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• Vf = Ki /O/ = (4.1 x 10 -6 ft /s) (0.017)/0.441 <br />= 1.6 x 10 -7 ft /s <br />= 5 ft /yr <br />The concentrations shown in the 50 year column of Table 32 were <br />measured in a sample collected after 0.316 pore volumes of effluent were <br />produced from lab test CR -B. The 50 year estimate of time was calculated <br />by multiplying 0.316 by Lf /vf = 150 years. The 210 year value was <br />similarly estimated. Data from lab test CR -B were used because these <br />data showed the slower rate of decline. <br />All data necessary for the application of equation 2 have not been <br />estimated. The effect of effluent from the backfill will be greatest <br />when the stream discharge is least. Therefore, we take Qu = stream <br />discharge to be 5 cfs, equation 2 becomes: <br />C = (2.4 x 10 -6/5 Cb <br />or <br />C = 4.8 x 10 -7 Cb <br />is <br />A mixing computation indicates that the backfilled channel will <br />increase the average concentration of a few common ions in the alluvial <br />groundwater in the reach in which channel relocation is proposed. For <br />example the average TDS concentration is expected to increase from an <br />estimated current value of 780 mg /l to about 820 mg /1. Concentrations <br />of trace elements are expected to remain unchanged within the accuracy <br />of determination. The hydrologic functions of the alluvial aquifer in <br />the affected reach will not be impaired. <br />Development Coal Waste Pile <br />Refuse Disposal Area <br />The proposed refuse disposal area will cover an area of about 66 <br />acres when complete. Surface runoff contacting the refuse will be routed <br />through a sediment pond before being discharged to the Purgatoire River. <br />Water balance computations indicate that only in abnormally wet years <br />• <br />(Revised 05111/94) <br />2.05 -78 <br />