The spill began at about noon at the pumping station at 790 Lehua Ave.

Athan Adachi, chief of the city's wastewater division, said the city was doing improvements at the pump station when a contractor opened a portion of a pressurized sewage pipe.

Adachi said a "miscommunication" between the contractor and a plant employee led to the pipe being opened.

"The pipe broke loose and the sewage started coming out," Adachi said. "They couldn't shut it down and the whole area started to flood with sewage."

The initial spill was contained on the pump station grounds, but about 1.4 million of the 2.3 million gallons that spilled wound up in Waiawa Stream and Pearl Harbor's Middle Loch, Adachi said. He said the flow was not stopped until 6:30 last night.

Adachi said the spill was difficult to stop because workers needed to pump the wastewater out of the station to get in and cap the pipe. He also said several pump trucks were delayed because they got caught in rush-hour traffic.

Crews were expected to work through the night to mop up the area. Warning signs have been placed around the affected areas and the Department of Health has been notified of the spill.

Yesterday's spill was the largest since March 2004 when about 2 million gallons of raw sewage spilled after a main that feeds the Sand Island Wastewater Treatment Plant ruptured. Two years earlier, a line near Ke'ehi Lagoon broke, spilling about 3 million gallons.