In a project that involves Spokane contractors and engineers, a 312-ton metal structure has been lifted from 200 feet beneath the surface of the reservoir behind Boundary Dam, in northeast Washington, to a concrete slab for a year-long, $1.5 million maintenance project.

The dam, located 12 miles north of Metaline Falls, Wash., on the Pend Oreille River, is owned by Seattle City Light.

The utility contracted with specialty contractors, both here and in the Seattle area, for different facets of the project.

William Winkler Co., of Spokane, and Spokane Rock Products Inc. were contracted in August to build a concrete pad that is 50 feet wide by 100 feet long, says Seattle City Light spokesman Scott Thomsen. In September, the utility drew down the water level behind the dam, exposing the structure that needed to be removed, which is called a sluice maintenance gate. Such gates are used to seal off, for maintenance, the dam's main sluice gates, which control the flow of water through a dam. Sluice gates are opened or shut to control water levels above the dam and below in the river.

In this project, once the sluice maintenance gate was exposed, it was detached from the dam and floated by pumping air into its ballast tanks, Thomsen says. The water level in the reservoir then was brought back up, lifting the massive gate to the surface. The gate was positioned at the reservoir's edge, and McClure & Sons, of Lynnwood, Wash., placed 4,000-pound dollies with hydraulic wheels under it. The water level once again was lowered, settling the gate on the dollies, and McClure & Sons moved the gate over a 12-hour day up a 10 percent slope to the new concrete pad, says the company's president, Les McClure.

Seattle City Light plans to call for bids later this month to construct an 18-foot-high steel-framed building around the sluice gate on the concrete pad. The Spokane office of Seattle-based GeoEngineers provided design recommendations for the concrete pad and building, and will monitor the construction process, says Jim Harakas, a GeoEngineers senior principal. Once that building is completed, the utility will begin cleaning, inspecting, repairing, and repainting the gate.

"Every so often, you have to do routine maintenance on the gate," Thomsen says. "The last time it was done was 27 years ago."

Once the maintenance work is completed, the process of moving the sluice gate will be repeated in reverse, McClure says. Afterward, the maintenance building will be moved to a permanent location and used as a warehouse, Thomsen says.