MUKILTEO – Surging storm water in Big Gulch has unearthed additional areas of Mukilteo’s main sewage line this month, raising concerns that it could break, sewer district officials said.

If the line breaks, raw sewage and other pollutants could be released into Big Gulch Creek and Possession Sound.

The Olympus Terrace Sewer District’s board of commissioners voted Monday night to declare an emergency so the district can repair the pipeline without soliciting bids.

“We believe it’s likely to rupture before this winter is over with,” district manager Patrick Sorensen said. “It could rupture at any time.”

The line carries wastewater from homes and business in the northern two-thirds of Mukilteo down Big Gulch to a treatment plant on Possession Sound.

Repair will likely involve building an estimated 600-foot bypass around the exposed sections, Sorensen said.

The repair could cost between $200,000 and $500,000, said Pete Weber, an engineering consultant working for the district.

“And that’s assuming we catch it before it breaks,” he said.

There would be a ceiling on the contract amount, Sorensen said. It’s hoped the repair can be done in the next few weeks.

The sewer line was originally buried 8 to 10 feet deep its entire length, Sorensen said.

Other parts of the 35-year-old concrete line have been exposed in recent years. The district has proposed replacing the line and, in addition, building a storm-water bypass line to reduce erosion in the gulch.

Replacing the entire sewer line is projected to cost $12 million, while building the pipeline and the storm-water bypass line is estimated at $13.5 million. Building the bypass line would lessen the need for restoration work on the streambed, officials say.

In July, the city of Mukilteo pulled out of a deal in which the cost of both pipelines would have been split three ways with the sewer district and Snohomish County, owner and operator of Paine Field.

The city said the county should pay more to reflect the airport’s effect on storm-water runoff.

Afterward, county officials also decided against helping the district pay for a bypass line, opting instead for building as many as seven retention ponds at the airport at a cost of up to $1.8 million.

The sewer line must be replaced, Sorensen said. District officials will decide over the winter whether to build the storm-water bypass line as well. Either way, a rate increase to pay for the projects is likely, he said.

The latest exposures of the pipeline are worse than the others because the creek is rushing over the line rather than alongside it, Sorensen said. There’s also a boulder just upstream that could be pushed into it.

The new exposure is in a cramped and hard-to-reach part of the gulch, meaning materials might have to be brought in by helicopter, officials said.

On Monday night, one of the sewer district’s three commissioners voted against the emergency declaration.

Commissioner Ed Caine said his vote was not against the repair but rather cast in protest against the city and county for pulling out of the deal – “which left us holding the bag.”