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Potential Amendment to California Vapor Intrusion Law

Proposed Development of a Vapor Intrusion Amendment

On April 28th, the California State Water Resources Board (Board) held an open forum to hear public comments on the proposed development of a vapor intrusion amendment. The Amendment is being created to develop a formal policy regarding the investigation and assessment of vapor intrusion as it relates to the Site Cleanup Program. Under the current program, vapor intrusion issues are being handled on a site-by-site basis, using applicable guidelines inconsistently.

What is Vapor Intrusion?

As an industry, we have learned more about the potential effects of vapor intrusion, especially those that exist on contaminated sites being redeveloped. Contaminated sites within the State of California have been found to have probable vapor intrusion issues, it is even possible for it to originate from an adjacent building. Vapor intrusion occurs when gases from contaminated soil or groundwater seep through cracks or openings typically in the foundation of a building. Vapor intrusion can be the result of many chemicals, including volatile organic compounds (VOCs), such as trichloroethylene (TCE), tetrachloroethene (PCE) and benzene, select semi-volatile organic compounds, such as naphthalene, elemental mercury, and some polychlorinated biphenyls and pesticides. Vapor exposure can be extremely harmful to humans and can, in some cases, cause liver, kidney, and central nervous system damage. Additionally, many of are considered probable carcinogens.


While the Environmental Protection Agency (EPA) provides basic information about vapor intrusion, the actual rules and regulations are generally created and reinforced on the state level. Certain states, like Michigan, have recently tightened regulations to the degree that sites that had been considered previously ‘closed’ may have to be reopened, re-evaluated, and/or further remedied. California is moving towards the Vapor Intrusion Amendment (Amendment) to State Water Board Resolution 92-49 (amended in 1994 and 1996). The process is going through the Substitute Environmental Documentation process, thus enabling public input through the process. Scoping meetings are in process, language developed for public comment and Board hearings, and thereafter an anticipated adaption in March 2024.