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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. 8y mid-sunnier, flow generally peaks <br />between 2.0 and 3.0 cfs; base flow during 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 />• vrater quality type distinctly becomes more dominated by the 504 <br />anion and mean TDS increases to 2548 mg/1 from 815 mg/1 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 (DMRs) for the past three quarters of 1986 are <br />provided in Appendix C. The MLRO 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/1. <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, v.~as 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 />n,7 <br />