Elevated total dissolved gas (TDG) levels are mainly caused by spilling water at hydroelectric dams on the Columbia and Snake Rivers. Water plunging from a spill entrains TDG at high levels. High TDG can cause “gas bubble trauma” in fish. Some spills are done to meet juvenile fish passage goals (helping them get past the dams).
Oregon and Washington wrote Total Maximum Daily Loads (TMDLs) to address TDG on the Columbia and Snake Rivers. Oregon and Washington have listed multiple reaches of the Columbia and Snake Rivers on their federal Clean Water Act 303(d) lists due to TDG levels exceeding state water quality standards.
The TMDLs included a status review in 2010 on the implementation of the TMDLs. Due to an increase in interest in the TDG requirements we are convening an advisory group comprising representatives of tribes, federal and state agencies, and others to evaluate appropriate points of compliance for this TMDL. This group is called the Adaptive Management Team (AMT).
Lower Columbia River
Mid Columbia River
Additional information is available on the Oregon Department of Environmental
Quality (ODEQ) website:
The Department of Ecology (Ecology) follows the rules of the federal Clean Water Act in its determinations that result in how much spill is allowed over dams in the Columbia and Snake rivers to help juvenile fish migrating to the ocean. We think it is helpful to emphasize that Ecology already allows more spill over dams, on a dam-by-dam scenario, through adjustments to state water quality standard rules. Ecology does not believe the overall benefits of additional spill versus detrimental effects to aquatic life is clear or sufficient to justify a rule revision of the water quality standards.
Click here for a complete description of the role of the adaptive management team (AMT). The first issue the AMT will address is the need and location of the 115% forebay TDG monitoring requirement.
Click here for related links (gas abatement plans, water quality standards, etc.).
If you would like to be added to the "interested parties" list please contact Chad Brown. For more information, or if you have comments or questions, please contact:
Columbia River Coordinator
Oregon Department of Environmental Quality
811 SW 6th Ave
Portland, OR 97204
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