Middlefield-Ellis-Whisman (MEW) Superfund Study Area

EPA Update Groundwater Feasibility Study

Presentation for Community Advisory Board

March 31, 2011

Penny Reddy, EPA Region 9

2

MEW / NAS Moffett Field Site – Shallow TCE Groundwater Plume

Fairchild

Intel

Raytheon

NEC/Renasas

SMI

Vishay/ SUMCO

NASA

Navy

Estimated Extent of Regional TCE Shallow Groundwater Plume

Purpose of Site-wide Groundwater Feasibility 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 Groundwater Cleanup

• 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

B1/A2 Aquifer B2 Aquifer

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 Excavation

Barriers – 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 and Disposal Technologies

Air SpargingAir injected into saturated zone at high pressure; strips solvents, which are extracted.

In Situ ThermalUses 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

Permeable Reactive Barriers• Intercepts and treats

contaminants as groundwater flows through reactive barrier

• Common reactive media ZVI;

• Construction – Depths generally less than 100 feet

• Lifespan (15 to 25 years)

• Issues – fouling/movement around wall

Continuous Wall

Funnel and Gate System (need to add photo)

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 Retained

1. 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. areas

3. Permeable Reactive Barriers (PRB)4. Monitored Natural Attenuation (as component of an

alternative)

Projected VOC Plume – A Aquifer (0 to 45 feet bgs)

1992 2009 2019

EPA Working Alternatives – Shallow A AquiferAlt. 1 (No Action)

Alt. 2A (P&T/Slurry Wall) -Existing Remedy

Alt. 2B (P&T/Slurry Wall) - Existing Remedy Optimized for mass removal

Alt. 3 (P&T/Slurry Wall) - Existing Remedy Optimized for mass removal, Monitored Natural Attenuation (MNA) (when demonstrated)Alt. 4 Facility 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. 5A Facility 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 Layout In Situ Redox in A Aquifer

• In Situ Redox in high concentrations areas >1,000 ppb (facility and regional plume)

• Groundwater pump and treat for remaining areas of plume until MNA demonstrated

In Situ RedoxTreatment Area (gridded or transect injections)

Alternative 4:In Situ Redox (Facility Specific Source Areas)In Situ Redox (High Concentration Areas)P&T (Medium and Low Concentration Areas)*MNA (when demonstrated)

DRAFT FOR DISCUSSION ONLY

Conceptual Layout with PRBs in A Aquifer

• PRBs downgradient of high concentration areas to treat residual contamination

• Modeling to determine number of PRBs

• Type of PRBs to be determined

In Situ Redox Treatment Area (gridded or transect injections)

PRB

Alternative 5A:In Situ Redox (Facility Specific Source Areas)PRBs (Range of Concentrations)P&T (Low Concentration Areas)*MNA (when demonstrated)

DRAFT FOR DISCUSSION ONLY

EPA Working Alternatives – Deeper Aquifers

Alt. 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. 4 Facility Specific Source Areas – In Situ Redox (see criteria)*

Regional Plume - P&T and MNA (when Demonstrated)Alt. 5A Facility Specific Source Areas – In Situ Redox (see criteria)*

Regional Plume -PRBs, P&T and MNA (when Demonstrated)

Alt. 5B Facility Specific Source Areas – In Situ Redox (see criteria)*

Regional Plume -P&T Barrier Wells and MNA (when Demonstrated)

Projected VOC Plume – B2/A1 Aquifer (50 to 75 feet bgs)

1992 2009 2019

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 Feasibility Study - 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

Discussion/Questions

Contact Information

For More Information

www.epa.gov/region9/mewwww.epa.gov/region9/moffettfield

Penny ReddyGroundwater Project ManagerEPA Region 9 Superfund Division415.972.3108Reddy.Penny@epa.gov