The Army Corps of Engineers has postponed bidding a planned $70 million renovation of Thurmond Dam's turbines to explore more advanced oxygenation systems to improve water quality in the Savannah River.
"Basically, they decided to look at it more closely regarding oxygen," said corps spokeswoman Vicki White. "Now we're thinking a contract could be awarded by Christmas."
Bids were to be sought in April.
Studies by Georgia's Department of Natural Resources and the U.S. Fish & Wildlife Service show discharges from Thurmond Dam fail minimum water quality standards five to six months each year due to oxygen deficiencies related to hydropower production.
In warm weather, de-oxygenated water 60 feet beneath the surface of Thurmond Lake is pumped into the turbines and discharged into the Savannah River. Lack of oxygen hampers fish growth and reproduction for 15 miles downstream.
Although Georgia and South Carolina have made repeated requests for an oxygenation system, the corps has declined to pursue improvements, mainly because it is a government agency not subject to the same environmental rules as commercial utilities that operate dams.
Last fall, however, the corps agreed - as part of a scheduled renovation to the 43-year-old turbines - to explore turbine venting as a means to increase dissolved oxygen by at least 2 parts per million.
Turbine venting involves mixing air with water pushed through hydropower turbines. The process requires specially designed turbine blades, but would add oxygen to water released into the Savannah River below.
However, even a 2 part per million increase still would leave portions of the river deficient on oxygen during extreme warm weather.
Ms. White said the corps is now studying more effective oxygenation systems that could add even more oxygen to the river. "They were talking about a 2 part per million increase," she said. "Now the goal is to decrease the dissolved oxygen deficit by 40 percent."
Assisting in the additional research are the Tennessee Valley Authority, operators of numerous hydropower dams; and the corps' Waterworks Experiment Station in Vicksburg, Miss., she said.
"They will design some kind of oxygen improving system," Ms. White said. "It could still end up being venting, or it could be some other type of technology."
The minimum standard for dissolved oxygen, used in Georgia and South Carolina, is 5 milligrams per liter. But readings taken last summer show levels as low as 1.8 in an Aug. 20, 1996 reading at Fury's Ferry Bridge.
More scrutiny has been focused on the Savannah River's oxygen problems in the past year for two reasons.
Georgia is experimenting with stocking trout, which require cold, oxygenated water, into the Savannah River rapids. Scientists have expressed doubts the program will succeed due to warm, deoxygenated water in the river.
Also, tests last year of Russell Dam's reversible hydropower turbines have been shown to impact water quality through Thurmond Lake and into the Savannah River below, where water temperatures were elevated slightly last year.
According to the Army Corps of Engineers, a six-month turbine test last year increased Thurmond Lake's temperature 7 degrees. That increase caused releases from Thurmond Dam into the Savannah River to increase 3 to 4 degrees.