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Naturally Occurring Asbestos


Naturally-occurring asbestos (NOA) may be found in at least 44 of California's 58 counties. Asbestos is the name for a group of naturally-occurring silicate minerals. Exposure to asbestos may result in asbestos fibers being inhaled or ingested, which over time and in some cases, may result in damage to the lungs or membranes that cover the lungs, leading to illness or even death.

Naturally-occurring asbestos, often found in serpentine rock formations, is present in several foothill areas of Placer County. When naturally-occurring asbestos-containing material is disturbed asbestos fibers may be released and become airborne, thereby creating a potential health hazard.

The brochure Asbestos-containing Rock and Soil: What California Homeowners Need to Know is available for homeowners or renters who are concerned about naturally occurring asbestos.

Note: The Placer County Air Pollution Control District is NOT delegated for Asbestos NESHAP enforcement, and accordingly notices concerning asbestos in construction and demolition should be referred to the California Air Resources Board.  Any questions regarding requirements for asbestos in construction materials should be made to the staff of the Air Resources Board or the staff of the U.S. Environmental Protection Agency.

Construction and Grading Requirements in NOA Areas

Naturally-Occurring Asbestos Dust Mitigation Plan (ADMP) Guidance has been developed to assist in the enforcement of the State’s Asbestos Airborne Toxic Control Measure for Construction, Grading, Quarrying, and Surface Mining Operations, and APCD Rule 228, FUGITIVE DUST requirements. The District requires that if an area to be disturbed is greater than one acre, and an owner/operator is subject to asbestos ATCM requirements, an Asbestos Dust Mitigation Plan must be submitted to the Air Pollution Control Officer (APCO). The Guidance uses the Enhanced Map by CGS and its derivatives to determine if an Asbestos Dust Mitigation Plan is required. Use of the ADMP Guidance Application form is encouraged as submission of an original plan will be subject to increased fees due to additional review time required in the approval process. For further information, follow the link to the Construction and Grading in NOA areas.

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Where are NOA deposits, or rock formations that may contain NOA, located in Placer County?

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. Roseville, Granite Bay, Rocklin, Lincoln, Loomis, Penryn, and Newcastle lay within these geologic areas. 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 at the link NOA Maps and Resources.

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.

Considering the findings of the U.S. Environmental Protection Agency (U.S. EPA) and the Agency for Toxic Substances and Disease Registry (ATSDR) activity-based air monitoring in El Dorado Hills in El Dorado County, will similar monitoring be conducted by the District?

For several reasons, the District does not believe that activity-based monitoring by the District is necessary at this time. Currently, the U.S. EPA does not plan to conduct monitoring of this type in Placer County.

The activity-based air monitoring conducted at Oak Ridge High School in El Dorado Hills by the U.S. EPA and ATSDR was intended to determine if activities (such as playing baseball, playing soccer, and jogging), and the associated disturbance of dust while performing the activities, increased exposure to asbestos fibers over background reference sampling. The area is known to have NOA-containing materials and NOA deposits. The results from the sampling indicate that the disturbance of dust-containing asbestos fibers will result in increased air concentrations of up to 43 times that of fiber counts for reference samples taken without activities occurring.

The U.S. EPA has stated that it is not currently possible to accurately assess the health risk for El Dorado Hills’ residents from the types of exposures that were observed in its study. Furthermore, the U.S. EPA has stated that a health assessment was not the purpose of the studies, but the results are of concern because of the potential for long-term development of asbestos-related diseases. Because the ATSDR's study was restricted to assessing the potential health risks contingent on activity-based sampling for NOA at Oak Ridge High School, in El Dorado Hills, the ATSDR was subsequently prompted by members of the El Dorado Hills community to determine what this finding meant to their health, and what they should do to protect their health.

To answer these questions for the community as a whole, the ATSDR used the EPA sampling results to estimate how much NOA an El Dorado Hills resident might breathe in throughout life. Several different risk assessment calculation methods were then compared to get a general sense of the risk of developing asbestos-related cancers from these exposures. Finally, results of additional studies on NOA in the El Dorado Hills area were examined.

The ATSDR concluded that while the predicted risks were high enough to warrant preventive measures, the risk of disease from asbestos exposure was difficult to predict. The ATSDR reached two important conclusions in the recently issued Health Consultation;

Conclusion 1: Breathing in naturally occurring asbestos (NOA) in the El Dorado Hills area, over a lifetime, has the potential to harm people’s health.

Conclusion 2: A health study of the community of El Dorado Hills would not provide helpful information at this time.

The ATSDR recommends that El Dorado County continue to enforce state and local dust regulations to limit people's potential exposure to asbestos, and that the county continue to provide the community information about where naturally-occurring asbestos is found so that people can avoid it or minimize their exposure during normal activities. The ATSDR also recommends that the state of California continue to monitor asbestos-related cancer incidence rates in the area in the event an increase should occur. The ATSDR Health Consultation for Public Comment – El Dorado Hills, California may be found here.

Consideration of the findings of the U.S. EPA and ATSDR from the air sampling studies conducted in El Dorado Hills, has led the District to the following conclusion regarding the need for activity-based sampling; In areas where NOA is known to be present in the soil and in surrounding areas, activity-based sampling would likely indicate an increase in exposures due to dust and soil being disturbed. However, as there are no means to evaluate the increased health risk from such increased exposures, little would be gained by the performance of such sampling. It is simpler and more direct for the assumption to be made that asbestos fibers may be present in dust and soil in areas where NOA is known to be present or more likely to be found, and to direct efforts and available resources toward reducing potential exposures to the fibers.

Air sampling conducted by the California Air Resources Board (CARB) in 1999 found low, but detectable, asbestos fiber concentrations at locations in Foresthill and Auburn. While paving of McKeon-Ponderosa Way, in Foresthill, has undoubtedly reduced dust disturbance, the results supports the District's reasonable conclusion that where NOA is found you are likely to find some asbestos fibers in the air. There is no level at which exposure to asbestos fibers is deemed to be free of risk. Since activities that disturb dust and soil that potentially contains NOA fibers will likely increase the concentration of fibers in the air, precautions should be taken to either minimize participation in the activity or to minimize dust disturbance for the activity, or both.

For further information, follow the link to the U.S. EPA Studies in El Dorado Hills.

Information on the ATSDR's studies in El Dorado Hills is available at the link El Dorado County Air Quality Management District.

For information regarding asbestos concentrations follow the link to the Air Monitoring for NOA in Placer County.
(NOTE: The PCAPCD has moved since the sampling was conducted, that is in above link. The location of the sampling was at
11464 "B" Avenue, Auburn)

What is being done to minimize the disturbance of NOA deposits, or rock formations that may contain NOA, in Placer County?

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 ATSDR’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 NOA may be present.

Since 1986 the District has had a control measure restricting the use of asbestos-containing materials in road surfacing applications, one of the earliest adopted in the State, and far in advance of the State Air Resources Board adoption in 1990 of the Asbestos Air Toxic Control Measure for Asbestos-Containing Serpentine Asbestos (revised and re-titled in 2001 as the Asbestos Airborne Toxic Control Measure for Surfacing Applications).

Among other steps taken independently by the District is the adoption of a local dust control regulation, RULE 228, FUGITIVE DUST, in 2003 that is one of the most stringent in the state. This local regulation goes beyond the state's measures by providing standards for the control of sources of fugitive dust, including dust from construction activities, and is not limited in applicability to areas where NOA is found.

Recently, a Dust Control Plan Instructions and Application document developed to assist in the enforcement of RULE 228 requirements has been finalized with an effective date of May 1, 2010. The District requires that if an area to be disturbed is greater than one acre, and if established as a Condition of Approval of a discretionary permit, a Dust Control Plan is required. Use of the Dust Control Plan Instructions and Application form is encouraged as submission of an original plan may be subject to increased fees if additional review time is required in the approval process.

In areas identified as having a higher probability for the presence of NOA and where NOA, or rock potentially containing NOA is known to be located, the District enforces the implementation of the State's Asbestos Airborne Toxic Control Measure for Construction, Grading, Quarrying, and Surface Mining Operations (ATCM). Recently, a Naturally-Occurring Asbestos Dust Mitigation Plan (ADMP) Guidance intended to assist in the enforcement and implementation of the State’s Asbestos ATCM and District Rule 228, has been finalized with an effective date of May 1, 2010. The Guidance contains an Asbestos Dust Mitigation Plan Application form that will serve as the applicant’s Asbestos Dust Mitigation Plan upon approval by the District. Use of the ADMP Guidance Application form is encouraged as submission of an original plan will be subject to increased fees due to additional review time required in the approval process.

The District recognizes that neither the fugitive dust rule nor the State’s asbestos control measures are effective without dissemination of the requirements to construction companies and enforcement. Beginning in fiscal year 2002-2003 the District enhanced its presence in the field by adding staff to conduct patrols throughout the County for dust violations and to visit construction sites.

The District has advised all land use and public works departments of all Placer County jurisdictions of the requirements for NOA control in land development and construction, and has allied with willing jurisdictions to enforce the dust control and NOA control requirements. The District has also conducted out-reach to construction firms operating in Placer County. Among the public out-reach efforts has been the development of an informational brochure for homeowners and renters, and a contract with the California Geological Survey of the Department of Conservation to develop improved maps of potential naturally-occurring asbestos areas in Placer County to aid the public in identifying these areas of concern. The District seeks to further educate the public and to partner with Placer County jurisdictions to more effectively manage both NOA and dust.

Members of the public can aid the District in controlling dust, in general, by reporting any dust from construction sites and from other activities where soil is disturbed. In particular, it is of concern to the District if the dust crosses a property line or a public road, or if a plume of dust rises into the air. Contact the District at 530-745-2330. After hours or on weekends, a call to that number will be routed to the Placer County Sheriff's Dispatch Office, to notify District on-call staff.

What is asbestos exposure and why is asbestos exposure a concern?

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, pg. 182)

For further information, follow the link to Health Effects of Asbestos.

What can I do to reduce my exposure and that of my family to NOA fibers?

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 ATSDR recommends these steps to reduce or prevent asbestos exposure in areas of naturally-occurring asbestos:


  • Walk, run, hike, and bike only on paved trails.

  • Play only in outdoor areas with a ground covering such as wood chips, mulch, sand, pea gravel, grass, asphalt, shredded rubber, or rubber mats.

  • Pave over unpaved walkways, driveways, or roadways that may have asbestos-containing rock or soil.

  • Cover asbestos-containing rock or soil in gardens and yards with asbestos-free soil or landscape covering.

  • Pre-wet garden areas before digging or shoveling soil.

  • Drive slowly over unpaved roads.


  • Keep pets from carrying dust or dirt on their fur or feet into the home.

  • Remove shoes before entering your home to prevent tracking in dirt.

  • Use doormats to lower the amount of soil that is tracked into your home.

  • Keep windows and doors closed on windy days and during nearby construction.

  • Use a wet rag instead of a dry rag or duster to dust.

  • Use a wet mop on non-carpeted floors.

  • Use washable area rugs on your floors and wash rugs regularly.

  • Vacuum your carpet

  • Additional Information Resources

    Additional websites with information on asbestos include: