Officials with the U.S. Army Corps of Engineers are considering their options to deal with a crack in a concrete tank at an adult fish-trapping facility at Lower Granite Dam west of Lewiston.
Corps spokesman Bruce Henrickson said the crack was discovered last month and appeared while a nearby well that is part of a wastewater treatment facility was being demolished.
"That apparently led to ground vibrations that apparently led to this concrete tank shifting," he said.
The concrete tank has a footprint of about 5 feet by 12 feet and is 27 feet high. It holds water while the dam's adult fish trap is being operated. During adult salmon and steelhead runs, the trap is used to capture migrating fish for research and to collect some adults for transportation to various hatcheries.
Henrickson said the crack occurred along an existing joint in the concrete structure. While it appears larger in photographs, the crack is one-quarter to three-eighths of an inch wide, according to corps inspectors.
The tank, which is used seasonally while adult salmon and steelhead are climbing the fish ladder at the dam, will be filled with water next week to determine if it is leaking. Henrickson said that test will determine what sort of repairs, if any, need to be made. He said there are PVC water stops between the joint on the inside of the tank that may have been damaged during the shift.
"There is no structural failure here," he said. "We call it a gap or movement along a construction joint. It's not a safety issue."
He said the trap is scheduled to go into seasonal operation in early March. The fish ladder at the dam will open Feb. 28.
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