Difference between revisions of "Structural practices summary"

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#REDIRECT [[Site considerations]]
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|+  <h3>'''LID Design Guide Detail'''</h3>
 
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!style="background: cyan; color: black"|
 
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!style="background: cyan; color: black"|Available Space
 
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!style="background: cyan; color: black"|Site Topography
 
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!style="background: cyan; color: black"|Available Head
 
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!style="background: cyan; color: black"|Soils
 
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!style="background: cyan; color: black"|Pollution Hot Spot Runoff
 
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!style="background: cyan; color: black"|Setbacks from Buildings
 
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!style="background: cyan; color: black "|Proximity to Underground Utilities
 
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!style="background: cyan; color: black"|Drainage Area and Runoff Volume
 
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!style="background: cyan; color: black"|Wellhead Protection
 
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!style="background: cyan; color: black"|Water Table
 
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!style="background: cyan; color: black"|Overhead Wires
 
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!style="background: cyan; color: black"|Flow Path Length Across Impermeable Surface
 
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!style="background: cyan; color: black"|Winter Operations
 
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!style="background: cyan; color: black"|Vehicle Loading
 
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!style="background: cyan; color: black"|Structural Requirements
 
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!style="background: cyan; color: black"|Roof Slope
 
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!'''Roof Downspout Disconnection'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Simple downspout disconnection requires a minimum flow path length across the pervious area (at least 5 metres) and suitable soil conditions. If the flow path length is less than 5 metres and soils are hydrologic soil group (HSG) C or D, roof downspouts should be directed to another LID practice such as a rainwater harvesting system, soakaway, swale, bioretention area or perforated pipe system.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Disconnected downspouts should discharge to a gradual slope that conveys runoff away from the building. The slope should be between 1% and 5%. Grading should discourage flow from reconnecting with adjacent impervious surfaces
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|If the infiltration rate of soils in the pervious area is less than 15 mm/hr, they should be tilled to a depth of 300 mm and amended with compost to achieve an organic content in the range of 8 to 15% by weight or 30 to 40% by volume.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Downspout disconnection can be used where land uses or activities at ground-level have the potential to generate highly contaminated runoff as long as the roof runoff is kept separate from runoff from groundlevel impervious surfaces
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|For simple downspout disconnection the roof drainage area should not be greater than 100 square metres
 
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!'''Soakaways, Infiltration Trenches and Chambers'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Facilities cannot be located on natural slopes greater than 15%
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Soakaways, infiltration trenches and chambers can be constructed over any soil type, but hydrologic soil group A or B soils are best for achieving water balance and channel erosion control objectives. If possible, facilities should be located in portions of the site with the highest native soil infiltration rates.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated by soakaways, infiltration trenches or chambers.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Facilities should be setback a minimum of four (4) metres from building foundations
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Local utility design guidance should be consulted to define the horizontal and vertical offsets. Generally, requirements for underground utilities passing near the practice will be no different than for utilities in other pervious areas
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|They can be designed with an impervious drainage area to treatment facility area ratio of between 5:1 and 20:1. A maximum ratio of 10:1 is recommended for facilities receiving road or parking lot runoff
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Facilities receiving road or parking lot runoff should not be located within two (2) year time-of-travel wellhead protection areas
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|The bottom of the facility should be vertically separated by one (1) metre from the seasonally high water table or top of bedrock elevation
 
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!'''Bioretention'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Designers should reserve open areas of about 10 to 20% of the size of the contributing drainage area. These are areas that would be typically set aside for landscaping. More space is required for designs with soft and shallow side slopes than those with hard, vertical edges.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Bioretention is best applied when contributing slopes are between 1 to 5%. Ideally, the proposed treatment area will be located in a natural depression to minimize excavation
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|If an underdrain is used, then 1 to 1.5 metres elevation difference is needed between the inflow point and the downstream storm drain invert. This is generally not a constraint due to the standard depth of storm drains. For bioretention without an underdrain, the design will only require enough elevation difference to move large event flows through the overflow or bypass without generating a backflow or flooding problem.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Bioretention can be located over any soil type, but hydrologic soil group A and B soils are best for achieving water balance benefits. Facilities should be located in portions of the site with the highest native soil infiltration rates. Where infiltration rates are less than 15 mm/hr (hydraulic conductivity less than 1x10-6 cm/s) an underdrain is required.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated by bioretention facilities designed for full or partial infiltration. Facilities designed with an impermeable liner (filtration only facilities) can be used to treat runoff from pollution hot spots
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|If an impermeable liner is used, no setback is needed. If not, a four (4) metre setback from buildings should be applied
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Designers should consult local utility design guidance for the horizontal and vertical clearances required between storm drains, ditches, and surface water bodies. It is feasible for on-site utilities to cross linear bioretention; however, this may require design of special protection for the utility. For road right-of-way applications, care should be taken to provide utilityspecific horizontal and vertical offsets
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Bioretention cells work best for smaller drainage areas, as flow distribution over the filter bed is easier to achieve. Typical drainage areas are between 100 m2 to 0.5 hectares. The maximum recommended drainage area to one bioretention facility is approximately 0.8 hectares (Davis et al., 2009). Ideally, bioretention should be used as a source control for small drainage areas and not as an end of pipe control. Typical ratios of impervious drainage area to bioretention cell area range from 5:1 to 15:1.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Facilities receiving road or parking lot runoff should not be located within two (2) year time-of-travel wellhead protection areas.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Bioretention should be separated from the seasonally high water table by a minimum of one (1) metre to ensure groundwater does not intersect the filter bed
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Designers should also check whether maximum future tree canopy height in the bioretention area will not interfere with existing overhead phone and power lines
 
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!'''Vegetated Filter Strips'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|The flow path length across the vegetated filter strip should be at least 5 metres to provide substantial water quality benefits (Barrett et al., 2004). Vegetated filter strips incorporated as pretreatment to another water quality best management practice may be designed with shorter flow path lengths.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Filter strips are best used to treat runoff from ground-level impervious surfaces that generate sheet flow (e.g., roads and parking areas). The recommended filter strip slope is between 1% to 5%
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Filter strips are a suitable practice on all soil types. If soils are highly compacted, or of such low fertility that vegetation cannot become established, they should be tilled to a depth of 300 mm and amended with compost to achieve an organic content of 8 to 15% by weight or 30 to 40% by volume
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated by vegetated filter strips.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Filter strips should only be used where depth to the seasonally high water table is at least one (1) metre below the surface
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|A limiting design factor is that the maximum flow path length across the impermeable surface should be less than 25 metres
 
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!'''Permeable Pavement'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|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
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Systems located in low permeability soils with an infiltration rate of less than 15 mm/hr, require incorporation of a perforated pipe underdrain
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated by permeable pavement
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|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.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|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.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|In general, the impervious area treated should not exceed 1.2 times the area of permeable pavement which receives the runoff
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Permeable pavement should not be used for road or parking surfaces within two (2) year time-of-travel wellhead protection areas
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|The base of permeable pavement stone reservoir should be at least one (1) metre above the seasonally high water table or bedrock elevation
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|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
 
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!'''Enhanced Grass Swales'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Grass swales usually consume about 5 to 15 percent of their contributing drainage area. A width of at least 2 metres is needed
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Site topography constrains the application of grass swales. Longitudinal slopes between 0.5 and 6% are allowable. This prevents ponding while providing residence time and preventing erosion. On slopes steeper than 3%, check dams should be used
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Grass swales can be applied on sites with any type of soils
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated by grass swales.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Enhanced grass swales should be located a minimum of four (4) metres from building foundations to prevent water damage.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Utilities running parallel to the grass swale should be offset from the centerline of the swale. Underground utilities below the bottom of the swale are not a problem.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|The conveyance capacity should match the drainage area. Sheet flow to the grass swale is preferable. If drainage areas are greater than 2 hectares, high discharge through the swale may not allow for filtering and infiltration, and may create erosive conditions. Typical ratios of impervious drainage area to swale area range from 5:1 to 10:1.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Designers should ensure that the bottom of the swale is separated from the seasonally high water table or top of bedrock elevation by at least one (1) metre
 
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!'''Dry Swales'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Dry swale footprints are approximately 5 to 15% of their contributing drainage area. When applied to residential areas, the swale segments between driveways should be at least 5 metres in length.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Dry swales should be designed with longitudinal slopes generally ranging from 0.5 to 4%, and no greater than 6% (PDEP, 2006). On slopes steeper than 3%, check dams should be used.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Dry swales can be located over any soil type, but hydrologic soil group A and B soils are best for achieving water balance benefits. Facilities should be located in portions of the site with the highest native soil infiltration rates. Where infiltration rates are less than 15 mm/hr, an underdrain is required
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated dry swales designed for full or partial infiltration. Facilities designed with an impermeable liner can be used to treat runoff from pollution hot spots
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Dry swales should be setback four (4) metres from building foundations. When located within 3 metres of building foundations, an impermeable liner and perforated pipe underdrain system should be used.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Designers should consult local utility design guidance for the horizontal and vertical clearance between storm drains, ditches, and surface water bodies. It is feasible for on-site utilities to cross dry swales; however, this may require the use of special protection (e.g., double-casing) for the subject utility line.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Dry swales typically treat drainage areas of less than two hectares. If dry swales are used to treat larger areas, the velocity through the swale becomes too great to treat runoff or prevent erosion. Typical ratios of impervious drainage area to dry swale area range from 5:1 to 15:1.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Facilities receiving road or parking lot runoff should not be located within two (2) year time-of-travel wellhead protection areas.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Designers should ensure that the bottom of the swale is separated from the seasonally high water table or top of bedrock elevation by at least one (1) metre to prevent groundwater contamination
 
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!'''Perforated Pipe'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Perforated pipe systems should be located below shoulders of roadways, pervious boulevards or grass swales where they can be readily excavated for servicing. An adequate subsurface area outside of the four (4) metre setback from building foundations and suitable distance from other underground utilities must be available
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Systems cannot be located on natural slopes greater than 15%. The gravel bed should be designed with gentle slopes between 0.5 to 1%
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Underlying native soil conditions do not constrain the use of perforated pipe systems but greatly influence their runoff reduction performance
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|To protect groundwater from possible contamination, source areas where land uses or human activities have the potential to generate highly contaminated runoff should not be treated by perforated pipe systems.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Facilities should be setback a minimum of four (4) metres from building foundations.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Local utility design guidance should be consulted to define the horizontal and vertical offsets. Generally, requirements for underground utilities passing near the practice will be no different than for utilities in other pervious areas
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Systems typically receive foundation drain water and runoff from roofs, walkways, roads and parking lots from multiple lots. They are typically designed with an impervious drainage area to treatment facility area ratio of between 5:1 to 10:1
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Facilities receiving road or parking lot runoff should not be located within two (2) year time-of-travel wellhead protection areas.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Designers should ensure that the bottom of the gravel bed is separated from the seasonally high water table or top of bedrock elevation by at least one (1) metre to prevent groundwater contamination
 
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!'''Green Roofs'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Green roofs are designed to capture precipitation falling directly onto the roof surface. They are not designed to receive runoff diverted from other source areas.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Load bearing capacity of the building structure and selected roof deck need to be sufficient to support the weight of the soil, vegetation and accumulated water or snow, and may also need to support pedestrians, concrete pavers, etc.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Green roofs may be installed on roofs with slopes up to 10%
 
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!'''Rainwater Harvesting'''
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Space limitations are rarely a concern with rainwater harvesting if considered during building design and site layout.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Site topography influences the placement of storage tanks and the design of the rainwater conveyance and overflow systems.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|The needed head depends on intended use of the water. For residential landscaping uses, the rain barrel or cistern should be sited upgradient of the landscaping areas or on a raised stand. Gravity-fed operations may also be used for indoor residential uses, such as laundry, that do not require high water pressure. For larger-scale landscaping operations, locating a cistern on the roof or uppermost floor may be the most cost efficient way to provide water pressure.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Cisterns should be placed on or in native, rather than fill, soils. If placement on fill slopes is necessary, a geotechnical analysis is needed. Underground tanks and the pipes conveying rainwater to and from them, including overflow systems, should either be located below the local frost penetration depth (MTO, 2005), or insulated to prevent freezing during winter
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Rainwater harvesting systems can be an effective stormwater BMP for roof runoff at sites where land uses or activities at groundlevel have the potential to generate highly contaminated runoff
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Rainwater harvesting system overflow devices should be designed to avoid causing ponding or soil saturation within three (3) metres of building foundations
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|The presence of underground utilities (e.g., water supply pipes, sanitary sewers, natural gas pipes, cable conduits, etc.), may constrain the location of underground rainwater storage tanks.
 
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!<span style="font-size:80%;background:white; color: black;text-align: left"|Underground cisterns should be placed in areas without vehicular traffic. Tanks under roadways, parking lots, or driveways must be designed for the live loads from heavy trucks, a requirement that could significantly increase construction costs.
 
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