Make a preliminary judgment as to whether site conditions are appropriate for the use of an infiltration practice, and identify the function of the practice in the overall treatment system.

A. Consider basic issues for initial suitability screening, including:

  • site drainage area (See the Summary of infiltration practices for given drainage areas table below);
  • site topography and slopes;
  • soil infiltration capacity;
  • regional or local depth to groundwater and bedrock;
  • site location/ minimum setbacks; and
  • presence of active karst.

B. Determine how the infiltration practice will fit into the overall stormwater treatment system.

  • Decide whether the infiltration practice is the only BMP to be employed, or if are there other BMPs addressing some of the treatment requirements.
  • Decide where on the site the infiltration practice is most likely to be located.

Stormwater infiltration BMPs - contributing drainage area
Link to this table

Stormwater BMP Recommended contributing area Notes
Infiltration Basin 50 acres or less A natural or constructed impoundment that captures, temporarily stores and infiltrates the design volume of water into the surrounding naturally permeable soil over several days. In the case of a constructed basin, the impoundment is created by excavation or embankment.
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. 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 feet is HIGHLY RECOMMENDED.
Infiltration Trench 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 Though feasible, larger underground infiltration systems may cause groundwater contamination as water is not able to infiltrate through a surface cover. In addition, wind flocculation, UV degradation, and bacterial degradation, which provide additional treatment in surface systems, do not occur in underground systems. Because performance research is lacking for larger features, it is HIGHLY RECOMMENDED that the contributing drainage area to a single device not exceed 10 acres.
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

References: Virginia, North Carolina, West Virginia, Maine, Lake Tahoe, Connecticut, Massachusetts, New York, Wisconsin, Vermont, New Hampshire, Ontario, Pennsylvania

This page was last modified on 26 August 2016, at 15:25.

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