Divers, inspections reveal extent of damage inside leaking Okanogan Reservoir

WENATCHEE — Temporary repairs to a city reservoir that was leaking up to 1 million gallons of treated water per day are expected to begin next month after the Wenatchee City Council awarded a $1.3 million construction contract June 25.

The council unanimously approved a contract with Pullman SST to complete repairs at the Okanogan Reservoir, which has remained out of service since September 2025 after engineers determined extensive repairs were needed before it could safely return to operation.

Water Shop Utility Supervisor Will Weems said months of engineering inspections revealed widespread deterioration throughout the aging concrete structure, including failing expansion joints, cracked roof sections, deteriorated protective membranes, exposed reinforcing steel and even tree roots growing through separated concrete joints.

During Thursday's presentation, Weems showed council members photographs and underwater inspection video documenting the damage. Divers traced leaks by injecting dye into damaged joints and watching it disappear through openings in the concrete, confirming where treated drinking water was escaping the reservoir.

If left unrepaired, Weems said, the reservoir was losing as much as 1 million gallons of water each day.

"We're wasting money and valuable resources," he said after Mayor Mike Poirier asked where the leaking water was going.

Weems explained the water drains through the reservoir's underdrain system, crosses nearby school property and eventually flows into the Columbia River.

The temporary repair project will replace deteriorated joint sealant throughout the reservoir, repair roof cracks and scaling, replace damaged membrane seals that protect the drinking water supply, patch deteriorated concrete and replace sections of exposed reinforcing steel that have lost structural integrity.

Engineers originally considered injecting low-pressure grout beneath portions of the reservoir, but Weems said that option was removed from consideration for the project after concerns it could damage the facility's underdrain system.

Although the work will restore the reservoir to service, Weems emphasized the project consists of temporary repairs needed to safely return the facility to operation while maintaining water system reliability.

The contract totals $1,304,946.90, which is approximately $600,000 below the engineer's estimate, and will be paid through the city's water utility fund as part of the approved capital budget.

Construction is expected to begin in mid-July following a preconstruction meeting and is anticipated to take about 40 working days.

City staff said returning the reservoir to service will strengthen wildfire resilience, restore drinking water capacity and support future growth within Wenatchee's water system.

Andrew Simpson: 509-433-7626 or andrew@ward.media