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cutoff to bedrock, and 3) an upstream clay liner. <br />ALTERNATIVES EVALUATED <br />A range of alternatives were considered as outlined above and as described below. <br />Alternative 1) Includes excavating a core trench into the center of the dam to a depth up to 35 feet <br />below the dam crest. This alternative will cutoff the seepage in the zone it pierces and will also add <br />considerable stability to the dam by removing and replacing the poorly compacted shale chunks found <br />in the dam. <br />Alternative 2) This alternative considered excavating a cutoff trench through the dam to bedrock using <br />bentonite slurry trench methods. The trench would be placed near the centerline of the dam and would <br />be approximately 18- inches in width. The trench would be stabilized with a bentonite slurry during <br />excavation and backfilled with the soils removed from the dam plus cement to form a soil- bentonite- <br />cement slurry. The slurry trench would be expected to develop a low permeability barrier to seepage <br />but would not significantly increase the sliding stability of the dam. The uncompacted shale layers in <br />the dam would not be impacted or modified by this construction. <br />Alternative 3) Includes placing a ten (10) foot thick clay liner on the upstream face of the dam to cut <br />off the seepage. This will require the removal and replacement of the riprap on the upstream face of <br />the dam. This option will reduce the seepage and has the advantage of cutting off water from the dam <br />crest to the toe. However, it will not have any impact on the existing layers in dam that are comprised <br />of uncompacted shale chunks. The overall stability of the dam will be increased but it stability to <br />sliding will not be increased significantly. <br />COST ESTIMATE <br />A summary of the cost estimates for the three alternatives are shown in the following table. <br />TABLE 2 <br />SUMMARY OF ESTIMATED PROJECT COSTS <br />ALTERNATIVE <br />DESCRIPTION <br />ESTIMATED COST <br />1 <br />Clay Core Trench <br />$ 600,006 <br />2 <br />Bentonite Slurry Trench <br />$ 758,355 <br />3 <br />Upstream Clay Liner <br />$ 971,565 <br />A more complete breakdown of the costs are shown in the Tables 1, 2, and 3 at the end of this report. <br />Foothills Dam- 03.076 Page 4 <br />