Grant County PUD Awards Environmental Assessment Services Contract To Assess Benthic Community Impacts As A Result Of Significant Water Level Reductions In The Wanapum Reservoir

EAS was awarded a contract to support Grant County Public Utility District to characterize benthic community impacts that may have resulted from a nearly 27-foot water level drawdown on the Columbia River in central Washington state.

The discovery of a crack in a spillway at Wanapum Dam prompted dam operators to reduce the water level of Wanapum Reservoir, behind the dam, from about 570 feet to as low as 543 feet. As a result, portions of the river shoreline were exposed that had been inundated since the dam was constructed in 1963. The water reduction potentially stranded freshwater mussels, snails, fish, including juvenile lamprey, and other organisms, many of which are state and federally listed species.

As part of its federal licensing agreement and mission to protect and conserve natural resources while generating power, EAS and Blue Leaf Environmental were requested to design a field study and conduct the surveys to assess stranding of benthic fauna, fishes, and other organisms as result of water level reductions in the reservoir.

The EAS team will characterize freshwater mollusks (mussel, clam, and snail) species composition and densities in de-watered areas and areas unaffected by the drawdown; characterize other benthic community fauna (fish, including juvenile lamprey, crayfish, and amphibians) potentially affected by the drawdown; and monitor water quality conditions to assess potential changes in pH, temperature, total dissolved solids, turbidity, and total dissolved gas.

Information gained from EAS’s land- and water-based surveys will assist Grand PUD and federal, state, and tribal governments make decisions on mitigating and restoring declining and protected species in the project area according to natural resource management plans.

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