The Pavillion Well Field, located east of Pavillion, Wyoming, consists of 181 oil and gas production wells, some in use since 1960. After domestic water well owners complained of a petroleum-like odor in wells and stray gas migration, the U.S. Environmental Protection Agency detected organic compounds in monitoring wells that closely matched compounds used for well stimulation. Dominic DiGiulio, Physical Science Research Associate in Stanford’s School of Earth, Energy & Environmental Sciences, and Woods Senior Fellow Robert Jackson (Environmental Earth System Science) did a comprehensive review of available information to evaluate impact to ground water from shallow (unlined pits used to dispose invert mud and production fluids), intermediate (invert or diesel-fuel based drilling mud remaining in boreholes), and “deep” (acid stimulation and hydraulic fracturing) contaminant source terms. DiGiulio will present results of the review.