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Client Memorandum <br />Geotechnical and Slope Stability Analyses <br />Sylvester Gulch Facilities Area <br />March 20, 2009 <br />Page 4 <br />Compaction tests (Standard Proctor) were performed on bulk samples of soils near the base of <br />the northwest test pit (TP-1) and the southeast test pit (TP-4). Results from these tests indicated <br />maximum dry densities (MDDs) of 109 and 110 pcf at optimum moisture contents of 16.5 and 15 <br />percent, respectively. These are typical for the primarily silty to sandy clays encountered. Most <br />of the in-situ soils appear to be at or below the optimum moisture content. <br />A direct shear test on the CH soil sample from TP-2 (tube sample) indicated an effective stress <br />friction angle (o) of 23 degrees and a cohesion (C) of 196 pounds per square foot (psf) at 2% <br />strain. A triaxial compression test on a remolded sample of sandy clay with gravel from TP-1 <br />indicated an effective stress friction angle of approximately 20 degrees with cohesion of <br />approximately 375 psf. The permeability of this compacted sample was determined to be <br />approximately 4.4x 10-9 cm/sec. <br />A swell-consolidation test was performed on a relatively undisturbed sample of silty clay <br />collected from TP-4 at a depth of approximately 1.5 ft bgs. The result from this test indicated a <br />consolidation of approximately 15 percent between 100 and 1,000 psf and approximately another <br />8 percent from 1,000 to 3,000 psf. The swell pressure was less than 100 psf in this test. <br />0 Discussion of 2008 Geotechnical Testing Results <br />The test pits indicate that the upper portion of the pond site could be excavated using standard <br />backhoe or bulldozer and front end loader equipment and that the material at the base of the test <br />pits could likely be excavated using a large backhoe or a bulldozer equipped with ripping teeth. <br />Based on the test data, the native materials should, for the most part, be adequate for compacted <br />embankments if the zones of high-plasticity clays are avoided. Such materials should be <br />separated during excavation, along with rock fragments larger than about 6 inches, for disposal <br />elsewhere. However, it is expected that very few, if any, high-plasticity clays may exist within <br />the pond construction area because only one sample out of several samples tested from the 2008 <br />sampling program, and no samples from the 1997 sampling program, indicated such conditions. <br />The one sample tested with a very high PI in 2008 appears to be anomalous. <br />The subsurface soils appear to have a relatively high consolidation potential, which will need to <br />be considered in the final design. This may require settlement plates or monitors for <br />embankments over a few feet high to determine when adequate consolidation has occurred to <br />allow for placement of a pond liner. <br />The laboratory results indicate a very low permeability for a compacted clay soil sample. <br />However, the presence of sandstone fragments in compacted soil in the field could result in <br />somewhat higher permeabilities. <br />• <br />Rev. 04109-TR116