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In addition to the three stratigraphic formations addressed, the alluvial deposits of the Colorado River flood plain can also be classified as an aquifer. The alluvium contains water from the river and presumably discharges water to the permeable units which subcrop beneath it. The strata in the Roadside mine plan area dip toward the Colorado River, whereas the strata in the Cameo mine plan area dip away from the Colorado River. Therefore, ground water from the Roadside mine plan area discharges to the Colorado River, whereas the Colorado River recharges the ground water system in the Cameo mine plan area. Presently, approximately 13 acre-feet of water is consumed annually within the Roadside mine through evaporation and absorption. Upon closure of the Roadside mine, ground water in the aquifers would resume its flow to the Colorado River. Approximately 225 acre-feet of water is produced within the Cameo mine as inflows. Some of this water is consumed within the Cameo mine by evaporation in ventilation air and absorption on the coal. The remaining water is pumped to the surface and discharged. The source of this inflow water is the Colorado River. Upon the closure of the Cameo mine, water will continue to flow from the Colorado River until the entire underground workings are filled with water. The applicant will have to submit evidence that adequate water will be obtained to replace the water which is lost from the Colorado River prior to mine closure. Until the mine closes down, there will be no problem with water balance, since the water is pumped back into the river, and mine closure is not anticipated until 1995 at the earliest. Although it is evident that the Colorado River is the major source of water which is discharged from the Cameo mine, the applicant has not supplied sufficient evidence to determine how much comes from dewatering the coal, perched water tables, or fracture and faults. However, it is evident that the mine is having an insignificant effect on the quantity of water in the Colorado River system as long as mine inflows are pumped out of the mine. The major effect of mining on the quality of water is through an increase in soluble salt levels. There is a slight increase in the pH of the inflow water over that of the Colorado River water, but this effect is insignificant. Because of the pH of the water, heavy metals would be relatively insoluble. Thus, they should pose no significant problem to water quality. The mine discharge water has a higher content of soluble salts than the Colorado River. Discharge from the mine is diluted by receiving waters, which results in a total increase in the soluble salt level of the Colorado River by an average of 0.1%. This is the current estimate but will be revised as new information becomes available as a result of NPDES requirements. -15-