In 2002 the United States Environmental Protection Agency's (USEPA) defined vapor intrusion as the migration of volatile chemicals in the subsurface into overlying buildings. Generally, mitigation implies an act of decreasing or reducing something.

However, if potential vapor intrusion risk has been identified for the occupants of future or existing buildings, then appropriate response actions dealing with the selection, design, and implementation of systems will need to be addressed.

In April 2009 the Department of Toxic Substances Control California Environmental Protection Agency (DTSC) released its "Vapor Intrusion Mitigation Advisory." It is designed to be used on sites "that may be impacted by soil vapor intrusion into outdoor air."

Although the advisory was designed primarily as a guide for the staff of the of Toxic Substances Control California Environmental Protection Agency it could very well be used to advantage by property developers, other agencies, community groups, environmental consultants, as well as other responsible parties.

The advisory describes mitigation alternatives that are designed to monitor or interrupt the vapor intrusion pathway in order to ensure the public's safety until the time that the volatile chemical concentrations that were shown to be evident in soil gas, soil, and/or groundwater have been confirmed to have been restored to levels of concentration that are below or at levels that are now considered to be safe for human exposure.

Included in the 77 page advisory are chapters entitled "Risk-Based Decision Making For Vapor Intrusion Sites", "Public Participation", "Vapor Intrusion Mitigation Methods", "Evaluation of Vapor Intrusion Mitigation Approaches", "Vapor Intrusion Mitigation System Design", "Vapor Intrusion Mitigation System Implementation." And there are 25 pages of additional resources and references.

If you ever felt as though you were lost in a maze while trying to figure out what various acronyms and abbreviations mean, then you will probably find that these additional pages will help to lead you to the answers you're seeking.

Another (older) source of information is The Vapor Intrusion Handbook. This handbook was developed by the Tri-Service Environmental Risk Assessment Work Group (comprised of the Departments of the Army, Navy, and Air Force). It was released by the Department of Defense (DOD) on April 3, 2009, although it is actually dated January 2009.

The handbook is designed to serve as a guide as well as a resource for remedial project managers who might be required to investigate the vapor intrusion pathway on either active and/or closed Army, Air Force, Marine Corps, and Navy bases as well as Formerly Used Defense Sites (FUDS).

The handbook is excellent and includes a substantial amount of valuable information. Within its pages you will find sections relating to health risk assessment, sampling and analysis, and mitigation measures.