AARST_Radon_Reporter_July_2022

THE RADON REPORTER | 21 VAPOR INTRUSION The Vapor Intrusion Pathway Mini-Series: Regulatory Closure Challenges David R. Gillay, Barnes & Thornburg LLP 1 This is the second in a series of articles focusing on an unseen villain known as vapor intrusion. This article discusses some of the challenges and new tools to secure and maintain regulatory closure of contaminated sites where this pathway is potentially present. Vapor intrusion (VI) is the migration of volatile chemicals from subsurface soil and groundwater into buildings. It shares many common characteristics with the intrusion of naturally occurring radon gas into buildings. This emerging contamination “pathway” has affected thousands of closed and contaminated sites across the country. The VI pathway reveals some of the potential future risks flowing from risk-based closure of contaminated sites. A risk-based approach generally allows the responsible party to tailor the remedy to the real-world exposures at each site, instead of simply removing all of the contaminant or achieving a numerical closure level for unrestricted use in certain environmental media. Risk-based decision-making is a mechanism to integrate source reduction and risk management of a cleanup to ensure it protects human health, applies sound science and common sense, and is flexible and cost-effective. Depending on known or anticipated risks to human health and the environment, an integrated risk- based approach may include monitoring and data collection, active or passive remediation, containment, institutional controls, or a combination of these actions. To effectively manage liability, a responsible party must find the balance between source reduction and risk management for residual contamination. Evolving VI pathway guidance and dramatic changes to a contaminant’s toxicity can disrupt this delicate balance. In late 2002, the United States Environmental Protection Agency (EPA) first released draft guidance on the VI pathway. The EPA finalized its VI pathway guidance well over a decade later, in the summer of 2015. During the EPA’s careful deliberation and release of its VI guidance, the vast majority of state environmental agencies published their own VI guidance. The VI guidance landscape remains in flux and continues to evolve, with more emphasis on the movement of soil gas in the subsurface.