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The following general assumption applies in calculating the credit for an Other BMP. If this assumption is not followed the stormwater volume and pollutant reduction credits cannot be applied. | The following general assumption applies in calculating the credit for an Other BMP. If this assumption is not followed the stormwater volume and pollutant reduction credits cannot be applied. | ||
*It is assumed that values entered into the Other BMP are based on a detailed analysis of the system it represents and that evidence can be provided and defended for each value entered into the Other BMP. | *It is assumed that values entered into the Other BMP are based on a detailed analysis of the system it represents and that evidence can be provided and defended for each value entered into the Other BMP. | ||
− | Examples of BMPs that may be used for Other | + | |
+ | ==Examples of BMPs that may be used for Other== | ||
The following BMPs are not included in the MIDS calculator but may be incorporated using the Other BMP in the calculator. | The following BMPs are not included in the MIDS calculator but may be incorporated using the Other BMP in the calculator. | ||
− | *Iron enhanced sand filter: this BMP will not achieve volume reductions but will reduce phosphorus and TSS. See the Minnesota Stormwater Manual | + | *[[Iron enhanced sand filter]]: this BMP will not achieve volume reductions but will reduce phosphorus and TSS. See the Minnesota Stormwater Manual |
− | *Enhanced turf or disconnected impervious surface: this BMP will achieve volume reductions and pollutant reductions both through infiltration and through filtration. To determine the filtration credits we recommend treating this BMP as a filter strip | + | *[[Turf|Enhanced turf]] or disconnected impervious surface: this BMP will achieve volume reductions and pollutant reductions both through infiltration and through filtration. To determine the filtration credits we recommend treating this BMP as a [[Vegetated filter strips|filter strip]]. |
− | *Sumps/SAFL baffle/grit chambers: These BMPs will not achieve volume reduction | + | *Sumps/[http://stormwater.safl.umn.edu/updates-december-2011 SAFL baffle]/grit chambers: These BMPs will not achieve volume reduction. However pollutant reduction can be estimated based on modeling analysis and entered into the calculator. |
The Other BMP allows user-defined stormwater volume and pollutant reduction amounts to be entered. This can be used for BMPs that are not in the calculator. Examples of some BMPs that may be used for this BMP are given at the end of this article. The user must be able to provide evidence and support for each of the stormwater volume and pollutant reduction amounts entered in the Other BMP.
For the Other BMP, the user must input the following parameters to calculate the stormwater volume and pollutant load reductions associated with the BMP.
The following is a required input into the MIDS calculator. If it is not met, an error message will inform the user to change the input to meet the requirement.
Required treatment volume, or the volume of stormwater runoff delivered to the BMP, equals the performance goal (1.1 inches for MIDS or user-specified performance goal) times the impervious area draining to the BMP plus any water routed to the BMP from another BMP. This stormwater is delivered to the BMP instantaneously following the Kerplunk method.
The volume reduction achieved by a BMP compares the volume capacity of the BMP to the required treatment volume. For the Other BMP, the volume reduction capacity of the BMP is entered by the user in the field called BMP volume capacity [V]. The user must therefore know the volume reduction capacity of the BMP (i.e. it is not calculated as with other BMPs in the calculator). Volume of retention provided by BMP is the amount of volume credit the BMP provides toward the performance goal. This value is equal to BMP volume capacity [V] as long as the volume capacity is less than or equal to Required treatment volume. If BMP volume capacity [V] is greater than Required treatment volume, then the BMP volume credit is equal to Required treatment volume. This check makes sure the BMP is not getting credit beyond the performance goal. For example, if the BMP is oversized the user will only receive credit for the required treatment volume routed to the BMP.
Pollutant load reductions are calculated on an annual basis. For this BMP, the pollutant removal rates are defined by the user. The annual volume reduction is defined by the user. All pollutants associated with stormwater that is reduced on an annual basis are captured for a 100 percent removal. Pollutant reduction rates for total suspended solids (TSS), dissolved phosphorus, and particulate phosphorus are defined by the user and applied to stormwater captured but not reduced/removed by the BMP.
NOTE: The user can modify event mean concentrations (EMCs) on the Site Information tab in the calculator. Default concentrations are 54.5 milligrams per liter for total suspended solids (TSS) and 0.3 milligrams per liter for total phosphorus (particulate plus dissolved). The calculator will notify the user if the default is changed. Changing the default EMC will result in changes to the total pounds of pollutant reduced.
An Other BMP can be routed to any other BMP, except for a green roof and a swale side slope or any BMP in a treatment sequence that would cause stormwater to be rerouted back to the Other BMP already in that treatment sequence. All BMPs can be routed to an Other BMP, except for a swale side slope.
The following general assumption applies in calculating the credit for an Other BMP. If this assumption is not followed the stormwater volume and pollutant reduction credits cannot be applied.
The following BMPs are not included in the MIDS calculator but may be incorporated using the Other BMP in the calculator.