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==Cooling Trenches==
==Cooling Trenches==
Cooling trenches typically consist of one or more geotextile wrapped perforated pipes embedded in a clear stone filled trench that is buried underground. Water temperatures are reduced through heat transfer from the water passing through the trench to the stone and surrounding soils. Cooling trenches may be installed downstream of the primary pond outlet or draw from a secondary orifice controlled outlet draining water from the pond at or below the permanent pool water level (e.g Van Seters and Graham, 2013<ref> Van Seters, T., Graham, C. 2013. Evaluation of an Innovative Technique for Augmenting Stream Baseflows and Mitigating the Thermal Impacts of Stormwater Ponds. Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority, Toronto, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/08/Cooling-trench-final-2013a.pdf</ref>.; TRCA, 2020<ref>Toronto and Region Conservation Authority (TRCA) 2020. Evaluation of a Thermal Mitigation System on the Heritage at Victoria Square Pond in Markham. Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2021/01/TM-Heritage-report-2021R.pdf</ref>). Further information about these innovative cooling trench features installed as part of the stormwater pond
Cooling trenches typically consist of one or more geotextile wrapped perforated pipes embedded in a clear stone filled trench that is buried underground. Water temperatures are reduced through heat transfer from the water passing through the trench to the stone and surrounding soils. Cooling trenches may be installed downstream of the primary pond outlet or draw from a secondary orifice controlled outlet draining water from the pond at or below the permanent pool water level (e.g Van Seters and Graham, 2013<ref> Van Seters, T., Graham, C. 2013. Evaluation of an Innovative Technique for Augmenting Stream Baseflows and Mitigating the Thermal Impacts of Stormwater Ponds. Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority, Toronto, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/08/Cooling-trench-final-2013a.pdf</ref>.; TRCA, 2020<ref>Toronto and Region Conservation Authority (TRCA) 2020. Evaluation of a Thermal Mitigation System on the Heritage at Victoria Square Pond in Markham. Toronto and Region Conservation Authority, Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2021/01/TM-Heritage-report-2021R.pdf</ref>). Further information about these innovative cooling trench features installed as part of the stormwater pond
operation design in two sites located in Markham, ON. visit the [https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/thermal-mitigation/thermal-mitigation-system-evaluation/ STEP project page]. The permanent pool of stormwater management ponds acts as a heat sink during the summer, resulting in warmer summer discharges during both storm and baseflow conditions.
operation design in two sites located in Markham, ON. visit the [https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/thermal-mitigation/thermal-mitigation-system-evaluation/ STEP project page]. The permanent pool of stormwater management ponds acts as a heat sink during the summer, resulting in warmer summer discharges during both storm and baseflow conditions.
*Performance of primary outlet cooling trenches is highly variable due to differences in cooling trench sizing, design, initial water temperature and degree of groundwater interaction
*Performance of primary outlet cooling trenches is highly variable due to differences in cooling trench sizing, design, initial water temperature and degree of groundwater interaction
*Based on case studies reviewed, primary outlet trenches without groundwater interaction may provide summer temperature cooling of the warmest flows by roughly 1 to 3⁰C if the trench storage volume is equal to or greater than 5% of the runoff volume discharged from the pond during the 25 mm event.
*Based on case studies reviewed, primary outlet trenches without groundwater interaction may provide summer temperature cooling of the warmest flows by roughly 1 to 3⁰C if the trench storage volume is equal to or greater than 5% of the runoff volume discharged from the pond during the 25 mm event.
==Infiltration Systems==
Infiltration systems may be used as an alternative to cooling trenches for mitigating the thermal effects of pond outflows in areas not constrained by water tables and space. As with cooling trenches, these may be installed on the main pond outlet or a secondary outlet. Since water tables at the pond outlet are often high, large void chambers may be more suitable than trenches as they provide greater storage per unit depth.
The volumes infiltrated may also be used to meet site water balance requirements. Proponents will need to consult with local approval agencies to determine whether the typical 1 meter separation depth to groundwater may be waived given that the infiltrated water has been treated through the pond.
Analysis of temperature and thermal load data from three monitored ponds showed that the bottom area of the infiltration area would need to be up to 7% that of the pond area depending on the infiltration capacity of the native soils. These areas could be reduced by 40% if the outlet draws water from 0.25 m below the surface, and further reduced for deeper outlets (Van Seters and Dougherty, 2019).<ref>Van Seters, T., Graham, C., Dougherty, J., Jacob-Okor, C., and David, Y. 2019. Data Synthesis and Design Considerations for Stormwater Thermal Mitigation Measures. Sustainable Technologies Evaluation Program. Ontario. https://sustainabletechnologies.ca/app/uploads/2019/04/Thermal-Synthesis-Final.pdf</ref>]].
{| class="wikitable" style="width: 1000px;"
|+'''Native Soil Infiltration Rate'''
|-
!<br>'''Pond A'''
!<br>'''Pond B''<br>
!<br>'''Pond C'''<br>
|-
|rowspan="6"|'''Site Preparation''' - after site clearing and grading, prior to BMP excavation and grading
|Natural heritage system and tree protection areas remain fenced off
|
|-
|ESCs protecting BMP layout area are installed properly
|
|-
|CDA is stabilized or runoff is diverted around BMP layout area
|
|-
|BMP layout area has been cleared and is staked/delineated
|
|-
|Benchmark elevation(s) are established nearby
|
|-
|Construction materials have been confirmed to meet design specifications
|
|-
|rowspan="4"|'''BMP Excavation and Grading''' - prior to installation of pipes/sewers and backfilling
|Excavation location, footprint, depth and slopes are acceptable
|
|-
|Excavated soil is stockpiled outside the CDA
|
|-
|Embankments/berms (elevations, slopes, compaction) are acceptable
|
|-
|Excavation bottom and sides roughened to reduce smearing and compaction
|
|-
|rowspan="4"|'''BMP Installation''' – after installation of pipes/sewers, prior to backfilling
|Structural components (e.g., foundation, walls) installed according to plans, if applicable
|
|-
|Impermeable liner installed correctly, if applicable
|
|-
|Installations of sub-drain pipes (e.g., locations, elevations, slopes), standpipes/monitoring wells are acceptable
|
|-
|Sub-drain trench dams installed correctly (location, elevation)
|
|-
|rowspan="4"|'''Landscaping''' – after final grading, prior to planting
|Filter bed depth and surface elevations at inlets are acceptable
|
|-
|Maximum surface ponding depth is acceptable
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|-
|Filter bed is free of ruts, local depressions and not overly compacted
|
|-
|Planting material meets approved planting plan specifications (plant types and quantities)
|-
|colspan="3" style="text-align: center;" |'''<u><span title=>Note:''' for Observation Column: S = Satisfactory; U = Unsatisfactory; NA = Not Applicable*</span></u>
|-
|}
==References==
==References==