Combined Sewer Overflow (CSO) Abatement

What are Combined Sewer Overflows?

Combined sewers convey both sanitary and storm flow. The combined storm and sanitary flow frequently exceeds the capacity of interceptor sewers and treatment plant and cause overflows of untreated wastewater. The events are referred to as Combined Sewer Overflows (CSOs).


CSO abatement is of great importance in enhancing public health protection. The abatement of CSO is the greatest challenge facing many communities. In most cases CSO Abatement is very costly and results in substantial disruption of municipal activities.

Another challenge is meeting federal and state regulations. Many regulations or interpretations thereof often change. At this time communities are required to prepare long term plans for CSO abatement.

Control Plan as a Resource

Long term control plans are a resource. A well thought out long term control plan can be a resource to a community with combined sewers. The plan can provide for an orderly abatement program that includes implementation schedules and estimates of cost. The plan is a valuable resource in projecting the needs of the community.


Jones & Henry has worked on CSO abatement for municipalities and sewer district with populations ranging from 3,000 to approximately 500,000. In the course of this work the firm has encountered practically every conceivable situation and performed the many tasks required for a successful program.

In the process of developing CSO abatement programs, Jones & Henry has conducted field investigation, developed system models, and prepared CSO abatement plans. The plans always evaluate abatement options including full separation, on-site treatment, storage and treatment and plant expansion. The plans have included financial capability analysis and proposed implementation schedules.

Design and construction normally follow the abatement plans. Jones & Henry is highly experienced in preparing plans, assisting during construction, preparing O&M materials and training personnel in the operation and control of CSO abatement facilities.


Jones & Henry is experienced in providing all the services necessary to arrive at an appropriate CSO abatement plan and the design of required facilities. When dealing with legal issues, we work with the entity’s legal counsel.

The services we offer include, but are not limited to:

  • CSO system inventory and mapping
  • Metering and sampling
  • Model development
  • Water quality impacts
  • Financial capability analysis
  • Plan preparation including proposed schedules
  • Assistance with permit and schedule negotiations
  • Public participation
  • Design of improvements
  • Engineering during construction
  • Start-up assistance
  • Personnel training


The most important result from the municipality and Jones & Henry’s engineering efforts is to enhance public health protection. Jones & Henry planning for CSO abatement normally results in a program that can be implemented without overwhelming municipal finances. Jones & Henry makes every effort to discuss the implementation program with the client before submitting the document to the regulatory agency. We also follow up with the agency to try to secure an implementation schedule that creates the least impact on the community.

When dealing with construction we make every effort to minimize disruption in the community and to keep affected parties informed about project progress.

Jones & Henry
Engineers, Ltd.