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South Cobb Tunnel

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After the success of the Chattahoochee Tunnel project, the Cobb County Water System (CCWS) determined that a deep tunnel would be the best alternative for providing needed sewer capacity in the south Cobb area. The South Cobb Tunnel is the largest capital improvement project in CCWS history. A $305,000,000 construction contract was awarded to Shea-Traylor J.V. (a joint venture of J.F. Shea Construction and Traylor Brothers) on March 26, 2008. Construction started in July 2008, and the tunnel portion of the contract was completed in May 2013, which was about a year ahead of schedule.

The South Cobb Tunnel project entailed constructing a 5.5 mile tunnel located in hard rock, with depths ranging from 150 feet to 400 feet. The tunnel was excavated using the large tunnel boring machine pictured below. The excavated diameter is 27 feet, and approximately 75 percent of the tunnel was lined with concrete to a finished diameter of 24 feet. Several six-foot diameter tunnels and one ten-foot diameter tunnel with lengths ranging from 100 to 3,200 linear feet were constructed also. This project allowed CCWS to eliminate two major pumping stations and about 87,000 linear feet of ageing sewer lines and force mains.

The main tunnel alignment begins near the intersection of Maxham Road and Old Alabama Road continues southeast along the county line then turns east just north of I-20 and continues east to the South Cobb WRF. To view a map of the project click here.

The project also included building a deep lift station with a capacity of 130 million gallons per day at the South Cobb Water Reclamation Facility (WRF) to convey wastewater flows from the tunnel to the plant for treatment. The lift station is 100 feet in diameter and 200 feet deep.