First LOTT digester refurbishment progresses toward 2026 restart 

LOTT Clean Water Alliance is close to finishing a complete rebuild of the first of four digesters at the Budd Inlet Treatment Plant in Olympia.

Principal Engineer Brian Topolski updated the LOTT Board of Directors on the agency's biggest infrastructure project to date at a meeting on Dec. 10.

The LOTT Board of Directors approved a 950 working day contract for $34,315,986.15 with Prospect Construction Inc. of Puyallup  in November 2024. The project aims to refurbish four digesters by October 2028. Startup of the first completed digester is expected in spring 2026.  

The current work builds on phase one, which wrapped up in 2024 with installation of a microaeration system, HVAC improvements and life safety equipment. 

"For phase two, the highlights of the project are complete refurbishment of all four digesters with new fixed stainless steel covers," Topolski said. 

The existing covers are floating, but Topolski said the fixed covers offer improvements to the system. In addition to the covers, the project installs new linear motion mixers, one in each digester, along with a new emergency gas burner, piping modifications, valve replacements, and inside concrete repairs and coatings. 

Crews cut the first digester floating cover into 14 pie sections weighing about 100,000 pounds each, and workers removed 100 concrete ballast pieces that controlled the old cover’s vertical movement. The contractor erected scaffolding inside the digester. 

"They had to get all these pieces in a 42-inch hatch, and then erect everything inside that digester," Topolski said. 

Workers installed a reinforced concrete ring beam around the digester perimeter after X-raying the existing structure to map prestressed concrete tendons, and crews then anchored rebar into the existing digester wall and poured 65 cubic yards of concrete in one day. 

The contractor, Topolski explained, mounted brackets and radial beams on the ring beam to support 32 stainless steel pie sections. All components required welding and vacuum testing, and workers then treated the welds. The equipment at the center of the digester moves vertically in the middle of the tank. 

"Stainless steel passivation is a chemical treatment, and it cleans the surface. It removes free iron and provides a thin protective coating of chromium oxide, which is highly effective in protecting the welds from corrosion," Topolski said. "The digester will have better treatment because of better mixing.” 

Construction crews spent roughly 10 months making piping modifications inside the digester building, and new stainless steel overflow piping extends below the digester through the headworks area into equalization basins. 

"It's not going to be used regularly. It's more of an emergency overflow device," Topolski said. 

LOTT also removed a methanol tank previously used for carbon supplementation, and the agency now uses Micro C, a glycerin product. The project also relocates the emergency waste gas flare. 

"It's more internal to the plant. It'll be, it won't be on a rooftop, and the new burner is actually shrouded, so you really won't see a flame," Topolski said. 

Workers completed an annular seal, and crews are preparing to apply 6 inches of foam insulation across the entire cover. A bridge will connect from the digester's edge to the center where the linear motion mixer sits, and electrical conduit will run along the bridge to service the mixer. 

Topolski said workers covered the digester to create optimal conditions for the remaining work. 

"The project's going really well. We're on track, we're on schedule, we're on budget," Topolski said. 

A tower crane installed in March assists with material access from Franklin Street NE, and the street between A Avenue NE and Market Street NE remains closed from 7 a.m. to 6 p.m. on weekdays throughout the project's duration. 

Parametrix of Puyallup serves as design engineer. LOTT is funding the project through its capital budget and low-interest loans from the Washington State Department of Commerce's Public Works Board.