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0 = 13,524 fta/day (Wadge Overburden) • <br />Q = 196 fta/day (Wadge Coal) <br />Q = 88 ft=/day (Wolf Creek Coal) <br />It is not possible to estimate discharges for the alluvial aquifers because aquifer <br />thicknesses and hydrologic properties are quite variable within the study area. Bedrock <br />aquifers probably discharge to alluvial aquifers in some areas, but this contribution to <br />the alluvial ground water system ceinnot be quantified due to the intermittent nature of <br />the surface water flows in the permit area. <br />Evapotranspiration (ET) is an important discharge mechanism for the alluvial aquifers in <br />the Seneca II-W area. Peabody conducted a detailed study of the hydrologic balance of the <br />Hubberson Gulch watershed in 1979 and 1980. Potential evapotranspiration (PET) was <br />calculated using the Blaney-Criddle equation (Schulz, 1976) which is appropriate for the <br />western United States. The Blaney-Cri ddle equation is expressed as: <br />PET = KF <br />where: <br />K = Crop use coefficient . <br />F = consumptive use factor <br />The crop use coefficient for the grass-sagebrush-scrub oak vegetation that is typical of <br />the Hubberson Gulch drainage is 0.60 annually and 0.70 monthly during the frost free <br />months of April-October. The consumptive use factor is calculated using the equation: <br />F = tp_ , <br />100 <br />where: <br />t = mean monthly air temperature, °F <br />p = percent of annual daytime hours at arty particular latitude <br />Table 7-6 shows data relevant to the calculation of PET for the period of July, 1979 <br />through June, 1980. Temperature data are corrected for the elevation difference between <br />the NOAA meteorological station at Hayden, Colorado (elevation 6337 ft), and the Hubberson <br />Culch watershed average elevation of 7400 feet. Precipitation values from Hayden have <br />also been corrected by a factor of 1.23; the Seneca II-W area has a mean annual <br />precipitation of about 19 inches, which is 23 percent greater than Hayden's mean annual • <br />precipitation of 15.45 inches. <br />26 <br />