One of the toughest parts of the Rim Rock job for EPC was dealing with the variable ground conditions, which required trenching crews to be especially flexible, according to Larson.

"Some of the soils were silty and very wet, then within 1,000 feet the trench might be going through hard rock," she says.

Another natural challenge involved Rim Rock's proximity to raptor habitats. Wildlife authorities signed off in 2008 on a plan for quarter-mile setbacks for the turbines from raptor nests, but officials subsequently decided setbacks should be a half-mile.

In early 2012, NaturEner worked with groups including the U.S. Fish and Wildlife Service and Montana Audubon to bring Rim Rock into compliance with the new standard.

"We decided on the fly to move 25 turbines to ensure we had at least a half-mile of setback from historic raptor nests," Copeland says. "Basically, we redesigned the entire east face—access roads, collector systems, turbine locations—within two months."

Project Facts

Power capacity: 189 MW

Location: 21,000 acres near Cut Bank, Mont.

Total cost: $370 million

Construction cost: $75 million

Project start: Fall 2011

Completion: June 2013

Owner: NaturEner USA LLC, San Francisco

Contractors: Mortenson Construction Renewable Energy Groups (general contractor), Minneapolis; EPC Services Co. (engineering), Billings, Mont.