Approximately 72% of the water supplied by Sierra Pacific Power Company is surface water. As a direct result of the federal/state Surface Water Treatment Rule (SWTR), all of Sierra Pacific's surface water must be filtered. Therefore, in conjunction with CH2M Hill, a new conventional water treatment facility was designed in two phases, (phase one is a 20 MGD nominal design, and phase two is a 40-60 MGD nominal design). The first phase was constructed and brought on line this spring, with the second phase scheduled for completion in 1996. Sierra Pacific wanted to demonstrate that CH2M Hill's nominal design filtration rate of 5.0 (gpm/ft2) could be increased to 7.5 (gpm/ft2), thereby increasing plant capacity by 50% without additional construction. According to Nevada State regulations the maximum filtration rate for conventional treatment cannot exceed 6.0 (gpm/ft2) unless pilot studies prove that higher rates are possible while keeping effluent water quality within all regulatory requirements. Therefore, Sierra Pacific constructed a pilot plant facility which was the mirror image of the new Clark Bluff treatment plant. Pilot studies were pursued for twelve months at a filter loading rate of 7.5 (gpm/ft2). During the study several filter medias were reviewed along with all applicable water quality parameters being monitored, and at all times effluent water quality met SWTR requirements. After demonstrating to the state of Nevada that high rate filtration (7.5 gpm/ft2) is possible while still maintaining excellent water quality in the effluent, S.P.P. Co. was granted a variance in May 1993.