Recommended contributing drainage area for infiltration BMPs

Recommended contributing drainage area for infiltration Best Management Practices
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Stormwater BMP	Recommended contributing area	Notes
Infiltration Basin	50 acres or less	Contributing drainage areas should have a maximum 5:1 ratio of impervious area to infiltration area. Infiltration basins must meet the required 48 hour drawdown time and must be sized in order to allow for adequate maintenance without increasing compaction.
Bioinfiltration Basin	5 acres or less	Bioinfiltration basins must meet the required 48 hour drawdown time and must be sized in order to allow for adequate maintenance without increasing compaction. It is HIGHLY RECOMMENDED that bioinfiltration basins be designed to prevent high levels of bounce as submerging vegetation may inhibit plant growth. A maximum wet storage depth of 1.5 to 2.0 feet is HIGHLY RECOMMENDED.
Infiltration Trench Synonym: Infiltration Gallery	5 acres or less
Dry Well Synonym: Infiltration Tube, French Drain, Soak‐Away Pits, Soak Holes	1 acre or less	Rooftop only
Underground Infiltration	10 acres or less
Dry Swale with Check Dams	5 acres or less
Permeable Pavement	It is RECOMMENDED that external contributing drainage area not exceed the surface area of the permeable pavement. It is HIGHLY RECOMMENDED that external contributing drainage area not exceed twice the surface area of the permeable pavement.	It is RECOMMENDED that external drainage area be as close to 100% impervious as possible. Field experience has shown that drainage area (pervious or impervious) can contribute particulates to the permeable pavement and lead to clogging. Therefore, sediment source control and/or pre-treatment should be used to control sediment run-on to the permeable pavement section.
Tree Trench/Tree Box	Up to 0.25 acres per tree	Reduced volume credit below certain minimum soil volume per tree. See link.