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-8- <br />and Bernstein (1978), it was determined that a peak horizontal ground <br />acceleration at the site would be about 0.109 if a maximum credible <br />earthquake were to occur on the Yampa Fault. <br />Design Earthquake: Based on the above evaluation, it appears likely <br />that peak ground accelerations at the site could be within the range <br />of 0.04 to 0.109. In evaluating stability of cortipacted refuse piles, <br />a pseudo-static seismic coefficient of 0.05 should be appropriate. <br />This coefficient corresponds to Seismic Zone 2, U.S. Army Corps of <br />Engineers (1977). <br />S[IDSURFACE QJNDITIONS <br />Subsurface conditions at our test boring locations are somewhat <br />uniform with relation to the material types encountered but vary <br />considerable in the depths of materials encountered across the <br />disposal area. The Ipgs of Exploratory Holes are shown on Figs. A-1 <br />through A-4. Test hole locations are plotted on Fig. 3. A <br />description of ead~ of the subsurface materials enountered and the <br />ground water conditions at the site follows: <br />Natural Soils: Beneath a layer of topsoil, our test borings <br />encountered natural overburden soils to depths of between 4 and <br />43 feet. The natural overburden soils are predominantly mixtures of <br />fine to medium sand, silt and clay. These soils classify as sandy to <br />very sandy clays (CL) or clayey sands (SC) depending rn the percentage <br />of material passing the U.S. No. 200 sieve. Occasional layers of <br />silty sand were encountered in the soil profiles. Based on the field <br />penetration testing and the laboratory testing, the clay soils appear <br />• <br />