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The Effect of Calcium Magnesium Acetate (CMA) Deicing Material on the Water Quality of Bear Creek, Clackamas County, Oregon, 1999 By Dwight Q. Tanner andTamara M. Wood Abstract INTRODUCTION This report presents the results of a study by the Calcium magnesium acetate (CMA) is a useful deic- U.S. Geological Survey, done in cooperation with the lng material for roadways. Its advantages over sodium- and Oregon Department of Transportation (ODOT), to calcium-chloride salts include less corrosiveness to automo- evaluate the effects of the highway deicing material, biles and to highway materials, and. less toxicity to roadside calcium magnesium acetate (CMA), on the water qual- vegetation (Transportation Research Board, 1991). The ity of Bear Creek, in the Cascade Range of Oregon. main disadvantage of CMA is its higher cost, which is ODOT began using CMA (an alternative deicer that 20 times that of salt (Transportation Research Board, 1991, has fewer adverse environmental effects than road salt) in the mid-1990s and began this study with the USGS p. 1). The adverse environmental effects of CMA used as an to ensure that there were no unexpected effects on the anti-icing material are mainly related to the acetate ion, C2H302-. Acetate can increase the biochemical oxygen water quality of Bear Creek. Streamflow, precipitation, demand (BOD) of streams, causing the depletion of dis- dissolved oxygen, pH, specific conductance, and water solved oxygen (Connolly and others, 1990). The conductiv- temperature were measured continuously through the ity of the water may increase with the addition of calcium, 1998-99 winter, magnesium, and acetate ions, and the addition of acetate to There was no measurable effect of the applica- a stream may increase the alkalinity, and consequently the tion of CMA to Highway 26 on the biochemical pH (Homer, 1988). oxygen demand (BOD), calcium concentration, or magnesium concentration of Bear Creek and its tribu- The effects of CMA on an environmentally sensitive taries. BOD was small in all of the water samples, area such as the Cascade Range have not been fully evalu- some of which were collected before CMA applica- ate& In December 1998, the Oregon Department of Trans- tion, and some of which were collected after applica- portation (ODOT) entered into a cooperative agreement tion. Five-day BOD values ranged from 0.1 milli- with the U. S. Geological Survey to measure and evaluate grams per liter to 1.5 milligrams per liter, and 20-day the effects of CMA highway applications on the water qual- BOD values ranged from 0.2 milligrams per liter to ity of Bear Creek, a tributary to the Sandy River located on 2.0 milligrams per liter, the western slope of the Cascade Range in Oregon (fig. 1). Dissolved copper concentrations in a small Bear Creek drains a small watershed that supports a cold- tributary ditch on the north side of Highway 26 water fishery. It is an ideal site for this study because CMA exceeded the U.S. Environmental Protection Agency is applied to Highway 26 at this elevation several times a aquatic life criteria on three occasions. These exceed- year as part of ODOT's normal operations. The small size ances were probably not caused by the application of of the creek and the fact that it closely parallels the highway CMA because (1) one of the samples was a back- for about 1 mile represent the maximum probable effect for ground sample (no recent CMA application), and (2) direct runoff of CMA into a receiving stream. Therefore, if dissolved copper was not detected in Bear Creek water the impacts of CMA application on Bear Creek are small, samples to which CMA was added during laboratory ODOT can proceed with some confidence that impacts on experiments, other streams throughout Oregon will probably be small.