An Introduction to Vapor Intrusion

Vapor intrusion (VI) occurs when contaminants in soil or groundwater drift into a building or facility through cracks and seams in the foundation. This article describes steps to mitigate VI at your facility.

Historically, most environmental remediation efforts have focused on groundwater protection. Over the past 10 to 15 years, that focus has shifted to include vapor intrusion (VI) mitigation, particularly of solvent and gasoline vapors, which are common concerns at numerous sites throughout the U.S.

VI occurs when chemicals in soil or a groundwater plume migrate into a building’s interior space. Dry cleaners, gas stations, and manufacturers that use volatile solvents are common sources of VI. VI is hardly a new phenomenon; however, with recent advances in our understanding of chemical toxicity — especially regarding certain chlorinated hydrocarbons, such as trichloroethylene (TCE) — VI has become a driver for many site investigations and an impediment to regulatory approvals for site closures.

VI is also a concern in property transactions with the potential for vapor encroachment conditions. ASTM International (formerly known as the American Society for Testing and Materials) has published standards for vapor encroachment screening in an effort to assist in characterizing the extent of VI issues on property involved in real-estate transactions (1). These standards are based on various studies involving VI and have been incorporated into environmental due diligence practices.

Since VI issues often arise due to soil and groundwater contamination under existing buildings, ongoing operations and inherent physical restrictions can make remediation difficult. Consequently, many sites contaminated with volatile organic compounds (VOCs) that have the potential for VI rely on mitigation methods rather than remediation. This article describes the basic methods employed to mitigate VI.