along with the spatial distribution of tritium in Q3 and Q4 2006 is presented in the following sections.

The CSM identifies the former SFP/IXP as the significant source area for tritium at YNPS. Tritium migrated from the SFP/IXP into the glaciofluvial aquifer and downward into the till in the period 1963-1965. Additionally, YAEC believes the SFP may have leaked periodically before a steel liner was installed in the period 1978-1981, based upon cracks observed in the concrete pool walls. However, the amount of SFP leakage in the 1970s was small and not discernable based on water-level changes and make-up rates.

The 1963-65 tritium release(s) created a significant plume of tritium-contaminated groundwater in the glaciofluvial aquifer as evidenced by concentrations of tritium in excess of 2,000,000 pCi/L measured in Sherman Spring in 1965 (Reference 1-2). Since the initial release in the 1960s, tritium concentrations in the glaciofluvial aquifer have decreased to less than 5,000 pCi/L in the downgradient portion of the glaciofluvial aquifer.

In addition to the impact to the glaciofluvial aquifer, tritium released from the. former SFP/IXP has migrated downward into the till and sand layers within the till. This is a function of the downward hydraulic gradient that occurs between the glaciofluvial and glacial till aquifers. This process resulted in significant tritium contamination in the till, as over 40,000 pCi/L of tritium has been detected in MW-I 07C screened in the upper till adjacent to the SFP/IXP as recently as April 2006.

Soil excavation during 2005 removed a significant portion of tritium-contaminated soil from the former SFP/IXP area. During the soil excavation activities, a slug of tritium-contaminated groundwater was released from the former SFP/IXP area into the glaciofluvial aquifer and has migrated through the downgradient portion of the YNPS site. This slug of elevated tritium has passed through the glaciofluvial aquifer during 2005 and 2006 as documented in the downgradient monitoring wells MW-104A, CB-6, MW-106A, and Sherman Spring (Figure 5-1). As shown in Figure 5-1, tritium concentrations (up to 14,000 pCi/L) in these downgradient monitoring wells had maximum concentrations in the late 2005 and early 2006 time period, followed by sharply decreasing tritium concentrations. These observations are consistent with a slug of tritium-contaminated groundwater migrating through the shallow, glaciofluvial aquifer.

Prior to the excavation activities in 2005, a plume of tritium-contaminated groundwater was established across the YNPS site in the glaciofluvial aquifer with tritium concentrations ranging from 5,000 to 10,000 pCi/L in the area adjacent to and directly downgradient of the former SFP/IXP area to concentrations less than 1,000 pCi/L in downgradient monitoring wells (References 1-3, 1-4, and 1-5).

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The tritium plume characterized for the Q I and Q2 2006 for the glaciofluvial aquifer identified the slug of tritium-contaminated groundwater in the downgradient portions of the site, and demonstrated that the plume characteristics in the glaciofluvial aquifer established prior to the 2005 soil excavation were in the process of being re-established across the site (i.e., highest concentrations in the upgradient portion of the site adjacent to the SFP/IXP, with lower concentrations downgradient of the SFP/IXP) (Reference 1-5, Figures 7-3 and 7-4). The tritium concentrations in the glacial till during QI and Q2 2006 were higher than those reported in the glaciofluvial aquifer, but with limited downgradient migration, consistent with the results of the pressure-transient and pumping tests conducted in summer 2006 (Reference 1-5, Figure 7-5).

5.1 Spatial Distribution of Tritium Third and Fourth Quarters 2006 The spatial distribution of detected tritium has been mapped for the glaciofluvial and upper till aquifers for the third and fourth quarter 2006 sampling events, and is summarized below.

5.1.1 Spatial Distribution of Tritium from Third Quarter 2006 The tritium plume in the glaciofluvial unit mapped for Q3 2006 is shown in Figure 5-2.

The downgradient slug of elevated tritium identified in QI and Q2 2006 is present in Q3 2006, and is part of a large plume of elevated tritium whose source is the former SFP/IXP area (Figure 5-2). Tritium concentrations up to 10,100 pCi/L (MW-101A) are present in the shallow glaciofluvial aquifer in the vicinity of the former SFP/IXP, with decreasing concentrations observed in the downgradient monitoring wells (Figure 5-2). The downgradient slug of elevated tritium (up to 5,280 pCi/L) has somewhat higher tritium values relative to the more intermediate downgradient monitoring wells (i.e., MW-104A, 1,430 pCi/L), and the distribution of tritium is consistent with the groundwater flow direction identified in the glaciofluvial aquifer (Figure 2-1).

In addition to the broad tritium distribution within the shallow glaciofluvial aquifer, tritium is also detected more locally in the till, glaciolacustrine, and bedrock aquifers.

While tritium in the bedrock and glaciolacustrine aquifers is limited to one location in each aquifer (MW-105B and MW-I 13C, respectively), sand lenses within the till contain a local tritium distribution downgradient of the SFP/IXP source area. This deeper zone of impact is smaller than the shallow plume but more concentrated in the vicinity of MW-107C because of the restricted groundwater flow within the discontinuous, low-yielding sand lenses within the till.

Figure 5-3 shows the detected tritium concentrations within sand lenses in the upper portion of the till for Q3 2006 in plan view. Tritium concentrations observed in Q2 2006 within the till are generally a little higher those detected in Q3 2006 (Table 4-1). The tritium plume in the upper sand lenses within the till is focused in the area immediately downgradient of the SFP/IXP source area and extends to MW-105C (1,650 pCi/L) but the non-detect value for MW-104D indicates that this plume has not migrated to the MW-104 well cluster. The highest tritium concentration is detected in MW-107C (32,500 24

pCi/L), but the Q3 2006 concentration is significantly lower than the 36,000 pCi/L reported for Q2 2006. This limited distribution is generally consistent with groundwater contours and flow direction interpreted for the upper sand lenses within the till (Figures 2-2 and 2-6) and the tritium plume characterized in the upper sand lenses during Q2 2006 (Reference 1-5, Figure 7-5).

• The vertical distribution of tritium is summarized in cross-sections A-A' through E-E' and the locations of the cross-sections are shown in Figure 5-4. Figures 5-5 through 5-9 are Geologic Cross-Section A-A' through E-E' showing contoured tritium concentrations during Q3 2006. Geologic Cross-Section A-A' is aligned generally in the direction of groundwater flow, toward the Deerfield River. Similar to Figure 5-3, which shows the horizontal tritium distribution, Figure 5-5 illustrates the vertical distribution of tritium impacts on cross-section A-A' during Q3 2006. This figure also shows that impacts within the deeper glacial till appear to originate adjacent tothe SFP/IXP source area and extend downgradient in the direction of ground water flow inferred in Figure 2-2 to a point midway between the SPF/IXP source area and CB-6 (Figure 5-5).

Tritium concentrations in the upper portions of the till for Q3 2006 range from 1,650 pCi/L in the downgradient portion of the plume (MW-105C) to 32,500 pCi/L in MW-107C, located adjacent to the SFP/IXP source area. As shown in Figures 5-3 and 5-5, the tritium distribution in the till is limited to the area directly downgradient of SFP/IXP, and in contrast to the tritium distribution in the shallow glaciofluvial aquifer, does not have a significant downgradient component. The 20,000 pCi/L MCL for tritium is exceeded in MW-I 07C, but sampling results for all other monitorng wells screened in the till, glaciolacustrine, and bedrock aquifers have tritium concentrations, where detected, consistently well below the MCL.

The limited distribution of tritium observed in the glacial till is further illustrated in cross-sections 13-B', C-C', D-D' and E-E' (Figures 5-6 through 5-9). The absence of a wide-spread plume within this unit is generally consistent with the results from the pumping test of MW-107C and the multiple pressure transient tests conducted during summer 2006 (Reference 1-5, Figures 5-23 through 5-29). The pumping test and the pressure transient tests demonstrated that the connectivity of the sand lenses in the till is highest in the area of the former SFP/IXP source area, with limited connectivity at distances greater than 100 feet. MW-105C was shown to have hydraulic connection with sand lenses in the till located in the SFP/LXP source area, consistent with the ongoing detection of tritium in MW- 105C. The combination of the tritium analytical results, pumping test, and pressure transient data suggest that the tritium plume in the glacial till sand lenses extends no further downgradient than the MW- 104 and MW-105 well clusters and has established equilibrium with the source area (Figure 5-3 and Figures 5-5 through 5-9).

Tritium is typically not detected in bedrock monitoring wells and during Q2 2006 has only been detected in MW-105B (3,290 pCi/L). The lack of tritium in most of the monitoring wells is consistent with upward gradients established between the bedrock and overlying glacial till or glaciolacustrine aquifers. The presence of tritium in MW-105B is is function of the relatively shallow bedrock in this area. Likewise, the pressure 25

transient testing identified a connection of MW-105B and sand lenses within the upper glacial till.

5.1.2 Spatial Distribution of Tritium from Fourth Quarter 2006 The tritium distribution in the glaciofluvial aquifer for Q4 2006 is shown in Figure 5-10.

The plume is very similar to the tritium distribution observed for Q3 2006, except tritium concentrations are lower. The downgradient slug of tritium is still observed, however the highest concentration is located farther downgradient, and the tritium concentration within the slug is significantly lower (Figures 5-2 and 5-10). These observations are consistent with the mapped groundwater flow direction and the continued migration of the slug towards the Deerfield River (Figure 2-5). Tritium concentrations in Q4 2006 are typically lower than those reported for Q3 2006 (Table 4-1 and Figures 5-2 and 5-10)

Figure 5-11 depicts the tritium plume in the upper glacial till sand layers for Q4 2006.

Similar to the distribution identified for Q3 2006, the highest concentration was reported in MW-107C (29,100 pCi/L), with the downgradient plume distribution including MW-105C (2,750 pCi/L). The non-detect concentration reported for MW-104D continues to limit the downgradient extent of the plume to an area upgradient of the MW-104 well cluster (Figure 5-11). The Q4 2006 distribution of tritium is consistent with the results for QI through Q3 2006, where the plume in the upper sand layers of the glacial till is limited to the area downgradient of the former SFP/IXP source area including MW-105C, but upgradient of the MW-104 well cluster (Figures 5-3 and 5-11 and Reference 1-5, Figure 7-5).

The vertical distribution of tritium is shown in Figures 5-12 through 5-16 where contours or isocons of tritium in cross section are depicted. Similar to the cross sections developed for Q3 2006, the Q4 2006 results indicate a deep tritium distribution beneath the former SFP/IXP area and an extensive downgradient tritium distribution in the shallow glaciofluvial aquifer (Figures 5-12 through 5-16).

Consistent with Q3 2006 results, tritium was only detected in one bedrock monitoring well, MW-I 05B (2,900 pCi/L). During 2006, tritium has been consistently reported in MW-105B ranging from 4,780 pCi/L in the May monthly sample to 2,900 pCi/L in Q4 2006 (Figure 5-17). As shown in Figure 5-17, the tritium concentration in MW-105B is decreasing, and has a statistically validated downward trend (see Section 5.3) 5.2 General Geochemistry of Site Groundwater The general geochemistry data for all Q2 2006 groundwater samples were presented in a Piper diagram (Reference 1-5, Figure 7-7). The YNPS groundwater samples were shown to have low magnesium and sulfate, with a wide range of bicarbonate+carbonate to chloride and calcium to sodium+potassium ratios. For all of the YNPS groundwater samples there is no cluster of data or specific chemical signature.

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When the groundwater samples were separated into their specific hydrogeologic units:

glaciofluvial, till, glaciolacustrine and bedrock, some specific geochemical signatures were apparent (Reference 1-5, Figures 7-8 through 7-11). The anion-cation data for the groundwater samples from the glaciofluvial aquifer indicated that the geochemistry of that unit was generally distinct from that of theftill, glaciolacustrine, and bedrock units, all three of which are very similar. The glaciofluvial groundwater has a more chloride-dominated anion component relative to the till, glaciolacustrine and bedrock, which are more bicarbonate/carbonate dominant. All hydrogeologic units were shown to have low sulfate.

The similarity of the till, glaciolacustrine and bedrock groundwater chemistry was interpreted as the result of glacial erosion of the bedrock and the subsequent glacial deposition of the derived material into glaciolacustrine and till soils. The glaciofluvial unit is also a result of glacial deposition, but the active agent in this process was melt water rather than ice and the resulting difference in grain-size distribution may affect its geochemical signature. Alternatively, the use of deicing salt on the roadways throughout the YNPS may be evident in the geochemical signature of the shallow aquifer.

The glaciofluvial aquifer is closest to ground surface and most permeable of the four units, allowing relatively more mixing with meteoric water. Although not tested for this study, meteoric (atmospheric) water likely has a different geochemical signature from groundwater derived from any of the stratigraphic units at YNPS and mixing with this water would likely result in a more distinct groundwater type. Regardless of the cause of the relative uniqueness of the geochemistry of groundwater from the glaciofluvial aquifer, the results of the anion-cation analyses tend to corroborate the conceptual model of the site, which presumes that groundwater flow in the glaciofluvial aquifer is largely isolated from flow in the deeper units.

5.3 Trend Analysis of Tritium To evaluate the long-term trend for tritium in groundwater, YNPS has completed a trend analysis for all monitoring wells included in the quarterly groundwater monitoring plan.

The trend analysis was conducted for tritium, as tritium is the only radionuclide identified in groundwater at YNPS. The trend analysis included all sample results from 2006 (including the monthly sampling) for all monitoring wells that are part of the quarterly sampling program. The analysis utilized Sens Slope Trend analysis, and all results indicating an upward or downward trend were confirmed using Kendall-Mann Upward Trend analysis (USEPA, 1989 and 1992). The two sigma value was used for all non-detect concentrations, and the results of the trend analysis are summarized in Table 5-1.

The complete trend analysis data and results are included in Appendix E. The trend analysis results are presented in terms of identifying either an upward trend, downward trend or no trend. The no trend result indicates that neither an upward nor downward trend is present, and is generally indicative of a stable trend. Time series plots of the tritium concentrations for the 2006 results for each monitoring well are also provided in Appendix E.

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The trend analysis was conducted on all 53 monitoring wells and Sherman Spring and a total of 272 tritium results were included in the analysis. Of the 272 total tritium results, 133 or 49% represent non-detect tritium concentrations. A summary of the tritium results utilized in the trend analysis for each monitoring well is also included in Appendix E.

Of the 54 monitoring locations, nine monitoring wells (CB-6, MW-101A, MW-105B, MW- 106A, MW- 107A, MW- 107D, MW- 107E, MW- 110A, and MW- 1 IA) and Sherman Spring have a defined downward trend (Figures 5-18 and 5-19). A total of 43 monitoring wells have no trend and one monitoring well (MW-I IOC) displays an upward trend. The upward trend determined for MW-10OC is based on the four quarterly 2006 results, as this monitoring well was not installed prior to 2006. The tritium concentration in MW-0I OC is relatively low ranging from 1,160 pCi/L in Q1 2006 to 21590 pCi/L in Q4 2006 (Figure 5-20). While the tritium concentration has clearly increased in MW-I IOC during 2006, the maximum concentration is still an order of magnitude below the tritium MCL of 20,000 pCi/L and significant increases are not expected in this portion of the site. MW-I IOC is downgradient of the former SFP/IXP area where significant soil remediation was conducted, and all other monitoring wells in this portion of the site have stable or decreasing tritium trends. The result for the first quarter 2007 will allow further evaluation of this upward trend determined for MW-1 lOC.

5.4 Fate and Transport of Tritium The processes of natural attenuation, including dilution, dispersion and radioactive decay, have significantly reduced the tritium levels in groundwater at YNPS since the 1960s.

The tritium concentrations are lower in the shallow aquifer because the higher hydraulic conductivity and more homogeneous flow domain in that unit have allowed more flushing and dilution compared to the deeper, discontinuous sand lenses where flow is more restricted because the sands are interlayered within a low permeability glacial till.

With a groundwater plume in equilibrium, a source area will release a contaminant to the aquifer at a relatively constant rate, and the dissolved contamination will attenuate in the downgradient aquifer as a function of processes including dilution, dispersion and radioactive decay. Continuation of these processes will slowly decrease the size of the plume as the contaminant mass in the source area decreases. Important characteristics of a plume in equilibrium are: 1) consistent plume shape over time, 2) relatively constant or slowly decreasing contaminant concentrations in groundwater, and 3) no increases in downgradient distance of contaminant migration.

The tritium plumes at YNPS appear to be in equilibrium with the source area. The plumes characterized for Q I through Q4 2006 have similar distributions, are slowly decreasing in concentration, and are not increasing in the downgradient direction. Of significance is the decrease in MW-107C that has occurred following soil remediation in the former SFP/IXP area. Soil removal in the former SFP/IXP was conducted from June 2005 through fall 2005. Prior to the soil remediation activity, tritium levels in MW-107C were fairly constant, varying between 48,000 pCi/L and 41,800 pCi/L from 2003 through 2005 (Figure 5-21). Lower tritium concentrations were reported in March and May 28

2004, however these lower concentrations were related to a damaged road box that allowed infiltration of surface water into the well, diluting the groundwater in MW-107C (References 5-1 and 5-2). Following completion of soil remediation in the former SFP/IXP, tritium levels in MW-107C began to decrease, and by Q4 2006 had decreased to 29,100 pCi/L.

MW-I 07C is directly adjacent to the former SFP/IXP and is believed to be very near to the tritium source area. The high, constant tritium concentrations observed in MW- 107C over the 2003 to late 2005 time period indicate that a significant source of tritium was degrading groundwater, and that the rate limiting process was most likely the contact time that groundwater had with the source. The high, relatively constant value of tritium detected in MW-107C was a function of relatively constant groundwater flow through the source area, and a large source that acted to maximize tritium concentrations in groundwater.

The decrease in tritium levels observed in MW-107C in 2006 has followed significant soil remediation and indicates that the rate limiting process for groundwater contaminant concentration is no longer the contact time of groundwater with the source area, but is a function of a continous decrease in the source mass. Prior to soil remediation in the SFP/IXP, the size and strength of the source area was most likely large relative to the contact zone for groundwater, and resulted in a high and relatively constant level of tritium groundwater contamination. Following the soil removal and associated source mass reduction, the rate limiting process for groundwater degradation no longer appears to be the contact time of a large source with a constant groundwater flux, but a constantly decreasing mass in the source area. Prior to the soil remediation the source mass was large enough that the amount of tritium removed via groundwater flow through the area was small relative to the mass of source contamination. The soil removal in the source area significantly reduced the source mass to the level where continued source reduction of tritium via precipitation recharge flushing and groundwater flow through the contaminated source soils is acting to continuously reduce the contaminant mass in the source area, resulting in a continuous decrease in groundwater tritium levels. The decreasing tritium concentrations may also be related to the slow diffusion of tritium from the low permeability glacial till into the adjacent more permeable sand lenses.

While most monitoring wells with elevated tritium experienced a decrease in concentration during 2006, CFW-6 located upgradient of the former SFP/IXP had a significant increase in tritium during 2006 (Figure 5-22). CFW-6 is located upgradient of the industrial area, adjacent to the drainage for Wheeler Brook (Figure 1-3). Prior to Q I 2006, tritium levels in CFW-6 were typically non-detect. During 2006, tritium rapidly increased from the non-detect concentration to 2,650 pCi/L in Q3 2006, followed by a decrease to near non-detect values in Q4 (Figure 5-22). Other monitoring wells in this area (CFW-5 and CFW- I) and nearby monitoring wells in the upgradient portion of the industrial area (CB-8 and CB-3) did not experience a similar increase in tritium during 2006 (Table 4-1).

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The sharp increase, followed by the rapid decrease in tritium concentration observed in CFW-6 suggests that a slug of tritium-contaminated groundwater migrated through the shallow groundwater in the CFW-6 area. The most likely source of tritium for this slug of tritium-contaminated groundwater is concrete rubble from the reactor support structure that was temporarily stored east of the industrial area (Figure 5-23). The concrete rubble had up to 100 pCi/gram of tritium and was located in that area from fall 2005 through early 2006. Following removal of the concrete rubble, final status survey results identified up to 40 pCi/g of tritium in surface soils within the area of concrete rubble storage (Figure 5-23). Tritium is readily leachable into the subsurface and would quickly migrate via infiltration to the shallow groundwater, creating the slug of tritium-contaminated groundwater observed in CFW-6. Based on the groundwater flow determined for this portion of the site, the slug of elevated tritium would flow from the CFW-6 area to the north and discharge to the Sherman Reservoir (Figures 2-1 and 2-5).

The monitoring network established at YNPS has provided a strong understanding of the horizontal and vertical extent of tritium contamination in site groundwater. The plumes defined in 2006 are all below the EPA MCL established for tritium except for MW-107C located adjacent to the source area. Based on the source removal completed in the former SFP/IXP area, tritium groundwater concentrations are expected to continue the general decrease in concentration observed in 2006.

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6.0 Groundwater Model 6.1 Introduction A three-dimensional flow and transport groundwater model has been developed to support the decommissioning of the Yankee Nuclear Power Station in Rowe, MA (YNPS). The modeling work began in July 2006. The model has been used to assist in the interpretation of the MW-I 07C pumping test in June 2006 and in the interpretation of the various pressure transient tests performed in onsite monitoring wells during June and July 2006. A number of other features of the detailed groundwater hydrographs of the site monitoring wells have been evaluated with the model, with the goal of gaining a better understanding of the conceptual site model. The model has also been used to simulate the movement of tritium from the IXP area from May 1963 onward and to predict the maximum concentration of tritium in a hypothetical "resident farmer" well if one were to be installed beginning as early as spring of 2007.

6.1.1 Scope and Objectives Although not required by any regulatory order or agreement, the development of a numerical simulation tool for YNPS was undertaken to assist in the evaluation of the complex layering of thick glacial till, interbedded sand seams, and glaciolacustrine deposits found under and downgradient of the area of the site with the highest residual radioactivity in groundwater. The model parameters have been highly refined in specific portions of the site where the residual tritium concentrations in groundwater have exceeded the EPA MCL of 20,000 pCi/L. The main questions have been how long the groundwater will continue to exceed the MCL and what would be the maximum concentration of tritium in a hypothetical resident farmer's well on the site.

The scope of this modeling exercise has been broad, covering the YNPS site in three dimensions and large areas of watershed above and below the site. Although the primary focus is the industrial area formerly occupied by the reactor and generating station, the overall model domain has to be sufficiently large to define reasonable boundary conditions. Because the Deerfield River acts as a discharge boundary and YNPS is located near that boundary, the model domain was extended to encompass surface water drainage basins on both the west and east sides of the Deerfield River. The scope of the modeling activity is summarized in the following bullets:

Physical Scope of the Model o The area known to have been the primary radioactive water release site (i.e., the Spent Fuel Pool (SFP) and Ion Exchange Pit (IXP)) westward to Sherman Spring is modeled in detail.

o The major drainages on the west and east sides of the Deerfield River, with YNPS in the approximate middle, are included for completeness.

o In the vertical dimension, the model incorporates saturated hydrogeologic units from the ground surface to as much as 800 feet below ground 31

surface. Total bedrock thickness from top of rock to model bottom is 500 feet.

o The thick valley fill deposits are represented by subdivision into as many as 13 individual layers to represent the glaciofluvial deposits on top, the thick glacial till with as many as three primary, nearly horizontal sand seams and a locally thick glaciolacustrine deposit on bottom with as many as two distinct primary sand seams.

Temporal Scope of the Model o Historical Operating Conditions (pre-closure), including simulation of the spread of the May 1963 Spent Fuel Pool/IXP leak.

o Post Closure Conditions (after completion of demolition activities),

reflecting changes to recharge conditions in the industrial areas and changes to soil permeability in the areas of deep soil remediation.

The physical scope of the modeling exercise is intended to be sufficiently robust to incorporate hydrologic boundary conditions in all three dimensions. The temporal scope is intended to provide an indication of the effects of long-term and short-term hydrologic transient events over the course of plant operation and closure. The modeling activity has assisted in refining the hydrogeologic conceptual site model, which is described in more detail in Sections 4 and 6 of Reference 1-5.

Several general and specific objectives were defined for the modeling activity. These objectives support data needs identified for groundwater monitoring and for strategic evaluation of the post-closure conditions at YNPS and are listed below:

" General Objectives o Produce a numerical simulation tool that is generally representative of observed site conditions at YNPS.

o Produce a numerical simulation tool that can be used to illustrate groundwater flow regimes within the hydrogeologic formations identified at YNPS.

o Produce a simulation tool that can support assessment of fate and transport of tritium originating within the former industrial area of the site.

o Assess the potential impacts of changing conditions related to termination of plant operations and performance of decommissioning activities at YNPS.

" Specific Objectives

1) to create a tool to confirm or refute the conceptual site model (e.g., testing various degrees of continuity of sand layers between wells with known intermediate-depth tritium contamination);

2) to predict how the tritium plume will migrate with time and change in concentration with time;

3) to determine where the deep tritium plume will discharge to the River and at what concentration; and,

4) to predict the concentration of tritium entering the "resident farmer" well.

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6.1.2 Modeling Software MODFLOW and MT3DMS are porous media models, but can be adapted to model flow and transport in fractured media. Although bedrock has been included in the YNPS model, it is only of minor importance to the fate and transport of radionuclide releases at the site. For the purposes of this model, the issues revolving around use of porous media models for fractured bedrock are not important due to the low importance of bedrock to the problems at hand. Most of the model development has been done with a regional model covering a large area on both sides of the Deerfield River valley. The flow models are constructed using the 1996 version of MODFLOW as developed by the US Geological Survey (USGS). Groundwater Vistas (GWV), GWV4, Version 4.25, has been used as the pre- and post-processor, as developed by Environmental Simulations, Inc. (ESI). Particle tracking used the USGS MODPATH program with pre- and post-processing by Groundwater Vistas. Solute transport was implemented using MT3DMS developed by the US Army Corps of Engineers (COE) with pre- and post-processing by Groundwater Vistas.

ArcView 9.1 was used to prepare data sets and present the final model results.

Rockworks was used to develop the geologic database and create gridded surficial unit surfaces and cross sections to aid in the 3-dimensional design of the model. Surfer was used to grid and contour some of the data.

Detailed individual "run logs" were created and saved in accordance with ASTM D5718.

6.1.3 Base Map Preparation and Spatial Location of Data The model base maps were constructed in ArcView, utilizing data available from the State of Massachusetts GIS web site and from site base maps and surveys prepared by YNPS or its contractors. These data were projected in Massachusetts Mainland NAD83 State Plane. The vertical datum of site-specific data is referenced in this work to NAVD88 in feet. Some data were available for the site in NAD 1927 datum and the original "NEPCO" (New England Power Co.) arbitrary vertical datum which was 106.66 feet below 1929 NGVD. Add 0.45' feet to NAVD88 to obtain 1929 NGVD on the site.

YNPS provided a recent bathymetric survey map of Sherman Reservoir, which was digitized and projected in ArcView to match the reservoir outline.

Base map work has been aided by color orthophotos at 1:5000 scale taken April 2001, USGS topographic contour maps at 3-meter contour interval, a detailed YNPS property contour map at a 5-foot interval, and other Arc "shape files" including streams, and sand and gravel aquifer maps. Results from Reference 2-2 include the most comprehensive geologic mapping of the site. Figures from that report were scanned and fit to the base map. Other miscellaneous reports, such as the report of the 1956 geophysics survey (Reference 2-1), which contained important data for model development such as depth to rock, were also scanned and fit to the base map where data needed to be geo-referenced.

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6.1.4 Rockworks Database and Surfer used for Geologic Data and Layer Elevations Site-specific boring and monitoring well data were used to develop the onsite model parameters, the locations of which are shown in Figure 6-2. Table 1 in Reference 2-4 summarizes monitoring wells placed on the site prior to 2003, only two of which were installed prior to plant shutdown in 1993. Since 2003, many additional supplemental investigations have been performed and reported to the Nuclear Regulatory Commission (NRC) by YNPS and to the State of Massachusetts by ERM.

All borings and monitoring well data for the site, along with simplified stratigraphic descriptions, were entered into a RockWorks database and geo-referenced. In addition, all points at which bedrock elevations were known or inferred from field mapping, seismic refraction work, or drilling, were compiled in RockWorks. No offsite well data within the model area were found in our research.

Geologic inference from inspection of topographic maps was used to estimate bottom elevations of the glaciofluvial deposit adjacent to the Deerfield River. The aerial distribution of the sand and gravel unit is available from the Massachusetts GIS website.

Experience (Reference 2-3) in mapping landslides along the Deerfield River Valley gave insight into the likely thickness of the sand and gravel unit away from the plant site where its thickness has been documented by borings. The detailed site bedrock topography map in the vicinity of the plant (IA) was made using the data points in Figure 6-1 to create a contour map through the minimum curvature algorithm, as shown on Figure 4-10 of Reference 1-5. An estimated depth to bedrock derived from a downhole camera shot at the Furlon House well provided a data point there, and the remainder of the bedrock elevations were derived from geologic inference from topographic map analysis. Most of the upland areas were assumed to have thin or no soil over bedrock.

Reference 1-5 contains numerous detailed geologic cross-sections along with groundwater head profiles and tritium concentration profiles. Reference 1-5 also contains detailed maps of the thickness of the glaciofluvial unit, the top elevation of the underlying till layer, and the top elevation of the underlying glaciolacustrine layer in the main industrialarea of the site.

6.2 Model Discretization A large regional model was constructed to encompass the YNPS site. It is apparent from looking at the topographic map of the area that groundwater that flows through the plant site could begin from as far away as several miles. Rather than estimate the flux of groundwater flow entering the site from the east and using constant flux boundaries to represent that flux contribution, the modelers elected to include a large naturally-bounded area (the watershed boundary) that would, by its nature, determine the flux. This was particularly important in light of the transient modeling that was performed where determining the flux under variable stress conditions would have been quite difficult.

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Although it is obvious that the discharge of any contaminants carried in groundwater from the site would enter the Deerfield River, it has not been established how far downstream that discharge could occur. Again, rather than trying to apply constant flux boundary conditions downstream of the area of interest on the River, the model boundaries have been extended out to the natural watershed divides and far enough downstream so these natural boundaries would allow the model to distribute the flux appropriately along the River.

The model was discretized into the standard rectangular finite-difference grid, but with irregular spacing. The model has 80 columns, 57 rows and 15 layers and a variable grid size that varies from 25-foot square finite-difference cells in the former plant area to 400-foot square cells at the model boundaries. Figure 6-3 shows the finite-difference grid overlain on the USGS base map. The model extends 21,000 feet east to west and 14,000 feet south to north. The origin is at Massachusetts NAD83 State Plane Coordinates, Mainland Division, x = 261,000 feet and y = 3,085,800 feet.

The top thirteen layers of the model consist of soil. In the upland areas, the layers are of equal thickness (0.5 feet) except where the soil is known to be thick, such as in the till slope southeast of the plant where seismic refraction was used to establish the soil thickness. In the immediate plant area where sufficient data were available to define specific geologic units such as the glaciofluvial layer, the till layer, and the glaciolacustrine layer, these surfaces were contoured in Rockworks and used to define individual layer elevations. In an effort to study the transport potentials of particular signature sand seams encountered during deep drilling in overburden that reaches up to 300 feet thick, 5 thin layers were created within the surficial section that were parameterized to represent through-going sand seams where data suggested those sand seams were significant, as from the studies reported in Reference 1-5. Table 6-1 gives a vertical cross-section description of how the model was discretized in the vertical plane.

Figures 6-6A and 6-6B show vertical cross sections through MW-107, east to west and south to north, respectively. The YNPS Interim Groundwater Report (Reference 1-5) contains figures showing the contours on the tops of the major surficial units and the thickness of the glaciofluvial stratum.

6.3 Boundary Condition Specification There are a variety of boundary conditions used in the modeling. No-flow boundaries (a special case of constant flux boundaries where flux is constant at zero--also called Neumann or Type 2 boundaries) are placed around the outside of the naturally-defined limits of the model, and under the bottom of the model. As calibration proceeded, areas of the uplands that were predicted by the model (most of the top 13 layers of Zone 9, which are defined as soil layers, each 0.5 feet thick) to become "dry" were then fixed as no-flow cells in order to improve the convergence of the regional model, which is highly non-linear as all layers including 14 and above were allowed to be simulated as "unconfined" if the layers above were not predicted to be saturated. There are a total of 23,878 active cells in the flow model. The area of transport in the MT3DMS model was 35

limited to the immediate site area and downstream along the Deerfield River lower valley area.

The Deerfield River and Sherman Reservoir within the model area are treated as constant head cells (also called Dirichlet or Type 1 boundaries). During pre-demo times (prior to 2006), Sherman Reservoir elevation was set at elevation 1106 feet NAVD88 for steady-state runs with average annual recharge-based simulations. There are a total of 171 constant head cells in the flow model. They are defined primarily in layer 1 of the model.

Several constant head cells in areas downstream of Sherman Dam occur in lower layers because there are some large finite-difference cells there that span the River and adjacent steep banks and the layering constraints forced the constant head cell to the layer where the cell bottom was just below River level in that cell.

Streams and upland rivers were defined as "drains" (also called Cauchy or Type 3 boundaries). This is a condition that allows discharge from the modeled groundwater system into the drain, but when the water table is predicted by the model to drop below the defined drain bottom elevation, there is no water contributed by the stream to the model. The resistance to discharge into the drain is controlled by the "conductance" value assigned to each drain cell. The conductance was relatively small, set at 100 cubic feet per day per square foot per foot of head difference between the defined stream elevation and the predicted water table. The drains were digitized in segments based on the USGS map elevations along streams defined on the State shape file of "streams" and in obvious large wetlands. Because some of the cells in the periphery of the model are large and the slopes are steep in many areas, the linear interpolation routine caused some "drain" cells to be defined below the top layer of the model where soil thickness was very thin. There are a total of 582 drains in the model.

A number of concrete slabs and foundations have been left in place on the site, but few, if any, of them are barriers to groundwater flow. Most foundations do not even extend through the top layer of the model.

Boundary conditions for the model are shown on Figure 6-4. The contours on the top of bedrock for the area near the site are shown on Figure 6-5.

6.4 Hydraulic Conductivity and Recharge Parameterization The conceptual site model forms the basic framework for parameterizing the computerized groundwater model. During the last continental glaciation, the Deerfield River valley was first scoured, then had glacial till plastered on the sideslopes. A glacial lake formed in the valley during deglaciation, leaving thick, localized silty thinly-bedded glaciolacustrine deposits with some interbedded sand seams. A late glacial pulse in the valley apparently overrode the glaciolacustrine deposits, and laid more till over the glacial lake deposits while periodic melting resulted in some significant sand seams interbedded in the till. In the final stages of deglaciation, glacial meltwaters deposited kames, kame terraces and outwash over the top of the till left in place in the valley.

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The bedrock underlying the site is well-bedded albite gneiss with a foliation that strikes northeast and a 20 to 35-degree dip to the southeast. Joints in the area are predominately high angle, but well distributed in strike. There is a slight preference for a northwest-southeast joint strike. Given the lack of strong evidence for a preferred bedrock fracture orientation throughout the model area, the grid is located north-south with no anisotropy imparted to the bedrock. Although there have been no bedrock pumping tests or rigorous photolineament studies, site monitoring well response to the new "plant" well southeast of the ISFSI suggests a north-south linear from the well through the MW-107 area.

Terrain analysis and contours on the bedrock surface, such as shown on Figure 6-5, suggest a northwest-southeast linear parallel to and just downstream of Sherman Dam.

Other bedrock fracture zones may occur throughout the model area but they are unlikely to be important to the transport of any contaminants that might have been released at the site.

The soils to the west of the former Vapor Containment (VC) area and in the area of the Plant well are quite thick. A large area of thick glacial till extends up the slope for several thousand feet southeast of the former industrial area. There is thick soil (up to 300 feet thick in places--for example, at the Furlon House well) at other locations under or next to the Deerfield River and down to approximately elevation 800 feet or even lower. Whether this is the thalweg of the river valley and whether this is continuous along the bottom of the river valley are not known. The model honors all bedrock data points, but not all the points of lowest elevation have been connected to create a thalweg at the lowest measured elevation, due to lack of data points in between and beyond MW-106B and the Furlon House well.

The vertical conceptualization of the model is given in Table 6-1. Table 6-2 summarizes the defined hydraulic conductivity zones and Figures 6-6 through 6-17 display the distribution of these hydraulic conductivity zones within the various layers of the model.

Initial hydraulic conductivity estimates for rock and soil came from Table 2 of Reference 2-3. The values for the glacial till were measured by high quality laboratory testing on undisturbed samples. Additional data on the hydraulic conductivity of the glaciofluvial deposit were taken from Reference 6-1. The'Executive Summary of Reference 6-1 states that the mean hydraulic conductivity value of the glaciofluvial unit is 1.1E-3 centimeters per second or 3.1 feet per day (with a range of 1.7E-7 to 6.5E-3 centimeters per second). The two hydraulic conductivity values used for layer I glaciofluvial were 5 and 10 feet per day. Calibration started from these initial values to obtain a set of heads that were generally the right order of magnitude based on the calibration wells using average annual recharge estimates.

Values were varied within reasonable ranges to calibrate the model to observed water elevations in monitoring wells. Recharge and the main hydraulic conductivity values were tested within Groundwater Vista's parameter estimation routine to get the first approximation. Once the heads in the upper glaciofluvial deposit were close to observed average annual values, the pumping test on MW-107C was simulated and parameters were refined. Next, the head differences observed at vertically-separated nested monitoring wells on the site were used to refine parameters. Then the results of the June 37

and July 2006 pressure transient testing were used to refine the location and hydraulic conductivity of individual sandy (permeable) layers. Finally, a variety of other special simulations were run (see below) to refine parameters in localized areas.

Layer 1 of the model is the most important because most of the leaked mass of radionuclides passed through this layer on its way to discharge in Sherman Reservoir and the Deerfield River. Below layer 1, transport also occurred, but at much lower rates and with much less total mass involved. Figure 6-6 can also be interpreted as a surficial geology map of the site. Zone 9, in yellow, represents the thin soil and exposed rock on the upland areas; Zone 2, in gray, represents the known areas of thick glacial till; Zones 1 and 3 represent the glaciofluvial deposits along the valley floor. In the following figures, there are changes only in the site area where the results of calibration to various pressure transient events dictated the location and magnitude of the local hydraulic conductivity values.

Average annual recharge distribution for the steady-state operational history modeling is shown in Figure 6-18 and described more fully in Table 6-3. Recharge was applied to the top active layer of the model. There is no published Natural Resources Conservation Service (NRCS) soil map for this area, nor published USGS nor State surficial geology map with any detail. The upland areas (where rock is shallow) and the steep sideslopes are represented by Zone 1 with a very low applied recharge rate. The sand and gravel areas in the valley floor are represented by Zone 2 with a much higher average rate. The valley floor sand and gravel deposits also receive a lot of runoff from the adjacent steep uplands. This runoff seeps into the soil and increases the apparent recharge rate. The application of runoff from upland areas was combined with the recharge rate of the valley floor deposits, rather than attempting to assign a constant flux boundary along the upland edge of the valley floor deposits. The effective average annual recharge rate on the upland areas is significantly lower than would typically be assigned to that soil type, but parameter estimation runs made during calibration essentially dictated the values of the recharge rate that were necessary to match measured average annual heads and vertical gradients. The overall average annual recharge rate for the calibrated model was, however, 5.3% of average annual precipitation (49.1 inches per year), which is reasonable for shallow bedrock and silty glacial till.

During plant operation, the Industrial Area (IA) was primarily impervious area served by catch basins that essentially prevented infiltration in the area shown in Figure 6-18 as having zero recharge. In the post-demolition state the recharge rates in the industrial area are set at 0.0025 feet per day for most areas, but zero in areas where significant areas of concrete slab have been left in place. The post-demo soil recharge rate for the IA is an estimate based on experience, since not even sieve analyses are available for most of the fill that has been placed on the site as part of soil remediation and final grading. Based on discussions with the site contractor that placed the fill, the fill was silty in nature and is probably a reworked till. Therefore, it is likely to have a lower infiltration capacity than the surrounding glaciofluvial deposits.

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6.5 Transient and Solute Transport Parameters Although transient simulations are not really necessary for long-term fate and transport analysis, a number of transient simulations were performed as part of calibration.

Calibration of the model can be greatly refined through attempting to match transient events. Because transient simulations were performed, it was necessary to estimate and then calibrate storativity or storage coefficient and specific yield (Sy). Because of the high topographic relief in the area encompassed by the model, specific storage (Ss) was specified rather than the storage coefficient (specific storage is equal to storage coefficient per foot of aquifer thickness). Specific storage works more accurately with unconfined model layers.

Storativity was initially calculated based on the results of the June MW-I07C pumping test, as shown in Table 5-1 of Reference 1-5. Simulation of the pumping test resulted in some localized zonation. Some special simulations of response to pressure transient testing, to reservoir fluctuation, to dam tailwater fluctuation, and to response to the on-off cycles of the plant water well were used to refine values locally. Figures 6-19 through 6-25 show the final zone distribution, and Table 6-4 describes the values assigned to each zone.

Table 6-4 also shows the porosity of the zones defined on Figures 6-19 through 6-25.

Porosity of the glacial till was calculated from standard geotechnical equations using the values of specific gravity, water content, and total unit weight in Table 2 of Reference 2-

3. The porosity of the glaciofluvial deposit of 0.3 was taken from Reference 6-1, which states in the Executive Summary that the effective porosity falls in the range of 0.24 to 0.37. The porosity of the bedrock zones was estimated from experience.

Tritium transport simulations required the specification of dispersivity and radioactive half-life. Several ranges of dispersivity values were tried during the initial simulation of transport of the IXP leak to Sherman Spring. The most reasonable spread of the leak in the longitudinal and transverse direction was obtained with the following values:

longitudinal dispersivity (DL) = 10 feet; transverse dispersivity (DT) = 1 foot; and vertical dispersivity (Dv) = 0. 1 foot. The vertical dispersivity was taken from experience as 10%

of the transverse dispersivity. These values were applied throughout the entire model domain.

The radioactive half-life of tritium was set at 4540 days, Reference 1-1.

Since no fate and transport runs were made with a sorbing solute, it was not necessary to define KD values that would create a retardation effect.

6.6 Model Calibration and Verification The calibration of the model was based primarily on a comparison of "observed" and "predicted" heads and on observed versus calculated vertical gradients for the 100-series monitoring wells on a pre-demo, long-term average annual basis. The pumping test on 39

MW-107C was used to refine values in the vicinity of that well. Some other localized changes were made in response to specialized simulations as described below. A "verification" data set made up on the non- 100-series monitoring wells was run with the calibrated model. Although traditional trial-and-error changes of parameters were used in calibrating to local conditions, the initial modeling approach was to use a parameter estimation procedure provided by Groundwater Vistas. Groundwater Vista's parameter estimation procedure employs Marquardt's modification to the Gauss-Newton nonlinear least-squares parameter estimation technique.

The average annual groundwater elevations for each monitoring well were calculated by simply averaging all available hand-measured readings for each well. The length of record and number of measurements varies from well to well. There were no directly applicable USGS long-term monitoring well records available to correlate individual records to average long-term averages. Most of the 100-series wells have been monitored since July 2003, whereas the CB and CW series have been monitored since 1993. As shown in Figure 6-26, at least the last two years of precipitation have been somewhat above the long term average at Readsboro, VT (5 miles to the north), of 49.08" per year (p. 6A-8 of Appendix 6-A of Reference 1-1). Therefore, the pre-demo calibrated model, which was calibrated with the I00-series monitoring well data sets, may over-predict the heads for the longer term wells, which is what the verification statistics show. The 100-series monitoring wells were chosen for calibration, however, because of the detailed hydrographs available for most of these wells and because multi-level wells exist at each cluster, enabling calibration by vertical gradients.

Calibration residuals (observed values minus predicted values) for the steady-state regional model are calculated by multiplying the difference between observed and predicted head by the weighting factor for each "target" or observation point. Weights for all observed data were assigned as 1.0 since all monitoring wells were accurately surveyed and a reasonable number of data points exist for each monitoring well through time.

The model is highly nonlinear due to the large variability in elevation across the model, thin soil layers over much of the model domain, and the choice of running the model as unconfined. The model would only run using the PCG2 solver (pre-conditioned conjugate gradient method of solving the matrix) with highly damped parameters. Initial solutions that converged required the use of a "rewet" algorithm that is rather crude, but kept the bouncing of predicted head elevations between iterations from causing the model to crash. After obtaining an approximate solution, upland areas of the model were successively turned to no-flow cells where they are predicted to go dry. This damps the solution process further. Eventually the rewet algorithm was turned off and the mass balance error came under control, although not so low as can usually be achieved (see Table 6-5). Once a steady-state solution was obtained, the model was run as a transient solution (but with constant recharge and all other conditions constant) for 600 days using the calibrated Ss and Sy and average annual precipitation recharge to further minimize the flow mass balance errors to something on the order of 0.1%.

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Chemical mass balance errors for the 20-year tritium fate and transport simulation discussed below were variable by layer, as shown in Table 6-6. Most of the layer chemical mass balance errors were in the normal range for this type of simulation.

Several layers had very localized high errors in one or two cells near constant heads, but it did not affect the mass distribution in the rest of the model area. The third-order total-variation-diminishing (TVD) scheme was used to solve the advective term with a Courant number of 1, which reduces numerical dispersion and artificial oscillation, but still creates some negative concentrations in upgradient directions. However, all of the Method of Characteristics (MOC) methods produced very large dispersion in the upgradient direction. Although the generalized conjugate gradient solver with full dispersion tensor helps to remove stability constraints on the transport time step size, the maximum time step was still only 0.5 days.

6.6.1 Single Head Calibration The model was calibrated for steady-state average annual heads and for steady-state average annual vertical gradients. Table 6-7 and Figures 6-27 and 6-28 summarize the individual head calibration statistics for the pre-demo steady-state condition. The residual mean is 0.34 feet with a standard deviation of residuals divided by the range of measured heads of 0.065 which is within normal criteria. Two of the largest residual errors were at MW-1I13C and MW-i1OD. MW-i113C is near the top of the high steep bank near the Deerfield River. That well is located in a grid cell that is 100 feet east-west and 50 feet north-south. Repeated attempts to improve the calibration in that area suggested the need to improve the horizontal cell size discretization, but that was not deemed necessary because of the relative unimportance of this area to the main focus of the model. It has been difficult to calibrate MW-I OD. This well is located quite close to the MW-I107 cluster and responded to the MW-I 07C pumping test, but has a measured head about 9 feet lower than MW- 107C, E, or F. In order to produce a reasonable connection that permitted the MW-1 OD well to respond in the right magnitude to pumping in MW-I 07C, the predicted head is much higher than would be the case if a much more muted connection was simulated. Fortunately, MW-1 OD is upgradient of the main area of interest in simulating future tritium concentrations.

6.6.2 Vertical Gradient Calibration Table 6-8 and Figure 6-29 show the calibration statistics for the pre-demo, vertical gradient predictions under average annual recharge. Vertical gradients are notoriously difficult to match, but the model does a reasonable job in this case. In this highly layered geologic environment, measured vertical head differences were as high as 54.5 feet. The standard deviation of the residuals divided by the range of head differences was 0.096, which is respectable for this model. Measured gradients between the bedrock and the next.higher monitoring well show both positive and negative values in the data set. A major objective in the calibration of vertical gradients is to get the direction correct, although the magnitude is often hard to match. As shown on Table 6-8, there are 5 pairs where the direction was not simulated correctly: MW-102C to B; MW-106D to B; MW-107B to D; MW-109B to D; and MW-I IOD to B. With the exception of the MW-109 41

pair, the other predicted gradients are very close to neutral, at least. It was very difficult to produce upward gradients in the bedrock in this model. It required putting in small high transmissivity zones that led from the upland area into the area of the well of interest. With the lack of data on where these linears might lie, it made such placement speculative. Fortunately, there are no areas of bedrock with high concentrations of tritium that would make it necessary to have a better understanding of the nature of bedrock flow.

6.6.3 Verification Data Set Calibration A "verification" data set was run with the same model that was used for the pre-demo calibration. The objective of using a verification data set is to test a separate set of points at which heads were measured to see how much the calibrated model was biased by adjusting local parameter values to achieve local head calibration. The more this localized parameter adjustment is needed and done, the less likely the verification data set will achieve good calibration. The verification data set was comprised of wells that were not in the 100-series designations. Many of the wells shown on the calibration statistics table in Table 6-9 have been monitored since 1993.

Although the verification data set standard deviation of residuals divided by the range of measured heads is 0.084 and in an acceptable range, the residual mean is -4.81 feet, which suggests the model over-predicts the heads (which, as discussed above, may be due in part to differences in recharge over the long term versus the short term with the two calibration data sets). Also, five of the residuals are fairly large: CB-4; CFW-2; CFW-3; CFW-4; and CW-10. CB-4 is in an area where the groundwater gradient on the bank of the River is very large and calibration is made more difficult by large grid cell sizes. CW-10 is in bedrock in an area where no particular attention was paid to bedrock well calibration and, as stated above, bedrock well calibration is difficult at best since less attention has been paid to characterizing the bedrock groundwater regime since it is not important to fate and transport issues at the site. CFW-2, 3, and 4 are in the Southeast Construction Fill Area. No attempt was made to calibrate wells in this area as it was outside of the main area of modeling interest. CFW-3 and CFW-4 are clustered wells with no drilling logs available so the assumed properties of the fill and soil in this area are apparently in error; however, not enough data exist to develop an accurate layering in this fill area. It is apparent from this that the fill is thicker and more permeable than assumed in the model development. Fortunately, in the main area of interest, the area from MW-107 down to Sherman Spring, the residual errors are quite small.

6.6.4 Discussion of Sensitivity Analyses Even very good calibration of a groundwater model does not mean that all of the properties are correctly spatially defined as there are many combinations of variables that can produce similar point predictions. The sparser the data set, the less unique the solution if it is based on water level matches alone. The systematic variation of individual parameter values above and below the calibrated value gives a good indication of which variables are the most important to the calibration. Sensitivity analyses have 42

been performed on horizontal hydraulic conductivity, vertical hydraulic conductivity, and recharge rates.

Parameter zones were chosen for sensitivity analysis if the zones covered a large area of the model or the zone had multiple site monitoring wells. The sum of squared residuals (SSR) is graphed on the Y-axis as it usually is the most sensitive calibration statistic with the widest range in this type of analysis. The parameter multiplier is given on the X-axis.

The parameter multiplier is what is multiplied by the value used in the calibrated model:

1.0 equates to the value used in the calibrated model. Ideally, the SSR would be lowest at a parameter multiplier of 1.0 and be higher for parameter multipliers that would be either higher or lower.

Many of the sensitivity analyses show Type I Sensitivity as defined by ASTM D 5611, meaning that variation of an input causes insignificant changes in calibration residuals as well as the model's conclusions. During the calibration process parameters were modified if Type II Sensitivity was indicated, even though changes may have produced little change in model conclusions. Some of the sensitivity analyses show Type III Sensitivity where variation of an input causes significant changes to both the calibration residuals and to the conclusions derived from the model and parameters were generally modified, unless otherwise noted, to minimize error. Type IV Sensitivity was not formally investigated where the change in calibration residuals is insignificant but the change in the model's conclusions would be significant. However, the extensive trial and error process used to build this model provided the opportunity to try many individual changes and combinations of changes of parameters and Type IV Sensitivity of at least the flow model parameters has been vetted fairly thoroughly.

6.6.4.1 Horizontal Hydraulic Conductivity Sensitivity The horizontal hydraulic conductivity was simultaneously increased in the same proportion in both the X- and Y-directions. The first eight graphs on Figure 31 show the sensitivity of Zones 1, 3, 6, 7, 8, 9, 10, and 14. Zones 1, 3, 6, and 9 are the most sensitive to perturbation of the Kxy value. With only a couple of minor exceptions where the parameter is not sensitive to change, the analyses show that a slight change in parameter could improve calibration slightly. Although an important portion of the model has Zone 2 silty till soils, only one of the calibration wells was in this zone. Notice that Zone 6, which is an implied high permeability zone in the valley bottom, is a very sensitive parameter. Although no direct evidence exists for the choice of permeability for Zone 6, the calibration of the model is quite dependent on it having a relatively high permeability.

6.6.4.2 Vertical Hydraulic Conductivity Sensitivity As often found in regional models, the vertical hydraulic conductivity is not a very sensitive parameter. As shown on Figure 6-31, the two most sensitive zones are the deep bedrock and the glaciofluvial deposits, where the model appears to be optimized. For some of the less sensitive zones, there is a suggestion that model calibration could be improved slightly by decreasing the Kz (except for Zone 3), but the effect would be 43

minor and the model has been constrained to normal ranges of ratios between Kxy and Kz.

6.6.4.3 Precipitation Recharge Rate Sensitivity The next to the last two sensitivity analyses graphs on Figure 6-31 are focused on the two primary recharge zones. The graphs suggest that Zone 1, over the upland areas of thin soils, is moderately sensitive, but the model seems to have an optimum value. Zone 2 covers the glaciofluvial deposit area and is the area within which the most monitoring wells occur. It is very sensitive to recharge rate, but again, the model appears to be optimized.

6.6.4.4 Drain Conductance Sensitivity The last sensitivity analysis in Figure 6-31 is on drain conductance. Notice that the parameter is sensitive, but the parameter used of 100 cubic feet per day per square foot per foot of head difference is very close to optimum. The analysis suggests that one could multiply the parameter by three to get a slightly better fit, which would also allow a slightly higher recharge rate to be used, but this has not been done because of the relatively minor impact on the model.

6.7 Discussion of Various Model Test Runs The pumping test on MW-I 07C was simulated early in the model development to assist in defining model parameters in the critical areas of tritium release on the site. Since there was no attempt to recreate the antecedent groundwater positions prior to the start of the pumping test, this does not classify as a calibration. The main interest was to reproduce the general magnitude and range of drawdown as measured in monitoring wells from the pumping of MW-107C. Similarly, a number of model test runs were made to evaluate the capability of the model to reproduce the effects of various pressure transients inferred from the hydrograph analyses. The recharge that occurs during any particular time frame is a complex function of antecedent moisture conditions, temperature conditions, snow cover, rainfall intensity and other factors that were not recreated before each of the specific test runs described in this subsection. The site history over the period 2003-2006 is very complicated in terms of when impervious cover (like asphalt and concrete slabs) was removed from certain areas, when certain drains were created or discontinued, and when certain excavations were created and backfilled.

The starting point for all these test runs was the model-predicted average annual heads under pre-demo conditions.

6.7.1 MW-107C Pumping Test Simulation This complex pumping test and the corrected water levels for each monitoring well are described in Reference 1-5. Figure 6-32 shows the individual graph comparisons of the measured and predicted conditions during a 2.3-day test period that started about half a day before the step drawdown test. The model was not set up to simulate the step 44

drawdown test, but rather the main 24-hour constant rate test. As one can see from the graphs, the "computed" heads all declined during the test period, but not necessarily in response to the pumping test. Starting from a set of initial heads, a transient simulation with small time steps with otherwise steady-state parameters will often produce small adjustments to heads in various model cells. The main thing to look for is the incremental change in the computed curve starting at about 1.2 days.

Although one might not infer it from looking at these graphs, the "computed" response to the pumping test was quite sensitive to the selection and arrangement of permeability and specific storage in the multiple layers of the model in the vicinity of MW-107. Many (meaning on the order of 100) different trial combinations of the parameters were tried to achieve the computer-simulated responses that were in the right order of magnitude of response as shown on these graphs. For those wells that had obvious measured responses such as MW- 102A, 107C, 107E, 107F, II OC, and 111 C, the computed responses are quite close in magnitude. For the special case of MW-I 07C, a special correction is needed for estimating the actual drawdown in a well simulated to be pumping in a finite-difference cell in which the drawdown is averaged over the size of the model cell containing the well. The correction formula can be found in Reference 6-2. Applying the correction for this particular case, the predicted drawdown would be 8.5 feet in the well itself beyond that predicted for the finite-difference cell. So the corrected computer-simulated drawdown in MW-107C would be 1101.3 feet, which are 3.6 feet more than measured, rather than 4.9 feet less than the measured drawdown shown on Figure 6-32.

6.7.2 Simulating the Effect of Plant Well Pumping Inspection of hydrographs indicated an occasional significant drawdown in some monitoring wells on the site. The hydrographs showed a typical form of well drawdown and recovery. Since there are no water wells within several miles of the site except for the plant well that now serves the ISFSI, the ISFSI well is assumed to be the source of the pressure transient. Information from Cushing & Sons well driller indicates that the well has a five gallon per minute capacity pump. March 17, 2006, monitoring well hydrographs suggested that the well was pumped for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> in the morning. By adjusting the length, depth, and permeability of a bedrock linear extending from the plant well northward through the MW-107 area, the following drawdowns were obtained as part of a 4.2-day simulation:

Mon. Well Measured head change, ft. Simulated head change, ft.

Plant Well No data 7.8 MW-lO1B No data 2.1 MW-102B 3.1 1.4 MW- 104B <0.1 .03 MW-105B 0.25 0.2 MW-107B 5.2 1.4 45

6.7.3 Simulating the Effect of Tailwater Elevation Fluctuation on MW-113C As shown on Figures 5-22A and 5-22B of Reference 1-5, MW-i 13C rose and fell in concert with Sherman Dam releases, which was translated into rise and fall of tailwater.

A crude rating curve was developed for the River cross section below the dam using the traditional Manning formula, which translated documented flow releases in cubic feet per second into river rise and fall. This was further translated into transient elevation changes in the constant heads defined for the River elevation with time steps of one hour, which is the recording interval for flow releases from the dam. The results of the simulation for 4.5 days showed the following results:

Mon. Well Measured head change, ft. Simulated head change, ft.

113C 0.8 0.6 106B 0.15 0.25 106D 0.2 0.3 106C <0.1 0.1 6.7.4 Effect of rise and fall of Sherman Reservoir Three monitoring wells appeared from the hydrographs to show closely-linked effects of the rise and fall of Sherman Reservoir: MW-I08, MW-105, and MW-I 13C. Transient constant head conditions were defined in Sherman Reservoir to simulate the change in Reservoir elevation in the early morning of March 14, 2006, using a one-hour time step, which is the recording interval for Reservoir elevation. Using a 3-day simulation, the following results were obtained:

Mon. Well Measured head change, ft. Simulated head change, ft.

105B 0.1 0.01 108A no change discernible 0.01 108C 0.5 1.0 113C no hydrograph no effect predicted The last entry in the table for MW-I 13C is significant because it appears from Figures 5-22A and 5-22B of Reference 1-5 that when the Reservoir fell 0.4 feet, MW-1 13C elevation decreased about 0.2 feet. It is not certain, at this time, how that pressure transient is transmitted.

6.7.5 Response to heavy rainfall events Simulating response to rainfall is a complicated task and usually requires the use of an unsaturated-saturated flow model if the unsaturated zone is much over a few feet thick.

However, model runs were made to simulate response to rainfall to gain some insight into the response capabilities of the model and the behavior of the recharge system.

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The period 11/20/04 through 12/3/04 was simulated when there were several multi-day heavy precipitation events during a relatively normal pattern of one- to two-foot variation in Sherman Reservoir level. If a daily rainfall event exceeded the average daily recharge rate, then that proportion was used to increase the recharge for that day.

Mon. Well Measured head change, ft. Simulated head change, ft.

CB-2 4.5 1.2 CW-6 3.5 1.9 CB-6 1.0 5.2 MW-107B 2.2 16.5 MW-105B 2.8 14.4 MW-105C 2.7 7.3 MW- 104B 2.0 4.6 Several things ate apparent from the above comparison table. The model over-predicts the bedrock well measured responses. The model shows a very fast response, whereas the measured response is slower and more diffuse. This is undoubtedly due to the lag time between the fall of the precipitation and its infiltration through unsaturated till and bedrock to reach the water table. In the glaciofluvial deposit represented by CW-6 and CB-6, one is overpredicted and one is underpredicted. In the till well in layer 2, CB-2, there is an underprediction. In the layer 3 sand layer represented by MW-105C there is an overprediction. The local infiltration of rainfall depends greatly on thickness of the unsaturated zone, the proximity to natural drainage features or even underground piping that might tend to act as a drain, and local runoff coefficients. Focusing on such micro-detail was beyond the scope of this model, which was more focused on large scale groundwater patterns over long periods of time where local surface variations in infiltration are not so important.

6.8 Groundwater Head Distributions, pre- and post-Demo Conditions Figures 6-33 through 6-40 show the pre-demo average annual simulated head equipotentials for all of the layers where sand lenses are simulated, plus the two bedrock layers. Since all layers of the model are treated as isotropic in the horizontal plane, flow would be perpendicular to the contours, except where two zones of different permeability were juxtaposed. In this latter case, flowlines are refracted according to Snell's Law in passing from one permeability zone into another. Figure 6-33 shows the phreatic surface, which is the most important to the transport of the IXP leak between the MW-107 area and Sherman Spring. Notice a very subtle groundwater divide is predicted just north of the MW-104 and MW-105 area and flow from MW-107 is directed generally west-northwestward. The flow pattern is similar but somewhat smoothed in layer 3 as shown on Figure 6-34. In Figure 6-35, which shows the pattern in layer 5, there is a subtle groundwater divide just north of the MW-107 cluster that keeps most of the flow going west-northwestward from that area. In layers 7, 10, and 12 (Figures 6-36, -37, and

-38) the flow is generally west-northwestward from the MW-107 area in the general direction of Sherman Spring. In the shallow bedrock, as shown in Figure 6-39, there is a rotation of the flow direction toward the southwest, westward of the axis of Sherman 47

Dam. Figure 6-40 shows the deep bedrock flow pattern throughout the entire model domain. Notice that the model is simulating two general focused discharge areas in the Deerfield River Valley, both of which are at the downstream foot of dams on the River where bedrock linears perpendicular to the River are defined, based on matching bedrock heads in the site area and the estimated water elevation of the Furlon House well.

In the post-demo state, some additional recharge has been added to the model in the industrial area, where in the pre-demo state the recharge was set at zero. Also, some local soil hydraulic conductivities have been changed in the model to reflect the placement of various fill materials in excavations made to remove underground structures, remove contaminated soils, or add a fill extension on the abutment of Sherman Dam. Figures 6-41 and 6-42 show the new hydraulic conductivity distributions in layers I and 2, respectively, of the model. The fill material consists of some onsite soils that were thermally treated for PCB removal, some broken up concrete into pieces smaller than one-foot across, some broken up asphalt, and some fill taken from an offsite borrow pit in what was likely silty glacial till. Of particular interest is the fact that the bottom ten feet of the excavation for soil removal that went below the water table in the Spent Fuel Pool/IXP area was filled with broken concrete, which was then topped by several feet of broken up asphalt before being topped with soil. Therefore, a small zone of high permeability material has been added in layer 2 east of MW-107 to reflect the rubble placement.

Figure 6-43 shows the net drawdown or increase in average annual water table that the model predicts will occur near the top of the water table. Negative numbers indicate that an increase in future water table elevation is predicted. In the industrial area, a water table increase of several feet is anticipated, increasing to the east, due mostly to an increase in recharge capability. One high spot to the northeast of the former VC is due to a combination of the placement of some low permeability fill to extend the Sherman Dam height to the east, and to a change in the elevation of drainage paths in that area. The area to the southwest of the ISFSI is probably due to a change in the specification of the elevation of the drainage ditches in that area.

Figure 6-43A shows the contours of the phreatic surface in the site area in the post-demo state. The head pattern is fairly similar to Figure 6-33. A forward particle track beginning at the mid-saturated depth of layer I at MW-107 follows a similar course to that shown in Figure 6-44 (discussed below), but it veers slightly south of Sherman Spring and goes deeper into the ground (as deep as model layer 7) compared with Figure 6-44, where the particle stays wholly within model layer 1.

6.9 Specific Fate and Transport Simulations 6.9.1 Reverse Particle Tracking from Sherman Spring One of the major objectives of the model development was to simulate the 1963 IXP leak and the long-term fate and transport of that leak. The first simulation that was performed after developing the calibrated model was to do a 760-day reverse particle tracking from 48

Sherman Spring using MODPATH, to see where the particle might have originated. On page 18 of Reference 1-3 it states that the apparent travel time for the "core" of the plume to travel from MW-107 to Sherman Spring in the glaciofluvial deposit is 760 days.

The reverse particle track for 760 days from Sherman Spring is shown on Figure 6-44 and basically confirms this calculation with the model. Notice the path from MW-107 travels north-northwesterly first toward MW-105, then turns westward to flow to Sherman Spring.

6.9.2 Simulation of the IXP Leak of 1963 Since the SFP/IXP leak was the single most significant release of radioactive water to the groundwater at the site, and since the concentration of tritium was measured in Sherman Spring from December 1965 onward, much of the model development and calibration work was focused on reproducing the record of measured tritium concentration with time at Sherman Spring. The key variables in generating the source term were the time span over which the release occurred, the average radioactive content of tritium in the source, and the rate at which the water was released to the ground. The combination of values that most closely approximated the December 1965 peak concentration measured in Sherman Spring was an average release rate of 1000 cubic feet per day, a tritium source strength of 32,000,000 pCi/L, and a 540-day release period starting March 1963. The timing for the start and stop of the leak is based on plant operating records. The tritium concentration in the ion exchange pit was described in Reference 6-3 as being in the range of 3.5 to 3.7E7 pCi/L. Based on conversations with YNPS employees, 1000 cubic feet per day is within the possible range. The spill was simulated by using injection wells in the location of MW-107. Since the elevation of the bottom of the Spent Fuel Pool and IXP is below the top of layer 2 of the model where the till starts, the well was defined as spread across both layers and the model was allowed to calculate the split between the layers of how the 1000 cubic feet per day was distributed. The mass balance calculation shows that 998:8 cubic feet per day went into the top layer and 1.2 cubic feet per day went into layer 2.

A model was run to simulate the initial leak followed by 210 days of no leak to get to Dec. 1965 when testing of Sherman Spring began. Then the model simulated 20 years of transport of the tritium that had already been distributed from the leak. Figure 6-45 shows the simulated concentration of tritium at Sherman Spring compared with the measured concentration of Sherman Spring. There is very good agreement although the curves diverge slightly about 1977. It appears that another source of tritium had developed and was causing a slight rise in concentration for a few years. Plant records indicate that the Spent Fuel Poll Liner was installed between 1978 and 1981 and likely stopped small leaks through hairline cracks in the concrete.

No site-wide groundwater monitoring existed in 1985, so we have used the model to simulate the distribution from the IXP leak for the first 20 years as well as 20 years later in 2005. Figures 6-46 through 6-50 show the change of tritium concentration with time in various layers of the model. Even at 20 years there was a remainder of the northward bifurcated plume going into Sherman Reservoir in layer 1, although that had dissipated 49

within 40 years. In layer 1 the remaining concentration of tritium at 40 years was in the Deerfield River below Sherman Dam. Notice that the plume in that area had decreased by an order of magnitude over 20 years and had actually withdrawn somewhat northward in the last 20 years rather than migrating downstream.

In layer 3 of the model, where the continuous sand seam was defined for several hundred feet around the MW-107 area, Figure 47 shows a more extensive presence of tritium than in layer 1 but still an order of magnitude reduction in the downgradient area from 1985 to 2005. The 2005 distribution does not agree with the known concentration of tritium in MW-107C from 2003 onward. It is apparent that other sources of tritium have leaked since the original IXP leak of 1963. In addition, the region around the VC was disturbed during decommissioning, thus releasing more mass of tritium from the unsaturated zone.

Figure 6-48 shows the distributions of tritium in layer 7. With depth, the movement of tritium is simulated to be slower and is less diluted. But the decrease between 2005 and 1985 is still an order of magnitude and the 2005 extent is less than the 1985 extent under the Sherman River.

Figure 6-49 shows the simulated distributions in model layer 14 or the top bedrock layer.

As discussed above, the plume turns more southwestward in the bedrock. Again, the tritium concentration reduction in 20 years (from 1985 to 2005) is an order of magnitude and there has been some retreat in the extent of the plume.

Figure 6-50 shows the tritium distribution in the deep bedrock. Notice it has not reached the area under the Sherman River and the concentrations, which are very low in any event, have decreased an order of magnitude in twenty years.

6.9.3 Simulation of Tritium Concentrations in MW-107C in 2006 The complete tritium release history at the site can never be known in detail. However beginning in 2006 with the end of most excavation activity and the extensive groundwater testing program of April 2006, there is a reasonably complete characterization of the tritium in groundwater at the site. The April 2006 tritium concentrations were contoured in three dimensions and reverse-interpolated into the initial concentration matrices of the 15-layer groundwater model. Once the existing distribution of mass was established, the post-demo model was run for two years from 4/26/06. Figure 6-51 shows a comparison between model-simulated tritium at MW-107C going forward and the measured tritium at MW- 107C from April through December 2006. There is a relatively close comparison, although the linear regression line through the measured data suggests there may be a more rapid decrease after 300 days than the model predicts. The MCL concentration of 20,000 pCi/L is predicted to be achieved by early summer 2007 based on the linear regression of the measured samples and February 2008 based on the model simulation. Also shown in Figure 6-51 is the tritium concentration with radioactive decay as the only attenuation mechanism for tritium. Clearly, processes including advective dispersion and associated mixing and dilution are very important in the fate and transport of tritium at YNPS.

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6.9.4 The "Resident Farmer Well" Scenario The License Termination Plan specifies that compliance with the groundwater quality requirements of the plan is met if the hypothetical "resident farmer" well does not produce water that exceeds the maximum dose specified in the LTP or the EPA MCLs, which for tritium is 20,000 pCi/L. The first issue in testing compliance is to locate the portion of the site that will produce the highest dose to a water well. Based on both the computer simulations and 2006 measurements of groundwater quality at the site, it is clear that the geologic units with the highest dose concentrations exist in the vicinity of MW-107C. The model simulates two years of pumping following April 2007 with a hypothetical "resident farmer" well located at the MW- 107C location and pumping continuously at 0.67 gallons per minute as defined in the LTP. MW-107C intercepts layer 3 of the model and, based on the pumping test analysis and computer simulation, there appears to be a relatively low permeability till lying above and below the MW-107C well. For the purposes of this simulation, we further assume that the tritium concentration in those layers is the same in April 2006 as measured in MW-107C at 41,300 pCi/L. Figure 6-52 shows the results of the simulation.

Initial attempts to simulate the well in just layer 3 or in layers 2, 3, and 4 were unsuccessful. Those layers went "dry" because the pumping rate exceeded the ability of the model to deliver water to a well pumping at 0.67 gallons per minute in those layers.

The maximum yield of these three layers is simulated to be 0.035 gallons per minute.

When model layer 5 was added (MW-107E and -107F are located in layer 5), the well was successful and layer 5 becomes the dominant water producer. The concentration plots of tritium in layers 2 and 4 of the model (the low permeability till units) lie almost on top of each other. The model predicts that tritium concentrations in all layers would decrease to less than 20,000 pCi/L within 2 years of April 2007. Model layer 3 tritium concentrations would decrease somewhat sooner than the model layers 2 and 4 (glacial till). Layer 5 concentrations would decrease to 5000 pCi/L within the two-year pumping period. There is more dilution and a lower initial concentration in model layer 5, so the rate of decline is slower there.

The concentration of water in the well is simulated for both April 2007 and for April 2009 as shown on Table 6-10. Using the model well flux from each layer times the concentration of tritium as predicted, divided by the total pumping rate, yields a weighted average concentration of tritium in the well of 8150 pCi/L in April 2007. In April 2009, the weighted tritium concentration in the well is simulated as 5 100 pCi/L.

When model layers 2, 3, 4, and 5 are used to pump at 0.2 gallons per minute, the maximum tritium concentrations in the well are not much different from the Table 6-10 numbers, which represented 0.67 gallons per minute: 8160 pCi/L in April 2007 and 5350 pCi/L in April 2009.

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In summary, the model predicts that if a resident farmer activated his well in April 2007, the maximum tritium concentration in the hypothetical resident farmer's well would be significantly below the MCL.

6.10 Summary A regional 3-D groundwater flow model based on MODFLOW96, as implemented in Groundwater Vistas GWV4.25, has been constructed to include the Yankee Nuclear Power Station site. This model covers a large area on both sides of the Deerfield River so that the model boundaries are naturally located on streams and groundwater divides far from the nuclear plant site. The finite-difference grid cells are discretized with variable spacing from 25 feet near the center of the plant site to as far apart as 400 feet near the outer limits of the model. The model consists of 15 layers: 13 soil layers and two bedrock layers. The model extends 500 feet into bedrock. All of the top 14 layers of the model were permitted to perform as unconfined layers if the layers above were dewatered by the simulation.

Data sources utilized to parameterize the model came primarily from YNPS records.

Some base maps and orthophotos were taken from the State of Massachusetts GIS database, but the only geological data of use from that source was a sand and gravel aquifer map. These sources were pre-processed with Rockworks, Surfer, and ArcView software. Forty-four monitoring wells from 13 well clusters with measured water levels from a variety of depths and geologic units were used as calibration targets for the steady-state pre-demo model. Both single head comparisons and vertical head difference comparisons were used for calibration. A verification data set made up of separate wells was also checked for calibration. Sensitivity analyses were run on the major variables involved with hydraulic conductivity, recharge, and drain conductance, and showed that optimum values were chosen except for several variables for which the calibration error was not sensitive to parameter changes in any event.

The model was tested against the results of the MW-107C pumping test and the results were used to refine the selection of hydraulic conductivity and specific storage parameters. The model simulated the groundwater head effects of pumping of the plant well, of fluctuations in tailwater elevation below Sherman Dam, of Sherman Reservoir elevation fluctuation, and of response to a heavy precipitation event.

The calibration goals were to achieve a standard deviation of residuals (observed versus predicted levels) divided by the range of measured values (highest value minus lowest value) of< 0.15 and to keep the vertical gradients in the right directions. The first goal was achieved in all cases; there were several exceptions to the second goal as explained in detail in the report.

The model was used to verify the direction and time of travel from the IXP to Sherman Spring and then to simulate the May 1963 leak from the IXP and compare measured Sherman Spring tritium concentrations over time with the simulated results. These results are in good agreement. The model has also been used to simulate the change in 52

tritium concentration from April 2006 through December 2006 at MW-107C, again, with good agreement.

With only minor exceptions that do not affect the overall tritium transport analysis from the area of the IXP leak site, the model reproduces well the transport of tritium in the glaciofluvial layer and within several signature sand layers embedded within the thick glacial till under the IA. The model reproduces the magnitude of pressure transient responses to the MW-107C pumping tests and a variety of other pressure transient events.

Although groundwater gradients between the bedrock and the next higher monitoring wells at several locations were not faithfully reproduced as to direction, most gradient directions were preserved among the 54 pairs tested.

The tritium transport simulations of the 1963 IXP leak suggest that the plume originally split into two main parts: one moving north to Sherman Reservoir, and one moving west to discharge in the Deerfield River. The portion discharging into the Deerfield River discharged to the River no farther than 1500 feet downstream of the toe of Sherman Dam.

Concentrations of tritium decreased in the downstream area by an order of magnitude between the 1985 and 2005 simulations, and the residual center of mass receded upstream. Concentrations in the deep bedrock are simulated to be very low.

Since the 1963 leak, other releases of tritium have occurred on the site and tritium has been released from unsaturated zones under slabs and pavements that have been removed as part of decommissioning. Therefore, although the 40-year simulation of the IXP leak is instructive in terms of showing the long-term fate and transport results of a major leak, the current distribution of tritium on the site cannot be based on assuming that the IXP leak is the only source of current tritium. To simulate results going forward, the comprehensive test results of the late April 2006 sampling were used to establish the distribution of tritium in the model layers at that time and then the model was run for three years to simulate that spread and attenuation.

Knowing that the tritium concentration currently exceeds the EPA MCL at MW-107C, the model was used to evaluate the potential attenuation of tritium in that area, which has been identified as the only portion of the site even close to exceeding LTP dose standards or EPA MCLs. Because the thin sand zone in which MW-107C is located cannot provide more than 5% of the needs of the hypothetical resident farmer well as specified in the LTP, other soil units above and below MW-107C were tried in various combinations that would produce the required well yield, but at the highest dose. This resulted in combining other soil units with lower tritium concentrations but higher flow rates, such that the well concentration would be 8150 pCi/L in April 2007, decreasing to 5100 pCi/L in April 2009. Therefore, a randomly-located resident farmer's well at the site would not produce water in excess of LTP dose limits or EPA MCLs. The model suggests, however, that the highest point concentrations of tritium will not decrease below the EPA MCL of 20,000 pCi/L until about April of 2009. These points are in the glacial till above and below MW-107C. MW-107C is predicted by the model to decrease below the tritium MCL in February 2008, although the current trend based on sampling suggests it may come into compliance about June 2007.

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7.0 Conclusions and Recommendations 7.1 Groundwater Quality Status The LTP groundwater monitoring program at YNPS provides the framework for data collection, quality assurance, and reporting groundwater quality status at the facility.

Analytical results from the quarterly sampling program implemented at YNPS provide the data for comparing to standards, regulatory limits, and developing metrics for evaluating overall groundwater quality and plume status at YNPS.

Groundwater contamination by plant-related substances of concern (SOCs) has been observed in the glaciofluvial, glacial till, glaciolacustrine and bedrock aquifers units currently described at the facility. Consistent with the CSM for YNPS, the general configuration of contaminant plumes extends from the area adjacent and immediately downgradient of the former SFP/IXP to the Deerfield River. The mapped plumes are well defined both horizontally and vertically, and based on modeling results presented in Section 6 and site history, the observed groundwater contamination at the plant appears to have originated from releases of contaminated waters within the SFP/IXP complex.

Tritium is the only radionuclide that is detected in site groundwater, and is broadly distributed across YNPS site. Plant-related tritium concentrations in groundwater have declined substantially in recent years, and only one monitoring well (MW-107C) currently has tritium concentration in excess of the EPA MCL concentration of 20,000 pCi/L.

A statistical trend analysis for tritium was conducted for all monitoring wells included in the YNPS quarterly sampling plan. The results of the trend analysis indicate that most of the monitoring wells are stable and have no trend. Nine monitoring wells (CB-6, MW-101A, MW-105B, MW-106A, MW-107A, MW-107D, MW-107E, MW-I IA, and MW-111) and Sherman Spring have defined downward trends, and one monitoring well (MW-11 OC) has an upward trend. The monitoring well with the identified upward trend (MW-11 OC) had tritium concentrations ranging from 1,160 pCi/L in Q1 2006 to 2,590 pCi/L in Q4 2006, well below the 20,000 pCi/L MCL.

7.2 Evaluation of LTP Closure Criteria The LTP requirement for closure is 25 mrem/yr dose rate for all media and pathways.

That is further refined to contributions from soil, concrete debris, subsurface partial structures, and groundwater, based on the media-specific Derived Concentration Guideline Level (DCGLs). The results of groundwater testing have demonstrated that tritium is the only radionuclide consistently detected at the YNPS site. Since tritium is the only target radionuclide consistently detected in groundwater YNPS, DCGLs were not specifically developed for tritium or other radionuclides in groundwater. To evaluate a DCGL for tritium, YNPS used the approved groundwater DCGL from the Connecticut 54

Yankee LTP to calculate the dose rate that tritium would generate at the MCL (20,000 pCi/L), and used that dose rate (0.77 mrem/yr) to establish the total dose rate for groundwater.

While DCGLs for other radionuclides were not developed by YAEC for the YNPS site, NRC License Amendment No. 158 identified specific threshold concentrations of site-generated radionuclides. If the threshold values are exceeded or if a sum of the fractions formed by dividing the detected concentration by the threshold value is greater than 2.0, YAEC would be required to evaluate the need for site-specific groundwater DCGLs.

These NRC threshold values are summarized in Table 3-1.

In addition to the tritium dose rate developed in the LTP and the threshold values identified in NRC Amendment 158, YNPS has also committed to meeting the EPA MCLs for available well water that meets the resident farmer scenario. As summarized in Table 9-1 of Appendix 6A of the YNPS LTP, the water use for the resident farmer scenario on a yearly basis is estimated to range from 957 to 1,689 cubic meters per year with a calculated median value of 1323 cubic meters per year (Reference 1-1). The median value of 1,323 cubic meters per year corresponds to a well pumping rate of 0.665 gallons per minute (gpm). Thus, for a water supply well to be able to meet the resident farmer scenario, the well will be required to be pumped constantly, delivering water at a minimum rate of 0.665 gpm.

In addition to comparing the 2006 quarterly groundwater data to the MCLs for the resident farmer and NRC threshold values, time series plots were generated for tritium, and trend analysis was conducted. Results of the tritium trend analyses meet the LTP termination requirements if the trends are steady state or decreasing at the end of the monitoring period, and below the respective NRC threshold limits. Trends were evaluated using recognized industry standard statistical analyses.

None of the NRC threshold values were exceeded during Q I through Q4 2006, as the only radionuclide detected in site groundwater was tritium. Tritium concentrations are below the MCL in all monitoring wells except MW-107C. MW-107C has had decreasing values during 2006 and has a statistically determined downward trend with concentrations decreasing from 41,300 pCi/L in QI 2006 to 29,100 pCi/L in Q4 2006.

All other monitoring wells in the monitoring program have either stable or no trend or downward trends, except for MW-I IC. The tritium concentration in MW-I IOC increased from 1,160 pCi/L in Q1 2006 to 2,590 pCi/L in Q4 2006. The tritium concentrations are an order of magnitude below the tritium MCL of 20,000.pCi/L and significant increases are not expected in this portion of the site. MW-I IOC is downgradient of the former SFP/IXP area where significant soil remediation was conducted, and all other monitoring wells in this portion of the site have stable or decreasing trends.

Recognizing that the tritium concentration currently exceeds the EPA MCL at MW-107C, a three-dimensional groundwater model was used to evaluate the potential attenuation of tritium in that area, which has been identified as the only portion of the site even close to exceeding LTP dose standards or EPA MCLs. Because the thin sand zone in which MW-107C is located is incapable of supplying the needs of the hypothetical resident farmer well as specified in the LTP, other soil units above and below MW-107C 55

were tried in various combinations that would produce the required well yield, but at the highest dose. This resulted in combining other soil units with lower tritium concentrations but higher flow rates, such that the well concentration would be 8,150 pCi/L in April 2007, decreasing to 5,100 pCi/L in April 2009. Therefore, we conclude that a randomly-located resident farmer's well at the site would not produce water in excess of LTP dose limits or EPA MCLs. The model suggests, however, that the highest point concentrations of tritium (in glacial till above and below the sand seam in which MW-107C is located) will not decrease below the EPA MCL of 20,000 pCi/L until about April of 2009. In the absence of any pumping, MW-107C is predicted by the model to decrease below the tritium MCL in February 2008, although the current trend based on sampling suggests it may come into compliance about June 2007.

Based on the groundwater sampling and model results, site groundwater meets the LTP closure requirements for License Termination.

7.3 Subsequent Sampling Recommendations Based on the review of the results of Ql through Q4 2006, quarterly sampling and observed long-term trends in wells, several recommendations concerning subsequent groundwater monitoring sampling events are as follows:

" Conduct one additional sampling round in the first quarter 2007 to confirm the tritium plume distribution and trend analysis developed in QI through Q4 2006

" The recommended analytical suite for the upcoming first quarter 2007 quarterly sampling event can be reduced and focused on those wells with high concentrations of tritium and increasing trends: MW-lOlA; MWI02D; MW-105B; MW-106A; MW-107A; MW-107C; MW-107D; MW-107E; MW-107F; MW-1 IOC; MW- I11C; and MW-I 13C.

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8.0 Acronyms CSM Conceptual Site Model DCGL Derived Concentration Guideline Level DI De-ionized DOE Department of Energy EPA Environmental Protection Agency FDR Field Daily Reports FSS Final Status Survey GEL General Engineering Laboratory GWV Groundwater Vistas HTD Hard-to-detect IA Industrial Area ISFSI Independent Spent Fuel Storage Installation IXP Ion Exchange Pit Kd Soil-water partition coefficient LSP Licensed Site Professional LTP License Termination Plan MADEP Massachusetts Department of Environmental Protection MCL Maximum Contaminant Level MDC Minimum Detection Concentration MDL Method Detection Limit MS Matrix Spike MSD Matrix Spike Duplicate MSL Mean Sea Level NAVD North American Vertical Datum NRC Nuclear Regulatory Commission NTU Nephelometric Turbidity Unit pCi/L picocurie per liter QAPP Quality Assurance Project Plan 57

QA/QC Quality Assurance/Quality Control Q1 First quarter water sampling period (April 18 to May 3, 2006)

Q2 Second quarter water sampling period (June 26 to July 12, 2006)

Q3 Third quarter water sampling period (September 12 to September 21, 2006)

Q4 Fourth quarter water sampling period (December 4 to December 14, 2006)

SCFA Southeast Construction Fill Area SFP Spent Fuel Pool SOC Substance of Concern SOP Standard Operation Procedure SSR sum of squared residuals TEDE Total Effective Dose Equivalent TVD total-variation-diminishing vig/L microgram per Liter USEPA United States Environmental Protection Agency USGS US Geological Survey VC Vapor Containment YAEC Yankee Atomic Electric Company YNPS Yankee Nuclear Power Station 58

9.0 References Reference 1-1 Yankee Atomic Electric Company, License Termination Plan,Rev 2, November 2006, as approved by NRC Safety Evaluation Report for License Amendment 158, dated July 28, 2005.

Reference 1-2 Yankee Atomic Electric Company, Site Ground Water Data Collection for YNPS Decommissioning,DESD-TD-YR-02-001, Rev 1, February 3, 2003.

Reference 1-3 Yankee Atomic Electric Company, Hydrogeologic Report of 2003 Supplemental Investigation, YA-REPT-00-004-04, March 15, 2004.

Reference 1-4 Yankee Atomic Electric Company, Report of ContinuingHydrogeologic Investigations in 2004, YA-REPT-00-010-05, April 14, 2005.

Reference 1-5 Yankee Atomic Electric Company, 2006 Interim GroundwaterReport, BYR 2006-112, 2006, November 28, 2006.

Reference 1-6 Yankee Atomic Electric Company, Groundwater Compliance Planfor License Terminationfor Yankee Nuclear Power Station, August, 2006.

Reference 1-7 Yankee Atomic Electric Company, AP-9601, Rev. 3; Site Characterization and Site Release Quality Assurance Program Plan (QAPP) for Sample Data Quality, April 2006.

Reference 1-8 Yankee Atomic Electric Company, AP-8601, Rev 4; Ground and Well Water Monitoring Program for the Yankee Nuclear Power Station Site, October 2003.

Reference 1-9 Yankee Atomic Electric Company, DP-9745; Groundwater Level Measurement and Sample Collection in Observation Wells.

Reference 2-1 Geophysical Survey Div., Gahagan Dredging Corp., 1956, Report of Seismic Survey, Yankee Atomic Electric Company Plant Site. A consultant report for Stone & Webster Engineering Corp., June 1956.

Reference 2-2 Weston Geophysical Corp., 1979, Geology and Seismology, Yankee Rowe Nuclear Plant. Consultant report prepared for Yankee Atomic Electric Company, January 29, 1979.

Reference 2-3 Gerber, R.G., 1981, Rowe Slope Stability, Consultant report to Yankee Atomic Electric Co., 5/26/81.

Reference 2-4 Framatome ANP, 2003, Site Ground Water Data Collectionfor YNPS Decommissioning. A consultant report to YNPS, 2/4/03.

Reference 3-1 YA-REPT-00-007-06, Data Assessment Report for Groundwater Sampling at YNPS January/February 2006.

Reference 3-2 YA-REPT-00-013-06, First Quarter 2006 Groundwater Report.

Reference 3-3 YA-REPT-00-014-06, Special Tritium Sampling Event, May 2006.

Reference 3-4 YA-REPT-00-0 17-06, Re-Analysis of 1st Quarter 2006 Samples for Tritium, Nickel-63 and Carbon-14.

Reference 3-5 YA-REPT-00-0 19-06, 2nd Quarter 2006 Groundwater Report.

Reference 3-6 YA-REPT-00-025-06, 3rd Quarter 2006 Groundwater Report.

59

Reference 3-7 YA-REPT-00-026-06, 4th Quarter 2006 Groundwater Report.

Reference 4-1 YA-REPT-00-016-04, Assessment of Boron Concentration in Groundwater at YNPS.

Reference 4-2 United States Environmental Protection Agency, 1999, Understanding Variation in PartitionCoefficient, Kd, Values, Volume II; Review of Geochemistry andAvailable Kd Values for Cadmium, Cesium, Chromium, Lead, Plutonium, Radon, Strontium, Thorium, Tritium and Uranium, EPA 402-R-99-004B, August 1999.

Reference 5-1 YA-REPT-00-0 13-04, Interim GroundwaterMonitoring Reportfor Yankee Nuclear Power Station, September, 2004.

Reference 5-2 YA-REPT-00-004-06, Summary GroundwaterReport for the Yankee Nuclear Power Station - 2005.

Reference 6-1 YA-REPT-01-008-03, 2003, Evaluation of GeoTesting Express Soil Testing and Determinationof Depth to Ground Water.

Reference 6-2 Rushton, K.R., and Redshaw, S.C., 1979, Seepage and Groundwater Flow. John Wiley & Sons.

Reference 6-3 Yankee Atomic Electric Company, 1965, Operation Report No. 51 for the Month of March 1965, a report for Yankee Nuclear Power Station submitted on April 27, 1965.

60

Table 1-1 Summary of Monitoring Well Completion Details Total Well Cement Well 8-Inch Date Depth Screen Well Screen Geologic Unit Screen Sand Diameter of Bentonite Grout Well Inside Well Screen Steel ScreenCmlee Interval WelID rildLeghDia. at Screen Pack Interval Sand Pack Seal Seal (in.) Wall Slot Size Casing CaIngevl(

(feet) (feet) (ft bg) Interval (ft bg) (inches) Interval (ft bg) Interval (PVC) (in.) Interval (ft (ft bo) bq)

CB-3 29-Apr-93 15 10 3 to 10 GF 3 to 15 5.000 2 to 3 0 to 2 2.25 Schd 40 I/U N/A CB-3R 29-Aug-06 16 10 6 to 16 GF 4 to 16 5.500 2.5 to 4 0 to 2.5 2.00 Schd 40 0.010 0 to 6*

CB-4 5-May-93 19 10 9 to 19 GF 8 to 20 5.000 7 to 8 0 to 7 2.25 Schd 40 I/U N/A CB-6 13-Sep-94 25 10 15 to 25 GF/UT 14 to 26 5.000 12 to 14 0 to 12 2.25 Schd 40 I/U N/A CB-8 20-Sep-94 19 5 14 to 19 GF 13 to 19 5.000 11.5 to 13 0 to 11.5 2.25 Schd 40 I/U N/A CW-10 8-Jun-98 30 15 15 to 30 Bedrock 14 to 30.5 4.000 13 to 14 0 to 13 2.00 Schd 40 0.010 N/A CFW-1 13-Dec-99 8 5 3 to 8 GF 2 to 8 4.000 1 to 2 0 to 1 2.00 Schd 40 0.010 N/A CFW-5 14-Dec-99 5 5 1 to 5 GF 0.5 to 5 5.000 0 to 0.5 1 to 0 2.00 Schd 40 0.010 N/A CFW-6 14-Dec-99 6 5 1 to 6 GF 0.5 to 6 5.000 0 to 0.5 0.5 to 0 2.00 Schd 40 0.010 N/A CW-5R 30-Aug-06 17 10 7 to 17 GF 6 to 17 5.500 4 to 6 0 to 4 2.00 Schd 40 0.010 0 to 7*

MW-100A 5-Aug-03 20 10 10 to 20 GF 8.3 to 20 5.500 6.0 to 8.3 0 to 6.0 2.00 Schd 40 0.010 N/A MW-100B 4-Aug-03 43 10 32.9 to 42.9 Bedrock 31.0 to 43 4.625 28.0 to 31.0 0 to 28.0 2.00 Schd 40 0.010 N/A MW-101A 11-Apr-06 23.5 5 18 to 23 GF/Fill 16 to 23.5 5.500 13 to 16 0 to 13 2.00 Schd 40 0.010 0 to 10*

MW-101B 13-Aug-03 156 10 142 to 152 Bedrock 140.2 to 156 4.625 138.5 to 140.2 0 to 138.5 2.25 Schd 80 0.010 0 to 11.25 MW-101C 15-Aug-03 99 5 94 to 99 LT-GL 92.1 to 99 5.500 90.0 to 92.1 0 to 90.0 2.00 Schd 40 0.010 0 to 15.3 MW-102A 31-Jul-03 39 5 33 to 38 UT 31.0 to 39 5.500 29.0 to 31.0 0 to 29.0 2.00 Schd 40 0.010 N/A MW-102B 24-Jul-03 131.5 10 120.2 to Bedrock 117.9 to 4.625 116.0 to 117.9 0 to 116.0 2.00 Schd 40 0.010 0 to 15 130.2 131.5 MW-102C 29-Jul-03 99 5 94 to 99 LT-GL 92.4 to 99 5.500 90.8 to 92.4 0 to 90.8 2.00 Schd 40 0.010 0 to 14.5 MW-102D 10-Feb-06 22 10 11 to 21 GF 9 to 22 5.500 7 to 9 0 to 7 2.00 Schd 40 0.010 0 to 8 MW-103A 17-Jul-03 26 10 15 to 25 GF 13 to 26 5.500 11 to 13 0 to 11 2.00 Schd 40 0.010 N/A MW-103B 10-Jul-03 295 10 284.5 to Bedrock 282 to 295 4.625 279 to 282 0 to 279 2.25 Schd 80 0.010 0 to 30 294.5 MW-103C 16-Jul-03 125 10 115 to 125 LT-GL 112.3 to 125 5.500 110.5 to 112.3 0 to 110.5 2.00 Schd 40 0.010 N/A MW-104A 6-Feb-06 27 10 10 to 20 GF 8 to 20 5.500 6 to 8 0 to 6 2.00 Schd 40 0.010 0 to 10 5.5:

MW-104B 3-Sep-03 194.5 10 184 to 194 Bedrock 182 to 194.5 182' to 187' 180 to 182 0 to 180 2.25 Schd 80 0.010 0 to 25 4.625:

187' to 194.5' MW-104C 11-Sep-03 99 10 87 to 97 LT-GL 84.8 to 99 7.625 82.8 to 84.8 0 to 82.8 2.25 Schd 80 0.010 N/A MW-104D 8-Sep-06 50 5 40 to 45 UT 38 to 46.5 5.500 35 to 38 0 to 35 2.00 Schd 40 0.010 0 to 25.5*

MW-105A 8-Feb-06 25 10 10 to 20 GF 8 to 20 5.500 6 to 8 0 to 6 2.00 Schd 40 0.010 0 to 8 MW-105B 20-Aug-03 75 10 64 to 74 Bedrock 61.8 to 75 4.625 59.6 to 61.8 0 to 59.6 2.00 Schd 40 0.010 0 to 25 MW-105C 21-Aug-03 45 10 27 to 37 UT 25.1 to 37 5.500 23.1 to 25.1 0 to 23.1 2.00 Schd 40 0.010 N/A MW-106A 30-Aug-04 22 10 12 to 22 GF 9.5 to 22 7.625 7.5 to 9.5 0 to 7.5 2.00 Schd 40 0.010 N/A Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 1 of 2, 2/8/2007 Condition Report

Table 1-1 Summary of Monitoring Well Completion Details Total Well Cement Well 8-Inch Date Depth Screen Well Screen Geologic Unit Screen Sand Diameter of Bentonite Grout Well Inside Well Screen Steel Well ID Completed Drilled Length Interval at Screen Pack Interval Sand Pack Seal Seal Dia. (in.) WallSlot Size Casing (feet) (feet) (ft bg) Interval (ft bg) (inches) Interval (ft bg) Interval (PVC) (in.) Interval (ft (ft bo _ bq)

MW-106B 27-Aug-04 265 10 251 to 261 Bedrock 249 to 265 4.625 230 to 249 0 to 230 2.25 Schd 80 0.010 N/A MW-106C 8-Sep-04 95 5 90 to 95 UT 86.5 to 95 5.500 80 to 86.5 0 to 80 2.00 Schd 40 0.010 0 to 25 MW-106D 14-Sep-04 155 10 144 to 154 LT-GL 142 to 154 5.500 132 to 142 0 to 132 2.25 Schd 80 0.010 0 to 25 MW-107A 5-Apr-06 30 5 21 to 26 GF 19 to 26 5.500 16 to 19 0 to 16 2.00 Schd 40 0.010 0 to 9 MW-107B 17-Sep-03 110 10 99.7 to 109.7 Bedrock 97.8 to 109.7 4.625 96.0 to 97.8 0 to 96.0 2.25 Schd 80 0.010 0 to 12.5 MW-107C 19-Sep-03 32 5 27 to 32 UT 25 to 32 5.500 23 to 25 0 to 23 2.00 Schd 40 0.010 N/A MW-107D 24-Sep-03 81.2 5 75 to 80 LT-GL 73 to 81.2 5.500 71.1 to 73 0 to 71.1 2.00 Schd 40 0.010 N/A MW-107E 15-May-06 70 5 52 to 57 UT 50 to 59 5.500 46 to 50 0 to 46 2.00 Schd 40 0.010 0 to 32 MW-107F 23-May-06 57 5 49 to 54 UT 47 to 55 5.500 40.5 to 47 0 to 40.5 2.00 Schd 40 0.010 0 to 25 MW-'108A 17-Jul-04 25 10 14.7 to 24.7 GF 10 to 25 5.500 6.1 to 10 0 to 6.1 2.00 Schd 40 0.010 N/A MW-108B 16-Jul-04 215 10 205 to 215 Bedrock 202.5 to 215 5.500 197.5 to 202.5 0 to 197.5 2.25 Schd 80 0.010 0 to 26 MW-108C 8-Jul-04 170 5 60 to 65 UT 57 to 67 7.625 51-57&67-170 0 to 51 2.00 Schd 40 0.010 0 to 26 MW-109A 3-Feb-06 20 10 10 to 20 GF 8 to 20 5.500 4 to 8 0 to 4 2.00 Schd 40 0.010 0 to 8 MW-109B 2-Aug-04 190 10 180 to 190 Bedrock 177.5 to 190 4.625 175.5 to 177.5 0 to 175.5 2.25 Schd 80 0.010 0 to 20 MW-109C 9-Aug-04 55 5 49 to 54 UT 46.8 to 55 5.500 42.5 to 46.8 0 to 42.5 2.00 Schd 40 0.010 N/A MW-109D 6-Aug-04 113 5 88.7 to 93.7 LT-GL 86 to 95 5.500 83-86&95-113 0 to 83 2.00 Schd 40 0.010 0 to 21 MW-110A 16-Feb-06 31 5 25 to 30 GF 22 to 31 5.500 17 to 22 0 to 17 2.00 Schd 40 0.010 0 to 10 MW-110B 6-Mar-06 110 10 100 to 110 Bedrock 98 to 110 4.625 93 to 98 0 to 93 2.00 Schd 40 0.010 0 to 38 MW-110C 20-Mar-06 51 5 46 to 51 UT 44 to 51 5.500 38 to 44 0 to 38 2.00 Schd 40 0.010 0 to 38 MW-110D 17-Mar-06 88 5 83 to 88 LT-GL 81 to 88 5.500 75 to 81 0 to 75 2.00 Schd 40 0.010 0 to 33 MW-i11A 30-Mar-06 23 5 18 to 23 GF 15.5 to 23 7.625 12 to 15.5 0 to 12 2.00 Schd 40 0.010 0 to 8 MW-111B 28-Mar-06 80 10 70 to 80 Bedrock 67 to 80 4.625 62 to 67 0 to 62 2.00 Schd 40 0.010 0 to 30 MW-111C 31-Mar-06 41 5 32 to 37 UT 30 to 37 5.500 26 to 30 0 to 26 2.00 Schd 40 0.010 0 to 29 MW-112A 30-Aug-06 24 10 13 to 23 GF 10 to 23 5.500 8 to 10 0 to 8 2.00 Schd 40 0.010 0 to 8.5*

MW-113A 27-Apr-06 25 10 15 to 25 GF 13 to 25 5.500 7.5 to13 0 to 7.5 2.00 Schd 40 0.010 0 to 8 MW-113C 26-Apr-06 140 10 127 to 137 UT 125 to 137 5.500 120 to 125 0 to 120 2.00 Schd 40 0.010 0 to 30 MW-6R 29-Aug-06 20 10 8 to 18 GF 6.7 to 20 5.500 4.5 to 6.7 0 to 4.5 2.00 Schd 40 0.010 0 to 8*

• =6-inch diameter steel casing Notes: ft bg=feet below grade; N/A=not applicable; Schd=schedule; all wells completed with # 0 (medium) sand pack I GF = Glaciofluvial stratified sand and gravel; UT = upper Till, including sand seams; LT-GL = lower Till and Glaciolacustrine, including sand seams Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 2 of 2, 2/8/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells Elevation Elevation Top Casing Ground Elevation Top Elevation Top Elevation (earlier (earlier PVC Casing Ground Northing Easting Well Number date installed survey) survey) (2003 survey) (2003 survey) (2003 survey) (2003 survey) (2003 survey)

CB-1 27-Apr-93 1126.80 1128.63 7128.63 1127.0 3093618.64 272442.49 CB-2 21-Apr-93 1119.87 1118.07 1118.47 1118.5 3093716.68 272148.03 CB-3 29-Apr-93 1139.97 1138.62 1138.76 1138.8 3093282.03 272493.16 CB-3R 28-Aug-06 CB-4 05-May-93 1087.21 1084.5 1085.61 1085.86 1084.1 3093627.45 271469.90 CB-5 04-Sep-94 1179.88 1176.1 1181.38 1181.49 1177.7 3093260.51 273112.20 CB-6 13-Sep-94 1113.79 1110.6 1112.06 1112.36 1110.1 3093781.64 272014.04 CB-7 07-Jan-97 1141.34 1139.73 1139.93 1139.9 3093398.20 272485.16 CB-8 20-Sep-94 1140.83 1139.14 1139.67 1139.6 3093424.39 272609.39 CB-9 19-Sep-94 1126.84 1124.69 1125.04 1125.0 3093562.03 272371.46 CB-10 19-Dec-97 1126.7 1126.70 CB-11A 18-Dec-97 1129 1126 1129.00 CB-12 10-Dec-97 1134.3 1134.20 CW-1 CW-2 29-Apr-93 1138.57 1136.87 1137.28 1137.3 3093387.17 272388.70 CW-3 03-May-93 1140.20 1138.38 1138.91 1138.9 3093532.13 272534.79 CW-4 04-May-93 1141.17 1139.13 1139.78 1139.8 3093367.75 272594.72 CW-5 27-Apr-93 1126.70 1124.92 1125.27 1125.3 3093690.69 272518.16 CW-5R 30-Aug-06 CW-6 23-Apr-93 1124.44 1122.25 1122.93 1123.0 3093596.29 272151.81 CW-7 13-Sep-94 1127.89 1126.16 1126.41 1126.4 3093769.82 272368.55 CW-8 14-Sep-94 1128.25 1126.49 1126.74 1126.7 3093660.04 272231.20 CW-9 CW-10 08-Jun-98 1120 1124.53 1124.79 1124.8 3093880.19 272659.52 CW-1I 11-Jun-98 1128.5 1128.20 MW-1 24-Apr-98 1140 1138.48 1138.88 1138.9 3093490.37 272484.97 MW-2 (metal) 24-Apr-98 1126 1125.97 1126.19 1126.2 3093492.13 272419.48 MW-3 24-Apr-98 1126.8 MW-5 13-Oct-99 1126.70 MW-6 14-Oct-99 1125.30 1127.10 1127.1 3093483.72 272280.07 MW-6R 28-Aug-06 MW-100A 05-Aug-03 1125.10 1126.05 3093668.12 272489.61 MW-IOB 04-Aug-03 1125.06 1126.12 3093665.06 272485.23 MW-101A* 11 -May-06 MW-101B 13-Aug-03 1125.68 1125.93 1125.9 3093485.38 272378.68 MW-101C 15-Aug-03 1125.43 1125.73 1125.7 3093487.09 272384.30 MW-102A 31-Jul-03 1125.62 1125.82 1125.8 3093576.50 272336.98 MW-102B 24-Jul-03 1125.67 1125.87 1125.9 3093573.63 272333.70 MW-102C 29-Jul-03 1125.55 1125.88 1125.9 3093570.88 272329.77 MW-102D* 10-Feb-06 I I Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 1 of 9, 1/31/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells Elevation Elevation Top Casing Ground Elevation Top Elevation Top Elevation (earlier (earlier PVC Casing Ground Northing Easting Well Number date installed survey) survey) (2003 survey) (2003 survey) (2003 survey) (2003 survey) (2003 survey)

MW-103A 17-Jul-03 1110.65 1110.91 1110.9 3093581-71 271903.99 MW-103B 10-Jul-03 1110.92 1111.10 1111.1 3093584.34 271907.73 MW-103C 16-Jul-03 1110.59 1110.71 1110.7 3093579.00 271899.45 MW-104A* 06-Feb-06 MW-104B 03-Sep-03 1117.75 1118.36 1118.4 3093729.75 272165.65 MW-104C 11-Sep-03 1118.17 1118.47 1118.5 3093726.18 272161.38 MW-104D 06-Sep-06 MW-105A* 08-Feb-06 MW-105B 20-Aug-03 1126.29 1126.52 1126.5 3093767.39 272372.83 MW-105C 21-Aug-03 1126.22 1126.48 1126.5 3093768.04 272367.91 MW-106A 30-Aug-04 1088.49 1088.91 1089.2 3093817.60 271790.77 MW-106B 27-Aug-04 1088.14 1088.92 1088.9 3093826.45 271815.71 MW-106C 08-Sep-04 1088.30 1088.72 1089.0 3093824.14 271808.43 MW-106D 14-Sep-04 1088.66 1088.89 1089.1 3093820.82 271799.26 MW-107A 05-May-06 MW-107B 17-Sep-03 1124.58 1124.93 1124.9 3093574.41 272399.33 MW-107C 19-Sep-03 1124.65 1125.00 1125.0 3093577.56 272396.49 MW-107D 24-Sep-03 1124.68 1125.03 1125.0 3093573.59 272391.42 MW-107E* 15-May-06 MW-107F* 23-May-06 MW-108A 17-Jul-04 1118.00 1118.40 1118.4 3093961.35 272329.51 MW-108B 16-Jul-04 1118.18 1118.52 1118.5 3093955.34 272329.93 MW-108C 08-Jul-04 1118.26 1118.68 1118.7 3093947.82 272330.90 MW-109A* 03-Feb-06 MW-109B 02-Aug-04 1123.70 1124.56 1124.6 3093544.64 272197.46 MW-109C 09-Aug-04 1123.40 1124.20 1124.2 3093559.34 272187.60 MW-109D 06-Aug-04 1123.38 1124.18 1124.2 3093552.59 272192.18 MW- 11OA* 16-Feb-06 MW-1 10B* 06-Mar-06 MW-1 10C* 20-Mar-06 MW-1 10D* 17-Mar-06 MW-111 A* 30-Mar-06 MW-11 B* 28-Mar-06 MW-111 C* 31 -Mar-06 MW-112A 29-Aug-06 MW-112 MW-1 13A* 27-Apr-06 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 2 of 9, 1/31/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells Elevation Elevation Top Casing Ground Elevation Top Elevation Top Elevation (earlier (earlier PVC Casing Ground Northing Easting Well Number date installed survey) survey) (2003 survey) (2003 survey) (2003 survey) (2003 survey) (2003 survey)

MW-1 13C* 26-Apr-06 CFW-1 13-Dec-99 1169.59 1167.4 1168.69 1169.59 1167.2 3093089.35 272941.07 CFW-2 15-Dec-99 1178.60 1175.3 1178.34 1178.60 1175.9 3093361.45 273029.58 CFW-3 15-Dec-99 1182.90 1179.2 1182.83 1182.90 1179.4 3093430.26 273120.86 CFW-4 13-Dec-99 1181.80 177.3 1181.77 1181.80 1177.6 3093431.19 273125.08 CFW-5 14-Dec-99 1144.57 1140.8 1143.93 1144.57 1140.9 3093499.54 273242.27 CFW-6 14-Dec-99 1140.40 1136.8 1140.07 1140.40 1137.0 3093653.22 273170.03 CFW-7 03-Aug-01 1180.78 1177.2 1180.58 1180.78 1177.4 3093400.13 273079.10 OSR-1 22-Oct-97 1158.2 1159.73 1159.98 1158.2 3093245.82 272938.97 NSR-1 22-Oct-97 1120 MW-no# 1159.73 1159.98 1158.2 3093245.82 272938.97 SG-1 1161.75 1159.3 3093217.67 272958.34 SG-3 1158.57 1158.94 1156.7 3093223.63 272883.52 SG-4 1160.96 1161.23 1158.1 3093238.88 272905.47 SG-5 1163.42 1163.67 1161.6 3093183.35 272959.81 SG-6 1161.55 1161.70 1158.7 3093206.85 272930.54 IP-1 30-Jan-97 1156 3093158.40 272736.30 Sherman Spring 1047.22 1091.0 3093796.22 271934.92 12" CMP Invert Sherman Spring Sample Point 1045.5 3093977.22 271739.42 Plant SupplyWell 1178.32 1175.60 3092867.76 272528.20 Furlon House Well 1183.1 3091285.14 270022.69 Elevations in green are top of steel casing-used to calculate 2004 quarterly levels MSL datum is 105.66 feet above plant datum (NEP)

• • • On Service Bldg Slab Coordinates are referenced to NAD 83 Elevations are referenced to NAVD 1988 Depths in red are pre-fill depths with corresponding pre-fill screened intervals

+change 4/6/06 102B & 102C were switched in first 2006 survey Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 3 of 9, 1/31/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells Elevation Elevation Elevation Elevation Elevation Elevation Top PVC Top Casing Ground Top PVC Top Casing Ground (Winter (Winter (Winter Northing Easting (Summer (Summer (Summer Northing Easting 2006 2006 2006 (Winter 2006 (Winter 2006 2006 2006 2006 (Summer 2006 (Summer 2006 Well Number survey) survey) survey) survey) survey) survey) survey) survey) survey) survey)

CB-1 CB-2 CB-3 CB-3R CB-4 .

CB-5 CB-6 CB-7 CB-8 CB-9 CB-10 CB-11A CB-12 -

CW-1 CW-2 1144.25 1144.39 1136.7 3093387.47 272388.51 CW-3 CW-4 CW-5 CW-5R CW-6 CW-7 CW-8 CW-9 CW-10 1128.71 1128.85 1124.4 3093880.33 272659.75 CW-1 1 MW-1 MW-2 (metal)

MW-3 MW-5 MW-6 MW-6R MW-1OA 1134.48 1134.95 1131.4 3093668.49 272490.28 1139.94+ 1140.84+ 1131.4+ 3093668.7+ 272490.23+

MW-100B 1134.07 1134.27 1131.4 3093666.10 272485.70 1139.33+ 1140.4+ 1131.4+ 3093666.67+ 272486.3+

MW-101A* 1146.13 1146.23 1138.0 3093489.73 272378.09 MW-101B 1145.52 1146.07 1137.3 3093486.75 272384.57 MW-101C 1145.78 1146.37 1137.3 3093484.74 272378.25 MW-102A 1139.28 1139.75 1133.8 3093570.92 272329.95 MW-102B 1139.82 1140.41 1133.8 3093573.61 272333.84 1139.12 1140.41 1133.80 3093575.98 272336.91 MW-102C 1139.12 1139.49 1133.8 3093575.98 272336.91 1139.82 1139.49 1133.80 3093573.61 272333.84 MW-102D 1 1141.91 1142.07 1133.8 3093580.02 272341.791 1 1 1_ _

Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 4 of 9, 1/31/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells Elevation Elevation Elevation Elevation Elevation Elevation Top PVC Top Casing Ground Top PVC Top Casing Ground (Winter (Winter (Winter Northing Easting (Summer (Summer (Summer Northing Easting 2006 2006 2006 (Winter 2006 (Winter 2006 2006 2006 2006 (Summer 2006 (Summer 2006 Well Number survey) survey) survey) survey) survey) survey) survey) survey) survey) survey)

MW-103A MW-103B MW-103C MW-104A* 1118.17 1118.37 1118.5 3093724.57 272155.55 MW-104B MW-104C MW-104D MW-105A* 1136.80 1137.21 1126.9"** 3093751.23 272380.38 MW-105B 1135.74 1136.07 1126.5 3093767.63 272373.00 MW-105C 1136.86 1137.17 1126.5 3093768.62 272368.08 MW-106A MW- 106B MW-106C MW-106D MW-107A 1140.07 1140.72 1135.1 3093568.57 272395.83 MW-107B 1140.00 1140.39 1135.1 3093573.79 272399.66 MW-107C 1139.89 1139.99 1135.1 3093577.27 272397.88 1139.75 1139.98 1134.30 3093577.05 272397.93 MW-107D 1139.18 1139.65 1135.1 3093573.72 272392.21 MW-107E* 1139.34 1139:72 1134.1 3093569.44 272402.36 MW-107F* 1138.08 1138.63 1134.2 3093581.57 272394.08 MW- 108A MW-108B MW-108C MW-109A* 1127.99 1128.23 1124.1 3093549.56 272185.04 MW-109B 1128.19 1128.51 1124.1 3093545.33 272197.15 MW-109C 1127.68 1128.35 1124.1 3093559.87 272187.55 MW-109D 1127.71 1127.93 1124.1 3093552.60 272191.96 MW-11OA* 1143.38 1144.36 1138.4 3093527.68 272446.20 MW-110B* 1143.40 1143.90 1138.2 3093529.81 272449.39 MW-110C* 1143.36 1144.17 1138.0 3093534.19 272447.061 MW-110D* 1143.38 1143.90 1137.7 3093531.59 272442.141 MW-111A* 1141.02 1141.51 1134.8 3093618.36 272430.18 MW-111B* 1141.75 1142.19 1135.8 3093610.31 272443.91 MW-111C* 1140.59 1140.95 1134.8 3093621.60 272437.36 MW-112A MW-112 MW-113A* 1084.74 1085.00 1083.2 3093679.89 271448.91 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 5 of 9, 1/31/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells Elevation Elevation Elevation Elevation Elevation Elevation Top PVC Top Casing Ground Top PVC Top Casing Ground (Winter (Winter (Winter Northing Easting (Summer (Summer (Summer Northing Easting 2006 2006 2006 (Winter 2006 (Winter 2006 2006 2006 2006 (Summer 2006 (Summer 2006 Well Number survey) survey) survey) survey) survey) survey) survey) survey) survey) survey)

MW-113C* 1084.83 1085.11 1083.2 3093678.29 271446.62 CFW-1 CFW-2 CFW-3 CFW-4 CFW-5 CFW-6 CFW-7 OSR-1 NSR-1 MW-no#

SG-1 SG-3 SG-4 SG-5 SG-6 IP-1 Sherman Spring 12" CMP Invert Sherman Spring Sample Point Plant SupplyWell Furlon House WV Elevations in gre used to calculati MSL datum is.1(

(NEP)

• • • On Service Bldg Slab Coordinates are Elevations are rn Depths in red ar corresponding p

+change 4/6/061 102B & 102C w(

survey Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 6 of 9, 1/31/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells 10/12/2006 10/12/2006 Elevation Top Elevation Top Elevation Ground Northing Easting PVC Casing (10/12/2006 (10/12/2006 Well Number survey) survey)

CB-1 CB-2 CB-3 CB-3R 1145-27 1145.58 1141.4 3093291.49 272491.14 CB-4 CB-5 CB-6 CB-7 CB-8 1146.06 1146.23 1142.9 3093424.82 272610.09 CB-9 CB-10 CB-11A CB-12 CW-1 CW-2 CW-3 CW-4 CW-5 CW-5R 1137.06 1137.49 1133.5 3093696.99 272515.06 CW-6 CW-7 CW-8 CW-9 CW-10 1128.89 1129.04 1126.1 3093880.33 272659.75 CW-1 1 MW-1 MW-2 (metal)

MW-3 MW-5 MW-6 MW-6R 1135.02 1135.32 1132.0 3093489.25 272286.05 MW-100A 1135.71 1135.96 1133.6 3093668.70 272490.23 MW-1O0B 1135.87 1136.14 1133.4 3093666.67 272486.30 MW-101A* 1139.40 1139.68 1136.5 3093489.73 272378.09 MW-101B 1139.64 1139.85 1136.7 3093486.75 272384.57 MW-101C 1139.13 1139.44 1136.6 3093484.74 272378.25 MW-102A 1135.14 1135.42 1131.9 3093570.92 272329.95 MW-102B 1135.15 1135.41 1132.1 3093575.98 272336.91 MW-102C 1135.55 1135.73 1132.1 3093573.61 272333.84 MW-102D* 1135.661 1135.97 1132.4 3093580.02 272341.79 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 7 of 9, 1/31/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells 10/12/2006 10/1212006 Elevation Top Elevation Top Elevation Ground Northing Easting PVC Casing (10/12/2006 (10/12/2006 Well Number survey) survey)

MW-103A MW-103B MW-103C MW-104A* 1125.94 1126.40 3093724.54 272155.20 MW-104B 1127-63 1128.06 3093729.54 272165.74 MW-104C 1126.62 1126.88 3093726.52 272161.07 MW-104D 1127.60 1128.00 1124.0 3093733.31 272162.11 MW-105A* 1130.79 1131.04 1128.5 3093751.23 272380.38 MW-105B 1129.69 1129.95 1128.0 3093767.63 272373.00 MW-105C 1129.79 1130.07 1128.1 3093768.62 272368.08 MW-106A MW-106B MW-106C MW-106D MW-107A 1137.35 1137.68 1135.1 3093568.57 272395.83 MW-107B 1137.25 1137.58 1135.1 3093573.79 272399.66 MW-107C 1137.44 1137.62 1134.9 3093577.05 272397.93 MW-107D 1137.35 1137.61 1134.8 3093573.72 272392.21 MW-107E* 1137.08 1137.45 1135.4 3093569.44 272402.36 MW-1 07F* 1137.10 1137.38 1134.6 3093581.57 272394.08 MW- 108A MW-108B MW-108C MW-109A* 1126.09 1126.35 1123.6 3093549.56 272185.04 MW-109B 1126.33 1126.54 1123.2 3093545.33 272197.15 MW-109C 1125.88 1126.16 1123.0 3093559.87 272187.55 MW-109D 1126.11 1126.38 1123.4 3093552.60 272191.96 MW-O11A* 1140.46 1140.71 1137.7 3093527.68 272446.20 MW-110B* 1140.54 1140.80 1137.7 3093529.81 272449.39 MW-110C* 1140.28 1140.69 1137.4 3093534.19 272447.06 MW-110D* 1140.19 1140.48 1137.3 3093531.59 272442.14 MW-111A* 1136.89 1137.17 1134.0 3093618.36 272430.18 MW-111 B* 1137.75 1138.02 1134.9 3093610.31 272443.91 MW-111C* 1137.07 1137.34 1134.0 3093621.60 272437.36 MW-112A 1134.05 1134.39 1131.0 3093694.78 272396.65 MW-112 1134.05 1134.39 1131.0 3093694.78 272396.65 MW-i 13A* I I I Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 8 of 9, 1/31/2007 Condition Report

Table 1-2 History of Surveyed Locations of Monitoring Wells 10/12/2006 10/12/2006 Elevation Top Elevation Top Elevation Ground Northing Easting PVC Casing (10/12/2006 (10/12/2006 Well Number survey) survey)

MW-1 13C*

CFW-1 CFW-2 ______ ____ __

CFW-3 CFW-4 CFW-5 CFW-6 CFW-7 OSR-1 NSR-1 MW-no#

SG-1 SG-3 .

SG-4 SG-5 SG-6 IP-1 Sherman Spring 12" CMP Invert Sherman Spring Sample Point Plant SupplyWell I Furlon House W Elevations in gr(

used to calculati MSL datum is 1t (NEP)

• • • On Service Bldg Slab Coordinates are Elevations are ro Depths in red ar corresponding p

+change 4/6/06 102B & 102C w(

Isurvey Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 9 of 9, 1/31/2007 Condition Report

Table 2-1 Inventory of Long-Term Pressure Transducer Records in Rowe Monitoring Wells

-akN-* 0 N 2 I F M S0 0 N 1 0 4 F I M A M 4 iI A I 3 6236322411211529 132231 101724131 17121287 141211286 111862512 I 191862330161312.27141115625116 15j222M5512119263 1011724131 7 142 5121 62 61219 16j23336135MMI76 132M02713 101172 I

I CB-8 CB-2 CB-6 1

~~I I I I I I I I I I I .~i I -lI I I I I I I I I I

I I I II it I I I

W-2M W,6 m Illllllllllll I III!I[IIIIIIIIIIII I I I I I I I I I I I I I I I I I I I I I I I I I I I I p i i I II I II I II III I I II I II I II I MW-IOA I I I I I I I g I I I I I I I t I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ICMW-IOB I I I I I I I I I I I I I I I I I I I I I I I I I I I II I I I I I I I I I I I I I I I I I I I I I It -i B I I I I I I I I I II I I I I I I I II I I I I I , I I I I I I I I I i I HI l l I l l l l l l l l E aI

• l l l l l l l l I MW-102A I 1 l l1 1 1l  ! I MW-102B I! MW-102C I I I I I I I I I I I I I I I I I I I I

34W.102C I I I I I II I I I I I I I I I I I I I I I I I I I I I I I p p i 18W 03C I I I I I I I I I I I I I I I I I I M9W-IO4B 111111 1 20W-104C I I I I I I I I I I I I I I M1W-IO5B M I 11111111 II 1 MW-105C SI II I I I I I I I I I I I II I I 23W-06A I I I I I I I II II iii11111111 ii i iil p p

.W-I.TB i i ii 1111 llll I I I I I I I I I I I I I 1 I I I I I I I I I I MW-108C I ~I 11111 IIIIIII I IIIIIIIlII I t I I I II 29 -lOGB I[' l  ! I

!111,11  ! I 111111 l l I l 11ll l I IIIli I IlllIlI1iIlII MW-lOgB I I , , , ,,11 MW-ISOA F' ' I .1I1"

. 1 1 1 1 1 1 1 1 1 I1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I I 1 .

. I.I.I.I..

.I I I. I.l.

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. ..i . . . . . . . . ll. I I I I I II tI I I II I E I I I I I I I

, II I I '

DaI i-5 ............ I . I I I . . . I I Yankee Nuclear Power Station, Rowe, MA 1/23/07 Final Groundwater Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Well Number 7/12/93 7/27/93 8/9/93 8/24/93 9/7/1993 9/24/93 10/4/93 10/18/93 11/1/93 11/15/93 11/30/93 12/30/93 1/11/94 1/25/94 3/8/94 3/16/94 3/28/94 CB-i 1116.05 1116.39 1115.88 1115.71 1115.21 1115.63 1116.13 1116.30 1116.63 1117.21 1117.88 1118.21 1117.38 1116.38 1115.96 1116.80 1118.21 CB-2 1103.57 1102.90 1102.49 1102.07 1101.82 1101.82 1101.99 1102.40 1102.65 1103.40 1104.40 1105.90 1105.07 1103.90 1102.24 1102.74 1104.49 CB-3 1134.12 1134.37 1134.20 1134.04 1134.20 1134.29 1134.54 1134.20 1135.12 1134.70 1134.95 1133.20 1133.04 CB-3R I I I I I II CB-4 1074.28 1074.31 1074.28 1074.21 1074.11 1074.11 1074.19 1074.19 1074.19 1074.28 1074.36 1074.36 1074.28 1074.19 1074.28 1074.36 CB-5 CB-6 CB-7 CB-8 CB-9 CB-10 CB-11A CB-12 CW-1 CW-2 1123.79 1123.79 1123.79 1123.95 1123.62 1124.20 1124.70 1124.54 1124.54 1124.79 1125.12 1124.87 1123.95 1123.29 1123.54 1125.12 1123.12 CW-3 1129.71 1129.71 1129.63 1129.96 1129.55 1129.88 1130.21 1130.05 1130.55 1130.21 1130.63 1129.63 1129.30 1128.88 1130.13 1130.13 1131.30 CW-4 1130.88 1130.83 1130.88 1131.05 1130.80 1130.96 1131.46 1131.05 1133.05 1131.21 1132.55 1130.71 1130.13 1129.80 1 CW-5 1114.50 1114.22 1113.92 1114.25 1113.34 1114.50 1115.84 1115.67 1117.34 1117.00 1118.42 1116.75 1115.75 1119.25 1120.00 CW-5R I I CW-6 1109.75 1109.58 1109.42 1109.33 1109.33 1109.67 1109.92 1109.83 1110.00 1110.33 1110.92 1110.83 1109.83 1109.08 1111.17 1109.92 1111.08 CW-7 CW-8 CW-9 CW-10 CW-1 1 MW-1 MW-2 (metal)

MW-3 MW-5 MW-6 MW-6R MW- 100A MW- 100B MW-101A MW- 101B MW- 101C MW- 102A MW-102B MW-102C MW-102D MW- 103A MW-103B MW-103C MW-104A MW-104B MW-104C Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 1 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Well Number 7/12/93 7/27/93 8/9/93 8/24/93 9/7/1993 9/24/93 10/4/93 10/18/93 11/1/93 11/15/93 11/30/93 12/30/93 1/11/94 1/25/94 3/8/94 3/16/94 3/28/94 MW-104D MW-105A MW-105B MW-105C MW- 106A MW-1068 MW- 106C MW-106D MW-107A MW-107B MW-107C MW-107D MW-107E MW-107F MW-108A MW-108B MW-108C MW-109A MW-109B MW-109C MW-109D MW-110A MW-110B MW-1i10C MW-110D MW-111A MW-111B MW-111C MW-1 12A MW-1 12 MW-1 13A MW-1 13C CFW-1 CFW-2 CFW-3 CFW-4 CFW-5 CFW-6 CFW-7 OSR-1 NSR-1 MW-no#

SG-1 SG-3 SG-4 SG-5 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 2 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Well Number 7/12/93 7/27/93 8/9/93 8/24/93 9/7/1993 9/24/93 10/4/93 10/18/93 11/1/93 11/15/93 11/30/93 12/30/93 1/11/94 1/25/94 3/8/94 3/16/94 3/28/94 SG-6 IP-1 Sherman Spring Elevations are referenced to NAVID 1988 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 3 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Well Number 4/10/94 4/27/94 5/11/94 5/26/94 6/10/94 6/23/94 8/10/94 10/5/94 10/8/94 11/8/94 12/6/94 1/5/95 2/13/95 4/6/95 5/31/95 8/30/95 10/4/95 CB-1 1119.05 1119.13 1118.71 1117.55 1117.55 1116.42 1117.46 1116.42 1116.80 1117.13 1117.96 1118.05 1118.55 1116.80 1116.55 1115.30 CB-2 1108.07 1108.32 1107.32 1106.57 1105.74 1105.24 1104.40 1107.32 1104.40 1104.82 1105.97 1106.87 1106.82 1107.74 1105.32 1102.17 CB-3 1134.95 1135.12 1133.95 1134.49 1133.95 1134.45 1133.95 1134.54 1135.12 1134.12 1135.04 1133.70 1134.20 CB-3R CB-4 1075.03 1074.94 1074.44 1074.28 1074.19 1074.32 1074.32 1074.36 1074.11 1074.44 1074.51 1074.44 1074.53 1074.44 1074.28 1074.21 CB-5 1153.96 1154.48 1154.58 1155.63 1156.13 1155.13 1154.13 1153.68 CB-6 1097.23 1097.23 1097.14 1097.66 1097.56 1097.48 1097.48 1097.48 1095.46 CB-7 CB-8 1134.81 1134.72 1135.64 1133.81 1135.22 1134.97 1134.22 CB-9 1117.19 1117.19 1117.11 1117.02 1117.19 1116.94 1115.86 CB-10 CB-11A CB-12 CW-1 CW-2 1126.95 1125.45 1124.70 1125.29 1123.95 1124.24 1124.04 1125.20 1124.04 1123.95 1125.54 1124.70 1124.79 1124.70 1123.79 1123.70 CW-3 1131.55 1130.80 1130.38 1130.30 1130.13 1130.13 1130.46 1130.46 1129.80 1130.05 1130.96 1130.38 1129.96 1130.63 1129.46 1129.80 CW-4 1132.71 1132.30 1131.88 1131.21 1131.80 1131.80 1130.88 1131.05 1133.96 1131.46 1131.71 1132.05 1130.71 1131.13 CW-5 1120.92 1120.17 1119.34 1119.17 1117.34 1116.42 1117.34 1117.34 1114.92 1117.34 1118.50 1117.75 1118.75 1117.17 1114.25 1113.92 CW-5R CW-6 1112.92 1111.75 1111.00 1112.67 1110.50 1110.42 1113.42 1111.75 1113.42 1113.50 1112.75 1112.25 1111.42 1113.17 1109.75 1109.35 CW-7 1107.24 1107.24 1107.08 1106.41 1108.49 1108.33 1108.91 1106.36 1105.16 CW-8 1107.74 1107.74 1107.99 1108.39 1108.74 1108.74 1109.49 1106.89 1106.49 CW-9 CW-10 CW-1 1 MW-1 MW-2 (metal)

MW-3 MW-5 MW-6 MW-6R MW-100A MW-100B MW-101A MW-101B MW-101C MW-102A MW-102B MW-102C MW-102D MW-103A MW-103B MW-103C MW-104A MW-104B MW-104C Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 4 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Well Number 4/10/94 4/27/94 5/11/94 5/26/94 6/10/94 6/23/94 8/10/94 10/5/94 10/8/94 11/8/94 12/6/94 1/5/95 2/13/95 4/6/95 5/31/95 8/30/95 10/4/95 MW-I__D MW-105A MW-105B MW-105C MW-106A MW-106B MW-106C MW-106D MW-107A MW-107B MW-107C MW-107D MW-107E MW-107F MW-108A MW-108B MW-108C MW-109A MW-1098 MW-109C MW-109D MW-110A MW-1i OB MW-110C MW-110D MW-11 1A MW-11 1B MW-111iC MW-112A MW-112 MW-113A MW- 113C CFW-1 CFW-2 CFW-3 CFW-4 CFW-5 CFW-6 CFW-7 OSR-1 NSR-1 MW-no#

SG-1 SG-3 SG-4 SG-5 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 5 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Well Number 4/10/94 4/27/94 5/11/94 5/26/94 6/10/94 6/23/94 8/10/94 10/5/94 10/8/94 11/8/94 12/6/94 1/5/95 2/13/95 4/6/95 5/31/95 8/30/95 10/4/95 SG-6 IP-1 Sherman Spring Elevations are referenced to NAVD 1988 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 6 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Well Number 12/5/95 1/10/96 4/4/1996 7/1/96 8/22196 9/30/1996 1/9/97 2/12/97 3/13/97 7/2/97 8/19/97 11/11/97 2/1/98 6/1/98 8/1/98 7/1/03 11/1/03 CB-1 1118.55 111596 1118.80 1117.46 1116.46 1116.46 1116.63 1116.62 1116.99 1118.25 1114.19 1114.62 CB-2 1106.40 1103.24 1105.15 1104.90 1103.15 1102.49 1103.82 1103.50 1103.62 1102.70 1104.28 1105.69 1107.28 CB-3 1134.29 1135.20 1136.04 1134.29 1133.87 1134.54 1129.62 1130.39 1134.66 1134.56 1134.03 1134.22 CB-3R I I CB-4 1074.61 1074.28 1074.78 1074.53 1074.61 1074.36 1074.28 1074.51 1074.56 1074.63 1074.74 1075.04 CB-5 1156.71 1155.46 1157.46 1155.55 1154.13 1154.55 1155.30 1154.74 1155.58 1156.08 1154.58 1151.39 CB-6 1097.56 1097.31 1097.14 1096.73 1096.31 1095.98 1096.56 1096.68 1094.01 1097.10 1097.21 1098.56 CB-7 1129.90 1127.73 1129.03 1129.69 1129.61 1128.77 CB-8 1131.47 1135.14 1134.39 1133.78 1134.81 1132.89 1133.78 1135.39 1135.08 1135.42 CB-9 1116.77 1115.52 1116.52 1117.19 1116.86 1116.56 1117.37 1117.15 1116.43 1118.35 CB-10 1123.87 1124.33 CB-11A 1125.91 1126.50 CB-12 1130.27 1131.20 CW-1 CW-2 1124.45 1123.45 1125.62 1124.29 1123.87 1125.04 1123.54 1125.12 1125.30 1125.27 1124.98 1125.17 CW-3 1129.96 1128.96 1127.13 1130.05 1129.88 1130.80 1129.88 1130.41 1130.78 1131.09 1131.52 1131.46 CW-4 1131.30 1130.05 1132.88 1131.05 1130.88 1131.88 1130.30 1131.37 1131.53 1132.43 1132.47 CW-5 1118.50 1114.59 1119.75 1115.75 1114.09 1117.42 1115.25 1115.99 1116.42 1116.76, 1116.26 1120.14 CW-5R CW-6 1110.67 1109.17 1111.50 1109.92 1108.83 1110.67 1110.25 1110.56 1110.99 1110.51 1111.27 CW-7 1109.08 1103.16 1106.99 1107.49 1106.16 1105.41 1106.49 1106.51 1110.75 1106.48 1108.20 CW-8 1107.91 1106.32 1107.07 1106.99 1106.49 1106.91 1106.41 1106.90 1107.08 1107.05 1107.03 CW-9 CW-10 1102.51 CW-11 1126.93 1127.09 MW-1 1125.22 1126.04 MW-2 (metal) 1123.07 1121.62 MW-3 I MW-5 1122.74 1121.00 MW-6 1120.55 1118.48 MW-6R MW-100A 1116.55 MW-100B 1115.68 MW-101A MW-101B 1105.00 1107.23 MW-101C 1091.23 1094.23 MW-102A 1111.92 1113.20 MW-102B 1102.97 1105.86 MW-102C 1090.22 1093.20 MW-102D MW-103A 1092.07 MW-103B 1073.02 1056.57 MW-103C 1073.09 1076.27 MW-104A I I MW-104B 1 1058.33 MW-104C 1 1078.80 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 7 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Well Number 12/5/95 1/10/96 4/4/1996 7/1/96 8/22/96 9/30/1996 1/9/97 2/12/97 3/13/97 7/2/97 8/19/97 11/11/97 2/1/98 6/1/98 8/1/98 7/1/03 11/1/03 MW-104D MW-105A MW-105B 1105.80 1106.95 MW-105C 1108.66 1109.62 MW-106A MW-106B MW-106C MW-106D MW-107A MW-107B 1105.75 MW-107C 1114.16 MW-107D 1096.25 MW-107E MW-107F MW- 108A MW-108B MW-108C MW-109A MW-1098 MW-109C MW-109D MW-110A MW-110B MW-110C MW-110D MW-111A MW-111B MW-1111C MW-112A MW-112 MW-113A MW-1 13C CFW-1 1165.72 1165.94 CFW-2 1154.33 1158.53 CFW-3 1145.99 1149.12 CFW-4 1145.86 1148.71 CFW-5 1139.40 1139.71 CFW-6 1134.18 1135.10 CFW-7 1154.16 1158.53 OSR-1 1153.08 NSR-1 MW-no#

SG-1 SG-3 SG-4 ----------

SG-5 I I Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 8 of 12, 2/8/2007 Condition Report

Table 2-2 Historyof Hand-MeasuredWater Elevations Well Number 12/5/95 1/10/96 4/4/1996 7/1/96 8/22/96 9/30/1996 1/9/97 2/12/97 3/13/97 7/2/97 8/19/97 11/11/97 2/1/98 6/1/98 8/1/98 7/1/03 1111/03 SG-6 IP-1 Sherman Spring Elevations are referenced to NAVD 1988 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 9 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Average GW Average GW Elevation Well Number 2/26/04 5/14/04 8/15/04 10/31/04 3113/05 11/7/05 4/18/06 6-26/06 9/11/06 12/4/06 Elevation 1990s 2003- June 2006 CB-1 1118.73 1116.48 1115.83 1117.06 1115.97 CB-2 1103.54 1108.34 1105.35 1103.89 1104.41 1105.68 0B-3 1133.41 1135.10 1134.30 1134.08 1132.28 1135.00 1135.14 1134.17 1134.05 CB-3R _ 1133.68 1133.46 CB-4 1074.51 1075.09 1074.61 1077.01 1076.84 1076.90 1077.69 1079.29 1074.38 1075.59 CB-5 1153.14 1151.38 1151.80 1155.15 1151.93 CB-6 1097.16 1097.76 1097.36 1097.35 1096.95 1098.36 1098.48 1099.18 1098.30 1097.98 1096.85 1097.84 CB-7 1127.83 1129.53 1128.80 1128.33 1129.19 1128.65 CB-8 1135.13 1135.88 1134.25 1134.63 1135.24 1135.69 1129.55 1129.24 1134.38 1135.18 CB-9 1114.94 1116.83 1116.57 CB-10 1122.73 1125.25 1 1124.05 GB-11A 1129.00 1127.42 1127.21 CB-12 1129.20 1131.19 1130.44 1129.93 1130.37 CW-1 CW-2 1124.45 1125.51 1125.12 1124.46 1125.05 CW-3 1130.09 1131.31 1131.45 1130.42 1130.08 1131.04 CW-4 1131.87 1132.25 1132.80 1132.50 1 1131.41 1132.38 CW-5 1 1119.72 1116.87 1115.61 1116.73 1117.72 CW-5R 1116.82 CW-6 1109.55 1111.81 1110.75 1111.26 1109.93 1110.78 1110.73 CW-7 1106.21 1110.96 1107.81 1107.98 1106.84 1107.04 1108.00 CW-8 1107.44 1107.03 CW-9 CW-10 1105.21 1103.93 1103.53 1104.43 1104.48 1105.14 1106.20 1103.85 1105.12 1104.43 CW-i1 1 _ 1127.01 MW-1 1126.29 1138.48 1129.01 MW-2 (metal) 1124.49 1123.72 1123.23 MW-3 MW-5 1120.98 1124.41 1123.69 1122.95 1122.63 MW-6 1117.41 1118.81 MW-6R 1123.35 1123.64 MW-100A 1118.41 1115.39 1114.55 1117.75 1119.78 1116.20 1115.71 1117.07 MW-100B 1116.42 1112.83 1113.90 1116.36 1118.34 1115.27 1115.14 1115.59 MW-101A 1122.88 1125.86 1126.72 1122.88 MW-101B 1104.94 1104.48 1103.47 1103.59 1104.77 1106.32 1104.54 1105.86 1104.98 MW-101C 1094.11 1091.93 1091.40 1090.75 1093.93 1096.32 1093.22 1094.60 1092.99 MW-102A 1111.33 1113.01 1111.13 1113.63 1114.87 1112.53 1112.45 1112.73 MW-102B 1102.77 1102.80 1101.46 1103.16 1104.07 1102.17 1103.43 1103.30 MW-102C 1091.65 1090.56 1089.88 1092.62 1093.46 1091.85 1093.25 1091.66 MW-102D 1118.46 1117.77 1117.23 1117.27 1118.12 MW-103A 1091.40 1092.50 1091.52 1091.55 1091.96 1102.75 1092.61 1092.87 1091.81 1092.48 1093.25 MW-103B 1054.96 1053.74 1053.32 1051.90 1053.87 1055.02 1054.06 1052.85 1052.92 1055.19 1055.93 MW-103C 1075.96 1076.28 1074.72 1074.87 1076.21 1075.74 1076.03 1075.87 1076.30 1076.20 1075.50 MW-104A 1 1109.67 1111.34 1106.31 1105.63 1110.51 MW-104B 1056.39 1056.25 1054.79 1056.88 1049.75 1056.63 1056.89 1056.52 1058.82 1055.74 MW-104C 1077.82 1078.07 1076.74 1076.89 1078.17 1079.37 1078.47 1078.81 1077.29 1079.38 1078.13 Yankee Nuclear Power Station Final Groundwater Rowe, MA Condition Report Page 10 of 12, 2/8/2007

Table 2-2 History of Hand-Measured Water Elevations Average GW Average GW Elevation Well Number 2/26/04 5/14/04 8/15/04 10/31/04 3/13/05 11/7/05 4/18/06 6-26/06 9/11/06 12/4/06 Elevation 1990s 2003- June 2006 MW-104D 1108.12 MW-105A 1110.85 1113.76 110897 1108.00 1112.31 MW-105B 1105.31 1107.29 1105.56 1105.77 1105.71 1106.88 1108.92 1106.03 1106.22 1106.47 MW-105C 1107.50 1108.74 1107.82, 1118.47 1106.74 1109.55 1113.41 1108.76 1107.83 1110.06 MW-106A 1081.89 1082.46 1080.59 1082.37 1083.00 1081.99 1082.89 1082.06 MW-106B 1049.14 1052.16 1052.69 1049.98 1053.42 1051.56 1054.181 1051.48 MW-106C 1049.40 1061.28 1059.90 1061.00 1061.96 1058.31 1061.45 1058.71 MW-106D 1044.96 1049.45 1056.16 1050.76 1051.54 1050.64 1051.05 1050.57 MW-107A 1122.80 1122.74 1122.81 1122.80 MW-107B 1103.06 1103.30 1101.76 1103.61 1102.501 1102.91 1103.87 1103.33 MW-107C 1110.73 1114.00 1112.33 1114.81 1116.28 1114.32 1114.37 1113.72 MW-107D 1094.56 1093.87 1094.23 1096.15 1097.06 1095.51 1096.65 1095.35 MW-107E 1113.00 1110.30 1110.11 1113.00 MW-107F 1112.98 1110.18 1109.95 1112.98 MW-108A 1105.69 1106.32 1105.25 1106.72 1105.65 1104.461 1106.00 MW-1086 1064.75 1067.98 1067.20 1068.21 1065.41 1067.94 1067.04 MW-108C 1104.06 1104.16 1104.23 1105.97 1103.37 1104.92 1104.61 MW-109A 1115.58 1114.95 1114.67 1114.68 1115.27 MW-109B 1095.00 1097.22 1084.74 1097.40 1095.29 1096.92 1093.59 MW-109C 1108.12 1107.51 1107.75 1112.18 1109.64 1108.89 1108.89 MW-109D 1085.51 1085.65 1082.06 1087.71 1086.49 1087.74 1085.23 MW-110A 1123.82 1124.20 1124.91 1125.13 1124.01 MW-110B 1103.98 1105.04 1103.19 1104.03 1104.51 MW-110C 1115.85 1117.37 1115.83 1116.05 1116.61 MW-110D 1094.02 1096.01 1094.34 1095.75 1095.02 MW-111A 1120.74 1122.22 1122.65 1122.47 1121.48 MW-111B 1106.50 1107.75 1106.67 1106.32 1107.13 MW-111C 1118.74 1120.08 1116.60 1116.08 1119.41 MW-1 12A 1112.67, MW-112 1113.18 MW-113A 1064.24 1064.03 1064.88 1064.24 MW-113C 1031.23 1029.70 1031.16 1031.23 CFW-1 1160.69 1165.89 1165.74 1165.49 1165.68 1166.34 1166.58 1165.02 CFW-2 1154.84 1157.51 1153.34 1154.12 1 1155.45 CFW-3 1146.33 1148.39 1145.43 1146.11 1146.90 CFW-4 1146.17 1148.02 1145.17 1145.95 1 1146.65 CFW-5 1139.33 1139.53 1139.33 1139.49 1139.38 1139.32 1139.80 1140.02 1139.44 CFW-6 1134.07 1134.79 1133.87 1134.13 1134.11 1134.47 1134.29 1135.00 1134.34 CFW-7 1154.68 1157.49 1153.33 1154.09 1155.38 OSR-1 1152.33 1154.90 1151.86 1150.34 1152.50 NSR-1 MW-no#_

SG-1 SG-3 SG-4 SG-5 Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 11 of 12, 2/8/2007 Condition Report

Table 2-2 History of Hand-MeasuredWater Elevations Average GW Average GW Elevation Well Number 2/26/04 5/14/04 8/15/04 10/31/04 3/13/05 11/7/05 4/18/06 6-26/06 9/11/06 12/4/06 Elevation 1990s 2003- June 2006 SG-6 P-1 Sherman Spring 1091 1091 1091 1091 Elevations are F referenced to NAVD 1968 _ _-_

I _ _ _ _ _ _ _ _-_ _ _ _

Yankee Nuclear Power Station Final Groundwater Rowe, MA Page 12 of 12, 2/8/2007 Condition Report

Table 2-3 Plant Well Weekly Water Usage Weekly Usage, Week. Ending Gallons 12/5/2005 2100 12/12/2005 2000 12/19/2005 2400 12/26/2005 6500 1/2/2006 1300 1/9/2006 1800 1/16/2006 1800 1/23/2006 1900 1/30/2006 2200 2/6/2006 2000 2/13/2006 1800 2/20/2006 1800 2/27/2006 1800 3/6/2006 2600 3/13/2006 2200 3/20/2006 2000 3/27/2006 2700 4/3/2006 2200 4/10/2006 2200 4/17/2006 1900 4/24/2006 1800 5/1/2006 2100 5/8/2006 1800 5/15/2006 2100 5/22/2006 1300 5/29/2006 1100 6/5/2006 1700 6/12/2006 2500 6/19/2006 500 6/26/2006 300 7/3/2006 200 7/10/2006 500 7/17/2007 500 Yankee Nuclear Power Station Final Groundwater Rowe, MA 1/31/2007 Condition Report

Table 2-4 Summary of Influences on Monitoring Well Water Levels Tailwater Dec. 2006 Plant Well Reservoir Elevation Long-term Vertical Average Earth Barometric Precipitation Snowmelt Pumping Fluctuation Fluctuation Temperature Gradient Purge Rate, Well ID Tide? Response? Response? Response? Response? Response? Response? Variation Direction gpm Notes large but gradual change; peak early CB-1 No Slight Yes N/D No Yes N/D November N/D N/D Slight; large but gradual CB-2 No Slight Yes Yes No delayed N/D change; peak early N/D N/D CB-3 N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D CB-3R N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D CB-4 N/D N/D N/D N/D N/D N/D N/D N/D N/D 9.55E-02 large but gradual change; peak late CB-6 No None Yes Yes No No N/D December N/D I 1.05E-01 large range; short CB-7 No None Yes N/D No No N/D record N/D N/D CB-8 N/D N/D N/D N/D N/D N/D N/D N/D N/D 1.44E-02 CFW-1 N/D N/D N/D N/D N/D N/D N/D N/D N/fD 5.56E-03 CFW-5 N/D N/D N/D N/D N/D N/D N/D N/D N/D 1.54E-02 CFW-6 N/D N/D N/D N/D N/D N/D N/D N/D N/D 1.85E-02 large range; short CW-10 No None N/D N/D No Yes N/D record N/D- 3.33E-02 large range; short CW-2 No None Yes Yes No No N/D record N/D N/D large range; short CW-3 No None Yes N/D No No N/D record N/D N/D Slight; large range; peak Shows drawdown during summer 2005 CW-6 No None Slight; delayed Yes No delayed N/D mid-October N/D N/D excavation and dewatering activities large range; short MW-100A No Slight Yes Yes No No N/D record downward 5-23E-02 MW-100B Yes No Yes Yes Slight No N/D moderate range N/D 2.67E-02 MW-101A N/D N/D N/D N/D N/D N/D N/D N/D downward 6.32E-03 moderate range; 2006 winter record too irregular to discern MW-101B Yes Yes No No Yes No N/D short record upward 2.41 E-02 earthtide low permeability well; pressure spike 3/7/06 when temp goes above freezing; influenced by MW-101C Yes slight Slight No No No N/D low range N/D 7.14E-03 filling of stormwater basin MW-102A Yes Slight Yes N/D No No N/D moderate range downward 2.68E-02 temperature affected by pumping MW-109C MW-102B Yes Slight Yes Yes Yes No N/D low range upward 2.48E-02 influenced by filling stormwater basin Shows drawdown during summer 2005 MW-102C Yes Slight Yes Yes Yes No N/D low range N/D 1.07E-02 excavation and dewatering activities Yankee Nucleai Power Station Final Groundwater Rowe, MA Page 1 of 3, 2/8/2007 Condition Report

Table 2-4 Summary of Influences on Monitoring Well Water Levels Tailwater Dec. 2006 Plant Well Reservoir Elevation Long-term Vertical Average Earth Barometric Precipitation Snowmelt Pumping Fluctuation Fluctuation Temperature Gradient Purge Rate, Well ID Tide? Response? Response? Response? Response? Response? Response? Variation Direction gpm Notes MW-102D N/D N/D N/D N/D N/D N/D N/D N/D downward N/D large range; peak MW-103A No None Yes N/D No No N/O mid-November downward 3.20E-02 MW-103B Yes Yes Yes Yes Slight Yes N/D low range N/D 1.52E-02 slow recovery from sampling; pressure spike MW-103C Yes Yes No Yes No No N/D low range downward 6.15E-03 3/7106 when temp goes above freezing Mw-104A N/D N/O N/D N/D N/D N/D N/D N/D downward 5.75E-02 MW-104B No Slight Yes Yes Slight Yes N/D low range N/D 2.83E-02 MW-104C Yes Yes Slight; delayed Yes No Yes N/D low range downward 1.78E-02 MW-104D N/D N/D N/D N/D N/D N/D N/D N/D upward 8.94E-03 MW-105A N/D N/D N/D N/D N/D N/D N/D N/D downward 3.27E-02 MW-105B No Slight Yes Yes slight See Note N/D low range downward 1.36E-02 slow, diffuse response to reservoir level Mod. Range; peak in MW-105C No None Yes Yes No No N/D mid-January N/D 1.54E-02 large range; peak Shows drawdown during summer 2005 MW-106A No Slight Yes Yes No No N/D early December downward 5.00E-02 excavation and dewatering activities MW-106B N/D N/D Yes N/D N/D N/D slight N/D upward 2.74E-02 MW-106C N/D N/D N/D N/D N/D N/D slight NiD downward 8.28E-03 MW-106D N/D N/U N/D N/D N/D Yes slight N/D N/D 1.51E-02 MW-1 07A N/D N/D N/D N/D N/D N/D N/D N/D downward 7.69E-03 influenced by filling stormwater basin delayed reaction to reservoir change; influenced by filling stormwater basin; temperature fluctuated in MW-1 07C pumping MW-107B Yes Yes Yes Yes Yes See Note N/D low range upward 1.30E-02 test excavation and dewatering activities; MW-107C Yes Yes Yes Yes Slight No N/D low range downward 6.90E-03 influenced by filling stormwater basin Shows drawdown during summer 2005 excavation and dewatering activities; MW-107D Yes Yes Yes Yes Yes No N/D low range N/D 8.70E-03 influenced by filling stormwater basin influenced by filling stormwater basin; temperature affected by pumping MW-107C &

MW-107E Yes N/D Yes N/D N/D N/D N/D N/D downward 1.71E-02 MW-109C influenced by filling stormwater basin; temperature affected by pumping MW-107C &

MW-107F Yes N/D N/D N/D N/D N/D N/D N/D downward 2.55E-02 MW-109C & MW-105C small response to high frequency drawdown; MW-108A No No N/D Yes No See Note N/D large range downward 8.33E-03 larger response to low frequency drawdown Slight, MW-108B No N/D N/D N/D N/D diffused N/D N/D N/D 1.50E-02, Yankee Nucleaw Power Station Final Groundwater Rowe, MA Page 2 of 3, 2/8/2007 Condition Report

Table 2-4 Summary of Influences on Monitoring Well Water Levels Tailwater Dec. 2006 Plant Well Reservoir Elevation Long-term Vertical Average Earth Barometric Precipitation Snowmelt Pumping Fluctuation Fluctuation Temperature Gradient Purge Rate, Well ID Tide? Response? Response? Response? Response? Response? Response? Variation Direction gpm Notes MW-108C Yes Slight N/D Yes No See Note N/D low range downward 1.80E-02 slow, diffuse response to reservoir level MW-109A N/D N/D N/D N/D N/D N/D N/D N/D downward 2.58E-02 Slight, MW-109B Yes Yes Slight; delayed Slight Slight diffused N/D low range upward 2.17E-02 large range; peak MW-109C Yes Yes Yes Yes No No N/D early November downward 3.27E-02 MW-109D No Slight Slight No No No N/D low range 1.19E-02 MW-110A No Yes Yes N/D No No N/D large range downward 6.55E-02 influenced by filling stormwater basin MW-110B Yes N/D N/D N/D N/D N/D N/D N/D upward 2.64E-02 temperature affected by pumping MW-107D temperature affected by MW-107C and MW-107F pumping tests; influenced by filling of MW-110C N/D N/D N/D N/D N/D N/D N/D N/D downward 8.OOE-03 stormwater basin MW-11OD Yes N/D N/D N/D N/D N/D N/D N/D N/D 2.30E-02 MW-111A N/D N/D N/D N/D N/D N/D N/D N/D downward 1.90E-02 influenced by filling stormwater basin MW-111B N/U N/D N/D N/D N/D N/D N/D N/D N/D 1.33E-02 influenced by filling stormwater basin influenced by filling stormwater basin; temperature affected by MW-107C pumping MW-11 C N/D N/D N/D N/D N/D N/D N/D N/D downward 8.46E-03 test MW- 12 N/D N/D N/D N/D N/D N/D N/U N/D N/D N/D MW-l13A N/D N/D N/D N/D N/D N/D N/D N/D downward 2.96E-02 MW-113C N/D N/D N/D N/D slight light Yes N/D N/D 1.26E-02 MW-5 No No Yes Yes No No N/D large range N/D N/D MW-6R N/D N/D N/D N/D N/D N/D N/D N/D N/D N/D Notes: N/D = Not Determined; gpm = gallons per minute Yankee Nucleai Power Station Final Groundwater Rowe, MA Page 3 of 3, 2/8/2007 Condition Report

Table 3-1 Summary of Laboratory Analysis for Quarterly Groundwater Sampling NRC MDC MCL Threshold Analyte Analytical Method (pCi/L) (pCi/L) Level (pCi/L)

Radionuclides (pCi/L)

Tritium (2) EPA 906.0 500 20000 NA Strontium-90 (2) EPA 905.0 Modified 1 8 3 Americium-241(2) Gamma Spec EPA 901.1 1 15 0.5 Cobalt-60 (2) Gamma Spec EPA 901.1 0.7 100 25 Cesium-134 (2) Gamma Spec EPA 901.1 20 80 14 Cesium-137(2) Gamma Spec EPA 901.1 2 200 15 Niobium-94 (2) Gamma Spec EPA 901.1 20 NA 50 Antimony-125 (2) Gamma Spec EPA 901.1 20 300 50 Europium-152 (2) Gamma Spec EPA 901.1 20 200 50 Europium-154 (2) Gamma Spec EPA 901.1 10 60 50 Europium-155 (2) Gamma Spec EPA 901.1 20 600 50 Silver-108m (2) Gamma Spec EPA 901.1 20 NA 50 Carbon-14 EPA EERF C-01 Modified 200 2000 200 Iron-55 DOE RESL Fe-1, Modified 200 2000 25 Nickle-63 DOERESL Ni-1, Modified 10 50 15 DOE EML HASL-300, Tc Technicium-99 RC Modified 25 900 15 Alpha Spec DOE EML HASL-Americium-241 300, Am-05-RC Modified 1 15 50 Alpha Spec DOE EML HASL-Plutonium-238 300, Pu-11-RC Modified 1 15 0.5 Alpha Spec DOE EML HASL-Plutonium-239 300, Pu-11-RC Modified 1 15 0.5 Alpha Spec DOE EML HASL-Plutonium-240 300, Pu-11-RC Modified 0.5 Alpha Spec DOE EML HASL-Plutonium-241 300, Pu-11-RC Modified 15 300 NA Alpha Spec DOE EML HASL-Curium-242 300, Am-05-RC Modified 1 15 NA Alpha Spec DOE EML HASL-Curium-243 300, Am-05-RC Modified 1 115 0.5 Alpha Spec DOE EML HASL-Curium-244 300, Am-05-RC Modified 1 15 0.5 Gross alpha/beta EPA 900.0 20 NA NA General Geochemistry (mg/L (1)

Alkalinity SM 2320B 2 NA NA Sulfate EPA 300.0 0.4 NA NA Chloride EPA 300.0 20 NA NA Calcium SW-846 3005/6010B 0.1 NA NA Magnesium SW-846 3005/6010B 0.3 NA NA Potassium SW-846 3005/6010B 0.15 NA NA Sodium SW-846 3005/6010B 0.15 NA NA Metals (ug/L)

Boron ISW-846 3005/6020 75 NAI NA

.Notes:

(1) General geochemistry and boron analyses were conducted for Q2 2006 only (2) For Q2 2006 sampling round both filtered (preserved sample at laboraotry) and unfiltred samples were taken NA - Not Available MDC - Minimum Dectction Concentration MCL Maximum Contaminant Level Yankee Nuclear Final Groundwater Power Station Page 1 of 1, 2/9/2007 Condition Report

Table 3-2 Summary of Groundwater Laboratory Analytical Program for Q4 2006 Q4 Sampling Q4 Sampling Well ID Program Well ID Program CB-3 ABCD MW-106B A CB-4 A MW-106C A CB-6 ABC MW-106D A CB-8 A MW-107A ABC CW-10 A MW-107B A CFW-1 A MW-107C ABCD CFW-5 A MW-107D ABCD CFW-6 A MW- 107E ABCD MW-100A A MW-107F ABCD MW-100B A MW-108A A MW-101A ABC MW-108B A MW-101B A MW-108C A MW-101C A MW-109A A Notes:

MW-102A ABC MW-109B A A - Tritium only MW-102B A MW-109C A B - Gamma MW-102C ABC MW-109D A C- Sr-90, TC-99, C-14 MW-102D ABCD MW-110A A D - Am-241, Pu-238, Pu-239/240 MW-103A A MW-110B A Pu-0241, CM-242, CM-243/244 MW-103B A MW-110C A MW-103C A MW-110D A MW-104A A MW-111A A MW-104B A MW-111B A MW-104C A MW-111C ABCD MW-104D ABCD MW-113A A MW-105A A MW-113C A MW-105B ABC SP-1 A MW-105C ABC MW-106A ABC Yankee Nuclear Final Groundwater Power Station Condition Report Rowe, MA 2/9/2007

Table 4-1 Summary of 2006 Tritium Analytical Results Non-Monitoring Filtered Q2 Filtered Well Jan-06 Feb-06 Q1 2006 May-06 2006 Q2 2006 Aug-06 Q3 2006 Oct-06 Nov-06 Q4 2006 CB-3 NS NS U NS U NA NS NS U NS U CB-4 U U U U U NA NS 403 NS NS 189 CB-6 14,730 12,100 7,680 4,300 1,910 2,090 2,090 959 451 NS 869 CB-8 NS NS U NS U NA NS 264 NS NS U CFW-1 NS NS 332 NS U NA NS U NS NS U CWF-5 NS NS U NS NS NA NS 225 NS NS U CWF-6 NS NS 300 NS 1,180 NA NS 2,650 NS 249 581 CW-2 NS NS U NS NS NA NS NS NS NS NS CW-10 NS NS U NS U NA NS 349 NS U 317 MW-100A NS NS U NS U NA NS U NS NS U MW-100B NS NS U NS U NA NS U NS NS 211 MW-101A NS NS 16,900 NS 8,520 NA 7,720 10,100 NS 4,740 3,880 MW-101B NS NS U U U NA NS U NS NS U MW-101C NS NS NS NS NS NA NS 323 NS NS U MW-102A NS NS 4,490 4,630 4,260 4,640 NS 4,470 NS NS 4,240 MW-102B NS NS U NS U NA NS U NS NS U MW-102C NS NS 4,610 3,920 4,980 4,590 NS 4,210 NS NS 3,520 MW-102D NS NS 16,100 6,890 11,100 8,810 NS 6,970 NS NS 6,530 MW-103A NS NS U NS 416 NA NS 337 NS NS U MW-103B NS NS U NS U NA NS 182 NS NS U MW-103C NS NS U NS U NA NS 249 NS NS U MW-104A NS 3,320 4,580 2,960 844 798 NS 1,430 NS NS 2,850 MW-104B NS NS U NS U NA NS U NS NS U MW-104C NS NS U NS U NA NS U NS NS U MW-104D NI NI NI NI NI NI NI NI U U U MW-105A NS NS U NS U U U 310 NS NS 175 MW-105B NS NS 3,970 4,780 3,860 NA NS 3,290 NS NS 2,900 MW-105C NS NS 1,990 NS 1,030 NA NS 1,650 NS NS 2,750 MW-106A 11,260 13,100 10,300 9,810 7,170 7,620 6,740 5,280 NS NS 3,010 MW-106B NS NS U NS U NA NS 528 NS U U MW-106C NS NS U NS U NA NS U NS NS 277 MW-106D NS NS U NS U NA NS U NS NS U MW-107A NS NS 4,910 5,050 5,910 6,130 5,600 5,410 NS NS 4,040 Yankee Nuclear Power Station Final Groundwater Rowe, MA. Condition Report Page 1 of 2, 2/9/2007

Table 4-1 Summary of 2006 Tritium Analytical Results Non-Monitoring Filtered Q2 Filtered Well Jan-06 Feb-06 Q1 2006 May-06 2006 Q2 2006 Aug-06 Q3 2006 Oct-06 Nov-06 Q4 2006 MW-107B NS NS U U U NA NS U NS NS U MW-107C NS NS 41,300 37,200 36,000 36,600 34,700 32,500 NS NS 29,100 MW-107D NS NS 11,900 12,000 11,800 13,300 11,600 11,000 NS NS 9,310 MW-107E NI NI NI 8,130 7,900 7,840 7,840 5,440 NS NS 5,700 MW-107F NI NI NI NI 10,900 10,900 NS 9,580 NS NS 3,210 MW-108A NS NS U NS U NA NS U NS NS U MW-108B NS NS U NS U NA NS U NS NS U MW-108C NS NS U NS U NA NS U NS NS U MW-109A NS NS U NS U NA NS U NS NS 231 MW-109B NS NS U NS U NA NS U NS NS U MW-109C NS NS U NS U NA NS U NS NS U MW-109D NS NS U NS U NA NS U NS NS U MW-110A 7,720 NS 2,930 2,770 2,990 2,810 2,810 1,680 NS NS 1,660 MW-110B NS NS U NS U NA NS U NS NS U MW-110C NS NS 1,160 NS 1,980 NA NS 1,870 NS NS 2,590 MW-110D NS NS U NS U NA NS U NS NS U MW-111A NS NS 4,440 3,940 3,050 3,640 3,640 2,650 NS NS 1,680 MW-111B NS NS U NS U NA NS U NS NS U MW-111C NS NS U NS 5,160 NA NS 4,250 NS NS U MW-113A NI NI NI U U U ND U NS NS 231 MW-113C NI NI NI NS 601 826 826 766 NS NS 798 SPool 4,340 4,610 4,670 2,650 1,420 NA 1,510 1,390 NS NS 1,100 Notes:

1) All tritium concentrations pCi/L

2) NS - Not Sampled

3) NA- Not Analyzed

4) NI - Not Installed Yankee Nuclear Power Station Final Groundwater Rowe, MA Condition Report Page 2 of 2, 2/9/2007

Table 4-2 Tritium Results for 2006 Replacement Monitoring Wells Non-Monitoring Filtered Filtered Well Jan-06 Feb-06 Q1 2006 May-06 Q2 2006 Q2 2006 Aug-06 Q3 2006 Oct-06 Nov-06 Q4 2006 CB-3 NS NS U NS U NA NS NS CB-3R U U CW-10 NS NS U NS U NA NS 349 _

CW-1OR I I I I I U 317 Yankee Nuclear Power Station Final Groundwater Rowe, MA 2/15/2007 Condition Report

Table 4-3 Summary of Q2 2006 Boron and Cation-Anion Analytical Results Boron Calcium Mangnesiuml Potassium Sodium Chloride Sulfate Bicarb Carb Well ID ug/L Mg/L CB-3 42.7 14.7 2.07 2.81 78.4 115 22.5 69.30 0.00 CB-4 14.2 17.7 2.97 3.17 83.8 110 13 57.89 0.01 CB-6 68.3 18 2.5 4.64 92.5 62.1 40.5 64.99 0.01 CB-8 7.5 29.9 8.07 6.23 30.5 780 18.1 36.60 0.00 CFW-1 6.8 2.32 1.09 1.31 2.66 0.457 3.57 6.85 0.00 CFW-5 45 31.9 5.08 5.7 4.1 14 0.628 108.97 0.03 CFW-6 7.3 22.4 3.37 3.18 1.85 8.01 0.875 81.18 0.02 CW-10 258 17.5 1.5 3.82 82 68.9 33.4 88.46 0.04 MW-1O0A 25.1 11.4 1.11 2.36 39 19.4 19.9 73.27 0.03 MW-100B 12.9 10.6 0.846 3.2 22.2 10.9 9.74 53.79 0.01 MW-101A 72.8 93.9 0.085 5.48 35.6 109 33.6 10.90 81.38 MW-101B 7.1 19.8 6.03 4 9.58 0.708 7.6 84.14 1.00 MW-102A 12 27.1 3.92 2.2 10.6 24.1 8.86 58.70 0.28 MW-102B 6.3 18.7 5.51 2.67 8.6 0.968 7.79 80.79 0.38 MW-102C 67.6 38.5 6.47 2.82 10.5 26 10.8 94.16 0.70 MW-102D 134 30 0.348 12.4 116 87.5 61.6 112.60 1.33 MW-103A 19.2 14.8 1.95 2.91 54.2 71.3 15.5 29.50 0.00 MW-103B 9.1 31.9 3.96 3.69 16.5 16.5 12.6 92.14 0.63 MW-103C 7.1 61.2 20.3 4.13 70 34.6 17.5 320.31 0.67 MW-104A 61.3 16.9 1.61 2.66 47.7 32 33.3 62.18 0.01 MW-104B 10.2 30.9 4.56 5.97 13.4 19.1 13.2 101.14 1.77 MW-104C 11.6 223 68.4 13.6 184 21.6 21 94.74 0.81 MW-105A 53.7 16.8 2.04 4.64 37.3 34.2 23.7 26.39 0.00 MW-105B 41.9 82.5 12.9 6.14 29.2 156 22.1 70.42 0.17 MW-105C 47.2 71.1 16.7 5.88 31.6 157 13.1 71.03 0.07 MW-106A 70.8 35.1 6.22 4.74 68.7 110 37.3 54.59 0.01 MW-106B 4 40.7 4.72 4.15 6.22 12.4 7.35 112.97 0.03 MW-106C 6.4 22.8 6.93 4.36 16 0.559 10.6 107.89 0.10 MW-106D 4.1 54 8.76 3.98 16.4 2.17 8.27 200.43 0.56 Yankee Nuclear Power Station Page 1 of 2 Final Groundwater Rowe, MA 2/15/2007 Condition Report

Table 4-3 Summary of Q2 2006 Boron and Cation-Anion Analytical Results Boron Calcium IMangnesium Potassium Sodium Chloride Sulfate Bicarb Carb Well ID u _/L Mg/L MW-107A 116 73.5 0.085 9.76 77.7 62.3 102 6.16 66.44 MW-107B 18.9 38.9 3.24 4.18 18.7 33.2 12.6 88.94 0.62 MW-107C 214 49.4 9.68 3.74 16.2 46.6 21.5 105.81 0.19 MW-107D 168 40.3 6.72 4.15 8.67 40.8 8.98 81.32 0.36 MW-107E 20.4 .25.7 3.48 2.21 7.87 13.4 7.87 65.79 0.56 MW-107F 10.8 29.5 4.66 2.34 7.67 22.6 8.63 68.93 0.62 MW-108A 8.5 102 14.1 11.5 83.2 230 2.24 172.95 0.05 MW-108B 4.6 27.8 2.94 3.02 6.36 3.58 9.94 76.55 2.38 MW-108C 5.2 74.8 18.4 5.96 15.2 61.3 12.8 194.06 0.91 MW-109A 18 12.6 1.53 4.93 82 68.5 27.3 99,35 0.23 MW-109B 7 18.8 5.69 3.05 8.71 0.673 7.32 81.29 0.38 MW-109C 4 17.4 2.22 1.42 8.19 0.81 13.7 56.44 0.42 MW-109D 8.4 38.3 12.4 3.64 28.6 0.772 13.1 86.26 0.13 MW-110A 43.9 123 0.085 14.1 72.8 35.5 25.6 12.18 233.73 MW-110B 10.9 38.8 2.81 4.88 9.63 12.1 15 88.06 0.41 MW-110C 4 25.1 3.23 2.08 6.04 22.7 8.55 53.25 0.50 MW-110D 6.3 40.3 8.6 7.09 16.2 67 11 66.02 1.56 MW-111A 30.5 116 0.085 25.2 80.9 34.1 23.7 3.31 156.09 MW-111B 25.4 42 3.45 5.86 30.1 70.4 18.9 65.46 0.04 MW-111C 168 25.4 4.46 2.55 89.7 60.4 10 160.73 0.26 MW-113A 21.8 20.6 3.24 3.94 87.5 107 14.5 65.00 0.00 MW-113C 5.4 28.3 5.84 3.31 11.2 4.48 10.4 107.79 0.20 SP-1 38.2 20.1 2.98 3.1 36.5 49.5 18.5 55.09 0.19 Yankee Nuclear Power Station Page 2 of 2 Final Groundwater Rowe, MA 2/15/2007 Condition Report

Table 5-1 Summary of Trend Analysis for Monitoring Wells Included in the LTP Monitoring Plan Tritium Tritium Well ID Trend Qi-0.4.2006 Trend Qi-Well ID 04 2006 CB-3 NT MW-106C NT CB-4 NT MW-106D NT CB-6 DT MW-107A NT CB-8 NT MW-107B NT CW-10 NT MW-107C DT CFW-1 NT MW-107D DT CFW-5 NT MW-107E DT CFW-6 NT MW-107F NT MW-100A NT MW-108A NT MW-100B NT MW-108B NT MW-101A DT MW-108C NT MW-101B NT MW-109A NT MW-101C NT MW-109B NT MW-102A NT MW-109C NT MW-102B NT MW-109D NT MW-102C NT MW-110A DT MW-102D NT MW-110B MW-lhOG NT MW-103A NT MW-103B NT MW-110D NT MW-103C NT MW-111A DT MW-104A NT MW-111B NT MW-104B NT MW-111C NT MW-104C NT MW-113A NT MW-104D NT MW-113C NT MW-105A NT SP-001 DT MW-105B DT MW-105C NT NT - No Trend MW-106A DT DT - Down Trend MW-106B NT UT - Up Trend Yankee Nuclear Final Groundwater Power Station Condition Report Rowe, MA 2/9/2007

Table 6-1 ConceptualModel Design in Vertical Cross Section Description in Plant Area Description in Upland Area Layer 1 5'-15' thick glaciofluvial = Zone 1 0.5' thick till zone = Zone 9 Layer 2 Low K Till = Zone 2 0.5' thick till zone = Zone 9 Layer 3 Locally 1st sand seam = Zone 12 or 13 0.5' thick till zone = Zone 9 Layer 4 Low K Till = Zone 2 0.5' thick till zone = Zone 9 Layer 5 Locally 2nd sand seam = Zone 3 0.5' thick till zone = Zone 9 Layer 6 Low K Till = Zone 2 0.5' thick till zone = Zone 9 Layer 7 Locally 3rd sand seam = Zone 3 0.5' thick till zone = Zone 9 Layer 8 Low K Till = Zone 2 0.5' thick till zone = Zone 9 Layer 9 Low K Glaciolacustrine - Zone 2 0.5' thick till zone = Zone 9 Layer 10 Locally 4th sand seam = Zone 3 0.5' thick till zone = Zone 9 Layer 11 Low K Glaciolacustrine = Zone 2 0.5' thick till zone = Zone 9 Layer 12 Locally 5th sand seam = Zone 1 or 3 0.5' thick till zone = Zone 9 Layer 13 Low K Glaciolacustrine = Zone 2 0.5' thick till zone = Zone 9 Layer 14 Upper 50' of rock (Zone 9), weathered, locally high K Upper 50' of rock = Zone 7 Layer 15 Lower 450' of rock (Zone 10), locally high K = Zone 8 Lower 450' of rock = Zone 10 Yankee Nuclear Final Groundwater Power Station 1/16/2007 Condition Report

Table 6-2 Pre-Demo Model Hydraulic Conductivity Zone Values Zone # Kx, Ft/day Ky, Ft/day Kz, Ft/day Geologic Material 1 10.0000 10.0000 1.0000 Glaciofluvial sand & gravel 2 0.0600 0.0600 0.0090 Thick silty glacial till 3 5.0000 5.0000 0.1000 Stratified sand & silt 4 0.1000 0.1000 0.0010 Stratified silt near MW-108 & MW-i113 Fill Material Placed in areas of soil 5 1.0000 1.0000 0.0100 remediation Inferred high K zone in bottom of valley 6 10.0000 10.0000 10.0000 above competent bedrock 7 0.0100 0.0100 0.0100 Upper 50' of bedrock in upland area Inferred high K zone downstream and 8 1.0000 1.0000 1.0000 paralled to Sherman Dam 9 0.1500 0.1500 0.1500 Thin. sandy till & wx bedrock 10, 0.0560 0.0560 0.0056 Lower 450' of bedrock 11 0.0060 0.0060 0.0004 Silty glacial till near MW-107 12 1.0000 1.0000 0.0100 Stratified fine sand & silt near MW-107 13 5.0000 5.0000 0.1000 Stratified fine sand & silt near MW-107 Inferred Shallow fractured rock zone from 14 10.0000 10.0000 10.0000 plant well through MW-107 Yankee Nuclear Final Groundwater Power Station 1/15/2007 Condition Report

Figure6-3 Pre-Demo Model Average Annual PrecipitationRate Kecnarge Rate, Rate, inches per Zone # Ft/day year Area Applied Upland Thin Till and Exposed 1 0.00009 0.38475 Bedrock ,

Glacio-fluvial deposits in the River 2 0.01000 42.75000 Valley Impervious Areas of Plant Prior to 3 0.00000 0.00000 Pavement and Building Removal Overall average land-applied recharge = 2.6 inches per year or 5.3% of precipitation Yankee Nuclear Final Groundwater Power Station 2/4/2007 Condition Report

Table 6-4 Model Specific Storage, Specific Yield, and PorosityZone Descriptions Specific Storage, Zone # /Ft Sy Porosity Geologic Unit Glacio-fluvial sand and gravel; upland thin glacial till; I1 1.00E-05 0.05 0.30 sand layers; thin high yield fractured rock zone 2 5.00E-06 0.05 0.20 Thick dense glacial till 3 1.00E-07 0.03 0.30 Glaciolacustrine deposits, layers 9 through 13 4 3.00E-06 0.01 0.01 Typical bedrock 5 5.00E-06 0.20 0.20 Mixed origin soil near MW-107 in layers 2, 3, and 4 Yankee Nuclear Final Groundwater Power Station 1/16/2007 Condition Report

Table 6-5 Pre-DemoModel A verageAnnual Recharge Mass Balance Inflow, Outflow, Description Ft3/day Ft3/day Recharge 71501.89 0.00 Constant Head 657.16 55831.25 Drain 0.00 15597.00 Storage 0.00 0.00 TOTAL 72159.06 71428.24 ERROR 1.02%

Yankee Nuclear Final Groundwater Power Station 1/16/2007 Condition Report

Table 6-6 Model Chemical Mass Balance for IXP Tritium Leak Simulation 1965-1985 Model Layer Chemical Mass Balance 1 -2.49%

2 -3.90%

3 -0.78%

4 -4.37%

5 -8.26%

6 -3.46%

7 -6.88%

8 -199%

9 -0.65%

10 -0.64%

11 -0.10%

12 48.07%

13 -199%

14 -199%

15 -120%

TOTAL -199%

Note that the large total mass balance is due to large errors at only a few cells not involved in the main transport pathways Yankee Nuclear Final Groundwater Power Station 2/4/2007 Condition Report

Table 6-7 Pre-DemoModel CalibrationStatisticsfor Steady-State Recharge Mon. Model Observed Computed Residual Well Layer Head, Ft. Head, Ft. Head, Ft.

MW-100A 1 1117.07 1120.32 -3.25 MW-100B 14 1115.59 1111.51 4.08 MW-101A 2 1122.88 1123.21 -0.33 MW-101B 14 1104.98 1104.49 0.49 MW-101C 10 1092.99 1103.94 -10.95 MW-102A 3 1112.73 1110.16 2.57 MW-102B 14 1103.3 1099.20 4.10 MW-102C 7 1091.66 1101.19 -9.53 MW-102D 1 1118.12 1122.47 -4.35 MW-103A 1 1093.25 1099.01 -5.76 MW-103B 14 1055.93 1049.89 6.04 MW-103C 7 1075.5 1072.54 2.96 MW-104A 1 1110.51 1101.19 9.32 MW-104B 14 1055.74 1057.17 -1.43 MW-104C 5 1078.13 1084.53 -6.40 MW-105A 1 1112.31 1119.14 -6.83 MW-105B 14 1106.47 1093.15 13.32 MW-105C 3 1110.06 1107.07 2.99.

MW-106A 1 1082.06 1084.72 -2.66 MW-106B 14 1051.48 1050.78 0.70 MW-106C 7 1058.71 1064.23 -5.52 MW-106D 12 1050.57 1052.97 -2.40 MW-107A 1 1122.8 1123.56 -0.76 MW-107B 14 1103.33 1102.72 0.61 MW-107C 3 1113.72 1114.33 -0.61 MW-107D 7 1095.35 1104.28 -8.93 MW-107E 5 1113 1107.87 5.13 MW-107F 5 1112.98 1107.77 5.21 MW-108A 1 1106 1108.49 -2.49 MW-108B 14 1067.04 1064.26 2.78 MW-108C 5 1104.61 1099.99 4.62 MW-109A 1 1115.27 1119.14 -3.87 MW-109B 14 1093.59 1080.05 13.54 MW-109C 3 1108.89 1105.85 3.04 MW-109D 7 1085.23 1084.47 0.76 MW-110A 1 1124.01 1125.24 -1.23 MW-110B 14 1104.51 1108.97 -4.46 Yankee Nuclear Final Groundwater Power Station Page 1 of 2, 1/15/2007 Condition Report

Table 6-7 Pre-DemoModel CalibrationStatisticsfor Steady-State Recharge MW-110C 3 1116.61 1117.19 -0.58 MW-110D 5 1095.02 1108.67 -13.65 MW-111A 1 1121.48 1122.26 -0.78 MW-111B 14 1107.13 1106.88 0.25 MW-111C 3 1119.41 1112.66 6.75 MW-113A 1 1064.24 1058.60 5.64 MW-113C 5 1031.23 1044.25 -13.02 Residual Mean -0.34 Res. Std. Dev. 6.02 Sum of Squares 1599.49 Abs. Res. Mean 4.65 Min. Residual -13.65 Max. Residual 13.54 Range 92.78 Std/Range 0.065 Yankee Nuclear Final Groundwater Power Station Page 2 of 2, 1/15/2007 Condition Report

Table 6-8 Pre-Demo Model VerticalGradientCalibrationStatisticsfor A verage Annual Recharge Observed Computed Residual Model Model Gradient, Gradient, Gradient, Name Layer 1 Layer 2 Ft. Ft. Ft.

MW-100A 1 14 1.5 3.58 -2.08 MW-101A 2 14 17.5 19.18 -1.68 MW-101C 10 2 -29.5 -19.73 -9.77 MW-101C 10 14 -12 -0.64 -11.36 MW-102A 3 14 10 11.07 -1.07 MW-102A 3 7 21 8.99 12.01 MW-102A 3 1 -5.39 -13.21 7.82 MW-102C 7 14 -11 1.46 -12.46 MW-102D 1 14 14 23.81 -9.81 MW-102D 1 7 25 21.70 3.30 MW-103A 1 14 38.5 45.95 -7.45 MW-103B 14 7 -20 -22.18 2.18 MW-103C 7 1 -17.5 -23.73 6.23 MW-104A 1 14 54.5 44.61 9.89 MW-104A 1 5 32.5 17.01 15.49 MW-104B 14 5 -22 -27.05 5.05 MW-105A 1 14 5.5 23.05 -17.55 MW-105C 3 1 -2 -13.34 11.34 MW-105B 14 3 -3.5 -14.05 10.55 MW-106A 1 14 30.5 30.47 0.03 MW-106A 1 7 23 18.97 4.03 MW-106A 1 12 31.5 28.13 3.37 MW-106B 14 7 -7 -13.39 6.39 MW-106D 12 14 -1 2.44 -3.44 MW-106C 7 12 8 10.31 -2.31 MW-107A 2 14 19.5 17.35 2.15 MW-107A 2 3 9 5.51 3.49 MW-107A 2 7 27.5 15.65 11.85 MW-107A 2 5 10 12.43 -2.43 MW-107B 14 3 -10.5 -11.92 1.42 MW-107B 14 7 8 -1.69 9.69 MW-107B 14 5 -9.5 -4.86 -4.64 MW-107C 3 7 18.5 10.07 8.43 MW-107C 3 5 0.7 6.83 -6.13 MW-107D 7 5 -17.5 -3.34 -14.16 MW-108A 1 14 39 44.76 -5.76 MW-108B 14 5 -37.5 -36.19 -1.31 Yankee Nuclear Final Groundwater Power Station Page 1 of 2, 1/15/2007 Condition Report

Table 6-8 Pre-Demo Model VerticalGradientCalibrationStatistics for A verageAnnual Recharge MW-108C 5 1 -1.5 -10.23 8.73 MW-109A 1 14 21.5 43.17 -21.67 MW-109A 1 3 6.5 13.69 -7.19 MW-109B 14 3 -15.5 -27.81 12.31 MW-109B 14 7 8.5 -5.41 13.91 MW-109C 3 7 23.5 22.34 1.16 MW-109D 7 1 -30 -36.28 6.28 MW-110A 1 14 19.5 17.13 2.37 MW-110A 1 3 7.5 7.76 -0.26 MW-110A 1 5 29 16.80 12.20 MW-110B 14 3 -12 -8.82 -3.18 MW-110C 3 5 21.5 8.39 13.11 MW-110D 5 14 -9.5 0.42 -9.92 MW-111A 1 14 14.5 17.98 -3.48 MW-111B 14 3 -12.5 -7.23 -5.27 MW-111C 3 1 -2 -10.07 8.07 MW-113A 1 5 33 14.80 18.20 Residual Mean 1.23 Res. Std. Dev. 8.81 Sum of Squares 4275.54 Abs. Res. Mean 7.32 Min. Residual -21.67 Max. Residual 18.20 Range 92.00 Std/Range 0.096 Yankee Nuclear Final Groundwater Power Station Page 2 of 2, 1/15/2007 Condition Report

Table 6-9 Pre-Demo Verification DataSet CalibrationStatistics Model Observed Computed Residual Mon. Well X Y Layer Head, Ft. Head, Ft. Head, Ft.

CB-1 272,442.5 3,093,618.6 2 1115.97 1118.67 -2.70 CB-10 272,458.1 3,093,542.6 1 1124.05 1124.90 -0.85 CB-2 272,148.0 3,093,716.7 2 1105.68 1105.20 0.48 CB-3 272,493.2 3,093,282.0 1 1134.05 1137.87 -3.82 CB-4 271,469.9 3,093,627.5 1 1075.59 1089.17 -13.58 CB-5 273,112.2 3,093,260.5 2 1151.93 1162.36 -10.43 CB-6 272,014.0 3,093,781.6 2 1097.84 1097.32 0.52 CB-8 272,609.4 3,093,424.4 1 1135.18 1139.81 -4.63 CB-9 272,371.5 3,093,562.0 2 1116.57 1118.53 -1.96 CFW-1 272,941.1 3,093,089.4 1 1165.02 1167.31 -2.29 CFW-2 273,029.6 3,093,361.5 2 1155.45 1171.80 -16.35 CFW-3 273,120.9 3,093,430.3 5 1146.9 1170.62 -23.72 CFW-4 273,125.1 3,093,431.2 7 1146.65 1170.04 -23.39 CFW-5 273,242.3 3,093,499.5 1 1139.44 1128.33 11.11 CFW-6 273,170.0 3,093,653.2 1 1134.34 1134.87 -0.53 CFW-7 273,079.1 3,093,400.1 2 1155.38 1163.75 -8.37 CW-10 272,659.7 3,093,880.3 14 1104.43 1120.34 -15.91 CW-11 272,450.3 3,093,523.8 1 1127.01 1125.37 1.64 CW-2 272,388.5 3,093,387.5 2 1125.05 1126.94 -1.89 CW-3 272,534.8 3,093,532.1 2 1131.04 1131.00 0.04 CW-4 272,594.7 3,093,367.8 2 1132.38 i137.25 -4.87 CW-5 272,518.2 3,093,690.7 1 1117.72 1119.32 -1.60 CW-6 272,151.8 3,093,596.3 2 1110.73 1109.49 1.24 CW-7 272,368.6 3,093,769.8 2 1108 1112.42 -4.42 CW-8 272,231.2 3,093,660.0 2 1107.03 1107.16 -0.13 MW-2 272,419.5 3,093,492.1 1 1123.23 1126.44 -3.21 MW-5 272,434.6 3,093,555.6 1 1122.63 1124.34 -1.71 MW-6 272,280.1 3,093,483.7 2 1118.81 1119.82 -1.01 OSR-1 272,939.0 3,093,245.8 1 1152.5 1159.52 -7.02 Residual Mean -4.81 Res. Std. Dev. 7.47 Sum of Squares 2288.23 Abs. Res. Mean 5.84 Min. Residual -23.72 Max. Residual 11.11 Range in Target Values 89.43 Std. Dev./Range 0.084 Yankee Nuclear Final Groundwater Power Station 1/16/2007 Condition Report

Table 6-10 Calculationof Weighted Tritium Concentrationin Resident Farmer Well Pumping Well Tritium Contribution Conc., pCi/L, from Each at start of Layer, pumping Flux times Model Layer Ft3/day April 2007 Mass 2 0.878 33,000 28,974 3 0.152 28,000 4,256 4 0.7 35,000 24,500 5 126.271 7,800 984,914 TOTAL 1,042,644 1,042,644 divided by 128 = 8146 pCi/L of tritium as weighted concentration Pumping Well Contribution Tritium from Each Conc., pCi/L, Layer, after 2 Years Flux times Model Layer Ft3/day of Pumping Mass 2 0.878 19,188 16,847 3 0.152 16,822 2,557 4 0.7 18,813 13,169 5 126.271 4,900 618,728 TOTAL 651,301 651,301 divided by 128 = 5088 pCi/L of tritium as weighted concentration Yankee Nuclear Final Groundwater Power Station 1/18/2007 Condition Report

258,000 260,000 262,000 264,000 266,000 268,000 270,000 272,000 274,000 276,000 278,000 280,000 282,000 284,000 286,000

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269,000 770,000 271,000 272.000 273,000 274,000 275,000 269,000 270,000 271,000 272,000 273,000 274,000 275,000 Yankee Nuclear Current 10 CFR Part 50 Final Groundwater Power Station Licensed Site Boundary Condition Report Rowe, MA Source: FSAR Figure 300-2 Aerial photos taken 4/15/97 1/29/07 Figure 1-2

271.100 271.20 2V1.3W 271,40 271,5W0 271.W 271.7W 271:800 V1,". 272000 2710 27,2W 272.3W 2727707 272.8W 2M2.900 273., 273.3W0 M7.400 273.5W 273.8W VIM7 VC I"

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Figure2-9 Ambient Air Temperature at YNPS Site 100 90 80 70 60 L-IA, 0

450 E

20 10

-10 0

-20 1 .4- 4i i- j .j 12/1/2004 1/30/2005 3/31/2005 5/30/2005 7/29/2005 9/27/2005 11/26/2005 1/25/2006 3/26/2006 5/25/2006 Yankee Nuclear Power Station Final Groundwater Rowe, MA 1/31/2007 Condition Report

MWest Side Storm Watei

/& Area of StormWater Removal Q

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