Quantifying Potential for Spills at Unconventional Gas Well Sites to Impact the South Platte Aquifer

With the rise in unconventional oil and gas development over the past decade, the public is concerned about how these stimulation, extraction, and production activities may impact groundwater resources. Although there are many possible ways for accidental leakage to occur and different fluids that could be released, the most probable contamination pathway is through surface spills of produced and hydraulic fracturing fluids. These fluids could potentially infiltrate through the vadose zone, reach the groundwater table, and be transported. The purpose of this study is to conduct fate and transport simulations of surface spills of chemical contaminants, such as biocides, friction reducers, surfactants, and hydrocarbons, typically found in hydraulic fracturing fluid and produced water. Accounting for degradation, sorption processes, co-contaminant interactions, and spill statistics, we seek to understand the hydrologic and site conditions under which a surface spill would pose risk to groundwater quality. This study focuses on the South Platte Alluvial Aquifer, which overlaps a zone of high-density oil and gas development in the greater Denver metro area. We propose a coupled analytical-numerical approach that could be reproduced by environmental consultants. Preliminary results suggest that risk of groundwater pollution, based on predicted concentration at the groundwater table, is low in most areas of the South Platte system for the contaminants investigated. However, substantial risk may exist in certain areas where the groundwater table is shallow. In addition, transport of certain contaminants is influenced by interactions with other constituents in produced or stimulation fluids. By helping to identify locations in the Front Range of Colorado that are at risk for groundwater contamination due to a surface spill, it is our hope that this work will aid in improving best management practices so that decision-makers can be better prepared to address accidental releases in Colorado.