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decreasing trend in calcium, magnesium and bicarbonate levels and an increasing trend in
<br /> sodium and chloride levels during periods of irrigation. Irrigation period trends for
<br /> well GW-N20 include decreasing calcium, magnesium, sodium, sulfate and TDS levels and
<br /> increasing chloride levels.
<br /> A summary of the ranges in concentration for trace elements in the Dakota coal wells is
<br /> presented in Table 7-8. Well GW-N14 water exceeds the CWQCC agricultural standards for
<br /> aluminum, iron, fluoride, manganese and pH; Well GW-N17P1 water exceeds the pH standard;
<br /> and Well GW-N20 water exceeds the iron, manganese and pH standards. In comparison to
<br /> livestock drinking water standards (see Table 7-9), Well GW-N14 water exceeds the aluminum
<br /> and fluoride standards and Well GW-N20 exceeds the aluminum standard. Measurable trace
<br /> element concentrations in the Dakota coal aquifer include aluminum, arsenic, beryllium,
<br /> boron, cadmium, chromium, cobalt, copper, fluoride, iron, lithium, manganese, nickel,
<br /> nitrite, nitrate, vanadium and zinc. The highest concentrations of aluminum, beryllium,
<br /> boron, cobalt, fluoride, iron, lithium, manganese, nickel, nitrite and zinc were measured
<br /> in the Dakota coal aquifer at the Nucla East mining area. Also, the lowest pH values were
<br /> recorded in this aquifer.
<br /> Three wells (GW-N13, GW-N16 and GW-N19) monitor the underburden aquifer water quality in
<br /> the Nucla East mining area. Statistical summaries of the water analyses performed on
<br /> water sampled from these wells are presented in Tables 7-24 through 7-26. Trilinear
<br /> diagrams representing analyses performed during periods of irrigation and no irrigation
<br /> are presented in Appendix 7-3. The individual water quality analyses for the underburden
<br /> aquifer wells in the Nucla East mining area are presented in Appendix 7-4. The well
<br /> locations are shown on Exhibit 7-1.
<br /> The three underburden monitoring wells exhibit three water types during periods of
<br /> irrigation. Well GW-N13 has a calcium magnesium sulfate water type, Well GW-N13 has a
<br /> calcium magnesium sulfate water type, Well GW-N16 has a sodium bicarbonate water type, and
<br /> Well GW-N19 has a sodium calcium magnesium bicarbonate sulfate water type. During the
<br /> non-irrigation periods the only water type change is at Well GW-N19 where the water type
<br /> becomes a sodium magnesium calcium sulfate bicarbonate. All three wells increase in TDS
<br /> during non-irrigation periods. The greatest increase in TDS, 220 mg/l, occurs at Well
<br /> GW-N19. Mean TDS levels for the three underburden wells (GW-N13, GW-N16 and GW-N19)
<br /> during periods of irrigation and no irrigation are 2,592 and 2,632 mg/l, 1,059 and 1,079
<br /> mg/l, and 1,204 mg/l and 1,424 mg/l , respectively.
<br /> 7-69 Revised 04/11/88
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