Corps confirms oil leak at 810-MW Lower Monumental hydro

The U.S. Army Corps of Engineers has confirmed an oil leak in the Unit 2 generator at its 810-MW Lower Monumental hydro plant.

Corps staff investigated a suspected leak, reported on Aug. 3, and were able to confirm that a slow leak had allowed oil to enter the water. An estimated 742 gallons of oil slowly leaked from the unit during about a seven-month-long period.

Lower Monumental Dam is located on the Snake River and impounds Lake Sacajawea. The project includes a concrete gravity-type dam, a powerhouse containing six turbine-generator units, a navigation lock, two fish ladders, and a juvenile fish facility. Construction began in 1961 and the project became operational in 1969.

The suspected oil leak was reported to the National Response Center (NRC), Environmental Protection Agency – Region 10, and Washington Department of Emergency Management, which is responsible for notifying the Washington Department of Ecology. A follow-up report confirming the leak was sent to the EPA and the Department of Ecology.

Operations officials shut down the unit when maintenance workers detected a discrepancy in the mass balance of turbine oil at the Lower Monumental powerhouse.

“Our oil accountability program led us to the decision to take unit 2 out of service while we investigate to conclusively determine if we have an oil leak from the turbine runner into the water. However, all six units’ oil systems are interconnected, making it very difficult to quantify the amount of oil in an individual unit,” said Don Redman, the Corps’ Walla Walla District environmental compliance coordinator, on Aug. 4. “If we confirm there is a leak, the unit will remain out of service until we can un-water it to conduct repairs.”

On Aug. 8, maintenance workers were preparing to remove the remaining oil from the turbine hub, preventing any additional unintended release of oil into the water. The Corps says the unit will remain out of service until it can be un-watered to conduct repairs.

“Because unit 2 is the primary generator at LoMo, it is constantly in operation, a slow leak like that, releasing a very small volume of oil per hour, wouldn’t likely be very noticeable in the water during normal operations,” said Redman. “We take our responsibility seriously to maintain and operate these dams in an environmentally sound manner, adhering to all federal and state regulations. We always strive to prevent pollutants from entering the river and will be taking action to help prevent this from happening in the future at all of our facilities.”

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