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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 />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 for fluoride and manganese and <br />the water at Wells GW-N15 and GW-N21 exceeded the manganese standard. In comparison to <br />livestock drinking water standards, Well GW-N 15 water exceeded 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, selenium and <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 aquifer water quality <br />in the New Horizon 2 mining area. The individual water quality analyses for the Dakota coal aquifer <br />wells in the New Horizon 2 mining area are presented in Peabody Appendix 7-4. The well locations <br />are shown on Map 2.04.7-1. <br />The three Dakota coal monitoring wells exhibited two watertypes during periods of irrigation. Wells <br />GW-N14 and GW-N30 showed magnesium calcium sulfate water types and Well GW-N17P1 <br />showed a sodium sulfate water type. During the non-irrigation periods, Well GW-N20 changes to <br />a calcium magnesium sulfate water type, The only significant TDS change when comparing <br />irrigation versus non-irrigation periods was at well GW-N20. The TDS level decreases 672 mg/I <br />during periods of no irrigation. Slight TDS increases occured at Wells GW-N14 and GW-N17PI <br />during periods of no irrigation. Mean TDS levels for the three Dakota coal wells (GW-N 14, GW- <br />N 17P and GW-N20) during periods of irrigation and no irrigation were 4,323 and 4,366 mg/I, 2,740 <br />and 1,798 mg/I, and 2,198 and 2,251 mg/I, respectively. <br />• Revised 18 Aug 2003 2.04.7-14 <br />