Market flood-control tunnel hits snag

The flood-control project designed to relieve Charleston’s troublesome Market area faces new costs and delays after a potentially dangerous and abandoned tunnel was discovered deep below.

The problem means engineers must dig a pump shaft on the harbor side of the Customs House some 60 feet deeper than previously anticipated, resulting in 206 additional days of work.

Charleston Public Works Director Laura Cabiness said if workers were to breach the older tunnel while sinking the new shaft, it could mean opening a potentially dangerous pocket capable of flooding where workers would be.

“Ou tunnel is too close to the ‘void’ space,” Cabiness said.

As a result of the change order, the cost of the project will increase by about $2.7 million to cover the expenses of going deeper, pouring more concrete and securing a tunnel 60 feet further below the surface.

Instead of putting the pump station’s vertical shaft down to 80 feet, it will go down 140 feet.