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Very little hydrologic documentation is available regarding the alluvium found along the small <br />tributaries draining the area. Peabody, the former operator, drilled one well in the alluvium of <br />Calamity 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 in <br />August and lowest water levels in January. Recharge is primarily derived from irrigation return <br />flow and secondarily from flow in Calamity Draw. Transmissivity varies from 6.6 to 10.1 ft2/day. <br />The hydraulic conductivity varies from 0.4 to 0.6 ft/day. The water is characterized as a saline, <br />hard, neutral pH, calcium sulfate water with average TDS of 3291 mg/l. <br />The aquifer overlying the coals in the upper strata of the Dakota Sandstone is unconfined and flows <br />generally toward the southwest. Water levels fluctuate between 3 and 23 feet below the ground <br />surface. Highest levels (closest to the surface) of this water table occur between June and August, <br />as a result of irrigation, and lowest levels between December and March. Two wells south of <br />Calamity Draw (GW -N31 and GW -N32 on permit Map 2.04.7-1A) exhibited limited water level <br />fluctuations since their construction in mid -1986. <br />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) varies <br />from 3 to 53 ft2/day, averaging 13.3 ft2/day. The McWhorter analysis of pit inflow conservatively <br />estimated that the hydraulic conductivity of the overburden was 0.61 ft/day. Hydraulic <br />conductivity calculations from field tests of the overburden showed a range of 0.39 to 1.05 ft/day, <br />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/l 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 water <br />levels in late fall. The aquifer is recharged from the east north-east and discharges to the west and <br />along Calamity Draw. The transmissivity varies from 0.92 to 6.0 ft2/day, based on hydraulic <br />conductivity values of 0.04 to 0.34 ft/day (average values of 0.19 ft/day), reflecting moderate flow <br />capabilities. <br />The water quality of the Dakota coal is unacceptable for most uses. The saline, sulfate -based water <br />has TDS levels varying from 1050-4444 mg/1, averaging 2822 mg/l. Three wells exhibit two <br />distinct geochemical characteristics. Two wells have calcium/magnesium sulfate water with the <br />pH averaging 5.4. One well, 17-P1, is an alkaline sodium sulfate water with the pH averaging 9.2. <br />Iron, manganese, aluminum, fluoride and pH levels exceed recommended water quality criteria <br />for agricultural use, and concentrations of aluminum and fluoride exceed recommended water <br />quality criteria for livestock. <br />13 <br />