Conestoga College South Campus stormwater management system long-term monitoring wrap-up

This presentation summarizes the stormwater management system performance and trends observed over a period of five years of environmental monitoring at Phase 1 of The Conestoga College Cambridge Campus expansion. The expansion represents a total developed area of 18.4 ha. The site is bounded by Highway 401 to the north west, Morningside Drive to the north east, and Fountain Street South to the south.  The college expansion consisted of a campus building and a parking lot, with future expansion areas defined and accounted for within the design. The site outlets to a previously ephemeral stream (tributary to Blair Creek) at the southwest corner of the property. Blair Creek is a primarily groundwater-fed cold-water creek.  Water quality, quantity, erosion, water balance, and thermal mitigation were all objectives for the stormwater management strategy to maintain or enhance water quality in Blair Creek. The stormwater management strategy included infiltration galleries for roof water, parking lot bioswales and infiltration chambers, oil/grit interceptors, and a detention basin outletting to a rock crib cooling trench.  Five years of monitoring results were analyzed to assess trends and performance, and identify adaptive management responses for the stormwater management system.

The stormwater management system successfully met peak flow targets for events greater than 25mm.  Monitoring results indicated positive performance of the cooling trench over the entire monitoring period. It effectively reduced the temperature of the outflow over the year, with maximum temperatures of 22^oC periodically observed but an average summer discharge temperature of 14^oC meeting the criteria of the sensitive outlet feature.   Water balance results based on the monitoring data indicated that the annual runoff volume exceeded the predicted values.  This increase was due in large part to a pond bypass system that has enhanced coldwater baseflow to the creek. The increase was not detrimental to the receiving creek as it has resulted in the previously ephemeral tributary morphing into a perennially flowing cool to coldwater tributary.  Groundwater level monitoring indicated enhanced groundwater recharge as a result of the infiltration galleries. Observations indicate that the receiving creek remains geomorphically stable.  Salt application is a continuous issue at the site.  User safety has attempted to be balanced with groundwater quality and chloride concentrations have increased over the five years of monitoring.  

This presentation shares the details of the results and trends observed over the monitoring period. Overall the system performed very well on all stormwater management objectives. Strategies that were successful will be highlighted. Adaptive management responses are also presented to mitigate identified issues and recommendations are shared for future LID installations and designs.