EVERETT — A major sewer spill that sullied North Creek with untreated waste last spring is likely to cost the city at least $4 million to replace nearly a mile of faulty sewer pipe.

Everett will also have to pay a $4,000 fine, under the proposed settlement announced Thursday by the city and the state Department of Ecology. City staff have recommended that the City Council approve the agreement at its Wednesday meeting. Everett has no plans to appeal, city spokeswoman Kate Reardon said.

“From our perspective, we don’t want to have a single spill,” Reardon said. “We did the best we possibly could to mitigate this one, including a major community outreach.”

Trouble started on the morning of April 12 with the rupture of a pressurized sewer line carrying waste near the 11800 block of Silver Way in south Everett. That released an estimated 1 million gallons of untreated sewage into North Creek, which flows through Everett, unincorporated Snohomish County, Mill Creek and Bothell before reaching Lake Washington. The waste also inundated a nearby home, resulting in a $200,000 damage claim against the city.

City crews repaired the break by the next day and diverted an additional 900,000 gallons of wastewater from the broken line.

In the aftermath, workers reported finding four dead fish along North Creek: three cutthroat trout native to the area and a goldfish.

Water-quality tests indicated pollution levels had returned to near-normal by the end of April.

State officials agreed that city crews did everything within their power to stop the spill after it was discovered.

“We felt obligated that we needed to have some kind of monetary penalty,” said Shawn McKone, a state water-quality permit engineer. “The $4,000 was at the low end of our authority to fine.”

The spill technically violated the terms of Everett’s state-issued waste-discharge permit,* which prohibits the unauthorized discharge of sewage. Fines for a spill that span two days range from a minimum of $1,000 to a maximum of $20,000.

The city’s initial repair involved replacing a 20-foot section of iron pipe. It carries waste from about 15,000 households in south Everett, including the Silver Lake area and parts of Mukilteo.

In May, the City Council fast-tracked a $1.8 million project to replace 1,000 to 1,500 feet of pipe. Later, crews determined they needed to replace a total of 5,000 feet of the pressurized main leading from a pump station on Silver Way.

“As they investigated over the summer, they determined that the entire length of pipe was in need of immediate replacement,” McKone said.

The proposed agreement calls for finishing that work by April 20. It also requires the city to evaluate which other pressurized sewer lines are at risk of failing and how it can improve its emergency response to sewage issues.

It’s still not clear what went wrong in April, other than that it started with a hole in the underground pipe.

“As it eroded away, it got bigger and bigger and blew out,” Reardon said.

Age itself wasn’t believed to be a factor. The 20-inch pipe was installed in 1981. They often last decades longer.

“The pipe itself prematurely wore out and failed,” McKone said.

The city repaired three small leaks of 50 to 150 gallons in 2011 on the same segment that failed in April. Crews prevented those spills from reaching water.

Noah Haglund: 425-339-3465; nhaglund@heraldnet.com.

Correction, Sept. 14, 2012: An earlier version of this story incorrectly stated the type of permit involved.