Correction: An earlier version of this report said the estimated replacement cost was $20 million.

Sewage spills are likely to continue in West Kapolei near Ko Olina until corroded pipes are replaced at an estimated cost of $34.6 million, a Honolulu City Council committee was told Wednesday.

Earlier this month a sewage line broke in West Kapolei near Ko Olina, spilling about 137,400 gallons of untreated sewage into an undeveloped part of the resort. The break occurred Jan. 2, but the city wasn’t notified until a day later.

The same line ruptured about one month earlier, causing over 200,000 gallons of untreated sewage to spill over an acre of undeveloped land near Ko Olina Golf Club. The line ruptured Nov. 29, but the city was again unaware of the spill for almost 24 hours.

The sewage line and a smaller one that runs nearby have had five spills in the last four years. Addressing these spills was among the topics covered during a briefing before the Committee on Public Works, Infrastructure and Sustainability.

Improving the monitoring system for spills is key to addressing them, said Lori Kahikina, director of the Department of Environmental Service.

The department monitors Oahu sewage lines 24 hours a day from remote offices, including one at Sand Island.

Staff at each office monitors a large number of sewage mains, but when a spill does occur, it’s hard to notice, Kahikina said.

A recent Ko Olina spill showed up as a “tiny, little blip” on a graph, she said.

In the two most recent line breaks, contractors working in the area happened to pass by, notice the spills and notify the city, she said.

“The operator at Sand Island didn’t even notice that there was a tiny increase in the flow that was being pushed out,” Kahikina said. “By the time we’re notified, it’s huge, it’s all over the ground.”

In addition to finding ways to improve the monitoring system, the department now sends a crew out to Ko Olina to drive along the lines weekly to check for spills, she said.

These types of pipes, called force mains, usually last 50 years. The two rupturing pipes near Ko Olina are only 29 years old, but in light of recurring main breaks, the city has opted to replace them.

Corrosion causes the sewer lines to break, but it’s unclear what exactly is causing the rapid corrosion, she said. Whatever the cause, there’s reason to believe the sewer line breaks will not stop.

“Until we can get those two force mains replaced, I suspect we’re going to be having more (spills),” Kahikina said.

If the city started immediately, it would take two years to replace the pipes and cost an estimated $34.6 million, she said.