Air Sampling for Vapor IntrusionUpdate

Former Naval Air Station Moffett Field

August 9, 2012

Site Background

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• Moffett Field is part of the Middlefield-Ellis-Whitman

(MEW) Superfund Study Area which has VOCs in

groundwater, primarily trichloroethene (TCE)

• EPA amended the ROD in August 2010 to include a remedy

for the vapor intrusion pathway, which included

designating areas of responsibility (AOR) to the Navy, NASA

and MEW companies

Site Background

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Navy (yellow), NASA (blue) and MEW Areas of Responsibility (green)

Vapor Intrusion

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Indoor exposure to VOCs can result from one or more of the followingpotential sources:

• Volatilization of VOCs from subsurface shallow soil andcontaminated groundwater into soil gas, and migration into a buildingstructure as vapor intrusion, including volatilization from directgroundwater contact with building foundation or subsurface structure;

• Occupational, household, orconsumer product use orstorage inside the building(indoor source);

• Contribution of VOCs inoutdoor air from outdoorsources, such as nearbyindustrial emissions (e.g.,drycleaners, vehicle emissions),and volatilization from thesubsurface to outdoor air nearthe building.

Indoor Air Cleanup Levels

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Chemical of Concern

Indoor Air Cleanup Level (μg/m3)

Residential Commercial

Trichloroethene (TCE) 1 5

Perchloroethylene (PCE) 0.4 2

cis-1,2-Dichloroethene 60 210

trans-1,2-Dichloroethene 60 210

Vinyl Chloride 0.2 2

1,1-Dichloroethane 2 6

1,1-Dichloroethene 210 700

ROD Amendment for the Vapor Intrusion Pathway (EPA, 2010)

Pre-sampling Building Surveys

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• Visually inspected all buildings within the Navy area that

are occupied or may be occupied – Nov 2011 and Apr

2012

• Interviewed each building manager about building use,

site operations, work hours for occupants, air quality

observations, and issues to be considered when

planning the air sampling (for example, security of

research areas, computer servers requiring cooling)

• Obtained information on HVAC operations, and

chemicals and solvents used or stored in the buildings

Indoor Air Sampling Program

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23 Buildings designated for sampling within Navy’s AOR

Air Sampling Scope

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• Sampling conducted between May 18 to June 12, 2012

• Sampled indoor air in 23 Buildings using 6-liter air canisters

• 258 samples from buildings including duplicates

• Sample periods varied based on the time workers were in thebuildings – 8 hours, 10 hours or 24 hours

• Sampled various levels (e.g., basements and multiple floors)

• Samples were analyzedby EPA Method TO-15SIM for the COCs

Air Sampling Scope

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• Buildings with HVAC systems were sampled with the HVAC systemson and off

• HVAC off samples were collected over Memorial Day weekend

• Buildings without HVACs were sampled with windows and doors shutwhen possible

• Sampled work areasand pathways (crawlspaces, utility conduits,elevator shafts,stairwells)

• Collected 29 ambientair(outdoor/background)samples

Response Action Tiering System

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Response Action Tiering System

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Results for Air Sampling

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• Majority of buildings had detected VOCs above outdoorair levels but below action levels.

• Only Buildings 10 and 126 had multiple samples thathad VOCs above action levels

• Buildings 3, 12, N210, and N239A (pathway locations)had samples from a single location that had a VOCexceeding action levels. None of the samples collectedfrom the work areas in these buildings exceed the actionlevels.

Current Status

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• Building N210 – HVAC system operation has beenmodified as an interim measure; indoor air is below theROD action levels with the measure in place

• Building 10 - a blower system has been installed in theutility corridor as an interim measure to preventmigration of vapors from the corridor into Building 10

• Building 126 – a groundwater investigation is planned inFall 2012 to address the VOC source near Building 126(Site 28)

• Building 239A – additional air samples will be collectedto determine the source and pathway of the detectedTCE vapors; this may be due to routine activities in oneof the adjacent utility rooms. Fall/Winter 2012tentatively

Future Activities

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• Air sampling report will include ranking the buildings tothe Response Action Tiering System (2010 EPA VI RODAmendment) and include recommendations for follow-on actions. Submit draft report in Fall 2012.

• Develop Remedial Design/Remedial Action Work Plansto implement future tiering requirements.

Air Sampling for Vapor Intrusion

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QUESTIONS ?

Building 10 Update

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Building 10 Update

• Chlorinated solvent vapors havebeen detected in Building 10above the action levels in theVapor Intrusion ROD Amendment

• The solvent vapors result fromintrusion of vapors emanatingfrom solvents that are dissolvedin the shallow groundwater

• The primary vapor intrusionpathway is through the utilitycorridor that goes from Building10 to Hangar 1

Vault

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Conceptual Site Model

• The dissolved solvents in the groundwater volatilize into the soilgas and migrate into the corridor though joints and cracks in thecorridor structure

• The vapors migrate into Building 10 at corridor connection

• Vapor intrusion is believedto occur primarily throughthe corridor

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Building 10 Update

• In May 2012, a temporary vapor control system was installed

• Placed a blower in the corridor entrance with the intakeapproximately 10 feet in the corridor, and placed a fan in thebuilding entrance

• Collected air samples

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Building 10 Update

• Results showed concentrations in the work areas weresignificantly lower than past results; however, the concentrationswere still above the ROD Amendment action levels for TCE (4 to 26ug/m3) and PCE (1.2 to 19 ug/m3)

• Based on sample results, adjustments to ventilate the utilitycorridor were needed

• Plans were developed to install ablower system in the corridor at avault access located approximately300 feet east of Building 10

• On July 11, a blower system and aplywood wall were installed insidethe corridor

Vault

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System Installation

• A 1/3 HP blower was installed that is capable of operating atapproximately 2,500 cubic feet per minute

• The barrier wall was sealed to prevent air flow and vapormigration from the east

• The vault was sealed to prevent ambient air from entering thecorridor

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Building 10 & Monitoring

• Indoor air in Building 10 was sampled for VOCs with air canisterson July 18 to evaluate the performance of the blower system

• The results showed that indoor air in the work areas were belowaction levels (TCE 0.89 to 1.1 ug/m3; PCE 0.098 to 0.21 ug/m3).The air quality at approximately 30 feet downwind of the exhaustwas also below action levels (TCE 1.2 ug/m3; PCE 0.63 ug/m3).

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Future Monitoring & Follow-up

• The results show the blower system successfully reduced indoorair concentrations to below action levels in the work areas

• Work area air quality will be checked monthly using fieldmeasurement instruments

• Work area air quality will monitored quarterly with air canisters

• The blower system will remain in place as an interim measure untillong-term plans are implemented

• An evaluation will be conducted for potential additional measuresof the utility corridor

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Building 10 Update

QUESTIONS ?

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