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- 10 - <br /> the underlying natural soils. Eventual silting of the basin will also <br />• <br /> be effective in sealing foundation soils. <br /> Ground water was generally mt encountered in the higher plateau <br /> area. Slow seepage was m°asured in hole D-15 several days following <br /> drilling. It has been our experience in areas such as this that some <br /> 'seepage below the topsoil layer can occur at times of seasonal runoff. <br /> Seepage rate is typically slow. The contractor should be prepared to <br /> dewater the excavation as required. <br /> Runoff Ponds #2 & #3 and Fresh Water Pond #2: Subsoils in the <br />' vicinity of these pond locations generally consist of approximately <br /> 3 to 14 feet of silty to clayey sands with occasional silt and clay <br /> layers overlying dense, coarse granular alluvial soils. These soils, <br /> other than topsoil and hose fill material should provide adequate <br /> support for the proposed maxima; embankement height of about 20 feet. <br />• <br /> Maximum foundation settlement during construction is anticipated to be <br /> between 1 to 3 ind~es. Following construction some additional differ- <br /> ential settlement due to wetting of the dryer near surface soils could <br /> occur but should not be detrimental to the ert~banlanent structure. <br />Near surface foundation soils typically consist of silty to clay <br />sands which appear to be semi-impervious. The underlying coarse <br />granular material would be relatively pervious and could provide a <br />flag path beneath the embanlanent. For low impoundment depths on the <br />order of 75 feet, there appears to be no necessity to construct an <br />impervious cutoff. A nominal depth impervious embankment key should, <br />however, be constructed to intercept any superficial irregularities or <br />as required for stability. We anticipate that silting will also help <br />• <br />