MEW / NAS Moffett Field Site – Shallow TCEGroundwater Plume Fairchild Intel Raytheon NEC/Renasas SMI Vishay/ SUMCO NASA Navy
Estimated Extent of Regional TCE Shallow GroundwaterPlume
Purpose of Site-wide GroundwaterFeasibility Study• Evaluate alternative technologies to accelerate groundwater cleanup – Efficiency of system decreasing – Minimize need for vapor mitigation by reducing groundwater concentrations (Vapor Intrusion RAO).• Feasibility Study Considerations: – Community Criteria and Suggested Strategy – Incorporating results of pilot tests
Scope of GroundwaterCleanup• Large disperse commingled plume with multiple source areas• Range of concentrations within plume• FS strategy treatment of source & high conc. areas; move to passive remedy• Cleanup timeframes key component of FS
EPA Screening of TechnologiesIn Situ Treatment Technologies: Enhanced Reductive Dechlorination (ERD), In Situ Chemical Oxidation (ISCO), and Abiotic Dechlorination using Zero Valent Iron (ZVI)Extraction, Removal, Treatment and Disposal Technologies – – Physical Treatment with Air Sparging – Groundwater Extraction and Treatment – Multiphase Extraction – In Situ Thermal – Removal by ExcavationBarriers – Permeable reactive barriers, phytoremediationMonitored Natural Attenuation
In Situ Treatment Technologies• Evaluating ERD (Intel/GTE study), In Situ Chemical Oxidation (ISCO), and Abiotic Dechlorination using Zero valent iron• Technologies rely on direct contact or create conditions to degrade contaminants.• Typically used for hot spot treatment/limited area.• Challenging to distribute material into heterogeneous subsurface. Multiple injections typically needed.• Technologies piloted at the site with varying success.
Extraction, Removal, Treatment andDisposal Technologies Air Sparging Air injected into saturated zone at high pressure; strips solvents, which are extracted. In Situ Thermal Uses electrodes or heaters attached to power supplies to heat subsurface and volatilize VOCs; vapor collection. Multiphase Extraction Uses a high vacuum system to extract soil vapor and groundwater simultaneously.
Barriers ContinuousPermeable Reactive Barriers Wall• Intercepts and treats contaminants as groundwater flows through reactive barrier• Common reactive media ZVI;• Construction – Depths generally less than 100 feet Funnel and• Lifespan (15 to 25 years) Gate System (need to add photo)• Issues – fouling/movement around wall
Monitored Natural Attenuation – Relies on natural processes to cleanup pollution in soil and groundwater. – Conditions monitored to ensure that contaminants are degrading and not migrating. – Criteria to demonstrate MNA: • Plume stability • Review of temporal trends in well • Geochemical and biological parameters indicate conditions supporting degradation – Component of alternative
Technologies Retained1. Groundwater Extraction and Treatment2. In Situ Redox Technologies (including Enhanced reductive dechlorination, In Situ Chemical Oxidation and Zero Valent Iron Injections) to treat high conc. areas3. Permeable Reactive Barriers (PRB)4. Monitored Natural Attenuation (as component of an alternative)
EPA Working Alternatives – Shallow A AquiferAlt. 1 (No Action)Alt. 2A (P&T/Slurry Wall) -Existing RemedyAlt. 2B (P&T/Slurry Wall) - Existing Remedy Optimized for mass removalAlt. 3 (P&T/Slurry Wall) - Existing Remedy Optimized for mass removal, MonitoredNatural Attenuation (MNA) (when demonstrated)Alt. 4Facility Specific Source Areas – In Situ Redox (see criteria)*Regional PlumeIn Situ Redox – High Conc. Areas (>1,000 ppb)P&T and MNA (when Demonstrated)Alt. 5AFacility Specific Source Areas – In Situ Redox (see criteria)*Regional PlumeIn Situ Redox – High Conc. Areas (>1,000 ppb)Permeable Reactive Barriers (PRBs)1, P&T and MNA (when Demonstrated)Alt. 5B – Will be evaluating P&T Barrier Wells in lieu of PRBs
Conceptual LayoutIn Situ Redox in A Aquifer DRAFT FOR DISCUSSION ONLY Alternative 4: In Situ Redox (Facility Specific Source Areas) In Situ Redox (High Concentration Areas) P&T (Medium and Low Concentration Areas)*• In Situ Redox in high MNA (when demonstrated) In Situ Redox Treatment Area concentrations areas (gridded or transect injections) >1,000 ppb (facility and regional plume)• Groundwater pump and treat for remaining areas of plume until MNA demonstrated
Conceptual Layout DRAFT FOR DISCUSSION ONLYwith PRBs in A Aquifer Alternative 5A: In Situ Redox (Facility Specific Source Areas) PRBs (Range of Concentrations) P&T (Low Concentration Areas)* MNA (when demonstrated) In Situ Redox • PRBs downgradient of Treatment Area (gridded or transect injections) high concentration areas PRB to treat residual contamination• Modeling to determine number of PRBs• Type of PRBs to be determined
EPA Working Alternatives – Deeper AquifersAlt. 1 (No Action)Alt. 2A (P&T/Slurry Wall) -Existing RemedyAlt. 2B (P&T/Slurry Wall) - Optimized for mass removalAlt. 3 (P&T/Slurry Wall) - MNA (when demonstrated)Alt. 4Facility Specific Source Areas – In Situ Redox (see criteria)*Regional Plume - P&T and MNA (when Demonstrated)Alt. 5AFacility Specific Source Areas – In Situ Redox (see criteria)*Regional Plume -PRBs, P&T and MNA (when Demonstrated)Alt. 5BFacility Specific Source Areas – In Situ Redox (see criteria)*Regional Plume -P&T Barrier Wells and MNA (when Demonstrated)
Groundwater Feasibility Study Summary• Focusing on high concentrations and source areas; moving to more passive remedy.• Evaluating reasonable timeframes to complete cleanup.• Scale of cleanup challenging.• Difficult to implement in situ technologies in developed areas.• Geology & matrix diffusion effects limit ability to accelerate cleanup.• Potential recontamination of areas treated within different portions of the plume.
EPA Site-wide Groundwater FeasibilityStudy - Tentative Schedule• TBD – Agenda topics for next CAB Meeting • Summer 2011 – Draft Feasibility Study Report for review• Fall 2011 – Remedy Review Board• Winter 2012 – Final Feasibility Study Report, Proposed Plan for public review• Spring 2012 – Public Meeting and Public Comment Period• Fall 2012 – Groundwater ROD Amendment**Community involvement activities throughout the process Updates and Meetings with Moffett Field RAB, MEW Community Advisory Board, City, Property Owners, Developers, Community Members