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Dames & Moore <br />• Flatiron Companies <br />May 17, 1982 <br />Page 2 <br />HYDROLOGIC IMPACTS OF THE EAST DUMP <br />PRE-DUMP CONDITIONS <br />The East Dump will occupy approximately 40 acres in the northeast <br />quarter of the Bourg property and will cover an area originally drained by a <br />small side-draw which is tributary to Mann Draw. This side-draw is about 64 <br />acres (0.1 square mile) in overall area. Under pre-mining conditions, surface <br />runoff from the side-draw was intermittent and estimated to be on the order of <br />2.9 acre-feet in a typical year. <br />Ground-water depth has not been ascertained for this area but based on <br />drill hole measurements made in an adjacent side-draw located immediately to <br />the southwest, the water table is estimated to be 25 to 50 feet below the <br />present surface. <br />• <br />No springs or wet weather seeps have been identified in the area to be <br />occupied by the East Dump. <br />The quality of the surface runoff which discharged intermittently from <br />this side-draw prior to the start of dump placement has not bee^ determined. <br />Neither has ground-water quality been evaluated but it is expected to be <br />similar to the ground water sampled in nearby exploratory drill holes and <br />summarized in Table 5 on Page I-6 (a) of the permit application. <br />DUMP FEATURES <br />Composition and Thickness <br />The East Dump will be composed principally of sandstone, siltstone and <br />shale from the Coalmont Formation. The thickness of the East Dump material <br />will range up to about 45 feet. Only a small portion of the dump, about 7.3 <br />• acres, will exceed 30 fee[ in thickness. <br />z <br />