Difference between revisions of "Permeable pavements"

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[[File:PP IWS.gif|frame|Conceptual diagram illustrating an adjustable storage underdrain configuration beneath permeable interlocking pavers]]
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==Overview==
==Overview==
Permeable pavements are an alternative to conventional impervious pavement that allows stormwater to drain through the surface and into a stone reservoir, where it infiltrates into the underlying native soil or is temporarily detained.  Depending on the native soil properties and physical constraints, the system may be designed with no underdrain for full infiltration, with an underdrain for partial infiltration, or with an impermeable liner and underdrain for a non-infiltrating, or detention and filtration only practice.


Permeable pavements, an alternative to traditional impervious pavement, allow stormwater to drain through them and into a stone reservoir where it is infiltrated into the underlying native soil or temporarily detained. They can be used for low traffic roads, parking lots, driveways, pedestrian plazas and walkways. Permeable pavement is ideal for sites with limited space for other surface stormwater BMPs. The following are some of permeable pavement types:
* Permeable interlocking concrete pavers
* Plastic or concrete grid systems
* Previous concrete; and
* Porous asphalt.
Depending on the native soils and physical constraints, the system may be designed with no underdrain for full infiltration, with an underdrain for partial infiltration, or with an impermeable liner and underdrain for a no infiltration or detention and filtration only practice (Figure  ). Permeable paving allows for filtration, storage, or infiltration of runoff, and can reduce or eliminate surface stormwater flows compared to traditional impervious paving surfaces like concrete and asphalt.


==Planning Considerations:==
Take a look at the downloadable Permeable Pavements Factsheet below for a .pdf overview of this LID Best Management Practice:
<h3>Common Concerns</h3>
Common concerns about permeable paving include the following:
* Risk of Groundwater Contamination: Most pollutants in urban runoff are well retained by infiltration                                                      practices and soils and therefore, have a low to moderate potential for groundwater contamination (Pitt et al., 1999). Chloride and sodium from de-icing salts applied to roads and parking areas during winter are not well attenuated in soil and can easily travel to shallow groundwater. Infiltration of deicing salt constituents is also known to increase the mobility of certain heavy metals in soil (e.g., lead, copper and cadmium), thereby raising the potential for elevated concentrations in underlying groundwater (Amrhein et al., 1992; Bauske and Goetz, 1993). However, very few studies that have sampled groundwater below infiltration facilities or roadside ditches receiving de-icing salt laden runoff have found concentrations of heavy metals that exceed drinking water standards (e.g., Howard and Beck, 1993; Granato et al., 1995).  
To minimize risk of groundwater contamination the following management approaches are recommended (Pitt et al., 1999; TRCA, 2009b):  
- Stormwater infiltration practices should not receive runoff from high traffic areas where large amounts of de-icing salts are applied (e.g., busy highways), nor from pollution hot spots (e.g., source areas where land uses    or activities have the potential to generate highly contaminated runoff such as vehicle fuelling, servicing or demolition areas, outdoor storage or handling areas for hazardous materials and some heavy industry sites);


- Prioritize infiltration of runoff from source areas that are comparatively less contaminated such as roofs, low traffic roads and parking areas; and,
{{Clickable button|[[File:P.P Pic.png|150 px|link=https://wiki.sustainabletechnologies.ca/images/7/7e/Permeable_Pavement_Factsheet.pdf]]}}
- Apply sedimentation pretreatment practices (e.g., oil and grit separators) before infiltration of road or parking area runoff.


*Risk of Soil Contamination: Available evidence from monitoring studies indicates that small distributed stormwater infiltration practices do not contaminate underlying soils, even after more than 10 years of operation (TRCA, 2008).
*Winter Operation: For cold climates, well-designed mixes can meet strength, permeability, and freeze-thaw resistance requirements. In addition, experience suggests that snow melts faster on a porous surface because of rapid drainage below the snow surface. Also, a well draining surface will reduce the occurrence of black ice or frozen puddles (Cahill Associates, 1993; Roseen, 2007). Systems installed in the Greater Toronto Area have generally not suffered from heaving or slumping (TRCA, 2008b). Permeable pavement is typically designed to drain within 48 hours. If freezing should occur before the pavement structure has drained, then the large void spaces in the open graded aggregate base creates a capillary barrier to freeze-thaw. Permeable pavers have the added benefit of having enough flexibility to handle minor heaving without being damaged. Permeable pavement can be plowed, although raising the blade height 25 mm may be helpful to avoid catching pavers or scraping the rough surface of the porous pavement. Sand should not be applied for winter traction on permeable pavement as this can quickly clog the system.
<h3> Design</h3>


*On Private Property: If permeable pavement systems are installed on private lots, property owners  or managers will need to be educated on their routine maintenance needs, understand the long-term maintenance plan, and may be subject to a legally binding maintenance agreement. An incentive program such as a storm sewer user fee based on the area of impervious cover on a property that is directly connected to a storm sewer (i.e., does not first drain to a pervious area or LID practice) could be used to encourage property owners or managers to maintain existing practices.
Permeable pavement types include:
*Clogging: Susceptibility to clogging is the main concern for permeable paving systems. The bedding layer and joint filler should consist of 2.5 mm clear stone or gravel rather than sand. Key strategies to prevent clogging are to ensure that adjacent pervious areas have adequate vegetation cover and a winter maintenance plan that does not include sanding. For concrete and asphalt designs, regular maintenance that includes vacuum-assisted street sweeping is necessary. Isolated areas of clogging can be remedied by drilling small holes in the pavement or by replacing the media between permeable pavers.
* Permeable interlocking pavers (concrete and composite materials)
*Road Salt: Care needs to be taken when applying road salt to permeable pavement surfaces since dissolved constituents from the road salt will migrate through the bedding and into the groundwater system. A well-draining surface will reduce the occurrence of black ice or frozen puddles and requires less salt than is applied to impervious pavement (Roseen, 2007).
* Permeable grid systems (concrete or composite materials)
*Structural Stability: Adherence to design guidelines for pavement design and base courses will ensure structural stability. In most cases, the depth of aggregate material required for the stormwater storage reservoir will exceed the depth necessary for structural stability. Reinforcing grids can be installed in the bedding for applications that will be subject to very heavy loads.
* Permeable articulated block systems  
*Heavy Vehicle Traffic: Permeable pavement is not typically used in locations subject to heavy loads. Some permeable pavers are designed for heavy loads and have been used in commercial port loading and storage areas.
* Pervious concrete (poured-in-place or pre-cast)
* Porous asphalt
{{textbox|Permeable paving is ideal for:
*Sites with limited space for other surface stormwater BMPs
*Projects such as low traffic roads, parking lots, driveways, pedestrian plazas and walkways}}


<h3>Physical Suitability and Constraints</h3>
'''The fundamental components of a permeable paving system are:'''
In general, permeable pavement systems can be used almost anywhere a traditionally paved system might have been installed. However, these systems have the same site constraints of any infiltration practice and should meet the following criteria:
* Pavement surface: interlocking pavers with open joints, grid systems, precast pervious slabs or pavers, poured in place asphalt or concrete Bedding layer as a levelling course (for precast systems)
*Wellhead Protection: Permeable pavement should not be used for road or parking surfaces within two (2) year time-of-travel wellhead protection areas.  
* Subsurface base storage reservoir of open graded aggregate
*Winter Operations: Sand or other granular materials should not be applied as anti-skid agents during winter operation because they can quickly clog the system. Winter maintenance practices should be limited to plowing, with de-icing salts applied sparingly (i.e., not as a preventative measure).  
* Edge restraints
*Site Topography: The slope of the permeable pavement surface should be at least one percent and no greater than five percent. The impervious land surrounding and draining into the pavement should not exceed 20% slope (Smith, 2006). Pervious surfaces should not drain onto the pavement
 
*Water Table: The base of permeable pavement stone reservoir should be at least one (1) metre above the seasonally high water table or bedrock elevation.
'''Additional components may include:'''
* Soils: Systems located in low permeability soils with an infiltration rate of less than 15 mm/hr (i.e., hydraulic conductivity of less than 1x10 -6 cm/s), require incorporation of a perforated pipe underdrain. Native soil infiltration rate at the proposed location and depth should be confirmed through measurement of hydraulic conductivity under field saturated conditions using methods described in Appendix C.
* an [[underdrain]] system
*Drainage Area and Runoff Volume: In general, the impervious area treated should not exceed 1.2 times the area of permeable pavement which receives the runoff (GVRD, 2005). The storage layer under the permeable pavement must be sized to accommodate runoff from the pavement itself and any impermeable areas draining to it.
* geotextile, at the discretion of design professional
*Pollution Hot Spot Runoff: To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff (e.g., vehicle fueling, servicing and demolition areas, outdoor storage and handling areas for hazardous materials and some heavy industry sites) should not be treated by permeable pavement.  
* impermeable geomembrane on sites where soil infiltration is not desired
*Setbacks from Buildings: Permeable pavement should be located downslope from building foundations. If the pavement does not receive runoff from other surfaces, no setback is required from building foundations. Otherwise, a minimum setback of four (4) metres down-gradient from building foundations is recommended.  
* geo-grids for sites with heavy vehicle loading
*Proximity to Underground Utilities: Local utility design guidance should be consulted to define the horizontal and vertical offsets. Generally, requirements for underground utilities passing under or near permeable pavement will be no different than for utilities in other pervious areas. However, permeable pavement has a deeper base than conventional pavement which may impact shallow utilities.
* monitoring wells and clean-outs
<gallery mode="packed-hover" perrow=5 widths=150px heights=150px>
File:Frankenthal - Versickerungsfähige Pflaster.jpg|Permeable Interlocking Concrete Pavers (PICP) on a roadway.  
File:Gridpaver.png.jpg|Permeable Grid System filled with gravel (Source: Alexander Eichler).
File:ArticulatedBlockPavers.png|Permeable Articulated Block Systems; mostly used for erosion control sites.  
File:perviousconcrete.png|Pervious Concrete applied to an alleyway in Chicago (Source: City of Chicago).
File:PorousAsphalt Stalls.png|Porous Asphalt in parking stalls (Source: EOR).  
</gallery>
 
==Planning considerations==
===Infiltration===
Permeable pavements can be constructed over any soil type, but hydrologic soil group (HSG) A and B are best for achieving water balance objectives.  Native soil infiltration rate at the proposed facility location and depth should be confirmed through in-situ measurements of hydraulic conductivity under field saturated conditions.  A liner will be required if native soils are contaminated.
 
Systems located in low permeability soils with an infiltration rate of less than 15 mm/hr (i.e., hydraulic conductivity of less than 1x10<sup>-6</sup> cm/s), require incorporation of a perforated pipe underdrain. Pavements require an impermeable geomembrane where the underlying soils are contaminated or the pavement is within two year time-of-travel wellhead protection area (see local drinking water source protection plan)
 
===Space===
[[File:IMAX permeable pavement.JPG|thumb|500px|Permeable pavement in the IMAX parking lot, Mississauga ON]]
Permeable pavements can be used for the entire parking lot, driveway or road surface, or be designed to to receive runoff from adjacent impervious surfaces. For example, the parking spaces of a parking lot or road can be permeable pavements while the drive lanes are conventional asphalt. The impervious area draining on to the permeable pavement should not exceed the area of the permeable pavement itself. Relatively clean drainage areas such as roofs may be up to 4 times the size of the pavement but should include filtration pretreatment to remove coarse debris prior to being conveyed directly to the storage reservoir.
 
Permeable pavements should be located down-gradient from building foundations. If the pavement does not receive drainage from other surfaces, no setback is required. If the pavement receives drainage from other surfaces a minimum setback of four metres down-gradient is recommended. A smaller setback may be permissible where foundations are protected by a geomembrane.
 
The use of permeable pavement on highway shoulders has been found to be technically feasible and can be cost-effective when compared to conventional practices.<ref> Weiss, P., Kayhanian, M., Gulliver, J.S., Khazanovich, L. 2019. Permeable pavement in northern North American urban areas: research review and knowledge gaps. International Journal of Pavement Engineering.Vol. 20, No. 2, 143-162. https://www.tandfonline.com/doi/full/10.1080/10298436.2017.127948</ref>
 
===Site Topography===
Permeable pavement surface slope should be at least 1% and no greater than 5%.  Steeper slopes may require additional features (see subgrade section below).  Pervious areas should not drain onto permeable pavements.
 
===Water Table===
Maintaining a separation of one metre between the elevations of the base of the practice and the seasonally high water table, or top of bedrock is recommended. Lesser or greater values may be considered based on groundwater mounding analysis. See [[Groundwater]] page for further guidance and a spreadsheet tool.
 
To protect groundwater from possible contamination, runoff from pollution hot spots should not be treated by permeable pavements designed for full or partial infiltration. Facilities designed with an impermeable liner (filtration-only) can be used.
Also see the [[Site considerations]] page.
 
===Private Sites===
If permeable paving systems are installed on private lots, property owners or managers will need education on their routine maintenance needs, understanding the long-term maintenance plan. They may also be subject to a legally binding maintenance agreement. An incentive program, such as a storm sewer user fee based on the area of impervious cover on a property that is directly connected to a storm sewer, could be used to encourage property owners or managers to maintain existing practices.


==Design==
==Design==
<h3>Aplications</h3>
[[File:PermeablePaving CrossSection.png|thumb|550px|Permeable Pavement cross-sections showing full and partial infiltration designs (without and with underdrains, respectively). Source: GVRD, 2005]]
 
===Subgrade===
For infiltrating pavements, subgrade slopes should be minimized so that runoff will be able to infiltrate evenly through the entire surface. For steeply sloped sites (>5%), check dams, berms or weir structures on the native soils of the pavement should be considered. If the system is not designed for infiltration, the bottom should be sloped at 1 to 5% toward the underdrain. Subgrades should be compacted to 95% Standard Proctor Density.  If a lesser value is desired to promote infiltration, a thicker sub-base should be considered.  Subgrade soils should not be scarified.
 
===Geotextile===
The use of geotextile fabric between layers within the permeable pavement cross-section can limit infiltration rates due to the collection of solids on the filter fabric that slows infiltration as the pavement ages.  While the use of geotextile fabric can improve retention of total suspended solids, the potential for clogging and the cost of rehabilitation typically negate the advantages of geotextile fabric.<ref> Weiss, P., Kayhanian, M., Gulliver, J.S., Khazanovich, L. 2019. Permeable pavement in northern North American urban areas: research review and knowledge gaps. International Journal of Pavement Engineering.Vol. 20, No. 2, 143-162. https://www.tandfonline.com/doi/full/10.1080/10298436.2017.127948</ref>
 
===Pretreatment===
In most designs, the permeable surface acts as pretreatment to the storage reservoir below. Since sediment accumulates in the permeable areas of the pavement, periodic vacuum sweeping and preventative measures like not storing snow, construction materials or landscaping materials on the pavement are critical to prevent clogging.
 
===Underdrain===
The diagram to the right displays permeable pavement cross sections showing full and partial infiltration designs.<ref>Greater Vancouver Regional District (GVRD). 2005. Stormwater Source Control Design Guidelines 2005. Prepared by Lanarc Consultants Limited, Kerr Wood Leidal Associates Limited and Goya Ngan. </ref> See [[Underdrains]] page for further guidance.
 
===Access Structures===
Access structures are used for periodic inspection and flushing. It could be a maintenance hole or vertical standpipe connected to the perforated pipe. For accessing the underdrain pipe with camera or cleaning equipment, 45° couplings should be used for standpipe connections.
 
===Overflow===
All designs require an overflow outlet connected to a storm sewer with capacity to convey larger storms. This is normally achieved with a catch basin outlet, but water may also be directed to a downstream practice (e.g. bioretention, swale). Another option is a gravel diaphragm or trench along the downgradient edge of the pavement that drains to the storage reservoir below.
 
The diagram to the left is an example of a porous asphalt system with overflow edge draining to a reservoir.<ref>Pennsylvania Department of Environmental Protection (PDEP). 2006.
Pennsylvania Stormwater Best Management Practices Manual. Prepared by Cahill Associates Inc., Harrisburg, PA.</ref> A flush curb extending into the base may be required as an edge restraint for some permeable pavement types.  Decorative stone is lined with a geotextile to prevent migration of fine sediment into the pavement base and facilitate maintenance.
 
===Finish course===
Consult the manufacturer for the design specifications of their product. In pervious concrete and porous asphalt systems, the concrete or asphalt mix specifications and construction procedures are key to proper functioning. These systems require well-trained and experienced contractors for installation.
 
{{:Permeable pavements: Specifications}}
 
===Foundation Aggregates===
[[File:OverflowEdge.png|thumb|Porous asphalt system with overflow edge draining to a reservoir. Source: Pennsylvania Department of Environmental Protection (PDEP). 2006.]]
 
All aggregates should meet the following criteria:
* Porosity of 0.4
* Maximum wash loss of 0.5%
* Minimum durability index of 35
* Maximum abrasion of 10% for 100 revolutions and maximum 50% for 500 revolutions
Most [[OPSS aggregates]] are not recommended for use in permeable pavements, with the exception of 'Granular O' type.
 
'''<u>Granular Subbase</u>'''
Should be clear, crushed 50 mm diameter stone, graded in accordance with ASTM D2940.
<u>'Rain ballast' aggregate (63 mm) would also be suitable</u>
 
'''<u>Granular Base</u>'''
Should be clear, crushed 20 mm diameter stone conforming to ASTM C33 No 57
 
'''<u>Bedding</u>'''
Should be clear, crushed 5 mm diameter stone, graded in accordance with ASTM C33 No 8, High Performance Bedding (1-9 mm diameter), or equivalent. Typical bedding thickness is between 40 mm and 75 mm.
 
For more information, also see [[Aggregates]] page.
 
 
===Sizing Stone Reservoirs===
The stone reservoir must meet both runoff storage and structural support requirements.
The bottom of the reservoir should be level so that water infiltrates evenly.
 
'''[[Permeable pavements: Sizing]]'''
 
===Geotextile===
[[File:PavementwithTrees.png|thumb|400px|Permeable pavers in Hoboken, NJ used around trees which allow air and water to reach the roots (Source: Bruce Ferguson)]]
[[Geotextiles]] are non-woven needle punched, or woven monofilament geotextile fabric that may be placed between the storage reservoir and native soil to maintain separation. Geotextiles are commonly used on low strength soils (CBR <4).  Where expansive clays are present, a non-infiltrating design may be necessary.  If used, geotextile socks around perforated pipes should conform to ASTM D6707 with minimum water flow rate conforming to ASTM D4491 (12,263 L/min/m2 at 5 cm head).
 
===Edge Restraints===
Pavers must abut tightly against the restraints to prevent rotation under load and any consequent spreading of joints. The restraints must be able to withstand the impact of temperature changes, vehicular traffic and snow removal equipment. Metal or plastic stripping is acceptable in some cases, but concrete curbs are preferred. Concrete curbs should be supported on a minimum base of 150 mm of aggregate.
 
===Landscaping===
Adjacent landscaped areas should drain away from permeable pavement to prevent sediments from running onto the surface. Urban trees also benefit from being surrounded by permeable pavement rather than impervious cover, because their roots receive more air and water.
 
[[Wells|Monitoring Wells]]: see “Deeper Wells” section
 
===Heavy Vehicle Traffic===
Permeable paving is not typically used in locations subject to heavy loads. However, some permeable pavements are designed for heavy loads and have been used in commercial port loading and storage areas.  A flexible geogrid structure may be used to improve the structural capacity of the pavement by spreading loads over a larger area.  Increasing the base thickness will also improve structural capacity.
<gallery mode="packed" widths=300px heights=300px>
File:Articulatedblocksystem.png|Permeable articulated block system at the LSRCA headquarters in Newmarket, ON is designed for heavy loads.
File:Geogitter-4.jpg|Geogrids like these are sometimes incorporated into the layers of permeable pavement foundation aggregates to provide additional stability and conserve aggregate material.
</gallery>
 
===Modelling permeable pavements in the Treatment Train Tool===
'''[[Permeable pavements: TTT]]'''
 
==Construction Considerations==
Properly installed permeable pavement requires trained and experienced construction contractors. The following general recommendations apply:
*'''Sediment Control''': The treatment area should be fully protected during construction so that no sediment reaches the permeable pavement system. Construction vehicle traffic should not be permitted on the permeable pavement and its drainage areas once the pavement has been installed.
*'''Base Construction''':  Aggregate should be placed in 100 mm to 150 mm lifts and compacted with a minimum 9 ton steel drum vibratory roller. A light weight deflectometer may be used to test compaction level of open graded stone and compare to specifications.
*'''Weather''': Porous asphalt and pervious concrete require a specific temperature range to set properly and the setting time can be several days<ref>City of Portland. 2004. Portland Stormwater Management Manual. Prepared by the Bureau of Environmental Services (BES). Portland, OR.</ref>.
 
==Inspection and Maintenance==
Permeable pavements require regular inspection and maintenance to ensure proper functioning. The limiting factor for permeable pavements is clogging of the surface course or joint filler between pavers. As these start to fill, the trapped sediment becomes finer and finer until they eventually become clogged. Ideally, signs should be posted on the site identifying permeable pavement. This can also serve as a public awareness and education opportunity. See: [[Permeable pavements: Maintenance]]
 
==Life Cycle Costs==
Initial construction costs for permeable pavements are typically higher than conventional asphalt pavement surfaces, largely due to the price of the surface course and thicker aggregate base needed for stormwater storage. However, the cost difference is reduced or eliminated when total life-cycle costs, or the total cost to construct and maintain the pavement over its lifespan, are considered. Other potential savings and benefits include reduced need for storm sewer pipes and other stormwater practices, less developable land consumed for stormwater treatment, and ancillary benefits (improved aesthetics and reduced urban heat island effect). These systems are especially cost effective in existing urban development where parking lot expansion is needed, but there is not sufficient space for other types of BMPs. They combine parking, stormwater infiltration, retention, and detention into one facility. See also: [[Cost analysis resources]]
 
==Performance==
{|class="wikitable"
|+Ability of Permeable Pavements to Meet Stormwater Management Objectives
|-
!BMP
!Water Balance
!Water Quality
!Erosion Control
|-
|'''Permeable pavement with no underdrain'''
|Yes
|Yes-size for water quality storage requirement
|Partial-based on available storage volume and native soil infiltration rate
|-
|'''Permeable pavement with underdrain'''
|Partial-based on available storage, native soil infiltration rate and if a flow restrictor is used
|Yes-size for water quality storage requirement
|Partial-based on available storage, native soil infiltration rate and if a flow restrictor is used
|-
|'''Permeable pavement with underdrain and impermeable liner'''
|No-some volume reduction occurs through evaporation
|Yes-size for water quality storage requirement
|Partial-based on available storage volume and if a flow restrictor is used
|}
 
===Water Balance===
Research on the volumetric runoff reduction performance of permeable pavements have been conducted on pavements with and without an underdrain in the base.  Volumetric performance improves when: 
* Native soils have high infiltration capacity.
* Impervious surfaces draining onto the permeable pavement surface is limited or absent.
* Underdrain is elevated above the native soil and/or a flow restrictor is installed on the underdrain or outlet storm sewer pipe.
 
All permeable pavements have very high surface infiltration rates when appropriately constructed and maintained.  Therefore, the surface course type (e.g. permeable interlocking concrete pavers, pervious concrete, porous asphalt, etc.) is not a key factor in determining volumetric runoff reduction performance.
 
{|class="wikitable"
|+Volumetric runoff reduction from permeable pavements
|-
!'''LID Practice'''
!'''Location'''
!'''<span title="Note: Runoff reduction estimates are based on differences between runoff volume from the practice and total precipitation over the period of monitoring unless otherwise stated." >Runoff Reduction*</span>'''
!'''Reference'''
|-
|rowspan="7" style="text-align: center;" | Permeable pavement without underdrain
|-
|style="text-align: center;" |King City, Ontario
|style="text-align: center;" |'''<span title="Note: In this study, there was no underdrain in the pavement base, but an underdrain was located 1 m below the native soils to allow for sampling of infiltrated water. Temporary water storage fluctuations in the base were similar to those expected in a no underdrain design." >99%*</span>'''
|style="text-align: center;" |<span class="plainlinks">[https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf TRCA (2008)]</span><ref>TRCA. 2008. Permeable Pavement and Bioretention Swale Demonstration Project. Seneca College, King City, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf</ref>
|-
|style="text-align: center;" |Pennsylvania
|style="text-align: center;" |90%
|style="text-align: center;" |Kwiatkowski et al. (2007)<ref name="example1">Kwiatkowski, M., Welker, A.L., Traver, R.G., Vanacore, M., Ladd. T. 2007. Evaluation of an infiltration best management practice utilizing pervious concrete. Journal of the American Water Resources Association. Vol. 43. No. 5. pp. 1208-1222.</ref>
|-
|style="text-align: center;" |Connecticut
|style="text-align: center;" |'''<span title="Note: Runoff reduction estimates are based on differences in runoff volume between the practice and a conventional impervious surface over the period of monitoring." >72%*</span>'''
|style="text-align: center;" |Gilbert and Clausen (2006)<ref>Gilbert, J. and J. Clausen. 2006. Stormwater runoff quality and quantity from asphalt,
paver and crushed stone driveways in Connecticut. Water Research 40: 826-832.</ref>
|-
|style="text-align: center;" |Washington
|style="text-align: center;" |97 to 100%
|style="text-align: center;" |Brattebo and Booth (2003)<ref name="example2">Brattebo, B. and D. Booth. 2003. Long term stormwater quantity and quality
performance of permeable pavement systems. Water Research 37(18): 4369-4376 </ref>
|-
|style="text-align: center;" |Guelph, Ontario
|style="text-align: center;" |90%
|style="text-align: center;" |James (2002)<ref>James, W. 2002. Green Roads: Research into Permeable Pavers. Stormwater.
March/April.</ref>
|-
|style="text-align: center;" |France
|style="text-align: center;" |97%
|style="text-align: center;" |Legret and Colandini (1999)<ref>Legret, M and V. Colandani. 1999. Effects of a porous pavement structure with a reservoir structure on runoff water: water quality and fate of metals. Water Science and Technology. 39(2): 111-117</ref>
|-
|rowspan="10" style="text-align: center;" | Permeable pavement with underdrain
|-
|style="text-align: center;" |Montreal
|style="text-align: center;" |26 to 98%
|style="text-align: center;" |Vaillancourt ''et al.'' (2019) <ref>Vaillancourt, C., Duchesne, S., & Pelletier, G. 2019. Hydrologic performance of permeable pavement as an adaptive measure in urban areas: case studies near Montreal, Canada. Journal of Hydrologic Engineering, 24(8), 05019020.</ref>
|-
|style="text-align: center;" |Mississauga
|style="text-align: center;" |61 to 99%
|style="text-align: center;" |<span class="plainlinks">[https://cvc.ca/wp-content/uploads/2018/05/IMAX-Low-Impact-Development-Monitoring-Case-Study-may-24.pdf CVC (2018)]</span><ref>CVC. 2018. Case Study: Monitoring Low Impact Development at the IMAX demonstration site. February, 2018. https://cvc.ca/wp-content/uploads/2018/05/IMAX-Low-Impact-Development-Monitoring-Case-Study-may-24.pdf</ref>
|-
|style="text-align: center;" |Seoul, Korea
|style="text-align: center;" |30 to 65%
|style="text-align: center;" |Shafique ''et al.'' (2018) <ref>Shafique, M., Kim, R. and Kyung-Ho, K., 2018. Rainfall runoff mitigation by retrofitted permeable pavement in an urban area. Sustainability, 10(4), p.1231.</ref>
|-
|style="text-align: center;" |Northern Ohio
|style="text-align: center;" |16 to 99%
|style="text-align: center;" |Winston ''et al.'' (2015) <ref>Winston, R. J., Dorsey, J. D., & Hunt, W. F. (2015). Monitoring the performance of bioretention and permeable pavement stormwater controls in Northern Ohio: hydrology, water quality, and maintenance needs. Chagrin River Watershed Partners. Inc. under NOAA award No. NA09NOS4190153.</ref>
|-
|style="text-align: center;" |Vaughan, Ontario
|style="text-align: center;" |'''<span title="Note: Runoff reduction estimates are based on differences in runoff volume between the practice and a conventional impervious surface over the period of monitoring.">45%*</span>'''
|style="text-align: center;" |<span class="plainlinks">[https://sustainabletechnologies.ca/app/uploads/2016/02/KPP-Ext_FinalReport_Dec2015.pdf Van Seters and Drake (2015)]</span><ref>Van Seters, T. and Drake, J. 2015. Five Year Performance Evaluation of Permeable Pavements. Kortright, Vaughan - Final Draft. December 2015. © Toronto and Region Conservation Authority. https://sustainabletechnologies.ca/app/uploads/2016/02/KPP-Ext_FinalReport_Dec2015.pdf</ref>
|-
|style="text-align: center;" |North Carolina
|style="text-align: center;" |98 to 99%
|style="text-align: center;" |Collins et al. (2008)<ref>Collins, K., W. Hunt and J. Hathaway. 2008. Hydrologic comparison of four types of permeable pavement and standard asphalt in eastern North Carolina. Journal of Hydrologic Engineering. </ref>
|-
|style="text-align: center;" |United Kingdom
|style="text-align: center;" |50%
|style="text-align: center;" |Jefferies (2004)<ref>Jefferies, C. 2004. Sustainable drainage systems in Scotland: the monitoring
programme. Scottish Universities SUDS Monitoring Project. Dundee, Scotland</ref>
|-
|style="text-align: center;" |United Kingdom
|style="text-align: center;" |53 to 66%
|style="text-align: center;" |Pratt ''et al.'' (1995)<ref>Pratt, C.J., Mantle, J.D.G., Schofield, P.A. 1995. UK research into the performance of permeable pavement reservoir structures in controlling stormwater discharge quantity and quality. Water Science Technology. Vol. 32. No. 1. pp. 63-69.</ref>
|-
|style="text-align: center;" |Maryland
|style="text-align: center;" |45% to 60%
|style="text-align: center;" |Schueler ''et al.'' (1987)<ref>Schueler, T. 1987. Controlling urban runoff: a practical manual for planning and designing urban BMPs. Metropolitan Washington Council of Governments. Washington, DC. </ref>
|-
| colspan="2" style="text-align: center;" |'''<u><span title="Note: This estimate is provided only for the purpose of initial screening of LID practices suitable for achieving stormwater management objectives and targets.  Performance of individual facilities will vary depending on site specific contexts and facility design parameters and should be estimated as part of the design process and submitted with other documentation for review by the approval authority." >Runoff Reduction Estimate*</span></u>'''
|colspan="2" style="text-align: center;" |'''85% without underdrain;'''
'''45% with underdrain'''
|-
|}
 
In a numerical modelling study comparing the predicted hydrologic performance of permeable interlocking concrete pavers without underdrains in New York and Hong Kong, Liu et al. (2017) found pavements performed significantly better in a relatively drier climate (e.g., New York), reducing nearly 90% of runoff volume compared to 70% in a relatively wetter climate (e.g., Hong Kong) and that runoff volume was found to be mostly governed by rainfall intensity.<ref> Liu, C.Y., Chui, T.F.M. 2017. Factors Influencing Stormwater Mitigation in Permeable Pavement. Water. 9, 988. https://www.mdpi.com/2073-4441/9/12/988</ref>
 
In Canadian and Swedish field studies, vacuum cleaning could only partially restore the surface infiltration capacity of permeable interlocking concrete pavers (PICP) with large spatial variability in the observed infiltration rates post cleaning.<ref> Drake, J., Bradford, A. 2013. Assessing the Potential for Restoration of Surface Permeability for Permeable Pavements Through Maintenance. Water Science and Technology. 2013, 68, 1950-1958. https://pubmed.ncbi.nlm.nih.gov/24225094/ </ref> <ref>Al-Rubaei, A.M., Stenglein, A.L., Viklander, M., Blecken, G.T. 2013. Long-Term Hydraulic Performance of Porous Asphalt Pavements in Northern Sweden. Journal of Irrigation and Drainage Engineering. 39 (6) June 2013. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29IR.1943-4774.0000569 </ref>  Potential options for rehabilitating clogged permeable pavements identified to date include combining pressure washing with pure vacuum sweeping to help dislodge sediment accumulated within joints of PICP and porous asphalt <ref> Seghal, K.S., Drake, J., Van Seters, T., Vander Linden, W.K. 2018. Improving Restorative Maintenance Practices for Mature Permeable Interlocking Concrete Pavements. Water. 10 (11), 1588. https://www.mdpi.com/2073-4441/10/11/1588 </ref> <ref> Winston, R.J., Al-Rubaei, A.M., Blecken, G.T., Viklander, M., Hunt, W.F. 2016. Maintenance measures for preservation and recovery of permeable pavement surface infiltration rate – The effects of street sweeping, vacuum cleaning, high pressure washing and milling.  Journal of Environmental Management.  169(2016):132-144. https://www.sciencedirect.com/science/article/pii/S0301479715304412c </ref> <ref> Al-Rubaei, A.M., et al., 2013. Long-term hydraulic performance of porous asphalt pavements in Northern Sweden. Journal of Irrigation and Drainage Engineering, 139 (6), 499–505. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29IR.1943-4774.0000569 </ref>, and in pores of pervious concrete<ref> Chopra, M., et al., 2010. Effect of Rejuvenation Methods on the Infiltration Rates of Pervious Concrete  Pavements. Journal of Hydrologic Engineering, 15 (6), 426–433. https://pennstate.pure.elsevier.com/en/publications/effect-of-rejuvenation-methods-on-the-infiltration-rates-of-pervi </ref>. Drainage performance evaluations of aged pervious concrete have shown its permeability does not decline as rapidly with age as PICP, but that vacuum cleaning techniques tested to date provide variable or insignificant restorative effect<ref> Drake, J., Bradford, A. 2013. Assessing the Potential for Restoration of Surface Permeability for Permeable Pavements Through Maintenance. Water Science and Technology. 2013, 68, 1950-1958. https://pubmed.ncbi.nlm.nih.gov/24225094/ </ref> <ref>Sustainable Technologies Evaluation Program (STEP). 2019. Permeable Pavements Maintenance. Technical Brief. October 2019. https://sustainabletechnologies.ca/app/uploads/2019/10/PDF-PP-maintenance-tech-brief_Oct2019.pdf </ref>
 
===Water Quality===
[[File:TSS - permeable pavement.JPG|200px|thumb]]
Like other stormwater practices, the water quality performance of permeable pavements is closely tied to the reduction of runoff volumes through infiltration. However, permeable pavements are also very effective stormwater runoff filters.  Most sediments and associated contaminants are trapped within the surface pores or gravel filled joints between the pavers.  A five year study of three permeable pavement surfaces in Vaughan showed total suspended solids (TSS) concentration reductions between 88 and 89% [https://sustainabletechnologies.ca/app/uploads/2016/02/KPP-Ext_FinalReport_Dec2015.pdf/ (Van Seters and Drake, 2015)].  Other STEP studies in the Greater Toronto Area have displayed similar results, with only 7% of 181 permeable pavement effluent samples having TSS concentrations above 30 mg/L (median = 7 mg/L)[https://sustainabletechnologies.ca/app/uploads/2015/06/SynthesisWaterQuality_Statistics_May2015.pdf/ TRCA, 2015].<br>
<br>
[[File:TP - permeable pavement.JPG|200px|thumb]]
The two box plot figures to the right show combined stormwater effluent quality results from STEP monitoring projects conducted over a 12-year time period (between 2005 and 2017) at sites within Greater Toronto Area (GTA) municipalities.  Total Suspended Solid (TSS) effluent concentration results for permeable pavement practices represent the combined results from 4 sites in the GTA and a total of 296 monitored storm events.  Median TSS concentration was found to be 8.95 mg/L and exceeded the Canadian Water Quality Guideline of 30 mg/L (CCME, 2002<ref>Canadian Council of Ministers of the Environment (CCME). 2002. Canadian water quality guidelines for the protection of aquatic life: Total particulate matter. In: Canadian Environmental Quality Guidelines, Canadian Council of Ministers of the Environment, Winnipeg</ref>) during only 12% of the 296 monitored storm events.  Median TP concentration was found to be 0.04 mg/L and exceeded the Ontario Provincial Water Quality Objective (PWQO) of 0.03 mg/L (OMOEE, 1994<ref>Ontario Ministry of Environment and Energy (OMOEE), 1994. Policies, Guidelines and Provincial Water Quality Objectives of the Ministry of Environment and Energy. Queen’s Printer for Ontario. Toronto, ON.</ref>) during 62% of the 300 monitored storm events.  In comparison, median TP effluent concentration for permeable pavements in the International Stormwater BMP Database was found to be 0.100 mg/L, based on 447 monitored storm events (Clary et al. 2020)<ref>Clary, J., Jones, J., Leisenring, M., Hobson, P., Strecker, E. 2020. International Stormwater BMP Database: 2020 Summary Statistics. The Water Research Foundation. [https://www.waterrf.org/system/files/resource/2020-11/DRPT-4968_0.pdf</ref>, which is also above the Ontario PWQO of 0.03 mg/L.  These results indicate that the design of permeable pavements draining to phosphorus-limited receiving waterbodies should include practices or design variations to improve [[Phosphorus]] retention. This could involve including a media filter manufactured treatment device as part of the treatment train design. An example of a design variation to improve phosphorus retention is including an additive to the permeable pavement base aggregate layer to improve phosphorus retention (Ostrom and Davis, 2019)<ref>Ostrom, T.K. and Davis, A.P. 2019. Evaluation of an enhanced treatment media and permeable pavement base to remove stormwater nitrogen, phosphorus, and metals under simulated rainfall. Water research, 166, p.115071.</ref>.<br>
<br>
Another group of studies of permeable pavements examines the quality of water infiltrated through soils beneath the installations.  In these studies the quality of infiltrated water is used as a measure of the potential for contamination of groundwater.  One such study of a permeable interlocking concrete pavement installed in a college parking lot in King City, Ontario, showed that stormwater infiltrated through a 60 cm granular reservoir and 1 metre of native soil had significantly lower concentrations of several typical parking lot contaminants relative to runoff from an adjacent asphalt surface [https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf/ (TRCA, 2008)].  These results are consistent with research on the quality of infiltrated water from permeable pavements in Washington<ref name="example2" /> and Pennsylvannia<ref name="example1" />.  As with all stormwater infiltration practices, risk of groundwater contamination from infiltration of runoff laden with road de-icing salt constituents (typically sodium and chloride) may be a concern in vulnerable areas for [[Source Water Protection]].  Chloride ions are extremely mobile in the soil and are readily transported by percolating water to aquifers.
 
===Stream Channel Erosion===
Permeable pavements help address stream erosion and flood flows by attenuating peak flows through temporary storage and release. A STEP study in Vaughan showed a 91% peak flow reduction due in part to flow restriction on the underdrain [https://sustainabletechnologies.ca/app/uploads/2016/02/KPP-Ext_FinalReport_Dec2015.pdf/ (Van Seters and Drake, 2015)].  A later study of three permeable pavements in a parking lot in Mississauga showed peak flow reductions between 39 and 84% for events greater than 25 mm [https://cvc.ca/wp-content/uploads/2018/05/IMAX-Low-Impact-Development-Monitoring-Case-Study-may-24.pdf/ (CVC, 2018)].
 
===Other Benefits===
[[File:Renovated Bartholdi Park (37898409602).jpg|thumb|400px|Permeable pavements (left) in Bartholdi Park, DC provides air and water to root systems contributing to healthier, longer lasting trees (Source: USCapitol)]]
* ''Winter Performance:'' Snow plow and deicing costs are reduced due to rapid drainage of snow melt. Puddling on parking lots is also reduced.  A two year study of PICP in Vaughan found that the PICP provides equivalent or higher levels of safety compared with asphalt when treated with de-icing products at medium (0.049 kg/m2) or low (0.024 kg/m2) salt application rates<ref>Marvin, J., Scott, J., Van Seters, T., Bowers, B., Drake, J. Winter Maintenance of Permeable Interlocking Concrete Pavement: Evaluating Opportunities to Reduce Road Salt Pollution and Improve Winter Safety, submitted to Transportation Research Record May 2020, under review</ref>.
*''Urban Heat Island Effect Reduction:'' Porous materials have less thermal conductivity and thermal capacity than traditional impervious pavement, thereby reducing the urban heat island effect <ref name="example3">Ferguson, B.K. 2005. Porous Pavements. Integrative Studies in Water Management and Land Development. Taylor and Francis: New York.</ref>.  Year round measurements of asphalt and PICP surface temperatures in King City, Ontario showed asphalt temperatures above  20°C approximately 12% more often than the adjacent permeable pavers [https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf/ (TRCA, 2008)].
*''Improved Street Tree Health:''  Permeable pavements installed around tree planting zones in hardscapes help provide air and water to root systems, thereby contributing to healthier, longer lasting trees that require less manual irrigation.
*''Quiet Streets:'' Porous asphalt surfaces absorb sound energy and dissipate air pressure around tires before any noise is generated. Tire noise is lower in loudness and pitch for a porous surface than a corresponding dense pavement <ref name="example3" />.  Segmented pavers do not share this benefit and are generally noisier than asphalt roads.
*''LEED Credits:'' Permeable pavement has the potential for earning Canadian Green Building Council LEED sustainable sites credits for reducing stormwater pollution and runoff, urban heat island mitigation, and conservation of materials and resources.
 
==External links==
{{:Disclaimer}}
===Pre-cast with joints===
*[https://www.pavedrain.com/ Pavedrain]
*[https://permacon.ca/en/landscaping/permeable-en/ Permacon]
*[https://santerrastonecraft.com/landscape/paving-stones/terra-flo Santerra, Terra-flow]
*[https://unilock.com/ Unilock]
 
===Pre-cast pervious===
*[http://hydropavers.ca/ Hydropaver]
*[http://www.storm-crete.com/ Stormcrete]
 
===Cast in place===
*[https://www.lafarge.ca/en/hydromedia#:~:text=Hydromedia%E2%84%A2%20is%20a%20fast,ground%20below%20where%20it%20belongs. Hydromedia]
*[https://www.purepave.com/ PurePave]
 
===Plastic grid===
*[https://www.ecorastergrid.com/ Ecoraster]
*[https://www.hahnplastics.com/Hanpave/808000.INT0100 HANH Hanpave]
*[https://www.hahnplastics.com/Heavy-duty-ground-grid/GH084060 HAHN Heavy duty ground grid]
*[https://permacon.ca/en/ Permacon]
 
==Gallery==
{{:Permeable pavements: Gallery}}
 
==References==

Latest revision as of 13:30, 21 March 2023

Conceptual diagram illustrating an adjustable storage underdrain configuration beneath permeable interlocking pavers

Overview[edit]

Permeable pavements are an alternative to conventional impervious pavement that allows stormwater to drain through the surface and into a stone reservoir, where it infiltrates into the underlying native soil or is temporarily detained. Depending on the native soil properties and physical constraints, the system may be designed with no underdrain for full infiltration, with an underdrain for partial infiltration, or with an impermeable liner and underdrain for a non-infiltrating, or detention and filtration only practice.


Take a look at the downloadable Permeable Pavements Factsheet below for a .pdf overview of this LID Best Management Practice:

P.P Pic.png


Permeable pavement types include:

  • Permeable interlocking pavers (concrete and composite materials)
  • Permeable grid systems (concrete or composite materials)
  • Permeable articulated block systems
  • Pervious concrete (poured-in-place or pre-cast)
  • Porous asphalt

Permeable paving is ideal for:

  • Sites with limited space for other surface stormwater BMPs
  • Projects such as low traffic roads, parking lots, driveways, pedestrian plazas and walkways

The fundamental components of a permeable paving system are:

  • Pavement surface: interlocking pavers with open joints, grid systems, precast pervious slabs or pavers, poured in place asphalt or concrete Bedding layer as a levelling course (for precast systems)
  • Subsurface base storage reservoir of open graded aggregate
  • Edge restraints

Additional components may include:

  • an underdrain system
  • geotextile, at the discretion of design professional
  • impermeable geomembrane on sites where soil infiltration is not desired
  • geo-grids for sites with heavy vehicle loading
  • monitoring wells and clean-outs

Planning considerations[edit]

Infiltration[edit]

Permeable pavements can be constructed over any soil type, but hydrologic soil group (HSG) A and B are best for achieving water balance objectives. Native soil infiltration rate at the proposed facility location and depth should be confirmed through in-situ measurements of hydraulic conductivity under field saturated conditions. A liner will be required if native soils are contaminated.

Systems located in low permeability soils with an infiltration rate of less than 15 mm/hr (i.e., hydraulic conductivity of less than 1x10-6 cm/s), require incorporation of a perforated pipe underdrain. Pavements require an impermeable geomembrane where the underlying soils are contaminated or the pavement is within two year time-of-travel wellhead protection area (see local drinking water source protection plan)

Space[edit]

Permeable pavement in the IMAX parking lot, Mississauga ON

Permeable pavements can be used for the entire parking lot, driveway or road surface, or be designed to to receive runoff from adjacent impervious surfaces. For example, the parking spaces of a parking lot or road can be permeable pavements while the drive lanes are conventional asphalt. The impervious area draining on to the permeable pavement should not exceed the area of the permeable pavement itself. Relatively clean drainage areas such as roofs may be up to 4 times the size of the pavement but should include filtration pretreatment to remove coarse debris prior to being conveyed directly to the storage reservoir.

Permeable pavements should be located down-gradient from building foundations. If the pavement does not receive drainage from other surfaces, no setback is required. If the pavement receives drainage from other surfaces a minimum setback of four metres down-gradient is recommended. A smaller setback may be permissible where foundations are protected by a geomembrane.

The use of permeable pavement on highway shoulders has been found to be technically feasible and can be cost-effective when compared to conventional practices.[1]

Site Topography[edit]

Permeable pavement surface slope should be at least 1% and no greater than 5%. Steeper slopes may require additional features (see subgrade section below). Pervious areas should not drain onto permeable pavements.

Water Table[edit]

Maintaining a separation of one metre between the elevations of the base of the practice and the seasonally high water table, or top of bedrock is recommended. Lesser or greater values may be considered based on groundwater mounding analysis. See Groundwater page for further guidance and a spreadsheet tool.

To protect groundwater from possible contamination, runoff from pollution hot spots should not be treated by permeable pavements designed for full or partial infiltration. Facilities designed with an impermeable liner (filtration-only) can be used. Also see the Site considerations page.

Private Sites[edit]

If permeable paving systems are installed on private lots, property owners or managers will need education on their routine maintenance needs, understanding the long-term maintenance plan. They may also be subject to a legally binding maintenance agreement. An incentive program, such as a storm sewer user fee based on the area of impervious cover on a property that is directly connected to a storm sewer, could be used to encourage property owners or managers to maintain existing practices.

Design[edit]

Permeable Pavement cross-sections showing full and partial infiltration designs (without and with underdrains, respectively). Source: GVRD, 2005

Subgrade[edit]

For infiltrating pavements, subgrade slopes should be minimized so that runoff will be able to infiltrate evenly through the entire surface. For steeply sloped sites (>5%), check dams, berms or weir structures on the native soils of the pavement should be considered. If the system is not designed for infiltration, the bottom should be sloped at 1 to 5% toward the underdrain. Subgrades should be compacted to 95% Standard Proctor Density. If a lesser value is desired to promote infiltration, a thicker sub-base should be considered. Subgrade soils should not be scarified.

Geotextile[edit]

The use of geotextile fabric between layers within the permeable pavement cross-section can limit infiltration rates due to the collection of solids on the filter fabric that slows infiltration as the pavement ages. While the use of geotextile fabric can improve retention of total suspended solids, the potential for clogging and the cost of rehabilitation typically negate the advantages of geotextile fabric.[2]

Pretreatment[edit]

In most designs, the permeable surface acts as pretreatment to the storage reservoir below. Since sediment accumulates in the permeable areas of the pavement, periodic vacuum sweeping and preventative measures like not storing snow, construction materials or landscaping materials on the pavement are critical to prevent clogging.

Underdrain[edit]

The diagram to the right displays permeable pavement cross sections showing full and partial infiltration designs.[3] See Underdrains page for further guidance.

Access Structures[edit]

Access structures are used for periodic inspection and flushing. It could be a maintenance hole or vertical standpipe connected to the perforated pipe. For accessing the underdrain pipe with camera or cleaning equipment, 45° couplings should be used for standpipe connections.

Overflow[edit]

All designs require an overflow outlet connected to a storm sewer with capacity to convey larger storms. This is normally achieved with a catch basin outlet, but water may also be directed to a downstream practice (e.g. bioretention, swale). Another option is a gravel diaphragm or trench along the downgradient edge of the pavement that drains to the storage reservoir below.

The diagram to the left is an example of a porous asphalt system with overflow edge draining to a reservoir.[4] A flush curb extending into the base may be required as an edge restraint for some permeable pavement types. Decorative stone is lined with a geotextile to prevent migration of fine sediment into the pavement base and facilitate maintenance.

Finish course[edit]

Consult the manufacturer for the design specifications of their product. In pervious concrete and porous asphalt systems, the concrete or asphalt mix specifications and construction procedures are key to proper functioning. These systems require well-trained and experienced contractors for installation.

Specifications for pervious concrete, porous asphalt, and permeable pavers
Material Specification Quantity
Pervious concrete
  • NO4-RG-S7 mix with air entrainment proven to have the best freeze-thaw durability after 300 freeze-thaw cycles.
  • 28 day compressive strength = 5.5 to 20 MPa.
  • Porosity between 14% to 31%.
  • Permeability = 900 to 21,500 mm/hr.
  • Proprietary pre-cast slabs meeting required specifications are also available.
Thickness will range from 100 mm - 150 mm depending on the expected loads.
Porous asphalt
  • Open-graded asphalt mix with a minimum porosity of 16%.
  • Polymers can be added to provide additional strength to heavy loads.
  • The University of New Hampshire Stormwater Center has detailed design specifications for porous asphalt.
Thickness will range from 50 mm - 100 mm depending on the expected loads.
Permeable Interlocking Pavements
  • Pavers shall meet the minimum material and standard specifications for precast concrete pavers (CSA A231.2 in Canada; ASTM C936 in United States).
  • Open space between pavers (i.e. joint space) typically ranges between 5 and 15% of the total surface area.
  • ASTM No. 8 (5 mm dia.) crushed aggregate is recommended for fill material in the paver joints (typically HPB).
  • For narrow joint pavers, a smaller sized aggregate may be used. Narrow joints are required where pavement must be AODA compliant.
  • For vehicle applications the minimum paver thickness is 80 mm
  • For pedestrian applications the minimum paver thickness is 60 mm and joint widths should be no greater than 15 mm.
Stone Resevoir
  • All aggregates should meet the following criteria: (i) maximum wash loss of 0.5%, (ii) minimum durability index of 35, (iii) maximum abrasion of 10% for

100 revolutions and maximum of 50% for 500 revolutions

  • Most OPSS aggregates are not recommended for PP, with the exception of ‘granular O’.
  • The granular subbase material shall consist of granular material graded in accordance with ASTM D 2940. Material should be clear crushed 50 mm diameter stone with void space ratio of 0.4.
  • The granular base material shall be crushed stone conforming to ASTM C 33 No 57. Material should be clear crushed 20 mm diameter stone.
  • The granular bedding material shall be graded in accordance with ASTM C 33 No 8. Typical bedding thickness is 40 to 75 mm. Material should be 5 mm diameter stone or as determined by the Design Engineer. In Ontario, high performance bedding (1 to 9 mm diameter) or equivalent is often used.
  • See LID Planning and Design Wiki (Permeable Pavements: Sizing) to size aggregate bed depth and multiply by application area to get total volume.
Geotextile
  • Should be woven monofilament or non-woven needle punched fabrics. Woven slit film and non-woven heat bonded fabrics should not be used as they are prone to clogging.
  • Primary considerations for Geotextile are:
    • suitable apparent opening size (AOS) for non-woven fabrics, or percent open area (POA) for woven fabrics, to maintain water flow even with sediment and microbial film build-up
    • maximum forces to be exerted on the fabric (i.e tensile, tear and puncture strengths required)
    • load bearing ratio of the underlying native soil (i.e. is geotextile needed to prevent downward migration of aggregate into the native soil?),
    • grain size distribution of the overlying aggregate material, and
    • permeability of the native soil.
  • Geotextiles are not always necessary and may be prone to eventual clogging. Consider using sand or fine aggregates instead. Where they are necessary (typically on low strength soils of CBR <4) between stone reservoir and native soil, material specifications should conform to Ontario Provincial Standard Specification (OPSS) 1860 for Class II geotextile fabrics. Geotextile socks on pipes should conform to ASTM D6707 with a min. water flow rate conforming to ASTM D4491 (12,263 L/min/m2 at 5 cm head).
Underdrain (optional)
  • PVC or HDPE, continuously perforated with smooth interior and a minimum inside diameter of 200 mm.
  • Perforations in pipes should be 10 mm in diameter.
  • A standpipe from the underdrain to the pavement surface can be used for monitoring and maintenance of the underdrain. The top of the standpipe should be covered with a screw cap and a vandal-proof lock.

Pipes should terminate 0.3 m short from the sides of the base.

Foundation Aggregates[edit]

Porous asphalt system with overflow edge draining to a reservoir. Source: Pennsylvania Department of Environmental Protection (PDEP). 2006.

All aggregates should meet the following criteria:

  • Porosity of 0.4
  • Maximum wash loss of 0.5%
  • Minimum durability index of 35
  • Maximum abrasion of 10% for 100 revolutions and maximum 50% for 500 revolutions

Most OPSS aggregates are not recommended for use in permeable pavements, with the exception of 'Granular O' type.

Granular Subbase Should be clear, crushed 50 mm diameter stone, graded in accordance with ASTM D2940. 'Rain ballast' aggregate (63 mm) would also be suitable

Granular Base Should be clear, crushed 20 mm diameter stone conforming to ASTM C33 No 57

Bedding Should be clear, crushed 5 mm diameter stone, graded in accordance with ASTM C33 No 8, High Performance Bedding (1-9 mm diameter), or equivalent. Typical bedding thickness is between 40 mm and 75 mm.

For more information, also see Aggregates page.


Sizing Stone Reservoirs[edit]

The stone reservoir must meet both runoff storage and structural support requirements. The bottom of the reservoir should be level so that water infiltrates evenly.

Permeable pavements: Sizing

Geotextile[edit]

Permeable pavers in Hoboken, NJ used around trees which allow air and water to reach the roots (Source: Bruce Ferguson)

Geotextiles are non-woven needle punched, or woven monofilament geotextile fabric that may be placed between the storage reservoir and native soil to maintain separation. Geotextiles are commonly used on low strength soils (CBR <4). Where expansive clays are present, a non-infiltrating design may be necessary. If used, geotextile socks around perforated pipes should conform to ASTM D6707 with minimum water flow rate conforming to ASTM D4491 (12,263 L/min/m2 at 5 cm head).

Edge Restraints[edit]

Pavers must abut tightly against the restraints to prevent rotation under load and any consequent spreading of joints. The restraints must be able to withstand the impact of temperature changes, vehicular traffic and snow removal equipment. Metal or plastic stripping is acceptable in some cases, but concrete curbs are preferred. Concrete curbs should be supported on a minimum base of 150 mm of aggregate.

Landscaping[edit]

Adjacent landscaped areas should drain away from permeable pavement to prevent sediments from running onto the surface. Urban trees also benefit from being surrounded by permeable pavement rather than impervious cover, because their roots receive more air and water.

Monitoring Wells: see “Deeper Wells” section

Heavy Vehicle Traffic[edit]

Permeable paving is not typically used in locations subject to heavy loads. However, some permeable pavements are designed for heavy loads and have been used in commercial port loading and storage areas. A flexible geogrid structure may be used to improve the structural capacity of the pavement by spreading loads over a larger area. Increasing the base thickness will also improve structural capacity.

Modelling permeable pavements in the Treatment Train Tool[edit]

Permeable pavements: TTT

Construction Considerations[edit]

Properly installed permeable pavement requires trained and experienced construction contractors. The following general recommendations apply:

  • Sediment Control: The treatment area should be fully protected during construction so that no sediment reaches the permeable pavement system. Construction vehicle traffic should not be permitted on the permeable pavement and its drainage areas once the pavement has been installed.
  • Base Construction: Aggregate should be placed in 100 mm to 150 mm lifts and compacted with a minimum 9 ton steel drum vibratory roller. A light weight deflectometer may be used to test compaction level of open graded stone and compare to specifications.
  • Weather: Porous asphalt and pervious concrete require a specific temperature range to set properly and the setting time can be several days[5].

Inspection and Maintenance[edit]

Permeable pavements require regular inspection and maintenance to ensure proper functioning. The limiting factor for permeable pavements is clogging of the surface course or joint filler between pavers. As these start to fill, the trapped sediment becomes finer and finer until they eventually become clogged. Ideally, signs should be posted on the site identifying permeable pavement. This can also serve as a public awareness and education opportunity. See: Permeable pavements: Maintenance

Life Cycle Costs[edit]

Initial construction costs for permeable pavements are typically higher than conventional asphalt pavement surfaces, largely due to the price of the surface course and thicker aggregate base needed for stormwater storage. However, the cost difference is reduced or eliminated when total life-cycle costs, or the total cost to construct and maintain the pavement over its lifespan, are considered. Other potential savings and benefits include reduced need for storm sewer pipes and other stormwater practices, less developable land consumed for stormwater treatment, and ancillary benefits (improved aesthetics and reduced urban heat island effect). These systems are especially cost effective in existing urban development where parking lot expansion is needed, but there is not sufficient space for other types of BMPs. They combine parking, stormwater infiltration, retention, and detention into one facility. See also: Cost analysis resources

Performance[edit]

Ability of Permeable Pavements to Meet Stormwater Management Objectives
BMP Water Balance Water Quality Erosion Control
Permeable pavement with no underdrain Yes Yes-size for water quality storage requirement Partial-based on available storage volume and native soil infiltration rate
Permeable pavement with underdrain Partial-based on available storage, native soil infiltration rate and if a flow restrictor is used Yes-size for water quality storage requirement Partial-based on available storage, native soil infiltration rate and if a flow restrictor is used
Permeable pavement with underdrain and impermeable liner No-some volume reduction occurs through evaporation Yes-size for water quality storage requirement Partial-based on available storage volume and if a flow restrictor is used

Water Balance[edit]

Research on the volumetric runoff reduction performance of permeable pavements have been conducted on pavements with and without an underdrain in the base. Volumetric performance improves when:

  • Native soils have high infiltration capacity.
  • Impervious surfaces draining onto the permeable pavement surface is limited or absent.
  • Underdrain is elevated above the native soil and/or a flow restrictor is installed on the underdrain or outlet storm sewer pipe.

All permeable pavements have very high surface infiltration rates when appropriately constructed and maintained. Therefore, the surface course type (e.g. permeable interlocking concrete pavers, pervious concrete, porous asphalt, etc.) is not a key factor in determining volumetric runoff reduction performance.

Volumetric runoff reduction from permeable pavements
LID Practice Location Runoff Reduction* Reference
Permeable pavement without underdrain
King City, Ontario 99%* TRCA (2008)[6]
Pennsylvania 90% Kwiatkowski et al. (2007)[7]
Connecticut 72%* Gilbert and Clausen (2006)[8]
Washington 97 to 100% Brattebo and Booth (2003)[9]
Guelph, Ontario 90% James (2002)[10]
France 97% Legret and Colandini (1999)[11]
Permeable pavement with underdrain
Montreal 26 to 98% Vaillancourt et al. (2019) [12]
Mississauga 61 to 99% CVC (2018)[13]
Seoul, Korea 30 to 65% Shafique et al. (2018) [14]
Northern Ohio 16 to 99% Winston et al. (2015) [15]
Vaughan, Ontario 45%* Van Seters and Drake (2015)[16]
North Carolina 98 to 99% Collins et al. (2008)[17]
United Kingdom 50% Jefferies (2004)[18]
United Kingdom 53 to 66% Pratt et al. (1995)[19]
Maryland 45% to 60% Schueler et al. (1987)[20]
Runoff Reduction Estimate* 85% without underdrain;

45% with underdrain

In a numerical modelling study comparing the predicted hydrologic performance of permeable interlocking concrete pavers without underdrains in New York and Hong Kong, Liu et al. (2017) found pavements performed significantly better in a relatively drier climate (e.g., New York), reducing nearly 90% of runoff volume compared to 70% in a relatively wetter climate (e.g., Hong Kong) and that runoff volume was found to be mostly governed by rainfall intensity.[21]

In Canadian and Swedish field studies, vacuum cleaning could only partially restore the surface infiltration capacity of permeable interlocking concrete pavers (PICP) with large spatial variability in the observed infiltration rates post cleaning.[22] [23] Potential options for rehabilitating clogged permeable pavements identified to date include combining pressure washing with pure vacuum sweeping to help dislodge sediment accumulated within joints of PICP and porous asphalt [24] [25] [26], and in pores of pervious concrete[27]. Drainage performance evaluations of aged pervious concrete have shown its permeability does not decline as rapidly with age as PICP, but that vacuum cleaning techniques tested to date provide variable or insignificant restorative effect[28] [29]

Water Quality[edit]

TSS - permeable pavement.JPG

Like other stormwater practices, the water quality performance of permeable pavements is closely tied to the reduction of runoff volumes through infiltration. However, permeable pavements are also very effective stormwater runoff filters. Most sediments and associated contaminants are trapped within the surface pores or gravel filled joints between the pavers. A five year study of three permeable pavement surfaces in Vaughan showed total suspended solids (TSS) concentration reductions between 88 and 89% (Van Seters and Drake, 2015). Other STEP studies in the Greater Toronto Area have displayed similar results, with only 7% of 181 permeable pavement effluent samples having TSS concentrations above 30 mg/L (median = 7 mg/L)TRCA, 2015.

TP - permeable pavement.JPG

The two box plot figures to the right show combined stormwater effluent quality results from STEP monitoring projects conducted over a 12-year time period (between 2005 and 2017) at sites within Greater Toronto Area (GTA) municipalities. Total Suspended Solid (TSS) effluent concentration results for permeable pavement practices represent the combined results from 4 sites in the GTA and a total of 296 monitored storm events. Median TSS concentration was found to be 8.95 mg/L and exceeded the Canadian Water Quality Guideline of 30 mg/L (CCME, 2002[30]) during only 12% of the 296 monitored storm events. Median TP concentration was found to be 0.04 mg/L and exceeded the Ontario Provincial Water Quality Objective (PWQO) of 0.03 mg/L (OMOEE, 1994[31]) during 62% of the 300 monitored storm events. In comparison, median TP effluent concentration for permeable pavements in the International Stormwater BMP Database was found to be 0.100 mg/L, based on 447 monitored storm events (Clary et al. 2020)[32], which is also above the Ontario PWQO of 0.03 mg/L. These results indicate that the design of permeable pavements draining to phosphorus-limited receiving waterbodies should include practices or design variations to improve Phosphorus retention. This could involve including a media filter manufactured treatment device as part of the treatment train design. An example of a design variation to improve phosphorus retention is including an additive to the permeable pavement base aggregate layer to improve phosphorus retention (Ostrom and Davis, 2019)[33].

Another group of studies of permeable pavements examines the quality of water infiltrated through soils beneath the installations. In these studies the quality of infiltrated water is used as a measure of the potential for contamination of groundwater. One such study of a permeable interlocking concrete pavement installed in a college parking lot in King City, Ontario, showed that stormwater infiltrated through a 60 cm granular reservoir and 1 metre of native soil had significantly lower concentrations of several typical parking lot contaminants relative to runoff from an adjacent asphalt surface (TRCA, 2008). These results are consistent with research on the quality of infiltrated water from permeable pavements in Washington[9] and Pennsylvannia[7]. As with all stormwater infiltration practices, risk of groundwater contamination from infiltration of runoff laden with road de-icing salt constituents (typically sodium and chloride) may be a concern in vulnerable areas for Source Water Protection. Chloride ions are extremely mobile in the soil and are readily transported by percolating water to aquifers.

Stream Channel Erosion[edit]

Permeable pavements help address stream erosion and flood flows by attenuating peak flows through temporary storage and release. A STEP study in Vaughan showed a 91% peak flow reduction due in part to flow restriction on the underdrain (Van Seters and Drake, 2015). A later study of three permeable pavements in a parking lot in Mississauga showed peak flow reductions between 39 and 84% for events greater than 25 mm (CVC, 2018).

Other Benefits[edit]

Permeable pavements (left) in Bartholdi Park, DC provides air and water to root systems contributing to healthier, longer lasting trees (Source: USCapitol)
  • Winter Performance: Snow plow and deicing costs are reduced due to rapid drainage of snow melt. Puddling on parking lots is also reduced. A two year study of PICP in Vaughan found that the PICP provides equivalent or higher levels of safety compared with asphalt when treated with de-icing products at medium (0.049 kg/m2) or low (0.024 kg/m2) salt application rates[34].
  • Urban Heat Island Effect Reduction: Porous materials have less thermal conductivity and thermal capacity than traditional impervious pavement, thereby reducing the urban heat island effect [35]. Year round measurements of asphalt and PICP surface temperatures in King City, Ontario showed asphalt temperatures above 20°C approximately 12% more often than the adjacent permeable pavers (TRCA, 2008).
  • Improved Street Tree Health: Permeable pavements installed around tree planting zones in hardscapes help provide air and water to root systems, thereby contributing to healthier, longer lasting trees that require less manual irrigation.
  • Quiet Streets: Porous asphalt surfaces absorb sound energy and dissipate air pressure around tires before any noise is generated. Tire noise is lower in loudness and pitch for a porous surface than a corresponding dense pavement [35]. Segmented pavers do not share this benefit and are generally noisier than asphalt roads.
  • LEED Credits: Permeable pavement has the potential for earning Canadian Green Building Council LEED sustainable sites credits for reducing stormwater pollution and runoff, urban heat island mitigation, and conservation of materials and resources.

External links[edit]

In our effort to make this guide as functional as possible, we have decided to include proprietary systems and links to manufacturers websites.
Inclusion of such links does not constitute endorsement by the Sustainable Technologies Evaluation Program.
Lists are ordered alphabetically; link updates are welcomed using the form below.

Pre-cast with joints[edit]

Pre-cast pervious[edit]

Cast in place[edit]

Plastic grid[edit]

Gallery[edit]

References[edit]

  1. Weiss, P., Kayhanian, M., Gulliver, J.S., Khazanovich, L. 2019. Permeable pavement in northern North American urban areas: research review and knowledge gaps. International Journal of Pavement Engineering.Vol. 20, No. 2, 143-162. https://www.tandfonline.com/doi/full/10.1080/10298436.2017.127948
  2. Weiss, P., Kayhanian, M., Gulliver, J.S., Khazanovich, L. 2019. Permeable pavement in northern North American urban areas: research review and knowledge gaps. International Journal of Pavement Engineering.Vol. 20, No. 2, 143-162. https://www.tandfonline.com/doi/full/10.1080/10298436.2017.127948
  3. Greater Vancouver Regional District (GVRD). 2005. Stormwater Source Control Design Guidelines 2005. Prepared by Lanarc Consultants Limited, Kerr Wood Leidal Associates Limited and Goya Ngan.
  4. Pennsylvania Department of Environmental Protection (PDEP). 2006. Pennsylvania Stormwater Best Management Practices Manual. Prepared by Cahill Associates Inc., Harrisburg, PA.
  5. City of Portland. 2004. Portland Stormwater Management Manual. Prepared by the Bureau of Environmental Services (BES). Portland, OR.
  6. TRCA. 2008. Permeable Pavement and Bioretention Swale Demonstration Project. Seneca College, King City, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf
  7. 7.0 7.1 Kwiatkowski, M., Welker, A.L., Traver, R.G., Vanacore, M., Ladd. T. 2007. Evaluation of an infiltration best management practice utilizing pervious concrete. Journal of the American Water Resources Association. Vol. 43. No. 5. pp. 1208-1222.
  8. Gilbert, J. and J. Clausen. 2006. Stormwater runoff quality and quantity from asphalt, paver and crushed stone driveways in Connecticut. Water Research 40: 826-832.
  9. 9.0 9.1 Brattebo, B. and D. Booth. 2003. Long term stormwater quantity and quality performance of permeable pavement systems. Water Research 37(18): 4369-4376
  10. James, W. 2002. Green Roads: Research into Permeable Pavers. Stormwater. March/April.
  11. Legret, M and V. Colandani. 1999. Effects of a porous pavement structure with a reservoir structure on runoff water: water quality and fate of metals. Water Science and Technology. 39(2): 111-117
  12. Vaillancourt, C., Duchesne, S., & Pelletier, G. 2019. Hydrologic performance of permeable pavement as an adaptive measure in urban areas: case studies near Montreal, Canada. Journal of Hydrologic Engineering, 24(8), 05019020.
  13. CVC. 2018. Case Study: Monitoring Low Impact Development at the IMAX demonstration site. February, 2018. https://cvc.ca/wp-content/uploads/2018/05/IMAX-Low-Impact-Development-Monitoring-Case-Study-may-24.pdf
  14. Shafique, M., Kim, R. and Kyung-Ho, K., 2018. Rainfall runoff mitigation by retrofitted permeable pavement in an urban area. Sustainability, 10(4), p.1231.
  15. Winston, R. J., Dorsey, J. D., & Hunt, W. F. (2015). Monitoring the performance of bioretention and permeable pavement stormwater controls in Northern Ohio: hydrology, water quality, and maintenance needs. Chagrin River Watershed Partners. Inc. under NOAA award No. NA09NOS4190153.
  16. Van Seters, T. and Drake, J. 2015. Five Year Performance Evaluation of Permeable Pavements. Kortright, Vaughan - Final Draft. December 2015. © Toronto and Region Conservation Authority. https://sustainabletechnologies.ca/app/uploads/2016/02/KPP-Ext_FinalReport_Dec2015.pdf
  17. Collins, K., W. Hunt and J. Hathaway. 2008. Hydrologic comparison of four types of permeable pavement and standard asphalt in eastern North Carolina. Journal of Hydrologic Engineering.
  18. Jefferies, C. 2004. Sustainable drainage systems in Scotland: the monitoring programme. Scottish Universities SUDS Monitoring Project. Dundee, Scotland
  19. Pratt, C.J., Mantle, J.D.G., Schofield, P.A. 1995. UK research into the performance of permeable pavement reservoir structures in controlling stormwater discharge quantity and quality. Water Science Technology. Vol. 32. No. 1. pp. 63-69.
  20. Schueler, T. 1987. Controlling urban runoff: a practical manual for planning and designing urban BMPs. Metropolitan Washington Council of Governments. Washington, DC.
  21. Liu, C.Y., Chui, T.F.M. 2017. Factors Influencing Stormwater Mitigation in Permeable Pavement. Water. 9, 988. https://www.mdpi.com/2073-4441/9/12/988
  22. Drake, J., Bradford, A. 2013. Assessing the Potential for Restoration of Surface Permeability for Permeable Pavements Through Maintenance. Water Science and Technology. 2013, 68, 1950-1958. https://pubmed.ncbi.nlm.nih.gov/24225094/
  23. Al-Rubaei, A.M., Stenglein, A.L., Viklander, M., Blecken, G.T. 2013. Long-Term Hydraulic Performance of Porous Asphalt Pavements in Northern Sweden. Journal of Irrigation and Drainage Engineering. 39 (6) June 2013. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29IR.1943-4774.0000569
  24. Seghal, K.S., Drake, J., Van Seters, T., Vander Linden, W.K. 2018. Improving Restorative Maintenance Practices for Mature Permeable Interlocking Concrete Pavements. Water. 10 (11), 1588. https://www.mdpi.com/2073-4441/10/11/1588
  25. Winston, R.J., Al-Rubaei, A.M., Blecken, G.T., Viklander, M., Hunt, W.F. 2016. Maintenance measures for preservation and recovery of permeable pavement surface infiltration rate – The effects of street sweeping, vacuum cleaning, high pressure washing and milling. Journal of Environmental Management. 169(2016):132-144. https://www.sciencedirect.com/science/article/pii/S0301479715304412c
  26. Al-Rubaei, A.M., et al., 2013. Long-term hydraulic performance of porous asphalt pavements in Northern Sweden. Journal of Irrigation and Drainage Engineering, 139 (6), 499–505. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29IR.1943-4774.0000569
  27. Chopra, M., et al., 2010. Effect of Rejuvenation Methods on the Infiltration Rates of Pervious Concrete Pavements. Journal of Hydrologic Engineering, 15 (6), 426–433. https://pennstate.pure.elsevier.com/en/publications/effect-of-rejuvenation-methods-on-the-infiltration-rates-of-pervi
  28. Drake, J., Bradford, A. 2013. Assessing the Potential for Restoration of Surface Permeability for Permeable Pavements Through Maintenance. Water Science and Technology. 2013, 68, 1950-1958. https://pubmed.ncbi.nlm.nih.gov/24225094/
  29. Sustainable Technologies Evaluation Program (STEP). 2019. Permeable Pavements Maintenance. Technical Brief. October 2019. https://sustainabletechnologies.ca/app/uploads/2019/10/PDF-PP-maintenance-tech-brief_Oct2019.pdf
  30. Canadian Council of Ministers of the Environment (CCME). 2002. Canadian water quality guidelines for the protection of aquatic life: Total particulate matter. In: Canadian Environmental Quality Guidelines, Canadian Council of Ministers of the Environment, Winnipeg
  31. Ontario Ministry of Environment and Energy (OMOEE), 1994. Policies, Guidelines and Provincial Water Quality Objectives of the Ministry of Environment and Energy. Queen’s Printer for Ontario. Toronto, ON.
  32. Clary, J., Jones, J., Leisenring, M., Hobson, P., Strecker, E. 2020. International Stormwater BMP Database: 2020 Summary Statistics. The Water Research Foundation. [https://www.waterrf.org/system/files/resource/2020-11/DRPT-4968_0.pdf
  33. Ostrom, T.K. and Davis, A.P. 2019. Evaluation of an enhanced treatment media and permeable pavement base to remove stormwater nitrogen, phosphorus, and metals under simulated rainfall. Water research, 166, p.115071.
  34. Marvin, J., Scott, J., Van Seters, T., Bowers, B., Drake, J. Winter Maintenance of Permeable Interlocking Concrete Pavement: Evaluating Opportunities to Reduce Road Salt Pollution and Improve Winter Safety, submitted to Transportation Research Record May 2020, under review
  35. 35.0 35.1 Ferguson, B.K. 2005. Porous Pavements. Integrative Studies in Water Management and Land Development. Taylor and Francis: New York.