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Near surface ground water in the Nucla area is partially recharged by irrigation return flow <br /> through Quaternary aeolian and alluvial deposits. The lower Dakota and underlying <br /> Morrison Formations are regional aquifers, although water from the Dakota Formation is not <br /> heavily utilized due to its high salinity. The Morrison Formation water is widely used for <br /> stock and domestic wells. <br /> Very little hydrologic documentation is available regarding the alluvium found along the <br /> small tributaries draining the area. Peabody drilled one well in the alluvium of Calamity <br /> Draw in mid-1986. The well appears to have been completed in a clay lens. The alluvial <br /> water table fluctuates seasonally within 5 to 10 feet of the surface with highest water levels <br /> in August and lowest water levels in January. Recharge is primarily derived from irrigation <br /> return flow and secondarily from flow in Calamity Draw. Transmissivity varies from 6.6 to <br /> 10.1 ftZ/day. The hydraulic conductivity varies from 0.4 to 0.6 ft/day. The water is <br /> characterized as a saline, hard, neutral pH, calcium sulfate water with average TDS of <br /> 3291 mg/l. <br /> The aquifer overlying the coals in the upper strata of the Dakota Sandstone is unconfined and <br /> flows generally toward the southwest. However, in the New Horizon Mine 1 area it <br /> discharges into both Tuttle and Calamity Draws (north and south respectively), Water levels <br /> fluctuate between 3 and 23 feet below the ground surface. Highest levels (closest to the <br /> surface) of this water table occur between June and August and lowest levels between <br /> December and March. Two wells south of Calamity Draw (GW-N31 and GW-N32 on the <br /> monitoring stations map) have exhibited limited water level fluctuations since their <br /> construction in mid-1986. <br /> The Upper Dakota aquifer is predominantly recharged by return flow from the Lower Second <br /> Park Irrigation Ditch and the West Lateral Irrigation Ditch (at New Horizon Mine 1 and <br /> New Horizon Mine 2 respectively). Some recharge is probably derived from infiltration of <br /> precipitation and subsurface ground water flow. The transmissivity of the overburden <br /> (Upper Dakota aquifer) varies from 3 to 53 W/day, averaging 13.3 W/day. The McWhorter <br /> analysis of pit inflow conservatively estimated that the hydraulic conductivity of the <br /> overburden was 0.61 ft/day. Hydraulic conductivity calculations from field tests of the <br /> overburden showed a range of 0.39 to 1.05 ft/day, indicating moderate permeability. <br /> The water found in the overburden is characterized as very haul, saline, calcium/magnesium <br /> sulfate water with neutral pH. TDS levels vary from 1494-10074 mg/l and average 4613 <br /> mg/l. Sulfate concentrations are very high, varying from 875 mg/l to 6872 mg/l 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 northeast and <br /> discharges to the west and along Tuttle and Calamity Draws. The transmissivity varies from <br /> 7 <br />