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 permeable pavement 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

• International Stormwater BMP Database: 2020 Summary Statistics (Clary et al. 2020)
  • 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 CWQG 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 federal (Environment Canada, 2004) and provincial (OMOEE, 1994) levels for TP in stormwater ((Clary et al., 2020).

One of STEP's sites located in Mississauga, ON. (Lakeview Neighbourhood), where P.P was installed in residential driveways. Full submission and details to the BMP can be selected on the map viewer and can be viewed here. (International Stormwater BM<P Database, 2021).

• (Xie, et al. 2019) - Permeable concrete pavements: A review of environmental benefits and durability.
  • This literature review paper looked at a multitude of studies highlighting the numerous benefits (hydraulic/water quality performance, heat-island mitigative effects, skid resistance ability and winter durability) associated with P.P and discussed some prominent papers' results. A project in Yakima, Washington (Yakima County website, 2012) compared effluent water samples collected in vaults adjacent to two pavement types (permeable and impermeable). The water samples collected from the P.P plot had significantly lower TSS values when compared to the control, impermeable plot's samples (25 mg/L vs. 320 mg/L). Whereas, Luck et al. (2008, 2009) found P.P to exhibit excellent mitigating characteristics for intensive, nearby agricultural practices (composted beef cattle manure) to help limit the amount of soluble phosphorus and total phosphorus in stormwater runoff (Xie, et al. 2019).

• (Ostrom and Davis, 2019) - Evaluation of an enhanced treatment media and permeable pavement base to remove stormwater nitrogen, phosphorus, and metals under simulated rainfall.
  • This article by Ostrom and Davis, 2019, out of the University of Maryland discusses a new treatment media that can be developed to improve dissolved pollutant removal and retention in permeable pavement practices. This structural media is called "High Permeability Media Mixture (HPMM)", and was designed as a base material for P.P practices that can retain phosphorus in stormwater that enters the practice. The results of this study showed that effluent total dissolved phosphorus (TDP) levels was lower than influent for all samples (12 storms). Removal efficiency was between 48 - 98% effective with a median effluent level of 0.045 - 0.05 mg/L (dependent upon the 3 configurations used) in comparison to TDP event mean concentrations of 0.22 mg/L (Ostrom and Davis, 2019.

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

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.

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.

Sustainable Technologies Evaluation Program

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 biological community, including humans and their natural environment.

Low impact development is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, small scale hydrologic controls to more closely mimic pre-development hydrologic functions.

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.

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.

The technique of removing pollutants from runoff as it infiltrates through the soil.