USING ELECTRICAL CONDUCTIVITY TO MONITOR CHLORIDE CONTAMINATION FROM ROAD SALTING IN SURFACE WATER AND GROUNDWATER IN EAU CLAIRE, WI

In cold weather regions, road salting is often employed to improve the safety of roadways affected by snowfall events. Runoff from these roadways can negatively impact surface and groundwater supplies through dissociation of salt causing high chloride concentrations, which can harm aquatic ecosystems. This project investigates chloride concentrations in surface 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. Measurements were taken from four 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 and melting had occurred. Similar data were acquired in the winters of 2011-2014; these data were analyzed to better understand the fluctuations in chloride concentrations 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. One well showed little correlation with chloride concentrations in streams, while the other well showed an approximately two week delay time between peak chloride concentrations in the well and a nearby stream. Relationships between temperature gradients and chloride concentrations in streams are also being investigated; initial results indicate that gradual warming events correspond to higher chloride concentrations than rapid warming, perhaps due to dilution of salt during more rapid melting events.

Data acquisition for the 2014-2015 season is still underway, but preliminary results show some expected trends. Smaller tributaries show more impact from road salting than larger streams, and more urban areas tend to have higher chloride concentrations than more rural areas; monitoring is now primarily focused on urban areas downstream of where infrastructure meets the tributaries. Large variations in chloride concentrations have been observed along relatively short stretches of a stream, reflecting rapid input of chloride from urban infrastructure along the stream.