Approved by the Energy, Environment, and Water Policy Committee on February 20, 2024 
Approved by the Public Policy and Practice Committee on May 1, 2024
Adopted by the Board of Direction on July 18. 2024

Policy

The American Society of Civil Engineers (ASCE) supports the Environmental Protection Agency’s (EPA) national policy statement for combined sewer overflow (CSO) systems that establishes a consistent national approach for controlling existing CSO discharges to meet Clean Water Act (CWA) goals. Specifically, ASCE supports:

  • Revisions to the EPA long-term control plan guidance on CSOs and green infrastructure to incorporate the strengths of green infrastructure that reduce the volume of stormwater flow into existing combined sewers.
  • Increased funding for achieving the required level of control, such as EPA funded clean water state revolving funds and construction grants to support implementation of long-term control plans.
  • Flexibility to adapt to applicable water quality standards at the local and regional level to reflect site-specific conditions.
  • Guidance for developing control options and strategies that include consideration of performance versus cost without sacrificing public health and safety.
  • Development and implementation of multi-year consent decrees that are openly and constructively negotiated between regulatory agencies and wastewater utilities that effectively balance the enforcement of water quality objectives with the ability of the utility to deliver and afford the CSO control facilities that will meet those objectives.
  • Cooperative partnerships and/or inter-agency agreements to successfully implement consent decrees and maintain long-term CSO compliance.
  • Disallowing the construction of new combined sewers.

Issue

ASCE recognizes the problems inherent with combined sewer systems, including the environmental and health risks resulting from overflow conditions. Historically, combined sewers had been an acceptable method to collect storm water, sanitary sewage, and industrial effluents in a single conduit for discharge to water courses. This practice is no longer acceptable because of today’s understanding of the environmental and health risks imposed by this practice. 

Combined sewer systems serve hundreds of communities that range in population from fewer than 10,000 people to millions of residents. Most communities with CSOs are located in the Northeast and Great Lakes Regions. 

Increased industrial and residential growth with reductions in green spaces and increased development with impervious surfaces, has accelerated the rates at which runoff enters the sewer systems, hydraulically overloading these systems and creating more frequent overflow conditions. Separation of flows in combined sewer systems, including roof leaders and other urban conduits that carry runoff, requires significant investment. In addition, separate stormwater discharges may require treatment to remove contaminants and debris that enter the storm systems. 

Many cities have reduced CSOs by providing storage within the collection system which captures excess flows until treatment capacity is available. Storage can be provided by increasing the capacity of sewer interceptors providing in-line storage, adding underground storage, and other methods. 

Green stormwater infrastructure should be evaluated as part of a sustainable adaptive management strategy to control CSOs. Potentially, large-scale traditional infrastructure approaches (tunnels, pipes, tanks) can be reduced in size and cost with judicious use of green stormwater infrastructure. The green infrastructure approach provides additional co-benefits including removal of pollutants from runoff, creation of green public space and the reduction of urban heat island effects. These measures were not available when the current federal regulatory structure and supporting long-term control plan guidance were developed and the language and process in that guidance will require updating in order to encourage appropriate consideration of this approach.

Federal regulatory requirements for CSO control vary across the country and dependent on the CSO discharge receiving water. The primary burden of financing and executing the remedial work required to comply with the current federal regulatory requirements fall on state and local governments and wastewater utilities. The costs for these improvements often exceed what sewer system rate payers can afford. Sustained federal grant and loan funding is required to ensure these systems can achieve regulatory water quality goals within reasonable timeframes. 

Rationale

Remedial CSO works projects designed to correct the problems of controlling combined sewer discharges are often large, complex, and economically challenging. Sustained increases grant and loan funding is required to achieve environmentally safe and functional sewer systems and new approaches for sustainable, adaptive management strategies to control CSOs need to be implemented.

ASCE Policy Statement 395
First Approved in 1992