Naturally-Occurring Asbestos - Air Monitoring

This page last review May 20, 2015

Asbestos Air Monitoring - Oakridge High School, El Dorado Hills

Measured Ambient Asbestos Concentrations - Oak Ridge High School

Oak Ridge High School At the request of the El Dorado County Air Quality Management District (EDCAQMD), the Air Resources Board's (ARB) Monitoring and Laboratory Division (MLD) performed ambient airborne asbestos sampling at Oak Ridge High School located in El Dorado County. This sampling was conducted to assess the nature and extent of asbestos fibers released during mitigation of naturally occurring asbestos (NOA) while completing the school's soccer fields. Mitigation consisted of covering asbestos containing soils and slopes with dirt, grass, concrete, etc., as appropriate for the site, as well as preventing dust emissions by wetting all soils present on the fields and soils brought to the fields.

Sampling was conducted for seventeen days beginning June 16, 2003 and ending on July 10, 2003. A fenceline network of samplers collected 10-hour duration samples around the soccer fields specifically to address construction/mitigation activities. A receptor network collected 23-hour duration samples at the school's basketball courts, tennis courts, and at a home located at the cul de sac south of the soccer fields. The purpose of the long duration samples was to better understand exposure to nearby residents from NOA that may leave the worksite during the construction. There were seventeen samplers in operation.

The following summarizes the findings of the ORHS NOA mitigation sampling:

  • The construction activities at the ORHS soccer field took place in an area where naturally occurring asbestos was shown to be present. Elevated ambient levels of asbestos would be expected during the field construction in the absence of proper mitigation. The project was subject to the Title 17, California Code of Regulations, section 93105, Asbestos Airborne Toxic Control Measure (ATCM) for Construction, Grading, Quarrying, and Surface Mining Operations. Therefore mitigation during construction was required.
  • Ambient monitoring specific to asbestos was performed during all phases of construction. Samples were taken at the edge of the field, near residences, and at locations the students and public usually had access. These areas were closed during construction. During this time, the field was encapsulated with fabric blanket, two feet of certified asbestos free soil was added to the original field surface, a fence was constructed, and various slope and drainage facilities were built.
  • Periodic asbestos fibers present in the air samples collected during the soccer field construction were caused by traffic on the field, grading, covering, drilling, and other activities of this project. The readings obtained during the construction do not represent air quality at the present time, rather a worst case scenario of exposure during the time NOA bearing soils were disturbed. The results indicate the ATCM effectively minimized asbestos concentrations on and off the construction site.
  • Sample analysis was by transmission electron microscope (TEM) following the AHERA method (40 CFR Part 763, Subpart E) with ARB modifications. Asbestos could be detected at levels 40 times lower than the AHERA classroom clearance criteria used to permit rooms to be reoccupied after asbestos removal (0.0005 versus 0.0200 structures per cubic centimeters or s/cc).
  • Of the 224 samples obtained during the field construction:
    • The maximum level recorded (0.0039 s/cc) was approximately five times lower than the AHERA classroom clearance level (0.02 s/cc).
    • The average concentration of all samples was 0.0008 s/cc, or about twice the detection limit of the method. The average receptor site concentration (off of the construction site) was at the level of detection, 0.0005 s/cc. The average on site concentration was approximately 0.0010 s/cc.
    • Thirty-seven percent of the samples had ambient asbestos concentrations below the method level of detection (0.0005 s/cc).
    • Five percent of samples were above 0.0020 s/cc, which is ten times lower than the classroom clearance level.
    • Eighty percent of the asbestos concentrations at the receptor sites were below the level of detection.
    • Chrysotile, tremolite, actinolite, and anthophyllite were the types of asbestos detected. Tremolite was found in 11 of the 140 samples that had detectable asbestos. Actinolite was the prevalent type of asbestos detected.
Air Monitoring Results
Estimated Risk Comparison - Summary of ARB Asbestos Ambient Monitoring from 1998 to 2003
ORHS Asbestos Fact Sheet
ORHS Monitoring Report  To request a copy of the appendicies on CD, please contact the Emission Assessment Branch at (916) 323-4327.