It isn’t at the finish line yet, but the Chattahoochee Tunnel project will soon reach the home stretch.
Officials celebrated the emergence of one of the 77-ton tunnel boring machines at the access shaft in the Cumberland area last month.
The machine, which started at Elizabeth Lane in August last year, cut through 4.5 miles of rock, hundreds of feet below the surface of Cobb County.
A second boring machine is making its way to an access shaft in the Indian Hills subdivision in east Cobb to complete the 9.5-mile-long Chattahoochee wastewater tunnel.
The 18-foot diameter tunnel is expected to provide service for the growing east Cobb community for at least the next 100 years.
“We are less than a mile from completing total tunneling in the project,” Water Systems Director Bob Brice said in October. He predicted the second machine would reach its goal by the end of the year.
The next step for workers will be to place partial concrete linings in both sections of the tunnel. The entire $113 million project is expected to be complete by mid-summer 2004.
Brice said everyone is very pleased with the results of the work. A comparable “open cut” wastewater line closer to the surface would have required many easements from private landowners, removed trees and torn up many roads - as well as made for a longer line.
“This has had the least impact on the environment and the community,” Brice said.
The project is on time and under budget, officials said.
The deep rock tunnel runs from 100 to 375 feet underground and will not just handle the wastewater for east Cobb.
It will also provide the Water System extra storage capacity during times of heavy rains, therefore preventing sewer overflows into the Chattahoochee River.
Brice said during such heavy flows, the tunnel will be able to store the wastewater until it can be sent into the treatment plant.
The tunnel boring machines are “amazing technology” that is able to provide smooth tunnel walls and move rock shavings along 22,000 feet of conveyor belt to the surface, Brice said.
Each of the 39 cutters on the tunnel boring machine weighs 400 pounds. The cutters are each able to exert 70,000 pounds of pressure.
The first tunnel boring machine, with its job complete, is being removed to start a similar project in the City of Atlanta.
While Atlanta is facing spending about $3 billion to update their system, Brice pointed to the comparitive $113.5 million the county is spending on the Chatahoochee Tunnel – the largest Water System project to date.
He said the support of the Cobb Board of Commissioners has allowed the county Water System to routinely keep its infrastructure up to date. “We have been able to keep our system in pretty good shape,” Brice said.