Crash Course for the new EPA Wet Weather Stress Testing Protocol

Treatment of peak flows during wet weather is a common challenge across the country for municipal wastewater collection systems with separate or combined sewer systems. Increases in wastewater flow resulting from infiltration and inflow (I/I) triggered by a combination of precipitation, snowmelt and high groundwater conditions during wet weather events can result in operational difficulties for publically-owned treatment works (POTWs) and compromise proper treatment and compliance with discharge permits or receiving water criteria. A need exists for POTWs to increase peak wet weather capacity while protecting the functionality of sensitive unit treatment processes. This is especially true since the biological process is typically required to hydraulically pass the peak hour flows, as opposed to treat peak hour flows. CDM Smith was contracted by the Environmental Protection Agency (EPA) to develop a protocol stress testing framework for POTWs that could be used for municipalities across the country embarking on multi-year, capital-improvement programs to upgrade their wastewater and storm water facilities.With increased demand on utilizing existing infrastructure at POTWs, identification of operational changes and/or cost-effective capital improvements demonstrated that municipalities can potentially reduce larger capital investments in new treatment facilities. This paper reports on the information discovered during the course of the literature review, information gathered from published examples of stress testing at POTWs, subsequent discussions with industry experts comprising the state of knowledge, as well as how this relates to EPA peak wet weather policy.