MONITORING THE EFFECTS OF ROAD SALTING ON CHLORIDE CONCENTRATIONS IN SURFACE WATER AND GROUNDWATER IN EAU CLAIRE, WI

In cold weather regions, road salting is often employed to improve the safety of roadways impacted by snowfall events. Runoff from these roadways can negatively impact surface water and groundwater supplies through high chloride concentrations, which can harm aquatic ecosystems. This project investigates chloride concentrations in surface water and groundwater in Eau Claire, Wisconsin. Previous work in this area has shown that there is a strong positive correlation between chloride concentrations and electrical conductivity (EC) measurements in surface water, so EC measurements were acquired frequently, and chloride samples were collected less often to verify the accuracy of the chloride-EC relationship. Measurements were taken from nine stream sites and two groundwater wells. Samples were acquired to capture both background chloride concentrations (no recent precipitation) and chloride concentrations soon after road salting had occurred. Similar data had been acquired at a subset of the sampling sites in the winters of 2011-2012 and 2012-2013, so comparing data from multiple years provides a better understanding of the fluctuations in chloride concentrations as a result of variable weather conditions over a longer time period. In addition to analyzing longer-term trends in chloride concentrations, this project investigates the connection between chloride concentrations in surface water and shallow groundwater and the delay time between road salting and peak chloride concentrations in a subset of streams. Possible relationships between temperature gradients, precipitation depths, and chloride concentrations in streams are also being investigated.

Data acquisition for the 2013-2014 season is still underway, but preliminary results show some expected trends. Streams located in more urban areas show chloride concentrations that are higher and have greater variability than chlorides in more rural waterways. Similarly, smaller tributaries show more impact from road salting than larger streams. Finally, large variations in chloride concentrations have been observed along relatively short stretches of a stream, reflecting rapid input of chloride from urban development along the stream.