Line 37: | Line 37: | ||
The following general assumption applies in calculating the credits for a sand filter. If this assumption is not followed, the pollutant reduction credits cannot be applied. | The following general assumption applies in calculating the credits for a sand filter. If this assumption is not followed, the pollutant reduction credits cannot be applied. | ||
− | *The sand filter has been properly [http://stormwater.pca.state.mn.us/index.php/Design_criteria_for_filtration designed], [http://stormwater.pca.state.mn.us/index.php/Construction_specifications_for_filtration constructed] and will be properly [http://stormwater.pca.state.mn.us/index.php/Operation_and_maintenance_of_filtration maintained] according to specifications for filtration systems | + | *The sand filter has been properly [http://stormwater.pca.state.mn.us/index.php/Design_criteria_for_filtration designed], [http://stormwater.pca.state.mn.us/index.php/Construction_specifications_for_filtration constructed] and will be properly [http://stormwater.pca.state.mn.us/index.php/Operation_and_maintenance_of_filtration maintained] according to specifications for filtration systems. |
− | + | ||
On the watershed tab, the following warning is given: | On the watershed tab, the following warning is given: | ||
“The calculator does not require sizing inputs for non-volume reducing BMPs. This BMP should be sized according to the guidelines in the MN stormwater manual.” Design and construction criteria can be found at [http://stormwater.pca.state.mn.us/index.php/Sand_filters this link]. | “The calculator does not require sizing inputs for non-volume reducing BMPs. This BMP should be sized according to the guidelines in the MN stormwater manual.” Design and construction criteria can be found at [http://stormwater.pca.state.mn.us/index.php/Sand_filters this link]. |
A Sand Filter does not reduce stormwater volume. While this BMP does not provide stormwater volume reduction toward the performance goal or on an annual basis, it does provide annual pollutant load reductions.
For the sand filter BMP, BMP watershed areas is the only required design parameter.
The required treatment volume, or the volume of stormwater runoff delivered to the BMP, equals the performance goal (1.1 inches or user-specified performance goal) times the impervious area draining to the BMP. This stormwater is delivered to the BMP instantaneously following the Kerplunk method.
This BMP does not provide volume reduction towards the performance goal.
Pollutant load reductions are calculated on an annual basis. A sand filter does not provide annual volume reduction. Fixed removal rates of 85 percent total suspended solids (TSS), 85 percent particulate phosphorus, and 0 percent dissolved phosphorus are applied to stormwater that travels through the sand filter.
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.
A sand filter can be routed to any other BMP, except for a green roof and a swale side slope or any BMP in a stormwater treatment sequence that would cause stormwater to be rerouted back to the sand filter already in the sequence. All BMPs can be routed to a sand filter except for a swale side slope.
The following general assumption applies in calculating the credits for a sand filter. If this assumption is not followed, the pollutant reduction credits cannot be applied.
On the watershed tab, the following warning is given:
“The calculator does not require sizing inputs for non-volume reducing BMPs. This BMP should be sized according to the guidelines in the MN stormwater manual.” Design and construction criteria can be found at this link.