An Old Problem

The Problem

Our sanitary sewer system works well most of the time, but rain water and snow melt can seep into the system and overload it. This excess water enters the sanitary sewer from yards, roofs, downspouts, foundation drains, improperly connected sump pumps, uncapped cleanouts, manhole covers, holes, cracks and breaks in pipes, joint failure, faulty connections and other openings. Relief points provide an outlet for the excess flow and discharges from these outlets are referred to as sanitary sewer overflows (SSOs). Excess flow can also cause sewage back-ups in the basement of homes or businesses.

Sewer overflows are not unique to Columbus. Cities across the country are experiencing the same problem: the amount of water entering the sanitary sewer system is exceeding the system's capacity to hold it. Until recently the solution was to increase the system's storage capacity by building larger pipes. But that is not truly a solution because it does not keep the rain water from entering the system in the first place.

How has the Problem Been Addressed?

The City of Columbus has been approaching the problem of sewer overflows and basement backups from different angles for a number of years. Until recently, the guiding document was the Wet Weather Management Plan submitted to the Ohio Environmental Protection Agency (OEPA) in 2005. This plan was developed in accordance with consent decrees the City entered into with the OEPA to reduce the number of overflows from the combined sewer system and eliminate basement backups and overflows from the separate sanitary system.

Projects that reduce overflows in the combined sewer system were scheduled in such a way that most of those issues have been addressed. The remaining projects largely focus on the separate sanitary sewer system. The 2005 plan included building two large, deep tunnels to take all of the flows in the sewers, including rain water that has leaked into the system, to the wastewater treatment plants.

Building these tunnels requires specialized machinery and operators and is therefore a very expensive endeavor. A German company manufactures the tunnel boring equipment and the process is jointly overseen by firms out of Japan and Chicago.