DTSC VAPOR INTRUSION GUIDANCE

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

1. Soil Gas
2. Groundwater
3. Soil Matrix (Method 5035)
4. 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 users 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
Chemical Protective 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
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
Indoor Air Sampling Results (minimum of 2 sampling events needed) Response Activities
Risk lt10-6 HQ lt1.0 Minimal Determine that the soil gas plume is stable
Risk 10-4 - 10-6 HQ 1.0 3.0 Monitoring Install and sample subslab and/or vadose zone monitoring probes
Risk gt10-4 HQ gt3.0 Mitigation Institute engineering controls and continue indoor air sampling
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
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
PCE Risk for nearest residence (PCE soil gas 48
ug/L)
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
26
PROTECTIVE SOIL GAS CONCENTATIONS
PCE soil gas concentration at nearest residence
48 ug/L
ug/L
Residential CHHSL (PCE) 0.2
Site-Specific Screening Value (PCE) 0.8 5.0
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
Indoor Air Sampling Results (minimum of 2 sampling events needed) Response Activities
Risk lt10-6 HQ lt1.0 Minimal Determine that the soil gas plume is stable
Risk 10-4 - 10-6 HQ 1.0 3.0 Monitoring Install and sample subslab and/or vadose zone monitoring probes
Risk gt10-4 HQ gt3.0 Mitigation Institute engineering controls and continue indoor air sampling
31
SOIL VAPOR EXTRACTION WELLS
32
Vapor Extraction Carbon Canisters
33
CONCEPTUAL CROSS SECTION
EXTRACTION WELLS
OBSERVATION 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)