DTSC VAPOR INTRUSION GUIDANCE California Industrial Hygiene Council 16 th Annual Conference

1. DTSC VAPOR INTRUSION GUIDANCE California Industrial Hygiene Council 16th Annual Conference Dan Gallagher Department of Toxic Substances Control California Environmental Protection Agency December 5, 2006

2. Vapor Intrusion – Conceptual Model Stack Effects (heating and air conditioning) Barometric Pressure Wind Temperature cracks Diffusion And Advection Diffusion VOC SOURCE

3. Vapor Intrusion Guidance Document Guidance is Presented as a Series of Steps Step 1: Identification of a Spill or Release • Knowledge of site history, and past and present industrial practices Step 2: Site Characterization • Site inspection (receptors and buildings) • Three dimensional definition of contamination

4. Plume Characterization Hierarchy of Sampling for the Evaluation of Vapor Intrusion • Soil Gas • Groundwater • Soil Matrix (Method 5035) • Flux Chambers

5. Screening Sites with Groundwater Groundwater monitoring wells must be screened properly

6. Flux Chambers Taken From LUSTLine Bulletin 44

7. Flux Chambers

8. Vapor Intrusion Guidance Document Step 3: Is the Site a Candidate for Vapor Intrusion? - Volatile organic compounds (VOCs) at the site (list provided in the guidance)? - Are buildings located near the VOCs (100 lateral feet)?

9. Vapor Intrusion Guidance Document Step 4: If Pathway is Complete, Evaluate Imminent Hazard • Receptor symptoms • Odors • Wet basements • Evaluate for fire and explosive conditions

10. Vapor Intrusion Guidance Document Step 5: Conduct Preliminary Screening for the Building • Senate Bill 32 required the Office of Environmental Health Hazard Assessment (OEHHA) to develop screening numbers for vapor intrusion • OEHHA screening numbers can be used to “estimate the degree of effort” for site cleanup but the numbers are risk-based • Cal-EPA published a user’s guide for the screening numbers (www.calepa.ca.gov)

11. California Human Health Screening Levels (CHHSLs) OEHHA generated soil screening levels in 2005 for seventeen volatile chemicals pursuant to SB 32 EXAMPLE OF SOIL GAS CHHSLs

12. Vapor Intrusion Guidance Document Step 6: Collect Additional Field Data • Collect air samples from crawl spaces • Collect soil gas samples directly under the building foundation (subslab) • Measure the physical properties of the soil, such as: • porosity • air permeability • moisture content • bulk density

13. Vapor Intrusion Guidance Document Step 7: Conduct a Site-Specific Modeling Evaluation for the Building • Use the Johnson and Ettinger Model (JEM) • Use site-specific geotechnical and building input parameters for modeling

14. Vapor Intrusion Guidance Document Step 8 and 9: Building Pathway Evaluation and Indoor Air Sampling • Building occupancy survey • Identify sources of indoor contamination with field analytical equipment • Sample indoor air twice over a year to evaluate human exposure using TO-14A / TO-15 [SIM]

15. Vapor Intrusion Guidance Document Step 10: Evaluation of Indoor Air Data

16. Vapor Intrusion Guidance Document Step 11: Mitigate Indoor Air Exposure • Remediate the subsurface contamination • Land use covenants to restrict property use • Engineering controls to eliminate exposure Long-term monitoring may be required

17. Land Use Covenants (LUCs) Title 22 CCR Section 67391.1 • LUC must be used when contamination exceeds residential standards • LUC is executed by DTSC and owner and should run with the land • Response action is not complete until LUC is signed and recorded at the county • Owners, operators, and proponents pay all cost associated with administration, including DTSC time

18. Land Use Covenants (LUCs) Protect Public from Unsafe Exposure • Identification of responsible party • Restrict building locations • Barriers and vent systems • Soil management plan • Monitoring and associated reporting • DTSC inspections (cost reimbursement)

19. CASE STUDY Chemical Distribution Center in Los Angeles

20. Definition of Attenuation Factor For reference, the OEHHA attenuation factor for existing residential structures is 0.002 (CHHSLs)

21. Chemical Distribution Center ABOVEGROUND STORAGE TANKS HAZARDOUS WASTE STORAGE AREA UNDERGROUND STORAGE TANKS 100 FEET

22. Shallow Soil Gas Plume 200 FEET TETRACHLOROETHYLENE (PCE) SOIL GAS CONCENTRATIONS: 5 FEET BELOW SURFACE

23. PROTECTIVE SOIL GAS CONCENTATIONS PRELIMINARY SCREENING Residential CHHSL for Tetrachloroethylene (PCE) is 0.2 ug/L PCE Soil Gas Concentration at Nearest Residence = 48 ug/L

24. Nearest Residential Structure

25. FATE AND TRANSPORT MODELING 13 Laboratory Geotechnical Measurements: 5 - 8 feet below grade PCE Risk for nearest residence (PCE soil gas = 48 ug/L)

26. PROTECTIVE SOIL GAS CONCENTATIONS PCE soil gas concentration at nearest residence = 48 ug/L

27. Homes Subject to Indoor Air Testing September 2004 Conducted by USEPA Declined

28. Indoor and Outdoor Sampling Results (2004) OEHHA Value for PCE in Indoor Air = 0.0004 ug/L (risk = 10-6)

29. Homes Subject to Vapor Intrusion Not Tested Indoor air in homes that tested positive for 1,1-DCE

30. Response Action DTSC Vapor Intrusion Guidance Document

31. SOIL VAPOR EXTRACTION WELLS

32. Vapor Extraction Carbon Canisters

33. CONCEPTUAL CROSS SECTION OBSERVATION WELLS EXTRACTION WELLS WAREHOUSE 0’ SILTY CLAY NO VACUUM RESPONSE 10’ ROI = 150 feet SILTY SAND 40’ CLAY CLAY 50’ SAND ROI = +250 feet 85’ GROUNDWATER

34. OFF-SITE VAPOR MONITORING WELLS Vapor Extraction Started in May 2005 Offsite Concentration Response in the Silty Clay

35. Indoor Air Sampling 11/05

36. Outdoor Air Sampling 11/05

37. Indoor and Outdoor Sampling Results (2005) OEHHA Value for PCE in Indoor Air = 0.0004 ug/L (risk = 10-6)