ASSESSMENT OF HUMAN EXPOSURE TO NATURALLY OCCURRING (UNPROCESSED) ASBESTOS AT THE CLEAR CREEK MANAGEMENT AREA, CALIFORNIA

The New Idria serpentenite ore body, located in the Southern Coast Ranges of California, is one of the largest asbestos deposits in the world at 22 kilometers (km) long and 6 km wide. Historically, the area has been extensively mined for chrysotile asbestos, mercury, chromite, and other commodities associated with serpentenite. The Clear Creek Management Area (CCMA), located on and around this ore body, is a popular 50,000 acre recreational area managed by the Bureau of Land Management (BLM). It provides 400-600 miles of unpaved vehicle routes and almost 3,000 acres of barren hill climbs for off-highway vehicle (OHV) users, as well as other recreational opportunities such as hiking, camping, hunting, and rock collecting.

Within the CCMA is a 30,000 acre area designated as a “Hazardous Asbestos Area”, due to elevated levels of naturally occurring (unprocessed) asbestos. The United States Environmental Protection Agency (U.S. EPA) and the BLM have long been concerned about potential health hazards associated with the generation and inhalation of airborne asbestos fibers by users of the area, particularly those operating OHV's on unpaved routes. U.S. EPA, in collaboration with BLM and the California EPA (DTSC), is in the process of gathering information to estimate asbestos exposure, as a basis for determining appropriate mitigation measures.

Air samples are being collected during both dry and wet seasons by individuals wearing personal monitors, while engaged in typical recreational activities. These activities include motorcycle riding, all terrain vehicle riding, sport utility vehicle driving, hiking, camping, and washing and vacuuming dusty vehicles. The exposure of child users is being specifically evaluated, by positioning monitors to mimic a child's breathing zone. Soil moisture and asbestos concentration along the user's route of travel are also being measured, to test whether these parameters correlate with airborne asbestos concentrations.