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site SW-N1. However, because there is no water quality data <br /> predating mining activities, it is impossible to know what <br /> premining baseline conditions were. The quality of the water <br /> at site SW-N3 can be classified as a Ca-Mg-SO4 type as <br /> indicated from Figure 2. From Figure 5, the effects of mining are <br /> clear. As depicted by the stiff diagrams, the estimated quality of <br /> the Second Park irrigation water (estimated from samples collected <br /> in 1986 from the West Lateral irrigation ditch) changes <br /> substantially in TDS load and water type as the irrigation return <br /> water flows through the mine area. As the Ca-HCO3 type irrigation <br /> water infiltrates into the undisturbed and disturbed (by mining) <br /> near surface ground water system, water type sharply changes to a <br /> Ca-SO4 type as indicated by the stiff diagrams for the Highwall <br /> Spring and the Spoils Spring #1, respectively. These waters <br /> strongly influence the type of water discharging from the mine area <br /> as reflected by the similarity of these waters to the water <br /> discharging from the NPDES 001 discharge point located immediately- <br /> upstream of SW-N3. As a result of the above-described process, TDS <br /> concentrations also increase approximately two times that of <br /> background concentration (observed at site SW-N7) as surface water <br /> flows through the mine area and is fed by spoils ground water. The <br /> resultant impact of the quality of the West Return Ditch on the <br /> quality of Tuttle Draw is reflected by the similarity in TDS <br /> concentration of SW-N3 to that of NPDES 001. <br /> As was similarly described for site SW-NI, water quality data <br /> collected at site SW-N3 reflect dramatic seasonal changes in <br /> quality with respect to TDS. As is evident from the chemograph <br /> depicted on Figure 6, TDS concentration averages 2139 mg/l and <br /> fluctuates between a low of approximately 1000 mg/l during the <br /> summer and a high of approximately 3300 mg/l during the winter. <br /> This flux is directly related to irrigation return flow. Figure 7 <br /> is a plot of TDS concentration versus flow at SW-N3; the direct <br /> relationship of increasing TDS concentration with decreasing flow <br /> is apparent. <br /> 26 <br />