Throughout the past decade, the risk of subterranean toxic vapors intruding into indoor environments has been getting closer examination from a concerned public as well as from scientists and the environmental regulatory universe.
The model below depicts intrusion of volatile organic compounds (VOCs). Common sources of such vapors are chlorinated solvents from dry cleaning operations and petroleum products from underground storage tank systems. Some of these compounds are antagonistic to human health.
In 2004, the Department of Toxic Substances Control (DTSC) in the California EPA generated an interim Vapor Intrusion Guidance document providing a step-wise approach to assessing the risk to inhabitants of buildings at sites where subsurface contaminants could potentially enter the indoor environment as vapors.
In October of 2011, DTSC released an updated version of the Guidance, which incorporates new procedures for screening and evaluating potential risks.
In addition, DTSC created the Vapor Intrusion Mitigation Advisory on mitigation and remediation of vapor intrusion. The Advisory provides a framework for adequate decision-making to
- determine whether mitigation is appropriate,
- establish the proper mitigation system to implement, and
- ensure that the implementation is sustainable for the duration of mitigation.
Staff at our firm prepared a PowerPoint presentation outlining the main points of the Guidance and the Advisory.
The presentation is available as a PDF here.