Seasonal hydrological and water quality performance of individual and in-series stormwater infrastructures as treatment trains in cold climate

The performance of stormwater treatment trains and of their individual green infrastructure was evaluated near Montreal, Canada. Three treatment trains were studied: Train 1 – five bioretention cells in series with a wet retention pond; Train 2 – an infiltration trench in series with a dry detention pond and Train 3 – Train 2 in series with a wet retention pond. A total of 47 rain events were monitored to quantity the hydrological performance, while water quality samples were taken during 24 rainfall events. During the summer, the bioretention cells led to a reduction in runoff volumes varying from 8 to 100%. Overall, the three studied treatment trains and all of the individual infrastructures, except for the dry pond, provided reductions in the mean concentrations of total suspended solids, chemical oxygen demand, total nitrogen and total phosphorous. Results also showed that the use of a train of stormwater infrastructures can be more effective to reach Quebec's legislated targets than single infrastructures to remove those four contaminants, but only if the infrastructures are sequenced properly. Indeed, the addition of a dry basin at the end of Train 2 reduced the removal efficiency of the four studied contaminants.