Influence of Modern Stormwater Management Practices on Transport of Road Salt to Surface Waters

Application of road salts in regions with colder climates is leading to ground and surface water contamination. However, we know little about how modern stormwater management practices affect the movement of road salt through urban watersheds. We investigated groundwater contamination and transport of road salts at two stormwater ponds in Baltimore County, Maryland. In association with the ponds, we documented a plume of contaminated groundwater that resulted in Cl^- loadings to the adjacent stream of 6574 to 40 008 kg Cl^- per winter, depending on winter snowfall. We also monitored Na⁺ and Cl^- ion concentrations and the temporal dynamics of conductivity at a range of stream sites in watersheds with and without stormwater management ponds. Streams draining watersheds with stormwater ponds had consistently higher conductivities and Cl^- concentrations during base flow conditions and often exhibited greater peaks in Cl^- and conductivity associated with winter storms and subsequent melting events, despite the degree of watershed development. Our results indicate that modern stormwater management practices are not protecting surface waters from road salt contamination and suggest they create contaminated plumes of groundwater that deliver Cl^- and Na⁺ to streams throughout the year.