Contributed by Ben Lightsey P.E., Senior Engineer, PPM Consultants
Since 2011, I have been involved in vapor intrusion projects – formerly as a regulator and now as an environmental consultant. From performing soil gas surveys, sub-slab sampling, crawl-space sampling, and indoor air sampling to installing Sub-Slab Depressurization Systems (SSDS), block-wall depressurization systems, and vapor barriers, I have seen and been involved in a variety of sites with vapor intrusion issues. Since vapor intrusion is becoming a much more important health, safety, and environmental issue to most regulatory agencies, I felt that sharing some basics about vapor intrusion would be helpful. Therefore, this article will be the first in a series of four addressing vapor intrusion: what it is, what sites it applies to, what regulatory requirements exist governing vapor intrusion, and what remediation methods exist to address vapor intrusion.
The most common vapor intrusion cases are ones that involve petroleum spilled or leaked from USTs. The petroleum odor is a quick tell-tale sign of an issue – solvent-related vapor intrusion issues may be harder to identify or detect. That’s why this first article will be covering the basics of vapor intrusion at petroleum-impact sites – like gas stations.
Are you an underground storage tank (UST) owner and going through the common issue of a petroleum release? You probably are well aware of soil contamination and groundwater contamination associated with a release, but have you ever thought about vapor intrusion? If you aren’t thinking about it, then it’s important you begin to because regulatory agencies are now weighing vapor intrusion risks heavily.
Many are aware of vapor intrusion issues associated with damp climates and building structures, but I’m talking about the off-gassing of volatile compounds (think gasoline) and those compounds entering a structure, like a convenience store, through the foundation.
Vapor intrusion at a petroleum release site may be detected as part of the initial investigation, if the indicators of a possible vapor intrusion site are present. On the other side of the equation, a vapor intrusion issue may unfortunately be caught, post investigation, as an after-thought or re-evaluation of the site due to change in personnel or odor complaints. Some of the worst vapor intrusion sites were only assessed and mitigated when on-site personnel complained of odors and headaches while working in a facility. In fact, some sites that have previously received a “closed” status may be re-opened to address vapor intrusion issues. A “no further action” determination for soil and groundwater does not necessarily include vapor intrusion concerns.
Soil and groundwater have long been the media of concern for environmental assessments and remediation activities, but as of 2002, the US EPA formally recognized vapor intrusion as an exposure pathway and drafted guidance for assessing the issue. Later in 2007, the Interstate Technology and Regulatory Council (ITRC) published a guidance document for assessing a vapor intrusion pathway. The ITRC and EPA have published more recent Vapor Intrusion Assessment and Mitigation guidance that should be taken into account when assessing your site. In addition to guidance documents, EPA developed a VI calculator to compare site specific data used in determining investigative needs.
So how do you know if you may have a vapor intrusion issue at a petroleum release site or former petroleum release site? Listen to your employees and customers – if you receive reports of odors or headache complaints, then this may indicate a vapor intrusion issue that deserves an investigation.
If you think an investigation is warranted, then where do you start? If available, evaluate boring logs and final soil and groundwater concentrations from previous investigations at your site. Take a look at plume migration maps at your site. With this information in hand, your environmental consultant can assist you in evaluating the possibility of vapor intrusion from past and present releases.
Evaluating a possible petroleum vapor intrusion issue has different criteria than that of a solvent-based issue and there are simple ways of ruling out vapor intrusion or there may be a glaring red flag staring out at you. Talk to your environmental consultant during ongoing investigations or if you have reason to be concerned about vapor intrusion.
If petroleum impacts at your site seem to be overwhelming, we at PPM are here to help simplify the complex. Feel free to reach out to me at firstname.lastname@example.org to discuss your vapor intrusion or just in general.