Changes

Of course, the real world is not black and white, and it is possible to blend these categories to meet a variety of different site stormwater management objectives.  The purpose of categorizing the treatment train types into design priorities is to highlight the need to consider different objectives, while recognizing that if the design priority of the treatment train is narrowly focused, objectives other than those targeted may not be met.

Of course, the real world is not black and white, and it is possible to blend these categories to meet a variety of different site stormwater management objectives.  The purpose of categorizing the treatment train types into design priorities is to highlight the need to consider different objectives, while recognizing that if the design priority of the treatment train is narrowly focused, objectives other than those targeted may not be met.

==Calculating [[Water Quality]] Performance of Treatment Trains==

==Calculating Water QualityPerformance of Treatment Trains==

The performance of a treatment train will vary based on the type of stormwater treatment practices implemented and their arrangement within the treatment train.  Various changes occur as [[Runoff volume control targets|runoff]] moves through the treatment train.  Key changes that need to be considered when [[Low impact development treatment train tool|calculating treatment train performance]] including:

The performance of a treatment train will vary based on the type of stormwater treatment practices implemented and their arrangement within the treatment train.  Various changes occur as [[Runoff volume control targets|runoff]] moves through the treatment train.  Key changes that need to be considered when [[Low impact development treatment train tool|calculating treatment train performance]] including:

Removal efficiency calculations are sensitive to influent concentration because facility effluent concentrations cannot be reliably reduced beyond a certain level, which varies by facility type.  For example, a pond may have an ‘irreducible’ effluent concentration of 30 mg/L for an average rainfall year.  If the TSS influent concentration to the pond is 200 mg/L, the pond removal efficiency would be 85%.  If the treatment practice(s) upstream of the pond reduce the pond influent concentration to only 100 mg/L, the TSS removal efficiency of pond would only be 70%. This value may be even lower if the 100 mg/L contains a higher percentage of fine particles than untreated runoff (which is often the case).

Removal efficiency calculations are sensitive to influent concentration because facility effluent concentrations cannot be reliably reduced beyond a certain level, which varies by facility type.  For example, a pond may have an ‘irreducible’ effluent concentration of 30 mg/L for an average rainfall year.  If the TSS influent concentration to the pond is 200 mg/L, the pond removal efficiency would be 85%.  If the treatment practice(s) upstream of the pond reduce the pond influent concentration to only 100 mg/L, the TSS removal efficiency of pond would only be 70%. This value may be even lower if the 100 mg/L contains a higher percentage of fine particles than untreated runoff (which is often the case).

===3. Changes in [[Runoff volume control targets|runoff volume]]===

===3. Changes in runoff volume===

Where runoff is being reduced along the treatment train through infiltration and evapotranspiration, there will be a change in [[water quality]] loading that needs to be considered.

Where runoff is being reduced along the treatment train through infiltration and evapotranspiration, there will be a change in [[water quality]] loading that needs to be considered.

The water quality load is the product of runoff concentrations and runoff volumes.  Hence, a change in either of these variables will result in a change in load.  As concentrations and volumes are affected by different variables it is best to consider the components separately, and then combine them to calculate overall load based performance for the treatment train under consideration.  

The water quality load is the product of runoff concentrations and runoff volumes.  Hence, a change in either of these variables will result in a change in load.  As concentrations and volumes are affected by different variables it is best to consider the components separately, and then combine them to calculate overall load based performance for the treatment train under consideration.

==Calculations for Load Based Performance==

==Calculations for Load Based Performance==