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Moffett RAB Presentation: Vapor Intrusion Update


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The Navy's Wilson Doctor gives an update on air sampling for vapor intrusion at the August 9, 2012, meeting of the Moffett Restoration Advisory Board.

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Moffett RAB Presentation: Vapor Intrusion Update

  1. 1. Air Sampling for Vapor Intrusion Update Former Naval Air Station Moffett Field August 9, 2012
  2. 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 2
  3. 3. Site BackgroundNavy (yellow), NASA (blue) and MEW Areas of Responsibility (green) 3
  4. 4. Vapor IntrusionIndoor 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 near 4the building.
  5. 5. Indoor Air Cleanup Levels Indoor Air Cleanup Level (μg/m3) Chemical of Concern Residential Commercial Trichloroethene (TCE) 1 5Perchloroethylene (PCE) 0.4 2 cis-1,2-Dichloroethene 60 210trans-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) 5
  6. 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 6
  7. 7. Indoor Air Sampling Program23 Buildings designated for sampling within Navy’s AOR 7
  8. 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 8
  9. 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 9
  10. 10. Response Action Tiering System 10
  11. 11. Response Action Tiering System 11
  12. 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. 12
  13. 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 13
  14. 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. 14
  15. 15. Air Sampling for Vapor Intrusion QUESTIONS ? 15
  16. 16. Building 10 Update
  17. 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 17
  18. 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 18
  19. 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 19
  20. 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 20
  21. 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 21
  22. 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). 22
  23. 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 23
  24. 24. Building 10 Update QUESTIONS ? 24
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