The soil and drain rock layers must be encased either by constructed walls (often concrete) or liner to prevent infiltration into surrounding soil.
Install a perforated pipe at the base of the facility to collect the treated runoff.
Use a raised drain or curb cut (as illustrated) to drain overflow back to the gray water system that exceeds the design rain event.
The planter must be designed to drain within 24 to 72 hours.
Maximize the surface footprint of the biofiltration cell, especially if multiple cells drain into a continuous rock layer below. Multiple surface expressions can be connected to maximize the bioretention footprint of a facility. Under-sized surface cells may be at risk for increased erosion or large amounts of debris.
Provide a pedestrian cut-through (at least 5 feet wide) approximately every 20 to 40 feet to facilitate access to the curb. Cut-throughs may separate cells or be provided as ramps.
Use native plantings that are suitable for each site or micro-climate, are able to handle seasonal flooding or drought, and require minimal irrigation or maintenance.
Discourage pedestrian trampling and reduce soil compaction by using low barriers or hardy vegetative ground covers.
Seating can be incorporated into the planter sides to improve the public realm for people. Review overall vertical drop from bench to bottom of facility. If drop exceeds 30 inches, review if bracing or fencing at back of bench may be needed.