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Long Hollow Reservoir <br />Feasibility Study <br />bridge. The bridge will have an 8-foot-wide wood deck and will be capable of supporting a <br />vehicle with a 10,000-pound axle load. <br />The geotechnical investigation identified some relatively permeable rock at the dam site. In <br />addition, high concentrations of sulfate were identified in sections of the rock core on both <br />abutments. These conditions will require final design features that will reduce seepage through <br />the abutments and the dam foundation. Three features to reduce seepage are included in this <br />feasibility-level design. The first is a grout curtain cut-off wall beneath the center of the dam. <br />This grout curtain wall extends to a depth of 100 feet and consists of angled grout holes spaced <br />on 10 feet center to center across the entire crest length of the dam. In addition, the overburden <br />soil and rock beneath the dam are sub-excavated to a depth of 10 feet and replaced with <br />compacted fill consisting of the Lewis Shale. Finally, a seepage blanket is placed on the slopes <br />and the floor of the reservoir upstream from the dam. The seepage blanket will be constructed by <br />removing the natural fractured rock in the area and replacing it with a compacted fill consisting <br />of Lewis Shale. The final seepage control features will depend on additional geotechnical <br />investigation and final design. <br />An instrumentation program of surface survey monuments and piezometers to monitor water <br />pressure in the embanknient at multiple levels is recommended for the enlarged embankment and <br />included in the cost estimate. <br />LHR is shown on E~ibit 3.1-1. The e~ibit contains a table that shows the coverage and <br />acreage on affected land parcels resulting from the enlargement. <br />An opinion of probable cost for the 5,400-AF enlarged dam and reservoir is presented in Exhibit <br />6-1. The estimated probable cost for the reservoir is approximately $13,476,000. This estimate <br />is considered to be accurate within a range of ~15 percent. The cost per AF of storage will be <br />$2,496. The operation, maintenance, and repair costs for the LHR are estimated to be <br />approximately $22,000 per year for operation and maintenance and approximately $30,000 per <br />year for replacement reserve. These operation, maintenance, and repair costs are based on <br />991-077.120 Wright Water Engineers, Inc. Page 5 <br />April 2005 <br />