The l30 foot lateral distances is woefully inadequate. In addition to the “precluding” factors, the lateral distance ignores the fact that many old tanks were removed without removing all of the contaminated soil and often leaving piping and other structures in place This process is more about preserving state UST funds than protecting human health -IMHO
Lawrence Schnapf
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From: Brownfields [mailto:brownfields-bounces@lists.cpeo.org] On Behalf Of Lenny Siegel
Sent: Sunday, November 09, 2014 5:06 PM
To: Brownfields Internet Forum
Subject: [CPEO-BIF] Keep It Simple: A Critique of the ITRC and EPA Guidances on Petroleum Vapor Intrusion
Keep It Simple: A Critique of the ITRC and EPA Guidances on Petroleum Vapor Intrusion
The new Interstate Technology & Regulatory Council (ITRC) guidance document on Petroleum Vapor Intrusion, though based on sound science, is unlikely to inspire public confidence because the process is backwards and there is no holistic strategy for protecting public health.
I originally drafted this essay about ITRC's document only, but I then went back to read EPA's April, 2013 External Review Draft Petroleum Vapor Intrusion Guidance, and I found that it took a similar approach. In retrospect, perhaps I should have reviewed the EPA document when it was circulated. Instead, I focused on the main EPA Vapor Intrusion Guidance, focused on chlorinated volatile organic compounds, because most of the sites where I have been engaged involve chlorinated compounds.
Due to subsurface biodegradation, the intrusion of petroleum hydrocarbon (PHC) vapors from the subsurface into homes and other buildings is unusual, particularly when compared to vapor intrusion of chlorinated solvents. When it occurs, PHC vapor intrusion may be swamped by background sources such as gasoline or auto exhaust. Nevertheless, I believe that PHC vapor intrusion investigations should be begin with the assessment of exposures.
The ITRC document calls for a complicated screening process, through which the risk of PHC vapor intrusion may be dismissed by determining the lateral and/or vertical distance from the source of PHCs to the building. Unless a known source is within 30 feet laterally and 5 to 18 feet (depending on the nature of the source) vertically of the structure, there is no need for further investigation, unless confounding or “precluding factors” are in play. Precluding factors include preferential pathways, karst geology, and ongoing releases, among others.
That is, investigators are expected to reach conclusions about whether toxic vapors are intruding into indoor air without measuring those substances in the indoor air. To do so they must rule out the precluding factors, and they must accurately determine the lateral and vertical distances. This is fraught with challenges when the source is stable, and without thorough investigation over time there is no way to know that the source is indeed stable.
There is a better approach, supported by the latest science.
It would be much more direct to begin by evaluating the indoor air of any building within a much larger radius of known contamination. If sampling at appropriate times finds that concentrations are below health-based risk levels, then the current risk of vapor intrusion may be ruled out. (It may still be useful, however, to use soil gas measurements to evaluate whether vapor intrusion is likely to occur whenever a vertical pathway to the building is opened up.)
However, the presence of PHC vapors does not prove that vapor intrusion is occurring. These same substances are commonly found inside buildings or in the outdoor air at levels approaching or exceeding typical vapor intrusion concentrations. Therefore, any one of a number of strategies should be pursued to determine if the contaminants in the indoor air are indeed coming from below. Many of these are described in the ITRC and EPA documents.
• Before sampling indoor air, household chemicals should be inventoried and those containing volatile substances, such as gasoline, paint thinner, and rubber cement should be removed.
• Ambient (nearby outdoor) air samples should always be taken at the same time as indoor air readings. This allows investigators to determine if indoor air contamination is coming from the outdoor air. Normal exhaust from nearby motor vehicles actually may include petroleum hydrocarbons at concentrations that exceed the health-based screening levels.
• Using the multiple lines of evidence approach, shallow soil gas samples may be taken, at the same time as indoor air samples, under each structure. If volatile compounds are not found in the subsurface soil gas, then it is unlikely that vapor intrusion is the source of indoor air contamination.
• Real-time or near-real-time sampling devices, such as handheld GC/MS (gas chromatography/mass spectrometry) devices and EPA’s Trace Atmospheric Gas Analyzer, which extends a sampling tube from a van, can be used to find pathways from the subsurface (such as cracks and holes in foundations) and background sources within structures, thus making it possible to determine where contamination originates. As smaller, less expensive equipment becomes available, this approach should be applied more widely, but it’s important to use devices capable of detecting contaminants of concern at or below the screening levels.
• By taking measurements when a building is pressurized and then de-pressurized, it is possible to determine whether contaminants are coming from below. Substances detected during pressurization are unlikely to have come from the subsurface. Depressurization overcomes the challenge of temporal variability by creating worst case situations.
• By measuring the ratio of elemental isotopes in contaminant vapor, investigators may be able to distinguish between indoor sources, which typically consist of the manufactured product, and the remainder of past releases to the subsurface, which have different ratios due to biodegradation. While most people understand little about stable isotope analysis, the samples are relatively easy to collect.
Using one or more of these approaches, investigators should be able to determine if petroleum hydrocarbon vapor intrusion is occurring. In cases, the cost of measuring and determining the source of contamination will be lower than the complex screening approach recommended by ITRC and EPA. In any case, where a spill has occurred nearby, the expenditure is justified.
The central advantage of the approach that I recommend is that building occupants can learn whether the air they breathe is safe. If vapor intrusion is the source of indoor air contamination, then standard mitigation techniques can lower contamination to acceptable levels. If the source is indoors, building occupants have the opportunity to protect themselves by removing the source. If it’s outdoors, then the agencies responsible for regulating outdoor air pollution should be brought into the picture.
Furthermore, if the indoor air is analyzed for the full suite of potential contaminants, investigators may find other substances, such as chlorinated volatile organic compounds, that may pose a threat to building occupants. That’s what happened at the Manhattan Center for Science and Mathematics, where elevated levels of tetrachloroethylene were found inside the school as a result of an investigation initially focused on petroleum hydrocarbons.
Finally, if the public learns that petroleum fuels or their byproducts are causing exposures to unsafe levels of petroleum hydrocarbon vapors, then they can make personal decisions or support policies designed to reduce the use of gasoline- and diesel-powered vehicles.
If the goal of site investigation is to protect public health, then agencies should require or conduct indoor air testing as the default approach to investigating potential petroleum hydrocarbon vapor intrusion. A strategy that ignores human health risk as someone else’s problem is unlikely to win public confidence.
Executive Director, Center for Public Environmental Oversight
a project of the Pacific Studies Center
Voice: 650-961-8918 or 650-969-1545