About the Tree Box Filter
General Information Performance Data Water Quality Treatment Process Design


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Design

The tree box filter’s basic design is a concrete vault filled with a bioretention soil mix (BSM), planted with vegetation, and underlain with a subdrain. The system evaluated at the UNHSC field site is a six-foot diameter, concrete vault with an internal bypass. It is underlain by a subdrain that discharges to existing stormwater drainage. The vault is open-bottomed to enhance infiltration.

The filter media is three feet deep, and composed of 80 percent sand and 20 percent compost. The mix was designed to maximize permeability while providing minimum organic content (at least 10 percent) to sustain vegetation.

Vegetation selected for these systems should consist of native, drought- and salt-tolerant species. Plants with aggressive root growth may clog the subdrain, and therefore may not be suitable for this type of system.

This tree box filter was sized for the water quality volume (WQ_v), and should allow for four to six inches of ponding. Larger storm events will be bypassed. The system’s filter media accommodates a high infiltration rate of 120 feet per day.