BMP group | BMP design variation | Average TP removal rateb | Maximum TP removal ratec | Average soluble P removal rated,g |
---|---|---|---|---|
Bioretention | Underdrain | 65 | 75 | 60 |
Infiltration | 100 | 100 | 100 | |
Filtration | Sand filter | 50 | 55 | 0 |
Dry swale | 0 | 55 | 0 | |
Wet swale | 65 | 75 | 70 | |
Infiltrationf | Infiltration trench | 100 | 100 | 100 |
Infiltration basin | 100 | 100 | 100 | |
Stormwater ponds | Wet pond | 50 | 65 | 70 |
Multiple pond | 60 | 75 | 75 | |
Stormwater wetlands | Shallow wetland | 40 | 55 | 50 |
Pond/wetland | 55 | 75 | 65 |
a Removal rates show in table are a composite of five sources: [(http://www.bmpdatabase.org ASCE/EPA International Database];
Caraco (Center for Watershed protection, 2001)];
Maryland Department of the Environment(2000)];
Winer (Center for Watershed Protection, 2000)];
P8 modeling (William Walker)]
b Average removal efficiency expected under MPCA Sizing Rules 1 and 3
c Upper limit on phosphorus removal with increased sizing and design features, based on national review
d Average rate of soluble phosphorus removal in the literature
e See section on calculating credits for each BMP in this Manual.
f Note that the performance numbers apply only to that portion of total flow actually being treated; it does not include any runoff that bypasses the BMP
gNote that soluble P can transfer from surface water to groundwater, but this column refers only to surface water
hNote that 100% is assumed for all infiltration, but only for that portion of the flow fully treated in the infiltration facility; by-passed runoff or runoff diverted via underdrain does not receive this level of treatment.