Mercer Island residents get OK to return home after evacuations

Mercer Island officials knocked on the doors of about 20 homes near 95th Court Southeast at around 9 p.m. Wednesday night, telling residents to evacuate immediately because of an imminent flood or landslide risk.

A geotechnical engineer had alerted the city late Wednesday afternoon that a 24-inch, high-pressure concrete and steel water pipe on the slope above the area was leaking underground, creating unstable soil conditions. Owned and maintained by Seattle Public Utilities, it’s the main line that provides water to the whole of Mercer Island. 

If that pipe had burst or the saturated soil loosened underway significantly, the results could have been “a catastrophic event,” according to City Manager Jessi Bon. 

It wasn’t a disaster, and by Thursday evening, residents of all 20 homes were told they could return. But for the period they were displaced, it was a significant inconvenience.

By Thursday morning, utilities and public works crews had turned off the water flowing into the main and put the city on a backup source. The process did not pose any water quality or safety concerns to residents, Bon said. 

All homes were deemed safe by Thursday afternoon, Mercer Island Chief of Administration Ali Spietz said in an email. City crews were able to restrict water flow in the affected area, reducing the risk of property damage if the water main were to break.

After the evacuations, many opted to stay Wednesday night in hotels in nearby Bellevue, Bon said. The Mercer Island Community & Event Center was also opened for evacuated residents to gather and get more information.

The affected area included some of the city’s North End neighborhoods, between Madrona Crest and Mercerwood, not far from Interstate 90. It’s lushly wooded with narrow roads. It’s not unheard of for a home there to sell well over the million-dollar range. 

Bon said officials had been monitoring the area for the past few days but did not say what spurred that action to begin with. 

On Thursday afternoon, orange and white sawhorse-style barricades remained at the entrances to 95th Court Southeast and 96th Avenue Southeast, both dead end streets. 

To estimate the extent of the pipe damage, crews must excavate some 6 feet below the surface of the slope it sits in. This involves Mercer Island officials coordinating between SPU, Eastside Fire & Rescue, King County’s Office of Emergency Management, American Red Cross and other public safety departments to secure the area and ensure the safety of affected residents. Crews were on the site all morning and into the afternoon, evaluating the soil conditions and coordinating the excavation process. 

Maintenance costs for the main are shared between Mercer Island and SPU per a wholesale water agreement.

The water main was installed in the 1950s. The leaking segment was installed in 1956, according to Wylie Harper, director of Seattle Public Utilities’ water transmission and distribution division. He said a segment of the main was scheduled for replacement in another year or two, but it was unclear if that was the affected segment.

The cause of the leak, Harper said, would not be revealed until workers could get into the ground to make a closer inspection of the pipe. 

He said the water main is regularly inspected but was unsure of the last inspection date. No one was out of water, and there was no significant dip in water pressure detected before shutting down water to the main, Harper said.

He did not speculate on the size of the leak or how long it would take to repair. But he did say SPU crews are trained to work in the rain on such repairs.

“We are moving as quickly as we can, regardless of weather conditions,” he said. 

Seattle Public Utilities hired a contractor on an emergency contract Thursday, said Spietz, to begin work assessing the slope and designing the repair of the water main. “Once that is complete, the contractor will begin excavation to uncover the pipe so SPU crews can inspect it and complete the repair,” said Spietz.

The backup water line, which runs along East Mercer Way, was providing an adequate supply of water, and officials were not asking residents to take special conservation measures, they said Thursday afternoon.

The island has two 2.4-million-gallon reservoir tanks that help store its water supply — Bon noted that one of the two is currently offline for planned maintenance, to reline the tank, but said that was not presenting any problems at this time.

“If circumstances change” and residents are asked to conserve water, “we will provide a citywide alert and let you know,” she said.

Eastside Fire & Rescue Chief Ben Lane said this incident also prompted crews to keep an eye on water services to Shorewood, Mercer Island’s largest apartment community, located about a mile southwest from the leak. Though it has not been directly impacted, the neighborhood contains some 645 apartment units. Two of those buildings have 39 units each and operate under a sprinkler fire safety system and have since been put under fire watch as an extra safety precaution, should anything happen to the backup water system the city is currently operating on.  

Lane said Eastside Fire & Rescue is “fully prepared” to channel backup resources to the Shorewood units, should there be a fire issue in that area.

Spietz said the city has “prioritized investments” and will be involved in multiple replacement projects for the city’s water, sewer and stormwater systems over the next five years.

Updates will be provided on the city’s website and Facebook page.