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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~sulf ate 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/1 and 2210 mg/l. For the period when the <br />ditch system is off (mid-Octob er through mid-April), TDS ranges from 1302 mg/1 to 3284 <br />mg/1. Again, Figure 7-25 graphically illustrates the higher levels of the major ions <br />. during the non-irrigation period. <br />Both TSS and FeT average lower during periods of no irrigation (34.8 mg/1 (TSS) and .64 <br />mg/1 (FeT), irrigation; 20.7 mg/1 (TSS) and .59 mg/1 (FeT), no irrigation). FeD shows <br />little variability between seasons at Site SW-N3 (.OS mg/1 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/1, average), in comparison with the averageMnT determined for <br />the irrigation period (.36 mg/1). <br />Because Site SW-N3 is located downgrad Tent of mining, a resultant diiminution 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 Hater 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-50 <br />type (see Appendix <br /> 4 <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, t he 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 />