This summer, EPA issued two, long-awaited final technical guides for assessing and mitigating the intrusion of hazardous vapors from subsurface contamination into overlying buildings.  EPA’s issuance of these technical guides on vapor intrusion assessment exemplifies its increased focus on vapor intrusion at contaminated sites.  Developers, builders, current landowners, prospective purchasers, and lenders dealing with contaminated sites, or sites adjacent to contaminated sites, should factor these guides into liability and risk planning, as EPA’s increased focus on vapor intrusion could increase the potential for long-term liabilities.

The first guide, the “Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air” (OSWER Vapor Intrusion Technical Guidance) is intended for use at sites being evaluated under various cleanup programs, including Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) or Resource Conservation and Recovery Act (RCRA) corrective action, and brownfield grant sites.  Generally, the guidance offers a two-step approach to vapor intrusion assessment starting with a preliminary analysis using available and readily ascertainable information to understand the potential for human health risks from vapor intrusion, followed by a detailed investigation if the preliminary analysis indicates subsurface contamination with vapor-forming chemicals is present beneath or near buildings.  The guide also calls for “prompt action,” such as indoor air testing or other evaluations, when there are reports of odors or physiological effects (e.g., dizziness, nausea, confusion) or when there is a wet basement in an area with groundwater known to contain vapor-forming chemicals.  Should vapor intrusion be determined to pose an unacceptable risk, mitigation measures may include remediation (i.e., removal or treatment) of the subsurface vapor source, engineered controls (e.g., sealing major openings, installing vapor traps or sub-slab depressurization systems, or treating air through activated carbon adsorption), monitoring, and institutional controls to restrict certain land uses or activities and notify other parties (e.g., restrictive covenants, deed restrictions, environmental covenants, or consent orders).

The second guide addresses petroleum vapor intrusion specifically due to the differences in biodegradation between petroleum hydrocarbons and other vapor forming chemicals, such as chlorinated solvents.  The “Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites” (Petroleum Vapor Intrusion Technical Guidance) applies to new and existing releases of petroleum-based fuels from leaking underground storage tanks (UST) sites.  Generally, the guidance calls for screening based on the vertical separation distance between the building and the vapor source.  Sites with commingled petroleum and chlorinated solvent plumes and petroleum-contaminated sites that are not comparable to UST sites (e.g., refineries, petrochemical plants, terminals, above-ground tank farms, pipelines, and large scale fueling and storage operations), however, are meant to be addressed under the more general first guide.

For sites where hazardous substances have been allowed to remain at levels above unrestricted use, periodic regulatory reviews provide an opportunity for regulators to reassess potential vapor intrusion issues.  As a result, sites at which vapor intrusion was not addressed, or inadequately addressed, may be reopened.  Parties should proactively incorporate vapor intrusion considerations into site assessments where contamination remains, as long-term care and continuing obligations may be required, thereby increasing potential long-term liabilities.  In addition, given EPA’s goal to promote national consistency for vapor intrusion assessments, the guides could be advanced as a standard of care by potential third-party plaintiffs claiming exposure to vapors from hazardous chemicals.  Accordingly, landowners, adjacent property owners, and all parties to contaminated, or potentially contaminated, property transactions should factor the technical guides into plans for limiting liability and reducing risk at such sites.