Changes

'''Example''':  A filtration facility drained by a catchment with temporary upstream water storage through oversized storm sewer pipes, parking lot storage and/or orifice controlled roof drains.  In the case of oversized storm sewers or parking lot storage, the pipe feeding the filtration facility would normally have an orifice to control flow rates draining into the facility.   

'''Example''':  A filtration facility drained by a catchment with temporary upstream water storage through oversized storm sewer pipes, parking lot storage and/or orifice controlled roof drains.  In the case of oversized storm sewers or parking lot storage, the pipe feeding the filtration facility would normally have an orifice to control flow rates draining into the facility.   

'''Performance calculation''': The capacity of this type of treatment train to improve performance depends on sizing of the downstream practice.  If this practice (e.g. proprietary filtration MTD) is sized to the new controlled flow rate (and the design storm remains the same), then the performance of the facility may be the same or similar to what would have been achieved without upstream controls because there would be a similar number of overflows (i.e flows that bypass the treatment chamber).  If the downstream practice is a settling device, such as an OGS, then the performance of the downsized facility may be slightly lower than without flow controls because performance of these devices are more sensitive than filters to the rate of flow through the treatment chamber (see performance curves and sizing tool for calculations below).

'''Performance calculation''': The capacity of this type of treatment train to improve performance depends on sizing of the downstream practice.  If this practice (e.g. proprietary filtration MTD) is sized to the new controlled flow rate (and the design storm remains the same), then the performance of the facility may be the same or similar to what would have been achieved without upstream controls because there would be a similar number of overflows (i.e flows that bypass the treatment chamber).  If the downstream practice is a settling device, such as an OGS, then the performance of the downsized facility may be slightly lower than without flow controls because performance of these devices are more sensitive than filters to the rate of flow through the treatment chamber See performance curves (TSS removal efficiencies vs surface loading rates) [[Oil and Grit Separator#Performance Test Results|'''on our OGS page here''']].

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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.