State warned gravel pit of slope instability 4 years before landslide

Washington's Department of Natural Resources warned a Naches, Yakima County, gravel pit four years ago that its operations might be destabilizing a portion of the slope that collapsed onto Highway 410 this week.

Records from 2005 show a department geologist noticed a 10-foot-wide fissure between the towering basalt cliffs and a broad talus slope below. The gravel mine appeared to have removed deposits that were buttressing the slope, documents say.

"Your surface mining activity may be exacerbating slope instability and, therefore, may be creating a potential hazard to adjacent property and danger to the public health, safety (and) welfare," says a notice issued to the mine owners in September 2005.

An official for state Department of Transportation (DOT) said it's too early to say what might have triggered the slide. But the agency will begin drilling into the mass of earth this week, looking for clues, said geotechnical engineer Tom Badger. "That really is where the answer lies."

At least one scientist says it's entirely possible the gravel pit could have played a role. "It's definitely premature to rule out the gravel pit as a contributing factor," said University of Washington geologist David Montgomery, a noted landslide expert. "They were definitely digging at the toe of an active landslide, and that's a recipe for a slide," added Montgomery, who examined Google maps of the site.

"Every geologist I show those images to has said: 'Oh, wow, that's not a good place to be excavating.' "

Robin Simmons, owner of Simmons and Son Hauling & Rock Crushing, said an analysis conducted for the company in 2007 found no reason for concern. "The geologists have stated the facts," she said Thursday.

The gravel mine was partly buried by the slide, and several of Simmons' family members lost their homes. The slide slammed into the Naches River, and the riverbed was uplifted dozens of feet. The river flooded over the Nile Loop Road.

Yakima geotechnical engineer Brad Card, who conducted the slope analysis for Simmons and Son, said the gravel mine was too small to have triggered the massive slides, one of the largest ever to hit a state roadway.

"It's way beyond the scope of this type of excavation," he said. "There's nothing you could have done to prevent that slide."

Card's measurements showed 1 to 3 feet of downward creep on the upper slope between 2006 and 2008. "The slide came from above," he said.

The Department of Natural Resources (DNR) file includes pictures from 2005 of a deep chasm in the rocky ground and a tall conifer tree leaning down the slope. It also includes a succession of letters insisting that Simmons conduct a thorough analysis and prepare a plan for regular monitoring of the slope. According to the most recent one, dated July 2008, the agency still had not received a monitoring plan.

Dave Norman, DNR state geologist, said the agency had been frustrated with the mine owners' reluctance to comply. "It's been a struggle," he said.

Records show the owners appealed to state Rep. Jim Clements, who organized a meeting between the owners and DNR officials, including then-Public Lands Commissioner Doug Sutherland. Norman, who attended the meeting, said Clements urged the owners to cooperate with the DNR.

The gravel pit was located at the margin of the landslide, not its epicenter. But that doesn't exonerate the pit, Montgomery said.

"Landslides tend to be pretty messy affairs," he said. "Once they actually start to go, they can grow and a bigger area can be destabilized."

Highway 410 is expected to remained closed at the slide site throughout the winter. Officials have said the highway will have to be rerouted around the slide.

With rain forecast in coming days, officials are keeping close watch on the mountain of earth, hoping it won't continue to slide, said Badger, the DOT engineer.

"We're concerned about the river. We're concerned about keeping [a local access] road open."

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com