lastic chambers perform the same function as concrete chambers but are lighter in weight. Some of these devices have numerous sidewall openings while others depend upon the wicking action of filter fabric.  Plastic chambers can be used in either trench or cluster formation.  When used in trench configuration, plastic chambers are designed to take advantage of the sidewall area without the use of stone.  Due to decreased sidewall contact, more plastic chambers are required if they are to be used in a cluster configuration.  Plastic chambers must meet the same sitting requirements as stone bed and must be installed per the manufacturer's specifications.