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• <br />ExxonMobil Global Services <br />Colony Shale Oil Project <br />ESR Reclamation Studies <br />Weighing Lysimeter Performance 1990-2003 <br />Project No. 353 <br />Page 4 <br />3.1,3 Topsoil Cover Required <br /> <br /> <br />In spite of studies performed in the 1960s and 1970s that suggested retorted shale <br />could bepre-treated and amended to create a suitable plant growth medium (Patahce, <br />TOSCO), all surface disposal piles permitted by the Colorado Mined Land Reclamation Board <br />in the 1970's an 1980's required a topsoil cover composed of natural soil materials salvaged <br />form the site and placed over the spent shale. This applied to above ground disposal piles such <br />at Colony and Unocal, and in-pit backfill for open pit mines, such as Chevron's Clear Creek <br />Project. The placement technique for the spent shale (loose dumped, v.s. compacted pile), and <br />thickness of topsoil cover varied from project to project. Colony's existing pemtit based on <br />the TOSCO II process required moderate compaction of the spent shale, which would <br />necessitate spreading the material in relatively thin lifts (e.g, about 12 to 18 inches loose lifts), <br />followed by compaction with a conventional roller. In some cases, the topsoil thickness <br />requirements specified in the pemuts were at least in part based on revegetation studies that <br />the shale project developers had conducted in the 1970s (Kilkelly, Harbert and Berg, 1981). <br />The negotiations during the pemrit application process were the mechanism for the developers <br />to present their case that their proposed technique was reasonably certain to produce a <br />permanent self-sustaining revegetated cover consistent with the post mining land use, which in <br />most cases was open range land and wildlife habitat, essentially the same as the pre-mining <br />land use. <br />The participants in the original Colony Development Pmject, for which pemutting <br />efforts started in the late 1970's, had shown by means of a series of revegetation test plots that <br />a topsoil cover of 12 inches over mildly compacted TOSCO II spent shale (basically anon- <br />plastic silt, or a "loam"), could sustain the plants if the surface of the spent shale was first <br />leached with irrigation water to remove the high level of salts in the material. Colony's cover <br />was based on the developers' assertion that the basic "loam" texture of the TOSCO II spent <br />shale made it suitable as a plant rooting medium with only nunimal pre-treatment (in this case, <br />LACHEL FELICE & Associates <br />