EPA Issues Draft Vapor Intrusion Guidance—Uncertainty and Higher Costs Lie AheadEnvironmental Alert May 7, 2013
EPA recently released for public comment two draft guidance documents for assessment and mitigation of vapor intrusion (VI). The first, "Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Sources to Indoor Air" (Revised Draft Guidance), broadly addresses vapor intrusion issues at "Superfund" and other hazardous waste sites subject to periodic review. The second, "Guidance for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites" (PVI Guidance), provides specific guidance on vapor intrusion related to petroleum hydrocarbons (such as gasoline, diesel, and jet fuel).
Intrusion of hazardous vapor from contaminated soil or groundwater into indoor air is of increasing concern to regulators, but it is only recently that analysis of the VI "pathway" from subsurface to overlying buildings has become an important element of contaminated site investigations and cleanups.
Significantly, the updated draft guidance indicates that EPA may "re-open" Superfund and other cleanup sites where VI analysis previously was not addressed. Although the updated draft guidance does not apply directly to voluntary cleanup sites, including sites addressed under a state brownfield cleanup program (e.g., Maine's Voluntary Response Action Program (VRAP)), it may encourage states to take a second look at these sites if VI was never evaluated.
Key updates found in the Revised Draft Guidance are as follows:
- Use of multiple lines of evidence, rather than a single line of evidence, is recommended to evaluate the complexity of the VI pathway.
- Establishment of a Vapor Intrusion Screening Level (VISL) Calculator as a tool for evaluating whether the VI pathway has the potential to pose a health concern.
- Identification of the circumstances under which preemptive mitigation is appropriate, even before data is available to confirm that VI poses a health risk.
- Evaluation of operations and maintenance of mitigation systems, and recommendations as to when to terminate VI mitigation and/or monitoring are provided.
- Recommendations are provided regarding the use and selection of institutional controls, such as deed restrictions, to address VI exposure risk.
Not clarified by this draft is how Occupational Health & Safety Administration (OSHA) indoor air standards will interact with recommended screening levels.
While EPA recognizes that a different approach is needed for petroleum sites, some of the recommendations in the draft PVI Guidance are highly conservative and likely to be costly to implement. For example, EPA recommends multi-year monitoring of groundwater due to the "transient nature" of groundwater migration. In addition, EPA advises that site soil be sampled for certain residual petroleum contaminants – even where there is no measurable amount of the contaminant found in onsite groundwater monitoring wells.
Both guidance documents recommend extensive community involvement and public participation in site cleanups where VI is an issue.
The deadline for comment on both guidance documents is May 24, 2013. It is unclear when EPA will issue the two guidance documents in final form.