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−=== Overview ===+=== Types of Settling ===+=== Key Design Parameters ===+===table===+=== Particle Settling and Particle Size Distribution ===+=== Best Practices for Sedimentation-Based Stormwater Treatment ===+===table===
== Overview ==
Sedimentation is a fundamental process used in stormwater treatment to remove pollutants from runoff. It relies on gravity to deposit suspended sediment and debris into a designated settling area for later removal. Many pollutants that adhere to solids, such as metals, phosphorus, and hydrocarbons, are also removed through this process.
Sedimentation is a fundamental process used in stormwater treatment to remove pollutants from runoff. It relies on gravity to deposit suspended sediment and debris into a designated settling area for later removal. Many pollutants that adhere to solids, such as metals, phosphorus, and hydrocarbons, are also removed through this process.
Stormwater treatment practices that primarily use sedimentation include:
Stormwater treatment practices that primarily use sedimentation include:
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* Underground storage tanks and chambers
* Underground storage tanks and chambers
* [[Stormwater wetlands]]
* [[Stormwater wetlands]]
−* [[Oil grit separators (OGS)]]
+* [[Oil and grit separators (OGS)]]
−* [[Catch basins]] and pre-treatment sumps
+* Catch basins and [[pre-treatment]] sumps
* [[Vegetated swales]]
* [[Vegetated swales]]
−== Types of Settling ==
Sedimentation occurs in two main forms:
Sedimentation occurs in two main forms:
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Practices such as ponds and wetlands rely on quiescent settling, whereas systems like oil grit separators and catch basins rely more on dynamic settling. The effectiveness of sedimentation systems is largely governed by the surface loading rate (SLR), which is the rate at which water is introduced to the settling area. Higher SLRs generally result in lower pollutant removal efficiency.
Practices such as ponds and wetlands rely on quiescent settling, whereas systems like oil grit separators and catch basins rely more on dynamic settling. The effectiveness of sedimentation systems is largely governed by the surface loading rate (SLR), which is the rate at which water is introduced to the settling area. Higher SLRs generally result in lower pollutant removal efficiency.
−== Key Design Parameters ==
The performance of sedimentation systems depends on several factors:
The performance of sedimentation systems depends on several factors:
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'''Inlet and Outlet Design''' – Properly designed structures reduce resuspension and short-circuiting of flow.
'''Inlet and Outlet Design''' – Properly designed structures reduce resuspension and short-circuiting of flow.
−<br>
{| class="wikitable"
{| class="wikitable"
+|+Permanent pool storage, surface loading rates and detention times for sedimentation practices. Calculations are based on a one hectare drainage area with 85% imperviousness, peak flow rate for 4 hour Chicago distribution for 25 mm event and runoff coefficient of 0.81.<ref>References include: MOE, 2003; City of Toronto catch basin standard (T 705.010); OGS vendor technical manuals, TRCA OGS sizing review tool.</ref>
|-
|-
! Practice
! Practice
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| colspan="6" | '''Pre-treatment Practices (approx. 30-50% TSS removal)'''
| colspan="6" | '''Pre-treatment Practices (approx. 30-50% TSS removal)'''
|-
|-
−| Oil Grit Seperator
+| Oil Grit Separator
| 12
| 12
| 4.7
| 4.7
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| 5 catch basins (0.6 x 0.6m) per Hectare. Permanent pool depth of 0.9m.
| 5 catch basins (0.6 x 0.6m) per Hectare. Permanent pool depth of 0.9m.
|}
|}
+<br>
−== Particle Settling and Particle Size Distribution ==
Settling velocity is influenced by particle size, shape, specific gravity, and water temperature. Coarser particles settle faster, whereas fine silts and organic matter take longer. Temperature affects viscosity, meaning lower temperatures reduce settling efficiency. Understanding particle size distributions at a site is critical for designing effective sedimentation systems.
Settling velocity is influenced by particle size, shape, specific gravity, and water temperature. Coarser particles settle faster, whereas fine silts and organic matter take longer. Temperature affects viscosity, meaning lower temperatures reduce settling efficiency. Understanding particle size distributions at a site is critical for designing effective sedimentation systems.
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Research has shown wide variations in particle sizes in urban runoff, influenced by factors such as native soil texture, tree canopy cover, traffic levels, and road maintenance practices. While laboratory analyses help determine particle size, field studies provide more practical insights into sedimentation system performance.
Research has shown wide variations in particle sizes in urban runoff, influenced by factors such as native soil texture, tree canopy cover, traffic levels, and road maintenance practices. While laboratory analyses help determine particle size, field studies provide more practical insights into sedimentation system performance.
−== Best Practices for Sedimentation-Based Stormwater Treatment ==
'''Design for Adequate Surface Area''' – Systems should have sufficient area to slow down flow and enhance settling.
'''Design for Adequate Surface Area''' – Systems should have sufficient area to slow down flow and enhance settling.
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'''Account for Seasonal Variability''' – Adjust design parameters based on temperature effects on settling velocity.
'''Account for Seasonal Variability''' – Adjust design parameters based on temperature effects on settling velocity.
−{| class="wikitable"
{| class="wikitable"
+|+Comparison of particle size distributions from previous studies in cold climates
|-
|-
! Land use
! Land use
! Number of <br />observations
! Number of <br />observations
! Location
! Location
−! Sample<br />location
+! Sampling<br />location
−! Sample<br />method
+! Sampling<br />method
! Analytical<br />method
! Analytical<br />method
! d<sub>10</sub><br />/µm
! d<sub>10</sub><br />/µm
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| 5.9
| 5.9
| 44
| 44
−| SWAMP<ref>Once overheard on the subway</ref>
+| SWAMP<ref name="SWAMP">https://sustainabletechnologies.ca/app/uploads/2013/01/Final_SWAMP_Synthesis.pdf</ref>
|-
|-
| Parking<br />lot
| Parking<br />lot
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| 9.0
| 9.0
| 92
| 92
−| SWAMP
+| SWAMP<ref name="SWAMP"/>
|-
|-
| Commercial<br />parking lot
| Commercial<br />parking lot
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| 52.5
| 52.5
| 145
| 145
−|
+| <ref>Winston, R. J., & Witter, J. D. (2019). Evaluating the particle size distribution and gross solids contribution of stormwater runoff from Ohio’s roads (Final Report, State Job Number 135258). Ohio Department of Transportation, Office of Statewide Planning & Research.</ref>
|-
|-
| Mixed use
| Mixed use
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|
|
|}
|}
+
+==References==