Changes

==Design Assumptions==

==Design Assumptions==

Infiltration trenches are an ideal technology for installing below any type of landscape with requirements to infiltrate excess stormwater while safely conveying excess flows during major storm events.  Components include: layers of coarse [[aggregates]] (to bed the pipe, store and redistribute water), [[underdrain|perforated pipe or underdrains]] and [[geotextile]]. <br>

Infiltration trenches are an ideal technology for installing below any type of landscape with requirements to infiltrate excess stormwater while safely conveying excess flows during major storm events.  Components include: reservoir [[aggregates| aggregate]] to store runoff water, perforated pipe to deliver and distribute flow to the trench, [[geotextile]], [[Inlets|inlet structures]], [[Pretreatment| pretreatment devices or features]] and [[Monitoring wells| monitoring wells]] to track drainage performance of the facility over its operating lifespan. <br>

Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:

Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:

* Native soil infiltration rates for Full, Partial and No Infiltration Design scenarios were assumed to be 20 mm/h, 10 mm/h and 2 mm/h, respectively, and a safety factor of 2.5 was applied to calculate the design infiltration rate.  

* Native soil infiltration rates for Full, and Partial Infiltration Design scenarios were assumed to be 20 mm/h and 10 mm/h respectively, and a safety factor of 2.5 was applied to calculate the design infiltration rate.  

* Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, removal of sediment from pretreatment structures annually, and removal of weeds twice a year (where applicable). Verification inspections are included every 5 years to confirm adequate maintenance, and every 15 years to confirm adequate drainage performance through in-situ surface infiltration rate testing (where applicable)

* Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, removal of sediment from pretreatment structures annually. Verification inspections are included every 5 years to confirm adequate maintenance, and every 15 years to confirm adequate drainage performance through in-situ trench water level monitoring during natural storm events.

* Designed with an impervious drainage area to treatment facility area ratio of between 5:1 and a maximum of 20:1.

* Designed with an impervious drainage area to treatment facility area ratio of between 5:1 and a maximum of 20:1.

* Length to width ratio of infiltration trench area recommended from facilities receiving road or parking lot runoff is 10:1.

* Length to width ratio of infiltration trench area recommended from facilities receiving road or parking lot runoff is 10:1.