That beautiful unpaved country road could be hazardous to your health if it was surfaced with serpentine rock. Associated with earthquake fault zones and mountainous regions, serpentine can have a high asbestos content. When automobiles travel down an asbestos-contaminated road, they kick up high levels of dust, releasing dangerous asbestos fibers into the air. Asbestos on roads can also be stirred up by wind and weathering.
Serpentine rock occurs naturally in the mountains of the western United States and on the East Coast in parts of Vermont, New York, and New Jersey. In California, serpentine is common in the Coastal ranges, the Klamath Mountains, and the Sierra foothills. It is also found in Greece, Turkey, Cyprus, Corsica, and South Africa. Problems may arise in any of these places if rural roads are surfaced with crushed serpentine rock.
An example of the challenges posed by serpentine-surfaced roads may be found in El Dorado County, California. In this area of naturally-occurring serpentine, roads and driveways are surfaced with serpentine. And serpentine may be disturbed during road building, home construction, and even in gardening. The California Air Resources Board has been conducting background air monitoring, discovering levels of asbestos that could greatly increase the rate of lung cancer in the county. (Asbestos deposits in El Dorado Hills Pose Construction, Community Dangers).
The Board uses a model called CALSRAM to predict public exposure to asbestos from unpaved roads surfaced with crushed serpentine rock (California Air Resources, Method 435, Asbestos Content of Serpentine Aggregate). The method requires random sampling and an overall sampling plan. It specifies types of augers, shovels, and other equipment.
On existing serpentine-covered roads, the California Air Resources Board suggests reducing asbestos dust by water wetting, speed controls, or covering the roads with 2 to 4 inches of non-asbestos rock. Better control methods, according to the Board, include chemical sealant, dust suppressants, chip seals, petroleum sealant, or asphalt cement paving (California Air Resources Board, Ways to Control Naturally-Occurring Asbestos Dust). Based on public concern about asbestos-contaminated roads and the known dangers of asbestos exposure, the Board lowered the amount of asbestos allowed in rocks used for road surfacing and ornamental applications in April 2001.