The U.S. Environmental Protection Agency (EPA) recently released final guidance on how best to assess and mitigate vapor intrusion, which occurs when vapors from below-ground contamination (soil or groundwater) rise into the indoor air of overlying buildings. EPA also has renewed efforts to include vapor intrusion in evaluations of sites for placement on the National Priorities List. AGC members should be aware of how EPA’s position on vapor intrusion may impact their operations.
EPA’s new vapor intrusion guidance documents – one covering petroleum vapor leaking from underground storage tanks (UST) and another covering vapor intrusion from other sources – are relevant to construction companies that build on or own property near contaminated sites, such as brownfield sites and industrial sites. Businesses may require a vapor barrier or a vapor migration system (active or passive) that diffuses vapors from the building to satisfy EPA’s recommendations. In addition, some predict EPA’s enhanced focus on vapor intrusion will likely increase environmental remediation obligations at contaminated sites, increase lawsuits claiming exposure to vapors from hazardous materials and contaminants, and increase transactional due diligence costs (involving the sale, purchase or leasing of real property) where parties associated with potential vapor intrusion issues call for investigation and mitigation.
EPA’s recommendations are nonbinding and do not impose any new regulations; however, it is expected that the guidance will promote national consistency and become the standard for vapor intrusion assessments and mitigating measures. EPA intends for the new documents to be used by federal and state agencies as well as grantees in EPA’s brownfields program as they evaluate sites under various cleanup programs, including the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) or the Resource Conservation and Recovery Act (RCRA).
Specifically, the new EPA guidance documents lay out EPA’s current recommendations for identifying, evaluating, and managing vapor intrusion, and provide some flexible technical approaches to accommodate site-specific conditions and circumstances. The documents apply to both residential and non-residential settings. Further, EPA released an updated Vapor Intrusion Screening Level (VISL) Calculator to assist in identifying applicable screening levels for a particular site (see also VISL User Guide). The two new vapor intrusion guidance documents supersede and replace EPA's 2002 Draft Vapor Intrusion Guidance.
PVI Guidance
As noted above, EPA has released guidance for assessing vapor intrusion from leaking petroleum underground storage tank sites, called “Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites” (PVI Guidance). The PVI Guidance applies to locations that housed leaking USTs or petroleum products such as gasoline, diesel, and jet fuel. It offers screening criteria based on the physical separation distances between vapor sources and potential receptors. The guide allows sites generally to be eliminated from further investigation if the vertical separation distance for the petroleum contamination is greater than six feet for dissolved contamination beneath buildings, or 15 feet for light non-aqueous phase liquid. Other features of the PVI Guidance are two “user-friendly” features: a table, and separate flowchart, each summarizing EPA’s recommended actions for addressing PVI at leaking UST sites, and an entire section discussing computer modeling of PVI.
OSWER VI Guidance
The other, more comprehensive guidance document is aimed at assessing vapor intrusion for sites with non-petroleum contamination, called “OSWER Technical Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air” (OSWER VI Guidance). It covers preliminary vapor intrusion assessments, sampling, risk assessments, exposure scenarios, mitigation, and subsurface remediation.
The OSWER VI Guidance lists five conditions that must be present for a vapor intrusion pathway to be complete: a subsurface source of vapor-forming chemicals near the building; a route to migrate toward the building; a building susceptible to soil gas entry; vapor-forming chemicals found in the indoor air; and the building is occupied. Per the guidance, decisions to undertake cleanup actions should be based on building-specific evidence – such as characterization of subsurface vapor sources’ strength and proximity to buildings, and building conditions – that demonstrate that vapor intrusion has the potential to pose an unacceptable human health risk.
In related news, a new EPA rule due out this fall would add vapor intrusion to the pathways evaluated under the Hazard Ranking Scoring (HRS) System for National Priority List (NPL) Superfund sites. The rule, which is undergoing final review by the White House Office of Management and Budget, would ensure that health risks associated with vapor intrusion are addressed and cleaned up as part of Superfund remediations. Opponents worry that it would lead to more sites being listed on the NPL.
Vapor intrusion occurs when toxic vapors from contaminated groundwater or soil rise into indoor air through dirt floors and cracked foundations, utility line openings or other pathways. EPA and state regulators are concerned that the vapors from the volatile chemicals that can migrate into in the indoor air may pose an unacceptable risk of chronic health effects due to long-term exposures, even when present at extremely low levels.
Authority to Protect Workers from Indoor Air Contamination
Notably, EPA is claiming “broad authority and distinct responsibilities” to protect workers from indoor air contamination in its new vapor intrusion guidance, rejecting arguments from some federal agencies and industry that EPA is trying to encroach on the Occupational Safety and Health Administration's (OSHA) responsibilities for ensuring worker health and safety. EPA’s prior 2002 guidance stated that OSHA, and not EPA, would take the lead in looking at occupational exposure to vapor intrusion. But the new 2015 guidance recommends that EPA’s risk-based standards, as opposed to OSHA permissible exposure limits (PELs or TLVs), should be used for evaluating health risks to workers from vapor intrusion in non-residential buildings (see Section 7.4.3 of the OSWER VI Guidance). EPA points to OSHA’s own acknowledgement on its website that its own PELs are “outdated and inadequate for ensuring protection of worker health.” The guidance also cites Memoranda of Understanding between OSHA and EPA dated Nov. 23, 1990, and February 1991, which govern the agencies’ relative responsibilities, and says that agreement remains in effect. EPA says OSHA's limits are not intended to protect sensitive workers and may fail to incorporate recent toxicological data because they are outdated. “For these and other reasons, EPA does not recommend using OSHA's PELs . . . for purposes of assessing human health risk to workers” through vapor intrusion in non-residential buildings, EPA says.
For more information, click here to see EPA’s website on Vapor Intrusion.