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Na abundance in winter (low flow) months seem to indicate that surface disturbances—rather than <br /> the discharge of subsurface waters—were most responsible for the Na behavior. However, as I am <br /> not well aware of most of the physical circumstances at the site through its history, this feature <br /> deserves further examination. <br /> Ca and Mg <br /> Neither Ca nor Mg concentrations demonstrate any recognizable change with time. This is <br /> consistent with the notion that most of the erodible materials that contributed to changes in the <br /> water quality characteristics were derived from Ca-sulfates (and possibly Na-sulfates) and from clay <br /> minerals rather than limestone or dolostone. <br /> Ca and Mg co-vary fairly strongly. This indicates either a common source (dolostone) or similar <br /> hydrochemical behavior. <br /> Sulfate <br /> Sulfate also aries with season, and increased in range and in median content after 1986. <br /> Sulfate does not co-vary with Ca (RZ = 0.01). This indicates that the sources of these two materials <br /> could not be gypsum or anhydrite, as might be expected for this area.__ <br /> Na, however, does vary linearly with SO, (RZ = 0.81). This relationship is moderately strong <br /> evidence that either the sources of Na and SO,are the same mineral, or that their chemical behavior <br /> in this system is co-dependant. (The latter explanation would be the less favored unless it could be <br /> shown that the inputs of these two components was constant, which is not likely.) This raises the <br /> question of a mineralogical source. NaZSO4i the mineral thenardite, forms in alkali lakes or <br /> lacustrine marls—these, in general, mark either an and terrestrial environment or an and mixed <br /> marine and terrestrial environment. As such, this mineral or some related derivative, could have <br /> formed in the Cretaceous section in the vicinity of the coal seams. Natural erosion or mining <br /> induced erosion would expose such sections and thereby release the materials to streams as dissolved <br /> phases. <br /> Fe <br /> Iron demonstrates a fairly strong seasonal control. There is no compelling evidence that Fe <br /> increased in abundance in 1987, like some of the other elements. <br /> Mn <br /> Manganese concentrations have not bene measured in the more recent years,so no further evaluation <br /> has been made of this element. <br /> Cl <br /> Chloride data were not collected prior to 1987 so an evaluation equivalent to most of those above <br /> cannot be made. <br /> 3 <br />