This bioretention basin detail features a twenty-four-inch minimum biotreatment soil mix layered over twenty-four inches minimum of Class 2 permeable material and uncompacted subgrade. A four-inch PVC SDR35 perforated subdrain is placed one inch below the top of the gravel layer and connects to an overflow storm drain inlet. Non-woven filter fabric or high-density polyethylene tree root barrier lines the sides typically. The basin is finished with landscaping maintaining a twelve-inch ponding depth and is bordered by rock slope protection with three to six-inch diameter cobbles at the inflow and three-to-one maximum side slopes compacted at ninety percent relative compaction.
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