More than ten years after issuing draft guidance regarding the increasingly significant subject of vapor intrusion (VI), the U.S. Environmental Protection Agency (EPA) has just released for public comment drafts of two guidance documents about VI assessment and remediation. The much anticipated documents include updated general guidance for assessing VI associated with releases of hazardous volatile chemicals, and a more focused VI guidance addressing releases of petroleum hydrocarbons from underground storage tanks. EPA will be accepting public comments on both draft guidance documents through May 24, 2013.
Vapor intrusion involves the migration of potentially hazardous chemical vapors from subsurface contaminant sources, such as contaminated soil or groundwater, through subsurface soils and into indoor air. Although there has been more focus on VI concerns in the past 10 years, the phenomenon is similar to intrusion of Radon gas that has been mitigated in some regions for many years. Additionally, regulatory authorities have recognized for some time that a wide range of building and foundation types may be prone to intrusion of underlying soil vapors, and that if not appropriately mitigated, human exposure to such vapors could pose potential health risks.
In November 2002, EPA’s Office of Solid Waste and Emergency Response (OSWER) issued Draft OSWER Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soil (Subsurface Vapor Intrusion Guidance) which provided general direction for evaluating the potential for VI pathways at cleanup sites. At the time, EPA noted the guidance did not include measures to delineate and mitigate potential VI risks. To fill these gaps, since EPA’s release of its 2002 VI Guidance, a number of state agencies and public and private sector technical working groups have developed additional guidance for assessing and managing VI. In 2009, EPA’s Office of the Inspector General (OIG) recommended that EPA update its 2002 vapor intrusion guidance to reflect the numerous technical advancements that had occurred in the VI field. According to EPA, the two draft VI guidance documents – which combined amount to almost 300 pages without many of the referenced supporting documents – address OIG’s recommendations and take into consideration more recent guidance developed by states and other technical working groups.
2013 VI Guidance
Once finalized, EPA’s OSWER Final Guidance For Assessing and Mitigating the Vapor Intrusion Pathway From Subsurface Sources to Indoor Air (2013 VI Guidance) will supersede and replace EPA’s 2002 Draft VI Guidance. According to EPA, the 2013 VI Guidance will be intended for use at any site being evaluated by EPA pursuant to CERCLA or RCRA, EPA’s brownfield grantees, or state agencies with delegated authority to implement CERCLA or RCRA where VI may be of potential concern. However, it is likely that EPA’s guidance will be looked to and considered by regulatory personnel and affected parties at a broader range of sites. Last year, EPA issued supplemental guidance for assessing the protectiveness of a remedy for VI at CERCLA sites undergoing five-year reviews. See Assessing Protectiveness at Sites for Vapor Intrusion: Supplemental Guidance to the Comprehensive Five-Year Review Guidance. (OSWER Directive 9200.2-84). These five-year assessments will now be expected to comport with EPA’s 2013 VI Guidance, if VI issues are present.
Key additions to the 2013 VI Guidance include:
Updated toxicity values and inclusion of a VI Screening Level calculator tool (available in a companion technical support document) to assist in comparing subsurface or indoor data against EPA recommended screening levels.
Emphasis on using multiple lines of evidence (MLE) to adequately evaluate the VI pathway and associated potential risks to human health; MLE consideration is the norm in many jurisdictions at this time.
Consideration of whether preemptive mitigation measures are appropriate, such as installation of vapor mitigation systems in new buildings, in lieu of performing a detailed VI assessment.
Guidance on potential options to mitigate and manage vapor intrusion, including performance of subsurface remediation, installation of VI prevention and mitigation systems for existing and new buildings, conducting follow-up operation and monitoring of installed VI control systems, and determining when VI mitigation is no longer necessary.
Guidance on when institutional controls and deed restrictions are appropriate.
To supplement the 2013 VI Guidance, EPA developed several technical supporting documents, which address, among other things, the development of conceptual model scenarios for the VI pathway; the evaluation and characterization of attenuation factors for
residential buildings; sampling and analysis methods for conducting VI investigations; and selecting, designing, installing, operating and maintaining VI mitigation systems. Links to these technical documents are posted on EPA’s VI Website (see Key Links section below). Overall, EPA’s 2013 VI Guidance provides an updated comprehensive toolbox for assessing and addressing potential VI risks, bringing EPA current with more established VI programs in many states.
2013 Petroleum VI Guidance
Petroleum vapor intrusion (PVI) associated with leaking underground storage tank (UST) sites typically involve three classes of chemicals: petroleum hydrocarbons (e.g., benzene, trimethylbenzenes) found in gasoline, diesel and jet fuel, volatile chemicals in fuel additives (e.g., methyl tertiary-butyl ether [MTBE]), and methane (a byproduct when petroleum hydrocarbons biodegrade). The presence of these chemicals in indoor air may pose both immediate threats to safety (e.g., fire/explosion potential from petroleum vapors or methane) and possible adverse health effects from inhalation (e.g., exposure to harmful levels of benzene).
To address OIG’s 2009 concern that EPA’s 2002 Draft VI Guidance did not address PVI at UST sites regulated under RCRA Subtitle I, EPA’s Office of Underground Storage Tanks (OUST) has issued for public comment Guidance For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (2013 Petroleum VI Guidance). According to EPA, when finalized, the 2013 Petroleum VI Guidance will apply to situations in which EPA, states, and tribes are either undertaking PVI investigations and corrective action at leaking UST sites or where UST owners and operators are required to undertake release investigation and corrective action activities pursuant to 40 CFR Part 280 requirements.
In its 2013 Petroleum VI Guidance, EPA outlines and describes a recommended course of action for assessing and mitigating PVI associated with leaking UST sites. Recommended steps include:
Assessing and mitigating immediate threats to safety.
Conducting a site characterization and developing a conceptual site model.
Delineating a “lateral inclusion zone” for purposes of assessing the potential for PVI for buildings located within a defined distance from contamination sources, for example, the presence of preferential transport pathways, such as subsurface utility corridors, could facilitate the migration of petroleum vapors to nearby buildings.
Identifying preferential transport pathways within the lateral inclusion zone and assessing whether such pathways, if present, could result in PVI into nearby buildings.
Determining whether contamination underlies any buildings within the lateral inclusion zone.
Identifying and implementing measures to mitigate PVI.
Several technical support documents are also included in the 2013 Petroleum VI Guidance to help explain EPA’s recommended actions.
Other VI Guidance
EPA notes in its 2013 VI Guidance that a number of state regulatory agencies have developed their own VI guidance and that such agencies may continue to implement such guidance under their respective statutory authorities.
For example, in California, the Department of Toxic Substances Control (DTSC) has developed several guidance documents dealing with various aspects of VI, including guidance on performing soil gas investigations, evaluating and mitigating subsurface VI to indoor air, remediating vapor source areas, performing long-term monitoring, and conducting public participation activities. Similarly, in September 2012, the California State Water Resources Control Board (SWRCB) issued an update to its Leaking Underground Fuel Tank Guidance Manual (LUFT Manual) that includes guidance on evaluating the potential for VI pathways at LUFT sites. Links to DTSC’s guidance documents and to the SWRCB’s LUFT Manual are posted on DTSC’s VI Website and the SWRCB’s LUFT Manual webpage, respectively (see Key Links below).
Given this federal/state overlap, parties performing VI assessments and mitigation will need to carefully assess which regulatory authorities and corresponding regulatory agency guidance may apply to their situation. Although many states have adopted their own screening levels, regulated industries and other affected stake-holders should expect such criteria to be re-evaluated in light of EPA’s new and updated screening levels.
OSWER Final Guidance For Assessing And Mitigating The Vapor Intrusion Pathway From Subsurface Sources To Indoor Air — External Review Draft (April 2013)
Guidance For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites—External Review Draft (April 2013)
Instructions on submitting comments to EPA
EPA Vapor Intrusion Website
DTSC Vapor Intrusion Website
SWRCB LUFT Manual