TRACING DISSOLVED CHLORIDE FROM ROAD SALT APPLICATION USING SPECIFIC CONDUCTANCE IN THE SOUTHERN REGION OF THE NASHUA RIVER WATERSHED, MA

Previous studies have shown correlations between the applications of road salt in winter months, with elevated specific conductivity values in streams and lakes. Elevated salt concentrations have been linked to impacting aquatic flora and fauna, causing nutrient depletion in soils through ion exchange, and possible damage to road infrastructure. Historical USGS gauging station data for several watersheds within Massachusetts indicate a strong positive correlation between specific conductance and dissolved chloride concentration with an R² value of 0.9528. This correlation allows for the determination of dissolved chloride concentrations from measured specific conductivity values. Gauging station sites within Massachusetts show that increases in dissolved chloride concentrations have occurred for decades. Increases are most likely due to a variety of factors such as increased road density for new communities necessitating increases of salt applied as well as the fact dissolved chloride from road salt is highly soluble and can steadily increase in the groundwater system for a long time.

The focus of this study is on three rivers, two of which have available historical data, five ponds, and a lake in the southern region of the Nashua River watershed, within Worcester County, MA. Sample locations in forested areas with low road density yield the lowest specific conductance that are as low as 31 µS for rivers and 25 µS for ponds. The low specific conductivity from the forested areas indicates background concentrations that have not been impacted by road salt applications. Sites located adjacent to high priority salting roads, especially highways I-190 and Rt-2, yield the highest specific conductance values that are as high as 1070 µS for rivers and 2517 µS for ponds. Differences in specific conductivity values relative to their road locations suggests that dissolved chloride from salting in the winter is not being washed away after each salting season, but is residing in groundwater and entering surface waters through baseflow even when no salt is actively applied.