TRACING CHLORIDE CONCENTRATIONS IN MASSACHUSETTS WATERSHEDS USING SPECIFIC CONDUCTANCE

Extensive data and historical evidence have led to the documented effects of road salt on water quality and surrounding ecosystems. EPA national criteria suggest that chloride concentrations above 860mg/l have acute impacts on aquatic life. Concentrations of chloride in aquifers around highways and roads can range from 1mg/l to more than 100,000 mg/l. In this study, specific conductance was used to correlate chloride concentrations in surface waters throughout all Massachusetts major watersheds. When specific conductance and chloride concentrations are plotted, slope and intercept values are used to determine a regression model. The regression model is used to estimate chloride concentrations from measured specific conductance in water bodies where chloride concentrations have not been measured. The validity of using specific conductance as a surrogate for chloride concentrations was demonstrated using pure NaCl conductivity in solution. Correlation plots can be used to track and monitor chloride concentrations without the need for costly chloride analysis.

Data retrieved from the USGS, NWIS, NAWQA and local watershed groups reveal that watersheds throughout Massachusetts demonstrate a similar, linear correlation between chloride and specific conductance. Fourteen out of the twenty-five watersheds in the commonwealth had historical and current data, ranging from 1952-2013. Results show that correlation slopes range from 3.56 to 5.97 with a mean of 4.33 while intercepts range from 18.76 - 85.25 with a mean of 56.29. Insufficient data was available to develop a correlation in eleven watersheds, indicating a need to collect more data. However, most of the data within these eleven watersheds are consistent with the results of the acceptable correlations. Results indicate that a statewide correlation may be possible. Using this model, correlation plots can be developed and used as a predictive and diagnostic tool to determine chloride concentrations and track the impacts of road salt application on surface water quality.