Slide 45 of 52
Notes:
Key elements of bioretention include a grass filter, sand layer, loamy soils, mulch layer, shallow ponding of stormwater and plantings of native trees and shrubs. Pretreatment mechanisms include a stone drop at the edge of the parking lot that leads over a grass filter strip and a sand layer. During storms, the water quality volume is ponded up to nine inches above the mulch. Runoff in excess of the water quality volume rises to a higher elevation, but is then diverted into a standard drop inlet connected to the storm drain system. The remaining runoff filters through the mulch and prepared soil mix, which is about four feet in depth. Typically, the filtered runoff is collected in a perforated underdrain and returned to the storm drain system.
