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<br />area is toward the center of the basin and may discharge into the Fish Creek <br />alluvial aquifer. Locally, some of the smaller, laterally discontinuous <br />aquifers discharge into the alluvium of Trout Creek, Middle Creek, and Foidel <br />Creek. <br />The alluvial aquifers are locally recharged by the bedrock aquifers, as well <br />as by direct infiltration from precipitation, irrigation return flows, and <br />surface runoff. The alluvial water is discharged into the adjacent stream or <br />consolidated aquifers, or may flow out of the basin via the Trout Creek <br />alluvium which discharges into the Yampa River alluvial system. <br />The Trout Creek Sandstone, which is thought to be a regionally significant <br />source of ground water, is usually characterized by sodium-sulfate type water <br />with an average total dissolved solids (TDS) concentration of about 1040 mg/1. <br />The Wadge Coal and overburden units are marginally acceptable as aquifers at <br />the Edna Mine site, however they are included in this discussion because this <br />unit as a whole is considered to be an aquifer at other mine sites within <br />Twentymile Park. <br />Aquifer properties were determined from single-hole aquifer tests. These <br />tests indicate that the transmissivity of the coal and overburden varies from <br />0.7 ftz/day to 39 ft2/day. These values indicate that the aquifer is <br />marginally useful as a water source in this area. <br />The Wadge Coal water chemistry is calcium/magnesium bicarbonate to sodium <br />sulfate, with TDS values varying between 490 mg/1 and 570 mg/1. <br />Ground water quality in the Wadge overburden decreases in the downdip <br />direction. Up-gradient monitoring locations indicate that the water is of <br />moderately good quality, characterized by low Sodium Absorption Ratio (SAR) <br />values and moderate levels of total dissolved solids. The down-gradient <br />monitoring wells, however, show increasingly higher levels of total dissolved <br />solids. This trend applies primarily to the Moffat Area, where undisturbed <br />conditions exist. <br />The vertical migration of water from the Trout Creek Sandstone to the Wadge <br />Coal, due to mining related disturbances is not expected to occur, primarily <br />due to the thick sequence of relatively impermeable interburden. <br />The two alluvial aquifer systems present within the Edna permit area are the <br />Oak Creek and Trout Creek alluvial aquifers. Both of the alluvial aquifers <br />are in direct hydraulic communication with each associated stream. <br />Baseline water quality data from the Trout Creek alluvial aquifer indicates <br />that the quality of this water is suitable for agricultural purposes. The <br />water is moderately low in TDS levels (less than 350 mg/1) and exhibits a low <br />SAR. The water quality of the Oak Creek alluvial aquifer is generally lower <br />than that found in the Trout Creek alluvium (TDS levels ranging from 400 to <br />1700 mg/1). This may be attributable to the levels of disturbance and <br />activities already present along the Oak Creek valley. These activities <br />include the presence of roads and railroads situated atop the alluvium and <br />disturbance from past mining activities. <br />-B <br />