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Soil Vapor Intrusion...

Soil Vapor Intrusion. A Decade of Regulatory Requirements & Experiences. Paul W. Locke MA DEP Bureau of Waste Site Cleanup One Winter Street Boston, MA 02108 617-556-1160 Paul.Locke@state.ma.us. Late 1980s…. Hillside School, Needham Mass…. Wow…that can happen?.

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Soil Vapor Intrusion...

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  1. Soil Vapor Intrusion... A Decade of Regulatory Requirements & Experiences Paul W. Locke MA DEP Bureau of Waste Site Cleanup One Winter Street Boston, MA 02108 617-556-1160 Paul.Locke@state.ma.us

  2. Late 1980s… Hillside School, Needham Mass… Wow…that can happen?

  3. MADEP Regulatory Response: • Place concern on radar screen • Incorporate into cleanup standards • Obtain “real world” data to gauge scope/parameters of problem • Provide tools/toolbox to regulated community

  4. #1: On the Radar Screen… Training/awareness: agency staff and regulated community Regulatory requirement to notify MADEP if pathway likely or confirmed

  5. Non-Cancer Risk Based Indoor Air Conc Cancer Risk Based Indoor Air Conc 50% Odor Threshold Calc Source Conc in GW Ceiling Conc 50% Solubility #2: Incorporate into Cleanup Standards Lowest of 3 or IAQ Background, whatever is higher Air Transport Model Groundwater Lowest of 3 or GW background or PQL, whatever higher GW Standard

  6. 1993 Standards Transport Model Johnson & Ettinger GW to Soil Gas: Assumed 10% Henry’s Law Equilibrium Condition Soil Gas to Indoor Air:  = 5 x 10-4 “crude and limited application of J&E”

  7. Calculated GW Standards (1993)

  8. 1996 Evaluation • Are these Standards Really Protective? • Let’s take a Look at our Files… GW Conc Soil Gas Conc Indoor Air Conc

  9. MADEP Records Review Database Search DEP Files 6000 Potential Sites Evaluated 177 Adequate Data 59 sites BTEX 23 (39%) Chlorinated 36 (61%)

  10. Findings: Were the 1993 Standards Generally Conservative & Protective? ☺ Petroleum Sites?  Chlorinated Solvent Sites?

  11. Proposed Revisions(2004) Chemical-Specific Evaluations Conservative Pathway Scenario Conservative Site/Soil Properties

  12. Key J&E Inputs (MADEP 2004) • Groundwater • 7 feet below grade; • 1 foot below basement floor • Building Depressurization • P= 4 Pa (40 g/cm-s2); • 0.45 air exchanges/hour • Sand, total porosity • n = 0.43 • Vadose Zone Moisture Content • [w] = ????

  13. Moisture Level Below Buildings Dry Soils?

  14. Vadose Zone Soil Moisture What is a realistic, conservative value….. beneath buildings? Little study data available, but…. Fair amount of chemical analytical data from soil samples beneath buildings!

  15. 0.06 *Moisture (w/w) to Soil Moisture(v/v)

  16. Proposed Revisions to Current MADEP Groundwater Standards (Soil Vapor Pathway) Up to an order of magnitude lower for some chlorinated solvents Public Comment Period Ended December 10, 2004 Stay Tuned…..

  17. #4: Provide Tools & Toolboxes Site-Specific Evaluations Guidance Documents Rules of Thumb

  18. Site-Specific Pathway Evaluation (Mandatory when > Generic GW Standard) • Key Tools: Soil Gas Assessment Indoor Air Analysis Vertical Profiling

  19. MADEP Recommended Approach

  20. MADEP Guidelines for Soil Gas Evaluation:

  21. MADEP Guidelines for Obtaining Soil Gas Samples Infiltration displaces/ solubilizes soil gases place probe below bldg/pavement for representative samples enclosed space grass pavement building foundation foundation cracks diffusing vapors depth to vadose zone groundwater Negative bias capillary zone dissolved chemical in groundwater

  22. Real World Example of Negative Bias: TCE Soil Gas Data from 2 Homes Date Interior Exterior 9/96 397 / 281 24 / <1 12/96 16 / 80 <1 / <1 3/97 6 / 64 <1 / <1 6/97 19 / 226 <1 / <1 8/97 157 / 594 4 / <1 All data ppb v/v TCE

  23. Obtaining Indoor Air Samples Winter months usually “worst case” - Other times may not rule out pathway Stack Effects windows closed frost layer Furnace combustion Vapors

  24. Groundwater/Vertical Profiling well Infiltration fresh water lens groundwater flow VOC plume

  25. For More Information….. • BWSC.Information@state.ma.us or BWSC.Regulation@state.ma.us • Characterizing Risks Posed by Petroleum Contaminated Sites: Implementation of the MADEP VPH/EPH Approach www.mass.gov/dep/bwsc/files/02-411.pdf • Indoor Air Sampling and Evaluation Guide www.mass.gov/dep/ors/files/indair.pdf • MCP Numerical Standards: GW-2 www.mass.gov/dep/bwsc/files/standard /gw2/gw2.htm

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