Construction work begins on I-90 dips

KELLOGG – Both directions of traffic on Interstate 90 around milepost 46 will be reduced to one lane for a little while as Idaho Transportation Department work crews focus on fixing the two dips in that area.

These dips, which have to varying degrees put a strain on the suspensions of any vehicle traveling in either direction, have been a nagging issue for motorists since early 2019.

Early on, the two prominent dips stretched completely from the south side of the eastbound lanes to the north side of the westbound lanes. The depressions became so pronounced that speed reductions had to be implemented and numerous temporary fixes had to be applied to keep some semblance of a flat roadway.

While the problem seemed to have lessened over time, it has never completely gone away.

ITD Facilities Business Operations Manager Chris Williams explains that workers took to the damaged stretch of I-90 on Tuesday to essentially rebuild the problem spots from the ground up.

“They’ll stay on the south side of the first dip and work all the way east past the second dip,” he said.

To fully resolve the issues, workers started by removing the median concrete rail- where it appeared that much of the recent sinking was occurring.

By Wednesday, the process of milling out all of the dips began with the goal of getting down to the subgrade, or native material underneath the constructed road.

“As soon as they get down into the subgrade, they’re going to make sure everything is good there and bring it back up, since it has settled a wee bit,” Williams said.

Once the subgrade and the drainage have been risen, the road will be repaved and the rails will be replaced.

The entire process is estimated to take 20-30 days. During that time, both directions of traffic will largely be reduced to one lane and a 14 foot max width restriction will be in effect during daytime work.

The initial cause of the two dips in the road has been the subject of much debate for over two years, but it appears that ITD and the Environmental Protection Agency have finally decided to agree to disagree on the matter.

The most popular theory within the community and local government was that the road damage was caused by work being done by the EPA and U.S. Army Corps of Engineers on the Bunker Hill Central Treatment Plant Upgrade and the Groundwater Collection System Project.

That project had been in progress primarily on the south side of I-90 between Smelterville and Kellogg since the summer of 2018. As part of the project, work crews had been installing 20-30 foot soil/bentonite underground walls between I-90 and the Central Impoundment Area (CIA, or locally referred to as the “slag pile” between Kellog and Smelterville) to catch contaminated runoff that attempts to flow into the South Fork of the Coeur d’Alene River. The project also included installing various wells and pipes for water extraction and collection.

Williams explained that from ITD’s perspective, this theory is the correct one.

“Water came from that south side of the road,” he said. “They (EPA/U.S. Army Corps.) put in some walls and some other different things and somehow (water) breached, came across, and ran underneath the road.”

“It was flowing across into the river,” he added.

During a previous workshop that was held in 2019 to determine the cause, it was pointed out that the areas of the South Fork of the Coeur d’Alene River that lined up with the dips showed significant turbidity- as if soils were flowing into the river at those points.

EPA Senior Public Information Officer Mark MacIntyre disagrees with this assessment and argues that the dips could be caused by other factors and is still under investigation.

“The EPA is not aware that any final conclusions have been reached regarding the cause and effect of the recent subsidence events in that particular stretch of freeway near Kellogg,” he said. “Since the area has a nearly two decade history of periodic subsidence incidents it has been difficult to draw any specific conclusions about what caused the latest round of dips in the pavement.”

He added, “EPA is committed to continuing to work with our partners, the U.S. Army Corps. of Engineers and their contractors on the project as well as the Idaho Transportation Department and Idaho Department of Environmental Quality to understand the multiple factors that may be influencing these periodic events. EPA has not determined the exact cause of the subsidence in those spots, but our work goes on to make the Silver Valley and the entire Coeur d’Alene Basin a safer, healthier place for people to live, work, and play.”

At that same 2019 workshop, EPA representatives stated that they had ruled out three possible causes for the collapse including water flowing under the underground wall in a localized area, water flowing through a gap or flaw in the wall, and water flowing around the east end of the wall.

Regardless of the cause, Williams doesn’t expect the dips to appear again, as pumps have been put in place to redirect water from those problem areas and to the Bunker Hill Central Treatment Plant.

“I think It will be nice and quick and should be much better,” Williams said of the repair work. “This winter we’ll be able to take care of the snow a lot better and we won't have to lower the speed again!”