Water Quality Inlets

Water quality inlets (WQIs), also commonly called trapping catch basins, oil/grit separators or oil/water separators, consist of one or more chambers that promote sedimentation of coarse materials and separation of free oil (as opposed to emulsified or dissolved oil) from stormwater (see Image on the right). To prevent turbulent flow from entering the unit and resuspending settled pollutants in Oil/water separation tanks, diffusion baffles are often fitted at the inlets of WQIs. Some WQIs also contain screens to help retain larger or floating debris and in newer design a coalescing unit to promote oil/water separation.

WQIs are appropriate for capturing hydrocarbon spills, but provide very marginal sediment removal and are not very effective for treatment of stormwater runoff. WQIs typically capture only the first portion of runoff for treatment and are generally used for pretreatment before discharging to other BMPs.

Because of WOIs’ ability to remove hydrocarbons, WQIs are ideal for sites that are related to automotive contamination in specific industrial areas, such as airport aprons, equipment washdown areas, vehicle storage areas, gas stations, loading/unloading areas, or parking lots. Since WQI residuals contain hydrocarbon by-products, they may require disposal as hazardous waste. WQIs can be relatively deep, they may be designated as confined spaces. OHSA confined space entry safety regulations should be complied, if it is required.

Click here for the detailed design of water quality inlet from the EPA’s Storm Water Technology Fact Sheet: Water Quality Inlets.

Copyright @ January,2005 Prepared by Transportation Environmental Resource Center (TERC)