A stormwater treatment system including a substantially water impermeable
treatment container for treating stormwater through a bioretention
mechanism. The treatment container includes an overflow/bypass opening to
receive stormwater that bypasses the treatment container filter media, or
is only partially treated as a result of high stormwater flows in excess
of the capacity of the container to treat the stormwater. The stormwater
is directed into the container through an inlet, such as an inlet pipe,
preferably connected to a roof drain system for processing and treating
stormwater from the roof of a building. The overflow/bypass opening may
be adjacent the top wall or bottom wall of the container.