2020 CPEO Brownfields List Archive

From: Lenny Siegel <lsiegel@cpeo.org>
Date: Fri, 21 Feb 2020 08:25:06 -0800 (PST)
Reply: cpeo-brownfields
Subject: Re: [CPEO-BIF] CalEPA Draft Supplemental Vapor Intrusion Guidance - Lenny's summary and comments
 

California’s February 2020 public draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion is a step forward. It took more than two years to get it to the point of public review, for no clear reason, but it’s a relief to see it.

It summarizes the contents:

“This Supplemental Guidance incorporates information from recent technical and regulatory publications that have highlighted the variable nature of vapor behavior and lessons learned in the assessment of VI.

“This Supplemental Guidance provides information and recommendations on the following topics:

“* Using United States Environmental Protection Agency (USEPA) 2015 attenuation factors

* Establishing a four-step evaluation process to assess VI

* Considering sewers as a potential VI migration route and pathway of exposure

* Building a California-specific VI database”

After hearing rumors that consultants for responsible parties and developers had convinced California’s agencies to adopt less protective default attenuation factors (the ratio of indoor air concentrations of vapor-forming chemicals to subsurface concentrations), I was pleased to see that the draft Guidance sticks with EPA’s default factors.

 

Medium

Attenuation Factor

Crawl Space Gas
1

Subslab Soil Gas

0.03

Soil Gas

0.03

Groundwater

0.001

 

I support use of those attenuation factors, particularly at development sites where there is no indoor air to measure. The uncertainty due to the spatial and temporal variability of vapor intrusion supports the imperative of a protective approach.

It also warns against using models, such as the Johnson-Ettinger model, to develop site-specific attenuation factors for initial site screening. However, it states, “alternative approaches may be used if supported by adequate technical and site information.”

The Guidance points out the weaknesses of EPA’s database used to create the default attenuation factors, and it establishes a system for collecting California data to eventually develop California attenuation factors, using the State Water Board’s Geotracker data base, currently used to automatically share site documents with the public.

My biggest concern, one I have been expressing for 17 years, is the preference for using soil gas sampling – particularly exterior soil gas sampling – to determine whether to sample indoor air. Not only is exterior soil gas sampling a notoriously inaccurate predictor of indoor air contamination, compared to subslab soil gas, but there is a long history of investigators failing to fully delineate both soil gas and groundwater plumes.

Perhaps more important, stakeholders – the people who live, work, recreate, study, and pray at potential vapor intrusion sites – have long told me that they are uncomfortable with “all-clear” findings based on calculations instead of indoor air sampling. It’s true that background sources – both indoor and outdoor – can create false positives for vapor intrusion, but there are now many accepted methods for distinguishing subsurface sources from other sources of vapor-forming chemicals.

I am also concerned about the indeterminate risk management approach for risk levels between an excess lifetime cancer risk of one in ten thousand (10^-4) and one in a million (10^-6). Decision-makers are offered a menu of risk-management approaches, including institutional controls, additional investigation/sampling, monitoring, refining risk assessment, mitigation, remediation, and “none.” I believe that there should be a preference for action. Mitigation makes sense because the near certainty of protection against unacceptable exposure costs very little under most circumstances. Remediation is usually required because California has non-degradation laws for groundwater, which is usually the source of subsurface vapors.

The Guidance also contains what appears to be new, valuable material on investigating large buildings, planning for future buildings, parking garage sampling, and sewer lines as a pathway - all worth reading if those apply at your site.

Lenny Siegel


On Feb 20, 2020, at 8:00 PM, Lenny Siegel <LSiegel@cpeo.org> wrote:



Begin forwarded message:

From: Department of Toxic Substances Control <vaporintrusion@dtsc.ca.gov>
Subject: CalEPA Draft Supplemental Vapor Intrusion Guidance
Date: February 14, 2020 at 9:30:17 AM PST




Dear Stakeholder:

Department of Toxic Substances Control (DTSC), State Water Board, and San Francisco Bay Regional Water Quality Control Board have developed supplemental vapor intrusion guidance for conducting vapor intrusion evaluations in California. The draft Supplemental Guidance: Screening and Evaluating Vapor Intrusion (Draft Guidance) is available for review and public comment from February 14 to April 30, 2020.

Availability of Draft Guidance

Electronic Copies


 
Hard Copies
 
Hard copies of the Draft Guidance are available for review at various locations. Please see the Public Notice (English version; Spanish version) for details.
 
Public Meetings & Webinars

DTSC and State Water Board will host a series of informational public meetings and webinars state-wide to answer questions and solicit public comments/feedback in April 2020. See the Public Notice (English version; Spanish version) for details regarding the public meetings and webinars.

For questions or assistance, please contact Mr. Dan Gallagher at (916) 255-6536 or send email to VaporIntrusion@dtsc.ca.gov.



--

Lenny Siegel
Executive Director
Center for Public Environmental Oversight
A project of the Pacific Studies Center
P.O. Box 998, Mountain View, CA 94042
Voice/Fax: 650-961-8918






--

Lenny Siegel
Executive Director
Center for Public Environmental Oversight
A project of the Pacific Studies Center
P.O. Box 998, Mountain View, CA 94042
Voice/Fax: 650-961-8918





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