EPA Proposes New Vapor Intrusion Guidance

May 10, 2013

The U.S. Environmental Protection Agency ('EPA") has released draft guidance that seeks to address a phenomenon known as "vapor intrusion," which occurs when pollution from sites with contaminated soil and groundwater migrates into foundations and enters into structures in gaseous form.  EPA is now accepting public comments on the guidance through May 24, 2013.

EPA previously released vapor intrusion guidance in draft form in 2002.  However, it was never finalized.  The new guidance includes a variety of dramatically more stringent standards from the older version, including new toxicity values, new preemptive action measures, new standards for mitigation systems, and new risk assessment approaches.

In order to evaluate the vapor intrusion "pathway" and the risks associated with vapor intrusion, site owners and operators are instructed to consider a variety of data, including the presence of hazardous vapors in soil and groundwater beneath a structure, a hazardous chemical's moisture content, and other more practical considerations such as building foundation conditions.

Even when a full vapor intrusion investigation has not been completed, EPA's new guidance recommends taking preemptive action measures if there is any reason to believe vapor intrusion may be occurring and poses a risk to the health of building occupants.  Further, EPA recommends the installation of monitor mitigation systems (such as passive barrier systems) in newly constructed buildings in areas where subsurface contaminants may eventually lead to vapor intrusion problems.  These preemptive measures, however, are not considered a final solution for remediation, and remediating any subsurface contaminants will generally still be required.

For existing buildings, the guidance calls for active depressurization technologies ("ADT") as the preferred choice for mitigation systems.  There are a variety of different ADT systems.  For example, sub-slab depressurization ("SSD") systems utilize suction pipes in the building slab to cause a pressure differential that prevents vapor intrusion, and sub-membrane depressurization ("SMD") systems involve installing a flexible membrane over basements or crawl spaces with dirt floors to seal off vapor intrusion.  While the guidance notes that ADT systems are not necessarily the only choice for mitigation, these systems are widely viewed as the most practical choice and are the generally recommended option.

In evaluating the risks to human health, the new guidance calls for aggregating the noncancer health risks associated with individual chemicals in determining whether a response action is warranted.  For example, even when no chemical, on its own, is present at a level high enough to require a response, if adding the risk levels of all the individual chemicals present (and assuming there are no synergistic or antagonistic interactions among the chemicals) results in a high enough risk level, the new guidance would call for a response action.

The new guidance is of particular importance to sites being investigated or remediated under the Comprehensive Environmental Response, Compensations and Liability Act ("CERCLA") or the Resource Conservation and Recovery Act ("RCRA").  Additional investigations may be required to comply with the new guidance, and parties in charge of remediation efforts could be required to remove more contamination than would otherwise be necessary or to install expensive solutions, such as vapor extraction systems, to address vapor intrusion problems.

Perhaps most noteworthy, the new guidance has the potential to require remediation efforts to be reopened at CERCLA sites where remediation was previously considered complete.  As part of EPA's five year reviews of these sites, the new guidance calls for EPA to review vapor intrusion data and evaluate how well the remedies already in place will provide for future protection against vapor intrusion risks.  If the remedies already in place are deemed unsatisfactory, parties that were not expecting any additional remediation costs could be on the hook to pay for additional vapor intrusion remediation activities.

Simultaneous with the release of the draft vapor intrusion guidance, EPA released separate draft guidance addressing hydrocarbons released from underground storage tanks ("USTs").  It calls for site characterizations that include determining the extent and characteristics of contamination and evaluating the moisture of contaminated soils and the geological conditions beneath neighboring structures.  Vapor intrusion sampling is also called for when contaminated groundwater is less than 15 feet below the surface of any structure located within a calculated lateral range of contamination, called the "lateral inclusion zone."  The deadline for submitting comments on the draft UST guidance is also May 24, 2013.

To learn more about EPA's draft vapor intrusion guidance or to file comments, please contact your Clark Hill Environment, Energy and Natural Resources attorney.