Vermiculite ore contained asbestos fibers of the tremolite-actinolite-richterite-winchite series

The Site consists of two primary parcels of land, one owned by MLB and presently leased to ADDI, and the other owned by Amtrak railroad. The overall site is approximately 8.4 acres.

The W.R. Grace/Zonolite facility processed vermiculite ore that was shipped from the mine in Libby, Montana. The vermiculite ore body in Libby, Montana also contained amphibole asbestos fibers of the tremolite-actinolite-richterite-winchite solid solution series (herein referred to as amphibole asbestos) (Bureau of Mines Monograph, 1928).

Unlike the commercially exploited chrysotile asbestos, the tremolite-actinolite material has never been used commercially on a wide scale, and for most of the mine’s operating life was considered a contaminant. The commercially exploited vermiculite was used in a variety of insulation products and construction materials, as a carrier for fertilizer and other agricultural chemicals, and as a soil conditioner.

At the mine in Libby, Montana, the vermiculite ore was strip mined using conventional equipment and then processed in an on-site dry mill to remove waste rock and overburden (beneficiation). Once beneficiated, the processed ore was trucked to a screening plant, which separated the milled ore into five size ranges for use in various products.

From there, the material was shipped across the country, predominantly by rail, for either direct inclusion in products, or for expansion (also known as exfoliation) prior to use in products.