Newly released documents from a Seattle Public Utilities (SPU) study say a catastrophic earthquake would devastate Seattle's water system partly by knocking out reservoirs, pump stations, elevated tanks and standpipes in various neighborhoods.

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Newly released documents from a Seattle Public Utilities (SPU) study say a catastrophic earthquake would devastate Seattle’s water system partly by knocking out reservoirs, pump stations, elevated tanks and standpipes in various neighborhoods.

As many as four reservoirs, eight pump stations, two elevated tanks and three standpipes would be rendered nonfunctional, according to a section of the study SPU previously had kept under wraps.

Seismic upgrades to the at-risk facilities are among $850 million in projects recommended by the SPU study through 2075.

The determination that SPU’s Eastside, Magnolia, Riverton Heights and View Ridge reservoirs would be knocked out by a magnitude 7 Seattle Fault earthquake was not included in a 13-page summary that until Friday was the only section of the study released to the public.

Nor was the determination that the Riverton Heights, View Ridge and Volunteer reservoirs would be rendered nonfunctional by a magnitude 9 Cascadia Subduction Zone quake included in the summary.

The 722-page study cost SPU $900,000 and took more than three years to complete. But the utility initially kept the entire study other than the summary private, including the table of contents, saying some sections contained information about vulnerable points in the water system and citing a U.S. Department of Homeland Security “Protected Critical Infrastructure Information” designation.

The utility had sought the designation to ensure the study would be “not subject to public disclosure,” according to an email to Homeland Security from SPU’s water-system seismic program manager.

That approach raised concerns, with former Washington Emergency Management director Jim Mullen calling the secrecy unnecessary.

Other utilities, including the Los Angeles Department of Water and Power and Oakland’s East Bay Municipal Utility District, had taken a more transparent approach with earthquake studies, making most information public and only withholding sensitive sections.

SPU now has posted six of the study’s eight sections online, along with references and appendices, citing the Homeland Security designation in continuing to withhold two sections on vulnerabilities at individual facilities.

The utility values transparency and didn’t intend to be secretive, water-planning director Alex Chen said in an email Friday.

“We sought protection of security sensitive information that terrorists could use to do maximum harm,” Chen said.

After questions from The Seattle Times, SPU went back to Homeland Security and asked for clearance to release most of the study.

Besides naming reservoirs and pump stations that would be knocked out, a newly released documents include a map showing where the water system would have more and less pressure immediately after such a quake.

For example, the map shows that many system nodes on Capitol Hill and in the Central District would have zero pressure, while many nodes in South Lake Union, Sodo and Georgetown would at that point retain pressure, with 60 to 100 pounds per square inch.

Chen described the map as a conservative representation (assuming transportation disruptions for SPU staff, for instance) and said actual pressure loss across neighborhoods would depend partly on the particular nature and location of an earthquake.

In general, neighborhoods with higher elevations would likely to lose pressure first, because neighborhoods with lower elevations tend to be served by larger reservoirs that would take longer to drain out.

“Water leaks from high points to low points,” Chen said.

The entire city would lose all water pressure within 24 hours, with water draining out of breaks and leaks, and SPU would need at least two months to entirely restore service, according to the study.

The distribution pipes that carry water within the city would see 1,400 to 2,000 breaks, according to another newly released section of the study. Repair crews would be expected to work 12-hour shifts, completing one repair per shift. An estimated 15 crews now could be put to work within three days and 30 crews within a week.

In making repairs, the utility would prioritize hospitals first, homes second and economic zones third, according to the study.

Repairing the transmission pipes that bring water from SPU’s mountain reservoirs would take much longer. Leak repairs would take three to seven days, and break repairs five to 10 days.

Transmission-pipe leaks and breaks under rivers could take six months to a year to fix. SPU probably would not use crews from other areas to help repair the transmission pipes because those crews might not have experience dealing with such large pipes.

Staff reporter Sandi Doughton contributed to this story.