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• The Colorado Human Health Standard for cadmium is 10 ug/1. This standard is exceeded <br />totally in some of the wells not affected by mining. Otavite solubility appears to limit <br />cadmium concentrations from 10 to 15 ug/1 but is dependent on other factors, such as <br />sulfate concentration, alkalinity, and pH. For wells and springs in spoil material at <br />Nucla, cadmium was not present above the detection limit of 5 ug/1, and is probably <br />controlled by otavite solubility. At Nue1a East, cadmium concentrations should not <br />appreciably increase as a result of mining. <br />Many of the samples appear to be undersaturated with respect to fluorite. Those with SI's <br />greater than zero are probably at equilibrium with fluorite, and have fluoride <br />concentrations of about 1.4 mg/1. The Colorado Human Health Standard is 4.0 mg/1, and the <br />Agricultural Standard is 2.0 mg/1. Mining is not expected to cause an increase in <br />fluoride concentrations. <br />Barium concentrations, where, detectable, may be limited by barite solubility at about 10 <br />to 20 ug/1. If barite controls barium concentrations, there is a~ pH Control. The <br />concentration of barium, as predicted by the calculations on GW-N15 water, should increase <br />• with decreasing pH, especially with a pH less than 6. Still, because of high sulfate <br />concentrations, barium concentrations will remain lon (PNREEOE predicted 12 mg/1 at pH <br />5.36). <br />At CW-N9, one analysis reported a concentration of 500 ug/1. However, the earlier <br />groundwater quality analyses did not indicate that an analysis was performed for barium <br />in this sample, and recent analyses show that barium concentrations are 20 ug/1. The <br />Colorado Health Standard for barium is 500 ug/1; there is no Agricultural Standard. <br />Again, no appreciable increases in barium concentrations are expected because of mining. <br />In summary, the major ion chemistry appears to be controlled by the solubilities of <br />calcite and gypsum, and, to a lesser extent, dolomite. As a result, the waters have a <br />high TOS content. In acid-producing horizons, carbonate minerals appear to be absent. <br />Concentrations of trace metals may also be solubility controlled or limited. While it is <br />relatively simple to examine solubility controls, it is more difficult to predict <br />concentrations, because of many interactions between constituents, and the different paths <br />through which the chemistry can evolve. Still, the fact that controls are demonstrated by <br />• the data strongly suggests that no major changes in chemistry as a result of mining should <br />be expected. Many of the trace metals appear to be controlled by the solubilities of <br />17-49 Revised 04/11/88 <br />