Bioretention facilities should be sized to accommodate runoff from approximately 5 to 20 times the footprint area of the facility. i.e. they should have an I/P ratio of 5 to 20. | Bioretention facilities should be sized to accommodate runoff from approximately 5 to 20 times the footprint area of the facility. i.e. they should have an I/P ratio of 5 to 20. |