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Discharge <br />Ground water is discharged through streams, evapotranspiration, wells, springs and seeps, and <br />by subsurface outflow to contiguous aquifers to the southwest. <br />Discharge rates from overburden, Dakota coal and the underburden can be calculated using <br />Darcy's law. Calculations of ground water flow (inflow) from the overburden, Dakota coal and <br />underburden indicate that the aquifers are discharging 77,058 ft3/day, 663 ft3/day, and 4,133 <br />ft3/day, respectively through the defined cross sections. Discharge from the Dakota coal and the <br />underburden is relatively small compared to the overburden. There may be some discharge from <br />the Dakota coal on the southern side of Tuttle Draw, but the overburden aquifer is the major source <br />of discharge (inflow) to the surface water baseflow (outflow) within the vicinity of New Horizon 1 and <br />new Horizon 2 mining areas. <br />In conclusion, the overburden aquifer is the primary source of discharge (inflow) which maintains <br />the surface water baseflow (outflow) of Turtle and Calamity Draws. The coal and underburden <br />aquifers discharge much less waterthan the overburden with most of that discharge being released <br />downstream of the lower surface water monitoring sites on Tuttle and Calamity Draws (SW-N3 and <br />SW-N103), respectively. <br />Evaaotransairation. Evapotranspiration (ET) is a major component of discharge at the New <br />Horizon mining areas. To determine the amount of ET, the Baseline Vegetation Studies Area Map <br />(Map 2.04.10-1) was used. The total study area encompasses 618 acres in and adjacent to the <br />proposed New Horizon 2 Mine permit area. Of the total acreage included in the study area 13 <br />percent (83 acres) are swales (wet standing waterwith hydrophytic vegetation), 25.6 percent (159 <br />acres) is irrigated pasture, 21.6 percent (133 acres) is in hay production,16.6 percent (102.4 acres) <br />is under annual crop production, 1.8 percent (11 acres) consists of orchards, 1.0 percent (6 acres) <br />consists of ponds and the remaining 20.4 percent (124 acres) is sagebrush grasslands, disturbed <br />areas, dwellings or roads. The percentages of each vegetation type are generally representative <br />of adjacent areas as well. Most of the ET or consumptive use rates used were taken from the Soii <br />Conservation Service (SCS) Colorado Irrigation Guide which is a field office technical guide. The <br />consumptive use rates used in the guide were calculated by a computer program that uses the <br />Revised 25 Jul 2002 2.04.7-10 <br />