Timetable Uncertain For Highway 95 Repairs

State transportation officials had hoped that, by this fall, drivers would be cruising the new stretch of U.S. Highway 95 north of Bonners Ferry.

But in the wake of October’s construction-related catastrophic mudslide, they can’t make any promises. Engineers still must decide exactly how to build the highway across landslide debris, and environmental regulators are laying down stricter rules about when work can be done.

“The earlier we stop in the fall and the later we start in the spring, the longer it takes to get this project done,” district engineer Scott Stokes said Monday.

Stokes is relieved by the just-released report of a landslide expert who concluded that the disaster couldn’t have been predicted.

But even the report’s author, Portland engineer George Machan, said Monday he would have required stricter construction guidelines at the site to cope with the anticipated, extremely wet conditions.

He said highway departments in Oregon, and possibly Washington, would have been less likely to leave it up to the contractor to decide the best way to deal with the challenge.

Construction began last summer on the long-awaited North Hill project, designed to eliminate dangerous curves. When the landslide hit Oct. 16-17, it undermined half of the existing highway, closing that portion of the state’s only major north-south route for three weeks.

The wet hillside fell so readily as trackhoes dug into it, according to Macham’s report, that Kiewet Construction used that sloughing as part of the excavation process. But trouble began on Sept. 15, when a trackhoe was buried in saturated sand. A much larger cave-in on Sept. 30 nearly buried a truck driver.

The October slide was likened to lava flow from a volcano.

No one knows yet when the ground will be dry enough to resume excavation this spring or what kind of changes might be made in the design plans.

“We have a pretty good concept, but we don’t have a final design,” Stokes said. “We are trying to gain as much information as we can about the strength of soils, water content, the location of (underground) water.”

Machan, of Landslide Technologies, urged caution. He said the department should expect to again find elevated water pressure that could lead to another explosive slide.

“I’d be concerned about expecting the best and getting the worst,” he said. “They’re looking at options to not have to dig into that ground again. If you really want to dig into it, you have to look for a way to drain it.”

Machan theorizes that the culprit in the Oct. 16-17 mudslide was an underground lake that was under pressure. Unlike the many seeps on the hillside, Machan said Monday, such “artesian” water had no natural escape route.

Workers could have unleashed the mud-flood when they removed 25 feet of historic landslide debris that was holding down the pool’s waterproof cap. They knew there was an irregularly shaped ridge of bedrock in the area, Macham said, but, “They didn’t think for one moment that it was actually acting as a dam.”

He complimented the preconstruction report on site conditions done by Golder Associates.

“They didn’t skimp on exploration. They reported at the higher end of professional work … It was definitely not a cookie-cutter report,” he said. “We may be too harsh to judge them based on what we know today.”

With the benefit of hindsight, Macham said, he looked for things that might have been done differently. For example, he noted that construction plan didn’t require “immediate backfill placement, staging of work, dewatering or limiting the size of the excavated portion.”

Those are the kinds of requirements that the U.S. Army Corps of Engineers will enforce at the U.S. 95 site this year, according to the corps’ Mike Doherty. Corps permits are required for construction work that impacts wetlands.

Doherty wants construction stopped by Sept. 15, when the chance of getting wet conditions increases.

Mike Hartz of the Idaho Division of Environmental Quality also is monitoring the site, watching for erosion. Hartz enforces water quality rules. Fortunately, he said, a drainage ditch at the bottom of the construction site has trapped most of the sediment, keeping it out of the Kootenai River.

Hartz isn’t sure when construction can reasonably start again.

“The ground has been frozen and it’s just starting to thaw up there,” he said. “Things will get a little dicier now. Management of this next construction season is real important.”