This dataset contains the lithologic class and topographic position index information and quality-assurance and quality-control data not available in the online National Water Information System for 54 domestic wells sampled by the U.S. Geological Survey in Clinton County, Pennsylvania, May-September 2017. The topographic position index (TPI) for each well location was computed on the basis of a 25-meter digital elevation model (U.S. Geological Survey, 2009) using criteria reported by Llewellyn (2014) to indicate potential classes for topographic setting. The bedrock geologic unit and primary lithology were determined for each well location on the basis of the digital bedrock geologic map of Pennsylvania (Miles and Whitfield, 2001). The quality-assurance and quality-control data (such as blanks or replicates) were collected at a subset of sites to ensure that the data met specific data-quality objectives outlined for the study.