Divers soon will plunge into Lake Erie and begin grinding up a giant mound of dead zebra mussels that has been accumulating at the entrance of an intake pipe that supplies water throughout the city.

The Water Board has signed a $396,000 contract with Buffalo Industrial Diving Co. to remove an underwater graveyard of mussel shells that has been expanding since the early 1990s. The pile of dead shells, 12 feet long by about 10 feet wide, is 8 feet high in one spot.

In one area, the shells are blocking about two-thirds of the pipe’s opening. While engineers said the shells are unlikely to cause problems for decades, they don’t want to take any chances.

The unusual operation will begin before Labor Day and could take four to six weeks, said Mark Judd, Buffalo Industrial Diving’s president and CEO.

“It’s a very serious situation when you have divers going down 80 feet, then another 300 feet [into the tunnel],” Judd said.

The team of six or seven divers will be equipped with some high-tech equipment, including cameras and lights mounted on helmets.

“We’ll be able to see everything they’re doing,” Judd explained.

While the underwater conditions pose challenges, City Engineer Peter Merlo said the operation will be fairly basic. Divers will scoop the shells and place them in a grinder attached to a hose. The ground-up material — essentially calcium — will be pumped back into the lake. The state Department of Environmental Conservation has given the city permission for the operation, with some conditions. If the discharge causes the water to become cloudy, work would have to be suspended. Merlo is confident this won’t occur.

“The discharge rate will never impact the flow stream at all,” Merlo said. “All we’re doing is putting it back where it came from — the lake.”

If state environmental regulators had forced the city to haul the shells on to a barge, then ship them to a landfill, some city officials estimated that the price tag could have been in the millions.

The project’s timing is important, said Oluwole A. McFoy, Water Board chairman. Launching an underwater operation too late in the year could cause weather-related delays.

“We definitely want it done before winter,” McFoy said.

The small mountain of shells demonstrates that a chlorine treatment system has been effective in controlling zebra mussels, officials stressed. But they incorrectly assumed that the chlorine injections had prevented a massive spread of the invasive invertebrate into the water intake.

A maintenance program is being established to monitor the intake and undertake smaller-scale cleanups. The Water Board periodically will use a remote-operated device to take video footage of the intake.

“We’ll then probably have someone go in there and do very minor cleaning every couple years,” Merlo said.

In fact, Buffalo Industrial Diving last cleaned the intake about eight years ago, recalled Judd, whose Grand Island-based company handles numerous underwater operations.

bmeyer@buffnews.comnull