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→Water Quality
{{textbox|Permeable paving is ideal for:
{{textbox|Permeable paving is ideal for:
*Sites with limited space for other surface stormwater BMPs
*Sites with limited space for other surface stormwater BMPs
*Projects such as low traffic roads, parking lots, driveways, pedestrian plazas and walkways}}
*Projects such as low traffic roads, parking lots, driveways, pedestrian plazas and walkways
*Locations where increased skid resistance and melting rate of snow and ice, and decreased demand for de-icing salt application during winter are desireable}}
'''The fundamental components of a permeable paving system are:'''
'''The fundamental components of a permeable paving system are:'''
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:
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.
* Native soils have high infiltration capacity.
* Impervious surface draining onto the permeable pavement surface is limited or absent.
* 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.
* 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.
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"
{|class="wikitable"
!'''LID Practice'''
!'''LID Practice'''
!'''Location'''
!'''Location'''
!'''<u><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></u>'''
!'''<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'''
!'''Reference'''
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|style="text-align: center;" |King City, Ontario
|style="text-align: center;" |King City, Ontario
|style="text-align: center;" |'''<u><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></u>'''
|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;" |<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>
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|style="text-align: center;" |Connecticut
|style="text-align: center;" |Connecticut
|style="text-align: center;" |'''<u><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></u>'''
|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,
|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>
paver and crushed stone driveways in Connecticut. Water Research 40: 826-832.</ref>
|-
|-
|style="text-align: center;" |Vaughan, Ontario
|style="text-align: center;" |Vaughan, Ontario
|style="text-align: center;" |'''<u><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></u>'''
|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;" |<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>
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|}
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>
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===
===Water Quality===
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].
[[File:Permeable_pavement_TSS.png|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>
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 lands designated as source protection areas. Chloride ions are extremely mobile in the soil and are readily transported by percolating water to aquifers.
<br>
[[File:Permeable_pavement_TP.png|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. 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, similar to STEP [[Bioretention#Water_Quality| Bioretention performance]] results. In comparison, median TSS effluent concentration for permeable pavements in the International Stormwater BMP Database was found to be 22.0 mg/L, based on 402 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 below the Canadian Water Quality Guideline, but considerably higher than results from STEP studies. 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 365 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 sorption media filter manufactured treatment device as part of the treatment train design. Another example of a design variation to improve phosphorus retention is including an [[Additives| 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===
===Stream Channel Erosion===