Publication Summary

The purpose of this literature review is to provide information to assess the appropriate water quality criteria for total dissolved gas (TDG) supersaturation in freshwater in Washington State.

The purpose of this literature review is to provide information to assess the appropriate water quality criteria for total dissolved gas (TDG) supersaturation in freshwater in Washington State. The Environmental Protection Agency, under the federal Clean Water Act, developed a national criterion of 110 percent for TDG in the 1970s. This criterion was based largely on lab research, performed on juvenile salmon in the Pacific Northwest, due to concerns over high TDG levels caused by spilling water over the Columbia and Snake River dams. Since the mid 1990s, Washington and Oregon have retained their 110 percent statewide criterion but adjusted their TDG criteria upward to 115 percent in the forebays and 120 percent in the tailraces on the Columbia and Snake Rivers. This was to allow spill when juvenile salmon are migrating so they can avoid harm from going through the turbines. Both states have an instantaneous limit during the fish spill season of 125 percent TDG. Oregon has a TDG criterion of 105 percent for waters shallower than one meter and British Columbia, Canada has a guideline of 103 percent for waters shallower than one meter.