Dissolved Oxygen Report Shows Continued Improvement at Alcoa Power Generating’s Yadkin Project

Water Leaving Yadkin Project Meets State Instantaneous Dissolved Oxygen Standard 99.9 Percent of the Time

Water leaving Alcoa Power Generating’s (APGI) Yadkin Project met a state standard for dissolved oxygen levels 99.9 percent of the time in 2010, according to a report submitted last week by APGI to the North Carolina Division of Water Quality (DWQ).

APGI’s Yadkin Project operates four dams along the Yadkin River. Water enters the project area at High Rock Dam, then flows through Tuckertown Dam, to Narrows Dam and exits the project at Falls Dam. The report demonstrates that water coming into the project at High Rock has relatively low levels of dissolved oxygen (DO). But there is a substantial improvement in DO at the Narrows Dam, where APGI installed new technology in 2008 and 2009 to enhance DO levels, and that improvement is maintained until the water exits the Yadkin Project at Falls dam.

The report on dissolved oxygen levels in the Yadkin Project tailwaters shows that discharges from the Falls Dam met the state instantaneous dissolved oxygen standard 99.9 percent of the time and daily average dissolved oxygen standard 97.4 percent of the time. Water coming into the project at High Rock, where a $40 million project to install DO enhancement technology awaits approval of APGI’s operating license by the Federal Energy Regulatory Commission (FERC), met the state instantaneous dissolved oxygen standard 65.1 percent of the time and daily average dissolved oxygen standard 43.1 percent of the time.

“This report shows continued improvement of dissolved oxygen levels in water below the Narrows Dam and demonstrates that new technology installed at Narrows is successfully increasing dissolved oxygen levels in downstream waters. This is true under the full range of unit operation, including ramp up, ramp down and other periods of relatively low operation,” said Kevin Anton, Chief Sustainability Officer for Alcoa. “These results provide reassurance that additional technology enhancements at Narrows and High Rock planned under a new federal license will further increase dissolved oxygen levels as part of our commitment to meet state DO standards.”

An adequate amount of oxygen in the water is necessary to support healthy aquatic life, and many states monitor DO levels as one way to help measure water quality in lakes and rivers.

Under state standards applicable to the Yadkin Project under a new federal license, DO concentrations must meet or exceed 4.0 mg/L when measured instantaneously, and DO concentrations must meet or exceed 5.0 mg/L when measured on a daily average basis.

APGI has developed a comprehensive plan for improving DO levels throughout the Yadkin Project that will cost up to $80 million, depending upon the final requirements. As part of its plan, APGI has been monitoring DO levels since 2007.

The DO report submitted to the Division of Water Quality summarizes the levels of dissolved oxygen measured in the Yadkin Project tailwaters since 2007. Data is recorded every 15 minutes, 7 days a week in the tailwaters of each dam between May 1 and November 30. The measurements are taken during this time period, when DO levels are typically at their lowest, at the state’s request.  Tailwaters are those waters immediately below the dams where dissolved oxygen levels would be influenced by water released through the dams. DO monitors are located in well-mixed areas that are representative of temperature and dissolved oxygen conditions throughout the tailwaters.  Normandeau Associates, a national firm specializing in environmental management and consulting, is responsible for quality assurance/quality control, calibration, maintenance and collection of data from the DO monitors. 

The report shows significant improvements since DO technology was installed at Narrows:

• For the third consecutive year, Falls tailwaters substantially met the state instantaneous DO standard: 99.9 percent in 2010, 99.7 percent in 2009, and 99.5 percent in 2008.

• Narrows tailwaters met the state instantaneous DO standard 93.4 percent of the time in 2010 — a 34 percent increase over 2007 levels (69.6 percent). Since 2007, APGI installed two draft tube air valves on Narrows Units 1 and 2 to improve DO levels. The same technology was installed on Unit 4 in 2001 and will be installed on Unit 3 once a new FERC license is issued.

• Dissolved oxygen levels are enhanced at Narrows even when generating units are operating as low as one megawatt, due to aeration from vacuum breaker valves. The vacuum breaker air valves open when the units are operating at lower settings and introduce air into the water.

• The High Rock and Tuckertown tailwaters met the state DO standard less frequently in 2010. High Rock met the state instantaneous DO standard 65.1 percent of the time, and Tuckertown met the state instantaneous DO standard 56.3 percent of the time.  This could be due annual variability in hydrologic and meteorological conditions or changes in the quality of the water entering High Rock.

The Yadkin Project’s Relicensing Settlement Agreement (RSA) outlines a schedule for installing “through-the-blade" aerating turbines for all three generating units at High Rock once a new FERC license is issued. The engineering, planning, and model testing of the new turbines has been completed and long lead-time items have been ordered. APGI has committed to install additional DO enhancement technology at Tuckertown and Falls if necessary to meet state DO standards.

“We have made great progress and have every reason to believe the technology enhancements will continue to increase dissolved oxygen levels and allow the Yadkin Project to meet the state DO standard,” Anton said. “Our commitment to reaching that goal has never been in question.”

Click here to read the full report.