DOE is using remote sensors suspended from helicopters to map the flow of groundwater that may be affected by energy projects.
In four states this past spring and summer, eyes have turned skyward as helicopters zig-zagged over hills and valleys, towing torpedo- or spiderweb-like contraptions that conjured up thoughts of Superman - "Look! Up in the sky!"
But the "x-ray vision" in this case isn't comic-book fantasy. Instead, using aerial remote sensing techniques, researchers working with the U.S. Department of Energy are "seeing" through solid ground to create three-dimensional images of the flow of groundwater as deep as 1,000 feet below the earth's surface.
The projects in the skies over Virginia, West Virginia, Wyoming, and Montana are part of the Office of Fossil Energy's effort to increase the nation's energy supplies while protecting and improving the environment. Groundwater is the primary focus of the current flyovers.
"We simply cannot produce and use energy without impacting water resources - underground aquifers, individual streams and rivers, and, sometimes, entire watersheds," said Mike Smith, the Energy Department's Assistant Secretary for Fossil Energy. "But we can make sure that our impact is minimal and temporary. By mapping groundwater flow, we can guard against mining disasters, protect precious water resources, and clean up the environment."
"Projects such as this help us meet the goals of the President's National Energy Policy," said Smith. "It is vitally important to our Nation's energy security that we increase domestic energy production, but, as the National Energy Policy states, we must show consideration for the air and natural lands and watersheds of our country."
The remote sensors can look like an airborne torpedo or a spider web, depending upon the type of technology employed.
To map the flow of groundwater, a helicopter flies a prepared grid pattern at about 200 feet above the ground, following the contours of the earth. Dangling about 100 feet beneath the belly of the helicopter is one of two types of remote sensors, both of which operate somewhat like sonar or radar, sending out signals and receiving back a sort of echo.
The "frequency-domain sensor" looks something like a torpedo or a super-sized sausage and sends out six different frequencies of electromagnetic waves. The "time-domain sensor," which looks like a giant spider web, uses a single, lower-frequency signal that penetrates deeper into the ground.
Since different substances echo differently, researchers are able to distinguish between solids and liquids, rocks and water. The technology also can roughly determine the quality of the water. More contaminated or salty water returns a stronger signal.
The aerial data are supplemented with more detailed, on-the-ground data collected with hand-held sensors. By analyzing the data using a geographic information system database, researchers can produce a three-dimensional image of groundwater flow called a conductivity depth image.
"Remote sensing isn't new, but the way we're using it is," says Terry Ackman, a researcher at the National Energy Technology Laboratory (NETL), which conducts the research for the Department of Energy's Office of Fossil Energy. "This technology was originally developed as a mining exploration tool, to help locate valuable minerals. We're applying it in a novel way, to improve and protect the environment, and to protect lives and property."
The flyovers focus on four specific areas related to coal mining and drilling for natural gas:
- Mine impoundments - massive ponds of water and fine particles of coal generated by coal preparation. Though rare, improperly constructed impoundments have failed belowground, flooding into active mines; and, they have burst their dams aboveground sending water sweeping through mountain valleys, sometimes causing widespread devastation and loss of life.
- Underground mine pools - large bodies of underground water caused by flooding of abandoned mines. Many of these mines were created up to a century or more ago and are either unmapped or incorrectly mapped, creating a safety hazard for active mines nearby. The Quecreek mine accident in 2002, which trapped nine Pennsylvania coal miners underground for 77 hours before their rescue, occurred when miners relying on an old, inaccurate map mined through a wall and hit an underground mine pool.
- Acid mine drainage - acidic waters caused by the disturbance of sulfide-bearing rocks during mining. Acid mine drainage has the approximate acidity of lemon juice or household vinegar. When acid mine drainage seeps from abandoned mines, it can damage watercourses by making them more acidic and coating stream bottoms with slimy iron- and aluminum hydroxides. Streams affected by acid mine drainage are typically rust-colored and support few aquatic plants and animals.
- Produced water - water of variable quality pumped to the surface from underground aquifers when extracting natural gas from coal seams. The water is pumped from the coal to reduce the pressure that holds the natural gas in place, and is usually discharged at the surface where it evaporates or flows into local watersheds. It can also be re-injected into aquifers, used for irrigation, or held in specially created reservoirs.
Mapping Mine Impoundments in West Virginia
Flyovers now underway in West Virginia are focusing on mine impoundments. NETL is working with the federal Mine Safety and Health Administration and the National Technology Transfer Center at Wheeling Jesuit University to map 13 mine impoundments in seven southern counties.
One of the seven, Logan County, was the site of the worst mine impoundment failure in U.S. history when the dam of a coal slurry pond burst on a rainy Saturday morning in February 1972. One hundred twenty-five people died, 1,100 were injured, and more than 4,000 were left homeless when 132 million gallons of coal-blackened water went coursing through the narrow Buffalo Creek hollow.
Mine impoundments are safer today, and no coal-waste impoundment dams have failed since new regulations were enacted following the Buffalo Creek disaster, but impoundments have burst into adjacent mines belowground. In Martin County, Kentucky, an impoundment containing more than 300 million gallons of water burst into an adjacent mine in October 2000. Thick, black sludge erupted through the mine portals and flowed into tributaries of the Big Sandy River, visibly contaminating waterways as far downstream as the Ohio River. No one was injured, but it was close; a mine examiner had exited the underground mine just fifteen minutes before the breakthrough.
Hundreds of large impoundments throughout the Appalachian coalfields need to be characterized and evaluated for long-term stability. "The overarching goal of the West Virginia flyovers is to provide a tool for evaluating the integrity of existing mine impoundments," says NETL's Ackman. "Ultimately, we hope this will protect property and save lives."
Helping Virginia Map Abandoned Underground Mines
Flyovers this past May surveyed four areas in Wise County, Virginia. A collaborative effort between NETL, the State of Virginia's Department of Mines, Minerals and Energy (DMME), and the federal Office of Surface Mining and Reclamation, the flyovers demonstrated how time-domain electromagnetic technology could address the specific needs of the region.
"Virginia has been working proactively for more than a decade to build an automated mapping database to help protect its coal miners, coalfield citizens, and the environment from the hazards posed by old, abandoned, and often-unmapped underground coal mine workings," said DMME Director Gene Dishner. "The use of state-of-the art airborne and ground-based geophysical technologies and automated mapping technology in this state/federal partnership promises to significantly expand and enhance the database and improve our ability to predict and prevent problems like last year's Quecreek mine inundation in Pennsylvania."
The Virginia flyovers were the first time that time-domain electromagnetic technology was used to map groundwater flow. Researchers hope to obtain a groundwater map down to 1,000 feet below the surface when the data is analyzed. This would be more than three times deeper than is possible using frequency-domain sensing.
Tracking Produced Water from Powder River Basin Coal Seams
In mid-June, NETL sponsored the first of two flyovers to survey about 50 square miles in the Powder River Basin area of Wyoming and Montana. This region is seeing a boom in mining for coalbed methane, the natural gas contained in coal seams. Farmers, conservationists, mining companies, and state and local governments are all concerned with the fate of the water extracted when the methane is produced.
"Ideally, the water would find beneficial uses - for irrigation, as drinking water for cattle, or, when its quality is good enough, to refill underground aquifers," says NETL's Ackman. "At the very least, we want to know where the produced water is going, and make sure it doesn't harm the environment."
Ackman says that the groundwater map generated this year will be compared to one obtained in a second flyover over the same region next year. This will help determine where the produced water flows back into the earth, and the impact it has on groundwater, streams, and irrigation systems.
"This information will be made available to the public and regulators who can use it to develop a balanced approach to coalbed methane extraction," says Ackman.
A 'Toolbox' Approach
"We use a toolbox approach, deploying different sensing devices depending on what we're looking for," continues Ackman. "Electromagnetic sensing is our 'workhorse' - we use it in almost every flyover - but we can also supplement it with other kinds of remote sensing, such as thermal infrared, which detects groundwater seeping out of the ground, and magnetometry, which gives us information about underground faults and other geologic features. We've had tremendous success so far, and the technology - specifically, the way we analyze and interpret data - continues to evolve and advance."
One of these successes came at Kettle Creek, in Clinton County, Pennsylvania, in 2002. The Kettle Creek watershed is riddled with underground coal mines dating back to the 1800s. Polluted water seeps from the abandoned mines into Kettle Creek, which then flows to the Susquehanna River.
Using multifrequency electromagnetic sensing and thermal infrared imaging, researchers mapped the groundwater in the watershed and located 53 seeps where polluted water flowed into Kettle Creek. This more than doubled the known number of seeps in the area, and provides a powerful tool for local watershed associations and State and Federal agencies to use in cleaning up the creek.
NETL's watershed science and technology program is part of the Office of Fossil Energy's coal research, development, and demonstration program, which works to ensure that coal is sustained as a clean and affordable source of energy. More information is available at the NETL website: http://www.netl.doe.gov/technologies/coalpower/ewr/water/index.html.