Slide 3 of 52
Notes:
Filter systems are comprised of the following four major design components:
The inflow regulator is designed to divert the desired water quality volume into the filter, while allowing larger flows to continue through the conveyance channel. With a few exceptions, most filtering systems are constructed off-line (i.e., runoff is diverted from the main conveyance system, treated, and then returned back to the conveyance system.
Pretreatment is needed in every design to trap coarse sediments before they reach the filter bed. Without pretreatment, the filter will quickly clog, and lose its pollutant removal capability. The most common pretreatment technique is a wet or dry settling chamber. Sediments deposited in the pretreatment chamber must be removed periodically to maintain the system.
Filter Bed and Filter Media
Each filtering system utilizes some kind of media such as sand, gravel, peat, grass, soil or compost to filter out pollutants entrained in urban stormwater, and some designs utilize more than one. Selecting the right media is important, as each has different hydraulic, pollutant removal and clogging characteristics.
Outflow/Overflow Mechanism
The two primary methods for handling filtered runoff are to collect it in perforated pipes and return it back to the conveyance system, or to allow it to exfiltrate into the underlying soils where it may ultimately reach groundwater.