Changes

'''Performance calculation''': If the downstream facility provides filtration, such as [[bioretention]] or [[Infiltration trenches|stone filled trenches]], the overall water quality performance of this facility would not increase with [[pretreatment]] because the coarse sediment and debris captured by the pretreatment device would be removed by the downstream facility even in the absence of pretreatment.  The purpose of adding pre-treatment is to prevent clogging or filling and thereby reduce the cost and effort of long term [[Inspections and maintenance|maintenance]] and delay requirements for major facility [[Maintenance, Rehabilitation and Repair|rehabilitation or replacement]].

'''Performance calculation''': If the downstream facility provides filtration, such as [[bioretention]] or [[Infiltration trenches|stone filled trenches]], the overall water quality performance of this facility would not increase with [[pretreatment]] because the coarse sediment and debris captured by the pretreatment device would be removed by the downstream facility even in the absence of pretreatment.  The purpose of adding pre-treatment is to prevent clogging or filling and thereby reduce the cost and effort of long term [[Inspections and maintenance|maintenance]] and delay requirements for major facility [[Maintenance, Rehabilitation and Repair|rehabilitation or replacement]].

[[File:Sump inelt to chamber system.JPG|thumb|500px|Example of a [[Pretreatment#Concentrated underground flow|overland flow sump inlet]] allowing sediment to settle out of influent stormwater before entering a large infiltration chamber housed under a parking lot/ The outlet control device can then drain into a [[dry pond]] furthu downstream or offsite (Source: Philadelphia Water Department. 2020)<ref>Philadelphia Water Department. 2020. Stormwater Management Guidance Manual: Version 3.2. Accessed from: https://www.pwdplanreview.org/upload/manual_pdfs/PWD-SMGM-v3.2-20201001.pdf</ref>]]

[[File:Sump inelt to chamber system.JPG|thumb|500px|Example of a [[Pretreatment#Concentrated underground flow|overland flow sump inlet]] allowing sediment to settle out of influent stormwater before entering a large infiltration chamber housed under a parking lot/ The outlet control device can then drain into a [[dry pond]] furthu downstream or offsite (Source: Philadelphia Water Department. 2020)<ref>Philadelphia Water Department. 2020. Stormwater Management Guidance Manual: Version 3.2. Accessed from: https://www.pwdplanreview.org/upload/manual_pdfs/PWD-SMGM-v3.2-20201001.pdf</ref>]]

These types of treatment trains combine practices that address different [[Screening LID options|design criteria]], in recognition that most individual stormwater facility types do not meet all design criteria as stand-alone facilities.  For instance, [[SWM ponds|stormwater wet ponds]] may provide [[water quality]], erosion and flood control but not water balance control (i.e. [[Runoff volume control targets|runoff volume control]]).  [[Bioretention]] provides good water quality and water balance control but are rarely designed for flood control.   

These types of treatment trains combine practices that address different [[Screening LID options|design criteria]], in recognition that most individual stormwater facility types do not meet all design criteria as stand-alone facilities.  For instance, [[SWM ponds|stormwater wet ponds]] may provide [[water quality]], erosion and flood control but not water balance control (i.e. [[Runoff volume control targets|runoff volume control]]).  [[Bioretention]] provides good water quality and water balance control but are rarely designed for flood control.