epa vi and source investigation rab mtg update august 7 2014rv1
DESCRIPTION
EPA presentation to the Moffett Field Restoration Advisory BoardTRANSCRIPT
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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
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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)
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TCE Hot Spot Area andResidential Air Sampling Area
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Legend:
TCE Hot Spot
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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.
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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
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TCE Shallow Groundwater ResultsResidential Areas (2005 - 2014)
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TCE Shallow Groundwater ResultsSeptember 2013/May 2014
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Sewer Flow Direction Map
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Storm Drainage Flow
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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
Jackie Lane
Community Involvement Coordinator
415.972.3236
EPA Websites –For More Informationwww.epa.gov/region9/mewwww.epa.gov/region9/moffettfieldwww.epa.gov/oswer/vaporintrusion
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