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Schoeller diagrams, showing mean milliequivalent values for the underburden wells for the <br /> two above-referenced time periods, are presented on Figures 7-15 through 7-17. During <br /> periods of no irrigation, Well GW-N13 shows slight increases in calcium, sulfate and <br /> chloride levels and slight decreases in magnesium and sodium levels; Well GW-N16 shows a <br /> decrease in magnesium and slight increases in sodium, bicarbonate and chloride levels; and <br /> Well GW-N19 shows a slight decrease in bicarbonate and increases in calcium, magnesium <br /> sodium, sulfate and chloride levels. <br /> The pH levels for the three underburden wells range from 7.0 to 9.1. Mean pH values for <br /> Wells GW-N13, GW-N16 and GW-N19 are 7.28, 8.44 and 7.8, respectively. <br /> There is a limited amount of seasonal variability in the chemistry of the underburden <br /> aquifer. In comparing spring versus fall chemistry, calcium, magnesium, sodium, potassium <br /> and sulfate levels tend to increase in the fall . Fall versus winter chemistry suggests <br /> that only calcium levels decrease in the winter. The only trend when comparing summer <br /> versus winter chemistry is an increase in chloride in the winter. <br /> Chemical trends over time are also evident in the underburden aquifer during irrigation <br /> periods. Well GW-N13 shows an increasing trend in magnesium, sulfate and TDS levels; Well <br /> GW-N16 shows an increasing trend in magnesium and bicarbonate levels; and Well GW-N19 <br /> shows a decreasing trend in bicarbonate and an increasing trend in magnesium, sodium, <br /> sulfate and TDS levels. <br /> A summary of the ranges in concentration for trace elements measured in the underburden <br /> wells is presented in Table 7-8. Well GW-N13 water exceeds the CWQCC agricultural <br /> standard for manganese and Well GW-N16 water exceeds the pH standard. Well GW-N19 water <br /> meets all of the standards. All three wells meet the livestock drinking water standards <br /> (Table 7-9). Measurable trace element concentrations in the underburden aquifer include <br /> aluminum, arsenic, boron, cadmium, copper, fluoride, iron, lithium, manganese, mercury, <br /> nitrate, vanadium and zinc. The highest concentrations of arsenic, mercury and copper <br /> were measured in the underburden aquifer at the Nucla East mining area. <br /> Springs. Three definable springs at the Nucla Mine have been located and monitored to <br /> date. These springs are Spoil Spring #1, Spoil Spring #2, and the highwall spring. The <br /> locations of the springs are shown on Exhibit 7-1. <br /> 7-73 Revised 04/11/88 <br />