Exfiltration trenches

File:Exfitlration .gif|thumb|600px|Typical flow pathway through one section of the Etobicoke Exfiltration system (see performance report for further details) For more details click here. A note: The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.
rect 195 134 260 179 Manhole
rect 28 285 153 312 Clear Stone Trench 
rect 231 366 404 386 Perforated Pipe 
rect 9 334 84 398 Perforated Pipe 
rect 319 159 416 195 Storm Sewer
rect 399 66 467 88 Catch Basin
Exfiltration trenches are similar to infiltration trenches but differ primarily inthe manner in which stormwater is delivered to the trench.
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.
==Overview==
Exfiltration systems can be thought of as infiltration trenches that are integrated with conventional stormwater conveyance systems (i.e. catch basins, solid pipes and maintenance holes), designed for both conveyance and infiltration of excess stormwater.
By attenuating runoff volume, they reduce contaminant loads delivered to downstream BMPs, end-of-pipe facilities or receiving waterbodies. 
Take a look at the downloadable Exfiltration Trench Systems Factsheet below for a .pdf overview of this LID Best Management Practice:
The fundamental components of an exfiltration system are:
* pre-treatment devices to retain coarse sediment, trash, debris and floatables,
*perforated pipes embedded in washed gravel connected to maintenance holes and catch basins,
*a gently sloping granular storage reservoir below the perforated pipe. 
Optional components include:
*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 also be referred to as perforated pipe systems, clean water collector systems and percolation drainage systems.
==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.
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.
===Infiltration===
For information about constraints to infiltration practices, and approaches and tools for identifying and designing within them see Infiltration.
===Native Soil===
Exfiltration trench systems can be constructed over any soil type, but hydrologic soil group (HSG) A or B soils are best for achieving water balance and erosion control objectives. Facilities should be located on portions of the site with the highest infiltration rates. Native soil infiltration rate at the proposed facility location and depth should be confirmed through in-situ measurements of hydraulic conductivity under field saturated conditions. For guidance on infiltration testing and selecting a design infiltration rate see Design infiltration rate.
===Site Topography=== 
Systems cannot be located on natural slopes > 15 %.
For more information on planning considerations and site constraints see Infiltration trenches.
For a table summarizing information on planning considerations and site constraints see Site considerations.
==Design==
===Geometry and Site Layout===
*Gravel beds in which exfiltration systems are installed are typically rectangular excavations with a bottom width between 0.6 and 2.4 m Greater Vancouver Regional District. 2005. Stormwater Source Control Design
Guidelines 2005. Prepared by Lanarc Consultants Limited, Kerr Wood Leidal Associates Limited and Goya Ngan. 
*The gravel beds should have gentle slopes between 0.5 - 1 %.
*Calculate maximum flow through perforated pipe
===Drawings===
Standard details for exfiltration trenches have been produced by City of Kitchener and City of Barrie. See Drawings
==Inspection and Maintenance==
Routine inspection and maintenance consists of checking and cleaning trash, debris and sediment from pretreatment devices, inlets and outlets twice a year in the spring and/or late fall, or when pretreatment device sump is half full. Use hydro-vac truck to remove sediment from catch basin sumps, OGS and isolated chamber row filter pre-treatment devices. To clean isolated chamber row filters use a vacuum truck equipped with rear-facing jet nozzle for cleaning large diameter pipes or culverts. 
Monitoring of storage reservoir water level during and after natural or simulated storm events using the monitoring well should be performed periodically to verify the facility drains within the required drainage time (typically 72 hours). Should be performed as part of inspections following construction or major rehabilitation prior to assumption, and every 15 years at a minimum, to track drainage performance over time and determine when replacement is needed. 
Take a look at the Inspection and Maintenance: Underground Infiltration Systems page by clicking below for further details about proper inspection and maintenance practices:
==Gallery==
==Materials==
==Performance==
===See also===
STEP and partners research and reports on exfiltration systems
==External resources==
*https://www.chijournal.org/C390
*http://www.civil.ryerson.ca/seminar/Papers/Draft%20Design%20manual%20of%20EES%20by%20Tran%20and%20Li%207-24-2015.pdf
==References==
Category:Infiltration
Category: Green infrastructure