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Inspection and Maintenance: Permeable Pavement (view source)
Revision as of 15:09, 11 August 2022
, 2 years ago→Inspection Time Commitments and Costs
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[[File:MaintenancePICP.png|thumb|400px|A Vacuum Truck used for [[permeable pavement]] maintenance, which sucks up excess sediment and fines trapped between the pores of block pavers. Conducting this maintenance regularly helps maintain the practice's optimal infiltration rate during large rain events. (Source: STEP).]]
Technician conducting sediment removal to ensure infiltration rates for the<br>
practice are able to maintain > 25 mm/h. [https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf Photo Source: TRCA, 2018]<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices - Bioretention. Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf</ref>
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==Overview==
==Overview==
[[Permeable pavements|Permeable Pavement]] Permeable pavements contain many small openings (i.e., joints or pores) that allow rainfall and snowmelt (i.e., stormwater) to drain through them instead of running off the surface as it does on impervious pavements like conventional asphalt and concrete. An overflow outlet is needed to safely convey flows during flood events. Depending on the permeability of the underlying soil and other constraints, the pavement may be designed with no sub-drain for full infiltration, with a sub-drain for partial infiltration, or with an impermeable liner and sub-drain for a no infiltration practice. The sub-drain pipe may feature a flow restrictor (e.g., orifice cap or valve) for gradually releasing detained water and optimizing the amount drained by [[infiltration]] into the underlying soil. <br>
[[Permeable pavements|Permeable Pavement]] Permeable pavements contain many small openings (i.e., joints or pores) that allow rainfall and snowmelt (i.e., stormwater) to drain through them instead of running off the surface as it does on impervious pavements like conventional asphalt and concrete. An overflow outlet is needed to safely convey flows during flood events. Depending on the permeability of the underlying soil and other constraints, the pavement may be designed with no sub-drain for full infiltration, with a sub-drain for partial infiltration, or with an impermeable liner and sub-drain for a no infiltration practice. The sub-drain pipe may feature a flow restrictor (e.g., orifice cap or valve) for gradually releasing detained water and optimizing the amount drained by [[infiltration]] into the underlying soil.
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[[File:P.p plan and profile view.PNG|thumb|400px|General plan and profile (cross-section) views showcasing key components and sections of a Permeable Interlocking Concerte Pavement (PICP).]]
{{textbox|Key components of [[Permeable pavements]] to pay close attention to are the:
{{textbox|Key components of [[Permeable pavements]] to pay close attention to are the:
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==Construction Inspection Tasks==
==Construction Inspection Tasks==
Construction inspections take place during several points in the construction sequence, specific to the type of LID BMP, but at a minimum should be done '''weekly''' and include the following:
Construction inspections take place during several points in the construction sequence, specific to the type of LID BMP, but at a minimum should be done '''weekly''' and include the following:
# During site preparation, prior to BMP excavation and grading to ensure the CDA is stabilized and/or flow diversion devices are in place and confirm that construction materials meet design specifications
# During site preparation, prior to BMP excavation and grading to ensure the CDA is stabilized and/or flow diversion devices are in place and confirm that construction materials meet design specifications
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# Prior to hand-off points in the construction sequence when the contractor responsible for the work changes (i.e., hand-offs between the storm sewer servicing, paving, building and landscaping contractors)
# Prior to hand-off points in the construction sequence when the contractor responsible for the work changes (i.e., hand-offs between the storm sewer servicing, paving, building and landscaping contractors)
# After every large storm event (e.g., 15 mm rainfall depth or greater) to ensure flow diversion devices are functioning and adequately maintained. View the table below, which describes critical points during the construction sequence when inspections should be performed prior to proceeding further. You can also download and print the table [https://wikidev.sustainabletechnologies.ca/images/9/9f/LID-IM-Guide-7.4-Permeable-Pavements.pdf '''here''']<br>
# After every large storm event (e.g., 15 mm rainfall depth or greater) to ensure flow diversion devices are functioning and adequately maintained. View the table below, which describes critical points during the construction sequence when inspections should be performed prior to proceeding further. You can also download and print the table [https://wikidev.sustainabletechnologies.ca/images/9/9f/LID-IM-Guide-7.4-Permeable-Pavements.pdf '''here''']<br>
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[[File:MaintenancePICP.png|thumb|400px|A Vacuum Truck used for [[permeable pavement]] maintenance, which sucks up excess sediment and fines trapped between the pores of block pavers. Conducting this maintenance regularly helps maintain the practice's optimal infiltration rate during large rain events. (Source: STEP).]]
{| class="wikitable" style="width: 1000px;"
{| class="wikitable" style="width: 800px;"
|+'''Bioretention/Swales: Construction Inspections'''
|+'''Permeable Pavements: Construction Inspections'''
|-
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!<br>'''Construction Sequence Step & Timing'''
!<br>'''Construction Sequence Step & Timing'''
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==Rehabilitation & Repair==
==Rehabilitation & Repair==
Table below provides guidance on rehabilitation and repair work specific to bioretention and dry swales organized according to BMP component.
Table below provides guidance on rehabilitation and repair work specific to permeable pavements organized according to BMP component.
{|{| class="wikitable" style="width: 1000px;"
[[File:Lifting paver to clean.JPG|thumb|340px|Removing a section of pavers (where infiltration has decreased markedly, or all pavers (if necessary) should occur if surface drainage performance remains unacceptable. Joint fill and bedding layer will need be replaced at this point with new materials to help obtain initial design specifications (Photo Source: Western Interlock Inc., 2020)<ref>Western Interlock Inc. 2020.How to Remove Pavers and Replace Them. Repair & Maintenance. Authored June 2020. Accessed: 21 July 2022. https://westerninterlock.com/how-to-remove-and-replace-a-paver/</ref>]]
{|{| class="wikitable" style="width: 900px;"
|+'''Permeable Pavements: Key Components, Typical Issues and Rehabilitation Requirements'''
|+'''Permeable Pavements: Key Components, Typical Issues and Rehabilitation Requirements'''
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[[File:Sediment removal.PNG|500px]]
==Inspection Time Commitments and Costs==
Estimates are based on a typical partial infiltration permeable pavement design (i.e., includes a sub-drain); estimates for other designs (i.e., full infiltration and no-infiltration) are described in
the [https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-7.4-Permeable-Pavements.pdf Low Impact Development (LID) Stormwater Management Practice Inspection and Maintenance Guide]<br>
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[[File:Task cost estimates p.p.JPG|thumb|left|400px|Per-task cost estimates for maintenance and rehabilitation of a partial infiltration permeable pavement LID feature (in 2016 $ figures).<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices. Permeable Pavements - Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Permeable-Pavement-Fact-Sheet.pdf</ref>]]
[[File:Maintenance & operation p.p.JPG|thumb|400px|General time commitments and costs for inspection of permeable pavement features with partial infiltration design (in 2016 $ figures).<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices. Permeable Pavements - Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Permeable-Pavement-Fact-Sheet.pdf</ref>]]
[[File:Life cycle estimate p.p.JPG|thumb|center|400px|Construction and life cycle cost estimates for permeable pavement features with partial infiltration design (in 2016 $ figures).<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices. Permeable Pavements- Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Permeable-Pavement-Fact-Sheet.pdf</ref>]]<br>
Estimates of the life cycle costs of inspection and maintenance have been produced using the latest version of the [[Cost analysis resources|LID Life Cycle Costing Tool]] for three design variations (full infiltration, partial infiltration and no infiltration) to assist stormwater infrastructure planners, designers and asset managers with planning and preparing budgets for potential LID features.
Assumptions for the above costs and the following table below are based on the following:
*Design variations for permeable pavements can be broken down into three main categories:
**Full Infiltration design, where the pavement drains through infiltration into the underlying subsoil alone (i.e., no sub-drain);
**Partial Infiltration design, where drainage is through the combination of a subdrain and infiltration into the underlying subsoil (i.e., with a sub-drain); or,
**No Infiltration (i.e., filtration only design) that includes an impermeable liner between the base of the BMP and the underlying native sub-soil, where drainage is through a sub-drain alone (i.e., with a sub-drain and impermeable liner).
*For permeable pavements it is assumed that rehabilitation of the pavement surface will be needed once the BMP reaches 30 years of age in order to maintain surface drainage performance at an acceptable level. Included in the rehabilitation costs are (de)mobilization costs, as equipment would not have been present on site.
*Design costs were not included in the rehabilitation as it was assumed that the original LID practice design would be used to inform this work. The annual average maintenance cost does not include rehabilitation costs and therefore represents an average of routine maintenance tasks, as outlined in Table Permeable Pavements: Key Components, Descriptions and Routine I&M Requirements, above. All cost value estimates represent the NPV as the calculation takes into account average annual interest (2%) and discount (3%) rates over the evaluation time periods.
*The costing presented in this section is specific to permeable interlocking concrete pavers (PICP), as defined in the Tool. This product has been selected for costing due to its popularity and well understood maintenance needs.
*For all permeable pavement design variations, the CDA has been defined as 2,000 m<sup>2</sup> of which 1,000 m<sup>2</sup> is impermeable pavement draining to the pavers, and 1,000 m<sup>2</sup> is permeable pavement. The impervious area to pervious area ratio (I:P ratio) used to size the BMP footprint is 1:1, which is in accordance with recommendations in the [https://sustainabletechnologies.ca/app/uploads/2013/01/LID-SWM-Guide-v1.0_2010_1_no-appendices.pdf LID SWM Planning and Design Guide (CVC & TRCA, 2010)].
**The Full Infiltration design does not include a sub-drain and assumes a native sub-soil infiltration rate of 20 mm/h. The base granular reservoir is 350 mm deep and is capable of storing runoff from a 61 mm rain event over the CDA. A monitoring well is included for inspection purposes.
**The Partial Infiltration design includes a sub-drain and assumes a native sub-soil infiltration rate of 10 mm/h. The base granular reservoir is 350 mm deep and is capable of storing runoff from a 9 mm rain event before the stored volume reaches the perforated underdrain pipe located 50 mm above the native sub-soil. Although a flow restrictor is recommended to maximize infiltration, the cost of this feature is not included due to its relatively low cost.
**The No Infiltration design includes a sub-drain pipe installed on the bottom of the sub-surface water storage reservoir and an impermeable liner. All other features are the same as the Partial Infiltration design variation.
*Estimates of the life cycle costs of PICP permeable pavements in Canadian dollars per unit CDA ($/m<sup>2</sup>) are presented in the table below. [[Cost analysis resources|LID Life Cycle Costing Tool]] allows users to select what BMP type and design variation applies, and to use the default assumptions to generate planning level cost estimates.
**Users can also input their own values relating to a site or area, design, unit costs, and inspection and maintenance task frequencies to generate customized cost estimates, specific to a certain project, context or stormwater infrastructure program.
**For all BMP design variations and maintenance scenarios, it is assumed that rehabilitation of the pavement surface will be necessary when the BMP reaches 30 years of age to maintain acceptable surface drainage performance. Rehabilitation of PICP pavements is assumed to typically involve the following tasks and associated costs:
***Remove pavers, bedding and joint fill and top 5 cm (2”) of base aggregate and replace with new material that meets design specifications
***Construction and Assumption inspection and testing associated with rehabilitation work to confirm that materials meet design specifications and installation is acceptable, including compaction and surface infiltration rate testing. <br>
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[[File:Minimum & hig hfreq cost p.p.PNG|thumb|center|900px|Life cycle cost estimates for all infiltration types of PICP [[permeable pavements]] an under minimum and high frequency scenarios (in 2016 $ figures).<ref>TRCA. 2016. Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide. Prepared by the Sustainable Technologies Evaluation Program. Vaughan, Ontario. https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-7.4-Permeable-Pavements.pdf</ref>]]
'''Notes:'''
<small>
#Estimated life cycle costs represent NPV of associated costs in Canadian dollars per square metre of CDA ($/m2).
#Average annual maintenance cost estimates represent NPV of all costs incurred over the time period and do not include rehabilitation costs.
#Rehabilitation cost estimates represent NPV of all costs related to rehabilitative maintenance work assumed to be needed after 30 years in service, including those associated with inspection.
#Full Infiltration design life cycle costs are lower than Partial and No Infiltration designs due to the absence of a sub-drain to construct, inspect and routinely flush.
#Rehabilitation costs for Full Infiltration designs are estimated to be 54.8% to 55.6% of the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.
#Rehabilitation costs for Partial Infiltration designs are estimated to be 53.5% to 54.3% of the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.
#Rehabilitation costs for No Infiltration designs are estimated to be 47.4% to 48.1% of the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.
#Maintenance and rehabilitation costs over a 25 year time period for the Minimum Recommended maintenance scenario are estimated to be 22.3%, of the original construction costs for Full Infiltration design, 22.6% for Partial Infiltration design, and 20.0% for No Infiltration design.
#Maintenance and rehabilitation costs over a 25 year time period for the High Frequency maintenance scenario are estimated to be: 39.0% of the original construction costs for Full, 38.9% for Partial Infiltration designs, and 34.5% for No Infiltration designs.
#Maintenance and rehabilitation costs over a 50 year time period for the Minimum Recommended Frequency maintenance scenario are estimated to be approximately: 1.07 times the original construction cost for Full, 1.06 times the original construction costs for Partial Infiltration designs, and 93.9.% the original construction cost for No Infiltration designs.
#Maintenance and rehabilitation costs over a 50 year time period for the High Frequency maintenance scenario are estimated to be approximately: 1.43 times the original construction cost for Full, 1.41 times the original construction costs for Partial Infiltration designs, and 1.25 times the original construction cost for No Infiltration designs.
</small>
==Inspection Field Data Sheet==
Feel free to '''download''' (downward facing arrow on the top righthand side) and '''print''' (Pinter emoticon on top right hand side) the following [[Permeable pavements]] Inspection Field Data Form developed by TRCA, STEP and its partners for the [https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-2016-1.pdf Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide]<ref>STEP. 2016. Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide. https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-2016-1.pdf</ref>.
The 4 page document prompts users to fill out details previously mentioned above on this page in other sections about various zones associated with [[[Permeable pavements]] features (i.e. CDA, pavement surface, associated control structures, outlets, etc.) and describe why each area is a pass or fail, and if remediate action is required and under what timeframe it would be completed by. Furthermore, the forms prompt the reviewer to determine what type of inspection is being conducted for the feature in question: Construction (C), Routine Operation (RO), Maintenance Verification (MV), or Performance Verification (PV). <br>
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[[File:Single ring infilt p.p.PNG|thumb|340px|Surface infiltration testing conducted with a simple single-ring infiltrometer and a timer on the technician's mobile phone.]]
<pdf width="900" height="800">File:Permeable Pavements inspection sheet.pdf</pdf>
==References==