GRANT COUNTY — The large crack in part of the Wanapum Dam spillway may have been there long before it was discovered late last month.
The crack, which measured about 2 inches wide by 65 feet long when divers first observed it near the base and across the full width of one of the dam’s concrete support piers, had algae growing on the fracture, Dawn Woodward, director of hydro operations for the Ephrata-based utility, told The Wenatchee World last week.
Other parts of the fracture appeared clean, indicating that they may have been more recent.
The Grant County Public Utility District (PUD) has hired Coeur d’Alene-based contractor Kuney-Goebel JV and subcontractors to do investigative drilling into the damaged pier to map the crack’s size and shape. Drilling began last week and is expected to take about nine days.
Earlier forensic studies, including ground-penetrating radar and echo imaging, allowed experts to see into the structure and bedrock, but they have provided no conclusive data about a cause, Woodward said.
No possibilities have been ruled out, Woodward said. She and other PUD officials declined to name suspected causes.
Investigators don’t yet know if other parts of the dam would also be vulnerable to cracking, Woodward said.
A review of seismic activity in January and February revealed no events that could have caused the damage, but they could expand their analysis to a larger time frame. They’re also looking at the dam’s relation to fault lines in the area, she said.
Nor does water appear to be getting under the dam to undermine it at its base, she said.
Analysis of the crack’s root cause could take a few more weeks, she said.
Investigators have suggested using “steel strand anchors” drilled from the top of the dam, through the concrete structure and into the bedrock to cinch the structure down and keep the crack closed, possibly rendering the structure strong enough to support a higher reservoir level while permanent repairs take place.
Woodward said it could take months to identify and fix the problem and raise the reservoir. There are no guarantees.