EPA Vapor Intrusion andTCE Potential Source Investigation

Update

Former NAS Moffett FieldRestoration Advisory Board Meeting

August 7, 2014

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Overview

MEW/Moffett FieldVapor IntrusionStudy area (asknown in 2013)

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Vapor Intrusion Pathway

What is TCE andwhy is it a concern?

• TCE or trichloroethene is a solvent used that waswidely used in past for degreasing and cleaning.

• TCE can readily evaporate into air and has potentialto migrate from shallow contaminated groundwaterupwards into overlying buildings through the vaporintrusion pathway.

• If TCE is in indoor air at high enough levels for a longenough duration, it may pose a potential healthconcern.

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MEW/Moffett FieldVapor Intrusion Study Area

• Generally defined by the area where TCEconcentrations in shallow groundwater aregreater than 5 micrograms per liter (mg/L), orparts per billion (ppb).

• In 2010, EPA selected a vapor intrusion remedyfor the MEW Site, which applies to all existingand future residential and commercial buildings,within the MEW Vapor Intrusion Study Area.

• EPA has set TCE indoor air cleanup levels thatare protective of both short-term and long-termhealth concerns.

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Slurry Wall

Ongoing Investigation (2013-2014) to delineatethe 5 ppb TCE plume boundary

Vapor Intrusion Study Area (>5 pbb TCE plume)

Residential Indoor Air Sampling Area

Classics homes built with vapor intrusion controlsystem

Wescoat Village Residential Area (2006 homesbuilt with vapor intrusion control system)

TCE Hot Spot Area andResidential Air Sampling Area

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Legend:

TCE Hot Spot

Indoor Air Sampling Results

• EPA sampled over 90 residences in expandedresidential areas, and over 140 residences

• No TCE was detected in most residences sampled.

• TCE was detected in some residences, but belowindoor air cleanup levels. These homes were re-sampled to confirm TCE below indoor air cleanuplevels.

• TCE was found in only two residences exceedingEPA’s TCE indoor air cleanup level of 1 microgramper cubic meter.

• Vapor intrusion control systems were installed tomitigate TCE indoor air concentrations to belowindoor air cleanup levels.

Groundwater Sampling (2005-2013)

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Sampling Summary and 2014Investigation Activities

• Results from all indoor air sampling to date showedvapor intrusion not a problem in most residencessampled.

• Based on groundwater and air sampling to date,areas that overlie lower TCE groundwaterconcentrations are considered as low vapor intrusionrisk.

• EPA conducting potential source investigation of TCEHot Spot Areas and conducted additionalgroundwater investigation to fill data gaps on FairchildDrive.

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2014 Residential Study Area

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Legend:

TCE Hot Spot

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EPA 2014 Grab Groundwater SampleLocations

TCE Shallow Groundwater ResultsResidential Areas (2005 - 2014)

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TCE Shallow Groundwater ResultsSeptember 2013/May 2014

Sewer Flow Direction Map

Storm Drainage Flow

EPA Mobile Lab and TAGA -Trace Atmospheric Gas Analyzer

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EPA Contact Information

Alana Lee

EPA Project Manager - Vapor Intrusion &TCE Potential Source Investigation

415.972.3141

Lee.Alana@epa.gov

Jackie Lane

Community Involvement Coordinator

415.972.3236

Lane.Jackie@epa.gov

EPA Websites –For More Informationwww.epa.gov/region9/mewwww.epa.gov/region9/moffettfieldwww.epa.gov/oswer/vaporintrusion

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