An estimated 44 gallons of transformer oil that leaked into the Snake River was being cleaned up by Army Corps of Engineers spill response teams Tuesday.
The spill occurred as work was under way to repair Ice Harbor Dam cooling units that gradually leaked as much as 1,680 gallons of transformer oil contaminated with polychlorinated biphenyls, or PCBs, into the river some time after June and continuing through January.
The earlier river contamination was caused by pinhole leaks that developed in metal tubing in the cooling units and grew over several months.
But the new spill was caused by human error.
Maintenance staff were running new transformer oil through lines to clean out old PCB-contaminated oil when the spill occurred, said Corps spokeswoman Gina Baltrusch.
Within 15 minutes, staff realized oil was escaping through an open transfer connection onto a concrete floor in the powerhouse and stopped work, she said. Some of the oil ran into a drain connected to a sump.
About 64 gallons of oil were believed to have leaked through the open transfer connection, but about 20 gallons were recovered before being discharged to the river.
About 11:40 a.m. Monday, an oil sheen was spotted downriver from the drainage discharge by one of the Corps employees scouting the river for signs of contamination.
During the months of gradual leakage of transformer oil, a sheen was not spotted on the water until Dec. 5 and that and subsequent sheens that were spotted spread quickly to a very thin layer on the surface of the water and were not considered recoverable by the Washington State Department of Ecology.
However, crews were able to use absorbent booms placed in the water to clean up the Monday spill. One boom was placed near the dam to prevent any further spread of oil.
Three more booms were used downstream near Eagle Island to soak up the oil, with boat response crews maneuvering them.
An additional spill-response team from Lower Monumental Dam joined Ice Harbor's crews Tuesday.
"We're conducting an investigation to determine the appropriate actions to help prevent this particular type of incident from happening again," said Lt. Cold. David Caldwell, the district commander, in a statement.
-- Annette Cary: 582-1533; email@example.com