LID site criteria and constraints

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Installation type Depth to high water or bedrock (m)[1] Typical ratio of
ImperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.
to Treatment Facility Area
Native soilThe natural ground material characteristic of or existing by virtue of geographic origin. infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. (mm/hr)[2] Head (m)[3] Space % [4] Slope % [5] Applicable in pollution hotspots [6] Set backs Water tableThe upper surface of the zone of saturation, except where the surface is formed by an impermeable body.Subsurface water level which is defined by the level below which all the spaces in the soil are filled with water; The entire region below the water table is called the saturated zone. separation[7] Wellhead protection area[8]
Rain Barrel Not applicable 5 to 50 m2 Not applicable 1 0 NA Yes None No None
Cistern Not applicable 1:1 Not applicable 0 0 0 Yes None No None
Roof downspout disconnection Not applicable 5 to 100 m2 Amend if < 15 mm/hr 0.5 5 to 20 1 to 5 Yes Building Foundation No None
SoakawayA pit into which liquids may flow and then percolate slowly into the subsoil.An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits., infiltration trench or chamber 1 5:1 to 20:1 Not a constraint 1 to 2 0 to 1 <15 % No 4m- Building Foundation
Underground Utilities, Trees,
Drinking Water Wellhead
Protection Areas
Yes 2 yr
Bioretention 1 5:1 to 15:1 Underdrain recommended
if < 15 mm/hr
1 to 2 5 to 10 0 to 2 No 4m- Building Foundation
Underground Utilities, Trees,
Drinking Water Wellhead
Protection Areas
Yes 2 yr
Stormwater planters Not applicable 5:1 Not applicable 1 to 2 2 to 5 0 to 2 Yes Building Foundation, Trees No None
Vegetated filter strip 1 5:1 Amend if < 15 mm/hr 0 to 1 15 to 20 1 to 5 No None No None
Permeable pavement 1 1:1 to 1.2:1 UnderdrainA perforated pipe used to assist the draining of soils. recoomended
if < 15 mm/hr
0.5 to 1 0 1 to 5 No 4m-Underground Utilities
Drinking Water Wellhead
Protection Areas
Yes 2 Yr
Enhanced grass swale(has checkdams) 1 5:1 to 10:1 Not applicable 1 to 3 5 to 15 0.5 to 6 No 4m- Building Foundation
Underground Utilities
Yes None
Dry swale (BioswaleLinear 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.) 1 5:1 to 15:1 UnderdrainA perforated pipe used to assist the draining of soils. recommended
if < 15 mm/hr
1 to 3 5 to 10 0.5 to 6 No 4m (3m if impermeable liner
is used)Building foundation,
Underground utilities, drinking
water wellhead protection areas
Yes 2 Yr
Perforated pipe system 1 5:1 to 10:1 Not a constraint 1 to 3 0 < 15% No 4m- Building Foundation
Underground Utilities, Trees,
Drinking Water Wellhead
Protection Areas
Yes 2 Yr
  1. Minimum depth between the base of the facility and the elevation of the seasonally high water table or top of bedrock
  2. Infiltration rate estimates based on measurements of hydraulic conductivity under field saturated conditions at the proposed location and depth of the practice
  3. Vertical distance between the inlet and outlet of the LID practice
  4. Percent of open pervious land on the site that is required for the LID practice
  5. Slope at the LID practice location
  6. Suitable in pollution hot spots or runoff source areas where land uses or activities have the potential to generate highly contaminated runoff
  7. Must have adequate separation from the seasonally high water table or top of bedrock elevation
  8. |Time-of-travel within wellhead protection areas