ML12275A555
| ML12275A555 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 02/15/2011 |
| From: | GZA GeoEnvironmental |
| To: | Entergy Nuclear Northeast, Entergy Services, Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| References | |
| RAS 23556, 50-247-LR, 50-286-LR, ASLBP 07-858-03-LR-BD01 IPEC00227561 | |
| Download: ML12275A555 (4) | |
Text
FINAL IPEC QUARTERLY LONG-TERM GROUNDWATER MONITORING REPORT QuARTER Two 2010 I PEC00227561 (REPORT No.10)
INDIAN POINT ENERGY CENTER BUCHANAN, NEW YORK PREPARED FOR:
ENTERGY NUCLEAR NORTHEAST, INC.
INDIAN POINT ENERGY CENTER 450 BROADWAY BUCHANAN, NEW YORK 10511 ON BEHALF OF:
ENTERGY SERVICES, INC.
INDIAN POINT ENERGY CENTER 295 BROADWAY, SUITE 3 P.O. Box308 BUCHANAN, NY 10511-0308 PREPARED BY:
GZA GEOENVIRONMENTAL OF NEW YORK 440 NINTH AVENUE, 18TH FLOOR NEWYORK, NEWYORK 10001 FEBRUARY 15, 2011 FILE No. 01.0017869.92 Copyright© 2010 GZA GeoEnvironmental of New York RIVR00076 Submitted: October 1, 2012 EXCERPT
FINAL QUARTERLY LONG-TERM GROUNDWATER MONITORING REPORT 02 2010 (REPORT NO. 1 0) 1.0 EXECUTIVE
SUMMARY
On behalf of Entergy Nuclear Northeast, Inc., GZA GeoEnvironmental of New York (GZA) has completed the Q2 2010 quarterly groundwater monitoring for the Indian Point Energy Center (IPEC), culminating in this report. Interpretations of the monitoring data have been made in the context of the current Conceptual Site Model. Development of this model began at the outset of the site investigations and has been iteratively enhanced as subsequent data has become available, in part through quarterly monitoring. The report has been written with a focus on the most recent quarterly data. Relationships to prior data, more in-depth technical explanations and exceptions to generalized statements and conclusions have typically been relegated to footnotes. This report format was chosen to allow efficient assimilation of the most current data and analyses by those already familiar with the project.
The footnotes contain important information and should be carefully read by all, but particularly by those less familiar with the technologies involved and the project history.
Based on the quarterly groundwater sampling data for Q2 2010, GZA concludes that groundwater contaminants continue* to migrate toward the Hudson River to the West, and have not migrated off the Site to the North, East or South.
Radionuclide concentrations measured during Q2 2010 were combined with previous quarterly and post-quarterly data to compute rolling average concentrations reflective of groundwater contaminant levels over the past twelve months. These data were multiplied by the associated individual zone-specific groundwater flux values, derived from the Precipitation Mass Balance Model 1, to compute yearly average radionuclide release rates to the Discharge Canal and Hudson River.
The Conceptual Site Model2 (CSM), upon which this radionuclide dose computation is based, continues to be validated through: (1) groundwater elevation data downloaded quarterly from a focused set of transducer-monitored well installations; and (2) the behavior of both the Unit 1 Strontium plume and the Unit 2 Tritium plume as evaluated each quarter: These data, in our opinion, continue to support the use of the current CSM as a basis for Long Term Monitoring Program design.
The overall Tritium activity in the Unit 2 plume is generally showing a historically decreasing trend, from both qualitative and quantitative perspectives. These overall reductions are seen on Figure G-17, where the total Tritium activity has decreased by approximately 28% since Q2 2007, and 86 %when compared to the bounding level Tritium activities, even with inclusion of the current peak in total Tritium (see discussion immediately below). This overall larger trend is also evident on Figures 6 and 6A, where the shaded plume3 no longer extends downgradient to the river, as first observed in the Q2 2009 quarterly report. It is further visually evident from 1 Refer to Appendix H of the Quarter 2 2009 Quarterly Long-Term Groundwater Monitoring Report for discussion of the recalibration of the Precipitation Mass Balance Model. Precipitation and groundwater elevation data were collected onsite between 2007 and 2009 and used to compute groundwater fluxes across the site. Based on analyses of these data, it was concluded that this data set sufficiently encompassed the historical variability in groundwater elevation and flux response to seasonal and yearly precipitation variability. Therefore, maximum onsite groundwater fluxes were calculated from the elevation data, and used to conservatively recalibrate the Precipitation Mass Balance Model, as discussed and employed in the Q2 2009 Quarterly L TM Report.
2 The formulation and basis for the overall CSM and the Precipitation Mass Balance model are presented in the Hydrogeologic Site Investigation Report, January 7, 2008, prepared by GZA GeoEnvironmental, Inc, on behalf of Enercon Services, Inc., for Entergy Nuclear Northeast, Indian Point Energy Center, 450 Broadway, Buchanan, NY 10511.
3 The plume shading on Figure 6 demarks the estimated boundary that separates Tritium levels greater than 5,000 pCi/L from those below this value. This plume delineation boundary value equates to one-quarter of the drinking water standard for Tritium. Although GZA emphasizes that drinking water standards (USEPA MCLs) do not apply to the IPEC property given that there are no drinking water sources on or proximate to the site, the MCLs do provide a useful benchmark for comparisons of relative human risk. IMlere yearly rolling average radionuclide activity data were available for multiple depths at a given location, GZA used the highest value to develop plume delineations. This is a typical approach to represent three-dimensional contaminant data sets on two-dimensional maps.
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Section 1.0 Executive Summary Figure SA that the core of the plume has also shown a marked decrease in concentration and extent over time in the vicinity of MW-111. These findings are consistent with our CSM, which anticipates overall decreasing trends in Tritium activity. Consistent with one of the purposes of thiS Report, we also point out and explain data which, when first considered, may initially appear inconsistent with the assumptions used to develop the CSM. Such examples, where Tritium has increased in recent quarters, include:
Peaks in Tritium levels have been observed in multiple sampling ports of MW-31 and MW-32 since Q1 2009, and to a lesser extent since monitoring began. This long-term variability appears to be consistent with episodic releases of Tritium historically stored in the subsurface via natural and anthropogenic Retention Mechanisms4. This conclusion is further supported by the tracer data and other analyses discussed in Section 3.6 of the Q1 2009 Long Term Monitoring Report.
While Retention Mechanisms clearly appear to impact Tritium levels as summarized above, the previous Q1 and post Q1 2010 sampling events measured more noticeable increases in Tritium levels in a number of intervals within MW-31 and MW-32, where Tritium activities peaked at levels higher than previously measured. Similarly elevated Tritium activities continued through the current Q2 and post Q2 2010 sampling events at these locations. These Q1 and Q2 2010 Tritium peaks are likely related to a Q4 2009 localized and transient Unit 2 RWST/R.O. processing skid surface spill which was first detected during routine 80-10 sampling of MH-9 in mid-January 2010.
A number of additional well locations also exhibited peaks in Tritium levels coincident with the RWST/R.O. skid surface spill, as discussed in more detail in Sections 3.4.4 and 3.4.5 below. In total, approximately 70% of the sampling intervals exhibited an increase in Tritium levels as compared to the previous, Q1 2010 quarter. An increase in the number of Unit 2 Tritium I.L. exceedances was also observed.
The number and degree of Tritium peaks measured in Q2 2010 has resulted in an increase in the Unit 2 plume total Tritium activity, as shown on Figure G-17 (Appendix G).
As above, this overall increase has also been attributed to the RWST/R.O. skid surface spill.
Pursuant to the RWST/R.O. surface spill, it is further noted that Tritium activity in MH-9 quickly returned to typical background levels once the spill was addressed.
It is therefore anticipated that the Tritium peaks attributed to the RWST/R.O. skid surface spill will also decrease over the next several quarters, and the graph of total Tritium activity in the Unit 2 plume should also then resume its downward trend.
Our review of data found no evidence that observed increases in Tritium activity were indicative of new, unidentified leaks in the Unit 2 SFP or other monitored Systems, Structures, or Components.
The overall Sr-90 activity within the Unit 1 plume had generally been stable to decreasing in response to the West Pool demineralization operations conducted by Entergy beginning in 2006.
However, the final defueling of the Unit 1 SFPs resulted in a noticeable increase in Strontium levels proximate to the SFPs, followed by downgradient increases (see Figure 7 and 7A). This is as was predicted given the requirement to temporarily raise the pool levels for fuel rod removal, thus increasing leakage rate from the SFPs5. As expected, the levels proximate to the pool have since decreased to pre-defueling Strontium activities and it is expected that levels 4 These Retentions Mechanisms are discussed along with the CSM in the previously cited Hydrogeologic Site Investigation Report.
5 As of late 2008, all the fuel rods have been removed from the Unit 1 SFPs and the pool water has been drained. As such, the Unit 1 SFPs is no longer an active source of radionuclides to the subsurface.
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Section,1.0 Executive Summary downgradient of the pool, currently exhibiting decreasing trends approaching pre-defueling levels, will also fully return to pre-defueling levels once this transient perturbation has passed through the groundwater flow system. It is anticipated that this flushing mechanism will be protracted given the impact of partitioning on Strontium levels in the groundwater.
Based on the data and analyses provided herein, our conclusion is that the Tritium and Strontium plumes are both undergoing overall long-term reductions in activity.
Given this conclusion, and the recognition that Entergy has terminated all identified leaks in the Unit 2 SFP6 and has decommissioned the Unit 1 SFPs, these plumes satisfy the requirements for Monitored Natural Attenuation (MNA), the remedial technology selected for the IPEC Site.
However, it is also concluded that, while a portion of the leakage from the above cited localized, transient spills traveled directly to the saturated groundwater regime and resulted in the observed transient "peaks" in radionuclide levels, additional portions of these releases likely remain above the water table as recharge to the various Retention Mechanisms. This additional unsaturated zone source recharge will likely be manifested in the future as additional non-specific peaks in radionuclide levels due to episodic releases to the groundwater flow regime from these mechanisms (e.g., from intense/prolonged precipitation events). These localized release events also interfere with the goal of resetting Site Investigation Levels (I.L.s); updating of Strontium I. L.s must therefore await return to the original Strontium baseline levels existing prior to Unit 1 defueling, and additional seasonal data is required to better assess Tritium response to precipitation-driven Retention Mechanism release variability. Therefore, the ultimate confirmation of the above conclusions will require monitoring over a number of years so as to allow ranges in seasonal variation to be adequately reflected in the monitoring data and thus demonstrate continued depletion of Tritium and Strontium from the Retention Mechanisms. In this regard, it is important to recognize that even with the somewhat increased Tritium levels currently observed due to the Unit 2 RWST/R.O. skid transient surface spill, the amount of radionuclides being released through the groundwater pathway is still small compared to permitted levels of Tritium discharge to the river through the Discharge Canal.
In summary, based on the data collected to date, the apparent strength of the CSM to evaluate that data, and the completion of source interdictions by Entergy, we believe all Program Objectives (see Section 3.0) are being met. These objectives are consistent with and fully encompass the guidance provided in the NEI Groundwater Protection Initiative (GPI).
6 Further justification for this conclusion can be found in Section 3.6 of the Q1 2009 Quarterly Monitoring Report as well as the Hydrogeologic Site Investigation Report. The Q1 2009 Report summarizes additional, more quantitative analyses which were completed to further investigate the integrity of the Unit 2 SFP. These analyses provide further support for the original conclusion that the Unit 2 SFP is no longer leaking. However, given the more recent behavior observed in the Unit 2 collection box data (see Section 3.6 of the Q1 2009 Long Term Monitoring Report), additional investigations/data evaluations are underway to further rule out potential.Unit 2 SFP leak mechanisms. In this regard, it is noted that these analyses cannot definitively and completely rule out the possibility of a remaining small leak which could then also be supplying Tritium to the groundwater flow regime in addition to the Retention Mechanism(s) and surface spill from the process skid discussed above. IM1ile ~ is not possible to quantify the size of the minimum detectable leak with any degree of certainty, we believe that the maximum leak rate from the Unit 2 SFP that could potentially remain undetected by the groundwater monitoring system is less than 10 to 30 gpd (0.007 to 0.021 gallons per minute). It is also likely that if a small leak exists in the Unit 2 SFP liner, it should not get worse with time. This opinion is based on liner evaluations previously conducted by Entergy. It is further emphasized that while a leak of more than 0.02 gallons per minute should be large enough to be readily detectable with the existing Long Term Monitoring Program; this amount of Tritium release to the river is still small compared to permitted levels of Tritium discharge to the river through the Discharge Canal.
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