Naturally Occurring Asbestos

The construction of the I-11 Design-Build Project will require the movement of more than 5 million cubic yards of rock and earth, a portion of which may contain Naturally Occurring Asbestos (NOA).  Construction activities could cause asbestos fibers to become airborne. In order to mitigate this risk to our project's work force and the public, we have put in place an extensive dust control and air monitoring program to verify that our construction activities are not increasing the risk of adversely impacting either of these groups. Additionally, for more than a year prior to construction, the Regional Transportation Commission of Southern Nevada (RTC) has measured the background ambient air quality at locations throughout Boulder City. During construction, we will continue to monitor the perimeter of the project right away and will make the data available on a monthly basis from this website. Protecting the health of our workforce and the public is our utmost priority.

Air Quality Monitoring Data

To view the latest air quality monitoring results, click on each monitor number below. Results are updated monthly.

Archival Data

Previous periods that are not included below can be found here.

See map for monitoring locations. Please also review our Frequently Asked Questions. Additional questions? Click here, contact us at, or call us at (702) 929-2013.

NOA Monitoring Results FAQs



Air Quality Monitoring

Naturally Occurring Asbestos

Naturally Occurring Asbestos (NOA) refers to asbestos that is present naturally in soil and rock, as opposed to asbestos that was commercially mined and applied to building materials. NOA is found in many places in the United States and is present in at least 44 of California’s 58 counties. When found, the amount of NOA ranges from less than 1 percent up to 25 percent concentration or more.

Natural weathering and human activities may disturb NOA-bearing rock or soil and release mineral fibers into the air, which may result in adverse health effects if inhaled. However, measures can be taken to minimize the release of these mineral fibers.

After geologists from the University of Nevada, Las Vegas (UNLV) notified NDOT and RTC in late 2013 of the potential for NOA in the Boulder City area, the RTC and NDOT contracted with independent consultants to conduct environmental testing for NOA in the project area.

Naturally Occurring Asbestos Frequently Asked Questions

Rock and Soil Test Results

Independent environmental engineering firms obtained and tested rock and soil samples from both NDOT Phase 1 and RTC Phase 2 project areas at depths ranging from ground level to more than 200 feet below the surface. Samples were tested to determine if NOA was present and, if so, where it occurs and at what levels.

  • All 150 surface and subsurface rock and soil samples tested in the NDOT Phase 1 project area had NOA concentrations below 0.25 percent.
  • Of the 194 surface rock and soil samples tested in the RTC Phase 2 project area, only one out of five samples detected NOA and only 2 samples (approximately 1 percent) had concentrations above 1 percent.
  • Of the 267 subsurface rock and soil samples tested in the RTC Phase 2 project area, more than half had NOA detected but only 12 samples (approximately 4 percent) had concentrations above 1 percent.
  • Overall, the independently conducted soil and rock tests confirmed that NOA is present in the project areas, but NOA concentrations are generally low.

Moving Forward

Despite the low concentrations of NOA in the project areas, the RTC and NDOT will utilize the following EPA recommended mitigation measures throughout the project to minimize exposure to dust potentially containing NOA:

  • Wetting work areas and unpaved road surfaces repeatedly using water trucks, hoses, spray systems or sprinklers
  • Clean equipment and vehicles to prevent tracking soil out of the work area
  • Reduce vehicle driving speeds in the work area
  • Reduce drilling and excavating speeds
  • Avoid overloading trucks
  • Excavate during periods of calm or low winds.

Additionally, the RTC and NDOT will conduct ongoing air monitoring to ensure the effectiveness of the mitigation measures throughout construction.

The information above was compiled in part from the Agency for Toxic Substances and Disease Registry (ATSDR) and the Environmental Protection Agency (EPA).

For more information, visit: and


Links (PDFs)

Naturally Occurring Asbestos Fact Sheet

Naturally Occurring Asbestos FAQs

Phase 1 – NDOT Naturally Occurring Asbestos Final Report

I-11 Boulder City Bypass Final Environmental Impact Statement Re-Evaluation

Phase 2 – Geologic Evaluation, Sampling, and Testing for Naturally-Occurring Asbestos (96 MB)

Phase 2 – Appendix B through H (12 MB)

Phase 2 – Attachment 1 (12 MB)

TEM data sample locations (Part 1 of the Phase 2 work)

PLM data sample locations (Part 2 of the Phase 2 work)

Note: Northings & Eastings in above files are in Universal Transverse Mercator coordinate system