Crews Continue Inspection of Priest Rapids Dam Spillway Monoliths

Grant PUD officials expect analysis to continue for the next several weeks

Crews continue investigating the leakage discovered in spillway monoliths at Priest Rapids Dam. Initial analysis shows that a disbonded lift joint is the source of the leakage. A lift joint is the area between two concrete blocks poured at different times.  A monolith is the structure that supports the piers holding up the spillway gates.

Priest Rapids Dam continues to generate electricity and operations continue as usual. There is no threat to property or people.  The monoliths are stable, but do merit further investigation.

The monolith lift joint has lost some of its bonding, resulting in the leakage of three to four gallons a minute, which has been detected by the investigative drilling.  This leakage has been found through the same lift joint near the base of four of the 22 spillway monoliths.

To date, inspection drilling has occurred through about half of the spillway and will continue throughout the remaining monoliths.  This is anticipated to continue into May. The spillway structure is stable and no movement has been detected in the structure.  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 inspection drilling is reducing pressure from the water inflow through the disbonded area of the lift joint.

Late last month, out of an abundance of caution, Grant PUD officials declared a non-failure emergency at Priest Rapids Dam.  This was discovered after inspection drilling revealed the leaking in spillway monoliths.

Grant PUD has reduced reservoir elevation behind the dam by approximately three feet.  This is still within the normal operating range while inspection work continues. Priest Rapids Reservoir will be held to operating elevations between 484.5 to 481.5 feet above sea level. The maximum reservoir elevation is 488.0 feet. The reservoir will remain at the lowered level at least until the inspection work is complete.

Established by local residents over 75 years ago, Grant PUD generates and delivers energy to millions of customers throughout the Pacific Northwest. What began as a grassroots movement of public power has evolved into one of the premiere providers of renewable energy at some of the most affordable rates in the nation. For more information visit www.grantpud.org or follow us on Facebook and Twitter.

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