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of chemical trends during periods of irrigation. Calcium and bicarbonate levels are decreasing slightly with time. The alluvial aquifer water exceeds the CWQCC agricultural standard for manganese. The water is acceptable for use as livestock drinking water. Measurable trace element concentrations in the alluvial aquifer include aluminum, boron, fluoride, lithium, manganese, nitrate, vanadium and zinc. Fourwells (GW-N15, GW-N18, GW-N18P1 and GW-N21) monitored the overburden water quality in the New Horizon 2 mining area. The well locations are shown on Map 2.04.7-1 The four overburden monitoring wells exhibited two water types during periods of irrigation. Well GW-N15 showed a magnesium sulfate type water and Wells GW-N18 and GW-N21 showed a calcium magnesium sulfate water type. During non-irrigation periods, none of the wells changed in water type. Measurable changes in TDS levels did occur when comparing irrigation versus non-irrigation periods. The TDS at Well GW-N15 decreased, and the TDS at Wells GW-N18 and CW-N21 increased during periods of no irrigation. The greatest change in TDS occured at Well GW-N15 where there was a 1,662 mg/I 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 irrigation and no irrigation were 8,310 and 6,648 mg/I, 2,527 and 2,832 mg/I, 3,154 and 3,450 mg/I, respectively. During periods of no irrigation, Well GW-N15 showed a slight decrease in calcium and a decrease in magnesium and sulfate, with increases in sodium, bicarbonate and chloride. Well GW-N18 showed a slight decrease in magnesium, slight increases in sodium and bicarbonate and increases in calcium and sulfate. Well GW-N21 showed 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 7.8 were measured at the four overburden wells. The mean pH values for wells GW-N15, GW-N18, GW-N18PI, and GW-N21 are 7.5, 7.61, 7.5 and 7.54, respectively. There appeared to be some seasonality to the overburden water chemistry at the New Horizon 2 mining area. In comparing spring versus fall chemistry, alkalinity, bicarbonate, chloride, potassium, sodium, sulfate and TDS levels tended to decrease in the fall. In comparing fall versus winter • Revised 18 Aug 2003 2.04.7-13