Priest Rapids Dam work progressing

Crews have finished drilling around 230 core samples in the Priest Rapids Dam and are installing instruments into the dam’s concrete monoliths to monitor the structure’s stability. Installation is slated to end in early Sept.

In March, Grant County Public Utility District declared a non-failure emergency at the dam when leaks were found in the layers of grout used to bind the structure’s large sections of steel and concrete. Crews have been working since to drain the structure, find the source of the leaks and install equipment that will help monitor if future problems occur.

The incident has never presented a safety risk to the public, according to utility district officials.

Thirty-seven new instruments are scheduled to be installed to measure if the dam’s monoliths shift, which could cause future leaks or failures. Normal operating conditions will likely resume by the end of the year, said utility district officials.

Though officials said that it is too early to tell what caused the leak, other old dams along the Columbia River have suffered leaks in the past as a result of pre-construction problems.

A crack discovered on Wanapum Dam four years ago was ultimately attributed to pre-construction design flaws. Water levels behind the dam were lowered 28 feet to reduce pressure on the structure during repairs, compared to only three feet of reservoir reduction behind the Priest Rapids Dam. The Priest Rapids Dam was built in 1961, and the Wanapum Dam was first operational in 1963.

Crews discovered the leaks in the Priest Rapids Dam when drilling test holes, a precautionary measure after the crack was discovered in the Wanapum Dam.

A three-foot reduction in reservoir levels is still within operating levels for the Priest Rapids Dam and energy-production has not been affected by the repairs, officials said.