ROAD SALT IMPACT ON SURFACE AND GROUNDWATER DURING SNOW MELT OFF AND RAINFALL EVENTS IN 2015 AND 2016 AT ALLENDALE MIDDLE SCHOOL, MICHIGAN

Application of road salt has led to long term increases of chloride in aquatic systems, even in large water bodies like the Great Lakes. While other studies have examined broadly how road salt has affected nearby streams, my students and I have focused on a small 1/2 acre site to characterize in some detail the distribution of chloride and conductivity in space and time during the winter and spring melt. Of interest is how chloride is transported through different reservoirs in our hydraulically connected system and what factors contribute to peak concentrations of chloride. At our site, runoff from a paved parking lot and road is discharged via stormwater pipe into a 1/4 acre pond. This pond is located upgradient and adjacent to a small stream that flows through the school campus. A shallow well was installed to intercept groundwater flow between the pond and the stream. The monitoring network consists of outflow from the stormwater pipe, and water from the pond, well and stream. Data loggers were used to record conductivity every 15 minutes and water samples were collected periodically at each source and daily during snow melt off events. Water samples were tested in the lab for conductivity and chloride.

 Results show a positive correlation between conductivity and chloride values. The number of melt off events varied as winter weather in Michigan in 2016 differed from the previous year. In 2015, over a foot of snow and thick pond ice formed as below freezing conditions persisted until early March, ending in a big snow melt off. In contrast, the more mild winter of 2016 produced several brief periods of runoff in January and February when temperatures rose above freezing. In 2015, chloride concentrations in the well and stream peaked during early snow melt off but then decreased significantly as snow melt and dilution continued. In 2015 in the pond, peak chloride concentrations were measured while still under ice cover. In contrast, in 2016 conductivity changes in the pond in 2016 follow a “stair step” pattern (~350 – 675 - 1000 ppm) that coincide with periodic melt off events that added chloride to the pond. The single large snow melt event in 2015 resulted in the highest chloride values in the stream. Of note, the pond has prevented stormwater with chloride concentrations exceeding 1500 mg/l from being rapidly introduced into the stream.