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is a Schoeller diagram of the milliequivalent distribution of major anions and cations for <br /> both the irrigation and non-irrigation periods at SW-N3. <br /> SW-N3 exhibits a calcium magnesium sulfate water type during both the irrigation and <br /> non-irrigation seasons (see Appendix 7-8). Figure 7-25 shows a similar trend (of greater <br /> proportions of all major anions and cations) during the non-irrigation season. Decreases <br /> in flows and increased levels of the principal ions result in higher average TDS yet <br /> similar water types for the non-irrigation period. <br /> pH values at SW-N3 averaged for both seasons (irrigation versus non-irrigation) are <br /> identical (7.7 units). Ranges in pH are also similar (6.8 to 8.1 , irrigation; 6.7 to 8.4, <br /> no irrigation). <br /> Average TDS at SW-N3 during the non-irrigation period (2649 mg/1) is almost double the <br /> average TDS during periods of irrigation (1470 mg/1). During the summer months <br /> (irrigation period), TDS ranges between 1040 mg/l and 2210 mg/l . For the period when the <br /> ditch system is off (mid-October through mid-April), TDS ranges from 1302 mg/l to 3284 <br /> mg/l . Again, Figure 7-25 graphically illustrates the higher levels of the major ions <br /> during the non-irrigation period. <br /> Both TSS and Fe average lower during periods of no irrigation (34.8 mg/l (TSS) and .64 <br /> mg/l (Fe T), irrigation; 20.7 mg/l (TSS) and .59 mg/l (Fe T), no irrigation). Fe shows <br /> little variability between seasons at Site SW-N3 (.05 mg/l both seasons). As previously <br /> discussed for Site SW-N1 , MnT is much greater at Site SW-N3 during periods without <br /> irrigation activity (.89 mg/l, average), in comparison with the average MnT determined for <br /> the irrigation period (.36 mg/1). <br /> Because Site SW-N3 is located downgradient of mining, a resultant diminution in water <br /> quality is expected and evident. Prior to mining, water quality at this location on <br /> Tuttle Draw was probably similar to that of present day water quality at Site SW-N1. <br /> However, because there is no water quality data predating mining activities, it is <br /> impossible to know what premining baseline conditions were. During both seasons, the <br /> quality of the water at Site SW-N3 can be classified as a Ca-Mg-SO4 type (see Appendix <br /> 7-8). Figure 7-26 presents the results of flow and water quality monitoring performed in <br /> Tuttle Draw and the West Return Ditch on July 10, 1986. From Figure 7-26, the effects of <br /> mining are clear. As depicted by the stiff diagrams, the estimated quality of the Second <br /> 7-130 Revised 04/11/88 <br />