EVALUATING CONTAMINATION POTENTIAL OF SURFACE SPILLS ASSOCIATED WITH UNCONVENTIONAL OIL AND GAS DEVELOPMENT ABOVE AN ALLUVIAL AQUIFER

Surface spills are recognized as the most likely pathway for groundwater contamination during oil and gas production operations. Contaminant fate and transport simulations were conducted with three objectives: 1) evaluate whether or not spills of aqueous fluids pose risks to groundwater quality in the South Platte aquifer system, (2) identify the key hydrologic and transport factors that determine these risks, (3) develop a screening level methodology that could be applied at other sites and for various pollutants. This screening level assessment considered a range of representative hydrologic conditions and transport behavior for benzene, a strictly regulated pollutant in production fluids. Realistic spill volumes and areas were determined using publicly available databases. Risk of groundwater pollution was based on predicted concentration of benzene at the groundwater table. Results of the study suggest that the risk of groundwater contamination from benzene in a produced water spill was relatively low in the South Platte aquifer. Spill size was the dominant factor influencing whether a contaminant reached the water table. Only statistically larger spills (spill volume per area ≥12.0 cm) posed a clear risk. Storm events following a spill were generally required to transport more typical (median)-sized spills (0.38 cm spill volume per area) to the water table; typical spills only posed risk to shallow groundwater if a 500-year storm or if a 100-year storm (followed by little degradation or sorption) occurred right after the spill. This methodology could be applied to evaluate spills occurring over other aquifers.