US EPA

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.

This product is a jounral article describing the scope and magnitude of potential climate change impacts on CSO mitigation efforts in the Great Lakes Region and New England Region. The paper describes the extent to which CSO long-term control plans may be under-designed if planners assume that past precipitation conditions are representative of future conditions.