The U.S. Geological Survey provided technical support to the Agency for Toxic Substances and Disease Registry for site selection and sample collection and analysis in a 2012 investigation of groundwater quality from 29 private domestic water-supply wells in the vicinity of petroleum production in southwestern Indiana. Petroleum hydrocarbons, oil and grease, aromatic volatile organic compounds, methane concentrations greater than 8,800 micrograms per liter, chloride concentrations greater than 250 milligrams per liter, and gross alpha radioactivity greater than 15 picocuries per liter were reported in the analysis of groundwater samples from 11 wells.