[4] Oregon Water Quality Commission OKs 2-Year TDG Waiver At Mainstem Dams

The commissioners who oversee Oregon's Department of Water Quality have approved a proposal from the Corps of Engineers, USFWS and NOAA Fisheries that grants a two-year waiver of the 110-percent total dissolved gas standard for the operation of mainstem dams on the lower Columbia River.

The waiver got the thumbs-up on June 21 and will allow the Corps to spill water for juvenile fish passage that has up to 120-percent TDG measured in dam tailraces and 115 percent in dam forebays for the 2008 and 2009 seasons.

Lower Columbia tribes, ODFW, WDFW, and many conservation and fishing groups had called for changes to the proposed waiver that would allow for more spill by increasing the 115-percent cap in dam forebays to 120 percent. They also pushed for elimination of the current monitors altogether and re-locating them in places where they said TDG readings would be more accurate.

The commissioners passed the waiver with several changes, according to a Department of Environmental Quality spokesperson. They reduced the five-year time frame in the proposal to two years, and called for an adaptive management process, beginning immediately, to evaluate the use of forebay monitors and speed up gas abatement activities. A staff report had recommended that the adaptive management component start no later than January 2011.

The DEQ staff report also did not agree with the call to boost forebay limits to 120 percent. It supported the Corps' method for computing gas levels as the average of the highest 12 hours in one day, rather than the tribes and state agencies' recommendation for averaging gas levels over the highest 12 consecutive hours.

The waiver will run from April to August, with a provision in March for a 10-day spill at Bonneville Dam for migrating hatchery fish from Spring Creek Hatchery.

Both Washington and Oregon issued a "total maximum daily load" ruling in 2002 for the lower Columbia that allows spills until 2020, when modifications like removable spillway weirs and operational changes to reduce total dissolved gas must be in place. -B. R.

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