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• 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 />There appeared to be some seasonality to the overburden water chemistry at the New Horizon 2 <br />mining area. In comparing spring versus fall chemistry, alkalinity, bicarbonate, chloride, potassium, <br />sodium, sulfate and TDS levels tended to decrease in the fall. In comparing fall versus winter <br />chemistry, alkalinity, bicarbonate, chloride, potassium and sodium levels increased and pH <br />decreased in the winter. In comparing summer versus winter chemistry, alkalinity, bicarbonate, <br />chloride and sodium levels increased and calcium levels decreased in the winter. <br />• <br />In addition to chemical seasonality, there were some overburden chemical trends during the <br />irrigation season with time. Well GW-N18 showed a decrease in calcium and an increase in <br />sodium, bicarbonate, sulfate and TDS levels. <br />Well GW-N18 waterexceeded the CWQCC agricultural standards forfluoride and manganese and <br />the water at Wells GW-N15 and GW-N21 exceeded the manganese standard. In comparison to <br />livestock drinking waterstandards,Well GW-N 15 waterexceeded the magnesium, sulfate and TDS <br />standards and Well GW-N18 water exceeded the fluoride standard. Well GW-N21 water was <br />suitable for use as livestock drinking water and water at well GW-N18P1 was suitable for both <br />agricultural and livestock use. Measurable trace element concentrations in the overburden aquifer <br />included aluminum, arsenic, boron, cadmium, cobalt, fluoride, iron, lithium, manganese, nitrate, <br />selenium,vanadium,silverandzinc. The highest concentrations of cadmium, nitrate,seleniumand <br />silver were measured in the overburden aquifer at the New Horizon 2 mining area. <br />Three wells (GW-N14, GW-N17P1 and GW-N20) monitored the Dakota coal aquiferwaterquality <br />• in the New Horizon 2 mining area. The individual water quality analyses for the Dakota coal aquifer <br />REVISED JULY 2006 2.04.7-19 <br />