Knowledge Bank

Technological advances in drilling have recently made it economically feasible to obtain natural gas through horizontal drilling and hydraulic fracturing well completion methods, known as “fracking”. These technologies involve directional drilling in a deep shale formation and the injection of high-pressured fluids to fracture the rock to release natural gas. Fluids used in hydraulic fracturing contain a mixture of water and about a dozen chemical additives containing many different organic constituents that enhance the fracturing process. One environmental concern is the possible contamination of shallow groundwater aquifers that might result from a short-circuit during the hydraulic fracturing process (e.g. borehole leakage, valve blowout, or surface release). The ultimate fate of these fluids and the volatile organic compounds (VOCs) in these fluids are of particular concern because of their possible health risks. In order to understand the natural attenuation of hydraulic fracturing fluids, we studied the aerobic degradation of organic constituents in sediment microcosm treatments over a period of 25 days. Microcosms contained a synthetic fracturing fluid representative of recipes being used in our region that was mixed with shallow sediments and groundwater. Bottles were maintained under oxygen-saturated conditions to simulate a shallow subsurface environment. Concentrations of dissolved organic carbon (DOC) decreased 68% ¬+0.22 over approximately a one-month period suggesting significant overall degradation of organic chemicals in these fluids. Samples from three time points (day 0, 7, and 25) were further analyzed for a suite of VOCs using EPA method 624. We detected 22 of 75 tested compounds, with the highest concentration constituents degrading at similar rates to that of the system DOC. These results provide us with preliminary insight as to how these fluids will attenuate if released to shallow environments and will provide us with a framework for future attenuation studies testing other subsurface environmental factors such as salinity, redox, and pressure gradients.