Army engineers began to control the water in Chicago`s flooded underground tunnels Wednesday, stabilizing the rate at which the water was draining out.
Water had been seeping out of the tunnels and into sewer pipes at a rate of nearly 1 inch an hour, making it difficult for engineers to maintain water levels, said Lt. Col. Randall Inouye, Chicago district commander for the Army Corps of Engineers, which is running the operation.
Engineers had worried that the water was coming out too quickly, building up pressure on the tunnels. To counter that, they turned off eight pumps Tuesday night, slowing the draining from 25,000 gallons per minute to 4,900 gallons per minute.
Although the water may still be seeping through the tunnel walls, engineers were able to stabilize the rate of receding water at 1 1/2 inches an hour.
On Wednesday, engineers gradually turned the pumps back on. There are a total of 11 pumps spread out at three pumping sites.
By 7 p.m. Wednesday, water levels had dropped to 24 feet below ground level, with an average pumping rate of 14,000 gallons per minute. Engineers will maintain that rate through Thursday to stabilize pressure in the tunnels and allow crews at the Kinzie Street bridge to prepare permanent plugs at the site of the leak in the Chicago River, Inouye said.
Divers inspected the tunnel Wednesday to determine what type of bulkhead will be most effective in sealing the leak.
Crews on both sides of the bridge continued sealing the three concrete plugs that initially stopped the flow of river water through the tunnel system. Inouye said further reinforcement is necessary before pumping can be accelerated.
”We want to make sure we have a good tight seal on them before we bring
(the water level) down to where we`re going to have maximum pressure on those plugs.”.
After levels drop 3 more feet, engineers will begin working with Illinois Department of Transportation officials to coordinate draining of the tunnel near the Hubbard`s Cave section of the Kennedy Expressway, Inouye said. Pumping in that area has averaged 1,000 gallons per minute, substantially lower than pumping elsewhere, to minimize pressures on the tunnel walls.
Nearly 38 million gallons had been pumped into the Deep Tunnel by early Wednesday night. Engineers still expect pumping to be finished by May 1, Inouye said.
