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• The cause of the initial high mineralization is probably the <br />result of groundwater dissolving minerals from the Evacuation <br />Creek and Parachute Creek members as it moves southward and <br />downward through these two members and into the Garden Gulch <br />member. Most of the recharge to the Garden Gulch unit is via <br />percolation of groundwater from the overlying Parachute Creek <br />member. <br />The water from the Parachute Creek member beneath Upper Davis <br />Gulch and IIpper Middle Fork Valley is of reasonably good quality <br />compared to the U.S. Public Health Service Drinking Water Stand- <br />ards except that the standards for total dissolved solids, hard- <br />ness, iron and fluorides are usually exceeded. The analyses of <br />samples collected during 1973 and 1974 show that rapid spring <br />recharge through the fracture system in the member reduces the <br />concentration of most of the chemical constituents and improves <br />the quality of the water considerably (Metcalf b Eddy, 1975). <br />• The Evacuation Creek member is high and well drained within most <br />of the project site. According to the analyses of water samples <br />from a test hole within the member, the relatively small quantity <br />of groundwater that the member does contain is highly mineralized <br />and apparently moves at a very slow rate. There is only one test <br />hole in which the water quality would be partly representative <br />of the member, but the hole penetrates the Parachute Creek member, <br />so the water sample analyzed is a mixture from both members (Metcalf <br />& Eddy, 1975). <br />The only groundwater of potable quality (although high in iron <br />and manganese) in the permit area occurs in the alluvium of <br />Upper Davis Gulch and the upper part of the Middle Fork of <br />Parachute Creek. in the two above areas, T.D.S. concentrations <br />are rather high for water of potable quality ranging from about <br />450 to S50 mg/1. Drinking water standards are compared against <br />typical analyses from the northern and southern boundaries of the <br />property for both alluvial and bedrock aquifers in Table G-11. <br />G-27 <br />