MONITORING OF CHEMICAL DEICER IMPACT ON SURFACE AND GROUNDWATER DURING SNOW MELT OFF EVENTS AT ALLENDALE MIDDLE SCHOOL, MICHIGAN

Michigan, like many cold weather states, uses chemical deicers on roadways during the winter. Dissolution of this salt can add chloride to runoff that can affect local aquatic systems and contribute to long term increases of chloride even in large water bodies like Lake Michigan. The purpose of the seminar project (Gentner) is to monitor water quality in a drainage pipe-pond-well-stream system and observe how the conductivity levels and chloride concentrations change during snow melt and precipitation events. Studying a hydrologically connected local system helps to identify under what conditions peak chloride concentrations occur. The small pond receives surface water runoff directly via drainage pipe from an adjacent parking lot. This pond is nearby and up gradient from a small stream. A shallow well was installed to intercept subsurface flow between the pond and the stream. A previous study at this site focused on the major melt off event that occurred in March of 2015. Peak chloride concentrations were detected in the stream and well during early snow melt off in 2015 but decreased as melt off continued, probably due to dilution. Peak chloride concentrations were detected in the pond under ice cover and before snow melt.

In our study, we are now sampling from the outlet of the drainage pipe and started sampling earlier (January). Water samples are collected from each source periodically and are taken daily during melt off events. These samples are then filtered and tested in the lab for conductivity and chloride. As previous studies have shown a positive correlation between conductivity and chloride, data loggers are now used to measure conductivity and improve our resolution of chemical changes. Monitoring is still underway but preliminary results show the impact of the mild winter in Michigan. Our typical "deep freeze" has been interrupted by brief periods of snowmelt and rain when temperatures rise above freezing. Such an event occurred on January 15, 2016 and released a pulse of high conductivity water into the drainage pipe that a day later was detected by the data logger in the pond. Pipe outlet samples during this event exhibited elevated conductivity levels (> 4000 μS/cm) and chloride concentrations (> 1200 mg/l). In our poster we will highlight climatic influences on peak chloride levels detected in our hydrologic system.