1988-04-11_PERMIT FILE - C1981008A (9)

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both during periods of irrigation and no irrigation. The mean TDS levels measured at GW-N4 during periods of irrigation and no irrigation are 6,684 and 6,836 mg/l , respectively. Schoeller diagrams, representing mean milliequivalent values for the two above-referenced time periods, are presented on Figure 7-3. Ions accounting for the slight TDS increase during periods of no irrigation are calcium, bicarbonate and chloride. A range in pH values from 6.7 to 7.3 have been measured at Wells GW-N4 and N4R. The mean pH for Well GW-N4 is 6.83. There is a limited amount of seasonal variability in the water chemistry of Wells GW-N4 and N4R. In comparing spring chemistry versus fall chemistry, alkalinity, bicarbonate pH and TDS tend to decrease and chloride and calcium tend to increase in the fall . A summary of the ranges in concentration for trace elements sampled at Wells GW-N4 and N4R is presented in Table 7-8. Well GW-N4 water exceeds the CWQCC agricultural standard for manganese and Well GW-N4R water exceeds the cadmium and manganese standards. Both wells yield water that exceeds the livestock drinking water limits for magnesium and TDS (Table 7-9). Measurable trace metal concentrations at the two sites include boron, fluoride, iron, manganese, cadmium, copper, nitrate and zinc. Four wells (GW-N1, GW-N3, GW-N5 and GW-N6) are used to monitor the underburden ground water quality at the Nucla mining area. Statistical summaries of the water analyses performed on water sampled from these wells are presented in Tables 7-12 through 7-15. 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 underburden aquifer wells are presented in Appendix 7-4. The well locations are shown on Exhibit 7-1. The four underburden monitoring wells exhibit three water types during periods of irrigation. Wells GW-N1 and GW-N3 have a calcium magnesium sulfate type water, well GW-N5 has a magnesium sodium sulfate type water, and Well GW-N6 has a magnesium calcium sulfate water type. During periods of no irrigation, only well GW-N5 changes in water type to a magnesium sodium calcium sulfate water type. Only small changes in TDS occur when comparing samples obtained during irrigation versus non-irrigation periods. Wells GW-N1 and GW-N6 increase in TDS while Wells GW-N3 and GW-N5 7-39 Revised 04/11/88