This three-year study evaluates the quantity and quality of runoff from an extensive green roof on a multistory building in Toronto. Laboratory physical, chemical, and leachate analyses of eleven commercially available green roof growing media were also undertaken to help identify the potential influence that the growing media may have on runoff chemistry. Continuous precipitation and runoff data collected over 18 months outside of the winter period indicated that the green roof discharged 63% less runoff than a neighbouring conventional modified bitumen roof. Runoff volumes from the green roof averaged 42% less than the conventional roof in April and November, and between 70 and 93% less during the summer months. Water samples were collected from both roofs during 21 rain events in 2003 and 2004 and analyzed for general chemistry (e.g., pH, total suspended solids), metals, nutrients, bacteria (n = 16), and polycyclic aromatic hydrocarbons (n = 18). Loads of most chemical variables in green roof runoff were lower than from the conventional roof. Exceptions included constituents such as calcium, magnesium, and total phosphorus, which were either naturally present in the media or were added to promote plant growth. Total phosphorus concentrations in green roof runoff were significantly higher than the conventional roof (α = 0.001), and regularly exceeded the Ontario receiving water objective (0.03 mg/L). Phosphorus concentrations fell significantly after the first year of monitoring (α = 0.001), suggesting that the nutrient is being leached from the media. Chemical analyses of green roof growing media showed that levels of most constituents were similar to or lower than typical background concentrations for agricultural soils in Ontario. However, leachate concentrations from several media exceeded receiving water standards for phosphorus, aluminum, copper, iron, and vanadium. This study highlights the importance of engineering green roof media to minimize leaching of nutrients and other contaminants while maintaining their ability to support plant growth.

Receiving water quality concerns associated with increased construction activities in recent years in the Greater Toronto Area has prompted the Toronto and Region Conservation Authority (TRCA) to evaluate design criteria for sediment control ponds employed during the construction period. Stormwater management ponds located in the towns of Richmond Hill and Markham were monitored to obtain stormwater runoff quantity and influent-effluent quality data during site development. The ponds were designed and constructed in accordance with the Ontario Ministry of the Environment Stormwater management planning and design manual 2003 for an enhanced level of protection (i.e., 80% total suspended solids removal). A hydrodynamic and sediment-transport model was used to examine the effect of pond geometry on sediment removal efficiency under varying storm events. The monitoring data and the modelling results clearly demonstrate the importance of proper pond size and geometry design. This paper focuses on the effect of the ratio of pond length to pond width in minimizing the short-circuiting effect and improvement of the sediment removal efficiency of stormwater management ponds. The results of this study will be useful in updating the design criteria for stormwater management ponds.

Stormwater runoff containing pollutants deposited on highways from vehicular traffic and urban activities has been identified as a serious threat to aquatic habitats. Although many urban stormwater management technologies serve to reduce the concentrations of pollutants from being transported to larger bodies of water, these stormwater management installations do not always meet the provincial water quality guidelines. In summer 2007, a compost biofilter was installed in a ditch near Highway 8 in Kitchener, Ontario and monitored for 18 storm events spanned over two years for both flow rate and water quality. The main objectives of the study were to determine highway runoff quality and biofilter pollutant removal efficiency. This study shows that the key factors that affect the build-up of the pollutants on a highway are the average annual daily traffic (AADT) and the antecedent dry days (ADD), and the main factors that affect the wash-off of pollutants, include total rainfall depth and rainfall intensity. Before filtration, highway runoff contaminant levels often exceeded the Ontario Provincial Water Quality Objectives (PWQO). However, the biofilter reduced the total suspended solids, zinc, copper and polycyclic aromatic hydrocarbons by 42, 32, 29, and 66%.

Several areas within the Lake Simcoe watershed, Canada, are experiencing rapid urban development. The construction of new homes and businesses is frequently associated with elevated rates of soil erosion stemming from land clearing and grading activities. During development, rates of soil erosion can climb to levels that are typically 200 times above background conditions, with the eroded sediments entering waterways and causing harm to the biota living therein. This is a serious challenge for the communities around Lake Simcoe because the transport of sediment has previously been identified as a contributor to the eutrophication of the lake's waters. To mitigate the negative impacts associated with development, many jurisdictions across North America and elsewhere have developed a suite of constructionphase stormwater management (CPSWM) guidelines, which entail the use of onsite best management practices that capture, detain, and treat sediment-laden surface runoff. Here, we review CPSWM guidelines for effluent discharge and receiving water quality and discuss the relative strengths and weaknesses of each approach. Finally, proposed revisions to the current Ontario guidelines are suggested based on a combination of field observations at predevelopment and active construction sites, as well as the reviewed literature. If adopted, the proposed revisions would help to reduce sediment transport from construction sites in rapidly urbanizing areas such as Lake Simcoe.