A decision by the U.S. Court of Appeals for the Eighth Circuit may finally offer a path to relief for operators of publicly owned treatment works (POTWs) confronted with the challenge of managing peak wet weather flows. The decision also may prompt the U.S. Environmental Protection Agency (EPA) to resolve regulatory uncertainty surrounding the permitting of mixing zones in certain waters. A recent pronouncement by the EPA regarding how the agency intends to apply the Eighth Circuit decision may inform how municipalities and municipal authorities plan their future capital projects.
Blending
Most POTWs direct incoming flows first through a primary treatment process and then through a secondary treatment process. Primary treatment removes coarse solids from wastewater, while secondary treatment removes organic matter, usually through biological processes. Wet weather conditions may subject aging sewer line infrastructure to infiltration and inflow (I/I). High volumes of I/I can overwhelm secondary treatment biological processes, which are extremely sensitive to variations in flow and pollutant concentration. In extreme cases, I/I can even render biological treatment facilities inoperable.
