SUBJECT:  Amphibole Mineral Fibers in Source Materials in Residential and Commercial Areas of Libby Pose an Imminent and Substantial Endangerment to Public Health

FROM:  Christopher P. Weis, Ph.D., DABT. Senior Toxicologist / Science Support Coordinator Libby Asbestos Site

TO:  Paul Peronard, On-Scene Coordinator Libby Asbestos Site

I PURPOSE

This memorandum presents the rationale for determination of imminent and substantial endangerment to public health from asbestos contamination in various types of source materials at residential and commercial areas in and around the community of Libby, Montana. With this memorandum, I confirm and extend a similar conclusion derived in two previous memoranda from my office to you (dated May 10, 2000, and July 9, 2001).

II SUMMARY OF FINDINGS

1. Asbestos occurs in ore and processed vermiculite obtained from the Libby mine.
2. Asbestos fibers of the type that occur in vermiculite ore from the mine in Libby are hazardous to humans when inhaled.
3. Asbestos material fibers that are characteristic of those that occur in materials from the Libby mine are present in a variety of different source materials at residential and commercial locations in and around the community of Libby. Outdoor source materials include yard soil, garden soil, driveway material, and assorted mine waste materials, while indoor source materials include dust and vermiculite insulation.
4. Disturbance of asbestos-contaminated source materials by activities similar to those that are likely to be performed by area residents or workers can result in exposure to respirable asbestos fibers in air.
5. The concentrations of fibers in air generated by disturbance of source materials may exceed OSHA standards for acceptable occupational exposure, and estimated excess cancer risks can exceed EPA's typical risk range (1E-04 to 1E-06) by an order of magnitude or more. There are several factors which suggest these risk estimates may be too low and that actual risks are even greater.

On this basis, I conclude that source materials such as soil and soil-like media, dust, and vermiculite insulation that contain friable asbestos minerals are a likely source of on-going release of hazardous fibers to indoor and/or outdoor air at multiple residences and commercial facilities in Libby. In light of clear biological evidence of human asbestos exposure in Libby and the associated increase in human risk, I recommend that EPA take appropriate steps to reduce or eliminate pathways of exposure to these source materials in order to protect area residents and workers.