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SUBSURFACE GEOTECHNICAL INFORMATION <br />Material Properties <br />The main sources of information are from borings and test pits installed <br />from 1976 to 1982 and from additional monitoring holes above the mine <br />portal. Borings were geotechnically logged by International Engineers Co., <br />Inc. (lECO) and representative samples were examined and then sent to <br />testing laboratories. Of the 35 ]ECO borings, eight are in or near the refuse <br />disposal site. Two test pits and nine water monitoring wells also provide <br />important subsurface conditions. Information from these pertinent holes are <br />included in Appendix B. <br />The topsoil and colluvium at the disposal site are at least 15 feet and up to <br />80 feet thick, overlying the shale-sandstone of the Mesa Verde formation. <br />The critical properties are those of the refuse pile itself, the colluvium, and <br />the weathered shales and sandstones. The unweathered bedrock properties <br /> <br />are not too critical because mine data show that these units are fairly <br />competent and are well below the projected critical slip surfaces. • <br />Undisturbed colluvial soil samples were recovered by IECO from selected <br />sites and the appropriate tests, including sieve analyses, Atterberg limits, <br />and triazial and direct shear tests, were performed (Appendix A). Samples <br />from existing underground development waste and coal refuse piles at West <br />Elk were also collected in 1983 and 1984. Shear strength and consolidation <br />tests were performed at Anaconda's Tucson Research Labs, while other <br />standard tests were contracted out to a commercial laboratory. Appendix C <br />contains the results of these tests. <br />Sampling Location <br />Samples were collected from the Mt. Gunnison temporary underground <br />development refuse pile near Portal ;•f 1. The refuse pile consisted mainly of <br />underclay material, floor-heave waste, sandstone-shale roof rock, and some <br />coal. The pile was generally moist, soft, and plastic, light gray with minor <br />angular coal fragments. <br />-14- • <br />