The U.S. Army Corps of Engineers will return to a spot on the Mount Ripinsky hillside to remove a small amount of contaminated soil remaining from a historic pipeline spill above Highland Estates.

The spill of about 4,000 gallons of aviation fuel occurred 40 years ago, during operation of the military pipeline between Haines and Fairbanks. About 400 cubic yards of contaminated soil were removed in 2008, near the site of a new borough water tank.

The remaining contamination is limited to a bluff located between borough and private property, according to Mary Jemin, project manager for the Corps. It’s less than a foot deep at the site and amounts to two or three scoops from a backhoe, she said during last week’s meeting of the local Restoration Advisory Board.

The removed and treated soil will be incorporated into local asphalt, under a contract between the agency and Southeast Roadbuilders.

“A lot of dirt roads and driveways have as much contamination. If we can come up with a process (for disposing treated soil) that doesn’t cost as much as removing it, we’ll do that,” Jemin said.

Also at last week’s meeting, Lutak tank farm cleanup contractor North Wind, Inc. said only two of 24 groundwater monitoring wells at the site showed petroleum products. About a gallon of chemicals was recovered.

North Wind geologist Arden Bailey said those samples reflect the company’s recent removal of 3,600 cubic yards of contaminated soil, now in contained treatment cells at the site.

“We hope taking out all this contaminated fill shows the groundwater is cleaner. We hope it makes a big difference,” he said.

North Wind also took 27 groundwater samples and four samples of surface water, with testing results due later this year.

Work at the site this year will include treatment of soil in the three cells to reduce levels of trimethyl benzene, which is in concentrations still above cleanup levels. The current level of contamination is not a concern for human health or environmental safety, but is a level the company agreed to meet.

Anne Marie Palmieri, project manager for Alaska Department of Environmental Conservation, said state and federal regulators are in agreement that there are areas of potential contamination at the site that still need to be characterized.

“The groundwater is still contaminated because there’s still contaminated source material that hasn’t been fully delineated,” Palmieri said. DEC knows there’s contamination between (the sites of) tanks 101 through 112, but doesn’t know the extent or concentration of it, she said.

DEC also wants more sampling of marine sediments at the former Army dock at Lutak, where at least one sample has found contamination exceeding cleanup levels.

Whether North Wind is responsible for work on additional potential areas of contamination is a topic of discussion between the company and federal cleanup officials.