MONITORING OF ROAD SALT IMPACT DURING SNOW MELTOFF AND RAINFALL EVENTS AT ALLENDALE MIDDLE SCHOOL, MICHIGAN

Michigan, like many other states, uses chemical deicers on roadways during the winter. Through meltoff and rainfall events, this road salt is washed off the roads, dissolved into runoff and drained into the surrounding watershed. In particular, the addition of chloride to surface and groundwater can affect local vegetation and biota. The purpose of the seminar project (Lynn) was to monitor water quality in a pond-well-stream system at the nearby Allendale Middle School and observe how the conductivity levels and chloride concentrations change during major meltoff and rainfall events. The small pond receives surface water runoff directly via pipe from an adjacent parking lot and road. This pond is near and upgradient from a small stream. A well was installed midpoint to intercept subsurface flow between the pond and the stream. Water samples were collected from each source every other day between mid February and early April of 2015 (daily during the meltoff event), and were then filtered and tested in the lab for conductivity and chloride. Water levels were recorded from stream and pond gauges and the well. When sampling started there was over a foot of snow and the pond surface was frozen.

Over the monitoring period, chloride concentrations ranged from 48 – 155 mg/l in the pond, 68 – 142 mg/l in the well and 22 – 87 mg/l in the stream. Higher chloride values were associated with elevated conductivity readings. The first major snow meltoff event occurred March 7-14, and was followed weeks later by several rainfall events. The chloride concentrations in the stream and well peaked during early snow meltoff but then decreased significantly as snow meltoff continued. Peak chloride concentrations in the pond were measured under ice cover and before meltoff. Our explanation is that the initial small amount of runoff from snow meltoff was heavily impacted by road salt and had a high concentration of chloride but that this chloride was later diluted by additional snow melt. This initial snowmelt peak was not observed in the pond, perhaps because melting ice cover enhanced the dilutional effect. Although chloride concentrations did not exceed the secondary drinking water standard of 250 mg/l, they do highlight the need for early meltoff monitoring and that dilution may mask the input of chloride to water bodies.