2021-03-06_PERMIT FILE - C1981008A

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outflow to contiguous aquifers to the southwest. Discharge rates from overburden, Dakota coal and the underburden can be calculated using Darcy's law. Calculations of ground water flow (inflow) from the overburden, Dakota coal and underburden indicate that the aquifers are discharging 77,058 ft3/day, 663 ft3/day, and 4,133 ft3/day, respectively through the defined cross sections. Discharge from the Dakota coal and the underburden is relatively small compared to the overburden. There may be some discharge from the Dakota coal on the southern side of Tuttle Draw, but the overburden aquifer is the major source of discharge (inflow) to the surface water baseflow (outflow) within the vicinity of New Horizon 1 and new Horizon 2 mining areas. In conclusion, the overburden aquifer is the primary source of discharge (inflow) which maintains the surface water baseflow (outflow) of Turtle and Calamity Draws. The coal and underburden aquifers discharge much less water than the overburden with most of that discharge being released downstream of the lower surface water monitoring sites on Tuttle and Calamity Draws (SW -N3 and SW -N103), respectively. Evapotranspiration Evapotranspiration (ET) is a major component of discharge at the New Horizon mining areas. To determine the amount of ET, the Baseline Vegetation Studies Area Map (Map 2.04.10-1) was used. The total study area encompasses 618 acres in and adjacent to the New Horizon 2 Mine permit area. Of the total acreage included in the study area 13 percent (83 acres) are swales (wet standing water with hydrophytic vegetation), 25.6 percent (159 acres) is irrigated pasture, 21.6 percent (133 acres) is in hay production, 16.6 percent (102.4 acres) is under annual crop production, 1.8 percent (11 acres) consists of orchards, 1.0 percent (6 acres) consists of ponds and the remaining 20.4 percent (124 acres) is sagebrush grasslands, disturbed areas, dwellings or roads. The percentages of each vegetation type are generally representative of adjacent areas as well. Most of the ET or consumptive use rates used were taken from the Soil Conservation Service (SCS) Colorado Irrigation Guide which is a field office technical guide. The consumptive use rates used in the guide were calculated by a computer program that uses the modified Blaney-Criddle method. In determining the ET rate for the study area it is assumed that the irrigation practices evenly distribute sufficient amounts of water to fulfill the consumptive use water demands required by each of the different vegetation types. Based on the vegetation types and the estimated consumptive use rates, there are approximately 1,299 acre feet of water evapotranspired within the study area. Evaporation from the pond was not included in this total. Excess irrigation water flows overland and contributes to the streamflow of Calamity and Tuttle Draws. The streamflow from Calamity and Tuttle Draws in turn contributes to the flow of the San Miguel River two and one half miles downstream of the mining disturbance. The total volume of water that could be evapotranspired from the vegetation study is assumed to be under ideal conditions. In reality the evapotranspiration rates are slightly less. In many areas shallow soils and rock ledges restrict rooting depths and inhibit maximum plant growth, thereby reducing ET rates. Aquifer Characteristics of the New Horizon Mining Areas Eleven aquifer tests were conducted within the New Horizon 1 leasehold, and the New Horizon 2 mining area and the immediate vicinity. A wide variety of aquifer testing and analysis techniques were employed because of the range of well yields and aquifer types. Aquifer testing techniques include constant discharge tests (Theis, 1935; Neuman, 1975; and Cooper and Jacob, 1946); slug injection and withdrawal tests (Cooper Page 2.04.7-9 March 2017 (TR -77)