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C = 0.0383 [Table 6, SCS Agronomy Note #50 re. #2, August 1982; 2005 and 2006 <br />vegetation cover data.] <br />P = 1.0 [Table 9, SCS Agronomy Note #50 re. #2, August 1982.] <br />The calculated soil loss rate derived from the USLE is 0.66 tons/acre/year. The T factor for the soils <br />in the Grassy Gap Mine area ranges from 2 tons/acre/year to 5 tons/acre/year. The calculated USLE <br />value of 0.66 tons/acre/year on the reclaimed mine area is well below the more conservative T factor <br />of 2-5 tons/acre/year. This demonstrates that the vegetative cover on the reclaimed mine is adequate <br />to control erosion. This also demonstrates that soil losses on the reclaimed lands can be expected to <br />be similar to adjacent non-mined lands, in accordance with the requirements of Rule 3.03.1(3)(b). <br />Evaluation Required by Section 3.03.2(2) <br />The Division has conducted an evaluation of the reclamation work at the Grassy Gap Mine, in <br />accordance with Section 3.03.2(2) of the Board's Regulations for Coal Mining. This evaluation <br />considered: the results of inspections and monitoring, the need for further reclamation work, whether <br />pollution of surface or subsurface water is occurring, and the probability of future occurrence of <br />such pollution. The 1993 Annual Hydrology Report for the Grassy Gap Mine provides the most <br />recent hydrologic monitoring data. Impacts to ground water and surface water are described below. <br />Ground Water Impacts <br />The six backfilled pits at the Grassy Gap Mine cover approximately 180 acres. Snowmelt and rain <br />water infiltrate the spoil backfill. Monitoring data from spoil monitoring wells in two of the pits and <br />from seeps near the pits indicate the infiltrated water has formed an alkaline leachate in the backfill <br />that has a high concentration of dissolved solids, with sulfate as a main chemical component. <br />Leachate sampled in spoil monitoring well SP-2 in 1992 had pH of 7.13 and total dissolved solids <br />(TDS) concentration of 1,460 mg/l. <br />Spoil leachate from the Grassy Gap Mine's pits can be expected to seep from the backfill into <br />undisturbed bedrock exposed in the downdip sides of the pits and then migrate downdip (northward) <br />parallel to bedding. The flow velocity of the migrating leachate should be significantly less than the <br />flow velocity of surrounding native ground water (which also is migrating northward into the Sand <br />Wash Basin) because the native ground water is recharged by snowmelt and rainwater in areas that <br />are at a much higher elevations than the pits. The significantly greater flow velocity of the native <br />ground water can be expected to result in the migrating leachate being diluted to near ambient <br />ground water quality a short distance from the pits. The pits at the Grassy Gap Mine were not in <br />direct hydrologic communication with alluvial aquifers; therefore, no impact to alluvial aquifers is <br />expected from migration of spoil leachate in the subsurface. Alluvial monitoring well MW-3, <br />located downgradient from the mine, indicates no adverse impacts from mining having slightly <br />alkaline pH and TDS concentrations between 940 and 1,112 mg/1 as measured in 1992. <br />The improbability of significant degradation to ground water indicates the Grassy Gap Mine is not <br />causing pollution of ground water and there is minimal potential for future pollution. The operation <br />is in compliance with the Basic Standards for Ground Water (Colorado Water Quality Control <br />Commission Regulation 41.5.C.6) because the operation caused no new disturbance after the date <br />Grassy Gap TOJ 6/5/2009 16