- Copyright ©2011. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.
One method to beneficially use water produced from coalbed methane (CBM) extraction is subsurface drip irrigation (SDI) of croplands. In SDI systems, treated CBM water (injectate) is supplied to the soil at depth, with the purpose of preventing the buildup of detrimental salts near the surface. The technology is expanding within the Powder River Basin, but little research has been published on its environmental impacts. This article reports on initial results from tracking water and solutes from the injected CBM-produced waters at an SDI system in Johnson County, Wyoming.
In the first year of SDI operation, soil moisture significantly increased in the SDI areas, but well water levels increased only modestly, suggesting that most of the water added was stored in the vadose zone or lost to evapotranspiration. The injectate has lower concentrations of most inorganic constituents relative to ambient groundwater at the site but exhibits a high sodium adsorption ratio. Changes in groundwater chemistry during the same period of SDI operation were small; the increase in groundwater-specific conductance relative to pre-SDI conditions was observed in a single well. Conversely, groundwater samples collected beneath another SDI field showed decreased concentrations of several constituents since the SDI operation. Groundwater-specific conductance at the 12 other wells showed no significant changes. Major controls on and compositional variability of groundwater, surface water, and soil water chemistry are discussed in detail. Findings from this research provide an understanding of water and salt dynamics associated with SDI systems using CBM-produced water.
Mark A. Engle is a research geologist at the U.S. Geological Survey in Reston, Virginia. He currently serves as chief of the produced waters project for the U.S. Geological Survey Energy Resources Program. He holds a Ph.D. in hydrogeology from the University of Nevada, Reno. His research interests include aqueous geochemistry and geochemometrics.
Carleton R. Bern is a research soil scientist at the U.S. Geological Survey in Denver, Colorado. He received his Ph.D. in ecology and evolutionary biology from the University of Colorado. His research interests include soil isotopic geochemistry and geochemical modeling of soil processes.
Richard W. Healy is a research hydrologist at the U.S. Geological Survey in Lakewood, Colorado. His research interests include estimating groundwater recharge and flow and solute transport within the unsaturated zone. He received his B.S. and M.S. degrees in mathematics from the University of Illinois.
James I. Sams is a hydrologist and a geographic information system analyst for the Geosciences Division, National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, Pennsylvania. He received his master's degree in environmental science from the Pennsylvania State University. His research interests include near-surface geophysics and geospatial analysis.
John W. Zupancic is a founding partner of BeneTerra, LLC, and serves as chief technical officer. As a soil scientist with an interest in water and the environment, he has worked to find beneficial uses for wastewater throughout his career.
Karl T. Schroeder earned a B.S. degree in chemistry from the University of Dayton and a Ph.D. in organic chemistry from Duquesne University. He has been employed as a research chemist at the U.S. Department of Energy for 35 yr. His early work concentrated on direct coal liquefaction technology but has shifted to environmental problems associated with fossil fuel production and use.