The EPA is considering adding vapor intrusion pathways as a component of the hazard ranking system.

The Environmental Protection Agency (EPA) is soliciting stakeholder input regarding a potential addition of a vapor intrusion component to the Hazard Ranking System (HRS). In a May 2010 report (EPA’s Estimated Costs to Remediate Existing Sites Exceed Current Funding Levels, and More Sites are Expected to Be Added to the National Priorities List, GAO Report to Congressional Requesters, GAO-10-380, May 2010), the Government Accountability Office (GAO) concluded that if vapor intrusion sites are not assessed and, if needed, listed on the NPL, there is the potential that contaminated sites with unacceptable human exposure will not be acted upon. GAO recommended that the EPA administrator determine the extent to which the agency will consider vapor intrusion in listing NPL sites and how this will affect the number of NPL sites listed in the future. The HRS is Appendix A to the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), which the EPA promulgated on July 16, 1982 (47 FR 31180) pursuant to section 105(a)(8)(A) of the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA). The HRS is the principal mechanism the EPA uses to place sites on the CERCLA National Priorities List (NPL).

The EPA is considering adding a new screening mechanism to the HRS enabling sites with vapor intrusion contamination to be evaluated for placement on the NPL. The potential addition would enable the HRS to directly consider the human exposure to contaminants that enter building structures through the subsurface environment. When hazardous substances, pollutants or contaminants are spilled on the ground or otherwise migrate to the subsurface, they can move in the subsurface environment and eventually enter buildings as a gas or vapor, or even as a liquid in some cases. Dry cleaning solvents and industrial de-greasers are products that contain hazardous substances that when released to the environment, can migrate into the soil and subsurface environment, enter buildings by seeping through cracks in basements, foundations, sewer lines and other openings and ultimately result in human exposures. Vapor intrusion is a particular concern because concentrations of vapors can rise to a point where the health of residents or workers in those buildings could be at risk. Intrusion of contaminants in a non-vapor state may also be a pathway of concern because of the potential for human exposure to the liquids, the resulting precipitates, or associated vapors.

Many sites on the NPL that have subsurface contaminant intrusion problems were placed on the NPL by evaluation of pathways other than a contaminant intrusion pathway. There are other contaminated sites that did not qualify for placement on the NPL under the current HRS. However, these sites may qualify for placement on the NPL if the threat from vapor intrusion was included in the HRS. A new HRS mechanism would enable EPA to identify situations in which individuals are exposed or potentially exposed to vapor or other contaminant intrusion in dwellings, work places, or other structures or enclosures. The Agency will conduct public outreach activities, including facilitating public listening sessions, providing public information documents, and establishing a website with more information regarding this potential addition to the HRS. The Agency will consider the information gathered from this Notice, listening sessions, and other sources before making a decision to issue a proposed rulemaking to add subsurface contaminant intrusion to the HRS. The Agency is therefore requesting comments only regarding this potential addition to the HRS, and is not considering changes to the remainder of the HRS.