At 2:45 p.m., Nicholas McClung’s cellphone chirps during a business meeting. He doesn’t bother to look at it; the special chirp says it all. He politely excuses himself from the meeting and rushes to the Tennessee Valley Authority’s (TVA’s) Advanced Technology for Impoundment Monitoring (ATIM) center in the basement of the company’s Chattanooga headquarters.
When he arrives at the ATIM center, McClung, TVA’s risk and quality assurance manager and a licensed geotechnical engineer, looks at the LED-monitor-filled wall (Figure 1) and sees that the situation is serious. The screens indicate that the Tennessee Valley has received over 10 inches of rain in a short period of time—200% more than the region normally receives in a month. His team has been studying the ash pond data for a week. Now it’s time to take action before an even more serious problem arises.
Coal Ash Mission Control
While this event was just a drill, McClung said that the TVA takes coal ash safety very seriously. It spent about $2 million developing the ATIM center to help identify and respond to any coal ash issues before they become emergencies.
The TVA’s ATIM center is the only facility of its kind in the U.S. utility industry. The center’s massive screen-packed wall can display geographic information system maps, weather details, earthquake information, sensor data, and even live video. The ATIM center provides McClung and his team a place to collaborate and share real-time information with all of TVA’s decision-makers.
“Think of the ATIM center as TVA’s ‘coal ash mission control,’” McClung said. “With a few clicks we can pull up sensor data and see real-time data or watch what’s happening at our impoundments via live video. What’s most important is that we can share information with everyone who is working on the problem.”
The federal government mandates safe coal ash storage. The TVA’s ash impoundments are classified as dams and must adhere to the TVA’s Dam Safety Governance safety program procedures (TVA-SPP-27 series).
To ensure it meets these strict federal standards, the TVA installed more than 7,000 real-time sensors to monitor ash impoundments. Every hour of every day, sensors send data to a centralized computer monitoring system.
“My team receives texts and emails if there is any irregularity,” said McClung. “If it is serious, we can immediately activate the ATIM center.”
To date, the TVA’s ATIM center has never been activated in response to a real event. If the day comes for the ATIM to truly come to life, the TVA team thinks they are prepared and they expect to receive the highest level of support.
“Having the ATIM process in place demonstrates how serious the TVA is about safe coal ash storage,” said McClung. “The ATIM center will provide our executives a single, complete source of information. We can quickly get the support we need to ensure public and environmental safety.”
A New Way to Store Coal Ash
The TVA is in the process of implementing improvements at each of its coal ash impoundments to reduce the risk of structural instability and surface and groundwater contamination. The company is closing its wet ash impoundments over the next four to six years in favor of dry ash storage. In addition, the TVA has pioneered intelligent compaction technology for dry ash storage.
“Think of dry ash storage as a parking lot,” said Jason Hill, TVA’s program manager for Risk and Quality Assurance at the Kingston Fossil Plant intelligent compaction project. “We wet the ash and mix it to the consistency of cookie dough. Then we lay ash down like pavement and compact it to a density of 95% or greater.”
As ash is laid down, heavy rolling machines drive over it to compact it (Figure 2), much like you would see on a road-paving project. The compacting machine is equipped with a vibrating drum and sensors that send real-time data directly to the operator and to TVA’s engineers (Figure 3).
2. Good vibrations. Coal ash is laid down and heavy rolling machines drive over it to compact it. Courtesy: Tennessee Valley Authority
3. Building a pyramid of ash, one layer at a time. Compaction is mapped in real time. Engineers analyze the data to ensure the compaction meets specifications. Courtesy: Tennessee Valley Authority
Hill noted that the array of sensors outfitted to the compacting machine is the game changer. “We see what the driver is doing in real-time,” said Hill. “If an area needs more compaction, I can immediately send the driver back over the area—it’s state-of-the-art.”
Traditionally, Hill and other TVA engineers would have had to be at the site to observe and test the material. Now Hill can monitor the ash and the compaction rates from his office in Chattanooga—more than 100 miles from the Kingston facility.
While compaction technology has long been used in road construction, the TVA claims to be the first utility in the U.S. to apply it to coal ash. However, deploying compaction technology isn’t cheap; it costs about a million dollars to outfit each facility. The system surpasses state and federal requirements, but the TVA believes the rewards in safety and long-term cost savings outweigh the startup costs.
“The 3-D technology far exceeds state and federal monitoring standards because we can monitor 100% of the ash stack for the life of the project,” Hill said.
It will take 40 years to complete the Kingston ash stack. During that time, the TVA will create a 3-D compaction map of each layer, which engineers will be able to analyze for years to come. The technology is also being applied at other TVA storage sites across the Valley. Bull Run Fossil Plant, located near Knoxville, is already using the equipment.
—Scott Fiedler is a public information specialist for the TVA.