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'''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==
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.
'''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). –provide links to the web page and tool.