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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 ft2/day, averaging 13.3 ft2/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 to <br />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 mg/l. <br />Sulfate concentrations are very high, varying from 875 mg/1 to 6872 mg/1 and averaging 3176 <br />mg/l. In some of the overburden wells, sulfate, TDS, manganese and fluoride exceed <br />recommended standards for livestock drinking water. In addition concentrations of manganese <br />and fluoride exceed the agricultural use standards in some wells. <br />The Dakota coal has been described as an aquifer. Wells completed in the Dakota show water <br />level fluctuations of 1.3 to 14.6 feet. The water table exhibits seasonal fluctuations with high <br />water levels in late fall. The aquifer is recharged from the east north-east and discharges to the <br />west and along Calamity Draw. The transmissivity varies from 0.92 to 6.0 ft2/day, based on <br />hydraulic conductivity values of 0.04 to 0.34 ft/day (average values of 0.19 ft/day), reflecting <br />moderate flow capabilities. <br />The water quality of the Dakota coal is unacceptable for most uses. The saline, sulfate-based <br />water has TDS levels varying from 1050-4444 mg/l, averaging 2822 mg/1 at New Horizon Mine. <br />Three wells at the New Horizon Mine 2 exhibit two distinct geochemical characteristics. Two <br />wells have calcium/magnesium sulfate water with the pH averaging 5.4. One well, 17-P1, is an <br />alkaline sodium sulfate water with the pH averaging 9.2. Iron, manganese, aluminum, fluoride <br />and pH levels exceed recommended water quality criteria for agricultural use, and concentrations <br />of aluminum and fluoride exceed 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 representative of <br />water within the lower Dakota Sandstone. This confined aquifer is recharged along the <br />Uncompahgre Plateau to the northeast and discharges towards the southwest. Transmissivity <br />was measured at six sites and varies from 3.0 to 88 ft2/day, averaging 38 ft2/day. Hydraulic <br />conductivity values varied from 0.07 to 4.5 ft/day, averaging 1.6 ft/day. This aquifer is not used <br />locally to any great extent. <br />The water in the underburden is characterized as hard, moderately alkaline saline water with high <br />sulfate concentrations (average sulfate concentrations of 695 mg/1). Two wells show a <br />calcium/magnesium sulfate type water while one well shows an alkaline sodium bicarbonate type <br />water. The TDS varies from 960-2648 mg/l, averaging 1619 mg/l. Dissolved iron levels vary <br />from 0.02 to 2.51 mg/1 and average 0.63 mg/1. The sodium bicarbonate well occasionally <br />exhibits pH levels that exceed the recommended agricultural standard. Another well shows <br />manganese levels that exceed the agricultural standards. All wells meet the recommended water <br />14