'Non-failure emergency' lifted at Priest Rapids Dam

PRIEST RAPIDS DAM — The non-failure emergency condition at Priest Rapids Dam has been lifted, as of Monday afternoon.

The dam had been operating under the non-failure emergency since March 28, according to a press release from the Grant County PUD. The reservoir was lowered behind the dam and an emergency was declared after test drilling revealed water was leaking in spillway supports.

“During the past six months, crews have been conducting more drilling to determine the source of the leaking and also relieve pressure in the leaking area,” the press release said. “Workers have been installing more monitoring equipment in the spillway. Through analysis of the spillway in the full operating range of the reservoir, officials have determined the emergency designation is no longer required.”

The investigation revealed the leaking was caused by a “disbonded lift joint,” a seam in the “mass concrete making up the spillway’s support structures.” Utility district officials drilled additional drain holes, reducing pressure in the area that’s leaking. That also allows PUD staff to monitor the joint and its current condition.

“Officials also are conducting a root-cause analysis to discover why the lift joint became disbonded and are determining if, and what, future remedies are needed.”

The reservoir was lowered “out of an abundance of caution,” and the “emergency never presented a safety risk for the public or PUD workers,” the press release said.

The reservoir was lowered three to five feet, which is at the low end of the dam’s normal operating range. Priest Rapids has 22 spillway monoliths; a monolith is “the expanse of concrete below each of the dam’s spill gates,” PUD officials said in an earlier press release. Crews drilled inspection holes downward from an internal passageway, called the grout gallery, that runs the length of the spillway.

Cheryl Schweizer can be reached via email at education@columbiabasinherald.com.