Vapor Intrusion

Vapor intrusion is the migration of volatile chemicals from the subsurface into overlying buildings. Volatile chemicals may include volatile organic compounds, select semivolatile organic compounds, and some inorganic analytes, such as elemental mercury and hydrogen sulfide. Vapor intrusion requires three components: a source, an inhabited building, and a pathway from the source to the inhabitants. Vapor intrusion has become a significant environmental issue for regulators, industry leaders, and concerned residents.

Degradation of the indoor air quality can cause fear and anxiety among building occupants, businesses, and other property owners. Nationwide, volatile organic contaminants in subsurface soil and groundwater are a recognized problem. Often, this contamination exists beneath occupied lands. Indoor air contaminant levels may be significant enough at sites with subsurface contamination to cause immediate regulatory action in some cases and drive remediation in others.

Current lack of knowledge about indoor air issues and evaluation techniques may oversimplify the problem and may cause air quality investigations and subsequent risk assessments to understate or overstate the problem. Indoor air quality is overlooked in many environmental site investigation and soil/groundwater plume contamination scenarios. Lack of knowledge regarding indoor air quality issues and cost considerations tend to contribute to the omission of indoor air sampling and evaluation.

Other organizations have generated various general guidance documents, trainings, and forums. However, no specific, concise documents addressing in detail specific sampling, characterization, and remediation technologies for indoor air have been published. The ITRC Vapor Intrusion Team—composed of representatives from 19 state environmental agencies, 12 environmental companies, and 4 federal agencies (including EPA)—developed an ITRC Technical and Regulatory Guidance document, Vapor Intrusion Pathway: A Practical Guide (VI-1, 2007), and a companion document, Vapor Intrusion Pathway: Investigative Approaches for Typical Scenarios (VI-1A, 2007). Both of these documents are summarized in an Internet-based training course for regulatory agencies and practitioners alike. This training provides an overview of the vapor intrusion pathway and information on the framework (evaluation process), investigative tools, and mitigation approaches. The training course uses typical scenarios to illustrate the process.

These team products facilitate an increased awareness of indoor air concerns and will help address them up front in an environmental project instead of later, when the project is considered closed. This approach reduces investigation costs by eliminating the need to reopen an investigation and/or revise remedial strategies for a project after the fact.