Naturally Occurring Asbestos: 

Approaches for Reducing Exposure 

Purpose and Intended Audience 

This fact sheet provides an overview of approaches for reducing exposures to naturally occurring asbestos (NOA). It is intended to make 

general information about management options available to state and 

local government officials, project managers, and environmental professionals. The information should serve as a starting point for identifying 

current NOA management practices. In general, selecting an appropriate 

approach to reduce NOA exposure should be determined on a locationspecifi c basis. 

Information contained in this fact sheet was obtained from the currently available literature, including state and local government publications. To obtain more information on NOA management 

approaches, including their performance and frequency of use, refer to the resources provided at the 

end of this fact sheet. 

NOA management 

approaches can reduce 

but may not completely 

eliminate potential 

exposures to naturally 

occurring asbestos. 

Naturally Occurring Asbestos 

NOA occurs in rocks and soil as a result of natural geological processes. Natural weathering or 

human activities may disturb NOA-bearing rock or soil and release mineral fibers into the air, which 

pose a greater potential for human exposure by inhalation. 

The U.S. Geological Survey (USGS) has an ongoing project to map the locations of historical 

asbestos mines, former asbestos exploration prospects, and natural asbestos occurrences. At least 35 

states have reported NOA locations. To locate NOA areas in a specific part of the country, begin by 

consulting the USGS reports (see below) and contact a state geologist. 

U.S. Geological 

Survey 

Eastern United States http://pubs.usgs.gov/of/2005/1189/ 

Central United States http://pubs.usgs.gov/of/2006/1211/ 

Rocky Mountain States http://pubs.usgs.gov/of/2007/1182 

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California 

Geological 

Survey 

Asbestos Reports, Maps and Guidelines for Geologic Investigations 

http://www.conservation.ca.gov/cgs/minerals/hazardous_minerals/asbestos/ 

Pages/Index.aspx 

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This fact sheet is intended solely to provide general information on approaches that may be useful when addressing naturally occurring asbestos 

(NOA). It is not intended, nor can it be relied upon, to create any rights enforceable by any party, including any party in litigation with the United States. 

EPA considers NOA to be in an altered form if it has been disturbed by human activity; NOA is not considered to be altered if modified solely through 

naturally occurring processes or phenomena, from a location were it is naturally found. This fact sheet may be revised periodically without public 

notice. Use or mention of trade names does not constitute endorsement or recommendation for use. 
 

 

In this fact sheet, NOA does not refer to commercially processed, asbestos-containing material, such 

as insulation and fire protection in buildings or automobile brake linings. Information about commercial asbestos-containing products is available in other publications, including the resources mentioned 

on EPA’s asbestos Web page http://www.epa.gov/asbestos. 

Approaches for Mitigating Exposures to NOA 

The following general approaches to mitigate inhalation exposures to NOA are aimed at reducing 

NOA releases from rock or soil into the air: 

• Leave NOA material in place and undisturbed 

• Cover or cap NOA material 

• Limit dust generating activities 

• Excavate and dispose of NOA material 

Depending on the situation, a combination of engineering controls, work 

practices, and institutional (administrative) controls may be needed to 

implement an approach and reduce potential exposures to NOA. Selecting 

an approach depends on factors including: 

Approaches for 

reducing NOA exposure 

are similar to practices 

used for asbestoscontaining materials in 

commercial applications. 

• Accessibility of NOA (ground surface vs. below ground surface) 

• Types of activities that disturb NOA (construction project vs. gardening) 

• Climate and weather conditions 

• Current and future land uses 

• Technical and administrative feasibility of the approach 

Typical engineering controls involve the use of covers and caps, vegetation, fencing, landscaping, and 

in some conditions, the application of water to suppress dust. Local factors, such as climate, influence 

the extent to which these approaches are implemented. For example, areas with dry or windy conditions may need more dust control than those with humid or less windy conditions. 

Common work practices include limiting activities on NOA-containing areas, reducing driving speed 

on unpaved roads that may contain NOA, and cleaning vehicles driven over NOA. For example, 

during road construction or maintenance activities on unpaved areas where NOA is present, the Asbestos Airborne Toxics Control Measure (ATCM) for Construction, Grading, Quarrying, and Surface 

Mining Operations of the California Air Resources Board (ARB) requires that vehicle speeds not 

exceed 15 miles per hour.1 Worker health and safety measures that include respiratory protection may 

be warranted. For information, consult with Occupational Safety and Health Administration Asbestos 

Standards for the General Industry and Asbestos Standards for the Construction Industry (http://www. 

osha.gov/SLTC/asbestos/hazards.html). 

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Examples of Engineering and Work Practices that Reduce Exposure to NOA
 

Excavation, 

Grading, or 

Utility Work at 

Construction 

Projects 

Wet road surfaces with water using trucks, hoses, or sprinklers1 

Wet piles of excavated material and cover them with tarps, plastic sheeting, 

or other items1 

Continuously mist the work area1 

Install wind barriers around the work area1 

Clean or decontaminate equipment and vehicles to ensure that no equipment 

or workers track soil out of the work area (a gravel pad, tire shaker, or wheel 

wash system may be used to clear soil from vehicles)1 

Wet the work area using a spray system attached directly to rock cutting 

or drilling equipment, such as a fine-mist sprayer or a variable-rate fogger 

nozzle (similar to those used in fire fighting)2 

Excavate utility trenches to an adequate depth and backfill them with clean 

soil so that future repair work will not need excavation into potential NOAcontaining materials3 

When transporting NOA-containing materials, avoid overloading trucks; 

keep the material below the top of each truck compartment and cover 

material with a tarp4 

Limit personnel and vehicle access to the work area5 

Identify NOA-containing areas with signs2 

Reduce driving speed1 

Reduce drilling or excavating speeds6 

Excavate during periods of calm or low winds1 

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Roads and 

Parking Areas 

(unpaved and 

gravel roads) 

Cover roads with non-NOA-containing rock, chemical sealants or dust 

suppressants, chip seals, limestone aggregate, petroleum sealants, or asphalt 

cement paving1, 7, 8 

Wet road surfaces with water1 

Install windbreaks or berms1 

Reduce driving speed1 

Avoid dusty areas, especially in windy conditions1 

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3
Around 

Communities 

(playgrounds, 

ball fields, 

pathways, and 

gardens) 

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Cover areas of rock and soil with clean soil, rock, vegetation, or other 

material (see next section, General Considerations for Using Covers or 

Caps)3, 9 

Pave over unpaved walkways, driveways, or roadways containing NOA1, 10 

Landscape areas with vegetation, such as NOA-tolerant plants, and add a 

layer of organic mulch or NOA-free soil. Water plants often until they are 

established to minimize erosion9 

Water garden areas before digging9 

Keep windows and doors closed on windy days and during periods when 

nearby rock or soil may be disturbed, such as during construction9 

Limit track-in by using entryway (door) mats, and wipe down pets before 

they enter buildings to reduce the amount of soil tracked indoors4, 9 

Allow children to play in outdoor areas only if the area has a ground 

covering, such as wood chips, mulch, sand, pea gravel, grass, asphalt, 

shredded rubber, or rubber mats4 

Relocate outdoor activities to areas that do not contain NOA (walk, run, hike, 

and bike only on paved trails)4 

Avoid dusty areas, especially in windy conditions11 

General Considerations for Using Covers or Caps 

One of the most common engineering controls is to place a cover system over the NOA. Cover materials may include clean soil or rock, concrete, chemical sealants or dust suppressants, chip seals, limestone 

aggregate, petroleum sealants, asphalt paving, geotextiles, wood chips, mulch, sand, pea gravel, shredded rubber, rubber mats, and vegetation. 

The complexity of cover systems can vary from simple (e.g., a single soil layer) to complex (e.g., multiple layers of varying materials). Several factors, including cover material properties and site characteristics, affect the type of cover system appropriate for a particular area. 

The availability of materials may influence the type of cover used. Materials that are readily available 

and close to the NOA area may be more desirable and cost effective than materials found farther away. 

For example, artificial turf and other imported materials may be more expensive than locally available 

soils. The cover material will likely need to be assessed for NOA or other undesirable constituents. 

Expected lifetime, maintenance, and monitoring requirements also affect the cost of covers. 

The slope of the NOA area may influence the type and thickness of the cover material used. For 

example, steep slopes may need vegetation or shotcrete (concrete or mortar sprayed onto a surface with 

a pressurized hose) to promote slope stabilization. Steep slopes typically have a higher potential for 

erosion and therefore may demand thicker cover material. 

The thickness of the cover material should provide a safety factor sufficient to ensure that airborne 

releases will not occur. Thicker covers may be needed in areas where there is a signifi cant potential 

for erosion. The surface of a cover should protect against erosion by wind and rain. Materials used for 

erosion control typically include a layer of topsoil and vegetation. In areas where adequate vegetation is 

not possible, gravel, admixtures, or riprap may be used for the surface layer. The thickness of the cover 

may also depend on the presence of other cover components, such as irrigation lines. 

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A geotextile, which is a geosynthetic material made of polymer fabric, may be placed below the cover 

material to mark the presence of NOA and serve as an erosional indicator. Geotextiles also can provide 

protection, reinforcement, drainage, and separation when applied to the soil surface or between layers 

of materials. The California Department of Toxic Substances Control (DTSC) recommends that landscaped areas and play fields at schools include a geotextile marker covered by sufficient cover material 

to provide an effective barrier to reduce NOA exposures.3 Placement of geotextile markers will demand 

additional time and expertise. 

Long-Term Management Approaches 

For long-term management of areas with NOA, institutional controls (ICs) and a maintenance plan may 

be desirable. In areas where NOA poses potential health concerns, local and state government officials 

should consider providing educational material to supplement engineering approaches for reducing 

exposures to NOA. The Agency for Toxic Substances and Disease Registry has developed a fact sheet 

about asbestos and NOA for the general public entitled “Asbestos and Health: Frequently Asked Questions.”4 

Institutional Controls 

Generally, ICs are administrative or legal mechanisms that are designed to 

help minimize the potential for human exposure to contamination They also 

protect the integrity of the engineering measures. ICs are generally divided 

into four categories: 

•	 Government controls include laws and permits (such as local zoning 

laws and permits required for excavating or digging). Work that may 

disturb NOA-containing soil may require government approval and may be subject to local or 

state construction guidelines. In California, the ATCM of the California ARB requires owners and 

operators to notify the local air quality management district within one business day of discovering 

NOA, serpentine mineral, or ultramafic rock in an area to be disturbed by construction, grading, 

quarrying, or surface mining operations.1

 In Virginia, the Fairfax County Health Department requires 

a compliance plan that includes air monitoring to ensure effective dust control during construction in 

areas containing NOA.2 

For additional 

information about ICs, 

refer to the Land Use 

Controls Web site at 

http://www.lucs.org 

•	 Proprietary controls include property use restrictions based on private property laws, such as land use 

easements or covenants. 

•	 Enforcement tools include legally binding documents that require individuals or companies to conduct 

or prohibit specifi c actions. 

•	 Informational devices include deed notices, public advisories, and other measures (such as warning 

signs and worker health and safety awareness training) that alert and educate people about an area. 

Maintenance Plan 

A maintenance plan can help ensure that engineering controls and work practices remain effective. In 

California, for example, DTSC and school districts enter into an agreement to develop and implement 

an approved long-term operation and maintenance plan under DTSC oversight. These plans generally 

contain information about the following topics:3 

• Building locations, utility line locations, and the thickness of cover material across the area 

• Routine inspections 

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• Maintenance work, including erosion and storm water control 

• Procedures for repairing cover damage 

• Monitoring activities, such as perimeter or personal air monitoring 

• Reporting format and frequency 

• Restrictions on future activities that may expose NOA 

• Management of imported soil and future excavation or trenching activities 

Additional 

Information 

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Agency for Toxic Substances and Disease Registry - http://www.atsdr.cdc.gov/NOA 

California Air Resources Board - http://www.arb.ca.gov/toxics/asbestos/asbestos.htm 

El Dorado County, California - http://www.co.el-dorado.ca.us/emd/apcd/asbestos.html 

Fairfax County, Virginia - http://www.fairfaxcounty.gov/hd/asb 

Sacramento County, California - http://www.airquality.org/compliance/ 

asbestosNaturallyOccurring.shtml 

U.S. Environmental Protection Agency - http://www.epa.gov/asbestos/pubs/clean.html 

References
 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

California Environmental Protection Agency (Cal/EPA) Air Resources Board (ARB). 2002. Asbestos 

Airborne Toxic Control Measure for Construction, Grading, Quarrying, and Surfacing Mining 

Operations. Final Regulation Order. Section 93105. July 22. http://www.arb.ca.gov/toxics/atcm/ 

asb2atcm.htm 

Fairfax County Health Department. Undated. “Control and Prevention of Asbestos Exposure from 

Construction in Naturally Occurring Asbestos.” http://www.fairfaxcounty.gov/hd/asb/pdf/tbrdpubfin.pdf 

Cal/EPA Department of Toxic Substances Control (DTSC). 2004. Interim Guidance: Naturally 

Occurring Asbestos (NOA) at School Sites. September 29. 

http://www.dtsc.ca.gov/Schools/upload/SMBRP_POL_Guidance_Schools_NOA.pdf 

Agency for Toxic Substances and Disease Registry. Undated. “Asbestos and Health: Frequently 

Asked Questions.” U.S. Department of Health and Human Services. 

http://www.atsdr.cdc.gov/NOA/Asbestos-and%20Health.pdf 

El Dorado County. 2003. Naturally Occurring Asbestos and Dust Protection. Ordinance. Chapter 

8.44. June 12. http://www.co.el-dorado.ca.us/emd/apcd/PDF/Naturally_Occuring_Asbestos_June_ 

12.pdf 

Fairfax County Health Department. Undated. “Basic Elements for a Naturally Occurring Asbestos 

Compliance Plan.” http://www.fairfaxcounty.gov/hd/asb/pdf/asb50.pdf 

Cal/EPA ARB. 2002. “Fact Sheet #3: Ways to Control Naturally-Occurring Asbestos Dust.” January. 

http://www.arb.ca.gov/toxics/asbestos/3control.pdf 

Cal/EPA DTSC. 2005. “DTSC Recommends Resurfacing of Serpentine Gravel Roads Based on 

Garden Valley Study.” April. http://www.dtsc.ca.gov/SiteCleanup/Projects/Garden_Valley.cfm 

Cal/EPA ARB. 2002. “Asbestos-Containing Rock and Soil – What California Homeowners and 

Renters Need to Know.” Compliance Assistance Program. CAP 03-035. http://www.arb.ca.gov/cap/ 

pamphlets/asbestosbrochure.pdf 

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10. Cal/EPA DTSC. 2006. “Fact Sheet: Recommended Housekeeping Activities to Reduce Exposure 

to Naturally-Occurring Asbestos in Schools.” October. http://www.dtsc.ca.gov/Schools/upload/ 

Recommended_Housekeeping_for_NOA_102306.pdf 

11. University of California Cooperative Extension. Undated. “Lake County Serpentine Landscape 

Demonstration Garden.” Asbestos Serpentine Soils Education Program. http://www.capcoa.org/noa/ 

%5B5%5D%20Lake%20County%20Serpentine%20Landscaping.pdf 

List of Acronyms 

ARB Air Resources Board 

ATCM Airborne Toxic Control Measure 

DTSC Department of Toxic Substance Control 

ICs institutional controls 

NOA naturally occurring asbestos 

USGS U.S. Geological Survey 

Office of Superfund Remediation EPA 542-F-08-001 

and Technology Innovation March 2008 

(5204P) www.epa.gov 

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