By Yves Pollart, P.E., vice president of environmental engineering, RETTEW
AMD can be a valuable resource for the oil and gas industry and result in cleaning up thousands of streams and rivers in the nation.
Abandoned mine drainage (AMD) has long been a cause of concern in key geographies of the United States, namely, the Appalachian region of the Northeast and the Rocky Mountain region. In Pennsylvania alone, more than 300 million gallons of water are discharged from mines into the state’s waterways each day. More than 5,500 miles of rivers and streams are affected by the toxic leakage. Drainage from abandoned mine sites, often filled with high levels of metals, acidity, and sulfates, seeps or flows into nearby streams and rivers, killing all life in the water resources. While it takes significant time and effort to fix the widespread problem, local watershed groups and conservation organizations are making headway. In Pennsylvania, companies in the oil and gas industry can use such water in their operations and, with a recent change in regulatory guidance, can more effectively work with environmental groups to see this valuable resource brought back to life.
In the past, industrial uses of AMD were not prevalent, mainly because of unclear liability issues after industries are finished using the resource, spurring energy industry possible users to find water resources elsewhere. However, as oil and gas companies continue to bolster economies in the U.S. and are continually in need of water resources, the tide is turning for AMD usage.
In the oil and gas industry, hydraulically stimulated wells require millions of gallons of water to extract natural gas from deep within the earth. This water supply has typically come from rivers, streams, and public water supplies. In states such as Pennsylvania, which is rich in nonpolluted water, energy industry giants have not traditionally explored the use of AMD. However, the Pennsylvania Department of Environmental Protection (PA DEP) released a white paper last year outlining a process to review AMD-use proposals from oil and gas operators. The document explores storage options for such water and describes possible solutions to long-term liability challenges. Because of this recent change, oil and gas companies could begin to install treatment systems, with the joint effect of cleaning up waterways while also using the treated AMD to continue hydraulic stimulation operations. The Pennsylvania Senate Appropriation Committee has already approved a bill (SB 411) shielding oil and gas developers from liability when using coal mine drainage.
A passive abandoned-mine treatment system uses little to no electricity to pass contaminated water from AMD discharges or contaminated streams through nearby aeration devices and settlement ponds, adding limestone along the way to increase the pH balance and alkalinity of the water. Aeration devices use gravity through step aeration, fountain aeration, or trompe aerators. This step provides oxygen needed for oxidation reactions, which are used to remove iron and acidity. The system adds limestone to create chemical reactions needed to start precipitating the metals, mostly aluminum and iron. As the pH increases, another chemical reaction occurs, and the metals take on a solid form. As the water comes to rest in a settling pond, the metals will slowly move to the bottom where they will be removed in a few years.
The water is then routed back into the nearby stream, still containing other nutrients, but with a high enough pH balance to cease the poisoning of the streams from the toxic metals. Aquatic life then begins to return to the surrounding waterways.
Some treatment systems combine passive with an active component, such as using water power to constantly add lime to the water. In rare cases, an active treatment system is installed that mimics a traditional wastewater treatment plant; however, such systems are not often utilized because it is difficult to find ongoing funding to operate them.
Cost of a passive treatment system can range from about $300,000 to $1.5 million. Watersheds and local organizations often secure grant funding to install the systems, which then can operate for several years with very little maintenance other than adding chemicals on an as-needed basis. As more of these systems have come online in recent years, they are becoming more efficient and easier to operate. As the results and details are shared, treatment systems continue to become easier to install and maintain.
The Oil And Gas Industry
Because of the change in guidelines from the PA DEP, exploration and production companies are in the early stages of discussing options for using AMD in their operations in the Northeast.
One of the concerns oil and gas businesses have is sulfates in the water. Treatment systems described here generally aim to remove metals and acidity from AMD, rather than sulfates, because sulfates are necessary to spawn aquatic life in rejuvenated bodies of water.
But for oil and gas industry use, the sulfates remaining in traditionally treated mine water could pose a challenge. In the process of hydraulically stimulating a natural gas well, other metals are released from frissons hundreds of feet underground. One of those metals released in the Midwest is barium, which, if mixed with sulfate-rich water, combines to become barium sulfate. The result forms a thicker, sticky substance that can block the gas releasing from the underground fractures. This outcome is known as “scaling” and can reduce production of a well. Sulfates can be removed from AMD, though it requires a large-scale ecosystem involving wetlands and other components or a chemically heavy process.
However, in a peer-reviewed study recently released by researchers at Duke University, it was demonstrated that, when AMD was combined with wastewater from a hydraulically stimulated well, the chemicals in the drainage acted to neutralize radioactive material from the wastewater. The sulfates in AMD attached to radium and barium and created a solid, nonradioactive mineral known as strontium barite. With this knowledge, there could be a use for treated AMD in recycling wastewater from natural gas operations.
As more and more drills come online in the next few years in the Marcellus shale play, it’s likely that natural gas operators will continue to explore options for AMD use. Stipulations include that operators must follow all applicable environmental laws and regulations when treating, using, storing, and moving the water.
In regions of the U.S. lacking in pervasive water supplies, AMD can be an important consideration for the energy industry. For instance, drought-stricken Colorado has 30,000 abandoned mines and more than 1,300 miles of affected streams. Water rights in that state differ from those in the Northeast, so AMD could be a viable source of water for natural gas drilling, reducing the need to source water from an already scarce supply so desperately needed for agricultural uses.
Using AMD has the potential to change operations for oil and gas companies. Operators could potentially partner with local watershed organizations to finance and construct the required treatment system. In these instances, the local community would operate the system, and the results would improve the environment and provide a necessary resource for operators. It becomes a win-win situation for all stakeholders.
Other effects of AMD use in the oil and gas industry include reduced truck traffic from having treated water potentially closer to well sites, rather than driven in from further afield, and consequently decreasing air pollution. This will also reduce the reliance on other sources of water by making a waste product — the treated AMD — now reusable and environmentally friendly.
Oil and gas companies utilizing AMD could also reduce their overall capital cost of developing a well and pass those savings on to consumers in the form of decreased gas prices.
As the oil and gas industry delves into using this valuable resource for its operations, streams throughout the country will come back to life and once again be a habitat for wildlife. Communities will work hand in hand with oil and gas companies to achieve environmental goals, leading to strong relationships as the industry continues to grow.
Yves Pollart, P.E., is the vice president of environmental engineering at RETTEW and is responsible for managing the group’s studies, designs, and reviews of water treatment and storage facilities; abandoned mine drainage studies and remediation; and natural gas flowback treatment. He has more than 32 years of professional experience.