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U~ /1 ~~~ -36- The applicant has provided an estimate (p. III-77a, revised 10/24/83)) of flow from the alluvium through the coal subcrop into the Eagle No. 5 Mine workings. Using an equation developed by McWhorter (1961), the applicant has predicted a maximum inflow from the river system into the coal seam of 180 gpm (0.40 cfs). This is a conservative estimate of flow through the "F" coal seam and Middle sandstone subcrops. This estimate, however, does not take into account fractures and faults which may intersect the mine workings and the stream/alluvial aquifer system. Tn the Eagle No. 5 Mine, these sources are the greatest contributors to mine inflows into the mine workings which are locdted below the level of the stream/alluvial aquifer systems. In the case of the Eagle No. 5 Mine, much of the anticipated stream flow depletion has already occurred. The operation has previously mined beneath the Williams Fork and Yampa Rivers, and the proposed mine workings in the 2 West area and the Empire Tract would be extensions of the existing workings east and west of the rivers, and also above the level of the rivers. As a worst-case estimate, it could be assumed that all of the present mine inflows to the Eagle No. 5 Mine (approximately 2 cfs) were flowing from the rivers. This would be a relatively small portion of low flow in the Yampa River. (Average low flow in September is 107 cfs at Maybell.) Since part of this inflow comes from other sources, the actual depletion of flow in the stream/alluvial system would be less. The applicant has estimated stream flow depletion resulting from the Eagle No. 9 Mine in the permit revision Submitted October 31, 1983. Past mining activities in the Eagle No. 9 Mine were limited to mine development beneath a portion of the Yampa River alluvium in Big Bottom. Under the proposed plan, the existing workings would be expanded beneath the Yampa River stream/alluvial system. This proposed operation hd5 a high potential for stream flow depletion through subcrops of aquifers and coal; through existing fractures; and through subsidence. Therefore, the applicant was required to predict the magnitude and significance of the potential stream flow depletion resulting from the No. 9 mining operation before the Division could propose approval for the Eagle No. 9 Mine. To satisfy these conditions, the applicant quantified the flows previously discussed and predicted that in total they would result in an insignificant depletion to stream flow. Worst case pro3ections were used. The revised sections of the permit application which cover these concerns are on pages III-76 to III-7Bd. The water that accumulates in the Eagle No. 5 and No. 9 Mines is treated and discharged to the Williams Fork River. Water discharging from the No. 5 mine is of the sodium bicarbonate type with very minor amounts of other cations. The high sodium content is reflected in the small increase in sodium found at the Williams Fork downstream. Dissolved solids average BOl mg/1 with a maximum of 875 mg/], indicating dissolved solids concentrations from the Eagle No. 5 Mine vary within a very small range of values. The pH values range from 8.24 to 8.60 and average 8.43, indicating the same relative consistency of mine discharge water quality found in the dissolved solids concentrations. Iron concentrations are low compared with values found in the Williams Fork and Yampa Rivers. Concentrations ranged from less than 0.03 mg/1 to 0.99 mg/1 and averaged less than 0.24 mg/1. Manganese values were also low, with values ranging from less than 0.02 mg/1 to 0.03 mg/1.