Publication Summary

Three dam operators on the Pend Oreille River monitored total dissolved gas (TDG) during mid-March through early August, 2001 through 2004. To fill data gaps and compare data between organizations, the Department of Ecology also monitored TDG during 2004 near Ruby and at the other monitoring stations.

TDG levels from upstream of Washington State and TDG generated by Box Canyon and Boundary Dams often exceed standards. The effect of natural processes on TDG is very small.

The TDG Total Maximum Daily Load (water cleanup plan) recommends allocations equivalent to 110% saturation at the 95th percentile low barometric pressure.

Monitoring of the Pend Oreille River from 2001 through 2004 at the Idaho state line near Newport, and in the forebays and tailraces of Box Canyon and Boundary Dams, shows that total dissolved gas (TDG) frequently exceeds water quality standards. As a result, the Washington State Department of Ecology (Ecology) listed the Pend Oreille River on its 2004 303(d) list of impaired waters and has determined the Total Maximum Daily Load (TMDL) for TDG in the Pend Oreille River.

The U.S. Environmental Protection Agency is issuing a TMDL for the section of the Pend Oreille River that flows through the reservation of the Kalispel Tribe of Indians. Ecology is issuing this TMDL for the Pend Oreille River in Washington State, other than the section flowing through the reservation.

Total dissolved gas was monitored in the Pend Oreille River with datalogging and profiling multi-parameter instruments from March through July 2004 near Newport, Ruby, Box Canyon Dam, and Boundary Dam. Data show that TDG changes over time at these sites. These data also allow comparisons to data collected by other organizations.

TDG data analyzed were from 2001 through 2004 during the high-flow season (mid-March through early August). The analysis shows TDG levels at the Idaho state line, TDG generation processes at Box Canyon and Boundary Dams, and the fate of TDG in the reservoirs of those dams.