LID opportunities at municipal facilities

Each distinct area of your site can be a source for runoff (referred to as a ‘source area’). Target these areas when introducing LID in your municipal facility.

Targeting hard surfaces

Municipal facilities have large parking lots to accommodate public demand. Parking areas represent the most significant source of pollutant loading from these sites and contribute significantly to increased runoff rates in comparison to natural conditions. Parking lots include areas for parking, areas for driving, and islands or landscape planters used for calming traffic, directing vehicles and improving pedestrian safety.

LID practices can be incorporated into all areas of a parking lot. You can use bioretention in parking lot islands and along the lot perimeter. Standard curbs with small cut-outs (called ‘curb cuts’) can allow water to easily enter biorentention practices while also preventing damage from cars.

Bioswales are excellent options in parking lot islands or along lot perimeters. Parking lots with existing perimeter ditching are ideal for bioswale integration due to their extended continuous flow path.

Prefabricated modular infiltration chambers are gaining acceptance for their easy integration with parking lot functions. These subsurface systems are typically installed over a coarse granular reservoir to provide storage and allow infiltration into native soils. Infiltration chambers under conventional asphalt system work well on sites where parking demand and other site uses do not allow space for a stormwater feature.

Stormwater planters beautify this building entrance. The entrance receives a lot of traffic during business hours, making it an ideal location for a high visibility LID practice. (Source: Aquafor Beech)

Permeable paving is also an option in large municipal parking lots. Pervious concrete, permeable interlocking concrete pavers, and porous asphalt can detain stormwater and increase infiltration.

Municipal facilities provide excellent opportunities for integrating rainwater harvesting systems. Rainwater harvesting systems have two requirements: an area for catchment of relatively clean runoff and a nearby demand for water usage. Municipal facilities often have large rooftop areas producing relatively clean runoff. Installing a cistern internal to the building or buried adjacent to the building can provide a sustainable source of water for site irrigation needs for landscaped areas, recreational fields and indoor use (e.g. flushing toilets and urinals).

Targeting highly visible areas

If your LID integration strategy involves highly visible LID practices, consider targeting areas with high-volume pedestrian traffic. This can help promote LID's visibility among the public and increase support for future LID projects.

Targeting pollution prevention opportunities

On some municipal sites, pollution prevention techniques and strategies outlined in Chapter 2 are the best approaches to mitigating the environmental impact of your site. Retrofits of municipal works yards require a different approach than other land uses discussed in this guide. Works yards do not offer substantial opportunities for public interaction. LID retrofits should focus primarily on reducing pollution generated on-site. Fuelling stations, waste storage areas, truck washing stations, sand and salt storage, staging areas and water conveyance features are ideal for pollution prevention.

Source areas

The best LID option for your site will depend what source areas are present. Types of source areas include:

Source areas within a typical community centre.

• Active use areas
• Passive use areas
• Pedestrian walkways
• Internal driveways
• Parking lots

On municipal sites, pollution prevention is often associated with changes to operations and maintenance practices and has not been included in the table below.

LID opportunities in municipal buildings
(** = Common, * = Possible, o = Unusual)

Source area	Permeable pavement	Bioretention	Enhanced grass swales / bioswales	Green roofs	Soakaways and infiltration trenches	Perforated pipe systems	Rainwater harvesting	Landscape alternatives	Prefabricated modules	Pollution prevention
Active use area	**	**	**	o	**	*	o	*	o	**
Passive use area	o	**	*	o	**	**	o	**	**	**
Pedestrian walkway	**	**	**	o	**	*	o	*	*	**
Internal driveway	**	**	**	o	**	**	o	o	**	**
Parking lot	**	**	**	o	**	**	o	o	**	**
Building	*	*	*	**	**	*	**	o	o	**

Large-scale projects require significantly more effort, budget, and staff than small-scale projects. Large-scale LID retrofits include:

• Bioretention
• Enhanced grass swales
• Bioswales
• Perforated pipe systems
• Permeable pavement
• Soakaways
• Infiltration chambers
• Rainwater harvesting (excluding rain barrels)
• Prefabricated modules
• Green roofs

Consider a large-scale project if your municipality or department would like to be a leader in sustainability. Large-scale projects are often highly visible and attract more public attention. Large-scale projects may also be the only solution to site-specific challenges. For example, if site infrastructure is at risk as a result of urban flooding, LID practices that detain large volumes of runoff and encourage infiltration are the most viable LID options. Before starting a large-scale retrofit project, consider the following distinctions that set these retrofits apart from small-scale projects.

Integration with capital works programs

Most large-scale LID retrofits must function with existing site infrastructure, such as storm sewers, catch basins, and pavement systems. The construction of large-scale LID practices often requires these systems to be removed, exposed, or replaced. The best time for this type of project to occur is when an infrastructure replacement or rehabilitation project is already planned.

When LID retrofits are worked into other construction projects, such as parking lot repaving, or grading or drainage improvements, there can be substantial cost savings. Whether big or small, every municipality spends relatively large sums of money and substantial time planning for major capital projects. This includes redevelopment of public building and spaces. Many communities who have undertaken retrofits recognize that even if a relatively small portion of the project funds goes towards LID retrofits, they can retrofit large impervious surfaces and avoid new stormwater management infrastructure projects17.

Municipal facility rehabilitation is typically forecast well in advance of the project. Parking lot paving is typically worked into municipal budgets based on expected life cycle and observed wear. As such, funds may be set aside prior to the project planning phases. Long-term forecast budgets may also be available for site revitalizations or expansions. These budget forecasts provide opportunities to compare the capital and life-cycle costs and benefits of the conventional construction project and LID retrofit.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

Tank used to store rainwater (typically roof runoff) for later use.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

Ground depression acting as a flow control and water treatment structure, that is normally dry.

Natural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.