A Screening Assessment of the Potential Impacts of Climate Change on the Costs of Implementing Water Quality-Based Effluent Limits at Publicly-Owned Treatment Works in the Great Lakes Region

Publicly owned treatment works (POTWs) discharge billions of gallons of effluent daily to receiving water bodies throughout the U.S. One of the principal pollutants associated with POTW effluent is organic matter. Naturally occurring microbial populations in receiving waters consume dissolved oxygen (DO) as they decompose organic matter. Low DO is a significant source of water quality impairment. Climate change is expected to increase the proportion of rainfall occurring in high intensity events, resulting in increased stormwater runoff. At the same time, a shift towards more intense storms will decrease infiltration and groundwater recharge, resulting in reduced low flow periods between events. Increased air temperatures and evaportraspiration could also result in reduced streamflow between rainfall events. Reduced low flow events in receiving waters could result in increased water quality impairement below POTWs due to reduced dilution of effluent.