Permeable pavements: Performance

TSS Reduction

The performance results for Permeable pavement/Porous Asphalt: Life Cycle Costs practices, located within TRCA's watershed originate from three primary sites:

• Kortright Centre Parking Lot
• Seneca College
• IMAX Corporation, head office

The mean performance value recorded at the outlet for Permeable Pavement practices' ability to remove Total Suspended Sediments (TSS) was was calculated based on 296 separate recordings between 2005-2007, and 2010-2017 amongst the three sites previously mentioned.

As can be seen in the corresponding boxplot the mean performance removal efficiency of the permeable pavement practices monitored are well below the suggested guideline of 30 mg/L (Canadian Water Quality Guideline (CWQG), or (background (assumed at <5 mg/L)+ 25 mg/L for short term (<24 hour) exposure) (CCME, 2002; (TRCA, 2021).

The median value of the 301 samples taken was 8.95 mg/L whereas the mean was 17.10 mg/L, with a 12% guideline exceedance.

Phosphorus Reduction

The performance results for Permeable pavement/Porous Asphalt: Life Cycle Costs practices, located within TRCA's watershed originate from three primary sites:

• Kortright Centre Parking Lot
• Seneca College
• IMAX Corporation, head office

The mean performance value recorded at the outlet for Permeable Pavement practices' ability to remove Total Phosphorus (TP) was calculated based on 300 separate recordings between 2005-2007, and 2010-2017 amongst the three sites previously mentioned.

As can be seen in the corresponding boxplot, the mean performance removal efficiency of the bioretention practices monitored are not meeting the acceptable upper extent range of nutrients as of 0.03 mg/L (30 µg/L) (Environment Canada, 2004; OMOEE, 1994).

The median value of the 355 samples taken was 0.04 mg/L whereas the mean was 0.08 mg/L, with a 62% guideline exceedance. Given the age of most of these practices, more inspection, maintenance and necessary rehabilitation will be needed to ensure they are able to meet the federal and provincial governments' guideline requirement for stormwater quality.

Please refer to the Phosphorus page and the additives page for more information on how LIDs can reduce contaminant loading in stormwater

Recent Performance Research

Shown here are the two variations of hydrodynamic separators (Oil and grit separators) used in the 6-year study conducted by Lee, et al., 2014. All four OGS' used were of different sizes. The first (Type A) was a dip cylindrical plate with a centershaft and the second (Type B) was a hollow cylindrical screen. All four sites where the OGS' were installed were in urban settings in Gyunggi Province, Korea, and discharge into Gyung-An stream, which deposits into the Pal-dang Lake. This lake is the the primary drinking water source for Seoul's Metropolitan area (Lee, et al. 2014

.

• (Clary et al., 2020) - International Stormwater BMP Database: 2020 Summary Statistics.
  • The International Stormwater Best Management Practices (BMP) Database is a publicly accessible repository for BMP performance monitoring study, design, and cost information. As of December 2019, the BMP Database contains data sets collected over four decades from over 700 BMP studies through the U.S., Canada, Sweden, New Zealand, Australia, China, etc. that are accessible on the project website ([www.bmpdatabase.org]). The performance data for both TSS and TP are as follows within the report:
    • Median TSS value of outflow/effluent of stormwater from P.P is 22 mg/L in comparison to 77 mg/L influent levels. These levels are computed using the BCa bootstrap method described by Efron and Tibishirani (1993). This value is below the required CCME levels for TSS in stormwater.
    • Median Total phosphorus (TP) value of outflow/effluent of stormwater from P.P is 0.10 mg/L in comparison to 0.17 mg/L influent levels. These levels are computed using the BCa bootstrap method described by Efron and Tibishirani (1993). This value is below the required CCME levels for TP in stormwater.

).

• (Jianghua, et al. 2009) - Performance Analysis of a Hydrodynamic Separator for Treating Particulate Pollutants in Highway Rainfall Runoff.
  • This study examined the separation characteristics of particles in runoff from paved roads using a OGS hydro cyclone design. The results indicated the TSS concentration ratio between the overflow and inflow (TSSover/in) decreased as a function of the operational pressure and the particle removal efficiency was mainly affected by the particle size. By using highway runoff results showed that removal efficiency was greater than 60%. The TSSover/in was (0.26 mg/L – 0.41 mg/L) below the Canadian Water Quality Guidelines (CWQGs) (Jianghua, et al. 2009).

• (Lee, et al. 2014) - Performance evaluation and a sizing method for hydrodynamic separators treating urban stormwater runoff.
  • This study conducted performance monitoring over a 6-year period (137 separate storm events) of four different hydrodynamic separators in Korean urban catchments between 2006 - 2012. Removal rates were relatively low at all four sites (1. Roadway site: Avg. Inflow = 239.32 mg/L vs Avg. Outflow = 122.2- mg/L / 2. Residential site: Avg. Inflow = 59.74 mg/L vs Avg. Outflow = 50.35 mg/L / 3. Roadway Site: Avg. Inflow = 62.50 mg/L vs. Avg. Outflow = 33.76 mg/L / 4. Residential(63.5%) & Roadway (36.5%) CDA site: Avg. Inflow = 236.24 mg/L vs. Avg. Outflow = 160.54 mg/L). The low removal rates were due to high rates of extreme overflow events occurring with most suspended sediment being quite small/fine in nature (<75μm)(Lee, et al. 2014.

Total suspended solids

Toronto and Region Conservation Authority

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.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

Total phosphorus

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

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 total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

Systems designed to remove trash, debris and some amount of sediment, oil and grease from stormwater runoff based on the principles of sedimentation for the grit and phase separation for the oil.

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

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.

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.

A biological community, including humans and their natural environment.