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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />'0 <br />I <br />I <br />I <br />l- <br />I <br />I <br />I <br />I <br />I <br /> <br />_,J~,,~ <br /> <br />top 10 feet of the dam. This material would be replaced after construction is complete. <br />The CB wall would have the effect of cutting off seepage through both the embankment <br />and foundation, thereby reducing the migration of fines downstream. <br /> <br />Alternative 2: Soil-Bentonite Slurry Cutoff Wall <br /> <br />The soil-bentonite slurry cutoff wall (SB wall) would be approximately 700 feet long and <br />80 feet deep. The SB wall would require the same site preparation as the CB wall. <br />Construction of the SB wall would also require mobilization of large equipment and <br />supplies such as bentonite. The soil for the backfill would be obtained at the reservoir. <br />The SB wall would have the effect of cutting off seepage through both the embankment <br />and foundation, thereby reducing the migration of fines downstream. <br /> <br />Alternative 3: Grout Curtain Cutoff Wall <br /> <br />The grout curtain cutoff wall would be'approxiII:ately600 feet long and 55 feet deep in <br />the foundation bedrock. As a result onhe-poor quality of the foundation bedrock, it is <br />-expected that the grout curtain cutoff wall would be a triple-curtain wall. The grouting <br />would be completed by advancing 2-inch diameter drill holes to a depth of 55 feet into <br />bedrock on approximately)O foot centers. It is expected that equipment can be moved <br />to the site on the current access road; however, it will still be necessary to construct an <br />adequate working platform. The grout curtain cutoff wall would have the effect of <br />cutting off seepage through the foundation, thereby reducing the migration of fines <br />downstream. --. <br /> <br />,.- <br /> <br />Alternative 4: Breach the Dam <br /> <br />The altermitive. to breach the dam would include complete removal of the embankment, <br />removal of the outl~t works, and regrading of the valley. The embankment material <br />would be removed and recompacted throughout the valley, the stream channel would be <br />regraded and riprapped, and the regraded areas would be seeded with native vegetation. <br />This alternative is presented primarily for comparative purposes. However, should the <br />other alternatives be economically infeasible, the breaching alternative may require <br />further evaluation. <br /> <br />23067/R 1. 7 09-03-93(10: ISam)/RPT <br /> <br />7-2 <br />