CORRELATIONS BETWEEN LAND USE AND THE EXTENT OF ROAD SALT CONTAMINATION IN SURFACE WATERS AND GROUNDWATER BASEFLOW - EASTERN MASSACHUSETTS

Approximately 15,000,000 tons of sodium chloride, commonly referred to as road salt, is applied to highways and major roads each year in the United States. Upon dissolution, the sodium and chloride ions from road salt quickly contaminate surface waters, groundwaters, and soils. Chloride is largely unreactive in the watershed environment, and its concentration in natural waters is therefore the best indicator of road salt contamination. The concentration of chloride in surface waters and groundwaters in urban regions of Canada, northern Europe, and the northern USA has been steadily increasing since significant road salt applications began in the 1960’s. As road salt application rates have risen, so have the rates of increase in the chloride concentration of natural waters. In many watersheds 50 percent or more of applied road salt does not leave the watershed system. Recent evidence suggests that the majority of it is preferentially accumulating in groundwaters. Groundwater baseflow is responsible for the majority of road salt removal, as much as 99 percent in some watersheds. This study characterized the extent of road salt contamination in surface waters and groundwater baseflow at 18 sites throughout the Saugus Watershed, a small semi-urban watershed, and quantified correlations between the observed chloride concentrations and the land use characteristics of the contributing areas to each sample site. ArcGIS was used to determine the land use characteristics, aid in chloride concentration analysis, and calculate the degrees of correlation between land use variables and mean chloride concentration. The most significant correlations were observed between the mean chloride concentration of baseflow and roadway density, especially highway and major road density.