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bility.of occurrence of percolation, the most probable percolation rate is <br />1.6 cm/year. Using the average percolation rate and available soil moisture <br />capacity, the elapsed time before percolating water will recharge ground- <br />water, is estimated to be between 500 and 1000 years. <br />(2) If water does percolate through the spoils, very little of it will contact <br />the waste as the permeability of the overburden is 10 to L00 times greater <br />than the waste. Percolating water can be expected to follow the path of <br />least resistance and will therefore tend to go around the waste body. <br />(3) The utility wastes which will be produced at the Craig Station are antici- <br />pated to be classified by EPA as nontoxic and non -hazardous. This is based <br />on the criteria given in RCRA of May 19, 1980. <br />(4) Contact of percolating water with the waste, if it should occur, will produce <br />leachate concentrations of aluminum, barium, chromium, sulfate, boron, and <br />molybdenum exceeding applicable EPA primary and proposed secondary drinking <br />water standards and NAS/NAE �rpeco�mmended limits fori�rr,igation water used con- <br />tinuously. <br />(5) Concentrations of these elements will be reduced through attenuation mechan- <br />isms by the overburden. With placement of the utility wastes in the mine <br />area in the proper ratios of waste to overburden, the attenuating capacity of <br />the overburden should be sufficient to reduce concentrations of all species <br />except sulfate to levels below drinking and irrigation water limits. <br />(6) The quality of the groundwater in the Trapper Mine can be contaminated by <br />sulfate leached from the Craig Station scrubber sludge. Sulfate will not be <br />attenuated by the overburden. However, sulfate contamination would require <br />the generation and migration of the waste leachate. <br />(7) The possibility of a hydrological connection between the Yampa River and the <br />Upper Williams Fork (the formation being mined by Trapper Mine) is very <br />remote. Piezometer studies have negated the existence of an up -section flow <br />component between the Yampa River alluvium and the Upper Williams Fork. It <br />4-25 <br />