OCCURRENCE OF ASBESTOS ON NATIONAL FOREST SYSTEM ROADS, STANISLAUS NATIONAL FOREST, CALIFORNIA

Naturally occurring asbestos (NOA) is prevalent throughout California and has become a high priority issue for the Forest Service. Much of the work dedicated to NOA has focused on areas within geologic settings conducive to serpentine outcropping associated with chrysotile. The bundles of thin fibers within the chrysotile have been linked to several respiratory problems upon inhalation. The Stanislaus National Forest has a unique problem in that serpentinite aggregate has been utilized as surfacing material on the forest dating back to 1979. Review of timber sale contract files and discussions with forest staff initially identified 56 roads, totaling 264 miles. Field review confirmed 21 roads or 37% of the roads were surfaced with serpentine aggregate.

Evaluation of each road was conducted by standards outlined in Method 435 by the California Environmental Protection Agency Air Resources Board. A copy of the test method is available at the following site (http://www.arb.ca.gov/testmeth/vol3/M_435.pdf). A hazard threshold of 0.25% of NOA in field samples is the current standard. Sampling was conducted on one, one-mile road segment and was found to contain 7.8% asbestos, based on the CARB 435 Method. A total of 181 samples were collected for analysis and will be tested for asbestos content.

Examination of the samples, using a hand lens and microscope, found large quantities of chrysotile, throughout the serpentinite aggregate. Pending completion of lab analysis on the aggregate samples, it is believed that the asbestos content will be well above the current hazard threshold. The results of assessment will be considered in the Forest’s Subpart A, Travel Management Plan,. It is also recommended that all Forest personnel, contractors, the public and private organizations operating within the Stanislaus be notified of the potential for exposure in these areas. Recommendations to mitigate the hazard will include: removal of the material or capping of the aggregate, road closures, and decreased speed limits.