Water quality at the Yadkin Project has improved dramatically since Alcoa Power Generating (APGI) invested more than $5 million in turbine upgrades and other enhancements specifically designed to increase the amount of oxygen in the water.
An APGI report delivered to the NC Division of Water Quality (DWQ) last week shows water discharged from the Narrows Dam contains the highest concentration of dissolved oxygen — a key indicator of water quality — since APGI began monitoring water quality in 2007. The data demonstrates that the Yadkin Project’s water quality is consistently improving, as measured by state standards for dissolved oxygen that will take effect when the hydro project receives a new federal license.
APGI has now completed upgrades at three turbines at Narrows Dam. Water discharged from the dam would have met the new state standard 100 percent of the time in 2011 — a 115 percent improvement since the majority of the new technology at Narrows was installed in 2007.
"These results clearly demonstrate that the Yadkin Project deserves the state water quality certificate it was issued in 2009. We were confident that this technology would significantly improve dissolved oxygen conditions and this data confirms that it has been extremely effective,” said Ray Barham, APGI’s Yadkin Relicensing Manager. “Once we complete the additional upgrades we have planned, the Yadkin Project will fully comply with state water quality standards."
APGI has committed to invest up to $80 million more to continue improving water quality at the Yadkin Project, beginning with a $40 million investment at High Rock Lake. APGI will install three “through-the-blade” aerating turbines at High Rock once the Federal Energy Regulatory Commission (FERC) issues a new license. The engineering, planning, and model testing of the new turbines has already been completed.
Alcoa’s water quality performance is already the best among hydro operators on the Yadkin River. Progress Energy, which operates two dams immediately downstream of the Yadkin Project, achieves state standards for dissolved oxygen less frequently. The NC Division of Water Quality issued Progress Energy a 401 Water Quality Certificate for its hydro project on September 12, 2008.
Dissolved Oxygen Levels Improve As Water Flows Through the Yadkin Project
Water enters the Yadkin Project at High Rock Lake with low concentrations of dissolved oxygen. After traveling 38 miles down the Yadkin River and passing through four dams operated by APGI, the water quality improves significantly before it is discharged at the Falls Dam.
In 2011, water discharged from High Rock Dam met the state standard for dissolved oxygen (measured on a daily average) just 41.7 percent of the time. It met those same standards 100 percent when discharged from Narrows Dam and 97.1 percent of the time when discharged from Falls Dam.
An adequate amount of oxygen in the water is necessary to support healthy aquatic life. Many states monitor dissolved oxygen levels as one way to help measure water quality in lakes and rivers.
Notable findings from the 2011 DO Report include:
- Falls Tailwaters Consistently Meet State Standard Over 99 percent of the Time: For the fourth consecutive year, Falls tailwaters substantially met the state instantaneous standard for dissolved oxygen: 99.8 percent in 2011, 99.9 percent in 2010, 99.7 percent in 2009 and 99.5 percent in 2008. Falls met the daily average standard 97.1% of the time. These results demonstrate that the enhancements at the Narrows Dam are improving dissolved oxygen concentrations downstream.
- Narrows Tailwaters Shows Remarkable Improvement: Narrows tailwaters met the state daily average standard for dissolved oxygen 100 percent of the time (a 115 percent improvement over 2007) and met the instantaneous standard 99.9 percent of the time (a 43.5 percent improvement compared to 2007). Since 2007, APGI has installed two draft air tubes on Narrows Units 1 and 2 to improve dissolved oxygen levels. Similar technology will be installed on Narrows Unit 3 once a new federal hydropower license is issued, in accordance with the Yadkin Project’s water quality certification.
- Technology Performs Well at Low Levels of Operation: The 2011 report found that dissolved oxygen levels are enhanced at Narrows even when generating units are operating as low as one megawatt or “spinning” (turning but not generating power), due to aeration from vacuum breaker valves. These valves open when the units are operating at lower settings and introduce air into the water.
Why is Dissolved Oxygen Important?
- An adequate amount of oxygen in the water is necessary to support healthy aquatic life, and many states monitor dissolved oxygen levels as one way to help measure water quality in lakes and rivers. APGI has been monitoring dissolved oxygen levels in the tailwaters of the Yadkin Project since 2007.
- Dissolved oxygen levels are measured in two ways: instantaneously and on a daily average basis. Under state standards applicable to the Yadkin Project under a new federal license, dissolved oxygen concentrations must meet or exceed 4.0 mg/L when measured instantaneously, and dissolved oxygen concentrations must meet or exceed 5.0 mg/L when measured on a daily average basis.
- These standards do not apply to the Yadkin Project until a new federal license is issued.
How Is Dissolved Oxygen Measured?
- The 2011 DO Report summarizes the levels of dissolved oxygen measured in the Yadkin Project tailwaters since 2007. Tailwaters are those waters immediately below the dams where dissolved oxygen levels would be influenced by water released through the dams.
- Data is recorded every 15 minutes, 7 days a week in the tailwaters of each dam between May 1 and November 30. Measurements are taken during this time period, when dissolved oxygen levels are typically at their lowest, at the state’s request. Monitors are located in well-mixed areas that are representative of temperature and dissolved oxygen conditions throughout the tailwaters.
- The 2011 DO Report was prepared with the assistance of Normandeau Associates, a national firm specializing in environmental management and consulting.
How Does Dissolved Oxygen Impact the Yadkin Project Relicensing?
- APGI must receive a Section 401 water quality certification from the state as part of its relicensing effort for the Yadkin Project.