The Walla Walla District of the U.S. Army Corps of Engineers recently identified metal tubing failures as the likely source of several inadvertent oil leaks from power transformer heat exchangers or “cooling units” at Ice Harbor Lock and Dam on the Snake River.
Determining the sources of the leaks was difficult and took time to diagnose because of the complexity of powerhouse systems, the Corps said in a press release. Upon discovering leak sources, the Corps immediately isolated the failed cooling units to stop leaks, and began repairs. The Corps notified state and federal agencies.
“As good stewards of the environment, we always seek to prevent pollutants from entering the river,” said District Commander Lt. Col. David Caldwell. “The Corps regrets this inadvertent incident. We’re taking appropriate actions to prevent this from happening in the future.”
There are three “water-cooled” transformer systems at Ice Harbor, and each transformer has two dedicated heat exchangers or “cooling units,” or a total of six cooling units. Each pair of cooling units circulates 8,000 gallons of transformer oil to cool a transformer during hydropower generation. Three of the six cooling units at Ice Harbor were found to be leaking after pinhole leaks in metal tubing apparently developed and grew during several months.
Diagnosing and troubleshooting the source of oil in the water was difficult because oil could have originated from several equipment sources at the dam, which operate intermittently. Adding to the challenge, each water-cooled unit’s metal tube bundles are immersed in oil contained inside a metal shell or sleeve, not easily inspected. An additional concern is small amounts of polychlorinated biphenyls in oil that apparently leached back into newer oil added later.
To reduce PCB levels of concern and remove contaminated water, the Corps is replacing oil in Ice Harbor’s cooling units. New oil does not contain PCBs. Also, all six cooling unit tube bundles are being replaced. The Corps continues to inspect and research the causes of metal tubing failures.
In addition, now that the Corps is aware of this specific problem, it’s testing for PCBs in oil in all systems at other dams in the district, and reviewing test records to prevent similar incidents.
The Corps first spotted light silver sheens on the water just below the dam on Dec. 5 when seasonal river flows were reduced and water below the dam became calmer. When the oil film was first spotted, the Corps immediately communicated with the Washington Department of Ecology. The state agency assisted the Corps with troubleshooting to find the source.
The appearance of a “rainbow” oil sheen on Jan. 9 triggered an official spill notification to the Department of Ecology, Washington Emergency Management and the National Response Center. Leak sources were later discovered to be in cooling units tubing. A review of oil inventory records helped establish the leaks had started at some point in time after June. During an 8-month period, up to an estimated 1,680 gallons of oil may have been lost, with no clear indication of those losses until Dec. 5.
Once leak sources were discovered, Ice Harbor shut down Transformer “TW1” on Jan. 12; it is planned to be back in service in February. Leaks were also discovered on Transformer “TW2” on Jan. 25; leaks were isolated, and it was placed back in service on Jan. 29. As repairs and testing continued, an additional leak was discovered on Jan. 27 in Transformer “TW3.” The leaking cooling unit was isolated, and the generator placed back in service that evening using a second cooling unit only.