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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 CW-N14 water exceeds the CWOCC agricultural standards for
<br />aluminum, iron, fluoride, manganese and pH; Well CW-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 CW-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 ad uminum, 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, CW-N16 and GW-N19) monitor the underburden aquifer water quality in
<br />the Nucla East mining area. Statistical suaenaries 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 CW-N13 has a calcium magnesium sulfate water type, Well GW-N13 has a
<br />calcium magnesium sulfate water type, Well CW-N16 has a sodium bicarbonate water type, and
<br />Well CW-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/1, occurs at Well
<br />CW-N19, Mean TDS levels for the three underburden wells (GW-N13, CW-N16 and GW-N 19)
<br />during periods of irrigation and no irrigation are 2,592 and 2,632 mg/1, 1,059 and 1,079
<br />• mg/1, and 1,204 mg/1 and 1,424 mg/1, respectively,
<br />7-69 Revised 04/11/88
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