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Missoula County contracts engineers to survey failing mountain roads

Six Mile Road near Huson, one of several damaged by spring flooding, will undergo a geological survey this summer to help inform repairs this fall. (Photo courtesy of Missoula County)

The Missoula County Public Works Department will contract a local engineering firm to conduct stability surveys on two failing county roads, taking the first step in completing repairs by the onset of winter.

The $125,000 agreement with Tetra Tech, approved by Missoula County commissioners on Thursday, covers Six Mile and Butler Creek roads near Huson, which were damaged by flooding this spring.

“They’ll provide the engineering services for the recommended repairs,” said county project manager Eric Dickson. “We’ll have an engineer’s estimate with those options and move forward with either contracted work, or depending on the kind of work, time and cost, it may be something we in public works can do.”

Of the two roads, Six Mile Road is in the worst condition.

Reported in March, flood damage has resulted in significant loss of the shoulder and a partial loss of the southbound lane and guard rail. The roadway is slumping downhill and has broken loose of the soil.

Damage to Butler Creek Road was also reported in March. While the damage is less significant, the roadway is also showing signs of slumping downslope. Failure of the roadway could also impact water quality, Dickson said.

“It’s maybe two or three feet horizontally and about 15 feet vertically,” Dickson said of the damage. “If we need to go clear down the total slope, it would involve a lot of permitting.”

Dickson said the services will reveal a host of geological information and help inform possible repairs. While the work isn’t likely to be completed when school starts up, it should be wrapped up by winter.

“Tetra Tech mentioned they have a drill rig coming from Butte for a different project in a couple weeks,” said Dickson. “They’ll do the subsurface investigation the last week of July and get that info to their lab.”