Ultramafic or serpentine rock, which often contains asbestos, has been used in surfacing applications subject to pedestrian, vehicular, and recreational use. Activity in areas with asbestos-containing rock or soil may create dust emissions containing asbestos fibers. Asbestos exposure primarily results from breathing in asbestos fibers, and less commonly from ingesting asbestos fibers. Asbestos fibers are too small to be seen by the naked eye. All types of asbestiform minerals are considered hazardous with no safe exposure level established for non-occupational exposures.
While exposure to low levels of asbestos for short periods of time is thought to pose minimal risk, asbestos fibers can penetrate body tissues and remain in lung or abdominal areas for a long time. Asbestosis is widespread scarring of lung tissue caused by breathing air contaminated with asbestos dust or fibers. Asbestos inhalation also can cause the two layers of membrane covering the lungs (the pleura) to thicken. The more a person is exposed to asbestos fibers, the greater the risk of developing asbestos-related diseases including lung cancer and rarely, mesothelioma - a rare cancer, mostly caused by asbestos, which may affect the pleura or peritoneum. The illnesses caused by asbestos may not be noticed for twenty years or more, with mesotheliomas usually developing 30 to 40 years after exposure. (Merck Manual of Medical Information, 1997, page 182)
For further information, visit the Health Effects of Asbestos website.
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Naturally Occurring Asbestos (NOA) deposits are most often found in ultramafic rock formations, often NOA is found in serpentine rock. Geologic maps prepared by the California Geologic Survey (formerly the California Division of Mines and Geology) show areas of higher probability for asbestos-containing rock within the broad zone of faults that follows the low foothills and lay in a south-east to north-west band. The Placer County communities of Auburn, Colfax, Meadow Vista, and Foresthill are among those that are within this fault band. Generally, the areas in Placer County that lay to the west of Folsom Lake and to the south of Wise Road are geologic areas that have a lower probability for the presence of NOA such as:
There are some isolated areas of higher probability for the presence of NOA within the Tahoe National Forest.
The identification of locations in Placer County that have the potential to contain NOA has been improved with the development of an enhanced 1:100,000 scale map by the California Geological Survey. This map denotes areas of Placer County that are more or less likely to contain NOA based on available soil and geologic studies, with some field verification. The enhanced map and accompanying report, Special Report 190, and information on how to purchase paper copies of the report are available at the California Geological Survey website. Enlarged maps have been prepared for different areas of Placer County where NOA may be found. These maps are available on the NOA Maps and Resources page.
The characterization of an area as having a lower overall probability of NOA presence means that although the likelihood is slight, in some instances NOA might be found within such an area. Similarly, locations in areas identified as being most likely to have NOA may not contain NOA.
NOA deposits have been found in rock other than ultramafic and serpentine rock; for example NOA deposits have been found in metavolcanic rocks such as the Copper Hill Volcanics in the Folsom vicinity. Metavolcanic rock formations are prevalent in areas to the northeast, north, and west of Auburn. Finally, in areas with sedimentary alluvial rock deposits such as those existing in western Placer County; it is possible that analytically detectable NOA may be found.
For several reasons, the District does not believe that activity-based monitoring by the District is necessary at this time. Currently, the U.S. Environmental Protection Agency (EPA) does not plan to conduct monitoring of this type in Placer County. Learn more on the Activity-Based Air Monitoring page.
The District believes that the best and most effective approach to minimizing and preventing impacts from naturally-occurring asbestos is a proactive program designed to minimize and control soil disturbance and thereby limit the release into the air of fine particulate matter, including any asbestos fibers that may be present. This approach is one that is endorsed by the conclusions of the Agency for Toxic Substances and Disease Registry's Health Consultation for El Dorado Hills, El Dorado County, and through the State Air Resources Board’s adoption of regulations that the District enforces to control and manage dust in areas where Naturally Occurring Asbestos (NOA) may be present.
Learn more on the Minimizing and Preventing NOA page.
Because there is no level of asbestos exposure established that is deemed to be without risk, and because of a latency period of 10 to 20 years or more for any signs or symptoms of asbestos-related disease to appear, precautions should be taken to minimize exposure to dust that potentially contains asbestos fibers. The Agency for Toxic Substances and Disease Registry (ATSDR) recommends these steps to reduce or prevent asbestos exposure in areas of naturally-occurring asbestos.