Landslide poses risk to Squak Mountain neighborhood’s utilities

April 22, 2011

By Warren Kagarise

NEW — 7 p.m. April 22, 2011

The city has agreed to spend $30,000 to gather data on a landslide creeping down a Squak Mountain hillside and threatening utilities leading to the Forest Rim neighborhood.

The landslide poses a risk to the only utility lines and road to the hilltop neighborhood of about 100 homes. Forest Rim is the highest-elevation neighborhood on the mountain.

“The earth essentially just decided it was time,” Sheldon Lynne, city deputy public works engineering director, told City Council members Monday. “It couldn’t hold itself up any longer.”

The landslide is inching down Squak Mountain near a switchback along Mountainside Drive Southwest, less than a mile downhill from Forest Rim. The section of displaced hillside is about 200 feet across and stretches about 100 feet from end to eroded end.

Only a road shoulder is closed so far, and the roadway remains open to traffic. The landslide also eroded soil from beneath guardrail posts along the street.

Lynne said the city started marking and photographing the guardrail posts on daily basis after the slide started April 2. The rain-soaked soil is continuing to shift.

The boundaries continue to change as earth slides, but the area disturbed by the landslide includes power and telephone lines to Forest Rim. In addition, the landslide poses a risk to the sole water main serving the neighborhood. Lynne said the main runs beneath the road shoulder closed due to the shifting ground.

If the landslide impacts the water main, Forest Rim residents could tap into reservoir in the neighborhood as the city mobilized repair crews.

“Usually, if we have a service interruption of that magnitude, the crew is out there within 30 minutes to an hour, and they’re working,” Lynne told council members. “The crew’s good. They can get it done.”

The landslide is not expected to impact the sewer line to the neighborhood. Lynne said the sewer main is buried closer to the center of the roadway center and farther from the slide.

The council agreed Monday to spend $30,000 to hire a geotechnical engineering firm to assess the slide. The figure does not include possible design or construction costs to remedy the problem.

“Sheldon, you’re asking for $30,000 for this budget request,” Councilwoman Eileen Barber said before the unanimous decision to fund the study. “Do we feel that these dollars will be enough to get the information that we need to make a decision on what’s going on there?”

Lynne said the funds should be sufficient to complete the study. The engineering firm the city selected should complete the assessment in about six to eight weeks — and allow the city to answer questions about the landslide.

“What are the risks? How do we mitigate them without stabilizing the whole hill? Or maybe we do need to stabilize the whole hill?” Lynne asked. “Those are what we’ll need to discern from the information. What’s the best way to stabilize the infrastructure for the public?”

The soggy spring also caused a landslide on the North Issaquah slope behind Fred Meyer and The Home Depot in early April.

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