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