If you have been involved in a property with contamination, you are likely aware of the concerns associated with the release of volatile vapors into the indoor air space of buildings located on or near the contamination. Volatile organic chemicals such as trichloroethylene, petroleum compounds, and even inorganics such as mercury, may all emit vapors which can become trapped inside of buildings. These vapors present both short and long-term health concerns, and in certain circumstances even create a risk of fire or explosion. Because such vapors may migrate offsite to neighboring properties, they may create the risk of a third party lawsuit as well. Both the U.S. Environmental Protection Agency (EPA) and various state agencies have recognized the potential environmental impacts of vapor intrusion (VI) for many years, and have developed a patchwork procedure for evaluating and mitigating these impacts.

EPA first addressed this issue formally in November, 2002, when 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). This document, which has never been finalized, was intended as a tool to help people conduct screening evaluations and determine if VI at a particular site posed an unacceptable risk to human health. The document did not provide recommendations for either delineating the extent of the risk or procedures to eliminate the risk. Since this draft guidance was published, numerous sites across the country have been evaluated and mitigated to reduce or eliminate potential risks. This work, along with research by private and government groups, has lead to a greatly improved understanding of the issues involved in assessing and managing VI. In 2009, EPA’s Office of the Inspector General (OIG) recommended that OSWER evaluate the 2002 report and update it to reflect the current understanding of VI evaluation and remediation. The new draft guidance documents are the result of the 2009 recommendation.

EPA has issued in draft form two guidance documents. One document is the comprehensive guidance for assessing vapor intrusion, making risk management decisions and implementing mitigation. This document, the OSWER Final Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Sources to Indoor Air (Final VI Guidance), is intended to replace the 2002 draft Subsurface Vapor Intrusion Guidance document. For petroleum hydrocarbons that arise from releases at Subtitle I underground storage tank (UST) systems, EPA has developed a companion to the Final VI Guidance. The companion guidance document, Guidance For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (OUST Guidance), provides information and guidance about how vapor intrusion should be assessed for petroleum hydrocarbons at petroleum UST sites and brownsfield sites with similar characteristics. The OUST Guidance is intended to supplement the Final VI Guidance, and both documents would be applicable to petroleum sites. The OUST Guidance was prepared as a result of the 2009 OIG report which noted that the 2002 draft guidance did not address vapor intrusion at petroleum sites and recommended the preparation of guidance for UST sites.

According to EPA, the Final VI Guidance is 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 vapor intrusion may be of potential concern. However, it is likely that the concepts and procedures developed in this guidance will be adapted for use at any site where VI is of concern.

The Final VI Guidance and OUST Guidance is intended to address the issues recommended in the 2009 OIG report. These issues include:

  • Updated toxicity values.
  • A recommendation(s) to use multiple lines of evidence in evaluating and making decisions about risks from vapor intrusion.
  • How risks from petroleum hydrocarbon vapors should be addressed.
  • How the guidance applies to Superfund Five Year Reviews.
  • When or whether preemptive mitigation is appropriate.
  • Operations, maintenance, and termination of mitigation systems.
  • When institutional controls (ICs) and deed restrictions are appropriate.

Affected parties to this guidance could include property developers, local and state regulatory agencies, land owners, consultants, and Potentially Responsible Parties (PRPs) at CERCLA sites. When finalized, these documents, even though they have no regulatory authority, will likely establish the “standard of care” going forward and determine how properties with VI issues are evaluated and remediated. It is important that interested parties evaluate these document and address any issues or concerns during the comment period. EPA will accept comments on the draft documents through May 24, 2013.