Drilling of an exploratory hole into Wanapum Dam¹s spillway pier monolith No. 4. Courtesy Grant County PUD.

A drilling team has completed six investigative holes into the Wanapum Dam spillway pier monolith No. 4 as part of the forensic examination of a fracture found in the structure on Feb. 27, Grant County PUD has announced.

Further drilling work is to be undertaken after a larger platform is constructed on the monolith to support the workers and their equipment.

Windy weather has created delays in the drilling process ­ all work on the monolith, which is only accessible by boat or crane, must stop in wind gusts that are more than 35 miles per hour. The platform construction and drilling is expected to take about three to four weeks without significant wind delays. The drilling will help determine the geometry of the fracture and how far it reaches into the monolith.

Grant PUD is on track with modifications to the fish ladders at Wanapum Dam, which is located in Washington, US. Workers are currently installing pumps in the dam¹s two fish ladders and will install weirs and flumes to help migrating fish navigate to the top of the ladders and then to the reservoir behind the dam. Grant PUD lowered the Wanapum reservoir in elevation to stabilize spillway pier monolith No. 4. This action made the fish ladders inoperable without the modifications.

Work on the fish ladders is expected to be completed by April 15, which is the start of the spring Chinook salmon run. At the request of agencies and stakeholders, Grant PUD now plans to initially trap fish at Priest Rapids Dam and haul them in trucks before releasing them above Wanapum or Rock Island dams during the first few weeks of the fish run while the effectiveness of the ladder modifications are evaluated.

Photo: Workers observe the drilling of an exploratory hole into Wanapum Dam¹s spillway pier monolith No. 4, as water flows from the fracture into the drill hole. A water-proof membrane has since been installed in front of the fractured area to prevent such flows. Courtesy Grant County PUD.