US EPA has released two draft final vapor intrusion guidance documents for public review and comments through May 24, 2013. The agency says it is working to issue final subsurface vapor intrusion guidelines so that they can be applied in forthcoming decisions.
EPA’s Office of Solid Waste and Emergency Response (OSWER) released its draft Final Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Sources to Indoor Air for external review. The document describes a recommended framework for assessing vapor intrusion that relies on collecting and evaluating multiple lines of evidence to support risk management decisions. It also provides guidance on monitoring and terminating building mitigation systems.
The second draft guidance document is from EPA’s Office of Underground Storage Tanks. The Guidance for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites focuses on underground storage tanks (USTs) typically located at gas stations and non-marketing facilities regulated under Subtitle I of the Solid Waste Disposal Act.
The guidance states that assessing the potential for petroleum vapor intrusion is an integral part of the response to a suspected or confirmed released from a regulated UST system. At any leaking UST site, it is important to have a thorough understanding of the release and other factors that may influence how contaminants disperse and impact human health and safety.
As background, EPA defines “vapor intrusion” as when hazardous gases travel through the soil and eventually enter buildings through cracks and gaps in basement floors and walls or foundations. Vapor intrusion is a general term used for the migration of hazardous vapors from any subsurface contaminant source, such as contaminated soil or groundwater, into indoor air.
Vapor intrusion can occur in many settings, including residential, commercial, and industrial, and affects buildings with any foundation type, such as basements, crawl spaces, or slab on grade. It is widely recognized as a potentially significant cause of human exposure to volatile hazardous chemicals in indoor spaces. When toxic vapors accumulate indoors, they can place the health of building occupants at risk. In addition, methane, and certain other volatile chemicals can pose explosion hazards when they accumulate in confined spaces.