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• the Dakota coal on the southern side ofTuttle 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 lesswaterthan the overburdenwith mostofthatdischargebeing released <br />downstream of the lower surface water monitoring sites on Tuttle and Calamity Draws (SW-N3 and <br />SW-N103), respectively. <br />Evapotranspiration. Evapotranspiration (ET) is a major component of discharge at the New <br />Horizon mining areas. TodeterminetheamountofET,theBaselineVegetationStudiesAreaMap <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 Soil <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 />modified Blaney-Griddle method. In determining the ET rate forthe study area it is assumed that <br />the irrigation practices evenly distribute sufficient amounts ofwater to fulfill the consumptive use <br />water demands required by each of the different vegetation types. <br />Based on the vegetation types and the estimated consumptive use rates, there are approximately <br />1,299 acre feet ofwaterevapotranspiredwithinthestudyarea. Evaporation from thepondwasnot <br />included in this total. Excess irrigation water flows overland and contributes to the streamflow of <br />Calamity and Tuttle Draws. The streamflow from Calamity and Tuttle Draws in turn contributes to <br />the flow of the San Miguel River two and one half miles downstream of mining and the proposed <br />mining disturbance. <br />• (REVISED6/28/01) 2.04.7-10 <br />