It has been a few weeks now since the United States Environmental Protection Agency (US EPA) released two new technical guides relating to the investigation and mitigation of vapor intrusion (VI).
One document is specific to addressing vapor intrusion at leaking underground storage tank sites (Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites). The other document is more generally focused on presenting the US EPA’s current understanding of VI and the pathway of VI into indoor air (OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air).
Translating the New VI Guidance
While both documents will likely play a role in how you approach your site assessment activity, I think the OSWER VI document (all 267 pages) is critical to understanding the basics of how the US EPA thinks with respect to VI investigation and mitigation.
As stated in this document, “One of its main purposes is to promote national consistency in assessing the vapor intrusion pathway.” At last count, I think there were 38 states that had established VI guidance. It will be interesting to see whether those states that already have VI guidance in place will amend them to be consistent with the federal position to promote this “consistency.” If there remains a difference between state and federal guidance, it may play into your strategy of whether you want the US EPA or a state agency in the lead role of your project.
OSHA PELs “not recommended”
To date, assessing VI exposure has been based on permissible exposure limits (PELs) that are enforceable, occupational-exposure standards developed by the Occupational Safety and Health Administration (OSHA).
It is widely known that many of OSHA’s PELs have not been updated since they were adopted in 1971.
According to the new EPA guidance, “PELs (and TLVs) … are not intended to protect sensitive workers, may not incorporate the most recent toxicological data, and may differ from EPA derivations of toxicity values … for these and other reasons, EPA does not recommend using OSHA’s PELs (or TLVs) for purposes of assessing human health risk posed to workers … by the vapor intrusion pathway or supporting final “no-further-action” determinations …”
Without going into great detail, what this may mean is the VI action levels may be lower by orders of magnitude. This is contrary to many state guidance documents. Further, requiring indoor air in all buildings to be evaluated against the US EPA screening levels will likely necessitate additional investigation, monitoring, and more long-term mitigation.
Complete VI Pathway?
Based on this guide, the vapor intrusion pathway is referred to as “complete” when the following five conditions are met under current conditions:
1) A subsurface source of vapor-forming chemicals is present (e.g., in the soil or in groundwater) underneath or near the building(s) (see Sections 2.1, 5.3, 6.2.1, and 6.3.1);
2) Vapors form and have a route along which to migrate (be transported) toward the building (see Sections 2.2 and 6.3.2);
3) The building(s) is(are) susceptible to soil gas entry, which means openings exist for the vapors to enter the building and driving ‘forces’ (e.g., air pressure differences between the building and the subsurface environment) exist to draw the vapors from the subsurface through the openings into the building(s) (see Sections 2.3 and 6.3.3);
4) One or more vapor-forming chemicals comprising the subsurface vapor source(s) is (are) present in the indoor environment (see Sections 6.3.4 and 6.4.1); and
5) The building(s) is (are) occupied by one or more individuals when the vapor-forming chemical(s) is (are) present indoors.
As I read this, all five conditions must be met in order to have a complete pathway. Once you think that there may be vapor-forming chemicals underneath or near the building, it appears that you are taking the “VI on ramp.” The devil will be in the details relative to how much data will be required to show (prove) that one or more of these conditions does not exist, especially as you move down the list of conditions.
Summa® Canisters: One of a number of methods to consider for collecting air samples to evaluate the vapor intrusion pathway (Photo Credit: Dragun Corporation).
The VI Off Ramp
With respect to finding an “off ramp” and attempting to make a determination that the VI pathway is “incomplete,” the document states the following:
“…and for the purposes of this Technical Guide, if one (or more) of the five foregoing conditions is currently absent and is reasonably expected to be absent in the future (e.g., vapor migration is significantly and persistently impeded by natural geologic, hydrologic, or biochemical (e.g., biodegradation) processes and conditions), the vapor intrusion pathway is referred to as “incomplete.” EPA recommends that any determination that the vapor intrusion pathway is incomplete be supported by site-specific evidence to demonstrate that the nature and extent of vapor-forming chemical contamination in the subsurface has been well characterized (Section 6.3.1) and the types of vapor sources and the conditions of the vadose zone and surrounding infrastructure do not present opportunities for unattenuated or enhanced transport of vapors (Sections 5.4 and 6.5.2) toward and into any building (see Section 7.3 for further discussion)” (emphasis added).
A few key words and phrases (bolded above) suggest that it will be relatively easy to on ramp, but not so easy to off ramp. The guidance states, “Multiple lines of evidence are particularly important for supporting “no-further-action” decisions regarding the vapor intrusion pathway (e.g., pathway incomplete determinations) to reduce the chance of reaching a false-negative conclusion (i.e., concluding vapor intrusion does not pose unacceptable human health risk, when it actually poses an unacceptable human health risk).”
The guidance further states, “When the vapor intrusion pathway is determined to be incomplete then vapor intrusion mitigation is not generally warranted” (emphasis added). So, even when there is a determination of incomplete, the door is still left open for mitigation.
Is the US EPA VI Assessment Contrary to State Guidance?
With respect to condition #4, “One or more vapor-forming chemicals comprising the subsurface vapor source(s) is (are) present in the indoor environment,” it is implied that the US EPA prefers indoor air samples. This is contrary to many state guidance documents that lean more toward sub-slab data. This has also proven to be problematic due to “background” interference of “ambient” chemicals in the indoor air. The guidance suggests the need for multiple rounds of indoor air samples to reflect seasonal variation. Accordingly, this path to an off ramp will take time. This could be a challenge for those who may be assessing VI in relation to property transactions, as they are typically on a fast track.
These are just a few “big picture” items that caused me to pause as I read the guidance. As I mentioned, the devil is in the details, and there are plenty within the document (e.g., sampling considerations, the use of modeling, calculating VI Screening Levels, attenuation factors, etc.).
No doubt there will be many weighing in on this issue, and, as we all implement this (or parts of this) guide, some of those devilish details will become more apparent.
One thing is certain: it will take a team of technical and legal counsel to navigate an appropriate path given the circumstances of each business scenario, albeit property transaction, continuing obligation considerations, Comprehensive Environmental Response Compensation and Liability Act (CERCLA) closures and interim actions, or Resource Conservation and Recovery Act (RCRA) Corrective Actions.
If you have any questions as it relates to this new guidance and how it might apply to your current or future assessments, please feel free to contact me (jbolin@dragun.com) at 248-932-0228, ext. 125.