Cold Climate Issues for Bioretention: Assessing Impacts of Salt and Aggregate Application on Plant Health, Media Clogging, and Groundwater Quality

Bioretention offers the potential to sustain pre-development water balances while minimizing effects on groundwater quality and providing a landscaped aesthetic. To study cold climate issues including potential trade-offs between groundwater quality and quantity and bioretention system lifespan, a salt and aggregate mixture is being applied to 10 outdoor bioretention columns with soil, mulch and vegetation layers. A detailed methodology and preliminary findings for experimental applications of the salt/sand mixture is presented. Pre testing infiltration rates for bioretention media averaged 24.8 m/day, matching published values. Background Na⁺ and Cl^– levels within the soil matrix averaged 736–1900 mg/L and 95–621 mg/L, respectively. Preliminary mass balance results, demonstrate a consistent response to Na⁺ and Cl^– loading, with increased Na⁺ output mass, and reduced Cl^– mass as compared to input in all columns. The evaluation of the effects of de-icer loading on bioretention systems is essential to the expansion of the functionality of bioretention systems to achieve stormwater management objectives in cold climates.