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

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

Vapor Intrusion Guidance Document 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 Guidance is Presented as a Series of Steps

Plume Characterization Hierarchy of Sampling for the Evaluation of Vapor Intrusion 1.Soil Gas 2.Groundwater 3.Soil Matrix (Method 5035) 4.Flux Chambers

Screening Sites with Groundwater Groundwater monitoring wells must be screened properly

Flux Chambers Taken From LUSTLine Bulletin 44

Flux Chambers

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)?

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

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 (

OEHHA generated soil screening levels in 2005 for seventeen volatile chemicals pursuant to SB 32 Chemical Protective Soil Gas Concentration (Residential) Benzene0.04 ug/L Trichloroethylene (TCE)0.5 ug/L Tetrachloroethylene (PCE)0.2 ug/L Vinyl Chloride0.01 ug/L EXAMPLE OF SOIL GAS CHHSLs California Human Health Screening Levels (CHHSLs)

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

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

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]

Indoor Air Sampling Results (minimum of 2 sampling events needed) ResponseActivities Risk: <10 -6 HQ: <1.0 Minimal Determine that the soil gas plume is stable Risk: HQ: 1.0 – 3.0 Monitoring Install and sample subslab and/or vadose zone monitoring probes Risk: >10 -4 HQ: >3.0 Mitigation Institute engineering controls and continue indoor air sampling Vapor Intrusion Guidance Document Step 10: Evaluation of Indoor Air Data

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

Land Use Covenants (LUCs) Title 22 CCR Section –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

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)

CASE STUDY Chemical Distribution Center in Los Angeles

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

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

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

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

Nearest Residential Structure

MedianConservative Total Porosity Water-Filled Porosity Permeability (cm 2 )5.8 x x MedianConservative Attenuation Factor (Modeling) PCE Cancer Risk1 x x Predicted PCE Indoors (ug/L) FATE AND TRANSPORT MODELING 13 Laboratory Geotechnical Measurements: feet below grade PCE Risk for nearest residence (PCE soil gas = 48 ug/L)

ug/L Residential CHHSL (PCE)0.2 Site-Specific Screening Value (PCE)0.8 – 5.0 PROTECTIVE SOIL GAS CONCENTATIONS PCE soil gas concentration at nearest residence = 48 ug/L

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

Indoor and Outdoor Sampling Results (2004) OEHHA Value for PCE in Indoor Air = ug/L (risk = )

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

Response Action DTSC Vapor Intrusion Guidance Document Indoor Air Sampling Results (minimum of 2 sampling events needed) ResponseActivities Risk: <10 -6 HQ: <1.0 Minimal Determine that the soil gas plume is stable Risk: HQ: 1.0 – 3.0 Monitoring Install and sample subslab and/or vadose zone monitoring probes Risk: >10 -4 HQ: >3.0 Mitigation Institute engineering controls and continue indoor air sampling

SOIL VAPOR EXTRACTION WELLS

Vapor Extraction Carbon Canisters

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

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

Indoor Air Sampling 11/05

Outdoor Air Sampling 11/05

Indoor and Outdoor Sampling Results (2005) OEHHA Value for PCE in Indoor Air = ug/L (risk = )