Charleston Water System to hold press conference at 10 a.m. Monday, August 9th at the Broad Street construction site
(August 5, 2004)—Charleston Water System is offering an opportunity for the media to photograph the tunneling boring machine (TBM), an impressive $1 million, six-foot-diameter machine that will “drill” the tunnel cavity for Charleston Water System's Ashley Sewer Tunnel replacement project.
The Ashley Tunnel is the second phase of Charleston Water System's four-phased Sewer Tunnel Replacement Project, which Charleston Water System began in 1998 and expects to complete by 2009 at a total cost of well over $100 million. “This is one of the largest infrastructure projects in the state and is critical to protecting public health and the environment in the City of Charleston,” said John Cook, P.E., Charleston Water System Assistant General Manager. “It's also one of the largest and most important projects in Charleston Water System's history, but it's not highly visible because the majority of construction work will take place more than 100 feet underground.”
Charleston Water System began construction on Phase II—the Ashley Tunnel—in March 2004 and expects to complete the tunnel in January 2006. The tunnel contractor, Affholder, Inc., of Chesterfield, Missouri, will construct the tunnel using seven 120-foot-deep shafts, which are located near the existing tunnel shafts, and will provide access to the tunnel depth during construction. The tunnel boring machine will arrive on Monday morning and will be lowered into the Broad Street shaft soon afterward to begin drilling the new tunnel.
The only visible signs of the tunnel construction are at the shaft sites; the underground tunneling will have no impact on the surface. Once the tunnel is complete, the shafts will be used to connect the new tunnel system into the existing sewer system.
History of the Sewer Tunnel
The existing sewer tunnel system was constructed in the late 1960s to carry wastewater to the Plum Island Wastewater Treatment Plant on James Island, which was built in 1970. The tunnel was constructed with steel ribs and wooden lagging boards in between those ribs, with a concrete carrier pipe inside to actually carry the wastewater. Prior to the existence of the tunnel and treatment plant, raw sewage was discharged directly into the Harbor, causing severe water quality problems and numerous, highly publicized fish kills.
In the late 1990's, divers discovered serious damage inside the tunnel system, caused by corrosion from sulfuric acid, which is produced under certain conditions when air reacts with wastewater. The technology and construction materials available at the time the tunnel was built did not account for air becoming entrained in the wastewater as it entered the tunnel, and over time, corrosion caused holes to develop in the carrier pipe. In some sections of the tunnel, the steel “ribs” supporting the tunnel structure have collapsed onto the carrier pipe.
In 1998, Charleston Water System began replacing the most deteriorated section of the tunnel system, the section stretching from the Battery, under the Harbor, to the Plum Island Wastewater Treatment Plant. This first phase of the replacement project, called the Harbor Tunnel, was completed in 2001 at a cost of $15 million, and is currently in service.
As Phase II, the Ashley Tunnel, is under construction, engineers are now working on the design of Phase III—the Cooper Tunnel—which is located along the east side of the Peninsula from Huger Street to Water Street.
The final phase of the replacement project is the West Ashley Tunnel, which connects carries all wastewater from the West Ashley area to the treatment plant. Charleston Water System is financing all four phases of the replacement project through existing and future revenue bonds, wastewater rates and fees, and federal funding.
*A brief press conference will be held at 10:00 a.m. on Monday, August 9th at the main construction site located at Broad Street and Lockwood Drive (across from the Coast Guard Station) in downtown Charleston. Project engineers will be available to answer questions and the tunnel boring machine will be available for photographs.
*Please note that there will not be another opportunity to photograph the TBM.
*More details about the Sewer Tunnel Replacement Project are available at www.charlestonCharleston Water System.com.