Vapor Intrusion in Washington State: Draft Guidance and Possible Rulemaking
The Department of Ecology has issued draft Vapor Intrusion Guidance (Guidance) that is being used by agency personnel for ongoing clean up actions. The basic framework in the Guidance is not expected to change when it is finalized sometime in early 2010.
Vapor intrusion (VI) is the migration of vapor-phase hazardous substances through the subsurface and into overlying structures. The Washington Department of Ecology (Ecology) has become increasingly focused on VI as a pathway of concern at cleanup sites. The Washington Model Toxics Control Act (MTCA) does not articulate clear requirements for assessing VI during a remedial investigation and does not provide a clear process for establishing cleanup levels for indoor air. Ecology may undertake regulatory revisions to MTCA to address these deficiencies. In the meantime, Ecology has issued draft Guidance that is being used by agency personnel for ongoing cleanup actions. Click here for the draft Guidance.
(Note that certain manufacturing jobs result in worker exposure to toxic, volatile substances and Ecology expressly acknowledges that this Guidance is not intended to address this type of exposure. Rather, Ecology recognizes that state and federal health and safety standards (WISHA and OSHA) regulate these types of industrial/manufacturing exposures.)
The Guidance states that Ecology will require parties to evaluate the potential for VI whenever volatile hazardous substances are present in the site subsurface. The draft Guidance provides direction on how to evaluate whether VI has the potential to contaminate indoor air and provides for a tiered approach if VI poses a potential problem.
First, a preliminary assessment is performed to determine whether site contaminants could pose or are posing a threat to indoor air quality. If the chemicals are of sufficient volatility and toxicity, and if buildings in the vicinity are or may be occupied, then further evaluation is warranted.
Further evaluation includes a Tier I assessment, which looks at the location and concentrations of the volatile contaminants in vadose zone soil and groundwater, and if necessary a Tier II assessment, which evaluates the actual impacts to indoor air and the potential for indoor air to be impacted in the future.
The Guidance suggests that parties should communicate with potentially affected persons if a preliminary assessment establishes the presence of subsurface volatile contaminants. It is not clear if Ecology will require or be involved in this type of communication. At formal cleanup sites (i.e., those being done under an Agreed Order, Consent Decree or Unilateral Order), Ecology will likely require communication on potential VI exposures very early in the assessment process and will likely be involved (and possibly even direct) communication with those potentially affected and/or the public generally.
The Guidance was not designed to address immediate safety concerns resulting from spills or other exposure scenarios that are causing a current harmful acute exposure. The Guidance does provide some limited information on potential mitigation and short-term solutions intended to protect indoor air receptors threatened or potentially threatened as a result of potential VI. Because the type and scope of the required mitigation is site specific, the Guidance merely mentions some possible mitigation measures (e.g., subslab depressurization) and directs the reader to other publications.
If contamination poses a threat to human health through the VI pathway, Ecology expects parties to identify cleanup levels that are protective of indoor air quality and to implement an appropriate remedy. The Guidance outlines the process for establishing cleanup standards (cleanup levels and points of compliance) for the VI pathway. It recognizes that institutional controls play a key role in addressing the VI pathway because institutional controls may be used to ensure that the building use that was assumed in the VI assessment does not change, or if it does, additional cleanup may be required. Institutional controls may also limit changes to the building structure that could result in new VI exposures.
The basic framework in the Guidance is not expected to change when it is finalized some time in early 2010. What is not clear is whether Ecology will be satisfied with this Guidance or instead decide to implement regulatory changes to address VI. If regulatory changes occur, they are not likely until at least 2011.