dtsc vapor intrusion guidance california industrial hygiene council 16 th annual conference
DESCRIPTION
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. Stack Effects (heating and air conditioning). - PowerPoint PPT PresentationTRANSCRIPT
DTSC VAPOR INTRUSION GUIDANCE
California Industrial Hygiene Council16th Annual Conference
Dan GallagherDepartment of Toxic Substances Control
California Environmental Protection Agency
December 5, 2006
Vapor Intrusion – Conceptual Model
VOC SOURCE
Diffusion
DiffusionAnd
Advection
Stack Effects(heating and air
conditioning)
cracks
Barometric PressureWind
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 (www.calepa.ca.gov)
OEHHA generated soil screening levels in 2005 for seventeen volatile chemicals pursuant to SB 32
ChemicalProtective Soil Gas
Concentration (Residential)
Benzene 0.04 ug/L
Trichloroethylene (TCE) 0.5 ug/L
Tetrachloroethylene (PCE) 0.2 ug/L
Vinyl Chloride 0.01 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)Response Activities
Risk: <10-6
HQ: <1.0Minimal
Determine that the soil gas plume is
stable
Risk: 10-4 - 10-6
HQ: 1.0 – 3.0Monitoring
Install and sample subslab and/or
vadose zone monitoring probes
Risk: >10-4
HQ: >3.0Mitigation
Institute engineering controls and
continue indoor air sampling
Vapor Intrusion Guidance DocumentStep 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 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
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
ionconcentrat gas soil
ionconcentrat air indoor )( factor nattenuatio
Definition of Attenuation Factor
For reference, the OEHHA attenuation factor for existing residential structures is 0.002
(CHHSLs)
Chemical Distribution Center
100 FEET
UNDERGROUNDSTORAGE
TANKS
HAZARDOUS WASTE STORAGE AREAABOVEGROUND 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
Median Conservative
Total Porosity 0.44 0.50
Water-Filled Porosity 0.30 0.19
Permeability (cm2) 5.8 x 10-9 1.9 x 10-8
Median Conservative
Attenuation Factor (Modeling) 0.00008 0.0005
PCE Cancer Risk 1 x 10-5 7 x 10-5
Predicted PCE Indoors (ug/L) 0.004 0.024
FATE AND TRANSPORT MODELING
13 Laboratory Geotechnical Measurements: 5 - 8 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 = 0.0004 ug/L(risk = 10-6)
0.0001
0.001
0.01
0.1
PC
E C
on
ce
ntr
ati
on
(u
g/L
)
OUTDOOR INDOOR
3 Samples 8 Homesand 2 Apts
Homes Subject to Vapor Intrusion
Indoor air in homes that tested positive for 1,1-DCE
Not Tested
Response ActionDTSC Vapor Intrusion Guidance Document
Indoor Air Sampling Results (minimum of 2
sampling events needed)Response Activities
Risk: <10-6
HQ: <1.0Minimal
Determine that the soil gas plume is
stable
Risk: 10-4 - 10-6
HQ: 1.0 – 3.0Monitoring
Install and sample subslab and/or
vadose zone monitoring probes
Risk: >10-4
HQ: >3.0Mitigation
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
CLAYCLAY
SILTY SAND
SAND
SILTY CLAY
WAREHOUSE
GROUNDWATER
OFF-SITE VAPOR MONITORING WELLSVapor Extraction Started in May 2005
Offsite Concentration Response in the Silty Clay
0.01
0.1
1
10
100
3/1/2005 5/1/2005 7/1/2005 9/1/2005 11/1/2005
TIME
PC
E C
on
ce
ntr
ati
on
(u
g/L
)
Indoor Air Sampling 11/05
Outdoor Air Sampling 11/05
Indoor and Outdoor Sampling Results (2005)
OEHHA Value for PCE in
Indoor Air = 0.0004 ug/L
(risk = 10-6)
0.0001
0.001
0.01
0.1
PC
E C
on
cen
trat
ion
(u
g/L
)
OUTDOOR INDOOR
7 Samples 8 Homesand 3 Apts