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Long Hollow Reservoir <br />Feasibility Study <br />A chimney drain will be placed on the downstream face of the central core and beneath the <br />downstream shell (Exhibit 3.1-5). <br />The crest elevation of the dam will be 6,330 feet, with a camber for settlement making the <br />m~imum elevation at the center of the dam approximately 6,336 feet. The upstream slope of the <br />dam will be constructed on 3 horizontal to 1 vertical slopes and will be covered with sandstone <br />riprap. Sandstone will be obtained from a quarry site in the Cliff House Sandstone that underlies <br />the Lewis Shale. This quarry site will have to be identified in the final design stage, and Wright <br />Water Engineers, Inc. (WWE) anticipates that it will be necessary to blast to obtain sandstone for <br />the riprap. The dam's crest will be 25 feet wide, as required by SEO regulations (Department of <br />Natural Resources 1988). The downstream slope will be constructed in an overall2'/2-to-1 slope. <br />A 10-foot-wide maintenance and instnunentation barrier may be appropriate at mid-height on the <br />downstream slope. <br />The outlet works for the embankment is a 48-inch-diameter welded steel pipe encased in <br />concrete. This conduit of steel-lined concrete will require firm, unyielding foundation support to <br />prevent excessive cracking of the concrete and displacement of the pipe. The alignment of the <br />new outlet pipe is shown on Exhibit 3.1-3. The final alignment will depend upon subsurface <br />conditions determined by additional exploration. <br />A 24-inch-diameter Howell Bunger (fixed-cone) valve will control the outlet pipe. This valve <br />will be located at the downstream end of the outlet pipe. A 12-inch-diameter Jet valve will be <br />placed on a Y pipe section near the fixed-cone valve. The Jet valve can be used for routine low- <br />level releases. <br />A vertical water-intake shaft will be constructed through the upstream slope of the dam. The <br />shaft will be gated with two 48-inch-by-48-inch sluice gates on the outlet pipe and a 30-inch-by- <br />30-inch sluice gate near the mid-height of the reservoir. This configuration of gates will allow <br />water to be released from either the bottom or the mid-height of the reservoir. The vertical shaft <br />for the operating gates will be accessed by a single-span prefabricated weathered-steel truss <br />991-077.120 Wright Water Engineers, Inc. Page 4 <br />April 2005 <br />