CHLORIDE LOADING PATTERNS IN TWO WATERSHEDS IN MASSACHUSETTS

Chloride based deicers, also referred to as road salts, are the most common substances used for maintenance of safe roadway surfaces during the winter months. Upon application, road salt reacts with the accumulated snow or ice to form brine-ice liquidus solutions in the salt-water system. Dissolved salts dissociate, 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 is the focus of this study.

For this study, we use a robust, four year dataset consisting of continuous (15 minute interval) specific conductance and discharge records collected from 2003 – 2007 by the USGS from the Saugus River (Station number 01102345), located in urban Eastern Massachusetts, and the Stillwater River (Station number 01095220), located in rural Central Massachusetts. Specific conductance values from each river were empirically calibrated to chloride concentrations in each river to obtain chloride concentrations from continuous specific conductance measurements. The continuous chloride concentration datasets, coupled with the corresponding stream flow values, are used to calculate total dissolved chloride loads for Saugus River and for Stillwater River. Both rivers exhibited seasonal fluctuation in dissolved chloride loads with the highest levels seen in winter and spring months and lowest levels seen during the summer and fall months. Over the four year record, the peak 15 day average of dissolved chloride load in Saugus River was 47.01 tons of chloride per day from January 15, 2005 to January 30, 2005 (a total of over 700 tons of chloride removed from this watershed during this 15 day period). In contrast, the peak 15 day average dissolved chloride load for Stillwater River was only 10.10 tons of chloride per day from March 18, 2003 to April 2, 2003 (a total of approximately 150 tons of chloride removed from the watershed during this 15 day period). The total dissolved chloride load in each river reflects road salt application practices in each local area, however, the dissolved chloride variation patterns point to a complex system controlled at different times and in different proportions by land use differences, precipitation, groundwater discharge to the river, evaporation and transpiration processes.