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major anions and cations) occasionally analyzed for at NPDES 001. Table 7-51 presents a • statistical summary of the historic water quality data collected at NPDES 001. Figure 7-32 presents a $choeller diagram of mean milliequivalent values for the major ions during both seasons at NPDES Site 001. The water type at NPDES 001 for both seasons is a calcium magnesium sulfate. From Figure 7-32, it can be seen that NPDE$ 001 exhibits a similar trend of higher levels of the major ions during periods of no irrigation as seen at Sites SW-N7 and SW-N6. During the irrigation season, pH averages 7.52 at NPDE$ 007 ranging from 6.0 up to 8.6. Between irrigation periods, the mean pH is 7.62 and ranges between 6.5 and 8.4, The mean TDS concentration determined for NPDES 001 during the irrigation season is 2,095 mg/1. The range in TDS for the irrigation season falls between 995 mg/1 and 3,470 mg/1. In between irrigation seasons, TD$ averages 2,963 mg/1, and ranges f~r om 892 mg/7 up to 3,650 mg/1. • Mean TSS, FeT and FeD all increase slightly at NPDES 001 between periods of irrigation. During the irrigation season, average concentrations of T55, FeT and Fep are 8.0 mg/1, .26 mg/1 and .04 mg/1, respectively. For the periods of no irrigation, TSS, FeT and FeD average 9.0 mg/1, .29 mg/1 and .OS mg/1, respectively. Total manganese (MnT) averages higher concentrations (.17 mg/1) for the months between irrigation seasons in comparison to the mean MnT typically exhibited at NPDES 001 during the irrigation period (.11 mg/1). NPDES 006 - Water Ouality. The NPDES 006 ou tf all is located on the lower end of the East Return Ditch near the eastern boundary of the Nucla Mine (see Exhibit 7-1). Water quality has been routinely monitored at this site as outlined and required by the Nucla NPDES Permit (No. CO-0000213, see Appendix 7-6) since December of 1982. Appendix 7-7 contains water quality data collected at NPDES 006 (including additional parameters occasionally analyzed) since 7982. A trilinear plot of the distribution of major ions for both seasons at this site is contained in Appendix 7-8. Table 7-52 presents a statistical summary of the historic water quality data collected at NPDES 006. Figure 7-33 is a $choeller diagram of mean milliequivalent values for the major ions during both seasons at NPDES Site 006. • Between irrigation periods, NPDES 006 exhibits a magnesium calcium sulfate water type. 7-156 Revised 04/11/88