Water quality inlets can be purchased as pre-cast units or can be constructed on site. Profile of a Typical Water Quality Inlet. Water quality inlets are commonly used where land constraints prohibit the application of other BMPs or where pretreatment of a portion of the runoff is desired. On-line units may not perform as well because of the increased turbulence of higher flows that cause resuspension of settled material in the sedimentation chamber. Infiltration Trench Infiltration trenches are designed to capture and filter small amounts of runoff, preferably the first flush.
Pollutant removal is achieved by filtration through the surrounding soils.
Trenches can achieve up to 90 percent removal of particulates, metals, organic compounds, and bacteria. Pollutant removal may be enhanced by adding organic material and loam to the trench subsoil. Upstream BMPs may be needed to pretreat runoff to remove sediments or hydrocarbons that may clog the trench. Industries can minimize the introduction of toxic and hazardous materials in the runoff by isolating areas of concern or by diverting flows from these areas away from the trench. Infiltration Trench Wet Detention Ponds Wet detention ponds provide both quality and quantity control of storm water.