About 1.5 acres of petroleum-contaminated soil at E.E. Wilson Wildlife Area will be left to break down naturally, the Oregon Department of Environmental Quality has decided.
A trench dug downhill from the contamination will keep it from spreading, and monitoring wells will be checked regularly for the next few years to make sure the approach is working.
Two acres of the wildlife area were contaminated on July 7 when a double tanker truck crashed into a ditch on Highway 99W near Adair Village, spilling between 3,000 and 3,400 gallons of gasoline and about 1,500 gallons of diesel.
The spill seeped beneath the road, creating a nearly three-week traffic mess as crews constructed a temporary lane for traffic, tore up the road, removed soil from the road bed and along the sides of the highway, and rebuilt the road.
Road work will be complete Thursday, when crews will put down a final layer of asphalt and add rumble strips and striping, said Bart Bretherton, a hazmat coordinator at the Oregon Department of Transportation.
Crews also excavated more highly contaminated soil from about a half-acre at the wildlife area, DEQ spokeswoman Katherine Benenati said.
In all, about 40,000 tons of contaminated soil were taken to nearby Coffin Butte Landfill for disposal, she said.
The wildlife area, managed by the Oregon Department of Fish and Wildlife, is home to dozens of species of birds, mammals, reptiles and amphibians.
The remaining contamination is under several feet of dirt in an area of the refuge known as Check Station Prairie.
Wildlife area manager Shawn Woods said that digging up the prairie would have more of an environmental impact than letting the contamination degrade on its own. There is about a foot of contamination, he said, but it is about five feet deep.
The trench is filled with carbon and active bacteria to help break down the petroleum, Woods said.
Salem-based Oregon Petroleum Transport will pay for the cost of environmental cleanup and for rebuilding the 800-foot stretch of highway.
Terry McEvilly, a corporate officer at the privately held company, did not respond to an interview request this week. He previously said that insurance will cover most of the cost.
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