Graduate Researcher: Carrie M. Fischer, P.E.
Salt and/or brine is applied to roadways in order to depress the freezing point of water and prevent the buildup of ice on pavements and reducing the number of accidents that occur during the winter months. As the snow/ice melt, the water containing salts move into the drainage system and either are discharged into streams or into stormwater treatment devices. An example of the amount of salt recommended to be applied to roads can be found in the New Hampshire guidance.
This multi-year project investigates the behavior of road salts (sodium chloride) in two bioretention systems in Lancaster, PA – both in Brandon Park. The upper basin, which receives runoff from Wabank St, was instrumented in November 2020 with both level-conductivity loggers and soil moisture-conductivity sensors. The lower basin, which receives runoff from the park roads and sidewalks, was instrumented in a similar manner in December 2021.
Brandon Park Bioretention System: (Left: between snow events, January 2021; Right: Snow event, February 2021)
An example of the soil sensor readings (figure below) highlights the response of the soil sensors to the road salt and meltwater moving into the basin. The blue lines are the electrical conductivity readings. Comparing these results to weather patterns, as temperatures rose (not shown), the snow/ice melted and salt-laden water moved into the basin and past the sensors. If the snow was followed by a rain, even light rain, the salt movement was greater. As the responses show, in general, the salt content of the soil (as measured by its electrical conductivity) is acceptable for salt-sensitive crops, but late winter storms can move salt into the basin at a time when plants may be more susceptible to salt.
The first year of research has been presented in multiple forums with the links below to the pdf of the presentations.
AWRA conference fischer bioretention 2021
Lancaster-Lebanon Watershed Forum 2021 Brandon Park Presentation