SACRAMENTO – Airborne levels of naturally-occurring asbestos were found to be extremely low during and after soccer field improvements over the summer at El Dorado County's Oak Ridge High School campus, the California Air Resources Board (ARB) reported.

Airborne asbestos concentrations were found to be well below the federal Asbestos Hazard Emergency Response Act (AHERA) level, which determines if children may reoccupy a classroom following asbestos abatement. The AHERA level is 0.02 structures per cubic centimeter (s/cc). Even during the worst case scenario, when soils were temporarily disturbed as new, clean fill was brought in for the entire field, the maximum measured asbestos levels were five times lower than the AHERA classroom clearance level.

"Mitigation efforts on the Oak Ridge High School soccer fields were successful," said ARB Executive Officer, Catherine Witherspoon. "Air monitoring during soccer field mitigation revealed very low airborne asbestos levels both on and off the construction site."

ARB conducted air monitoring for 17 days starting on June 16 and ending July 10, 2003, as requested by the El Dorado County Air Quality Management District (EDCAQMD) and the El Dorado County Union High School District. A total of 17 samplers and two meteorological stations were placed, taking measurements each ten-hour workday and 23-hour daily readings. Monitoring was not conducted on weekends since work on the fields only took place on weekdays. The soccer field construction period was selected for monitoring because it was expected to be the time when the most asbestos fibers would have been disturbed and could have the highest airborne concentrations.

Many samples taken at receptor sites, which included both the basketball and tennis courts and a cul-de-sac located south of the soccer fields, were below the level of detection. The most prevalent type of asbestos found in the samples was actinolite, an amphibole. Tremolite, anthophyllite and chrystotile structures were also found. The range of asbestos concentrations from all of the valid samples was from less than 0.0005 to 0.0039 s/cc.

Oak Ridge High School is located in an area of known asbestos-bearing soil in western El Dorado County near a fault zone where amphiboles are expected to occur. The ARB has been working closely with the EDCAQMD, school district, local residents and other state and local agencies to mitigate airborne asbestos emissions on and around the campus.

Health effects from asbestos exposure include asbestosis and mesothelioma, a cancer of the lung and esophagus lining. The risk of disease depends on the intensity and duration of exposure. The ARB identified naturally-occurring asbestos as a toxic air contaminant, a known cancer causing pollutant, in 1986.

"It is best to exercise caution when living, working or playing in an area where naturally-occurring asbestos is known to exist," added Witherspoon.

In 2000, the ARB updated a rule prohibiting the use of ultramafic rock (including serpentine rock) that contains asbestos for surfacing applications subjected to vehicular, pedestrian, or non-pedestrian use, such as cycling and horse-back riding. In 2001, the Board adopted rules requiring construction, grading, quarrying and surface mining activities to control dust emissions when they take place in areas with asbestos containing rocks or soils. The soccer field construction and other mitigation activities were required to comply with this measure.

A copy of the final report and a fact sheet summarizing activities at Oak Ridge High School. General information on naturally-occurring asbestos, past monitoring done by the ARB and health effects.