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The Upper Dakota aquifer is predominantly recharged by return flow from the West Lateral <br /> Irrigation Ditch. Some recharge is probably derived from infiltration of precipitation and <br /> subsurface ground water flow. The transmissivity of the overburden (Upper Dakota aquifer) <br /> varies from 3 to 53 ftZ/day, averaging 13.3 ftZ/day. The McWhorter analysis of pit inflow <br /> conservatively estimated that the hydraulic conductivity of the overburden was 0.61 ft/day. <br /> Hydraulic conductivity calculations from field tests of the overburden showed a range of 0.39 <br /> to 1.05 ft/day, indicating moderate permeability. <br /> The water found in the overburden is characterized as very hard,saline, calcium/magnesium <br /> sulfate water with neutral pH. TDS levels vary from 1494-10074 mg/1 and average 4613 <br /> mg/l. Sulfate concentrations are very high, varying from 875 mg/l to 6872 mg/I and <br /> averaging 3176 mg/l. In some of the overburden wells, sulfate, TDS, manganese and <br /> fluoride exceed recommended standards for livestock drinking water. In addition, <br /> concentrations of manganese and fluoride exceed the agricultural use standards in some <br /> wells. <br /> The Dakota coal has been described as an aquifer. Wells completed in the Dakota show <br /> water level fluctuations of 1.3 to 14.6 feet. The water table exhibits seasonal fluctuations <br /> with high water levels in late fall. The aquifer is recharged from the east north east and <br /> discharges to the west and along Calamity Draw. The transmissivity varies from 0.92 to <br /> 6.0 ft2/day, based on hydraulic conductivity values of 0.04 to 0.34 ft/day (average values of <br /> 0.19 ft/day), reflecting moderate flow capabilities. <br /> The water quality of the Dakota coal is unacceptable for most uses. The saline, <br /> sulfate-based water has TDS levels varying from 1050-4444 mg/l, averaging 2822 mg/1 at <br /> New Horizon Mine 2. The three wells at New Horizon Mine 2 exhibit two distinct <br /> geochemical characteristics. Two wells have calcium/magnesium sulfate water with the pH <br /> averaging 5.4. One well, 17-P1, is an alkaline sodium sulfate water with the pH averaging <br /> 9.2. Iron, manganese, aluminum, fluoride and pH levels exceed recommended water quality <br /> criteria for agricultural use, and concentrations of aluminum and fluoride exceed <br /> recommended water quality criteria for livestock. <br /> The aquifer underlying the coal is identified as the underburden aquifer. The wells in the <br /> underburden have been completed 17 to 64 feet below the coal, and samples are <br /> representative of water within the lower Dakota Sandstone. This confined aquifer is <br /> recharged along the Uncompahgre Plateau to the northeast and discharges towards the <br /> southwest. Transmissivity was measured at six sites and varies from 3.0 to 88 ftZ/day, <br /> averaging 38 ftZ/day. Hydraulic conductivity values varied from 0.07 to 4.5 ft/day, averaging <br /> 1.6 ft/day. This aquifer is not used locally to any great extent. <br /> The water in the underburden is characterized as a hard, moderately alkaline saline water <br /> with high sulfate concentrations (average sulfate concentrations of 695 mg/1). Two wells <br /> show a calcium/magnesium sulfate type water while one well shows an alkaline sodium <br /> bicarbonate type water. The TDS varies from 960-2648 mg/I, averaging 1619 mg/l. <br /> Dissolved iron levels vary from 0.02 to 2.51 mg/I and average 0.63 mg/l. The sodium <br /> bicarbonate well occasionally exhibits pH levels which exceed the recommended agricultural <br /> standard. Another well shows manganese levels which exceed the agricultural standards. <br /> 8 <br />