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

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decrease slightly when no irrigation is occurring. The greatest change in TDS occurs at Well GW-NG where the mean TDS level increases by 188 mg/l during non-irrigation periods. Mean TDS levels for the four underburden Wells GW-N1 , GW-N3, GW-N5 and GW-N6 during irrigation and non-irrigation periods are 2,997 and 3,096 mg/l , 2,843 and 2,765 mg/1 , 691 and 670 mg/l, and 3,981 and 4,119 mg/l, respectively. Schoeller diagrams, representing mean milliequivalent values at the four underburden wells for the two above-referenced time periods, are presented on Figures 7-4 through 7-7. Well GW-N1 increases slightly in magnesium, bicarbonate and chloride; Well GW-N3 decreases in calcium and sulfate and increases in sodium, bicarbonate and chloride; Well GW-N5 decreases in calcium, bicarbonate and sulfate and increases in chloride; and Well GW-N6 decreases in calcium and increases in magnesium, sulfate and chloride during periods of no irrigation. A range in pH values from 6.5 to 9.5 have been measured at the four underburden monitoring wells. The mean pH values for Wells GW-N1, GW-N3, GW-N5 and GW-N6 are 6.75, 6.70, 8.34 and 6.56, respectively. There is some suggestion of seasonal variability in the water chemistry of the underburden wells. In comparing spring versus fall chemistry, calcium, chloride, pH, sulfate and TDS levels decrease in the fall . A comparison of summer versus winter chemistry shows that bicarbonate, chloride, magnesium, sodium and TDS levels increase and calcium levels decrease in the winter. There is also some suggestion of overall chemical trends in the four underburden wells. The TDS appears to be decreasing with time at Wells GW-N1 , GW-N5 and GW-N6 and increasing at GW-N3. Other trends include decreasing calcium and bicarbonate levels, and increasing magnesium and sulfate levels at Well GW-N1 . Until the time GW-N5 was removed, there was a trend towards decreasing calcium levels and increasing magnesium and bicarbonate levels. A summary of the ranges in concentration for trace elements analyzed at the underburden wells is presented in Table 7-8. Well GW-N1 exceeds the CWQCC agricultural standards for iron and manganese and Well GW-N3 exceeds the cadmium and manganese standard. None of the wells exceed the livestock drinking water standards. Measurable trace metal concentrations at the four wells include boron, cadmium, fluoride, iron, manganese, nickel, nitrate and zinc. One well, GW-N27, intercepts sufficient water to permit monitoring of the spoil aquifer at 7-45 Revised 04/11/88