Difference between revisions of "Exfiltration: Performance"

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Performance results from a limited number of field studies indicate that subsurface stormwater infiltration practices are effective BMPs for pollutant removal <ref>Toronto and Region Conservation (TRCA). 2009. Review of the Science and Practice of Stormwater Infiltration in Cold Climates. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario.</ref>. These types of practices provide effective removal for many pollutants as a result of sedimentation, filtering, and soil adsorption. It is also important to note that there is a relationship between the water balance and water quality functions. If an infiltration practice infiltrates and evaporates 100% of the runoff from a site, then there is essentially no pollution leaving the site in surface runoff. Furthermore, treatment of infiltrated runoff continues to occur as it leaves the facility and moves through the native soil. The performance of perforated pipe systems would be expected to reduce pollutants in runoff in a manner similar to infiltration trenches.
Performance results from a limited number of field studies indicate that subsurface stormwater infiltration practices are effective BMPs for pollutant removal <ref>Toronto and Region Conservation (TRCA). 2009. Review of the Science and Practice of Stormwater Infiltration in Cold Climates. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario.</ref>. These types of practices provide effective removal for many pollutants as a result of sedimentation, filtering, and soil adsorption. It is also important to note that there is a relationship between the water balance and water quality functions. If an infiltration practice infiltrates and evaporates 100% of the runoff from a site, then there is essentially no pollution leaving the site in surface runoff. Furthermore, treatment of infiltrated runoff continues to occur as it leaves the facility and moves through the native soil. The performance of perforated pipe systems would be expected to reduce pollutants in runoff in a manner similar to infiltration trenches.


Several studies of exfiltration systems in Ontario have examined their water quality benefits. Seasonal contaminant load reductions in the order of 80% were observed for most constituents, with the exception of chloride, in the study of the system installed in a low density residential neighbourhood in Etobicoke <ref>Stormwater Assessment Monitoring and Performance (SWAMP) Program. 2002. Performance Assessment of a Swale/Perforated Pipe Stormwater Infiltration System – Toronto, Ontario. Toronto and Region Conservation Authority, Toronto, Ontario.</ref><ref>Stormwater Assessment Monitoring and Performance (SWAMP) Program. 2005.
Several studies of exfiltration systems in Ontario have examined their water quality benefits. Seasonal contaminant load reductions in the order of 80% were observed for most constituents, with the exception of chloride, in the study of the system installed in a low density residential neighbourhood in Etobicoke <ref name=SWAMP2002>Stormwater Assessment Monitoring and Performance (SWAMP) Program. 2002. Performance Assessment of a Swale/Perforated Pipe Stormwater Infiltration System – Toronto, Ontario. Toronto and Region Conservation Authority, Toronto, Ontario.</ref><ref name=SWAMP/>. Perforated pipe systems that incorporate grassed [[swales]] as [[pretreatment]] have been observed to reduce loads of suspended sediment, [[phosphorus]], [[nitrogen]], copper, lead and zinc in runoff flowing from the system between 75 to 90% in comparison to a similar catchment with conventional catchbasins and storm sewers <ref>J.F. Sabourin and Associates Incorporated. 1999. Research Project for the Updated
Synthesis of Monitoring Studies Conducted Under the Stormwater Assessment
Investigation of the Performance Evaluation of Grass Swales and Perforated Pipe
Monitoring and Performance Program.. Toronto and Region Conservation Authority,
Drainage Systems. Executive Summary. Prepared for the Infrastructure Management
Toronto, Ontario.</ref>. Perforated pipe systems that incorporate grassed [[swales]] as [[pretreatment]] have been observed to reduce loads of suspended sediment, [[phosphorus]], [[nitrogen]], copper, lead and zinc in runoff flowing from the system between 75 to 90% in comparison to a similar catchment with conventional catchbasins and storm sewers (J.F. Sabourin and Associates, 1999; and 2008a). The Nepean systems were shown to release significantly less pollutants than the conventional sewer system, even after 20 years of operation (J.F. Sabourin and Associates, 2008a).
Division of the City of Ottawa. Ottawa, Ontario.</ref>. The Nepean systems were shown to release significantly less pollutants than the conventional sewer system, even after 20 years of operation<ref name=Sabourin/>.
 


{| class="wikitable sortable"
|+Pollutant removal efficiencies of exfiltration systems
|-
!Practice
!Location
!Lead %
!Copper %
!Zinc %
![[Total suspended solids]] (TSS) %
!Total [[Phosphorus]] %
!Total [[Nitrogen]] (TKN) %
|-
|Soakaway||Valence, France<ref>Barraud, S., Gautier, A., Bardin, J.P., Riou, V. 1999. The Impact of Intentional Stormwater Infiltration on Soil and Groundwater. Water Science and Technology. Vol.
39. No. 2. pp. 185-192.</ref>||98||-||54 - 88||-||-||-
|-
|[[Infiltration trench]]||Various<ref>ASCE
(2000)Pollutant removal efficiencies are reported as ranges because they are based on a synthesis of several performance monitoring studies that were available as of 2000.</ref>||70 - 90||70 - 90||70 - 90||70 - 90||50 - 70||40 - 70
|-
|Grass swale/perforated pipe||North York, ON<ref name=SWAMP2002/>||75||96||93||24||84||84
|-
|Grass swale/perforated pipe||Nepean, ON<ref name=Sabourin/>||- 99||66||0||81||81||72
|-
|Grass swale/perforated pipe||Nepean, ON<ref name=Sabourin/>||> 99||> 99||90||96||93||93
|}


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[[category: performance]]

Latest revision as of 17:28, 23 July 2020

Ability of exfiltration systems to meet SWM objectives
Water balance benefit Water quality improvement Erosion control benefit
Yes Yes Partial: depending on soil infiltration rate

Water balance[edit]

The degree to which water balance objectives are met will depend on the underlying native soil type on which the system is located. Several Ontario studies have assess the performance of exfiltration systems in cold climates.

Volumetric runoff reduction achieved by exfiltration systems
Practice Location Underlying soil type Runoff reduction
Grass swale/perforated pipe Nepean, ON[1] Silty till 73 %
Grass swale/perforated pipe Nepean, ON[1] Sandy silty till 86 %
Perforated pipe Etobicoke, ON[2] Clay/clayey silty till over silty sand 95 %
Perforated pipe North york, ON[2] Silty sand 89 %

Runoff reduction estimate = 85 % on HSG A and B soils.
Runoff reduction estimate = 45 % on HSG C and D soils.

Pollutant removal capacity[edit]

Performance results from a limited number of field studies indicate that subsurface stormwater infiltration practices are effective BMPs for pollutant removal [3]. These types of practices provide effective removal for many pollutants as a result of sedimentation, filtering, and soil adsorption. It is also important to note that there is a relationship between the water balance and water quality functions. If an infiltration practice infiltrates and evaporates 100% of the runoff from a site, then there is essentially no pollution leaving the site in surface runoff. Furthermore, treatment of infiltrated runoff continues to occur as it leaves the facility and moves through the native soil. The performance of perforated pipe systems would be expected to reduce pollutants in runoff in a manner similar to infiltration trenches.

Several studies of exfiltration systems in Ontario have examined their water quality benefits. Seasonal contaminant load reductions in the order of 80% were observed for most constituents, with the exception of chloride, in the study of the system installed in a low density residential neighbourhood in Etobicoke [4][2]. Perforated pipe systems that incorporate grassed swales as pretreatment have been observed to reduce loads of suspended sediment, phosphorus, nitrogen, copper, lead and zinc in runoff flowing from the system between 75 to 90% in comparison to a similar catchment with conventional catchbasins and storm sewers [5]. The Nepean systems were shown to release significantly less pollutants than the conventional sewer system, even after 20 years of operation[1].

Pollutant removal efficiencies of exfiltration systems
Practice Location Lead % Copper % Zinc % Total suspended solids (TSS) % Total Phosphorus % Total Nitrogen (TKN) %
Soakaway Valence, France[6] 98 - 54 - 88 - - -
Infiltration trench Various[7] 70 - 90 70 - 90 70 - 90 70 - 90 50 - 70 40 - 70
Grass swale/perforated pipe North York, ON[4] 75 96 93 24 84 84
Grass swale/perforated pipe Nepean, ON[1] - 99 66 0 81 81 72
Grass swale/perforated pipe Nepean, ON[1] > 99 > 99 90 96 93 93
  1. ↑ 1.0 1.1 1.2 1.3 1.4 J.F. Sabourin and Associates Incorporated. 2008a. 20 Year Performance Evaluation of Grassed Swale and Perforated Pipe Drainage Systems. Project No. 524(02). Prepared for the Infrastructure Management Division of the City of Ottawa. Ottawa, Ontario.
  2. ↑ 2.0 2.1 2.2 Stormwater Assessment Monitoring and Performance (SWAMP) Program. 2005. Synthesis of Monitoring Studies Conducted Under the Stormwater Assessment Monitoring and Performance Program.. Toronto and Region Conservation Authority, Toronto, Ontario.
  3. ↑ Toronto and Region Conservation (TRCA). 2009. Review of the Science and Practice of Stormwater Infiltration in Cold Climates. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario.
  4. ↑ 4.0 4.1 Stormwater Assessment Monitoring and Performance (SWAMP) Program. 2002. Performance Assessment of a Swale/Perforated Pipe Stormwater Infiltration System – Toronto, Ontario. Toronto and Region Conservation Authority, Toronto, Ontario.
  5. ↑ J.F. Sabourin and Associates Incorporated. 1999. Research Project for the Updated Investigation of the Performance Evaluation of Grass Swales and Perforated Pipe Drainage Systems. Executive Summary. Prepared for the Infrastructure Management Division of the City of Ottawa. Ottawa, Ontario.
  6. ↑ Barraud, S., Gautier, A., Bardin, J.P., Riou, V. 1999. The Impact of Intentional Stormwater Infiltration on Soil and Groundwater. Water Science and Technology. Vol. 39. No. 2. pp. 185-192.
  7. ↑ ASCE (2000)Pollutant removal efficiencies are reported as ranges because they are based on a synthesis of several performance monitoring studies that were available as of 2000.

The downward movement of water through the soil, the downward flow of runoff from the bottom of an infiltration BMP into the soil.

Loss of water from a drainage system as a result of percolation or absorption into the surrounding medium (e.g., the infiltration of water into the native soil through a perforated pipe wall as it is conveyed).

Stormwater Management

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

Includes the protection of soil from dislocation by water, wind or other agents.

The rate at which stormwater percolates into the subsoil measured in inches per hour.

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

The natural ground material characteristic of or existing by virtue of geographic origin.

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.

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 shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.

1. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter. 2. A soil texture class. 3. (Engineering) A fine-grained soil (more than 50 percent passing the No. 200 Sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System).

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.

Deposition of material of varying size, both mineral and organic away from its site of origin by the action of water, wind, gravity or ice.

Settling-out or deposition of particulate matter suspended in runoff.

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

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 land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

Total suspended solids

An underground water storage reservoir into which stormwater is directed and allowed to percolate into the underlying native subsoil.

An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Toronto and Region Conservation Authority

Sustainable Technologies Evaluation Program

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

The water below the surface, and typically below the groundwater table.

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