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• A larger water quality data base is necessary to determine if there is any seasonal water quality <br />variability in the alluvial aquifer irrespective ofthe general irrigation effects. There is a suggestion <br />of chemical trends during periods of irrigation. Calcium and bicarbonate levels are decreasing <br />slightly with time. <br />The alluvial aquiferwater exceeds the CWQCC agricultural standard for manganese. The water <br />is acceptable for use as livestock drinking water. Measurable trace element concentrations in the <br />alluvial aquifer include aluminum, boron, fluoride, lithium, manganese, nitrate, vanadium and zinc. <br />Fourwells (GW-N15, GW-N18, GW-N18P1 and GW-N21) monitored the overburden waterquality <br />in the New Horizon 2 mining area. The well locations are shown on Map 2.04.7-1. <br />The four overburden monitoring wells exhibited two water types during periods of irrigation. Well <br />GW-N15 showed a magnesium sulfate type water and Wells GW-N18 and GW-N21 showed a <br />calcium magnesium sulfate watertype. During non-irrigation periods, none of the wells changed <br />in water type. Measurable changes in TDS levels did occur when comparing irrigation versus <br />. non-irrigation periods. The TDS at Well GW-N15 decreased, and the TDS at Wells GW-N 18 and <br />CW-N21 increased during periods of no irrigation. The greatest change in TDS occured at Well <br />GW-N 15 where there was a 1,662 mgll drop in TDS during non-irrigation periods. Mean TDS levels <br />forthe three overburdenwells (GW-N15, GW-N18 and GW-N21) during periods ofirrigation and no <br />irrigation were 8,310 and 6,648 mg/I, 2,527 and 2,832 mg/I, 3,154 and 3,450 mg/I, respectively. <br />During periods of no irrigation, Well GW-N15 showed a slight decrease in calcium and a decrease <br />in magnesium and sulfate, with increases in sodium, bicarbonate and chloride. Well GW-N18 <br />showed a slight decrease in magnesium, slight increases in sodium and bicarbonate and increases <br />in calcium and sulfate. Well GW-N21 showed a slight decrease in calcium, a slight increase in <br />bicarbonate, increases in magnesium, sodium and sulfate and a large increase in chloride. <br />A range in pH values from 7.3 to 7.8 were measured at the four overburden wells. The mean pH <br />values for wells GW-N15, GW-N18, GW-N18PI, and GW-N21 are 7.5, 7.61, 7.5 and 7.54, <br />respectively. <br />• (REVISED6/28/01) 2.04.7-13 <br />