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Ground Water <br />Monitoring and on -site investigations have identified four aquifer systems at the Edna <br />Mine. These units are: 1) Trout Creek Sandstone, 2) Wadge Coal and overburden, 3) <br />Quaternary alluvium, and 4) replaced spoils. With the exception of the Quaternary <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 are generally recharged at <br />their outcrops near the edge of the basin. Flow direction from the recharge 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 of <br />the smaller, laterally ,discontinuous aquifers discharge into,the alluvium of Trout Creek, <br />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 runoff. 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 1 040 milligrams /liter (mg/1). ; <br />The Wadge Coal and overburden units are marginally acceptable as aquifers at the Edna <br />Mine site; however, they are included in this discussion because,this unit as a whole is <br />considered to be an aquifer at other mine sites within Twentymile Park. Aquifer <br />properties were determined from single. hole aquifer tests. These tests indicate that the <br />transmissivity of the coal and overburden varies from 0.7 ft2 /day fo 39 ft2 /day. These <br />values, indicate that the aquifer is marginally 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. Ground water quality in the <br />Wadge overburden decreases in the,downdip direction. Up- gradient monitoring locations . <br />indicate that the water is of moderately good quality, characterized by low Sodium_ . <br />Absorption Ratio (SAR).values and moderate levels of total dissolved, solids. The <br />down - gradient monitoring, wells, however, show -increasingly higher levels of total <br />dissolved solids. This trend applies primarily to the Moffat Area. <br />The vertical migration of water between the Trout Creek Sandstone and the Wadge Coal <br />due to mining related disturbances has not occurred, primarily due to the thick sequence <br />of relatively impermeable interburden. <br />C1980 -001 Edna Mine Permit Renewal No. 6 8 <br />