Water Intake Line Replacement and Extension

Water Intake Line Replacement and Extension

The Sierra Lakes County Water District (SLCWD, District) provides water and sanitary sewer services to the residents of the Serene Lakes community on Donner Summit. Serene Lakes is part of the North Tahoe area located in the northern Sierra Nevada Range. The District service area spans 2,450 acres, serving roughly 830 private homes of the 1,000 residential lots in the development. The Serene Lakes themselves, Lake Serena and Lake Dulzura, are lakes of about 40 acres each and are joined via a small gap. Both lakes are closed to gasoline-powered watercraft. The Serene Lakes are situated approximately 6,900 feet above mean sea level. SLCWD is proposing to replace and extend a portion of the existing Serene Lakes intake pipe to alleviate water quality issues in the raw water supply. The existing intake pipe is located on the northern end of Lake Serena, adjacent to SLCWDs Bales Road Lake Intake Pump Station. The proposed Project includes two components: (1) extension and replacement of existing pipe sections and (2) replacement of the existing inlet with an engineered passive intake screen. The existing 12-inch (in) intake pipe is approximately 320 linear feet (ft) long and extends to a depth of 9.5 ft, where it is elevated 2 ft above the lake bottom. The inlet consists of approximately 10 to 15 linear feet of perforated polyvinyl chloride (PVC) pipe resting on cinder blocks. SLCWD proposes to replace the terminal 30-ft section of the intake pipe and inlet with a new, 200-ft-long PVC pipe, thereby extending its total length by approximately 180-ft, to a depth of 18 ft. Everything within the 30-ft section would be removed and replaced (i.e., a section of 12-inch pipe, two 45-degree fittings, the perforated 12-in pipe, and the cinder blocks). The new intake pipe would be installed directly on the lakebed surface. Restrained joint pipe will be used to maintain pipeline integrity under hydraulic and environmental loading conditions. The bottom of the pipe from the existing tie-in to the new assembly (200 LF of 8in pipe) and the intake assembly (~14 LF of 6in pipe) will be in contact with the lakebed. This total area is approximately 141 square feet. The project would also replace the perforated PVC pipe with a stainless-steel passive intake screen. The intake screen assembly would measure 9.6 ft wide by 5 ft tall and would be secured with a stainless-steel chain connected to a 2 galvanized pipe driven into the lakebed. A 6-inch pipe assembly filled with air will be connected to the intake screen. The air within the 6-inch pipe will provide buoyancy to counter the weight of the intake screen. The project would directly affect the lake through the installation of new pipe along the lakebed. Temporary, indirect environmental effects could occur during construction; however, impacts to aquatic resources will be avoided and minimized to the maximum extent practicable. The design further reduces potential impacts to the lakebed by utilizing an 8-inch pipe smaller than the existing 12-inch pipe and elevating the intake screen above the lakebed to limit disturbance.

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