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UNDERGROUND MINING Mining Consumption This includes water consumption by mining equipment and machinery, primarily for dust control. In Utah, estimates of this type of operationa] consumption for mines in the Mud Creek Basin CHIA area have been made, based on a figure of 3.2 gallons per ton of coal mined (p. 68, tqud Creek Drainage Basin CHIA, May 1984). Annual consumption for the five CHIA area mines ranges from 1 to 53 acre-feet. The CHIA document cautions, however, that the estimates are worst-case assumptions based on maximum production capacity rather than actual production. The CrIIA adds that the water consumed is derived from ground-water storage and will ultimately result it reduced surface discharge in the basin. Tne 3.2 gallon-per-ton-of-coal figure is an easily-applied number. However, because the annual consumption estimate is based on widely divergent individual mine production amounts and because the effe.:t on streamflow is indirect and possibly very long term, it is recom~nended tnat depletions from this effect be estimated only for mines with an annual production in excess of 1 million tons and only where the source of water is from surface diversions or is clearly derived from alluvial aquifers either by means of alluvial wells or mine inflows via subcropping of affected aquifers beneath alluvial aquifers. If the individual mine has estimated operational consumption, this figure should be used in lieu of the 3.2 gallons-per-ton figure. Ventilation consumotion This includes evaporation from the coal seam induced by low-humidity incoming air wnicn becomes nearly saturated before it exits the mine. Tnis loss is directly proportional to the areal extent of the underground workings. Estimates of ventilation loss for the Mud Creek Drainage Basin CHIA area are based on a figure of 0.014 acre-feet/year/square mile of underground workings and range from 4 to 65 acre-feet/year for the five ' mines. Tne CHIA indicates that this loss is derived from ground-water storage and will ultimately result in reduced surface discharge to the basin. Although the 0.014 acre-feet/year/square mile figure is easily applied, widely divergent mine areas and probable significant attenuation of the indirect, long-tens effects on streamflow argue against generally estimating such losses for all mines. It is recommended that consumption from this effect be estimated only for mines with more than 1.0 square mile of underground workings--and only where mine inflows are clearly le rived from subcroppings of affected aquifers beneath channel alluvium. If the individual mine nos estimated ventilation loss, its figure should be used in lieu of the 0.014 acre-feet/year/square mile figure. -2-