Living Near Naturally Occurring Asbestos Deposits: Homeowner Guide

Asbestos does not only come from building materials. It forms naturally in rock and soil across at least 26 US states, and homeowners in those areas can be exposed without ever touching a ceiling or floor tile. If you live near serpentine rock outcrops, unpaved roads through ultramafic terrain, or certain mountain regions, disturbing the soil around your home can release asbestos fibers. The risk is real, but manageable.

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What Naturally Occurring Asbestos Is

Naturally occurring asbestos (NOA) refers to asbestos mineral fibers that form in the earth rather than in manufactured products. The US Geological Survey has identified NOA deposits in dozens of states, concentrated in regions underlain by serpentinite, ultramafic, and mafic rock.

The most common types found naturally:

• Chrysotile (white asbestos): Found in serpentine rock formations throughout California's Coast Ranges and Sierra Nevada foothills.
• Tremolite: Found in talc deposits, marble, and dolomite formations. Libby, Montana's vermiculite mine is the most documented US case of tremolite contamination.
• Actinolite and anthophyllite: Found in metamorphic rock in Appalachian states including Virginia, North Carolina, and Pennsylvania.

Per the EPA's guidance on naturally occurring asbestos, these fibers behave the same way as manufactured asbestos once airborne. The body cannot distinguish them by source.

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Which States Have the Highest NOA Risk

California has the most thoroughly documented NOA problem in the country. The El Dorado Hills community east of Sacramento received an EPA health study after residents raised concerns about asbestos released during residential development. Serpentine rock underlies much of the Sierra Nevada foothills, the Mother Lode region, and coastal ranges from Oregon to San Diego County.

California is not alone. Other high-risk states include:

• Montana: Lincoln County and the Libby area, where tremolite-contaminated vermiculite was mined and distributed to households for decades. The Agency for Toxic Substances and Disease Registry (ATSDR) declared Libby a public health emergency in 2009.
• Virginia: The Piedmont region contains significant serpentinite formations. Parts of Fairfax, Fauquier, and Albemarle counties have documented NOA.
• North Carolina: The western mountain counties have tremolite and actinolite occurrences in metamorphic rock.
• Nevada and Arizona: Desert terrain with ultramafic rock in counties throughout both states.
• New York, Pennsylvania, Maryland, and Vermont: Appalachian serpentinite belts run through all four states.

The USGS maintains a national NOA map that identifies counties with known or suspected deposits. If your county appears on that map, the information below applies to you.

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How Exposure Happens at Home

Most naturally occurring asbestos sits locked in rock and compacted soil. It stays harmless when undisturbed. Exposure happens when that rock or soil gets broken apart and the released fibers become airborne.

Common triggers for homeowners:

Grading and excavation. Site preparation for a new home, driveway, or addition in a NOA area can release significant fiber concentrations. The El Dorado Hills EPA study found that residential grading activities elevated airborne asbestos levels above background across the community, not just at the construction site.

Unpaved driveways and roads. Vehicles driving over unpaved roads through serpentine soil crush rock and raise dust. If that road or driveway passes over asbestos-bearing rock, repeated vehicle traffic creates a chronic low-level exposure pathway for nearby residents.

Landscaping and soil disturbance. Digging garden beds, installing irrigation, pulling out stumps, or regrading a yard all disturb soil. In NOA areas, this is a meaningful exposure risk, especially during dry months when dust does not settle quickly.

Children playing on bare soil. Kids who dig, play, and track dust indoors in NOA zones can bring fibers inside on their clothing and shoes.

Outdoor air during dry, windy conditions. Naturally weathered serpentine rock releases fibers over time. In dry seasons with high winds, background fiber levels can rise even without active disturbance.

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Practical Steps to Reduce Exposure

You do not need to panic or move. NOA is a manageable risk when you know what triggers exposure and take straightforward precautions.

Check whether you are in a NOA zone. Look up your county in the USGS NOA occurrence database or search the California Geological Survey's NOA viewer if you are in California. Knowing your specific geology matters. Not all serpentine terrain has equal fiber concentrations.

Keep soil covered. Grass, ground cover, and mulch stabilize soil and prevent fiber suspension. Bare soil in a NOA zone is a chronic source of dust. Landscaping is a practical protective measure, not just an aesthetic one.

Wet-work before you dig. Saturate the soil with water before any digging, grading, or excavation. Wet fiber cannot become airborne. This single step dramatically reduces exposure during routine yard work.

Pave or stabilize unpaved driveways. If your driveway crosses serpentinite soil, paving it eliminates a major chronic exposure source. A gravel base with a bound surface is an acceptable alternative.

Control indoor dust. Remove shoes at the door. Use a damp mop rather than dry sweeping. Run HEPA air filtration if you have ongoing outdoor dust sources nearby.

Talk to your contractor before any construction. In California, contractors working in NOA-designated areas must follow the California Air Resources Board Asbestos Airborne Toxic Control Measure (ATCM) for construction, grading, and quarrying. Know whether your county or municipality has similar requirements.

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When to Get an Air or Soil Test

Ambient air testing for asbestos requires trained professionals and specialized equipment. It is not the same as a mail-in bulk material test for ceiling or floor tiles. If you have concerns about airborne fiber levels near your home, contact your state environmental agency or an industrial hygienist certified by the American Industrial Hygiene Association.

A bulk asbestos test (the kind a home test kit covers) does not apply to outdoor soil or rock. It is designed for built materials: drywall, insulation, floor tile, ceiling texture. If you need soil testing, you need a professional.

What a home test kit does help with: if you live in a NOA zone and have an older home, you likely have both an outdoor NOA risk and a potential indoor building-material risk. Those are two separate exposure pathways. A mail-in test kit addresses the indoor materials side.

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FAQ

Does naturally occurring asbestos cause mesothelioma?

Yes. The same fiber types found in industrial asbestos occur naturally in rock, and the health outcomes are the same. Epidemiological studies from El Dorado Hills, Libby, MT, and Tuscany (Italy) document mesothelioma cases linked to residential NOA exposure, not occupational exposure. The risk is lower than for heavily exposed workers, but it is not zero. Source: ATSDR, Libby Community Health Investigation.

How do I know if my neighborhood has naturally occurring asbestos?

Check the USGS Open-File Report 2004-1304, which maps NOA occurrences by county across the US. California residents can also use the CGS NOA viewer, which maps occurrences down to the parcel level in some counties.

Can I test my soil for asbestos myself?

No. Soil and outdoor air testing for asbestos requires a trained environmental professional using calibrated air sampling equipment or polarized light microscopy for bulk soil samples. Home test kits are designed for solid building materials only. Contact your state environmental agency or an AIHA-certified industrial hygienist.

Is it safe to garden in a NOA area?

With precautions, yes. Wet the soil before digging to prevent dust. Work during low-wind conditions. Wear an N95 or better respirator when disturbing soil. Wash hands and clothing after working outdoors. Keep garden beds mulched to stabilize the surface between sessions.

Do I have to disclose NOA when selling my home?

Disclosure requirements vary by state. California requires sellers to disclose known environmental hazards, and some counties with documented NOA include it in standard disclosures. Consult a licensed real estate attorney in your state for requirements that apply to your specific situation. This site does not provide legal advice.