A day after reopening it Monday with plans to closely monitor its structural integrity, state highway officials closed the Kummer Bridge on State Route 169 near Black Diamond.

The bridge closed on Tuesday night and could remain closed for up to six months.

Closure of the bridge, which according to officials handles about 9,000 vehicle trips daily, will have an impact on Black Diamond residents, as well as the city and Mountain View Fire and Rescue, which serves Black Diamond and surrounding unincorporated King County neighborhoods.

City administrator Gwendolyn Voelpel said the city is taking steps to deal with the immediate impacts, including detoured traffic.

“Our public works director is working with (the state Department of Transportation) on a mitigation agreement to cover future improvements needed due to the impacts of increased traffic on Roberts Drive/Auburn-Black Diamond Road,” Voelpel said.

She added the City Council was scheduled Thursday to consider setting weight limits on the road.

“We understand the detour through our city is a temporary solution, but we of course want to protect the infrastructure for our citizens, and that large of an increase (of traffic) could seriously degrade an already less-than-optimal roadway,” Voelpel said.

In addition, Voelpel said, city officials will try to come up with strategies “to assist businesses that will be more cut off from highway traffic for the next three to six months.”

Department of Transportation (DOT) officials said Tuesday that closing the bridge to traffic was necessary for both drivers and the bridge.

“I can’t emphasize enough that this closure is about safety,” said state Secretary of Transportation Paula Hammond. “We will do what is necessary to keep the public safe and preserve the bridge.”

Data collected over last weekend led the DOT’s geotechnical engineers to believe the soil supporting the bridge is showing unusual movement that could be aggravated by recent heavy rain. This creates concern that the southern most bridge pier can’t be supported by the soil, and if it slides, the pier could slide with it, according to DOT regional director Lorena Eng.

“The geotechnical experts watched the slide through the weekend and determined that something had accelerated the rate and direction this slide is moving,” Eng said. “With the next storm set to hit Wednesday, we don’t want to take any chances with safety.”

Safety is also a concern for personnel with Mountain View Fire, said department spokesman Tim Perciful, though “it probably won’t impact us much unless there is a major incident.”

“It is all about timing if any of our crews are on another call, or at a major incident,” Perciful said. “We have coverage south of the bridge with a crew at Station 94. We have coverage from the north from a crew at Station 98, or possibly Station 99, or Station 97. So, on most aid calls, illegal burns or other day-to-day calls, we’re probably fine. Where we may run into an issue is when a crew is on a call in their area, then a second call in their area comes in. Our response will be delayed because access may be limited.”

Timing is important because Mountain View is a mix of career and volunteer firefighters. As a result, not all stations are staffed 24 hours a day.

Perficul said the bridge closure will impact the department’s aid crew and could impact mutual-aid when Mountain View requires assistance or helps other fire departments.

“Medic 12 is based out of Station 94, and their response time will increase any time they need to go north of the bridge,” Perciful said. “If we have a major incident and need to call for help from other departments, they may have a delayed response because of the bridge. To complicate matters, they are probably not familiar with the detour.”

While everyone copes with the closure, the state will be fixing the bridge so that is can be reopened. During the next six months, repairs – which DOE estimated will cost $10 million – will be made to the bridge in two phases:

• Crews will remove excess water by clearing trenches, unplugging manholes and installing pumps to help drain water from the unstable hillside.

• Then the soil that is putting pressure on the bridge pier will excavated. Crews will dig out a section of roadbed 30 feet deep and 300 feet long just south of the bridge and replace it with lighter weight material.

DOT reported Monday that bridge experts believed Kummer Bridge – also known as the Green River Bridge – was safe for traffic. The bridge reopened at 6 p.m. last Saturday. Officials said there had been no significant movement in the soil supporting the span since Nov. 11. Shifting earth caused DOT and the State Patrol to close the bridge in the mid-afternoon Nov. 12.

A hillside near the bridge was the subject of extensive work to reinforce it, beginning last summer and ending in October. Drain pipes, soil “nails” and concrete were used by DOT to stabilize the slope near the southeast end of the span.

Staff writer Kris Hill can be reached at (425) 432-1209 (extension 5054) and khill@reporternewspapers.com

Earlier versions of this story appeared in the Reporter’s online edition beginning Nov. 18.