Fixing a damaged tunnel-boring machine stuck beneath Bothell will take months longer than originally thought, further delaying completion of a pipeline that will carry sewage from the $1.8 billion Brightwater sewage-treatment plant to Puget Sound.

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The Brightwater sewage-treatment project, which is costing local ratepayers $1.8 billion, is delayed yet again because fixing a damaged tunnel-boring machine stuck deep underground will take months longer than originally thought.

King County wastewater-treatment officials said Tuesday the machine, which has been idled 340 feet beneath Bothell since May, won’t resume digging until early next year. They had expected the machine to be back in action last month to continue work on a pipeline that will carry treated sewage from Brightwater to Puget Sound.

The delay likely will push completion of the project — originally scheduled for 2010 — into 2012, project manager Gunars Sreibers said Tuesday.

It isn’t yet known how much repairs will cost and how much of the cost might be paid by the county, the contractor or the manufacturer of the damaged machines, but, Sreibers said, “We’re in the tens of millions of dollars of money at issue.”

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The existing $1.8 billion tab for the project is roughly double what the Metropolitan King County Council was told when it first approved the project. The plant is the most expensive public-works project in county history. It will serve 189,000 residents, 109,000 of them in Snohomish County.

King County officials expect to begin testing the plant in August 2011, but without the 13-mile underground pipeline that eventually will carry treated water to Puget Sound. Wastewater treated at Brightwater will go to plants in Renton and Seattle until the tunnel and pipe are finished.

Wastewater Treatment Director Christie True said the county is spending a little more than $6 million to modify a pump station to redirect the treated water and has conditionally agreed to pay contractor Vinci/Parsons RCI/Frontier-Kemper $10 million for completed tunnel-machine repair work. The county may seek to recover that money, but more repair costs lie ahead.

Two boring machines were shut down for repairs and more than 120 workers laid off in May and June after damage was discovered on the rims of both devices. One 17 ½-foot-diameter machine is under Bothell, the other under Lake Forest Park.

It has taken longer than expected to repair the Bothell machine because six wells weren’t completely successful in removing water from soil around the repair area. Workers later removed some of the water by drilling 10 drains from the tunnel into the soil.

The amount of water is important because too much water means air in the work space must be pressurized, forcing repair crews to spend most of their work time going through decompression. With water largely removed now, Sreibers said, workers will need far less decompression time.

The machine under Lake Forest Park will dig ahead 300 feet to where wells are being drilled down, and it will then be fixed. Wells were drilled last summer to the Bothell machine.

“At the end of the day these kinds of things happen in projects,” True said. “That’s why we carry a contingency in our budget. We actually have low usage of our contingency to date. We don’t know that it means our budget will go over at this point in time and we don’t know who ultimately will be responsible for all of these costs.”

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