Vapor Intrusion is the migration of chemical vapors from the subsurface into commercial and residential buildings. Vapors can migrate through soil and into buildings through cracks in foundations, basements, crawl spaces and sewers. In February 2020, the Department of Toxic Substances Control, the San Francisco Bay Regional Water Quality Control Board, and the State Water Resources Control Board issued in draft form Supplemental Guidance: Screening and Evaluating Vapor Intrusion which recommends a consistent approach when screening buildings for subsurface vapor risk to occupants and describes a framework for deciding when cleanup and/or mitigation is needed. The regulated community expected regulators to finalize the long-awaited Guidance, but that may be delayed now that recent studies performed by the DTSC have emerged showing that the Supplemental Vapor Intrusion Guidance may have gone too far in its estimation of risk. The delay may provide some relief to site owners due to concerns that the attenuation factors prescribed in the Guidance were too conservative and would have made it impossible to achieve closure for sites with soil vapor contamination.

1. December 15, 2020
Vapor Intrusion
Developments and
Concerns in California

2. 2
Presenters
2
Viviana Heger, Of Counsel
• Water Law
• Environmental Law
• Natural Resources Law
• Land Use Law
707 Wilshire Boulevard, 24th Floor
Los Angeles, CA 90017
213.626.2906
vheger@meyersnave.com
Jeffrey V. Dagdigian, PhD
Managing Principal Environmental Scientist
jdagdigian@waterstone-env.com
2936 East Coronado Street
Anaheim, CA 92806
714-414-1122
Mark Shifflett, Principal
Environmental Scientist
mshifflett@waterstone-env.com

3. 3
• History and legal framework
• Uncertain future of Feb. 2020
Draft Supplemental Guidance
• Recent DTSC “California” AF study
evaluating California-specific attenuation
factors
• Legal and other concerns
Vapor Intrusion Past, Present, Future

4. 4
Migration of chemical vapors
from the subsurface into buildings
About Vapor Intrusion

5. 5
• Public school in El Cajon, CA
• Closed for 2015–2016 academic year
• Amid concerns about TCE vapor intrusion
Effect of Vapor Intrusion

6. 6
Vapor-forming Chemicals include
– Any chemicals that volatize
easily, including volatile
organic compound (VOCs)
– Trichloroethylene (TCE)
and tetrachloroethylene (PCE,
perchloroethylene “perc”),
and their degradant products
(e.g., vinyl chloride)
– Gasoline (benzene, toluene, ethylbenzene,
xylenes) and fuel oxygenates
– Paint thinners and related solvents
Vapor Intrusion Chemicals

7. History and Legal Framework

8. 8
Timeline of Key Federal EPA Guidance
2002 and
2015
• Draft guidance in 2002 finalized in 2015
• Focus on chronic risk from chemicals
2012
• Superfund five-year review process requires VI
evaluation
2014
• Acute TCE exposure thresholds developed by EPA Region IX
• “Accelerated response” threshold of 2 µg/m3 for
residential properties

9. 9
• 2002: EPA began to focus
on vapor intrusion
• 2009: Criticism of inaction
• 2015: Guidance issued
and has become source
of attenuation factors used
in California’s Draft
Supplemental Guidance
• Introduces recommendation
for assessment of site and
contiguous property
EPA’s 2002 - 2015

10. 10
• Vapor intrusion must be evaluated when evaluating
remedy protectiveness during the Superfund five-year
review process (OSWER Pub. No. 9200.2-84 (Dec. 3, 2012).)
• Evaluation is required even if it was not originally
considered as part of the selected remedial alternative.
EPA’s 2012 Actions

11. 11
• EPA Region IX was the first to
act in response to a criticized
review in 2011 by EPA’s
Integrated Risk Information
System (IRIS)
• EPA Region IX in July 2014
issued a memorandum with
an acute TCE exposure
threshold of 2 µg/m3 for
residential properties
• Proper “accelerated
response” is unclear
EPA Region IX – 2014 Action

12. 12
Focuses on Outdoor, not Indoor, Air Quality
• EPA does not directly regulate
the concentration of VOCs in
indoor air, the Clean Air Act
• Occupational Safety and Health
Act (OSH Act) directs Occupational
Safety and Health Administration
(OSHA) to establish binding
regulations that protect worker health
Federal Clean Air Act
Overlap of
OSHA and EPA
authority
causes
confusion
within
regulated
community

13. 13
Clarity at First; Confusion Later
• EPA’s 2002 Draft OSWER Guidance
– OSHA generally would take the lead role
– In addressing “occupational exposures” involving indoor VI
• EPA’s 2013 OSWER Guidance
– Shifted EPA’s position
– EPA has authority to protect the public and workers' health
In nonresidential setting
Where hazardous vapors may be intruding
into occupied buildings from VI
EPA versus OSHA

14. California’s Draft
Supplemental Guidance

15. 15
California’s Draft Supplemental Guidance
February 2020
Draft for
Public Comments

16. 16
How Did We Get Here?
EPA VI
Database
EPA
Technical
Guide
Draft
Release
Public
Comments Final??
Supplemental VI Guidance

17. 17
Regulatory Implementation
• Use Empirical 0.03 AF
• No More Johnson & Ettinger Modeling
• Didn’t want CA to be less conservative than USEPA
RESULT = Triggers need for Indoor Air Sampling

18. 18
USEPA VI Database Study
USEPA VI Database Study
Ref: Ettinger, others, 2018. Empirical Analysis of Vapor
Intrusion Attenuation Factors for Sub-Slab and Soil Vapor.
Presentation.
Critique and Comments
• Collected in colder climates
(Northeast and Midwest)
• >75% Residential Bldgs. with
basements
 vs. Commercial Buildings
 Larger air volume
 Increased exchange rates
• Limited California data collected
– SF Bay Area
• No sites in Southern California

19. 19
Feb. 2020 Draft Supplemental VI Guidance
1. VI Soil Gas Attenuation Factor=0.03
2. Evaluation of Conduit Transport of Vapor Contamination
3. Four-step Process for VI Assessments
4. California VI Database
5. Petroleum-Specific Considerations
(2012 Low Threat UST Case Closure Policy)

20. 20
Chlorinated Chemicals v. Petroleum Hydrocarbons
Volatile Organic Compounds (VOCs)
Chlorinated Solvents
• Trichloroethene
(TCE)
• Tetrachloroethene
(PCE)
• 1,1-Dichloroethene
(DCE)
• Vinyl Chloride
Petroleum
Hydrocarbons
•Gasoline
•Benzene, Toluene,
Ethylbenzene,
Xylenes
• Alkyl benzene
compounds

21. 21
Comparison of Attenuation Factors

22. 22
Soil Gas Screening Levels ( in ug/m3)
Existing Bldg. Future Bldg.
AF=0.001 AF=0.0005 AF=0.03
PCE 2.0 2,000 4,000 67
TCE 3.0 3,000 6,000 100
AF=0.002 AF=0.001 AF=0.03
PCE 0.46 230 460 15
TCE 0.48 240 480 16
Residential
Chemical
Indoor Air
Screening
Level
(10
-6
risk)
DTSC 2011 VIG
Draft
SVIG
(All Bldgs.)
Commercial

23. 23
HELP IS ON THE WAY!! – WE HOPE
• Geographically more representative
• Greater number of pairs and more sites
• More diverse types of buildings
• Appropriate climatic conditions
DTSC 2020
AF Study
Definite
Improvement!

24. 24
DTSC AF Study - 2020
• DTSC Study findings presented in webinar at
2020 California Land Recycling Conference
(https://www.cclr.org/civicrm/event/info?id=310&reset=1)
 Climate
 Commercial buildings
 Fewer basements
 Different foundations
• CA is Different than EPA Database Sites

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DTSC AF Study - 2020
Different AFs for building types and sampling locations:
 Sub-slab to indoor air
 Soil gas to indoor air
 Groundwater to indoor air
 Varying depths and locations
 Background (Ambient Air) concentrations
– CARB Study (SG>Background)

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DTSC Study of AFs
Draft SVIG
Existing Future Existing Future
Subslab 0.05 -- 0.05 -- 0.03 0.005
Soil Vapor 0.002 0.001 0.001 0.0005 0.03 0.0009
Groundwater 0.002 0.001 0.001 0.0005 0.001 0.001
Land Use
DTSC
AF Study
Residential Bldg. Commercial Bldg.
DTSC 2011 VIG
Residential/
Commercial

27. 27
DTSC AF Study – Next Steps
Complete peer review
and review comments
Revise AF Study Report
as appropriate
Finalize Report
December 2020

28. Legal and Other Concerns

29. 29
• Mitigation measures
sometimes may be less costly
than remedial actions
• Access and other legal
concerns
Concerns About California’s Approach

30. 30
Collecting soil gas,
indoor air, and
other samples
from property
neighboring a site
is often difficult
Access and Notices
Use access agreements, notices and disclosures

31. 31
• Feb. 2020 DTSC Guidance is not binding
– Because it does not satisfy California’s Administrative
Procedures Act (APA)
• But VI Guidance is for a “statewide standard practice”
– To be used when screening buildings
• Agency staff may be following the guidance in draft form
– Even prior to its release
• The Guidance should proceed through formal process
for adopting a regulation
Underground Regulation

32. 32
Due Diligence
Possible
Shift
Stepwise
Multiple
lines of
evidence
Samples from different media,
including indoor air, collected
on contemporaneous basis
Indoor samples
are a final step

33. 33
Discussion
Q&A
33