OGS: Performance

TSS Reduction

Inlet

The performance results for OGS practices, located within TRCA's watershed originate from three primary sites:

• Woodside SmartCentre (Markham)
• North Queen Street & The Queensway (Etobicoke)

The mean performance value recorded at the inlet for OGS practices' ability to remove Total Suspended Sediments (TSS) was was calculated based on 46 separate recordings between 1997 - 1998 amongst the two sites previously mentioned.

As can be seen in the corresponding boxplot the mean performance removal efficiency of the OGS 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 46 samples taken was 109.50 mg/L whereas the mean was 145.07 mg/L, with a 96% guideline exceedance.

Outlet

The performance results for OGS practices, located within TRCA's watershed originate from three primary sites:

• Woodside SmartCentre (Markham)
• North Queen Street & The Queensway (Etobicoke)

The mean performance value recorded at the inlet for OGS practices' ability to remove Total Suspended Sediments (TSS) was was calculated based on 46 separate recordings between 1997 - 1998 amongst the two sites previously mentioned.

As can be seen in the corresponding boxplot the mean performance removal efficiency of the OGS 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 91 samples taken was 44.50 mg/L whereas the mean was 64.60 mg/L, with a 61% guideline exceedance. Given the age of of these practices and the dates monitoring took place, these systems will likely need major maintenance and/or rehabilitation if not full replacement, as they near the end of their working lifecycle, especially given forthcoming Ontario guidelines on removal efficiencies, set to release later in 2023 (Low Impact Development Stormwater Management Guidance Manual). Read more about the performance efficiency of these specific OGS installations located within TRCA's watershed here, in the following document - Performance Assessment of Two Types of Oil & Grit Separator for SWM in Parking Lots (SWAMP, 2004).

Refer to the Oil and Grit Separator page for more information related to updated requirements through laboratory testing in accordance with the Procedure for Laboratory Testing of Oil-Grit Separators PDF (TRCA/CETV Program) testing protocol and will have current and valid ISO14034: Environmental Technology Verification (ETV) program.

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.

• (Greenway, 2001) - Stormwater Treatment Demonstration Project - Oil water/grit separator followed by a sand filter.
  • This project took place for Harding Township in New Jersey back in 2001. The performance assessment showcased the ability of a Vortechnics Oil/Grit separator followed by a sand filter's removal ability over three years located at a rest stop off a nearby highway. A full storm analysis was conducted over the three-year project and found that the average TSS (mg/L) entering the Oil/Grit separator was 492 mg/L whereas the outlet of the separator had only 35.18 mg/L of TSS remaining (a ~93% reduction rate). Once water passed through the sand filter after the OGS, the removal efficiency increased to 98.12%, with only 9.28 mg/L of TSS remaining (Greenway, 2001).

• (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

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.

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.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

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.

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.

A biological community, including humans and their natural environment.