Naturally-Occurring Asbestos

This page provides requirements and information about naturally-ocurring asbestos. For information about asbestos requirements for building demolition/renovation, please click here.

Naturally-Occurring Asbestos (NOA)

Naturally-occurring asbestos may be found in at least 44 of California’s 58 counties, including Butte County. Asbestos is a naturally occurring fiber which is commonly found in ultramafic rock.  The asbestos fibers are released into the air when they are broken or crushed through man-made or natural processes. Asbestos has been identified by the State as a toxic air contaminant. Inhalation (breathing) is the main route of exposure and may cause lung cancer or cause other health hazards which may not become apparent until after many years.

Naturally-occurring asbestos, often found in serpentine rock formations, is present in foothill areas of Butte County. See this map for areas within Butte County with known formations that may contain naturally-occurring asbestos. Contact the District if you require more detailed information such as .kml or .shp files can be used in geospatial programs. The Butte County Air Quality Management District (District) implements the requirements of State’s Airborne Toxic Control Measures (ATCMs) for NOA.

In summary of the ATCMs requirements, if NOA is discovered prior to or when performing cleanup activities, owners/contractors must notify the District by the next business day and implement dust mitigation measures within 24-hours. The following dust mitigation measures are required during any construction or grading activities subject to this ATCM, regardless of work area size:

  • Construction vehicle speeds at the work site must be fifteen (15) miles per hour or less;
  • Prior to any ground disturbance and during work activities, sufficient water must be applied to the area to be disturbed to prevent visible dust from crossing the property line;
  • Storage piles must be kept adequately wetted, treated with a chemical dust suppressant, or covered when material is not being added to or removed from the pile;
  • Equipment must be washed down before moving from the property onto a paved public road; and,
  • Visible track-out on the paved public road must be cleaned using wet sweeping or a HEPA filter equipped vacuum device within twenty-four (24) hours.

Although there is an exemption for owners and tenants working on their own properties disturbing one (1) acre or less, following the control measures above is strongly recommended to protect public health.

The  two Asbestos ATCMs contains the specific requirements for various earthwork and aggregate operations.  The Asbestos ATCM for Construction, Grading, Quarrying, and Surface Mining ( requires the implementation of mitigation measures to minimize emissions of asbestos-laden dust. The Asbestos ATCM for Surface Applications ( restricts the asbestos content of material used in surfacing applications such as unpaved roads, parking lots, driveways, and walkways.

Additional information is available from the following websites:

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