Editing Permeable paving (section)

== Disadvantages ==

=== Runoff volumes ===
Permeable pavements are designed to replace Effective Impervious Areas (EIAs), but can be used, in some cases, to manage [[stormwater]] from other impervious surfaces on site.<ref>{{Citation |last=Fassman |first=Elizabeth |year=2010 |title=Urban Runoff Mitigation by a Permeable Pavement System over Impermeable Soils |journal=Journal of Hydrologic Engineering |volume=15 |issue=6 |pages=475–485 |publisher=American Society of Civil Engineers |doi=10.1061/(ASCE)HE.1943-5584.0000238 |url=https://ascelibrary.org/doi/full/10.1061/%28ASCE%29HE.1943-5584.0000238 |access-date=2020-12-08|hdl=10983/24857 |hdl-access=free }}</ref> Use of this technique must be part of an overall on site management system for stormwater, and is not a replacement for other techniques.

During large storm events, the water table below the porous pavement can rise to a higher level, preventing the precipitation from being absorbed into the ground. Some additional water is stored in the open graded or crushed drain rock base, and remains until the subgrade can absorb the water. For clay-based soils, or other low to 'non'-draining soils, it is important to increase the depth of the crushed drain rock base to allow additional capacity for the water as it waits to be infiltrated.

=== Pollutant load ===
Runoff across some land uses may become contaminated, where pollutant concentrations exceed those typically found in stormwater. These "hot spots" include commercial [[Plant nursery|plant nurseries]], [[recycling]] facilities, [[Filling station|fueling stations]], industrial storage, [[marina]]s, some outdoor [[Loading dock|loading facilities]], public works yards, hazardous materials generators (if containers are exposed to rainfall), vehicle service, washing, and maintenance areas, and steam cleaning facilities. Since porous pavement is an infiltration practice, it should not be applied at stormwater hot spots due to the potential for groundwater contamination. All contaminated runoff should be prevented from entering municipal storm drain systems by using [[Best management practice for water pollution|best management practices]] (BMPs) for the specific industry or activity.<ref>{{Cite web|date=2007
| author= Capital Regional District, British Columbia 
|title=Regulating Stormwater Discharges
|url=https://www.crd.bc.ca/watersheds/regulations.htm|access-date=2023-01-29|website=www.crd.bc.ca| archive-url= https://web.archive.org/web/20070712104515/https://www.crd.bc.ca/watersheds/regulations.htm 
| archive-date= 2007-07-12 
|language=en}}</ref>

=== Weight and traffic volumes ===
Reference sources differ on whether low or medium traffic volumes and weights are appropriate for porous pavements due to the variety of physical properties of each system. For example, around truck loading docks and areas of high commercial traffic, porous pavement is sometimes cited as being inappropriate. However, given the variability of products available, the growing number of existing installations in North America and targeted research by both manufacturers and user agencies, the range of accepted applications seems to be expanding.<ref>{{Citation |last=Ajamu |first=S.O. |year=2012 |title=Evaluation of Structural Performance of Pervious Concrete in Construction |publisher=International Journal of Engineering and Technology |url=https://www.researchgate.net/publication/271486843 |access-date=2020-12-06}}</ref> Some concrete paver companies have developed products specifically for industrial applications. Working examples exist at fire halls, busy retail complex parking lots, and on public and private roads, including intersections in parts of North America with quite severe winter conditions.

=== Siting ===
Permeable pavements may not be appropriate when land surrounding or draining into the pavement exceeds a 20 percent slope, where pavement is down slope from buildings or where foundations have piped drainage at their footers. The key is to ensure that drainage from other parts of a site is intercepted and dealt with separately rather than being directed onto permeable surfaces.{{Citation needed|date=December 2020}}

=== Climate ===
Cold climates may present special challenges. Road salt contains chlorides that could migrate through the porous pavement into groundwater. Snow plow blades could catch block edges of concrete pavers or other block installations, damaging surfaces and creating [[potholes]]. Sand cannot be used for snow and ice control on porous surfaces because it will plug the pores and reduce permeability.<ref>{{Citation |last=van Duin |first=B. |year=2008 |title=Characterization of Long-Term Solids Removal and Clogging Processes in Two Types of Permeable Pavement under Cold Climate Conditions|publisher=11th International Conference on Urban Drainage |page=09|url= https://www.researchgate.net/publication/228513692|access-date=2020-12-13}}</ref> Although there are design modifications to reduce the risks, infiltrating runoff may freeze below the pavement, causing frost heave. Another issue is [[spall]]ing damage, which exclusively occurs on porous concrete pavement from salt application during the winter season. Thus porous paving is suggested for warmer climates. However, other materials have proven to be effective, even lowering winter maintenance costs by preserving salt in the pavement itself. This also reduces the amount of storm water runoff that is contaminated with salt chlorides.<ref>{{Cite news|url=http://stormwater.wef.org/2012/01/porous-pavement-performance-in-cold-climates/|title=Porous Pavement Performance in Cold Climates - The Stormwater Report|date=2012-01-05|work=The Stormwater Report|access-date=2018-03-23|language=en-US}}</ref> Pervious concrete and asphalt designed to reduce frost heave and spalling damage has been used successfully in [[Norway]] and [[New Hampshire]].<ref>{{Citation |last=Drake |first=Jennifer |year=2014 |title=Hydrologic Performance of Three Partial-Infiltration Permeable Pavements in a Cold Climate over Low Permeability Soil |journal=Journal of Hydrologic Engineering |volume=19 |issue=9 |publisher=American Society of Civil Engineers Library |doi=10.1061/(ASCE)HE.1943-5584.0000943 |s2cid=128619797 |url=https://ascelibrary.org/doi/full/10.1061/%28ASCE%29HE.1943-5584.0000943 |access-date=2020-12-13}}</ref> Furthermore, experience suggests that preventive measures with rapid drainage below porous surfaces be taken in order to increase the rate of snow melt above ground.

=== Cost ===
It can be difficult to compare cost impacts between conventional impervious surfaces and permeable surfaces given the variables such as lifespan, geographic location, type of permeable paving system and site specific factors. Some estimates put the cost of permeable paving at about one third more expensive than that of conventional impervious paving.<ref>{{Citation |last=Wright |first=G.B. |year=2011 |title=Urban creep in Scotland: stakeholder perceptions, quantification and cost implications of permeable solutions |journal=Water and Environment Journal |volume=25 |issue=4 |pages=513–521 |doi=10.1111/j.1747-6593.2010.00247.x |location=Edinburgh |bibcode=2011WaEnJ..25..513W |s2cid=109698597 |url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1747-6593.2010.00247.x |access-date=2020-12-13}}</ref> Using permeable paving, however, can reduce the cost of providing larger or more stormwater [[Best management practice for water pollution|BMPs]] on site, and these savings should be factored into any cost analysis. In addition, the off-site environmental impact costs of not reducing on-site stormwater volumes and pollution have historically been ignored or assigned to other groups (local government parks, public works and environmental restoration budgets, fisheries losses, etc.). Permeable paving systems, specifically pervious concrete pavers, have shown significant cost benefits after a [[Life Cycle Assessment]] was performed, as the reduction in total weight of material needed for each unit is reduced by nature of the porous design.<ref>{{Citation |last=Yuan |first=Xueliang |year=2018 |title=Environmental and economic impacts assessment of concrete pavement brick and permeable brick production process - A case study in China |journal=Journal of Cleaner Production |volume=171 |publisher=Journal of Cleaner Production Vol. 171 |pages= 198–208 |doi=10.1016/j.jclepro.2017.10.037 |bibcode=2018JCPro.171..198Y |url=https://www.sciencedirect.com/science/article/pii/S0959652617323284 |access-date=2020-12-13}}</ref>

=== Longevity and maintenance ===
Permeable paving systems, especially those with porous surfaces, require maintenance in order to keep the pores clear of fine aggregates as to not hinder the systems ability to infiltrate stormwater. The frequency of cleaning is again dependent on many site specific factors, such as runoff volume, neighboring sites and climate. Often, cleaning of permeable paving systems is done by [[Suction excavator|suction excavators]], which are alternatively used for excavation in sensitive areas and therefore are becoming increasingly common. If maintenance is not carried out on a regular basis, the porous pavements can begin to function more like impervious surfaces.<ref name="Scholz2007" /> With more advanced paving systems the levels of maintenance needed can be greatly decreased, [[#Bound recycled glass porous pavement|elastomerically bound glass pavements]] requires less maintenance than regular concrete paving as the glass bound pavement has 50% more void space.

Plastic grid systems, if selected and installed correctly, are becoming more and more popular with local government maintenance personnel owing to the reduction in maintenance efforts: reduced gravel migration and weed suppression in public park settings.

Some permeable paving products are prone to damage from misuse, such as drivers who tear up patches of plastic & gravel grid systems by "joy riding" on remote parking lots at night. The damage is not difficult to repair but can look unsightly in the meantime. Grass pavers require supplemental watering in the first year to establish the vegetation, otherwise they may need to be re-seeded. Regional climate also means that most grass applications will go dormant during the dry season. While brown vegetation is only a matter of aesthetics, it can influence public support for this type of permeable paving.

Traditional permeable concrete paving bricks tend to lose their color in relatively short time which can be costly to replace or clean and is mainly due to the problem of [[efflorescence]].