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i <br /> <br /> Executive Summary <br /> <br /> 1. The Colorado Department of Transportation plans to increase its use of magnesium <br /> chloride liquid deicers. Advantages of deicer solutions on roadways at high elevation include <br /> reduction in the use of salt and sand mixtures and improvement of road conditions during storms <br /> beyond what is possible by the use of sand and salt mixtures alone. <br /> <br /> 2. In preparation for increased use of magnesium chloride deicers on roadways at high <br />elevations, the Colorado Department of Transportation (CDOT) initiated environmental <br />investigations during late 1996. These environmental investigations focused on the effects of <br />magnesium chloride deicers on water quality and aquatic ecosystems. The studies included <br />analysis of water quality and aquatic communities as well as biotoxicity testing. <br /> <br /> 3. The field and laboratory studies of magnesium chloride deicers were preceded by a <br />literature review. The review showed that magnesium and chloride, the main ingredients of <br />magnesium chloride deicers, are unlikely to produce adverse environmental effects except under <br />very unusual circumstances. Chloride may damage vegetation very close to roadways, but is <br />diluted by runoff to such an extent that it is very unlikely to exceed the concentrations that are <br />known to be harmful to aquatic life. Aside from the main ingredients, magnesium chloride <br />deicers can be expected to contain rust inhibitors as well as substances in lower amounts that are <br />included inadvertently. Rust inhibitors and minor constituents of deicers have seldom been <br />studied. <br /> <br /> 4. The expected dilution of deicers on roadways was estimated as one means of <br />evaluating the expected concentrations of deicer components in runoff as it enters the <br />environment. The median expected dilution of deicer is approximately 1 to 500 prior to its exit <br /> <br /> <br />