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