For 1 1/2 years the Seattle Water Department conducted direct filtration pilot plant studies at the Tolt Reservoir, obtaining data on techniques to remove amphibole and chrysotile asbestos from drinking water. Research showed that filtered water turbidity should be 0.1 ntu or lower in order to effectively remove fibers. Flocculation was necessary but sedimentation was not. Amphibole fibers are more readily removed than chrysotile, but both types could be reduced to below detectable limits or to not statistically significant counts by treatment with alum, lime and a filter aid (nonionic or anionic polymer); or alum, cationic polymer and a filter aid; or cationic polymer and a filter aid. Asbestos fiber content of filtered water increased sharply when filtered water turbidity rose above 0.1 ntu because of filtration rate changes, interruption of chemical feed, or turbidity breakthrough associated with the end of the filter run. The association of rising fiber counts and turbidities in filtered water would enable a plant operator to estimate fiber removal by observing turbidity if the filter was operated in the manner done in this work.

Prepared for U.S. Environmental Protection Agency, Office of Research and Development, Municipal Environmental Research Laboratory, under Grant no. 804422. "EPA 600-2-79-125." "August 1979." Cover title. Includes bibliographical references (pages 95-96).