On April 11, 2013, the EPA released draft final vapor intrusion guidance (“Guidance”) for assessing and mitigating vapor intrusion pathways from subsurface sources to indoor air. The Guidance presents EPA’s current recommendations for identifying and considering key factors when assessing vapor intrusion, making risk management decisions, and implementing mitigation measures pertaining to this potential human exposure pathway. The Guidance addresses both residential and nonresidential buildings that may be impacted by vapor intrusion from subsurface contamination. The Guidance applies to 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 vapor intrusion may be of potential concern. For State lead sites, stakeholders still should consider the application of State guidance on vapor intrusion issues, such as the California Dept. of Toxic Substances’ “Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air” (Oct. 2011).
EPA defines vapor intrusion as follows: “certain hazardous chemicals that are released into the subsurface as liquids or solids may form hazardous gases (i.e., vapors) that migrate through the vadose zone and eventually enter buildings as a gas by migrating through cracks and gaps in basement floors and walls or foundations, including perforations due to utility conduits and any other openings (e.g., sump pits).” “Vapor intrusion is the general term given to migration of hazardous vapors from any subsurface contaminant source, such as contaminated soil or groundwater, through the vadose zone and into indoor air.” “Vapor intrusion can occur in a broad range of land use settings, including residential, commercial, and industrial, and affect buildings with virtually any foundation type (e.g., basement, crawl space(s), or slab on grade).”
Topics addressed in the Guidance include: (1) a conceptual modeling of vapor intrusion; (2) considerations for nonresidential buildings; (3) preliminary analysis of vapor intrusion; (4) detailed investigation of vapor intrusion; (5) setting a risk management framework; (6) building mitigation and subsurface remediation; (7) preemptive mitigation/early action; and (8) planning for community involvement. Appendices to the Guidance include: a list of chemicals of potential concern for vapor intrusion; a list of generic attenuation factors used to develop screening levels; data quality assurance considerations; and a formula for calculating vapor source concentrations from groundwater data.
EPA recommends consideration of these Guidelines when making “current human exposures under control” environmental indicator determinations at RCRA corrective action facilities and National Priorities List sites under CERCLA;
when undertaking removal actions, remedial actions, pre-remedial investigations, remedial investigations, and five-year reviews under CERCLA; and when undertaking RCRA facility investigations and corrective actions and site investigations and cleanups at federal facilities and brownfield sites.
Along with its Guidance, EPA released additional guidance providing information and direction about how vapor intrusion should be assessed for petroleum hydrocarbons (“OUST Guidance”). The OUST Guidance may be useful in informing decisions about vapor intrusion and petroleum hydrocarbons at brownfield sites.
EPA also issued a Vapor Intrusion Screening Level (“VISL”) Calculator which is a recommended spreadsheet that: identifies chemicals considered to be typically vapor-forming and known to pose a potential cancer risk or noncancer hazard through the inhalation pathway; provides generally recommended screening-level concentrations for groundwater, near-source soil gas (exterior to buildings), sub-slab soil gas, and indoor air based upon default residential or nonresidential exposure scenarios, a target cancer risk level of one per million, and a target hazard quotient of one for potential non-cancer effects; and facilitates calculation of site-specific screening levels based on user-defined target risk levels, exposure scenarios, and semi-site-specific attenuation factors.
EPA is accepting comments on the draft final Guidance until May 24th, 2013. You can find the Guidance and OUST Guidance here.