THE EFFECT OF ROAD SALT ON THE HYDROLOGIC SYSTEM IN 2017 AT ALLENDALE MIDDLE SCHOOL, MICHIGAN

Road salts are commonly used during the winter season in the northern states but can dissolve into runoff and enter nearby ponds, streams and groundwater. The purpose of this seminar project (Suess) was to monitor water quality in a small ½ acre study area to observe how conductivity and chloride change during runoff events and identify conditions when peak concentrations occur. The hydrologic system at our site consists of a storm water pipe that discharges runoff from a paved road and parking lot to a small ⅛ acre drainage pond. This pond is adjacent to and upgradient from a small stream. Groundwater wells were installed to intercept subsurface flow between the pond and the stream, with the exception of one well upgradient of the pond. Hobo dataloggers were used to measure conductivity every 15 minutes in the storm water pipe, pond, well, and stream. Over 80 discrete water samples were collected and analyzed for conductivity. Previous results show a positive correlation between conductivity and chloride at the study area.

Throughout the study period of January 1 through February 10, 2017, six peak conductivity events were detected, coinciding with periods of runoff when temperatures rose above freezing. Conductivity values in the pipe could increase by a factor of 4 or 5 during these melt off events and conductivity in the stream could double. Timing of the peak conductivity in the pond typically lagged that in the pipe by several hours to half a day. For the pipe, pond and stream we observed a rapid rise in conductivity in the initial stage of the melt off event, followed by an often abrupt decrease, probably due to dilution by continued snow melt. Our study also highlights the challenges in using discrete water samples alone to characterize road salt impact and identify peak concentrations.