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and dam embankment fdls. [n order to meet the moistwe content spe~catioas, the contraUOr should <br />anticipate adding water to the fill materials site. Due to the excessive mois[we content of the clays <br />encountered upstream of the proposed dam, we believe that these materials will have to be dried out <br />prior to placing or compacting [hem. Therefore, we do not recommend that these materials be used in <br />the embankment fills. <br />In ow opiniov, excavation of the overbwden soils and near surface bedrock should be possible with <br />heave duty, conventional excavation equipment with rippers. Some blasting or other rock breaking <br />techniques may be required where thick beds of highly cemented sandstone aze encountered. Due to <br />the presence of a fairly shallow water table and granular soils in the sedimentation pond area, <br />excavation of these soils may be d~cult and dewatering measwes during and after the construction is <br />completed will be required. The na[wal soils in the vicinity of the sedimentation pond site will pump <br />or deform excessively under the wheel loads of heavy construction vehicles. Construction equipment <br />used in this area should be as light as possible [o avoid this difficulty. <br />SEDIMENTATION POND CONSIDERATIONS <br />Due to the relatively shallow groundwater table and the depth to the underlying bedrock, we do not <br />believe that i[ will be Feasible [o construct an effective cutoff trench below the embankment [o reduce <br />underseepage. Therefore, we recommend that the dam embankment be constructed with a toe drain <br />• and/or a horizontal drainage blanket on the downstream side of the embankment. The purpose of <br />[here drainage features is to permit free Flow and dissipation of presswe without disruption of the <br />foundation structwe and loss of fine grained soil particles. <br />Based on the test hole information obtained at the sedimentation pond site, it appears that sands and <br />clays may also be encountered in [he reservoir site located upsveam and underneath the dam <br />embankment. The laboratory permeability tests yielded a permeability rate of 1.2 x 10-8 <br />centimeters/second for the sample obtained From test hole 25 at a depth of 9 feet and a permeability <br />rate of 4.4 x 10-8 centimeters/second Eor the sample obtained from test hole 22 at a depth of B feet. If <br />these values produce an unacceptable rate oFseepage then we believe that the conswction of a day <br />liner would be the most cos[ effective way of reduang seepage. If a clay liner is used, we recommend <br />that a minimum of two siz-inch layers of impervious clay be placed along the bottom and side slopes of <br />the reservoir. The clays should be compacted to at least 95% of the standazd Proctor density within <br />2% of the optimum moistwe content. <br />Due to the high groundwater table and soft consistency of the soils in the proposed pond area, <br />dewatering may be required prior to fill placement in eitlter the dam location or within the pond itself. <br />In addition, we recommend that a geotextile stabilization Fabric, such as M'vafi 500X, be used at the <br />base of the dam embankment fdl. The use of the fabric will increase the overall stability of the fill and <br />reduce settlement. <br /> <br />7 <br />