Vapor Intrusion: Acute Exposure Regulatory Developments and Litigation Trends¹

by J. Tom Boer^* and Suedy Alfaro^**

Over the last decade, regulators have accelerated their focus on vapor intrusion risk at hazardous cleanup sites. This has led to new cleanup standards, policies and guidance to evaluate potential risks, environmental investigation requirements for brownfield redevelopments, and the reopening of previously closed remedial actions. Recently, attention has turned from chronic to acute vapor intrusion risk. Although protection of human health is paramount, this recent focus has been plagued with concerns about the validity of the underlying science and a lack of comprehensive guidance from regulators on how to respond. This article explores the evolution of vapor intrusion regulation, particularly developments addressing acute risk, as well as trends in vapor intrusion-related litigation.

Vapor intrusion occurs when vapor-forming chemicals migrate from contaminated soil or groundwater into overlying occupied spaces. Chemicals may collect under structures and infiltrate into buildings. This has been found to occur through cracks in foundations and conduits such as sewers and electric lines. Once inside a building via a completed pathway, concentrations of vapor-forming chemicals may increase and cause health risks. Regulatory attention has focused predominately on volatile organic compounds ("VOCs"), particularly trichloroethylene ("TCE") and tetrachloroethylene ("PCE"), and their degradant products (e.g., vinyl chloride), as well as petroleum-related constituents like benzene. VOCs historically have been used in a variety of industrial settings, particularly as solvents and for dry cleaning. Given this widespread use, vapor-forming chemicals have been identified at cleanup sites nationwide. Some cleanup sites have been closed by regulators, in the period before attention was focused on vapor intrusion, and in some cases, properties have been transferred or redeveloped. Now, with increased attention on vapor intrusion risk, regulators must grapple with how to address the issue at both active and previously closed cleanup sites.

Regulatory focus on vapor intrusion has evolved over the last 30 years. During the 1980s, regulators were concerned with the risks of radon from natural sources. By the 1990s, attention began to turn to potential chronic exposure risk to vapor intrusion from VOCs and other industrial chemicals. By the early 2000s, regulators increasingly were incorporating vapor intrusion remedial requirements into ongoing cleanups to mitigate potential risk from chronic exposure, while also looking at closed sites to require, in some instances, further investigation and remediation to address vapor intrusion risk not previously evaluated.