Pilot plant research conducted in 1974 at Duluth, Minnesota, demonstrated that asbestiform fiber counts in Lake Superior water could be effectively reduced by municipal filtration plants. During the study engineering data were also obtained for making cost estimates for construction and operation of both granular and diatomaceous earth (DE) filtration plants ranging in size from 0.03 to 30 mgd. Data provided to the contractor by the Ontario Research Foundation are presented in Appendix E. ORF performed asbestiform fiber analysis of water samples by the transmission electron microscope method in this project. In order to place the data in better perspective, a description of the analytical method used by ORF is reproduced in Appendix E. In Appendix F, the amphibole mass data obtained by the National Water Quality Laboratory in Duluth are presented. This appendix also includes information on the analytical method used at NWQL. The x-ray diffraction analysis for amphibole mass provided confirmation of electron microscope amphibole fiber result. Fiber count data obtained at the University of Minnesota at Duluth are tabulated in Appendix G. A statement describing the electron microscope analytical method is also included.