Repair work continues on Kenmore sinkhole

Engineers closely monitoring ground conditions as tunneling resumes

Engineers and construction managers with the Brightwater project have determined that the sinkhole at the intersection of 61st Avenue Northeast and Northeast 195th Street was related to a nearby Brightwater tunnel construction project. One of the project’s tunnel boring machines had been operating overnight about 150 feet under ground in the vicinity of the sinkhole.

While the cause remains under investigation, engineers believe the tunnel boring machine may have excavated too much material at one time, causing a void in which surface soils weakened and were pulled downward by gravity. The machine had been mining successfully in similar soil conditions prior to the incident.

Although ground settlement can occur during deep tunneling, it’s considered unusual. The county has successfully completed several deep tunneling projects in recent years.

To avoid a similar incident, surveyors have installed monitoring equipment along the alignment and observation crews on the surface areas will be in constant communication with the tunneling crew so work can be stopped to enable workers to take corrective action if needed.
Damage from the sinkhole was primarily confined to the roadway, a sidewalk and some public right-of-way. There were no reported injuries or impacts to underground utilities.

County employees will continue working with impacted residents, as well as City of Kenmore, local utilities, and King County Road Services to complete repairs.

Both lanes of 61st Avenue Northeast are expected to remain closed through the week to protect public safety.

The Brightwater project includes a treatment plant now under construction at the intersection of State Route 9 and SR-522 north of Woodinville, a 13-mile conveyance tunnel that will run beneath SR-522, Northeast 195th Street and the King-Snohomish County line, and a deep-water marine outfall a mile off of Point Wells in Puget Sound.

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People enjoy clean water and a healthy environment because of King County's wastewater treatment program. The county’s Wastewater Treatment Division protects public health and water quality by serving 17 cities, 17 local sewer districts and more than 1.4 million residents in King, Snohomish and Pierce counties. Formerly called Metro, the regional clean-water agency now operated by King County has been preventing water pollution for more than 40 years.

Note to editors and reporters: Visit the WTD Newsroom, a portal to information for the news media about the Wastewater Treatment Division, King County Department of Natural Resources and Parks: http://www.kingcounty.gov/environment/wtd/Newsroom.aspx.

This release is also posted on the Web site for the Department of Natural Resources and Parks at http://www.kingcounty.gov/environment/dnrp/newsroom.aspx.