Effects of Deicing Salts on the Clogging of Stormwater Filter Media and on the Media Chemistry

Stormwater filter media (SFMs) play a vital role in decreasing flooding and preventing urban contaminants from polluting surface and ground waters. The infiltration rate of a SFM is a governing factor in the hydrological and environmental performance of the stormwater management systems. This paper describes the effect of a common deicing salt (sodium chloride) in reducing the infiltration capacity of two types of SFMs, which were prepared using a clayey silty sand, one with compost and another without compost. This paper also describes the effect of sodium chloride application in the release of zinc, calcium, nitrogen, magnesium, phosphorous, potassium, and sulfur from the SFM, and whether their release was accelerated or reduced from the SFM with compost. Laboratory constant-head infiltration tests were conducted using sodium chloride (as the deicing salt) at concentrations of 150 and 1,200 mg/L. After conducting the tests for comparable cumulative pore volumes of infiltration, soil only SFM experienced significantly smaller reduction (p=0.0045) in flow rate than the soil with compost SFM. However, 1,200 mg/L salt concentration did not result in significantly higher reduction (p=0.96) of flow rate compared with the 150 mg/L salt concentration. At 150 mg/L salt application, a significant increase (p<0.001) of the sodium adsorption ratio (SAR) was observed due to salt application, compost addition, and the interaction of salt and compost. In general, sodium adsorption resulted in the reduction of cation exchange capacity, increased SAR, and leaching of organic matter, nutrients, other cations, and zinc, with these losses being greater for compost-amended media. These results suggest that piling snowmelt laden with deicing salts close to stormwater management systems may result in their poor performance or premature failure. Further research is needed to understand the effect of various salt concentrations, pore structure differences, and temperature on the infiltration rate.