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Chloride shows strong seasonal variation. It is strongly co-variant with Na OM = 0.87). This co- <br /> variance with Na suggests a common mineral source, or a common chemical behavior. As both Na <br /> and Cl are conservative, that is, they do not form mineral species and they are not adsorbed readily <br /> by other mineral precipitates except under extreme conditions, one would expect their chemical <br /> behavior to be similar. Thus, the covariance of their concentrations indicates a common mineral <br /> source. <br /> Compared with the Na:SO4 relationship, the stronger correlation between Na and Cl seems to <br /> indicate that halite is probably the most likely source of the Na and Cl. Both halite and thenardite <br /> would be expected in the same depositional environments, and both should be preserved in a <br /> sedimentary section to about the same degree, albeit, only to a slight degree as both are extremely <br /> soluble in fresh water. For the moment at least the sources of the Na and Cl, and perhaps the SO4 <br /> as well, remain unknown and, except for their unusual occurrence in these fresh waters, they are <br /> unremarkable. Their effects on the aquatic environment may be worth examining as they do not <br /> occur in ordinary fresh water. <br /> DISCUSSION <br /> The changes in water quality that began in 1987 have not reverted to their pre-1987 characteristics. <br /> This change resulted in an average increase in pH of about 0.5 standard units, and accompanied <br /> increases in most metals and in most major cations and anions. Whether this represents a shift <br /> toward more natural local conditions, whether it reflects greater stresses on the waters due to <br /> mining, how it relates to activities in the Rock Tunnel,whether it represents a permanent condition- <br /> -none of these are known. <br /> Although most measurements of metal concentrations utilized detection limits above the appropriate <br /> levels, they are probably close enough to indicate that there are not significant problems with <br /> metals in Coal Creek, below the site. Measurements above and upon the site were evaluated, <br /> peripherally, and show that the site has released a few metals during several measurement events, <br /> but there are no consistent trends or recurrent sources. <br /> The cause of aquatic life problems in the next receiving stream seem to be related, spatially, to the <br /> discharge of Coal Creek, but the water quality of Coal Creek itself, based on the available <br /> measurements, seems fit to support most aquatic life. Apparently, there is something more in the <br /> system, not apparent in this data set, that is affecting the stream in ways not yet determined. <br /> An interesting aside, not altogether unrelated to the task at hand, is the source of Na, Cl, and SO4 <br /> in this system. As indicated, Na appears to be most strongly associated with chloride and slightly <br /> less so with sulfate, so the inference is strong that they derive from the same minerals. Na-sulfates <br /> are rare, but where they exist, they most often represent an unusual component of a series of <br /> sedimentary rocks that form due to the extensive evaporation of terrestrial waters or mixed <br /> terrestrial and ocean waters. Preservation of these minerals is rare, and even so, they are commonly <br /> 4 <br />