The U.S. Army Corps of Engineers says between 200 and 300 gallons of oil at Lower Monumental Dam cannot be accounted for and may have leaked into the Columbia River from a turbine in Unit 2, prompting the agency to take the unit off line.

The potential leak was discovered during the first week in August and is still being investigated, according to an email from Corps spokesman Joseph Saxon, who added that the unit will not return to service until the issue is resolved.

As required by law, the Corps notified the Environmental Protection Agency, National Response Center and Washington Department of Ecology. It also notified Columbia Riverkeeper, which had sued the Corps over oil spills at eight dams—including Lower Monumental—resulting in a 2014 settlement. The settlement required the agency to apply for water pollution permits from the EPA, but the EPA has declined to issue those permits, a news release from Riverkeeper says.

Riverkeeper now has unresolved lawsuits against the Corps for oil losses at Chief Joseph Dam, and against Grant and Douglas County PUDs for oil losses at three mid-Columbia dams. The Chelan County PUD settled before a lawsuit was filed.

“Shockingly, the Army Corps faces no penalties for fouling the Snake River with toxic oil,” Riverkeeper’s senior attorney Miles Johnson said in a news release about the most recent oil losses. His statement added, “Oil pollution from Lower Monumental Dam is just one more reason to remove the four obsolete, aging dams on the lower Snake River.”

Saxon said his agency is doing everything possible to reduce the risk of oil releases, but there are no direct means to detect a leak from turbine runners, especially—as in this case—when the leak is too small to cause a visible sheen on the water.

To help prevent oil leaks, the agency is replacing seals when needed and working to identify improved seal technologies that work better on aging turbine runners, Saxon said.

The agency is also testing and evaluating environmentally acceptable lubricants, and looking for better ways to meter oil transfers to improve early detection of oil releases. “We’ll continue refining these procedures because our goal is to not spill any oil,” his email said.

K.C. Mehaffey covers fish issues for Clearing Up, and is editor of the NW Fishletter. She joined the NewsData writing team in February 2018. From lawsuits to scientific studies, she is enjoying the deep dive into the Columbia Basin's many fish topics.