Filtration of Stormwater Contaminants in Bioretention Cells.

Heavy metals like copper, cadmium, and zinc are ubiquitous in stormwater runoff and stormwater is often introduced into surface waters without treatment. Thus, receiving waters are impacted, with serious consequences for aquatic organisms and the food web.

Bioretention systems are suitable elements to reduce the contaminant load of stormwater and manage the amount of stormwater introduced to receiving waters. But most effective compositions of bioretention systems need yet to be determined.

We built 16 mesocosms with different porous media to study the contaminant retention capacities. We used four media (mix 1: 80% sand, 20% compost; mix 2: 60% sand, 40% compost; mix 3: 60% sand, 15% compost, 15% shredded cedar bark, 10% water treatment residuals; mix 4: 60% sand, 30% compost, 10% water treatment residuals) that had been replicated four times. We continuously acquired outflow data since 2011 and measured the contaminant transport for several storms.

For 2013, we have monitored two storm events (April 10 and May 28). On average, our mesocosms have reduced the total load of heavy metals significantly (copper: 74 and 65%; zinc: 98 and 97%; cadmium: 58 and 50% for the first and second storm, respectively). The amount of total suspended solids was reduced (97% and 93%) while dissolved organic carbon values increased (223 and 128%).