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Quaternary alluvium, and 4) replaced spoils. With the exception of the Quatemary <br />alluvium and replaced spoils, it is thought that each of the identified aquifers are <br />hydrologically discontinuous with each other, due to the relatively impermeable nature of <br />the intervening strata. <br />The consolidated (bedrock) aquifers of Twentymile Park basin aze generally recharged at <br />their outcrops neaz [he edge of the basin. Flow direction from the rechazge area is toward <br />the center of the basin. Ground water cannot flow out of the basin because bedding <br />generally dips toward the center of the basin at all locations in the basin. Locally, some <br />of the smaller, laterally discontinuous aquifers discharge into the alluvium of Trout <br />Creek, Middle Creek, and Foidel Creek. <br />The alluvial aquifers are locally recharged by the bedrock aquifers, as well as by direct <br />infiltration from precipitation, irrigation return flows, and surface mnoff. The alluvial <br />water is discharged into the adjacent stream or consolidated aquifers, or may flow out of <br />the basin via the Trout Creek alluvium which discharges into the Yampa River alluvial <br />system. <br />The Trout Creek Sandstone, which is thought to be a regionally significant source of <br />ground water, is usually characterized by sodium-sulfate type water with an average total <br />dissolved solids (TDS) concentration of about 1040 mg/I. <br />The Wadge Coal and overburden units are marginally acceptable as aquifers at the Edna <br />Mine site; however, they aze included in this discussion because this unit as a whole is <br />considered to be an aquifer at other mine sites within Twentymile Park. <br />Aquifer properties were determined from single-hole aquifer tests. These tests indicate <br />that the transmissivity of the coal and overburden vazies from 0.7 ft2/day to 39 ftZ/day. <br />These values indicate that the aquifer is mazginally useful as a water source in this area. <br />The Wadge Coal water chemistry is calcium magnesium bicarbonate to sodium sulfate, <br />with TDS values varying between 490 mg/1 and 570 mg/1. <br />Ground water quality in the Wadge overburden decreases in the downdip direction. <br />Up-gradient monitoring locations indicate that the water is of moderately good quality, <br />characterized by low Sodium Absorption Ratio (SAR) values and moderate levels of total <br />dissolved solids. The down-gradient monitoring wells, however, show increasingly <br />higher levels of total dissolved solids. This trend applies primarily to the Moffat Area, <br />where undisturbed conditions exist. <br />The vertical migration of water from the Trout Creek Sandstone to the Wadge Coal, due <br />to mining related disturbances, is not expected to occur primarily due to the thick <br />sequence of relatively impermeable interburden. <br />Etlna Mine 5 Permit Renewal No. 4 <br />