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

This report describes the potential scope and magnitude of climate change impacts on combined sewer overflow (CSOs) mitigation efforts in the Great Lakes Region and New England Region. The report 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. Combined sewer systems (CSSs) 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 could thus present a risk of increased CSO frequency and resulting water quality impairment.

Following the public comment period, the report will undergo an external peer review. The report will then be revised to address comments and posted on the NCEA web page. EPA will consider any public comments submitted in accordance with this notice when revising the document.

Comments on this report may be submitted and reviewed using the e-Government Regulations.gov Web site. From the site, select Environmental Protection Agency and the keyword EPA-HQ-ORD-2007-0239 (for the docket ID) to comment on this report.

U.S. EPA. A Screening Assessment of the Potential Impacts of Climate Change on Combined Sewer Overflow (CSO) Mitigation in the Great Lakes and New England Regions (External Review Draft). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-07/033A.