MITIGATION PRACTICES FOR NOA

Increasing attention is being focused on the presence of naturally occurring asbestos (NOA) in rock and soil in California prior to development of the site. Presently the only regulation of NOA at private sector sites consists of requirements to control dust during grading and post grading stabilization as promulgated by the California Air Resources Board. For long-term liability protection, most private sector developers appear to be choosing to exceed these regulatory standards. The common practice is to cap exposed NOA with imported soils that are free of NOA. Many developers are also choosing to perform expensive perimeter airborne NOA monitoring during grading to document effective dust control.

For public schools in California, there are much stricter NOA control regulations and long-term mitigation requirements promulgated by the California Department of Toxic Substances Control. This agency currently considers NOA a potentially serious health hazard at extremely low concentrations. Detailed analysis, work plans, and public notification is required at new school sites that contain NOA, much the same as sites with hazardous substance remediation.

This presentation describes commonly used mitigation practices for NOA in the San Francisco Bay area on private and public school sites. Capping thickness decisions often vary based on the anticipated depth of potential disturbance during utility installation, landscaping, slope stability, and cost considerations. Surprising results from the search for NOA-free capping materials in the greater San Francisco Bay area is also presented.