Stormwater bioretention filtration system with overflow/bypass capability

1. A stormwater treatment system comprising a substantially water impermeable treatment container having an enclosed side wall, a bottom wall, and at least a partially open top to define a container interior, said partially open top including a substantially water impermeable top slab defining an opening substantially centrally of said top slab with a grate mounted therein through which plant material may grow out, an underdrain pipe located substantially horizontally in proximity to said bottom wall and exiting said container through an underdrain pipe opening in said side wall, said underdrain pipe including a plurality of perforations to receive treated stormwater, a stormwater inlet pipe communicating through an inlet pipe opening in said side wall at a location closer to said top than to said bottom wall, and an overflow/bypass outlet pipe communicating through an outlet pipe opening in said side wall, said overflow/bypass outlet pipe receiving at least partially untreated stormwater that flows through said inlet pipe at rates in excess of that capable of treatment within said container, said inlet pipe opening and said outlet pipe opening closer to a side wall in plan view than to said substantially central opening of said top slab, a substantially horizontally oriented dissipation plate within said container and located below the position of said inlet pipe opening to receive stormwater flowing through said inlet pipe opening and dissipating the stormwater before it falls into the treatment container interior located below said dissipation plate, wherein said treatment container is positionable below ground level with said partially open top in communication with the atmosphere, said container interior including a filter media that fills the container to a level no higher than the level of the dissipation plate, said filter media comprising a layer of mulch overlying a soil mixture of non-organic and organic material and live plant material growing in the filter media, said plant material capable of growing out through the top of the container above ground level, and wherein said dissipation plate extends from a side wall a distance toward the center of the container to lie below the entire inlet pipe opening and having a free edge, said filter media within the container interior extending up no higher than said free edge, and further comprising a horizontally oriented interior overflow/bypass pipe extending from said inlet pipe opening and communicating with said outlet pipe opening, said interior overflow/bypass pipe including a plurality of downwardly directed openings oriented above and spaced from said dissipation plate so that stormwater through said interior overflow/bypass pipe will fall through said downwardly directed openings onto said dissipation plate and into the container interior, and wherein said outlet pipe opening is substantially level with said inlet pipe opening and said interior overflow/bypass pipe extends substantially horizontally from said inlet pipe opening to said outlet pipe opening so as to enable high stormwater flow through said stormwater inlet pipe into said interior overflow/bypass pipe to bypass the filter media and exit directly through said outlet pipe opening, said dissipation plate extending substantially horizontally and parallel with said overflow/bypass pipe and closer to a said wall in plan view than to said substantially central opening of said top slab.

2. The stormwater treatment system of claim 1 , wherein said stormwater inlet pipe is connectable to a roof drain structure that receives stormwater from a roof of a building.

3. The stormwater treatment system of claim 1 , wherein a narrow layer of rocks lies on said mulch layer adjacent said free edge of said dissipation plate.

4. The stormwater treatment system of claim 1 , wherein said dissipation plate includes a vertically oriented wall extending upward from said free edge of said dissipation plate.

5. The stormwater treatment system of claim 4 , wherein said dissipation plate includes a pair of vertically oriented walls spaced apart from each other to define a slot through which stormwater will fall off the dissipation plate into the container interior therebelow.

6. The stormwater treatment system of claim 1 , wherein said outlet pipe opening and said underdrain pipe opening share a common opening that lies in proximity to said bottom wall.

7. The stormwater treatment system of claim 6 , wherein said interior overflow/bypass pipe extends through said dissipation plate in a direction downward toward said bottom wall and is in communication with said outlet pipe opening.

8. The stormwater treatment system of claim 1 , further comprising a collection chamber integral with said container and located outside the container interior adjacent a side wall, said outlet pipe opening and underdrain pipe opening in fluid communication with said collection chamber, said collection chamber having enclosed side walls, one of which is the container side wall exterior, and a chamber bottom wall, said chamber side walls coterminous with the height of the container side wall, said chamber further including an enclosed chamber top wall, said chamber further including a chamber outlet opening positioned in proximity to said bottom wall, wherein said chamber serves to collect the treated and untreated stormwater from said outlet pipe opening and underdrain pipe opening prior to the stormwater exiting through said chamber outlet pipe opening.