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The aquifer overlying the coals in the upper strata of the Dakota Sandstone is unconfined and flows generally toward the southwest. However, in the Nuc1a area it discharges into both Tuttle and Calamity Draws (north and south respectively). Water levels fluctuate between 3 and 23 feet below the around surface. Highest levels (closest to the surface) of this water table occur between June and August and lowest levels between December and March. Two wells south of Calamity Draw (GW-N31 and GW-N32 on Exhibit 7-1) have exhibited limited water level fluctuations since their construction in mid-1986. The Upper Dakota aquifer is predominantly recharged by return-flow from the Lower Second Park Irrigation Ditch and the West Lateral Irrigation Ditch (at Nucla and Nucla East respectively). Some recharge is probably derived from infiltration of precipitation and subsurface ground water flow. The tr~nsmissivity of the overburden (Upper Dakota aquifer) varies from 3 to 53 ft /day, averaging 13.3 ft2[/day. The McWhorter analysis of pit inflow conservatively estimated that the hydraulic conductivity of the overburden was 0.61 ft/day. Hydraulic conductivity calculations from field tests of the overburden showed a range of 0.39-1.05 ft/day indicating moderate permeability. The water found in the overburden is characterized as very hard, saline, calcium/magnesium sulfate water with neutral pH. TDS levels vary from 1494-10074 mg/1 and average 4613 mg/1. Sulfate concentrations are very high, varying from 875 mg/1 to 6872 mg/1 and averaging 3176 mq/1. In some of the overburden wells sulfate, TDS, manganese and fluoride exceed recommended standards for livestock drinking water. In addition concentrations of manganese and fluoride exceed the agricultural use standards in some wells. The Dakota coal has been described as an aquifer. Wells completed in the Dakota show water level fluctuations of 1.3' to 14.6'. The water table exhibits seasonal fluctuations with high water levels in late fall. The aquifer is recharged from the east north east and discharges to the west and a14ng Tuttle and Calamity Draws. The transmissivit,y varies from 0.92 to 6.0 ftZ/day, based on hydraulic conductivity values of 0.04 to 0.34 ft/day (average values of 0.19 ft/day), reflecting moderate flow capabilities. The water quality of the Dakota coal is unacceptable for most uses. The saline, sulfate-based water has TDS levels varying from 1050-4444 mg/1, averaging 2822 mg/1 at Nucla East, and TDS levels varying from 5438-7100 ma/1 and averaging 6701 mg/1 at Nucla. The three wells at Nucla East exhibit two distinct geochemical characteristics. Two wells have Calcium/magnesium sulfate water with the pH averaging 5.4. One well, 17-P1, is an alkaline sodium sulfate water with the pH averaging 9.2. Iron, manganese, aluminum, fluoride and pH levels exceed recommended water quality criteria for agricultural use, and concentrations of aluminum and fluoride exceed recommended water quality criteria for livestock. The aquifer underlying the coal is identified as the underburden aquifer. The wells in the underburden have been completed 17' to 64' below the coal and samples are representative of water within the lower Dakota Sandstone. This confined aquifer is recharged along the Uncompahgre Plateau, to the northeast, and discharges towards the southwest. Transmissivity was measured at six sites and varies from 3.0 to 88 ft2/day, averaging 38 ftZ/day. Hydraulic conductivity values varied from 0.07 to 4.5 ft/day, averaging 1.6 ft/day. This aquifer is not used locally to any great extent. _11-