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collected since 1980 are presented in Appendix B and statistically <br /> summarized in Table 16. Continuous flow data are presented in <br /> Table 17. A hydrograph constructed from weekly and monthly <br /> instantaneous flow measurements is shown in Figure 10. A trilinear <br /> plot of the major ions is depicted in Figure 11. <br /> The continuous flow data collected from this site further <br /> convey the seasonal effects of irrigation on the hydrologic <br /> regime of the mine site. Ry mid-summer, flow generally peaks <br /> between 2.0 and 3.0 cfs; base flow dur-ing the winter is usually <br /> less than 0.5 cfs. There is no indication from the record that <br /> base flow has detectably changed during the past six years. <br /> Discharge from the NPDES 001 discharge point contributes <br /> approximately 15 percent of the flow to Tuttle Draw as measured <br /> at site SW-N3. <br /> The effects of mining on the diminution of water quality in the <br /> West Return Ditch are clearly expressed at NPDES 001. The <br /> water quality type distinctly becomes more dominated by the SO4 <br /> anion and mean TDS increases to 2548 mg/l from 815 mg/l as measured <br /> at site SW-N6. Despite this diminution in quality, NPDES effluent <br /> limitations have not been exceeded but once since 1980. Discharge <br /> monitoring reports (DMPs) for the past three quarters of 1986 are <br /> provided in Appendix C. The MLRD has communicated to PCC that they <br /> have on file all earlier DMRs. The one excursion which took place <br /> during the past six years was during the second quarter of 1984 for <br /> total suspended solids (TSS) with a mean value for the quarter of <br /> 40 mg/l . <br /> As a result of this permit revision, the surface water control <br /> plan for the Nucla Mine has been revised. The revision of the <br /> control plan, described in detail in Appendix 7-1 of the Nucla Mine <br /> Permit Revision, was in part necessary because the present storage <br /> capacity and spillway configuration of the 001 pond are inadequate. <br /> Remedial compliance measures will be to excavate the ponding area <br /> to provide the necessary storage capacity, to construct properly <br /> designed principal and emergency spillways, and to modify the <br /> 47 <br />