The document summarizes indoor air sampling results for vapor intrusion at buildings on the former Naval Air Station Moffett Field Superfund site. Air samples were collected from 23 buildings and found VOCs exceeding indoor air cleanup levels in Buildings 10 and 126. Building 10 was found to have vapor intrusion occurring through a utility corridor connected to a contaminated groundwater plume. An interim vapor mitigation system was installed in the corridor involving sealing and installing a blower. Post-mitigation sampling found indoor air VOC levels in Building 10 reduced below cleanup levels. Continued monitoring is planned while long-term solutions are developed.

1. Air Sampling for Vapor Intrusion
Update
Former Naval Air Station Moffett Field
August 9, 2012

2. Site Background
• 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
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3. Site Background
Navy (yellow), NASA (blue) and MEW Areas of Responsibility (green)
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4. Vapor Intrusion
Indoor exposure to VOCs can result from one or more of the following
potential sources:
• Volatilization of VOCs from subsurface shallow soil and
contaminated groundwater into soil gas, and migration into a building
structure as vapor intrusion, including volatilization from direct
groundwater contact with building foundation or subsurface structure;
• Occupational, household, or
consumer product use or
storage inside the building
(indoor source);
• Contribution of VOCs in
outdoor air from outdoor
sources, such as nearby
industrial emissions (e.g.,
drycleaners, vehicle emissions),
and volatilization from the
subsurface to outdoor air near
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the building.

5. Indoor Air Cleanup Levels
Indoor Air Cleanup Level (μg/m3)
Chemical of Concern
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)
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6. Pre-sampling Building Surveys
• 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
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7. Indoor Air Sampling Program
23 Buildings designated for sampling within Navy’s AOR
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8. Air Sampling Scope
• 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 the
buildings – 8 hours, 10 hours or 24 hours
• Sampled various levels (e.g., basements and multiple floors)
• Samples were analyzed
by EPA Method TO-15
SIM for the COCs
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9. Air Sampling Scope
• Buildings with HVAC systems were sampled with the HVAC systems
on and off
• HVAC off samples were collected over Memorial Day weekend
• Buildings without HVACs were sampled with windows and doors shut
when possible
• Sampled work areas
and pathways (crawl
spaces, utility conduits,
elevator shafts,
stairwells)
• Collected 29 ambient
air
(outdoor/background)
samples
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10. Response Action Tiering System
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11. Response Action Tiering System
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12. Results for Air Sampling
• Majority of buildings had detected VOCs above outdoor
air levels but below action levels.
• Only Buildings 10 and 126 had multiple samples that
had VOCs above action levels
• Buildings 3, 12, N210, and N239A (pathway locations)
had samples from a single location that had a VOC
exceeding action levels. None of the samples collected
from the work areas in these buildings exceed the action
levels.
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13. Current Status
• Building N210 – HVAC system operation has been
modified as an interim measure; indoor air is below the
ROD action levels with the measure in place
• Building 10 - a blower system has been installed in the
utility corridor as an interim measure to prevent
migration of vapors from the corridor into Building 10
• Building 126 – a groundwater investigation is planned in
Fall 2012 to address the VOC source near Building 126
(Site 28)
• Building 239A – additional air samples will be collected
to determine the source and pathway of the detected
TCE vapors; this may be due to routine activities in one
of the adjacent utility rooms. Fall/Winter 2012
tentatively
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14. Future Activities
• Air sampling report will include ranking the buildings to
the Response Action Tiering System (2010 EPA VI ROD
Amendment) and include recommendations for follow-
on actions. Submit draft report in Fall 2012.
• Develop Remedial Design/Remedial Action Work Plans
to implement future tiering requirements.
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15. Air Sampling for Vapor Intrusion
QUESTIONS ?
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16. Building 10 Update

17. Building 10 Update
• Chlorinated solvent vapors have
been detected in Building 10
above the action levels in the
Vapor Intrusion ROD Amendment
• The solvent vapors result from
intrusion of vapors emanating
from solvents that are dissolved Vault
in the shallow groundwater
• The primary vapor intrusion
pathway is through the utility
corridor that goes from Building
10 to Hangar 1
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18. Conceptual Site Model
• The dissolved solvents in the groundwater volatilize into the soil
gas and migrate into the corridor though joints and cracks in the
corridor structure
• The vapors migrate into Building 10 at corridor connection
• Vapor intrusion is believed
to occur primarily through
the corridor
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19. Building 10 Update
• In May 2012, a temporary vapor control system was installed
• Placed a blower in the corridor entrance with the intake
approximately 10 feet in the corridor, and placed a fan in the
building entrance
• Collected air samples
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20. Building 10 Update
• Results showed concentrations in the work areas were
significantly lower than past results; however, the concentrations
were still above the ROD Amendment action levels for TCE (4 to 26
ug/m3) and PCE (1.2 to 19 ug/m3)
• Based on sample results, adjustments to ventilate the utility
corridor were needed
• Plans were developed to install a
blower system in the corridor at a
vault access located approximately
Vault
300 feet east of Building 10
• On July 11, a blower system and a
plywood wall were installed inside
the corridor
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21. System Installation
• A 1/3 HP blower was installed that is capable of operating at
approximately 2,500 cubic feet per minute
• The barrier wall was sealed to prevent air flow and vapor
migration from the east
• The vault was sealed to prevent ambient air from entering the
corridor
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22. Building 10 & Monitoring
• Indoor air in Building 10 was sampled for VOCs with air canisters
on July 18 to evaluate the performance of the blower system
• The results showed that indoor air in the work areas were below
action 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 exhaust
was also below action levels (TCE 1.2 ug/m3; PCE 0.63 ug/m3).
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23. Future Monitoring & Follow-up
• The results show the blower system successfully reduced indoor
air concentrations to below action levels in the work areas
• Work area air quality will be checked monthly using field
measurement instruments
• Work area air quality will monitored quarterly with air canisters
• The blower system will remain in place as an interim measure until
long-term plans are implemented
• An evaluation will be conducted for potential additional measures
of the utility corridor
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24. Building 10 Update
QUESTIONS ?
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