Colloquia – Eric Peterson

Transport and fate of chloride from road salt within mixed urban and agricultural watersheds.

Eric W. Peterson, Chair & University Professor Department of Geography, Geology, and the Environment, Illinois State University

In a typical winter season, approximately 471,000 tons of road salt are applied along Illinois roadways. An estimated 45% of the deposited road salt will infiltrate through the soils and into shallow aquifers, and agricultural practices can also contribute to elevated chloride in soils. Transported through shallow aquifers, chloride has the potential to reside within groundwater for years based on the pathway, the geologic material, and the recharge rate of the aquifer system. Utilizing MODFLOW and MT3D, simulations employing various road salt application rates were conducted to assess the net accumulation of chloride and the residence times of chloride in an agricultural dominated watershed that originates in an urban area. A positive-linear relationship was observed between the application rate of chloride and both the maximum chloride concentration and total mass accumulated within the watershed. Simulated recharge rates along impacted surfaces ranged from 1,000 mg/L to 10,000 mg/L. After 60 years of application, simulated chloride concentrations in the groundwater ranged from 197 mg/L to 1,900 mg/L, with chloride concentrations within the groundwater rising at an annual rate greater than 3 mg/L. While concentrations increase throughout the system, most of the chloride accumulation occurs near the roads and the urban areas.