Water quality

Under the CCME Water Quality Guidelines for the Protection of Aquatic Life. Freshwater – Long-term Suspended Sediment Concentration: “Maximum increase of 25 mg/L from background levels for any short-term exposure (e.g., 24-h period).” Assumes background level of 5 mg/L and objective of 30 mg/L total (CCME, 2002

Overview

Improvements in the quality of stormwater runoff is one of the primary benefits of low impact development strategies. Although some chemical changes occur inside the practices, much of the pollution reduction of low impact development strategies comes from runoff reduction. i.e. diverting excess water through infiltration or evapotranspiration.

Nutrients

Plants (including algae) require three macro nutrients to grow: Nitrogen, potassium, and phosphorus. Of these three, phosphorus is the often the "growth-limiting" nutrient. i.e. the local environment may have an abundance of nitrogen and potassium, but algae won't develop unless phosphorus is available too. See Phosphorus page for more on phosphorus. See Additives page for guidance on filter media additives to enhance retention of phosphorus and other types of pollutants in Bioretention, Bioswale, Stormwater Planter and Stormwater Tree Trench facilities.

Under the Provincial Water Quality Objectives set out by the Ministry of Environment and Energy in 1994, Total phosphorus effluent leaving a SWM facility should be below a concentration level of 30 μg/L. (0.03 mg/L) (MOEE, 1994)

Practice-specific Water Quality

You can find practice-specific water quality results from STEP-associated projects over a 25-year period (1997 - 2021). Additional results will be added to this database on an ongoing basis. Click on any of the LID BMPs below to see how the removal efficiencies of these practices compares to the CWQG requirements for Phosphorus and TSS

• Bioretention: Performance
• OGS: Performance
• Permeable pavements: Performance
• Infiltration Trench: Performance
• Rainwater Harvesting: Performance
• Green Roof: Performance

Note: The water quality performance data was collected by the Sustainable Technologies Evaluation Program (STEP). Disclaimer: STEP cannot guarantee the validity of the information found here. While we use reasonable efforts to include accurate and up to date information, we make no guarantees as to the accuracy of the content and assume no liability for an error or omission in the content).

Heavy metals

The heavy metals noted as particularly harmful to aquatic ecosystems are:

• Chromium(Cr),
• Copper (Cu),
• Lead (Pb), and
• Zinc (Zn)

Laboratory experiments on bioretention media have demonstrated that the organic matter significantly improves retention of lead (Pb), copper (Cu), and zinc (Zn) . This research also found that extended detention of the stormwater in the cell did not improve this water quality benefit.

Cores of media were extracted from five 10 year old bioretention cells in Queensland, Auz and tested for a suite of heavy metals: “Although trace amounts of several heavy metals (most prominently Mn and Zn) were found in most of the basins, all heavy metal levels found in the soil were either below detectable limits, or within acceptable limits based on legislated health-based investigation levels.”

External Links

• Environment Canada on Phosphorus and Excess Algal Growth
• Lake Simcoe phosphorus reduction strategy
• Canadian LID BMP Database

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

Stormwater Management

Sustainable Technologies Evaluation Program

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

A stormwater design features that provides for the gradual release of a volume of water in order to increase settling of pollutants and protect downstream channels from frequent storm events.

Ground depression acting as a flow control and water treatment structure, that is normally dry.

A bioretention BMP featuring an impermeable liner and underdrain that prevents infiltration of runoff into the underlying native soil; provides sedimentation and filtration of urban runoff as it passes through the mulch layer, engineered filter media and vegetation root zone.

A bioretention cell that features an impermeable liner that collects and treats stormwater through sedimentation and filtration only (i.e., no infiltration).

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.