A Screening Assessment of the Potential Impacts of Climate Change on Combined Sewer Overflow (CSO) Mitigation in the Great Lakes and New England Regions

Combined sewer systems collect and co-treat storm water and municipal wastewater. During high intensity rainfall events, the capacity of CSSs can be exceeded resulting in the discharge of untreated storm water and wastewater directly into receiving streams. These combined sewer overflow events (CSOs) can result in high concentrations of microbial pathogens, biochemical oxygen demand, suspended solids, and other pollutants in receiving waters. Climate change in many parts of the country is expected to increase the proportion of rainfall occurring in high intensity events, resulting in increased stormwater runoff. Climate change thus presents a risk of increased CSO frequency and water quality impairment.