LAKE STEVENS — Leaders at the sewer district that serves the Lake Stevens area have accused Mayor John Spencer of thwarting their plan to save customers millions of dollars.

Spencer says that’s not true.

The dispute has been simmering for years. It began to boil over late last month after sewer commissioners passed a resolution to move ahead with refinancing $27 million in bonds.

Spencer soon fired off a letter, taking commissioners to task for bypassing an advisory group. The mayor also argued that the Lake Stevens Sewer District’s resolution would unnecessarily hold up the reunification of the city and sewer district, something that’s set to take place in 2033.

The sewer district issued a press release Tuesday: “City of Lake Stevens jeopardizes $15 million in rate payer savings.”

“I struggle to understand why Mayor Spencer would impair the marketability of the refinanced bonds at the expense of its citizens,” Kevin Kosche, president of the sewer commission, said in the release. “Beyond jeopardizing the District’s bond refinance, the Mayor’s actions also effectively risk two municipal bond issues under consideration, one of which would fund the necessary infrastructure to support Costco coming to Lake Stevens.”

Sewer commissioners contend that Spencer’s Aug. 28 letter incorrectly implies that there’s an ongoing legal matter that could sideline their bond plan.

Spencer, on Tuesday, said that any allegations that the city was standing in the way of selling the bonds was incorrect.

The district hopes to sell the bonds now while interest rates are low. They would be paid off by 2033, district leaders said, years sooner than the current payment schedule.

“The city has said over and over again, we think that’s a very good idea, and we think they should go forward with that,” Spencer said. “We don’t need to amend the inter-local agreement.”

The city offered to withdraw the letter if the bond resolution was removed. The district wouldn’t, the mayor said.

“The city has no interest in causing our citizens to not get an advantage of any kind of financial benefit,” he said.

The district serves about 12,000 homes and businesses within Lake Stevens and its urban growth area. Its infrastructure includes about 120 miles of pipe and a state-of-the-art treatment plant.

The sewer district assumed control of the city’s sewer infrastructure in 2005.

The original plan, adopted at that time, was for the entities to reunite within two decades of building a new treatment plant. The plant was completed in 2013, at a cost of more than $100 million.

The bonds now in dispute are paying down debt from that project.

“We’ve been really diligent and worked really hard to have a good relationship with the city,” sewer district general manager Tonya Christoffersen said.

For several years now, the city has been exploring the possibility of taking control of the sewer district sooner than the current 2033 merger date.

A merger would make the sewer district part of city government and put it under the control of the seven-person Lake Stevens City Council.

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