Some Mercer Island residents received knocks upon their doors at approximately 9 p.m., and evacuations came soon after.

After the city of Mercer Island learned of a landslide risk due to a leaking underground water pipe on the late afternoon of April 3, staffers later alerted residents of about 20 nearby homes in the vicinity of 95th Court Southeast about the situation and directed them to depart their properties until further notice.

The leaking 24-inch high-pressure water pipe, which provides water to the Island, has created unstable soil conditions, the city explained in a social media post issued late on the night of April 3.

“There was a concern, and the reason that we evacuated homes is that if the pipe were to break, that it could cause dangerous flooding or a landslide. I want to reiterate, that did not happen,” said City Manager Jessi Bon during a press conference on April 4 at the Mercer Island Community & Event Center.

“That pipe has been shut off. It has very little water in it right now, so that risk has been alleviated,” she added. During a Reporter visit to the neighborhood on April 4, there were two streets blocked off and some homes had orange “Unsafe” notices taped to their doors emblazoned with information about the situation.

The pipe is owned and maintained by Seattle Public Utilities (SPU), which engaged in a six- to eight-hour process of turning off the supply to the city’s main water line while the Island is receiving water into its reservoir tank and running it through its backup line.

“That was one of the critical things that we had to get done overnight,” said Bon, adding that the Island’s water quality hasn’t been impacted and residents don’t need to conserve water.

According to the city, a geotechnical engineer was reviewing the soil conditions on April 3 and informed the city of the landslide risk in the cul-de-sac. Bon explained to the media that the city and SPU had been monitoring the area for a potential leak for a few days prior to April 3 and landed on the approximate location for the engineer to survey.

Press conference speaker Wylie Harper, who is SPU’s Water Transmission and Distribution director, said the segment of the concrete cylinder pipe where the engineer located the leak was installed in 1956. It is routinely checked and is scheduled for replacement in a year or two as part of the Capital Improvement Program project.

“We don’t know the cause at this point, so the next steps in responding and addressing the leak are to excavate above the pipe and actually get eyes on where the water is leaking,” said Harper of the approximately six-foot dig. At press time, engineers along with city and SPU staff were evaluating the soil conditions and then they’ll determine how long the repairs will take. A timeline on those processes is unknown at this juncture.

“We’re confident we’ll get it fixed securely,” said Harper, adding that the pipe is on order and that weather won’t play a factor in completing the work with immediacy after they receive the pipe.

For evacuated residents and their pets living downstream of the leak, the Mercer Island Community & Event Center (8236 SE 24th St.) is serving as a gathering place and information site for the Islanders.

Bon said it’s not clear when the residents may return to their abodes.

“Of utmost importance is safety, so it is a priority to get them back into their homes as soon as it is safe to do so,” said Bon, who added that the residents were graceful and appreciative during and after the evacuations. She said that most of the residents spent the night in Bellevue hotels.

Eastside Fire & Rescue Chief Ben Lane said at the press conference that the Shorewood community — which has two of its buildings operating on a fire sprinkler system — is not directly impacted by the unstable soil situation.

“The residents themselves will not be experiencing any sort of water fluctuation or pressure issues,” said Lane, adding that his department has directed the Shorewood community to post a fire watch for the two buildings while the city utilizes its backup water line.

The city is coordinating with SPU, Eastside Fire & Rescue, King County’s Office of Emergency Management, American Red Cross and other public safety departments to ensure the impacted residents are safe and protected, the post reads.

The city will post updates on its website and social media accounts.

Streets are blocked off in the vicinity of 95th Court Southeast. Andy Nystrom/ staff photo

Some residents near 95th Court Southeast have these signs taped to their doors describing the landslide risk and were directed to evacuate their premises on April 3. Andy Nystrom/staff photo