The USGS published a study that investigates the occurrence of methane and benzene in drinking water near unconventional oil and gas sites in the Eagle Ford, Fayetteville, and Haynesville shale formations in Texas, Arakansas and Louisana. Using groundwater-age tracers scientists determined that methane isotopes and hydrocarbon gas compositions indicate most of the methane in the wells was biogenic and not from thermogenic shale gas. The rate of the tracer movement indicates that this study may not be conclusive for decades, or longer.