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
The following summarizes the findings of the ORHS NOA mitigation
- 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
- 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
- Eighty percent of the
asbestos concentrations at the receptor sites were below the level of
- 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.