CHLORIDE PATTERNS IN TWO RIVERS LOCATED IN URBAN AND RURAL AREAS IN EASTERN AND CENTRAL MASSACHUSETTS

Chloride based deicers (NaCl and CaCl₂) are the most common substances used for the purpose of roadway ice and snow removal. The use of chloride based deicers, commonly referred to as road salt, have been increasing in the United States since their introduction in the 1930's. Upon application, road salt readily dissolves and dissociates, causing increased concentrations of the respective ions in nearby soils, surface water and groundwater. Of the ions present in road salt, chloride is the most conservative and will be the focus for this study. The EPA has suggested limits of 230 ppm chloride for chronic aquatic life exposure and 860 ppm chloride for acute aquatic life exposure in surface waters.

For this study, we use a robust dataset consisting of continuous temperature, specific conductance and discharge records collected by the USGS from two rivers, one located in a highly urbanized area and one located in a rural setting. Specific conductance values from each river were calibrated to chloride concentrations to indirectly measure the chloride concentrations in each river for their respective periods of record. The Stillwater River is located in central Massachusetts, has a drainage area that is 75.2% forested, and shows a peak chloride concentration under 100 ppm. In contrast, the Saugus River is located in the Greater Boston Area, has a drainage area that is 55.9% urban, and shows a peak chloride concentration greater than 1,000 ppm, above the acute exposure for aquatic life limit suggested by the EPA. Both rivers exhibit seasonal fluctuation of chloride concentrations with peak levels seen during the winter months, when road salt application rates are at their highest point. Here we compare and contrast the chloride concentrations of the Saugus and Stillwater Rivers with respect to time, precipitation, and temperature.