Gas and Vapor Intrusion

Introduction

Gas and Vapor Intrusion

Gas and vapor intrusion is defined as the migration of volatile organic or inorganic compounds into occupied buildings from underlying contaminated groundwater or soil. Contaminant exposure via gas and vapor intrusion could pose a significant risk to the public.

Vapor intrusion is defined as vapor-phase migration of volatile organic compounds or volatile inorganic compounds into occupied buildings from underlying contaminated groundwater or soil. Until recently, this transport pathway was not routinely considered under the Resource Conservation and Recovery Act (RCRA); the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA); or underground storage tank investigations. Therefore, the number of buildings or homes where vapor intrusion has occurred is undefined.

However, considering the vast number of current and former industrial, commercial, and waste processing facilities in the United States capable of causing volatile organic or inorganic groundwater or soil contamination, contaminant exposure via vapor intrusion could pose a significant risk to the public. Also, consideration of this transport pathway may necessitate review of remedial decisions at RCRA and CERCLA sites, as well as implementation of risk-reduction technologies at brownfield sites where future development and subsequent potential exposure may occur.

EPA's Office of Solid Waste and Emergency Response (OSWER) developed guidance to facilitate assessment of vapor intrusion at sites regulated by RCRA and CERCLA, where halogenated organic compounds constitute the bulk of risk to human health. EPA's Office of Underground Storage Tanks is considering modifying the guidance to include underground storage tank sites where petroleum compounds are the primary risk and biodegradation in subsurface media can be a dominant fate process. EPA's National Risk Management Research Laboratory (NRMRL) and the National Exposure Research Laboratory (NERL) are conducting research and providing technical assistance to EPA program offices, regional offices, and states in the area of vapor intrusion.