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V <br /> <br /> 15. For chloride, two different sources are likely to raise concentrations and mass <br /> <br /> transport above background: magnesium chloride and salt with sand. Background concentrations <br /> of chloride are very low (0-2 mg/L); the combination of magnesium chloride and salt with sand <br /> raises these background concentrations by 50 to 100 mg/L during winter, when dilution is lowest. <br /> Even so, the peak concentrations were below concentrations that could be considered potentially <br /> hannfid to the most sensitive forms of aquatic life. Annual transport of chloride is accounted for <br /> mainly by chloride added to highways in the form of salt with sand. When deicer and salt with <br /> sand are applied together, magnesium chloride deicer accounts for 10 - 50% of the total. <br /> <br /> 16. Sodium is added to highways as salt with sand, but not as a component of <br /> magnesium chloride. Use of salt with sand raises the peak concentrations of sodium in stream <br /> waters from the range 2-5 mg/L to the range 20-:50 mg/L. These concentrations are not <br /> considered environmentally damaging, however. The sodium added as salt with sand can be a <br /> high percentage of the natural annual transport. <br /> <br /> 17. Concentrations of other inorganic substances were studied at the 6 field sites through <br />routine monitoring extending from late 1997 to spring 1999. Substances that were monitored <br />included arsenic, cadmium, chromium, copper, lead, mercury, and zinc. In addition, hardness of <br />the water was measured at each site on each monitoring date because regulatory limits for some <br />metals are determined on the basis of hardness. The amounts of substances in the water were <br />undetectable or rarely detectable in most cases. Cadmium, copper, and zinc were detected <br />commonly at some sites. The analysis, therefore, focused on cadmium, copper, and zinc. For <br />sites that are unaffected by mine drainage (main stem of Straight Creek and Laskey Gulch), <br />intersite comparisons show that the application of magnesium chloride deicer has no detectable <br />effect on the concentrations of the substances that were analyzed; concentrations were <br /> <br /> <br />