Effects of Road Deicers on Water Quality in Selected Watersheds Along the Interstate 95 Corridor, 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. As part of this study, the effects of road deicers on chloride concentrations in groundwater are being assessed to help determine effects on stream-water quality. Concentrations of chloride and other constituents in groundwater can affect stream-water quality and have important consequences in aquatic criteria for acute and chronic toxicity.

Specific conductance and temperature were monitored continuously at sites upstream and downstream of I-95 on four streams, and in piezometers at two of the downstream sites. Data collected in streams during winters indicate downstream peaks of specific conductance that correspond to winter storms or subsequent melting events.

Specific conductance in shallow groundwater varied considerably between piezometers at the Four Mile River site (FM) and the Jordan Brook site (JB). At FM, specific conductance in shallow groundwater ranged from 1,020 to 1,500 microsiemens per centimeter at 25 degrees Celsius (mS/cm) from February to November 2010. Specific conductance in the stream ranged from 33 to 174 mS/cm and increased during storm events. Groundwater levels also increased during storms, indicating that the shallow groundwater contributes salt to the stream during increased groundwater discharge. At JB, specific conductance in the shallow groundwater ranged from 59 to 200 mS/cm from July to November 2010. Specific conductance in the stream at JB had a baseline of about 230 mS/cm and generally was higher than in groundwater but decreased during storms indicating that shallow groundwater is not a source of salt to the stream. The difference in salt contribution from groundwater in the two streams apparently is due to land-use differences.