Work finished on structure needed to renovate Grace impoundment dam

W.R. Grace is one step closer to addressing structural deficiencies at an impoundment dam that holds asbestos-laden tailings near Rainy Creek.

Anthony Penfold, a remediation manager with W.R. Grace, said on Aug. 12 that the company completed construction of a cofferdam on the site following delays owing to the novel coronavirus. This watertight enclosure will allow workers to replace a spillway for the Kootenai Development Impoundment Dam.

Regulators have expressed concern that the spillway could fail during a major storm or earthquake, releasing the more than 424 million gallons of asbestos-laden water it holds back into Rainy Creek and even the Kootenai River.

The impoundment dam, also known as the Zonolite Tailings Dam, is a 151-foot earthen dam that is classified by the U.S. Army Corps of Engineers as a “high hazard dam.” This designation is based on the potential consequences of a dam failure rather than the probability of failure.

Penfold announced the completion of the cofferdam during a meeting of the Lincoln County Board of Commissioners. According to Penfold, the newly built dam will be in place for the next four to five years and is meant to keep water out of an area where workers will be renovating the spillway.

The cofferdam is rated to withstand up to 500-year storms, which Penfold said is more robust than most structures built for similar renovation purposes.

Penfold told commissioners that the spillway repair project remains in the contracting phase. According to W.R. Grace’s 2019 fourth quarter review and 2020 outlook published in February, the ultimate costs of the renovations are estimated to run between $50 and $100 million.

The company plans to award the construction contract within the next few months and begin the repair work as soon as the snow melts next year, said Penfold. W.R. Grace has shortlisted three firms for the multi-year project.

With all the uncertainty generated by the COVID-19 pandemic, Penfold said the company is especially eager to hire area workers and draw on local expertise. He said the company had already faced challenges with other projects due to travel restrictions and approval processes required to transport workers.

Work in the next three to four years will involve placing a large amount of steel and concrete to construct the “heavy robust structure,” Penfold said. He anticipates working as long as the weather cooperates each year.

Penfold also told commissioners that W.R. Grace also is interested in working with county officials to reopen the portion of Rainy Creek Road that leads to Tub Gulch.