Presentation on theme: "Brunswick Nuclear Plant Storm Drain Stabilization Pond Groundwater Investigation and Remedial Evaluation Presentation Prepared and Presented by: Silar."— Presentation transcript:
Brunswick Nuclear Plant Storm Drain Stabilization Pond Groundwater Investigation and Remedial Evaluation Presentation Prepared and Presented by: Silar Services, Inc.
Project / Presentation Overview Investigation Status Final Groundwater Investigation Report completed 3/2008 Review of ongoing monitoring data for groundwater and surface water Quarterly reports for ongoing groundwater/surface water monitoring activities Remedial alternative selected, engineering design process underway in 1 st quarter 2008 Remedial Evaluation Remedial Action Objectives (RAOs) Potential Remedial Options Remedial alternative selected, engineering design process underway in 1 st quarter 2008 Summary/Questions
Objectives and Methodologies Initial Scope Characterize the nature and extent of tritium in groundwater adjacent to the SDSP in accordance with the Groundwater Protection Initiative (GPI); Develop a conceptual site model for the SDSP that establishes the relevant transport pathways and potential receptors associated with the release of tritium from the SDSP Establish a comprehensive groundwater monitoring program Based on results of investigation, additional scope included: Determine applicable or relevant and appropriate requirements (ARARs) and establish remedial action objectives (RAOs) Screen and evaluate remedial alternatives available to address site conditions and RAOs
Field Investigation Summary Completed an initial evaluation of data and physical characteristics of the SDSP and surrounding environs Established access to remote, wooded areas around the SDSP that required investigation Installed a network of 15 shallow groundwater monitoring wells, 7 intermediate-depth wells,1 deep bedrock monitoring well, and 6 marsh wells (additional pre-existing wells were evaluated and incorporated into the monitoring network, where appropriate) Collected soil samples for geotechnical parameters Completed “preliminary” groundwater monitoring and real-time data evaluation throughout the effort Identified site conditions and data gaps in real time Allowed for completion of the groundwater investigation during a single mobilization
Field Investigation Summary (continued) Completed an initial hydraulic characterization of the groundwater aquifers via pump tests and rising head slug tests Completed a 3-month synoptic hydraulic study to evaluate hydraulic relationships between the SDSP, groundwater aquifers, and surface water (tidal effects) Developed a conceptual site model and analysis of transport pathways for all associated groundwater pathways Completed area reconnaissance to identify off-site groundwater uses/withdrawals
Development of the Groundwater Monitoring Program Designed and installed a GeoSmart groundwater monitoring system consisting of a dedicated bladder pump, teflon ® tubing, heavy duty bladder, and integrated well head system Facilitate consistent, program-wide hardware and sample collection methodology Provide user friendly interface and rugged hardware for long-term deployment Appropriate for collecting groundwater samples consistent with USEPA low-flow methodology Established a monthly groundwater monitoring program for associated shallow, intermediate, deep, and marsh wells Trained facility personnel to properly perform monthly groundwater sampling activities
Groundwater Investigation Summary Final Groundwater Investigation Report submitted in March 2008 Findings Area underlain by 3 individual aquifers (shallow, intermediate and deep) Widespread tritium impacts in shallow, isolated impacts in intermediate, no impacts in deep. Tritium observed in marshes and adjacent creeks Site hydraulic are such that impacts will migrate off-site Shallow to Nancy’s Creek and Shallow to Intermediate to Off-site Migration of tritium in on-site groundwater to off-site groundwater has not been observed SDSP Area Achieves EPRI Program Level 3 Status
Monitoring Well and Hydrogeologic Cross Section Location Map
Hydrogeologic Cross Section
Groundwater Flow – Shallow Aquifer
Shallow Aquifer Groundwater Results for Tritium (pCi/L) - October 2007
Trend Analysis - Shallow Aquifer
Result of Reducing Source Term Elimination of Primary Source of Tritium to SDSP (June 2007)
Groundwater Flow – Intermediate Aquifer
Intermediate Aquifer Groundwater Results for Tritium (pCi/L)
On-going Monitoring Weekly monitoring of surface water 17 surface water monitoring waypoints Monthly monitoring of groundwater 40 groundwater monitoring stations Findings Tritium concentrations in groundwater generally consistent with initial results Reduced source term to the pond appears to have positive result on groundwater concentration at the source Increasing concentration of tritium in groundwater samples collected from intermediate monitoring well ESS-19B raises concerns regarding vertical migration from shallow to intermediate aquifer (i.e. potable supply aquifer) Detectable concentrations of tritium in surface water samples
Off-site Detections in Surface Water
Evaluation of the Marsh and Creek SDSP tritiated water seeps through dike and transports to marsh Groundwater flows from the SDSP through the upper sand into the creek as baseflow Ongoing evaluation to determine appropriate method, model and model inputs to facilitate dose calculations associated with unmonitored release to the adjacent creeks accounting for these two mechanisms Groundwater flow / tritium fate and transport modeling Use of ongoing monitoring data to calculate dose per unit time Model to account for tidal effects and heterogeneity
Remedial Options – Remedial Action Objectives Remedial Action Objectives (RAO) were developed for the Stabilization Pond release based on Federal, State and Local rules and regulations along with industry best management practices RAOs include: Reduce the continual migration of tritium in groundwater on-site and off-site to protect human health and the environment Control future uncontrolled releases of tritiated water through the SDSP to the environment Reduce the concentration of tritium in groundwater to a concentration less than the Federal MCL of 20,000 pCi/L
Remedial Options – Potential Remedial Actions Six remedial actions were evaluated in the Final Report including: Monitored Natural Attenuation (MNA) Containment (Barrier Wall) with MNA Containment (Impoundment) with MNA Containment (Barrier Wall and Impoundment) with MNA Site-wide Groundwater Extraction with MNA Focused Groundwater Extraction with Containment (Impoundment) and MNA Each alternative was evaluated against the primary criteria of: effectiveness, implementability, and cost.
Remedial Options – Alternative 1 - MNA MNA involves no active remedial measures and relays on natural processes to achieve the RAOs Assumes status monthly monitoring to plant closure Evaluation criteria summary Effectiveness – will not meet any of the RAOs, provides no protection to human health or the environment Implementability – easily implemented, continue monthly monitoring, no construction activities Leads to high decommissioning costs Summary – Alternative 1 will not achieve the RAOs
Remedial Options – Alternative 2 - Containment (Barrier Wall) with MNA Alternative 2 involves installation of low permeability vertical barrier wall to control horizontal flow of tritiated groundwater in the shallow aquifer Assumes wall would be construction around ~90% of the pond, approximately 6,400 ‘ long, 45’ deep and 3’ wide Evaluation criteria summary Effectiveness – shallow groundwater within the impoundment would be controlled, but increases vertical migration into deeper aquifers Implementability – using fairly typical construction equipment, 6-12 months Summary – Alternative 2 would control shallow groundwater within the impoundment, it would not achieve the RAOs since it would not address impacted groundwater outside the impoundment or the vertical migration of shallow groundwater to the intermediate aquifer
Remedial Options – Alternative 3 - Containment (Impoundment) with MNA Alternative 3 involves construction of a low permeability impoundment within the SDSP to control the future uncontrolled releases of tritium into the environment Assumes lined impoundment (2 liner systems evaluated), 350,000 sq.ft., mg capacity. Evaluation criteria summary Effectiveness – will control future releases to the environment, will not effect continual migration of tritiated groundwater Implementability – with fairly typical construction equipment, 6-12 months Summary – Alternative 3 would control future releases to the shallow aquifer, however it would not achieve the RAOs since groundwater outside the impoundment would continue to migrate horizontally and vertically on-site and off-site.
Remedial Options – Alternative 4 - Containment (Barrier Wall and Impoundment) with MNA Alternative 4 involves the primary element of Alternatives 2 and 3. Assumes construction of a barrier wall and impoundment (non-RCRA liner) as previously described Evaluation criteria summary Effectiveness – Shallow groundwater within the barrier wall will be controlled and future uncontrolled releases to the environment through the SDSP would be eliminated Implementability – with fairly typical construction equipment, 6-12 months Summary – Alternative 4 would control shallow groundwater within the impoundment and eliminate continual releases through the SDSP, however it would not achieve the RAOs since it would not address impacted groundwater outside the impoundment or the vertical migration of shallow groundwater to the intermediate aquifer.
Remedial Options – Alternative 5 – Site-Wide Groundwater Extraction with MNA Alternative 5 involves extracting groundwater from the shallow aquifer throughout the impacted area to achieve the RAO of 20,000 pCi/L Assumes – installation of over 200 extraction wells with total withdrawal of 154,000 gpd Evaluation criteria summary Effectiveness – would control the off-site migration of tritium in the shallow groundwater Implementability – with fairly typical construction equipment, significant long-term O&M Summary – Alternative 5 would control horizontal migration of groundwater in the shallow aquifer to off-site receptors, it would not eliminate uncontrolled releases through the SDSP or achieve the RAOs.
Remedial Options – Alternative 6 - Focused Groundwater Extraction with Containment (Impoundment) and MNA Alternative 6 involves focused groundwater extraction to control off-site migration and installation of an impoundment within the SDSP to control the future uncontrolled releases of tritium into the environment Assumes elements of Alternative 3 and up to 50 extraction wells to control off-site migration and restore aquifer Evaluation criteria summary Effectiveness – Would be effective in elimating future releases and controlling migration of tritiated groundwater Implementability – with fairly typical construction equipment, some long- term O&M Summary – Alternative 6 would achieve all RAOs.
Selected Remedial Alternative Alternative 6 - Focused Groundwater Extraction with Containment (Impoundment) and MNA is the only remedial option that could achieve the RAOs in the long term. Alternative 6 will: Reduce the continual migration of tritium in groundwater on-site and off- site to protect human health and the environment by: constructing a lined impoundment thereby eliminating the on-going source of tritium impacts (percolation through the bottom of the pond) and extracting groundwater at strategic locations to control the horizontal migration of shallow groundwater to off-site receptors (i.e. Nancy’s Creek) and the vertical migration into the intermediate aquifer. Control future uncontrolled releases of tritiated water through the SDSP to the environment by: constructing a lined impoundment thereby eliminating the on-going source of tritium impacts (percolation through the bottom of the pond).
Selected Remedial Alternation - con’t Reduce the concentration of tritium in groundwater to a concentration less than the Federal MCL of 20,000 pCi/L by: Controlling the source (i.e. eliminating future loading of tritiated water into the shallow aquifer by constructing a lined impoundment) and extracting shallow groundwater with elevated concentration of tritium. Extracted groundwater will be conveyed to the impoundment for subsequent releases to the intake canal under NDPES permit. Groundwater extraction with MNA could reduce the tritium concentrations in groundwater below 20,000 pCi/L thereby reducing decommissioning costs.
Highlights of the Investigation Process The dedication of the Progress Energy management team facilitated the successful implementation of the investigation program Development of CSM utilizing up-to-date knowledge base leads to updated FSAR and site understanding Avoided pitfalls associated with reliance on historic data collected by others Established low-maintenance, easy to use groundwater sampling system, procedure, and monitoring program implemented by internal resources Improved operational performance as a result of the awareness and identification of SSCs associated with SDSP and BNP Successful media and public relations activities through open house forums and regular contact with local media and officials
Highlights of the Remedy Selection Process Remedial evaluation incorporated detailed short and long-term financial, technical, and environmental considerations Selected remedy incorporates long-term management considerations and environmental objectives with fiscally- responsible remedial approach Selected remedy incorporates existing NPDES-permitted outfall such that it constitutes a redevelopment rather than a new source/discharge Selected remedy is flexible such that pre-design activities can determine treatment requirements, impoundment sizing, well spacing, etc.
Summary/Conclusions Widespread shallow groundwater impacts due to uncontrolled releases for the SDSP On-going monitoring indicates impacts off-site in Nancy’s Creek and increased migration into the intermediate aquifer Six remedial options evaluated Alternative 6 - Focused Groundwater Extraction with Containment (Impoundment) and MNA would achieve the RAOs