City crews spilled about 800 gallons of raw sewage into the Ala Wai Canal yesterday while switching on a bypass conduit designed to carry wastewater through a pipe sunk in the canal to the treatment plant.

Even a small release of untreated sewage is a reminder of the 48 million gallons of sewage pumped into the canal last March and the problems that still loom with Honolulu's aging sewer system.

The good news is that the bypass has been in place since July and was ready to handle the wastewater when sewer-main damage turned up during construction work yesterday.

That contrasts with the situation in March, when a pipe ruptured following weeks of heavy rain and resulted in the state's largest recorded raw sewage spill. With no backup or bypass available, Mayor Mufi Hannemann was faced then with a choice of sending raw sewage into the canal or risking it backing up into hotels, homes and businesses.

In 2004, the city was warned that the pipe was among those in "very critical" shape. The city set aside $30 million for sewer work in Waikiki, but repairs were not made before the break on Kai'olu Street contaminated waters off some of the state's most famous beaches.

As a precautionary measure yesterday, the city posted warning signs asking people to stay out of the canal right behind Ala Wai Elementary School and at the Ala Wai Yacht Harbor and Magic Island for a few days while water quality tests are conducted.

City officials advise people to avoid the affected waters. City environmental services workers and lifeguards warned beachgoers, surfers and canoe paddlers about the spill.

City engineer Eldon Franklin, who works for the city Department of Design and Construction, said the spill occurred on the mauka side of the canal near the school because a valve was improperly set. "It's just unfortunate that we missed that one," Franklin said.

He said most of the wastewater was safely transferred through the pipe, which connects to a pumping station that eventually sends sewage to the Sand Island Wastewater Treatment Plant.

State Health Department spokeswoman Janice Okubo said the city notified the state immediately. "That's actually a relatively small spill," she said.

The need to use the bypass was prompted by a crack in the 42-year-old sewer main in Waikiki.

STREET PIPE CRACKS

Crews were preparing to remove and replace a section of the sewer main in the coming weeks, and that would have prompted the use of the bypass anyway. But it was pressed into service sooner when workers doing prep work for that operation discovered a crack about 3 feet long and 4 inches wide, said Craig Nishimura, deputy director of the Department of Design and Construction.

The crack in the pressurized sewage line occurred next to the Beachwalk pumping station, which is on Kuhio Avenue at Kai'olu Street. That line normally carries wastewater from Waikiki and surrounding neighborhoods toward the Ala Moana pumping station and on to the Sand Island plant.

Nishimura said contractors were excavating around the pipe when the pit filled with wastewater, alerting workers to a problem.

The leaking wastewater — estimated at 15,000 gallons — was pumped back into the sewer system for treatment, Nishimura said. While crews are working to repair the broken line, diesel-powered pumps will force the raw sewage into the temporary pipe to avoid the cracked pipe and the pump station.

BYPASS KICKS IN

The emergency bypass is expected to be used for about two months following this incident, he said.

The big dark bypass pipe runs along the Ala Wai Canal and submerges part of the way, where the S-shaped path can be traced by moored markers.

The city has been working on what's called the Waikiki Beachwalk bypass project since March's major rupture.

"Had we not already installed the emergency pumps and pipes, we'd be facing another crisis today," Hannemann said.

The federal Environmental Protection Agency has yet to issue its enforcement action against the city for the March 24 spill. That is expected to include fines and other sanctions against the city.

Reach Robbie Dingeman at rdingeman@honoluluadvertiser.com.