Increasing evidence of seismic activity at property slated for King County's future sewage-treatment plant has officials revamping science studies associated with the project. King County announced yesterday it...

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Increasing evidence of seismic activity at property slated for King County’s future sewage-treatment plant has officials revamping science studies associated with the project.

King County announced yesterday it will complete a supplemental environmental-impact statement — something it has resisted publicly and in court — on the effect an earthquake could have on a proposed plant at its property off Highway 9 north of Woodinville.

As part of the impact statement, it will reopen public comment on the new studies, creating an even tighter time frame for completing permit applications before construction can begin next year on the proposed plant, known as Brightwater.

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King County used its initial environmental-impact statement (EIS) to select the Highway 9 site over alternatives. It cannot obtain required permits without a completed EIS.

County officials said they will run out of sewage capacity in King and Snohomish counties if a new plant isn’t operational by 2010.

The new study, estimated to cost about $500,000, comes on the heels of a U.S. Geological Survey study of several lineaments — or strands of active faults — running through the 114 acres King County wants for the Brightwater plant.

Ground studies conducted in October show solid evidence of at least two earthquakes having occurred at the northern end of the Brightwater property, said Craig Weaver, a coordinator for the USGS National Earthquake Program.

While the USGS has yet to determine when they occurred, the two quakes are comparable to evidence of quake activity within the past 12,000 years about a mile or so from the Brightwater property.

Under one theory, land from Kenmore to Monroe is laced with many fault lines, looking much like the delta of a river, that still could be active, Weaver said.

Another theory under consideration is that many of the lineaments are connected to an earthquake event thousands of years ago, much like the cracking that occurs in porcelain, Weaver said.

Still inconclusive is what damage could occur during another earthquake there. Studies link these faults to the much larger Southern Whidbey Island fault, which scientists say once caused a magnitude-7 earthquake about 3,000 years ago.

Under a recent King County hearing examiner’s decision, county officials are obligated to complete another environmental-impact statement now that more concrete evidence of regional earthquakes has been established. King County is appealing that ruling, but mounting evidence has led officials to begin studies while waiting for a March hearing.

The county, which already has said it will construct many of the plant’s facilities to account for potential earthquakes, hopes to release the new study by February, then begin collecting comments in March, finally finishing the supplemental EIS in May.

If all stays on schedule, said Brightwater project manager Christie True, construction permits to begin building conveyance piping between the plant site and Bothell still could be ready by summer, when construction is expected to begin. The cost of the plant to date is expected to be near $1.5 billion.

“One could debate at this point whether finding an active fault is significant new information, but we’re just not going to debate it,” True said.

While the assumed lineaments running through the property would still be several hundred feet from key plant buildings, True said it’s virtually impossible to avoid fault lines when building in the region.

USGS officials won’t comment on the selection of the property for the plant, but Weaver said it’s well known that many Seattle, Tacoma and Everett structures, including Safeco Field and Qwest Field (formerly Seahawks Stadium), are built on or near active faults.

“Our job is simply to find faults, estimate ground motions,” he said. “It’s up to others to decide how to handle these hazards.”

Opponents of the project called yesterday’s decision a victory. The grass-roots Sno-King Environmental Alliance has spent nearly $80,000 on geological experts and lawyers to fight the plant’s location. The alliance has been the plaintiff in the King County hearing-examiner cases.

“We feel vindicated because we’ve been trying to get them to further study this for three years,” said Charley Blaine, an alliance member. “We’re glad they’re doing it, but now we want to make sure they do it right.”

Based on the supplemental EIS, Blaine said his group most likely will request that King County reconsider other sites eliminated during the initial process. But True said that’s unlikely to happen.

“We still believe [the Highway 9] property is definitely a good site,” True said.

In King County’s initial EIS, it also considered a site near Edmonds but determined that environmental hazards there and the property’s smaller size made the Highway 9 site more suitable.

Christopher Schwarzen: 425-783-0577 or cschwarzen@seattletimes.com