Brightwater costs up; sewer rates to rise, too

King County's $1.8 billion cost estimate for the Brightwater sewage-treatment plant understates the likely cost by at least $41 million, a consultant reported Wednesday.

Engineering firm R.W. Beck, hired to oversee construction and costs for the Metropolitan King County Council, estimated the final cost of the plant — scheduled to go into service in mid-2011 — at $1.84 billion to $1.85 billion.

Beck's report to the council's Capital Budget Committee also warned that an 81-day delay in digging the eastern portion of a deep pipeline tunnel is expected to push the end of construction to late February 2011 and full plant startup to late July of that year.

Wastewater-treatment director Christie True said more delays on the treatment plant and 14-mile tunnel are possible, but that the county so far has held close to the goal it set in 1998 of completing the county's third sewer plant in 2010.

Brightwater is being built on Highway 9 north of Woodinville to treat wastewater from fast-growing suburbs in southern Snohomish County and northern King County. More than half the cost is for the tunnel and pipelines.

The Metropolitan King County Council on Monday voted to raise sewer rates from the current $27.95 a month to $31.90 starting next January, mostly to finance the Brightwater plant.

True said the difference between the county's cost estimate and R.W. Beck's estimate is no more than 2.6 percent of the total project cost.

"I want us to hold our feet to the fire to deliver the project at our cost estimate," she said

Beck found that the Wastewater Treatment Division had understated the cost of the pipeline by $15 million to $17 million and the treatment plant by $26 million to $30 million.

The consultant disagreed with the county's decision to reduce the contingency funds intended to handle unexpected expenses on the tunnel and the plant.

Keith Ervin: 206-464-2105 or kervin@seattletimes.com