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• periodically for preventive maintenace. The minimal discharges recorded for 1997 do <br />not reflect changes of inflow into the mine. <br />WATER QUALITY <br />Summaries of the water quality data for the mine discharge are presented in Tables 17 <br />through 20. The #5 Mine sump discharge is NPDES discharge point #003. The 7 North <br />Angle Discharge is NPDES discharge point #024. The #5 Mine discharge water quality <br />indicates a slight increase in dissolved solids concentrations over time which has now <br />stabilized at just under 1000 mg/L . The plot of dissolved solids presented in Figure 18 <br />shows that the average dissolved solids in the #5 Mine discharge water have increased <br />slightly from about 800 mg/I in 1982 and 1983 to almost 1000 mg/I in 1995. A minor <br />reduction to approximately 900 mg/I is noted for 1997. The average dissolved solids <br />• concentration for the 7 North Angle discharge continued to hold stable at about 950 <br />mg/I in 1997 as compared to 1285 mg/I in years 1991 and 1992. This trend is related to <br />the accumulation of water in the North Angle Sump location while the pump was out of <br />order. This water was allowed to equilibrate within old workings and subsided longwall <br />panels. The maximum concentration of 1474 mg/I represents this equilibrium <br />concentration and also provides an indication of the expected post mining TDS <br />concentrations in rubbelized zone of underground mine workings. Likewise, this <br />decrease illustrates the effects of flushing upon the TDS concentrations with normal <br />periodic discharge. <br />• C-01-044 1997AHR Page 7 <br />