An Update on the Columbus Wet Weather Management Plan


Undergoing a system wide program for a metropolitan area of over 1 million people to address SSOs is a challenge. The same can be said for addressing CSOs throughout a system. Columbus is addressing both at once, creating a particularly daunting challenge. Columbus submitted one large report, the Wet Weather Management Plan (WWMP), to the Ohio EPA on July 1, 2005. This paper presents the major challenges of developing the plan as well as the Ohio EPA’s reaction to the plan. As such, it will provide a very current update on a compendium of wet weather issues and their interrelationships.

Columbus, Ohio entered into two consent orders with Ohio EPA to improve its overall wet weather program over the past three years. The consent orders required that Columbus develop plans to mitigate both sanitary and combined sewer system overflows by providing adequate management, operations and maintenance; and collection system and treatment capacity throughout its entire collection system by July 1, 2005. This required that the System Evaluation and Capacity Assurance Plan (SECAP) portion of its CMOM program and a CSO Long Term Control Plan (LTCP) Update be developed concurrently. The background, methodology, results, and recommendations of these studies were combined into a single document, the WWMP.

This paper provides an overview of one of the first and largest system-wide wet weather management plans that have been done in the country using the combination of the CMOM draft policy provisions and long-term control plan guidance. The City of Columbus has embraced a program to reduce overflows throughout its system by concurrently improving its operation while developing a long-range plan of necessary capital improvements. This effectively provides both short-term and long-term overflow and WIB reduction.

There are many challenges to Columbus’ wet-weather program. The plan is comprehensive and will be very costly, stretching its affordability to the community to its limit. The Columbus Division of Sewerage and Drainage (DOSD) staff and ultimately its satellite communities face such challenges as the need to oversee an enormous planning, design and construction program for the mitigation of overflows and water in basements (WIBs), the rehabilitation of deteriorating infrastructure, and the provision of services to new customers as the communities grow. In addition, while a program of new initiatives for improving management, operations and maintenance (MOM) is being put into place for both the collection system as well as the treatment plants, the ability to sustain the improvements without lapsing into old ways will ultimately define the success of the program.

The efforts leading to the development of this plan have involved a large integrated team of consultants, City employees with a diversity of responsibilities, the OEPA and the public. The completion of the capacity study is only the beginning of the program and the challenges the team faces will continue as the City works to achieve the goals established in the Consent Orders for decades to come.

Columbus’ separate sewer system comprises about 90 percent of the geographical area of the entire system. Approximately 101 designed sanitary relief points (DSRs) were identified throughout Columbus’ separate sanitary system, not including satellite communities. Eighteen have been eliminated since the inception of the CMOM program. The remaining DSRs activate, causing SSOs with a variety of frequencies. One DSR activates approximately 40 times per year; about 75 DSRs activate between 1-30 times per year; and the balance of the DSRs are not known to be active at all. Approximately 25 combined sewer overflows (CSO) regulators are located in and around the downtown area. These activate, on the average, much more frequently than the DSRs. One of the CSO locations contributes approximately 85 percent of the total annual CSO volume. Figure 1 shows the overall wastewater collection system service area, about 600 square miles, outlined in blue, and the combined sewer area shaded in green. Main trunk sewers are red.

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