DESERT AIRE, Wash. — A “non-failure emergency” condition has been lifted at Priest Rapids Dam seven months after greater-than-normal leaking was discovered. Operations have returned to normal.
A loss of bonding in a lift joint, or seam, resulted in a flow of 3 to 4 gallons per minute through the joint at the base of one the dam’s 22 spillway monoliths. Lift joints are areas between two concrete blocks poured at different times, and monoliths are large expanses of concrete supporting piers holding spillway gates.
Concrete is porous so there is always some leaking but inspection drilling revealed the greater than normal flow last March 28. There was no imminent danger, but a non-failure emergency was declared by the dam operator, which is Grant County Public Utility District.
The dam’s 19-mile-long reservoir, which can hold up to 237,100 acre-feet of water, was lowered to the normal minimum operating level of 481.5 to 484.5 feet above sea level during further inspections. The maximum reservoir elevation is 488.0 feet.
More drilling was done to determine the source of the leaking and relieve pressure. Workers also installed more monitoring equipment.
Through analysis of the spillway in the full operating range of the reservoir, officials have determined the emergency designation is no longer required. The PUD working with the Federal Energy Regulatory Commission removed the non-failure emergency Oct. 15.
Officials are also conducting an analysis to discover why the lift joint became “disbonded” and are determining if and what future remedies are needed.
PUD spokesman Chuck Allen said he does not know if there was a loss of power generation.
The concrete gravity dam is 178 feet tall and it has 10 turbines that can generate up to 955.6 megawatts of electricity. The dam cost $91.8 million to build between 1956 and 1961. It is four miles south of Desert Aire and 47 miles northwest of Richland.