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• presented in Table 7-8. The alluvial aquifer water exceeds the CWOCC agricultural standard for manganese. The water is acceptable for use as livestock drinking water (Table 7-g). Measurable trace element concentrations in the alluvial aquifer include aluminum, boron, fluoride, lithium, manganese, nitrate, vanadium and zinc. Four wells (GW-N15, GW-N 18, GW-N 18P1 and CW-N 21) monitor the overburden water quality in the Nucla East mining area. Statistical summaries of the water analyses performed on these wells are presented in Tables 7-17 through 7-20. Trilinear diagrams representing analyses performed during periods of irrigation and no irrigation are presented in Appendix 7-3. The individual water quality analyses for the overburden aquifer wells in the Nucla East mining area are presented in Appendix 7-4. The well locations are shown on Exhibit 7-1. The four overburden monitoring wells exhibit two water types during periods of irrigation. Well GW-N15 is a magnesium sulfate type water and Wells CW-N18 and GW-N21 have a calcium magnesium sulfate water type. To date no water analyses have been ~obtai ned from Well GW-N1BP7 during the irrigation period. During non-irrigation periods, none of the wells • change in water type. Measurable changes in TDS levels do occur when comparing irrigation versus non-irrigation periods. The TDS at Well GW-N15 decreases, and the TDS at Wells GW-N18 antl GW-N21 increase during periods of no irrigation. The greatest change in TDS occurs at Well CW-N15 where there's a 1,662 mg/1 drop in TDS during non-irrigation periods. Mean TDS levels for the three overburden wells (GW-N15, GW-N18 and GW-N21) during periods of no irrigation are 8,310 and 6,648 mg/1, 2,527 and 2,832 mg/1, 3,154 and 3,450 mg/1, respectively. Schoeller diagrams, showing mean milliequivalent values for Wells GW-N15, GW-N18 and GW-N21 for the tno above-referenced time periods, are presented on Figures 7-9 through 7-11. During periods of no irrigation, Well GW-N15 shows a slight decrease in calcium and a decrease in magnesium and sulfate, with increases in sodium, bicarbonate and chloride. Well GW-N1B shows a slight decrease in magnesium, slight increases in sodium and bicarbonate and increases in calcium and sulfate. Well GW-N21 shows a slight decrease in calcium, a slight increase in bicarbonate, increases in magnesium, sodium and sulfate and a large increase in chloride. A range in pH values from 7.3 to 7.B have been measured at the four overburden wells. The • mean pH values for wells GW-N15, GW-N 18, GW-N18P1, and GW-N 21 are 7.5, 7.61, 7.5 and 7.54, respectively. 7-53 Revised 04/11/88