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livestock drinking water standards, well GW -N14 water exceeded the aluminum and fluoride standards and
<br />well GW -N20 exceeded the aluminum standard. Measurable trace element concentrations in the Dakota
<br />coal aquifer included aluminum, arsenic, beryllium, boron, cadmium, chromium, cobalt, copper, fluoride,
<br />iron, lithium, manganese, nickel, nitrite, nitrate, vanadium and zinc. The highest concentrations of
<br />aluminum, beryllium, boron, cobalt, fluoride, iron, lithium, manganese, nickel, nitrite and zinc were
<br />measured in the Dakota coal aquifer at the New Horizon 2 mining area. Also, the lowest pH values were
<br />recorded in this aquifer.
<br />Three wells (GW -N 13, GW -N 16 and GW -N 19) monitored the underburden aquifer water quality in the New
<br />Horizon 2 mining area. The individual water quality analyses for the underburden aquifer wells in the New
<br />Horizon 2 mining area are presented in Attachment 2.04.7-7 (Peabody Appendix 7-4). The well locations
<br />are shown on Map 2.04.7-1 A.
<br />The three underburden monitoring wells exhibited three water types during periods of irrigation. Well
<br />GW -N13 showed calcium magnesium sulfate water type, well GW -N13 showed a calcium magnesium
<br />sulfate water type, well GW -N16 showed a sodium bicarbonate water type, and well GW -N19 showed a
<br />sodium calcium magnesium bicarbonate sulfate water type. During the non -irrigation periods the only
<br />water type change was at well GW -N19 where the water type became a sodium magnesium calcium sulfate
<br />bicarbonate. All three wells increased in TDS during non -irrigation periods. The greatest increase in
<br />TDS, 220 mg/l, occurred at well GW -N19. Mean TDS levels for the three underburden wells (GW -N13,
<br />GW -N16 and GW -N19) during periods of irrigation and no irrigation were 2,592 and 2,632 mg/l, 1,059 and
<br />1,079 rag/1, and 1,204 mg/1 and 1,424 mg/l, respectively.
<br />During periods of no irrigation, well GW -N13 showed slight increases in calcium, sulfate and chloride levels
<br />and slight decreases in magnesium and sodium levels; well GW -N16 showed a decrease in magnesium and
<br />slight increases in sodium, bicarbonate and chloride levels; and well GW -N19 showed a slight decrease in
<br />bicarbonate and increases in calcium, magnesium sodium, sulfate and chloride levels.
<br />The pH levels for the three underburden wells ranged from 7.0 to 9.1. Wells GW -N13, GW -N16 and
<br />GW -N19 were 7.28, 8.44 and 7.8, respectively.
<br />There was a limited amount of seasonal variability in the chemistry of the underburden aquifer. In
<br />comparing spring versus fall chemistry, calcium, magnesium, sodium, potassium and sulfate levels tended to
<br />increase in the fall. Fall versus winter chemistry suggested that only calcium levels decreased in the winter.
<br />The only trend when comparing summer versus winter chemistry was an increase in chloride in the winter.
<br />Chemical trends over time were also evident in the underburden aquifer during irrigation periods. Well
<br />GW -N13 showed an increasing trend in magnesium, sulfate and TDS levels; well GW -N16 showed an
<br />increasing trend in magnesium and bicarbonate levels; and well GW -N19 showed a decreasing trend in
<br />bicarbonate and an increasing trend in magnesium, sodium, sulfate and TDS levels.
<br />Trace elements measured were also measured in the underburden wells. Well GW -N13 water exceeded the
<br />CWQCC agricultural standard for manganese and well GW -N16 water exceeded the pH standard. Well
<br />GW -N19 water met all of the standards. All three wells met the livestock drinking water standards.
<br />Measurable trace element concentrations in the underburden aquifer include aluminum, arsenic, boron,
<br />cadmium, copper, fluoride, iron, lithium, manganese, mercury, nitrate, vanadium and zinc. The highest
<br />concentrations of arsenic, mercury and copper were measured in the underburden aquifer at the New
<br />Horizon 2 mining area.
<br />Page 2.04.7-13 March 2017 (TR -77)
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