Mercer Island residents evacuate due to risk of possible landslide
MERCER ISLAND, Wash. - Several Mercer Island residents were evacuated from their homes late Wednesday due to the risk of flooding or a possible landslide, city officials said.
The city of Mercer Island informed about 20 homes near 95th Court Southeast to evacuate their property after a 24-inch underground water pipe started leaking and created unstable soil conditions, which put their homes at risk.
"There was a concern, and the reason why we evacuated homes, is that if the pipe were to break that it could cause dangerous flooding or landslide," said Jessi Bon, Mercer Island city manager. "We would be potentially looking at a catastrophic event."
A geotechnical engineer analyzed the soil conditions and informed the city.
According to officials, Seattle Public Utilities (SPU) owns and maintains the high-pressure water pipe which provides water to Mercer Island.
"The segment in particular that we’re looking at where we’ve identified the leak location was installed in 1956. The pipe is called a concrete cylinder pipe. It is a combination of steel encased in concrete," said Wylie Harper, director of Water Transmission and Distribution Division for Seattle Public Utilities.
On Wednesday night, SPU turned off the water supply to the line and the city is receiving water from a secondary water main.
Residents were told to evacuate immediately until further notice.
"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. That will tell us quite a bit about both the fix itself and potentially the cause," said Harper.
With rain in the forecast, there is a sense of urgency to address the leak. Geologists with the Washington Geological Survey, a division of the state's Department of Natural Resources, said extra water could affect the stability of the soil surrounding the leaking pipe.
"Any time you load, add extra weight to a slope, it changes the stability of that slope. And so that’s why big, big rainstorms that drop a lot of water are the times when landslide hazards go up because everything weighs more," said Alex Steely, assistant director of Geologic Hazards and Mapping for the Washington Geological Survey. "That’s why we often see landslides happen after long, soaking rains because water is pretty heavy."
The city's community and event center is where evacuated residents and their pets can gather. Bon said most families chose to stay at hotels or with relatives.
Mercer Island is continuously working with SPU, Eastside Fire and Rescue, King County's Office of Emergency Management, the American Red Cross and other departments to keep affected residents safe.
This is a developing story and will be updated.
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