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December 14, 2016

EPA Adds Vapor Intrusion to Criteria Used to Score Potential National Priorities List Sites


Vapor intrusion (VI) is generally understood to be gas (radon; volatile organic compounds; mercury and some pesticides to name just a few) migrating through soil and into overlying buildings from subsurface sources such as contaminated soil or groundwater. In 1990, when the United States Environmental Protection Agency (EPA) last updated the Hazard Ranking System (HRS) governing how contaminated property is evaluated and ranked for possible listing on the federal National Priorities List (NPL), VI was not well understood. However, advances have been made in testing for VI and in certain circumstances subsurface intrusion is now viewed as a material risk to human health and the environment.

As part of a flurry of last minute rule adoptions, EPA recently amended the HRS to include a VI component for ranking contaminated sites. EPA does not expect this change to materially increase the number of sites that are added to the NPL each year. However, this long awaited new rule could change the characteristics of sites that are added to the NPL in the future. Of potentially greater importance, the inclusion of VI in the HRS could increase the scrutiny that these issues receive from state and federal regulators at non-NPL sites. Therefore, to avoid needless expense and delay, parties engaged in the investigation and clean-up of hazardous waste sites should work with their technical consultants and counsel to anticipate and address VI issues and may even find themselves addressing potential VI "re-openers" at sites that have previously received regulatory approvals.


The Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) mandates that EPA establish criteria for determining priorities for responding to the risks posed by inactive hazardous waste disposal sites. The NPL is the list of the nation's top priority sites and the HRS is the primary mechanism for placing sites on the NPL. The HRS is a scorecard used to rank the relative risk associated with a site using various factors considered to be related to, or indicative of, risk. The vast majority of sites evaluated using the HRS never make it to the NPL. As of September 2016 EPA had ranked nearly 53,000 sites and listed 1,782 on the NPL. EPA typically adds between 10 and 20 sites to the NPL each year.

VI issues first came to the public's attention in the late 1980s due to concerns about radon and dry cleaning establishments. At that time there were few health-based benchmarks for indoor air quality and testing techniques were not yet standardized. In addition, the potential for contaminated groundwater to serve as a source of VI was not well understood. As a result, VI was not included as a HRS risk factor. However, since 1990 there has been a growing recognition that vapor entering buildings through sewers, drains or foundation defects could be an important exposure route. Over the past two decades numerous states have adopted statutes, rules and guidance addressing some aspect of VI. Some of these policies deal specifically with the industrial solvent trichloroethylene (TCE). In California, for example, VI mitigation measures may be required as part of the local development permit process for buildings located over contaminated groundwater plumes. Since 2008, legislation in New York has required property owners to notify all of their tenants of any test results related to indoor air contamination associated with VI. The New Jersey Department of Environmental Protection has also developed a detailed vapor intrusion screening protocol that is mandatory during site investigations. In 2010, the US Government Accounting Office noted that the HRS might be underestimating the risks posed by certain sites where VI risks were present. As a result, EPA undertook a comprehensive evaluation of the HRS' ability to properly rank threats posed by subsurface intrusion and in 2011 EPA announced an opportunity for public input on the potential addition of VI to the HRS. Following this outreach effort, in February 2016 EPA formally proposed changes to the HRS and on December 7, 2016 announced adoption of amendments to the HRS to address VI.

Changes to the HRS

In the recently announced rule, EPA addresses VI by adding new terms and concepts without altering any core elements of the HRS framework. In particular the rule renames 'soil exposure' to 'soil exposure and subsurface intrusion' (SsI). The new requirements for evaluating SsI all follow the well-established HRS approach of using readily available information to assess the probability of exposure, the magnitude and duration of a release, toxicity, migration pathways, and size of likely receptor populations.

The new rules attempt to track existing methods for evaluating risks from other exposure pathways such as outdoor air or groundwater. However, VI is different and there are several aspects of the new rule that caused concern among the regulated community. There concerns included the fact that because contaminated source zones (groundwater, soil) are already considered and scored during the HRS process, VI data is duplicative. In addition, several interested parties expressed concern that establishing an observed exposure to vapors from subsurface intrusion is too difficult at the preliminary HRS stage because of the highly variable nature of indoor air quality and the risk of false positives due to the presence of volatile chemicals in the workplace. In response, EPA did adjust the weighting applied to certain VI factors. However, none of the comments caused EPA to make substantial changes and the rule (which had been in the works for at least five years) has been issued for final publication.

At the moment there is plenty of speculation about how the in-coming administration will deal with pending regulations. However, in the absence of executive action or some sort of general moratorium, these changes to the HRS are scheduled to become effective 30 days after publication in the Federal Register and will only apply to future HRS rankings of prospective NPL sites. Of course, any responsible party at a site that is proposed for NPL listing after the effective date of this new rule will need to carefully consider VI issues. Moreover, experience suggests that state regulators and regional EPA offices use the release of new rules and guidance as a basis (or pretext) to review existing projects. This has been especially true on VI issues which may not be as familiar to the regulated community or agency staff as more traditional soil and groundwater issues. Therefore, regardless of whether your remediation project involves a new proposed NPL listing or ongoing work at a site with VI issues, working with counsel who are experienced with site remediation issues can help minimize the risk that this technical change to the HRS results in unnecessary costs or expense.