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ALLUVIAL VALLEY FLOOR DETERMINATION <br />MCCLANE CANYON MINE <br />COAL MINE WASTE PILE <br />GARFIELD COUNTY, COLORADO <br />time in the past, the creek downcut through the older alluvium becoming entrenched, <br />limiting its ability to maintain the wider floodplain. The floodplain was subsequently <br />encroached upon by deposits from the canyon walls (colluvium) and fans from side <br />canyons or small drainages. The landslide occurred more recently (it covers all of the <br />other deposits, with the exception of the youngest alluvium in the active channel). <br />Ground Water <br />Ground water data from the investigation area indicates that the water table in the <br />various unconsolidated deposits is greater than 25 feet from the surface at monitoring <br />well GW-9 (Appendix C). Most likely, any ground water entering the unconsolidated <br />deposits from McClane Canyon or other side channels is flowing toward East Salt Creek. <br />Because East Salt Creek is greatly incised, it probably is a gaining creek through this <br />reach. The ground water quality at the GW-9 location is poor with electrical conductivity <br />values of more than 9,000 umhos/cm, consistent with that of the creek and general <br />regional water quality. There is no indication that any of the investigation area is subject <br />to subirrigation. <br />Alluvial Valley Floor Determination <br />The geologic investigation indicates that nearly 95 percent of the footprint (15 acres) <br />of the proposed waste storage pile is covered with various unconsolidated deposits that <br />meet the listed criteria in section 2.06.8(c)(ii)(C) of the regulations for determining that <br />an AVF does not exist. These deposits may overlie older alluvium at some locations, but <br />the alluvium has been covered for a considerably long period of geologic time <br />With respect to section 2.06.8(c)(ii)(B), this study did not investigate the adequacy of <br />the water supply to irrigate this area because the area does not meet the minimum <br />qualifications for cultivation. <br />Two areas within the investigation area have alluvium exposed at the surface (Figure <br />2). These areas are approximately 0.1 and 1.1 acres. A review of existing irrigated areas <br />along East Salt Creek indicates that the smallest cultivated and irrigated parcel is 9.1 <br />acres (Figure 3). The average of nine parcels is slightly more than 30 acres. Based on <br />6 ERO <br />Resources <br />Corporation