Penn Cove opened late Friday, but Oak Harbor and Crescent Harbor are still closed to shellfish harvest and other water recreation as a result of a large sewage leak from Oak Harbor waterside treatment plant Sept. 3.

In the meantime, Public Works Operations Manager Bob Jarski said the city staff members have investigated the cause of the leak and are working to prevent it from happening again.

The leak was caused by a hole in a ductile iron force main just outside the sewage treatment plant. Jarski said he believes that the hole was caused by corrosion through a process called electrolysis.

“A charge difference, positive or negative, causes a chemical reaction to occur,” said city engineer Larry Benfield, “and eat away at the pipe.”

Saltwater and soil type can contribute to the corrosion.

Jarksi said an expert in ductile iron pipes is coming to the city later this months to see if the rest of the 7,800 feet of pipe is corroding.

City Attorney Phil Bleyhl said the city’s new insurance company, Washington County Insurance Association, is also investigating the cause. The city’s coverage began Sept. 1.

According to Jarski, the leaky pipe was fixed Sept. 7. Workers attached “sacrificial zinc anodes” to the pipe to prevent electrolysis-related corrosion in the future.

Jarski said staff members from many different departments came together to tackle the problem, working day and night.

“It was a team effort,” he said.

About 100,000 gallons of raw sewage leaked into the harbor before the break in the pipe was noticed. Millions of gallons of partially-treated waste water was discharged because of the overtaxing of the system.

As a result, the Department of Health closed beaches from Crescent Harbor to Penn Cove.

Kathleen Parvin, environmental health specialist at the Island County Health Department, said Oak Harbor’s beaches — especially the City Beach Lagoon — and Crescent Harbor remain closed to shellfish harvest and swimming because of high levels of fecal bacteria.

She said the closures remain until the test results show safe levels.

Godwin Pump of Kent brought in about 8,000 feet of pipes, as well as pumps, to move the water from the City Beach sewage treatment plant to the sewage lagoons at the Navy’s Seaplane Base.

Jarski said he doesn’t yet have a clear estimate of the cost of the leak. He said the pipe rental and the help from Krieg Construction will probably cost between $30,000 to $50,000. Staff overtime will be more.

In addition, the owner of Penn Cove Shellfish estimates his losses of up to $200,000.