dominant nutrient, the appropriate mix would include a higher proportion of vegetated area such as 80% vegetated, 20% open water. For dry extended vegetated detention basins, vegetated swales, and filter strips, select a variety of plant species that are drought tolerant, but can also survive periodic inundation. Provide an irrigation system, if necessary, for plant establishment and maintenance. Biotreatment BMPs shall incorporate amended media and soils designed for the intended function of the BMP. Select amended media for use in bioretention systems that is effective at removing pollutants of concern, can absorb and evapotranspirate runoff, and where appropriate, can facilitate infiltration. Select and soils that will not potentially leach pollutants, specifically dissolved nutrients and metals in some cases. Amend soils in dry extended detention basins, swales, and filter strips to provide suitable soils for supporting plants, which can absorb and evapotranspire runoff and where appropriate facilitate infiltration. Design wet detention basins (wet and constructed stormwater wetlands using soils that support growth of attached plants. BMPs hydraulics shall be designed to maximize pollutant removal functions. For all biotreatment BMPs, design inlets or overland flow entry to BMPs to prevent scour or re-entrainment of pollutants. Provide maximum flow path distance between outlet and inlet and with sufficient length to width ratio to limit short circuiting. For constructed stormwater wetlands and wet detention basins, provide the storage capacity for the DCV in the wet pool at a minimum. Seasonal constructed stormwater wetlands and seasonal wet detention basins should not be used unless is a reasonable expectation that tributary land uses will provide dry weather flows during seasonally wet period to maintain vegetation and prevent stagnant water. For constructed stormwater wetlands and wet detention basins designed to be continually wet (opportunities may be limited in Orange County), ensure that a low-flow source of is present to maintain vegetation and prevent stagnant conditions. Design features shall allow for monitoring of drawdown such as depth markers and monitoring ports. For bioretention systems, provide media contact time sufficient for pollutant removal, with upper limitations on contact time to avoid leaching of retained pollutants. Traditional media should generally be designed in the range of 2 to 12 inches per hour, while specialized media can be effective for many pollutants of concern at much higher flowrates (residence times on the order of several
dominant nutrient, the appropriate mix would include a higher proportion of vegetated area such as 80% vegetated, 20% open water. For dry extended vegetated detention basins, vegetated swales, and filter strips, select a variety of plant species that are drought tolerant, but can also survive periodic inundation. Provide an irrigation system, if necessary, for plant establishment and maintenance. Biotreatment BMPs shall incorporate amended media and soils designed for the intended function of the BMP. Select amended media for use in bioretention systems that is effective at removing pollutants of concern, can absorb and evapotranspirate runoff, and where appropriate, can facilitate infiltration. Select and soils that will not potentially leach pollutants, specifically dissolved nutrients and metals in some cases. Amend soils in dry extended detention basins, swales, and filter strips to provide suitable soils for supporting plants, which can absorb and evapotranspire runoff and where appropriate facilitate infiltration. Design wet detention basins (wet and constructed stormwater wetlands using soils that support growth of attached plants. BMPs hydraulics shall be designed to maximize pollutant removal functions. For all biotreatment BMPs, design inlets or overland flow entry to BMPs to prevent scour or re-entrainment of pollutants. Provide maximum flow path distance between outlet and inlet and with sufficient length to width ratio to limit short circuiting. For constructed stormwater wetlands and wet detention basins, provide the storage capacity for the DCV in the wet pool at a minimum. Seasonal constructed stormwater wetlands and seasonal wet detention basins should not be used unless is a reasonable expectation that tributary land uses will provide dry weather flows during seasonally wet period to maintain vegetation and prevent stagnant water. For constructed stormwater wetlands and wet detention basins designed to be continually wet (opportunities may be limited in Orange County), ensure that a low-flow source of is present to maintain vegetation and prevent stagnant conditions. Design features shall allow for monitoring of drawdown such as depth markers and monitoring ports. For bioretention systems, provide media contact time sufficient for pollutant removal, with upper limitations on contact time to avoid leaching of retained pollutants. Traditional media should generally be designed in the range of 2 to 12 inches per hour, while specialized media can be effective for many pollutants of concern at much higher flowrates (residence times on the order of several
OC_TGD_Appendices_5-19-11.docx