Stormwater Design Recommendations to Enhance Phosphorus Removal

Summary of stormwater design recommendations to enhance phosphorus removal.
Link to this table

BMP Design	Design recommendations
Bioinfiltration	Bioinfiltration is a preferred practice.
Filtration (includes bioretention with an underdrain)	Organic filters are a source of soluble phosphorus and should not be used. Biofiltration is acceptable when the appropriate filter media is used. Employ finer-grained media in the filter bed with a small diameter (15 microns), or provide a finer-grained layer at mid-depth in the filter profile. The process for pre-treatment and/or filtration should extend from 36 to 48 hours, where possible. Filters should be oriented to provide maximum solar exposure. Wet swales are not recommended. Open channels should be designed to be either self-cleansing or promote maximum sediment retention. Open channels should not be relied on as the only BMP to remove phosphorus at a site, with the exception of an engineered dry swale.
Stormwater Ponds	Design wet ponds with a depth no greater than 10 feet to prevent stratification and potential release of phosphorus from bottom sediments. Avoid the use of dry or dry extended detention ponds Designers should consider the snowmelt runoff volume and design ponds for seasonal operation Use a surface or mid-depth release from the pond. Landscape pond to discourage geese. Add shallow benches and wetland areas to enhance the plankton community. Follow mosquito advisories in Chapter 6.
Constructed Stormwater Wetlands	Pond/ wetland system is the preferred wetland design. Use a surface or mid-depth release from the wetland. Maximize surface micro-topography. Landscape wetland to discourage geese. Follow mosquito advisories in Chapter 6.
Infiltration	Infiltration BMPs are preferred practices. Provide a minimum 3-foot separation from the seasonally-high water table, bedrock or impervious soil layer.