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{{float right|[[File:perf pipe.gif|border|600 px|Exfiltration trench under high flow and exfiltration conditions]]}}
{{float right|[[File:Perf pipe resize small.gif|417 × 194 px|Exfiltration trench under high flow and exfiltration conditions]]}}
Exfiltration trenches are similar to [[infiltration trenches]] but differ primarily in the the manner in which stormwater is delivered to the trench.<br>
Exfiltration trenches are similar to [[infiltration trenches]] but differ primarily in the the manner in which stormwater is delivered to the trench.<br>
Runoff enters infiltration trenches directly by infiltration from the surface. In exfiltration systems, surface runoff is collected by drainage [[inlets]] and delivered to the trench via subsurface perforated [[pipes]].
Runoff enters infiltration trenches directly by infiltration from the surface. In exfiltration systems, surface runoff is collected by drainage [[inlets]] and delivered to the trench via subsurface perforated [[pipes]].
*All new road/storm sewer constructions where no constraints to infiltration exist,
*All new road/storm sewer constructions where no constraints to infiltration exist,
*Tight urban spaces where no landscaped practices can be squeezed in, and there is a low risk tolerance for flooding.}}
*Tight urban spaces where no landscaped practices can be squeezed in, and there is a low risk tolerance for flooding.}}
Take a look at the downloadable Exfiltration Trench Systems Factsheet below for a .pdf overview of this LID Best Management Practice:
{{Clickable button|[[File:Exfiltration.png|150 px|link=https://wiki.sustainabletechnologies.ca/images/4/4e/Exfiltration_systems_final.pdf]]}}
'''The fundamental components of an exfiltration system are:'''
'''The fundamental components of an exfiltration system are:'''
*pre-treatment devices to retain coarse sediment, trash, debris and floatables,
*[[pretreatment| pre-treatment devices]] to retain coarse sediment, trash, debris and floatables,
*perforated [[pipes]] connected to maintenance holes and catch basins,
*perforated [[pipes]] embedded in washed gravel connected to maintenance holes and catch basins,
*a gently sloping granular [[reservoir aggregate| storage reservoir]] below the perforated pipe.
*a gently sloping granular [[reservoir aggregate| storage reservoir]] below the perforated pipe.
'''Optional components include:'''
'''Optional components include:'''
*[[Geotextile]] to prevent migration of fines into the reservoir.
*[[Geotextile]] to prevent migration of fines into the reservoir;
*Trench plugs to help disperse stormwater throughout the trench and enhance infiltration; and
*Perforated maintenance hole or catch basin risers.
Exfiltration systems can be used in place of conventional storm sewer pipes, where topography, water table depth, and [[water quality]] conditions are suitable. They are suitable for treating runoff from roofs, walkways, parking lots and low to medium traffic roads, with adequate [[pretreatment]].
Exfiltration systems can be used in place of conventional storm sewer pipes, where topography, water table depth, and [[water quality]] conditions are suitable. They are suitable for treating runoff from roofs, walkways, parking lots and low to medium traffic roads, with adequate [[pretreatment]].
Exfiltration systems can also be referred to as perforated pipe systems, clean water collector systems and percolation drainage systems.
Exfiltration systems can also be referred to as perforated pipe systems, pervious pipe systems, clean water collector systems and percolation drainage systems.
==Planning==
==Planning==
If properly located, designed and maintained, perforated pipe systems can greatly reduce runoff volume while having little or no surface footprint, which helps to conserve highly valued developable land.
If properly located, designed and maintained, perforated pipe systems can greatly reduce runoff volume while having little or no surface footprint, which helps to conserve highly valued developable land.
Systems should be located below shoulders of roadways, [[permeable paving]] or [[swales]] where they can be readily excavated for servicing. An adequate subsurface area outside of the 4 m setback from building foundations and suitable distance from other underground utilities must be available.
Systems should be located below shoulders of roadways, [[permeable pavements]] or [[swales]] where they can be readily excavated for servicing. An adequate subsurface area outside of the 4 m setback from building foundations and suitable distance from other underground utilities must be available.
===Site Topography===
===Site Topography===