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-4- <br />' f'.2 GEOTECHNICAL CONDITIONS <br />' The three borings undertaken for geotechnical purposes confirmed that the <br />geotechnical conditions beneath and in the immediate vicinity of the initial <br />' waste rock pile are essentially identical to those defined during previous <br />geotechnical investigations at other locations on this lower bench. <br />' The subsurface soils consist principally of low plasticity clays and sandy <br />clays (CL and CL-SC in the Unified Soil Classification System described on Plate <br />' A-1 of the Appendix.) Small rock fragments, usually sandstone, are present <br />throughout. Penetration resistance indicates the soil to be generally very stiff <br />to hard. Water content varies from moist to slightly moist, typically being <br />within the range of 12 percent to 16 percent. Cobbles and boulders are present <br />in scattered layers throughout the soil. Bedrock shales, siltstones, sandstones, <br />and coal of the Mesa Verde Formation lie at an average depth of 50 feet below <br />surface. A topsoil layer of soft silt and clay with a high organic content is <br />typically one to two feet thick. This topsoil will be removed prior to the <br />construction of the pile. <br />The results of testing on representative samples of subsurface soils are <br />presented in the Appendix. ~ <br />1 I2.3 HYDROLOGIC CONDITIONS i <br />]~ The three geotechnical boreholes (numbered Borings 1 through 3) and two <br />1 shallow hydrologic boreholes (numbered Borings lA and 1B) which were angered at <br />the proposed initial waste rock disposal site were used to study hydrologic <br />J conditions. The locations of all borings are indicated on Plates 1 and 2. The <br />three geotechnical boreholes reached bedrock without encountering any water- <br />bearing or saturated soils. Borings No. 2 and 3 had 2z inch PVC casing <br />installed, with a perforated zone covering the contact between overburden and <br />bedrock, so that they would serve as long term monitoring wells. Details of the <br />l construction of these monitoring wells are shown on Plate 3. Two shallow <br />11 boreholes (Borings lA and 16, which were 15 and 10 feet deep respectively) were <br />drilled in the immediate vicinity of Boring No. 1 to ascertain the permeability <br />of the upper portion of the colluvial soils'. <br />ceoNreaoeoHw~mw we I <br />