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-g- <br />• and sandstone partings. Recovery and RQD was low in the coal. <br />RQD in the coal ranged from 34 to 56 percent with an average <br />RQD of 45 percent. <br />Free ground water was encountered in the coal bed at most <br />boring locations. The coal bed is the most pervious and con- <br />tinuous aquifer encountered during the investigation. <br />interiayered Tertiary Sandstone and claystone, Middle <br />Park Formation <br />The sedimentary rocks encountered along the east slope of <br />the open pit are soft to hard claystones and poorly cemented sand- <br />stones. The interiayered sandstone and claystone are variable <br />because of the depositional sequence and additionally vary along <br />the east slope of the mine due to the 38 to 45 degree dip of the <br />formation. and the weathering characteristics of the materials. <br />• The dip of the formation orients any uniformity which may be found <br />within the formation at a 38 to 45 degree dip. Therefore, ma- <br />terials vary in an east-west direction on a horizontal plane. The <br />claystone and sandstone also varied significantly with depth due <br />to weathering. The upper 100 feet was weathered and has strength <br />characteristics similar to a very stiff clay. Below a depth of <br />100 feet, the sandstones and claystone are relatively unweathered <br />and have higher strength. An indication of the soundness of the <br />rock is shown on Table I, Summary of Rock Quality Designation <br />Determinations. The RQD of the interiayered claystone and sand- <br />stone along the east wall increased significantly below a depth <br />• <br />