PORTLAND, Ore. – Water levels at Big Cliff Reservoir will be lower Oct. 13-27 to allow the U.S. Army Corps of Engineers to conduct sediment sampling.
The Corps is collecting the sediment samples as part of a Remedial Investigation to determine the nature and extent of any contaminants in the immediate area. Corps employees discovered construction debris during an emergency reservoir drawdown in 2009 and have conducted several smaller sampling events since that time.
Since the initial discovery of construction debris, the Corps has identified that contaminants of concern are present in the sediment; however, samples of surface water, collected last year, found no exceedances of risk-based screening levels indicating that there are no risks to downstream communities and water users.
“We are proceeding with a more comprehensive investigation in order to understand the nature and extent of contaminants in the sediment. The results will be used to determine if further actions, including clean up, are warranted,” said Mark Dasso, Portland District project manager. “We’ve been very methodical about our process of collecting and analyzing information to better understand the site,” he continued. “This round of sampling will focus on sediments in the area.”
The water drawdown will begin Oct. 13 and reach approximately 1175 feet by 8 a.m. Oct. 16. This is about 27 feet lower than typical low levels at Big Cliff. Corps regulators will further lower the reservoir to 1167 feet for continued sampling before increasing back to 1175 feet until Oct. 27.
Additionally, lower water levels may expose boaters and other reservoir users to vegetation and other potential hazards that are normally submerged well below the water surface. People recreating at the reservoir should be alert for these hazards as well as floating debris. The reservoir will be back to normal levels, Oct. 31.
Release no. 17-050