Charleston tunnel construction could prove dangerous

The construction of a $26.5 million sewage project in Charleston could prove more dangerous than city planners realized.

Charleston’s commissioners recently learned the city’s two major sewer tunnels are deteriorating and have failed in several places. Each tunnel houses a smaller pipe that carries raw sewage to a treatment plant. If the pipe deterioration continues, the tunnels’ contents could end up spilling into Charleston Harbor.

The city hopes to begin construction on two new tunnels soon. The project will take two years to complete. Unlike the current, 12-inch-wide sewage lines, the new tunnels would be eight feet wide and two miles long.

The problem exists deep below the old city streets. Because the city is built on consolidated sands and silts, workers will have to drill the tunnel 100 feet underground, where there is marl, a material that will be strong enough to drill through. Drilling so deep through unstable material will be dangerous.

Charleston Public Works has taken about 50 soil samples to find out what kind of materials the workers will find when drilling the tunnel. One of the most dangerous days will be when the new tunnel crosses the old tunnel near Bee and Courtney streets. The old tunnel is flooded, and the new tunnel will drill just below the flooded sewage. If a mistake is made, the old tunnel could cave in on top of the workers. Another risk contractors face is that there might be antiquated tunnels that were never on a map.

Affholder Construction, of Chesterfield, Mo., won the contract with a $26.5 million bid. Although the company was not the lowest bidder, its bid was the lowest that met the utility’s bidding rules. As long as no complications occur, the utility had estimated the work to cost $27 million.