The long-term closure of the venerable Kummer Bridge – the most direct link between Enumclaw, Black Diamond and all points north and south – will certainly cause aggravation as drivers add 10 to 15 minutes to their commutes.

But what isn’t known is if the closure, estimated to be at least six months by the state’s Department of Transportation, will have any long-lasting impacts.

Early indications are that Plateau residents and visitors will simply shrug and deal with the added miles.

“People are just frustrated that they have to add 10 minutes to their commute,” said Cathy Rigg, executive director of the Enumclaw Chamber of Commerce. Only time will tell if the bridge closure has any impact upon the local retail scene, she added.

Enumclaw City Administrator Mark Bauer said the bridge closure will have no immediate impacts, but those in emergency services are aware of the additional miles and slower response times. Enumclaw officials have mutual aid agreements with agencies north of the river.

In Black Diamond, 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 is considering 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.”

Dealing with the bridge closure from a public safety perspective are those at Mountain View Fire and Rescue.

“It probably won’t impact us much unless there is a major incident,” spokesman Tim Perciful said.

“It is all about timing if any of our crews are on another call, or at a major incident,” he 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.”

The bridge, a link in state Route 169 spanning the Green River Gorge, was built in 1932. For more than a decade, it has been compromised by the steep southern wall of the canyon. Engineers with the DOT have been monitoring the shifting soil since 1995 and were recently taking steps to stabilize things.

But it’s a slippery slope, indeed.

Heavy rains that began Nov. 12 caused the hillside to slip and prompted the DOT to close the bridge for parts of four days. It was opened for traffic Nov. 15 but that lasted less than 72 hours; on Nov. 18 the DOT, citing safety concerns, put up barricades and announced major work was needed before the bridge could safely be traveled.

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

After reviewing extensive data gathered by electronic sensors in the landslide, geotechnical engineers determined the bridge was vulnerable to significant land movement. They expressed a concern that the soil may not be able to support one of the southernmost bridge piers. If the soil slides, engineers said, the pier could move with it.

“The geotechnical experts watched the slide…and determined that something had accelerated the rate and direction this slide is moving,” said Lorena Eng, DOT regional administrator.

Now, the DOT is looking at a two-step process aimed at heading off future troubles.

First, crews will remove excess water by clearing trenches, unplugging manholes and installing pumps to help drain water from the unstable hillside. Second, crews will excavate the soil that is putting pressure on the bridge pier. They 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.

All the work will be done as an emergency contract and will cost about $10 million, according to a DOT press release.

Drivers can follow project progress at: www.wsdot.wa.gov/projects/sr169/greenriverrepair.

Reach Kevin Hanson at khanson@courierherald.com or 360-802-8205.