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Asbestos in the United States: Occurrences, Use and Control
(Released April 2008)

  by Andreas Saldivar & Vicki Soto  


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Case Study: El Dorado Hills,California


While it has long been known that exposure to asbestos can cause disease, it has generally been thought that the exposure would come from working in a mine, living near a mine, manufacturing ACM products, or being exposed to ACM products. Another way to be exposed is to live in an area with naturally occurring asbestos. Asbestos is not man-made, it is a naturally occurring mineral. There are many places in the United States where veins of asbestos are part of the local geology. They may be exposed in surface outcrops of rocks, in road cuts, or occur just below the surface. In these areas the surface soil may contain asbestos weathered from the surrounding veins. If a town or community is built in area with naturally occurring asbestos, the residents run the risk of long-term exposure.

El Dorado Hills is a community of about 40,000 people located in the Sierra foothills 30 miles northeast of Sacramento. The local geology is primarily volcanic rock and some ultramafic rock. Ultramafic rock is iron and magnesium rich and can provide conditions where asbestos minerals can form within the rock (Meeker, Lowers, Swayze, Van Gosen, & Brownfield, 2006).

Picture 14: Geologic and Street map of El Dorado Hills, CA
geologic map street map

In 2002 during the construction of a vein of asbestos was disturbed at Oak Ridge High School during the construction of 2 soccer fields. In 2003 the U.S.EPA was asked to evaluate the asbestos exposure in public areas around the high school. The U.S.EPA collected over 400 air samples and about 180 soil samples. Air samples were collected as the U.S.EPA investigators participated in recreational and sport activities. Some of the samples were personal air samples in which the individual wears the sampling apparatus and some were ambient samples taken just outside the area of activity (U.S. Environmental Protection Agency, 2005).

man being observed sliding onto home plate
Picture 15: Testing asbestos exposure during recreational activities
"U.S. EPA found that asbestos fibers were present in almost all El Dorado Hills air samples, whether from sports and play activities or from samples collected nearby, but outside the areas of the activity sampling. The dominant fiber type for most air samples, especially for the longer PCME fibers, was amphibole (mainly actinolite and tremolite). However, short chrysotile fibers were also present at high levels from activities at the Community Park baseball fields and at the children's playground." (U.S. Environmental Protection Agency, 2005)

Generally the U.S.EPA found that the asbestos levels were higher on the personal air samples than on the ambient air samples (U.S. Environmental Protection Agency, 2005).

The findings generated concern in the community. Steps were taken to reduce the exposure. They included:

  • "Mitigation of soccer fields, including grading and covering native soils with geotextile fabric, 24 inches of clean topsoil, and sod, was completed in 2003. Cut banks were also sprayed with materials to reduce erosion or other release of asbestos fibers.
  • Mitigation of the baseball and softball fields, which included replacement of fill materials with clean fill, was completed in 2004.
  • The track around the football field was paved in 2003.
  • Paths and bare areas were paved or landscaped in the spring and summer of 2004.
  • Mitigation of remaining areas (bare soil under bleachers, piles of removed soil) was completed in the summer of 2004." (Agency for Toxic Substances and Disease Registry, 2006)

rolling out installation fabric
Picture 16: El Dorado Hills, CA remediation strategies
The U.S. Department of Health and Human Services Agency for Toxic Substances and Disease Registry further evaluated the site as to how it related to human exposure and risk. They concluded that current exposure had been minimized because of the steps taken. Future exposure would be dependent on maintaining of the installed barriers, proper cleaning, and not disturbing other veins. They concluded that based on past exposures the individuals most likely to have an increased risk of asbestos related disease were coaches, outdoor maintenance staff, and student athletes (Agency for Toxic Substances and Disease Registry, 2006).

The entire ASTDR report can be viewed at

It is likely, that as the populace becomes more aware of this type of exposure, more instances of exposure to naturally occurring asbestos will be identified and investigated. The United States Geological Survey (USGS) and the U.S. EPA have produced maps for historic asbestos mines and naturally occurring asbestos. An example of a map can be found at:

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