In 1986, the California Air Resource Board (ARB) identified asbestos (which includes seven fibrous minerals) as a toxic air contaminant. In 1990, The ARB adopted an airborne toxic control measure (ATCM) that limited the asbestos concentration of serpentine rock used for surfacing to five percent. The ARB revisited the Asbestos ATCM in 2000; at which time, the allowable asbestos content was reduced to 0.25 percent. This regulation also relied on the use of geologic maps to identify areas where asbestos-containing materials would be most likely to be found. These areas were identified by the staff of the California Geologic Survey as the geographic units indicated as ultramafic (or ultrabasic) rock or geographic ultramafic rock units or GURUs. The control measure limited the used of any material originating from one of these geographic areas for surfacing purposes. The following year, the ARB adopted another Asbestos ATCM that regulated the dust-generated activities occurring in these GURUs that affected construction, grading, quarrying, and surface mining operations.

While the State Air Resources Board is charged with the development and adoption of airborne toxic control measures, the local air district must implement them. In the San Francisco Bay Area, that responsibility falls to the Bay Area Air Quality Management District. This posed a unique responsibility because this area is both highly developed and has many areas with outcroppings of serpentinite. To address this unique combination, the District identified the municipalities that were most likely to be affected by the Asbestos ATCM. Staff also developed easy-to-follow forms that (once completed and approved by the District) would serve as required dust mitigation plans for construction projects affected by the control measure. These forms were made available on our website.

To date, there have been a small number of construction projects that have been affected by the Asbestos ATCM. Some of these projects included the Third Street Light Rail Extension and the seismic retrofit of the Golden Gate Bridge. However, staff continually fields questions and addresses concerns regarding the impact of naturally occurring asbestos in such an urbanized area.