Lower Snake Dissolved Gas TMDL Planby Mike O'Bryant
The lower Snake River dissolved gas Total Maximum Daily Load (TMDL) plan is ready for review.
The Washington Department of Ecology will unveil its plan to improve the levels of dissolved gas in the section of river that is on its 303(d) list and consistently out of compliance with the state's 110 percent TDG limits due to operations at U.S. Army Corps of Engineer dams, at a public meeting in Kennewick, Wash. March 25.
Ecology, the U.S. Environmental Protection Agency, Columbia River tribes and the state of Oregon have been working on Columbia River Basin dissolved gas and temperature TMDLs for a couple of years, according to Ecology's Ann Butler. They completed a lower Columbia River temperature TMDL late last year. Ecology began its review of the lower Snake River dissolved gas TMDL in April 2002 saying that the primary source of gas in that section of river is caused by spill at the Corps-owned and operated Ice Harbor, Lower Monumental, Little Goose and Lower Granite dams.
"The Corps in operating the four lower Snake River dams has identified a number of things and working on actions they can take to help the issue," Butler said. "They've been working on this TMDL with us."
She said the plan must balance fish passage and TDG levels so there is enough water for fish, while also keeping gas levels in compliance. Gas levels can rise during either voluntary spill for fish, or it can occur during involuntary spill at the dams due to high water levels that exceed each dam's powerhouse capacity. Waivers to 120 percent TDG requested by the Corps in order to provide spill to meet NOAA Fisheries' 2000 biological opinion are typically approved each spring and summer.
"Clearly, if spilled water is the cause of elevated TDG levels but is required for fish passage, care needs to be taken not to implement gas abatement measures that may benefit water quality, while damaging the beneficial uses, such as juvenile migration, that the federal Clean Water Act was designed to protect," according to Ecology's gas TMDL.
The TMDL and implementation plan identify ways to reduce TDG in the lower Snake River from the Idaho border to the Snake River's confluence with the Columbia River. Ecology has also begun TMDL proceedings that will look at dissolved gas levels on the mid- and upper-Columbia River.
The federal Clean Water Act (1972) requires that every river not in compliance with state water quality standards must have a TMDL, which defines the maximum allowed pollution for a water body and allocates pollutant loads among the various sources. The Columbia River is on Washington's and Oregon's 303(d) list of water quality impaired bodies of water for temperature and dissolved gas, and the lower Snake River is on the Washington and Idaho 303(d) list.
Spilling water over dams for fish passage or for natural reasons has led to elevated gas levels in Northwest rivers. That has put a number of rivers on the 303(d), or water quality impaired lists in both Oregon and Washington, and so the federal Clean Water Act requires the states to complete a TMDL for those rivers.
A recently approved lower Columbia River gas TMDL calls for millions of dollars in structural improvements at four dams in that section of the river. The agencies that developed that TMDL (EPA, Ecology, Oregon Department of Environmental Quality and tribes) hope those improvements will eventually help the dams meet the states' 110 percent saturation of dissolved gas limits, even though some say there is little evidence that dissolved gas will harm juvenile salmon until levels reach above 125 percent.
Ecology's implementation plan for the TMDL incorporates the actions described in other documents, including the 2000 BiOp and the Corps' Dissolved Gas Abatement Study. Phase I focuses on meeting fish performance standards identified in the 2000 BiOp, while Phase II includes further structural modifications.
"Structural work has already been carried out to reduce TDG at the four lower Snake River dams," according to Ecology's TMDL document. It goes on to say "Ecology is confident that the collaborative effort with the dam operators toward reducing gas will continue and be balanced through this TMDL. The track record for Congressional funding for these projects is good, and there is reason to believe that further funding of projects will continue."
Those projects include the completed installation of flow deflectors or "flip lips" at Ice Harbor Dam, endbay deflectors at Lower Monumental Dam and the removable spillway weir at Lower Granite Dam. Further actions are planned, but they are dependent on Congressional funding, according to Ecology. Those include endbay deflectors at Little Goose Dam, bypass outfall relocation at Lower Monumental Dam and divider walls at dams as appropriate.
Some operational actions include scheduling routine maintenance during low power load and low flow periods, preventive maintenance to prevent breakdowns during critical flow periods and optimizing power purchases to minimize involuntary spill.
Butler said public comment is open until April 4. The TMDL/implementation plan can be found on Ecology's web site at www.ecy.wa.gov/biblio/0303020.html. After the public comment period closes, Ecology will incorporate comments into the final document and submit it for approval to the EPA in May, which has 30 days to deny or approve the plan.
The March 25 public meeting in Kennewick will begin at 6:30 p.m. at Ecology's field office, located at 1315 W. 4th Ave.
Washington Department of Ecology: www.ecy.wa.gov
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