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Summary. The analysis of geochemical controls on ground water quality suggests that <br />• the water chemistry and concentrations of most elements of concern are controlled by <br />mineralogic reactions that will resist changes in water chemistry. Boron concentrations <br />do not appear to be controlled by mineral solubility. Production of acid may occur in <br />very local settings (and is probably most prevalent in the coal, which will be mined); <br />calculations indicate that neutralization of the acid will occur rapidly with mixing of <br />water, or with movement of acidic water into calcite-bearing rocks. <br />Additionally, the methodology developed by Hounslow et al. (1978) also indicates that <br />chemical changes are not likely to occur. Although the approach is not specific to the <br />setting at Nucla, it was developed by using data from many mines in a variety of settings, <br />including mines of similar character. <br />Last, the water sampled from spoils at Nucla is typical of ground water in the Nucla and <br />Nucla East areas, and is of better quality than most. There is no evidence of the <br />production of acid, increased mobility of toxic elements, or even increases in TDS. <br />Boron, the element not addressed by the geochemical modeling, shored no evidence of <br />• increased concentrations. <br />In summary, mining is not likely to cause significant changes in ground-water quality <br />(removal of the coal may actually improve water quality), and certainly will not impact <br />its use, which is limited by its naturally poor quality. <br />Potential Impacts of Replaced Spoils on Surface Water Ouality. For purposes of assessing <br />the mining impacts on the receiving stream surface water chemistry, seasonal impacts were <br />compared against mean annual impacts to determine which analysis provided the worst case <br />scenario. For the seasonal analysis, same day flows were measured and samples were <br />collected from the San Miguel River above the Calamity Draw confluence and beiw. the <br />confluence with Tuttle Draw. At the same time flow measurements and samples were taken at <br />Monitoring Sites SW-N3, SW-N1 and SW-N103 on Tuttle and Calamity Draws, respectively. <br />Same day samples and measurements were obtained on 4/3/87 and 10/5/87 representing the <br />ends of the non irrigation and irrigation periods, respectively. Tables 17-15A and 17-158 <br />show the flow, TDS and chemical load input parameters measured and used in the same day <br />(seasonal) and mean annual impact analyses, respectively. <br />• Since Calamity Draw, at the present time, does not represent impacted water quality, the <br />17-61 Revised 04/11/88 <br />