Laserfiche WebLink
Very little hydrologic documentation is available regarding the alluvium found along the small <br />tributaries draining the area. Peabody drilled one well in the alluvium of Calamity Draw in <br />mid -1986. The well appears to have been completed in a clay lens. The alluvial water table <br />fluctuates seasonally within 5 to 10 feet of the surface with highest water levels in August and <br />lowest water levels in January. Recharge is primarily derived from irrigation return flow and <br />secondarily from flow in Calamity Draw. Transmissivity varies from 6.6 to 10.1 ft2 /day. The <br />hydraulic conductivity varies from 0.4 to 0.6 ft /day. The water is characterized as a saline, hard, <br />neutral pH, calcium sulfate water with average TDS of 3291 mg /1. <br />The aquifer overlying the coals in the upper strata of the Dakota Sandstone is unconfined and <br />flows generally toward the southwest. Water levels fluctuate between 3 and 23 feet below the <br />ground surface. Highest levels (closest to the surface) of this water table occur between June and <br />August, as a result of irrigation, and lowest levels between December and March. Two wells <br />south of Calamity Draw (GW -N31 and GW -N32 on permit Map 2.04.7 -1A) exhibited limited <br />water level 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) <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 /l and average 4613 mg /1. <br />Sulfate concentrations are very high, varying from 875 mg /l to 6872 mg /1 and averaging 3176 <br />mg /1. 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 /1, 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 />14 <br />