Bellevue landslide: Investigations on the cause of the landslide and review of the age and condition of water main that broke

The City of Bellevue launched an investigation after a landslide caused an occupied house to slide off its foundation and collapse on January 17. Officials said the investigation could take weeks or even months to determine the cause of the landslide.

"Our focus right now is initiating an investigation on what happened with that slide, and there’s a number of different possibilities. Regarding financial responsibility, that’s going to be assessed in the coming weeks and months," said Linda De Boldt, Bellevue’s utilities assistant director.

Officials confirmed that a water main break occurred near the home. The city said several 911 calls were received around 4 a.m. on January 17 reporting water flowing down the street and hillside near 139th Place Southeast and Southeast 51st Place in the Somerset neighborhood.

The city said when first responders arrived, the occupied home was partially collapsed. Firefighters helped homeowner John Surdi rescue his wife and dog who were stuck inside.

Officials with the Washington State Department of Natural Resources said this is the highest number of landslides they have seen in the state in the past year.

Kate Mickelson, manager of the DNR’s Landslide Hazards Program, said engineers are assessing the hillside. City and state engineers are working to determine whether the recent amount of rain and snow may have put pressure on the water main causing it to burst, or if the pipe itself was the problem.

"We’ve seen a record number of landslides this season due to the rain that we’ve had. So, that could have caused the pipe to fail. And I think the city is investigating the roots of that landslide—is it natural? Or was there some other contributing factor to it?" said Mickelson.

The city’s utility mapping program shows the water main that burst was 8-inches in diameter, made of asbestos cement material. The map also shows the water main was installed in the 1960s, and officials further clarified the year was 1961. This means the water main is more than 60 years old, but according to De Boldt, a typical water main should last much longer than that.

"Water mains normally last around 100 to 125 years. So, depending upon when it was installed, we would be putting it on our replacement schedule. So, I mentioned that this main was built in the 60s. So, it is definitely in that age grouping that we would be considering replacing it in the future. Again, we have an ongoing program of replacing approximately five miles of main per year in the city. And so this would be included in that analysis," said De Boldt during a news conference, on Tuesday.

In a written statement on Wednesday, City of Bellevue Utilities said, "Our experience shows us that the longevity of AC main pipe is dependent on the size of the pipe.  We have AC main pipe ranging primarily from 4" up to 16" pipe.  We are focused on replacing the pipe that is the most vulnerable, which is the smaller 4" to 6" diameter pipe."

Asbestos cement is made up of 12 to 15% asbestos. The city’s utility map shows other water mains throughout the community were installed using asbestos cement material. Bellevue has already spent several millions of dollars replacing "aging" asbestos cement water mains across the city for years, according to 2013 planning documents. Bellevue Utilities also slated several AC replacement projects in 2020 as part of its capital improvement plans, including the area near the landslide.

Bellevue Utilities offers detail on safety guidance in its Water Engineering Standards, published in January 2021. The document includes information about safety measures regarding asbestos cement.