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The consolidated aquifers of Twentymile Park basin aze generally recharged at their outcrops near the edge of the basin. Flow direction from the recharge area is toward the center of the basin probably dischazging into the Fish Creek alluvial aquifer. Locally, some smaller, laterally discontinuous aquifers discharge into the alluvium of Trout Creek, Middle Creek, and Foidel Creek. The alluvial aquifers are locally recharged from the bedrock aquifers, as well as by direct infiltration from precipitation,irrigation return flows, and swface runoff. The alluvial water is discharged into the adjacent stream or consolidated aquifers, or may flow out of the basin via the Trout Creek alluvium which in turn discharges into the Yampa River alluvial system. The Trout Creek Sandstone, thought to be a regionally significant sowce of ground water, is characterized by sodium-sulfate type water with an average total dissolved solids (TDS) concentration of about 1040 mg/1. The Wadge Coal and overbwden units are marginally acceptable as aquifers at the Edna Mine site; however they are included in this discussion because this unit as a whole is considered to be an aquifer at other mine sites within Twentymile Pazk. Aquifer properties were determined from single-hole aquifer tests. These tests indicate that the trarumissivity ofthe coal and overbwdenvariesfrorn 0.7 ftZ/day to 39 ft /day. These values indicate that the aquifer is marginally useful as a water sowce in this area. The Wadge Coal water chemistry is calcium magnesium bicazbonate to sodium sulfate, with TDS values varying between 490 mg/1 and 570 mg/l. The vertical migration of water between these units is not anticipated because of the thick sequence of relatively impermeable interbwden. Groundwater quality in the Wadge overbwden deteriorates in the downdip direction. Up-gradient monitoring locations indicate that the water is of moderately good quality, characterized by low Sodium Absorption Ratio (SAR) values and moderate levels of total dissolved solids. The down-gradientmonitoring wells, however, show increasingly higher levels of total dissolved solids, demonstrating that longer residence time in the bedrock aquifer results in greater dissolution of sulfate and total salts and leads to the degradation of water quality. The two alluvial aquifer systems within the Edna permit area are the Oak Creek and Trout Creek alluvial aquifers. Both are indirect hydraulic communicationwith each associated stream. Baseline water quality data from the Trout Creek alluvial aquifer indicates that the water is suitable for agricultwal purposes. It is moderately low in TDS levels (less than 350 mg/1) and exhibits a low SAR. The water quality of the Oak Creek alluvial aquifer is generally lower than that of the Trout Creek alluvium (TDS levels ranging from 400 to 1700 mg/1). This is probably attributable to the greater levels of distwbance and activities present along the Oak Creek valley, including roads, railroads and historic coal mining activity on the alluvium. Edna Mine 5 permit Renexal No. 3