The California Department of Toxic Substances Control released new guidance April 28 to help developers, environmental consultants, regulators, and others prevent volatile organic gases at contaminated sites from seeping into homes and other buildings.

The department and state water quality officials will preview the document, Vapor Intrusion Mitigation Advisory, and related guidance documents at workshops June 3-4 at California Environmental Protection Agency headquarters in Sacramento and June 9-10 at the Water Resources Control Board office in Los Angeles. The agency will accept comment on the document through Oct. 31.

The new document builds on a 2005 guidance document that recommended an approach for evaluating potential vapor intrusion pathways at cleanup sites and outlined mitigation measures, according to the department. The department said it is planning to reissue the earlier document, Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion into Indoor Air, later this year.

The newly released document provides a framework for determining if mitigation is appropriate for a project site and selecting site-specific mitigation technologies for existing or future buildings. It also outlines steps for managing risks to current and future building occupants and provides guidance for public participation-related activities.

As industrial solvents, petroleum products, and other volatile chemicals spilled at contaminated sites evaporate, they produce vapors that can travel up through soil.

The vapors can enter nearby buildings through crawl spaces and cracks and other openings in foundations and contribute to unhealthy levels of the chemicals in indoor air.

Copyright 2009, The Bureau of National Affairs, Inc.