Rainwater Harvesting: Performance

TSS Reduction

The performance results for Rainwater harvesting practices, located within TRCA's watershed originate from fours sites:

• Minto Hotel (Toronto)
• Metro Label 1 (Scarborough)
• Metro Label 2 (Scarborough)
• Brookside P.S (Scarborough)

The mean performance value recorded at each of the rainwater cistern practices, was to measure their ability to remove Total Suspended Sediments (TSS), which was calculated based on 24 separate recordings from 2007-2010 at each of the aforementioned locations listed above.

As can be seen in the corresponding boxplot the mean performance removal efficiency of the rainwater cistern 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 24 samples taken was 1.25 mg/L whereas the mean was 3.98 mg/L, with a 4% guideline exceedance.

Phosphorus Reduction

The performance results for Rainwater harvesting practices, located within TRCA's watershed originate from fours sites:

• Minto Hotel (Toronto)
• Metro Label 1 (Scarborough)
• Metro Label 2 (Scarborough)
• Brookside P.S (Scarborough)

The mean performance value recorded at each of the rainwater cistern practices, was to measure their ability to remove Total Phosphorus (TP), which was calculated based on 24 separate recordings from 2007-2010 at each of the aforementioned locations listed above.

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

The median value of the 24 samples taken was 0.05 mg/L whereas the mean was 0.11 mg/L, with a 100% guideline exceedance. Given the small sample size of just 24 grab samples further monitoring projects will be required to ensure that the results collected are as accurate as possible to ensure these practices can meet federal and provincial governments' guideline requirements for TP 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

• (Jeon et al., 2022) - Long-Term Monitoring of an Urban Stormwater Infiltration Trench in South Korea
  • This paper discusses a long-term monitoring program (8 years) to measure the performance of an infiltration trench and develop a model to be used to estimate influent and effluent stormwater quality based on average removal efficiencies. The study found that the specific trench configuration used (with a primary settling tank with a vertical layer of woodchips, along with horizontal layers of gravel, sand and bottom ash (see associated image to the right on this page). Over the 8-year study (2013 - 2022, in 2017 no monitoring took place due to construction) was able to remove an average of 83% of TSS and 79% of TP (39.31 mg/L & 0.17 mg/L respectively for effluent water quality) (Jeon et al., 2022).

Schematic drawing of the infiltration trench design configuration used by (Jeon et al. 2022) at Kongju National University Cheonan Campus in South Korea. The facility includes a primary settling tank with vertical layer of woodchips, and horizontal layers of gravel, sand and bottom ash. This configuration promotes settling, filtration and adsorption. The use of woodchips allows microorganisms that assist in the removal of nitrogen and phosphorus to create an ideal environment to establish themselves and help improve overall water quality.(Jeon et al., 2022).

Total suspended solids

Toronto and Region Conservation Authority

Tank used to store rainwater (typically roof runoff) for later use.

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.

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.

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

The attachment of gas, vapour or dissolved matter onto the surface of solid materials.

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.