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mine site. By mid summer, flow generally peaks between 0.6 and <br /> 1.0 cfs; base flow during the winter is usually less than 0.05 cfs. <br /> There is no indication that base flow has detectably changed during <br /> the past five years. Discharge from the NPDES 006 discharge point <br /> contributes approximately 10 percent of the flow to Tuttle Draw as <br /> measured at site SW-N3. <br /> The effects of mining on the diminution of water quality in the <br /> East Return Ditch appear to be significantly less that those <br /> described at site NPDES 001 for the West Return Ditch. This <br /> conclusion is drawn from the fact that the mean TDS <br /> concentration is 1520 mg/l , significantly lower than at NPDES 001, <br /> and the fact that the mean water quality is a Ca-Mg-HCO3 type <br /> showing a significantly lower percent of SO4 anion than shown at <br /> NPDES 001. <br /> 2. Site SW-N4 Site SW-N4 is located on the East Return Ditch immediately <br /> above its confluence with Tuttle Draw as shown on Exhibit 1. This <br /> site was dry three of the four times that it was monitored in 1980; <br /> the data are presented in Appendix B. Monitoring at this site was <br /> abandoned in the fall of 1980 because upstream monitoring at NPDES <br /> 006 and downstream monitoring at SW-N3 precluded the need for this <br /> site. Consequently, considering the limited data, no further <br /> discussion is hereby provided. <br /> 66 <br />