Recommendations for the Investigation of Vapor Intrusion

Since 2000, regulators and the regulated community have become increasingly concerned about the potential for exposure to volatile organic compounds VOCs through vapor intrusion to indoor air at sites with contaminated soil or groundwater. Detailed investigations at a limited number of corrective action sites have documented elevated levels of chlorinated VOCs in houses located above contaminated groundwater DiGiulio et al., 2006 Tillman and Weaver, 2005. In response, the U.S. Environmental Protection Agency EPA and many state regulatory agencies have issued guidance specifying screening and field investigation procedures for the identification of vapor intrusion impacts at corrective action sites. Although the specific recommended investigation procedures vary significantly between guidance documents, the majority of these documents utilize a step-wise evaluation process that includes preliminary screening followed by field investigation, if needed. Of the available regulatory guidance on vapor intrusion, the EPA guidance U.S. EPA, 2002 is currently most widely applied. This guidance document has been formally adopted by some states e.g., Ohio and is also widely used in states that have not issued their own guidance documents. Currently available vapor intrusion regulatory guidance leaves the investigator with a number of potential questions concerning implementation of a field investigation. Key questions include Collection of Groundwater and Soil Gas Samples How should groundwater and soil gas samples be collected to generate data suitable for pathway screening Identification of Indoor Air Impacts What field investigation program will provide a cost-effective and timely evaluation of the presence or absence of vapor intrusion impacts