This compact subsurface treatment is well suited for space-constrained sites, where a larger, surface treatment is impractical. Depending on regulations, these devices are used by themselves, or as pretreatments with other stormwater systems. The system is comprised of two devices in series. The first, Aqua-Swirl, is a four-foot diameter hydrodynamic separator. The second, Aqua-Filter, is a larger chamber with 24, one-cubic foot, nylon bags filled with perlite beads that act as a filter. Both are made from recycled high-density polyethylene pipe.

The Aqua-Swirl uses vortex settling to remove sediment, trap debris and trash, and separate floating oil and grease. The Aqua-Filter has internal spillways that direct influent across a suspended platform and through its filter media. Stormwater collects in the lower half of the Aqua-Filter chamber, and then exits when water levels reach outlet elevation.

Presumably, the manufacturer can alter the filter to target specifi ccontaminants. Unobstructed access to the Aqua-Swirl and lack of moving parts enable easy maintenance. In the Aqua-Filter, frequency of filter replacement depends on site contaminant loading characteristics. Maintenance includes the periodic removal of solids by a vacuum truck.