Changes

==Overview==

==Overview==

A treatment train uses a combination of source (LID), conveyance and/or end-of-pipe practices to meet water quality, water quantity, water balance, and erosion design criteria for the site.  These may be implemented to reduce the burden of facility maintenance, address a broader range of design criteria, increase overall treatment system performance, and/or control the rate of flow through downstream facilities.  Examples of applications designed to address specific objectives include the following listed in the corresponding sections below.

A treatment train uses a combination of source (LID), conveyance and/or end-of-pipe practices to meet water quality, water quantity, water balance, and erosion design criteria for the site.  These may be implemented to reduce the burden of facility maintenance, address a broader range of design criteria, increase overall treatment system performance, and/or control the rate of flow through downstream facilities.   

==1. Treatment trains designed to reduce maintenance burdens==   

 

 

===1. Treatment trains designed to reduce maintenance burdens===   

These are the most common types of treatment trains.  They typically involve installation of one or more [[pretreatment]] devices upstream or at the [[inlet]] of the primary stormwater treatment facility.   

These are the most common types of treatment trains.  They typically involve installation of one or more [[pretreatment]] devices upstream or at the [[inlet]] of the primary stormwater treatment facility.   

'''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]].

==2. Treatment trains designed to address one or more design criteria==  

 

===2. Treatment trains designed to address one or more design criteria===  

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.   

'''Performance calculation''':  Treatment trains designed to address multiple design criteria may improve overall water quality performance by, for example, reducing water quality concentrations in the first facility and reducing water quality loads (through infiltration/evapotranspiration) in a second facility.  Even if the effluent concentration from facility one and facility two are the same, the overall load reduction of the treatment train may be greater than provided by any one of the facilities alone.

'''Performance calculation''':  Treatment trains designed to address multiple design criteria may improve overall water quality performance by, for example, reducing water quality concentrations in the first facility and reducing water quality loads (through infiltration/evapotranspiration) in a second facility.  Even if the effluent concentration from facility one and facility two are the same, the overall load reduction of the treatment train may be greater than provided by any one of the facilities alone.

==3. Treatment trains designed to enhance overall treatment system performance==

 

===3. Treatment trains designed to enhance overall treatment system performance===

The design intent of these treatment trains is to enhance overall system performance.  The previous category of treatment train may enhance performance, but the objective may not always be to address a broader range of stormwater criteria.   

The design intent of these treatment trains is to enhance overall system performance.  The previous category of treatment train may enhance performance, but the objective may not always be to address a broader range of stormwater criteria.   

'''Performance calculation''':  In the example above, the [[bioretention]] facility would provide water quality load reductions through filtration (water quality concentration reductions) and infiltration (volume reductions).  Since the second facility would receive effluent from the [[underdrain]] of the bioretention, no further reduction in TSS concentrations would be expected (ie. the TSS concentration would already be at the ‘irreducible’ level).  The TSS water quality load would be reduced in the second facility only by further reductions in volumes through infiltration.  If the parameter of interest was total [[phosphorus]] (TP) rather than TSS, there is the potential that the second facility may further reduce TP through filtration/adsorption, especially if the second facility contained [[Sorbtive media|reactive media]] designed to remove phosphorus.

'''Performance calculation''':  In the example above, the [[bioretention]] facility would provide water quality load reductions through filtration (water quality concentration reductions) and infiltration (volume reductions).  Since the second facility would receive effluent from the [[underdrain]] of the bioretention, no further reduction in TSS concentrations would be expected (ie. the TSS concentration would already be at the ‘irreducible’ level).  The TSS water quality load would be reduced in the second facility only by further reductions in volumes through infiltration.  If the parameter of interest was total [[phosphorus]] (TP) rather than TSS, there is the potential that the second facility may further reduce TP through filtration/adsorption, especially if the second facility contained [[Sorbtive media|reactive media]] designed to remove phosphorus.

==4. Treatment trains designed to optimize treatment facility sizing through flow control==

 

===4. Treatment trains designed to optimize treatment facility sizing through flow control===

Upstream controls in this type of treatment train are intended to control flow rates to one or more downstream facilities rather than provide treatment.  Controlling the rate of flow to the downstream facility allows it to either be sized for a lower treatment flow rate than would otherwise be the case (which reduces costs) or enhance the performance of the downstream facility by slowing the rate of inflows (treatment practices often perform better at lower inflow rates) and reducing the frequency of bypass flows.  

Upstream controls in this type of treatment train are intended to control flow rates to one or more downstream facilities rather than provide treatment.  Controlling the rate of flow to the downstream facility allows it to either be sized for a lower treatment flow rate than would otherwise be the case (which reduces costs) or enhance the performance of the downstream facility by slowing the rate of inflows (treatment practices often perform better at lower inflow rates) and reducing the frequency of bypass flows.