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File:PorousAsphalt Stalls.png|thumb|500px|Porous Asphalt in parking stalls (Source: EOR).]]

[[File:PorousAsphalt Stalls.png|thumb|500px|Porous Asphalt in parking stalls (Source: EOR).]]

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==Overview==

==Overview==

[[Permeable pavement|Porous Asphalt]] is an alternative to traditional impervious pavements that allow stormwater to drain through them and into a storage reservoir below. Porous asphalt's performance and integrity is similar to that of other standard asphalt pavements. Similar to permeable pavers, porous asphalt has an underlying stone aggregate bed that provides drainage of incoming runoff and pluvial water. The benefit of porous asphalt in comparison to some other permeable pavements is that it doesn't require third party, proprietary components, nor specialized paving equipment for installation. <ref>Speight, J.G., 2016. Asphalt materials science and technology (pp. 437-474). Butterworth-Heinemann is. https://link.springer.com/article/10.1557/mrs.2016.267#article-info</ref>

[[Permeable pavement|Porous Asphalt]] is an alternative to traditional impervious pavements that allow stormwater to drain through them and into a storage reservoir below. Porous asphalt's performance and integrity is similar to that of other standard asphalt pavements. Porous asphalt contains air pockets, which are created during the development process of the paver due to the inclusion of less fines and [[sand]] content in comparison to traditional asphalt. The "air pcokets" or greater void spaces are what allow stormwater to infiltrate through the surface level to the underlying stone [[Reservoir aggregate|aggregate layer]] bed<ref>City of Toronto. 2017. Toronto Green Streets Technical Guidelines. Version 1.0. August, 2017. https://www.toronto.ca/legdocs/mmis/2017/pw/bgrd/backgroundfile-107515.pdf</ref>. The benefit of porous asphalt in comparison to some other permeable pavements is that it doesn't require third party, proprietary components, nor specialized paving equipment for installation<ref>Speight, J.G., 2016. Asphalt materials science and technology (pp. 437-474). Butterworth-Heinemann is. https://link.springer.com/article/10.1557/mrs.2016.267#article-info</ref>.

Depending on the native soil properties and site constraints, the system may be designed for full infiltration, partial infiltration, or as a non-infiltrating detention and filtration only practice. They can be used for low traffic roads, parking, driveways, and walk ways, and are ideal where space for other surface BMPs is limited. Permeable pavement types include:

Depending on the native soil properties and site constraints, the system may be designed for full infiltration, partial infiltration, or as a non-infiltrating detention and filtration only practice. They can be used for low traffic roads, parking, driveways, and walk ways, and are ideal where space for other surface BMPs is limited. Permeable pavement types include:

• permeable interlocking pavers (concrete or composite materials)

*permeable interlocking pavers (concrete or composite materials)

• grid systems (concrete or composite materials)

*grid systems (concrete or composite materials)

• pervious concrete (poured-in-place or pre-cast)

*pervious concrete (poured-in-place or pre-cast)

• porous asphalt

*porous asphalt

• permeable articulating block/mat systems  

*permeable articulating block/mat systems  

For the sake of this page and associated costs/figures below the information found here relate to '''Porous Asphalt''', for costs and information associated with [[Permeable pavements: Life Cycle Costs|Permeable pavements click here]]. STEP conducted life cycle costs estimates for each of permeable pavements 3 design configurations which can be viewed below. To design your own life cycle cost estimates that can be adapted to fit your project budget and unique development needs access the updated [https://sustainabletechnologies.ca/lid-lcct/ LCCT Tool here].

For the sake of this page and associated costs/figures below the information found here relate to '''Porous Asphalt''', for costs and information associated with [[Permeable pavements: Life Cycle Costs|Permeable pavements click here]]. STEP conducted life cycle costs estimates for each of permeable pavements 3 design configurations which can be viewed below. To design your own life cycle cost estimates that can be adapted to fit your project budget and unique development needs access the updated [https://sustainabletechnologies.ca/lid-lcct/ LCCT Tool here].

==Design Guidance==

===Design Assumptions===

Permeable pavers are ideal for sites with limited space and projects such as low traffic roads, parking lots, driveways and walkways. Components include: interlocking pavers, precast pervious slabs, cast in place surface, bedding course, and underground storage layer. Additional components include an underdrain to remove excess water and soil additives to enhance pollutant removal.

Porous asphalt is ideal for sites with limited space and projects such as low traffic roads, parking lots, driveways and walkways. Components include: a porous asphalt surface, a stabilizer course, and a base layer for storage.

Additional components include an underdrain to remove excess water and surface drains to deal with runoff flows in excess of design capacity.

====STEP recommendations:====

Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:

*[[Bedding layer]] and [[Permeable pavements: Specifications|joint filler]] should consist of [[clear stone]] and [[gravel]] rather than [[sand]] to prevent [[clogging]].

*Native soil infiltration rates for Full, Partial and No Infiltration Design scenarios were assumed to be 20 mm/h, 10 mm/h and 2 mm/h, respectively, and a safety factor of 2.5 was applied to calculate the design infiltration rate.

*Granular materials should not be applied as anti-skid agents during [[winter]] because they can quickly clog the system.

*Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, and vacuum sweeping annually. Verification inspections are included every 5 years to confirm adequate maintenance, and every 15 years to confirm adequate drainage performance through in-situ surface infiltration rate testing.

*[[Winter Management|Winter maintenance]] practices should be limited to plowing, with [[Salt|de-icing salts]] applied sparingly.

* Impervious drainage area to permeable surface area (I:P area) ratio of 1:1

*The [[Permeable pavements: Specifications|slope]] of the permeable pavement surface should be at least 1% and no greater than 5%.

* Default Stabilizing course/ Choker layer (19 mm dia. clear stone) depth of 50 millimetres.

*The impervious land surrounding and draining onto the pavement should not exceed the area of the permeable pavement (1:1 / I:P ratio).

* Default Asphalt depth of 110 millimetres.

*Pervious surfaces should not drain onto the pavement.

* Default Stone resevoir (50 mm dia. clear stone) depth of 230 millimetres.

*The [[Permeable pavements: Specifications|storage layer]] must be [[Permeable pavements: Sizing|sized to accommodate runoff]] from the pavement and any impermeable areas draining to it.<br>

* A 150 mm diameter perforated underdrain pipe is included in Partial Infiltration and No Infiltration design configurations only.<br>

====Tool defaults based on STEP recommendations:====

===Notes===

* Maximum drainage area to surface area ratio of 1:1 (or 4:1 for roofs that contribute clean runoff to the practice)

* Operation and maintenance cost estimates include removal of sediment from the catchbasin, by annual surface vacuum sweeping, repairing of potholes and assume no rehabilitation of the porous asphalt surface is required over the 50 year timeframe.

* Default Bedding depth of 50 millimeters.

* The tool calculates costs for new (greenfield) development contexts and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal.  

* Default Base depth of 100 millimeters.

** Land value and equipment mobilization and demobilization costs are not included, assuming BMP construction is part of overall development site construction.

* An underdrain (minimum 150 mm perforated pipe) is only needed when native soil infiltration is less than 15 mm/hr or infiltration is precluded.

** Design and Engineering cost estimates are not calculated by the tool and must be supplied by the user.

 

===Design Notes===

* The tool calculates costs for new designs and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal. Mobilization and demobilization costs not included. The tool adds 10% contingency and additional overhead.

* Unit costs are based on 2018 RSMeans standard union pricing.

* Design and Engineering cost estimates are not calculated by the tool and must be supplied by the user.

* Additional costs associated with retrofit or redevelopment contents is assumed to be 16% higher than the cost for new (greenfield) development contexts.

* Unit costs are based on 2018 pricing; the tool automatically adds inflation. See the Assumptions sheet in the tool for further details.

** Retrofit construction cost estimates are included in the 'Costs Summary' section for comparison.<br>

* The cost of retrofitting is ~16% higher than the cost of new construction.

** Retrofit costs are included in the 'Costs Summary' section and can be added to the Total Construction Cost for increased accuracy.<br>

<small>'''Note''': Permeable Pavements (all 3 design scenarios): Assumes that replacement of pavers occurs at 8 years, and a full rehabilitation of the practice is performed at 30 years.</small>

==Construction Costs==

==Construction Costs==

[[File:Construction Breakdown PP No Infil.PNG|thumb|right|400px|'''Construction Costs Per Unit Drainage Area (CAD$/m²) - No Infiltration Design, 25 mm Retention''']]

[[File:Construction Breakdown PA No Infil.PNG|thumb|right|400px|'''Construction Costs Per Unit Drainage Area (CAD$/m²) - No Infiltration Design, 25 mm Retention''']]

[[File:Construction Breakdown PP Full Infil.PNG|thumb|left|400px|'''Construction Costs Per Unit Drainage Area (CAD$/m²) - Full Infiltration Design, 25 mm Treatment''']]

[[File:Construction Breakdown PA Full Infil.PNG|thumb|left|400px|'''Construction Costs Per Unit Drainage Area (CAD$/m²) - Full Infiltration Design, 25 mm Treatment''']]

[[File:Construction Breakdown PP Partial Infil.PNG|thumb|center|400px|'''Construction Costs Per Unit Drainage Area (CAD$/m²) - Partial Infiltration Design, 25 mm Retention''']]

[[File:Construction Breakdown PA Partial Infil.PNG|thumb|center|400px|'''Construction Costs Per Unit Drainage Area (CAD$/m²) - Partial Infiltration Design, 25 mm Retention''']]

Above you can find a cost breakdown of a 1000m² in three different configurations:<br>

Above you can find a cost breakdown of a 1000m² in three different configurations:<br>

#[[Permeable pavements#Design|Non-infiltrating/filtration only Permeable Pavement]],  

#[[Permeable pavements#Design|Non-infiltrating/filtration only Porous Asphalt]],  

#[[Permeable pavements#Design|Partial infiltration Permeable Pavement]]

#[[Permeable pavements#Design|Partial infiltration Porous Asphalt]]

#[[Permeable pavements#Design|Full infiltration Permeable Pavement]]  

#[[Permeable pavements#Design|Full infiltration Porous Asphalt]]  

As can be seen the greatest cost for this practice (regardless of configuration type) will be Material & Installation, which include costly components such as the, [[Liner|impermeable membrane/liner]], the [[underdrain]], the [[Permeable pavements#Foundation Aggregates|sub-base]] of 50mm [[clear stone]], base of 19mm [[clear stone]] and the [[Bedding layer|bedding pavers themselves]].

As can be seen the greatest cost for this practice (regardless of configuration type) will be Material & Installation, which include costly components such as the, [[Liner|impermeable membrane/liner]], the [[underdrain]], the [[Permeable pavements#Foundation Aggregates|porous asphalt sub-base]] of 50mm [[clear stone]], the conventional asphalt base course (stone reservoir) of 230mm Granular A, [[clear stone|the 19mm Stabilizing course]] and the [[Permeable pavements: Specifications|asphalt (both conventional and permeable)]].

==Life Cycle Costs==

==Life Cycle Costs==

Below are both the capital and life cycle costs of the three [[bioretention]] configuration practices over a 25 and 50-year time horizon based on a detailed assessment of local input costs, maintenance requirements, rehabilitation costs and design scenarios relevant to Canadian climates. The costs of maintenance and rehabilitation (Life cycle costs) are set at "Present Value" of these activities in 2022.  

Below are both the capital and life cycle costs of the three [[permeable pavements|porous asphalt]] configurations over a 25- and 50-year time horizon based on a detailed assessment of local input costs, maintenance requirements, rehabilitation costs and design scenarios relevant to Canadian climates. The costs of maintenance and rehabilitation (Life cycle costs) are set at "Present Value" of these activities in 2022. The estimates of maintenance and rehabilitation (life cycle) costs represent net present values (NPV). Operation and maintenance costs are predicted to represent between 26 to 29% of total life cycle costs over the 25-year evaluation period, and increase to between 37 to 40% of total life cycle costs over the 50-year period, due to costs associated with increased surface vacuuming, restriping, repairing of potholes and cleaning out underground pipes (underdrain and overflow) to prevent [[clogging]] assumed to be continually required after 25 years of operation.

 

Looking at the pie charts below for each configuration we can see that they are all relatively close to being the same cost with a variation of a few hundred dollars between each over both a 25 and 50-year time horizon. The percentage of the [[Bioretention: Full infiltration|Full Infitlration]] configuration is greater than the other two due to the lesser cost of the overall installation for material and Installation, (no underdrains, no gravel storage layer or impermeable membrane, etc.).

===25-Year life cycle cost break down===

===25-Year life cycle cost break down===

[[File:25yr LCCT PP Full Infil.PNG|thumb|left|400px|'''Permeable Pavement: Full infiltration''']]

[[File:25yr LCCT PA Full Infil.PNG|thumb|left|400px|'''Porous Asphalt: Full infiltration''']]

[[File:25yr LCCT PP No Infil.PNG|thumb|right|400px|'''Permeable Pavement: Non-infiltrating''']]

[[File:25yr LCCT PA No Infil.PNG|thumb|right|400px|'''Porous Asphalt: Non-infiltrating''']]

[[File:25yr LCCT PP Partial Infil.PNG|thumb|center|400px|'''Permeable Pavement: Partial infiltration''']]

[[File:25yr LCCT PA Partial Infil.PNG|thumb|center|400px|'''Porous Asphalt: Partial infiltration''']]

===50-Year life cycle cost break down===

===50-Year life cycle cost break down===

[[File:50yr LCCT PP Full Infil.PNG|thumb|left|400px|'''Permeable Pavement: Full infiltration''']]

[[File:50yr LCCT PA Full Infil.PNG|thumb|left|400px|'''Porous Asphalt: Full infiltration''']]

[[File:50yr LCCT PP No Infil.PNG|thumb|right|400px|'''Permeable Pavement: Non-infiltrating''']]

[[File:50yr LCCT PA No Infil.PNG|thumb|right|400px|'''Porous Asphalt: Non-infiltrating''']]

[[File:50yr LCCT PP Partial Infil.PNG|thumb|center|400px|'''Permeable Pavement: Partial infiltration''']]

[[File:50yr LCCT PA Partial Infil.PNG|thumb|center|400px|'''Porous Asphalt: Partial infiltration''']]

==Total Cost & Design Summary==

==Total Cost & Design Summary==

As previously discussed the three [[Permeable pavement]] configurations total cost summary vary greatly dependent on whether you want your feature to possess full infiltration, no infiltration, or partial infiltration. In short the most expensive of these options is the '''Permeable Pavement: No infiltration''' option ($187,356.33 vs. $168,085.10 - partial infiltration and $162,491.78 - full infiltration). The same can be said for construction + associated retrofit costs with each configuration design ($217,333.34 vs. $194,978.72 - partial infiltration and $188,490.47 - full infiltration). This configuration costs more than the other two predominantly due to the addition of an over 1,100m² [[Liner|Impermeable membrane]] (0.762 mm High Density Polyethylene-HDPE), which costs $24,181.47. This difference in price accounts for all three configurations possessing the exact same surface area footprint of 1,000m². As a reminder, it is important to understand your site's surrounding native soil infiltration rate to ensure you are selecting the appropriate design and if your site is located within a [[Source Water Protection#LID Site Considerations|WHPA]] or [[Pollution prevention|Pollution hotspot]], thus requiring a non-infiltration practice such as the aforementioned configuration of a permeable pavement feature. <br>

Total life cycle cost estimates for the three porous asphalt configurations vary substantially with the No Infiltration design being highest ($160,519.90), compared to the Partial Infiltration design ($138,144.27), and followed closely by the Full Infiltration design ($131,972.30).

 

A final note regarding the accuracy of the LCCT. A follow up sensitivity analysis study was conducted by CVC & STEP back in 2019 to test the tool's accuracy. The analysis took designs from 6 completed projects (4 [[bioretention]], 1 [[permeable pavement]], and 1 [[infiltration trench]]), and ran them through the tool comparing construction costing results from the LCCT to actual construction costs for the projects. The accuracy target set for the tool was plus-or-minus 30% of actual construction costs.<br>

'''The analysis found that the tool was on average (±14%) to actual construction costs'''<ref>Credit Vally Conservation (CVC). 2019. Life-cycle costing tool 2019 update: sensitivity analysis. Credit Valley Conservation, Mississauga, Ontario. https://sustainabletechnologies.ca/app/uploads/2020/04/LCCT-Sensitivity-Analysis_March2020.pdf</ref>

It is notable that a sensitivity analysis was conducted in 2019 to compare construction cost estimates generated by the tool to actual costs of implemented projects. '''The analysis found that tool estimates were typically within ±14% of actual construction costs'''<ref>Credit Vally Conservation (CVC). 2019. Life-cycle costing tool 2019 update: sensitivity analysis. Credit Valley Conservation, Mississauga, Ontario. https://sustainabletechnologies.ca/app/uploads/2020/04/LCCT-Sensitivity-Analysis_March2020.pdf</ref>.

===Full Infiltration===

===Full Infiltration===

[[File:PICPchicago.jpg|thumb|500px||Permeable Interlocking Concrete Pavement (PICP) on a narrow road between buildings in Chicago (Source: ICPI)]]

[[File:Kane-porous.jpg|thumb|800px|An example of installed porous asphalt in a designated biking lane, with curb cut inlets leading to adjacent bioswale features, located in the in the City of Gresham, Oregon (Source: Sightline Institute, 2012<ref>Sightline Institute, 2012. Surprisingly Ambitious Permeable Projects. Written by Lisa Stiffler. February 22, 2012. Accessed Dec. 16, 2022. https://www.sightline.org/2012/02/22/surprisingly-ambitious-permeable-projects/</ref>).]]

[[File:Design Table PP Full Infil.PNG|700px]]<br>

[[File:Design Table PA Full Infil.PNG|700px]]<br>

</br>

</br>

===Partial Infiltration===

===Partial Infiltration===

[[File:Design Table PP Partial Infil.PNG|700px]]<br>

[[File:Design Table PA Partial Infil.PNG|700px]]<br>

</br>

</br>

===Non-Infiltrating/filtration only===

===Non-Infiltrating/filtration only===

[[File:Design Table PP No Infil.PNG|700px]]<br>

[[File:Design Table PA No Infil.PNG|700px]]<br>

==References==

==References==