EFFECTS OF ROAD DEICERS ON WATER QUALITY IN SELECTED WATERSHEDS, SOUTHEASTERN CONNECTICUT

A U.S. Geological Survey study in cooperation with the Federal Highway Administration and the Connecticut Department of Transportation was initiated in 2008 in response to concerns about the effects of the expansion of Interstate 95 (I-95) on the water-quality and biological resources of intersecting watersheds. Chloride (Cl), temperature, and specific conductance (SC) were measured upstream and downstream of I-95 at four watersheds—Four Mile River (FM), Oil Mill Brook (OM), Stony Brook (SB), and Jordan Brook (JB), and in shallow groundwater at the FM and JB sites. SC and temperature were monitored continuously and chloride was measured approximately monthly at stream sites. Cl concentrations were estimated using regression models that described the relation among measured Cl concentrations, SC, and instantaneous streamflow.

During winter, downstream peaks of SC corresponded to storms or subsequent melting events. Continuous SC peaked as high as 860 microsiemens per centimeter (μS/cm) at stream monitoring sites during winter storms, but at other times averaged between 83 and 200 μS/cm. Estimated Cl concentrations in the four watersheds were well below the U.S. Environmental Protection Agency recommended chronic and acute Cl toxicity criteria of 230 and 860 milligrams per liter, respectively. Deicers also affected shallow groundwater and subsequently contributed to salts in streams. SC in shallow groundwater varied considerably between piezometers at FM and JB as a result of land-use differences; groundwater provided a much larger contribution of salt to the stream at FM compared to JB.

The estimated Cl yields for a period from 2008 to 2009 at the four stream sites downstream from I-95 ranged from 0.07 ton per day per square mile (ton/d)/mi² at OM, one of the least developed watersheds, to 0.21 (ton/d)/mi² at JB, the watershed with the highest percentage of urban development and impervious surfaces. FM and OM had low estimated Cl yields and reflect the low percentages of developed land and impervious area. Estimated Cl yields at JB and SB were relatively high but were not as high as those estimated in more urbanized watersheds in Connecticut. High concentrations of chloride and other constituents in road deicers can affect groundwater and stream-water quality to the extent that they exceed aquatic criteria for acute and chronic toxicity.