Advanced Stormwater Treatment Considers Deicing Salts’ Impact on Heavy Metals

Ongoing research reveals the extent to which heavy metals in runoff is damaging the environment. A little-considered component of the damage is how the addition of deicing salts to roadways and parking lots impacts the mobility of heavy metals. The problem occurs when heavy metals trapped in soil or stormwater treatment systems during the summer are released back into stormwater during the winter. Addressing this issue is of paramount importance, especially for snowbelt states throughout North America. To design and operate effective stormwater treatment systems, it is essential to look beyond site and climate conditions, and factor in how deicing salts accelerate the movement of heavy metals. Only then can we prevent toxic effects on ecosystems as much as possible. Because not all metals, including zinc and copper, exist predominantly in their particulate phase, developing treatment protocols that include reducing dissolved metal concentrations must be a priority. Unlike solids, dissolved metals cannot be removed mechanically, for example, by sedimentation or filtration. A second treatment step – such as a filter media – is necessary to reduce high concentrations of metals. Significant progress to address the challenge created with deicing salts can be made by (1) incorporating filter media in stormwater systems that trap heavy metals, and (2) developing a test protocol for filtration manufactured treatment device (MTDs). Through widespread understanding of the impact of deicing on heavy metals and a comprehensive testing protocol, we can advance toward our ultimate aim: protecting our groundwater, watersheds and waterways.