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Priest Rapids “stable” after drilling uncovers monolith leaks, says Grant PUD

Priest Rapids Hydropower Plant

Officials from Grant County Public Utility District have discovered leakage at its Priest Rapids Dam is being caused by dis-bonded lift joints in the structure’s spillway monoliths.

Grant PUD discovered the leak during inspection drillings late last month, causing the Washington-based utility to declare a “non-failure emergency” in which it reduced the reservoir behind the dam by about three feet.

Subsequent examination of Priest Rapids has already found lift joint leaks at the same height in four of Priest Rapids Dam’s 22 spillway monoliths, indicating they are occurring where one concrete pour was completed and another began.

“To date, inspection drilling has occurred through about half of the spillway and will continue throughout the remaining monoliths,” Grant PUD said in a statement. “This is anticipated to continue into May.”

The utility noted there “is no threat to property or people”, and that operations at Priest Rapids its 955.6-MW hydroelectric plant have not been affected.

“Once the investigation and analysis are complete, Grant PUD officials will make a determination on what, if any, remedies are needed beyond the drilling,” the utility said.

The 10,103-foot long Priest Rapids Dam — located on the Columbia River 24 miles south of Vantage, Wash. — was completed in July 1956.

The facility is currently undergoing a $198 million refurbishment, with major works including the upgrade and replacement of runners, wicket gates, lubrication systems and other associated components.

Grant PUD’s initial review of Priest Rapids began as precautionary work after the utility completed repairs at its Wanapum Dam, where a spillway monolith cracked in February 2014. The incidents, however, are not similar.