This dataset contains quality-assurance and quality-control data (QA/QC) not publicly available in the online National Water Information System (NWIS) for the Pennsylvania Groundwater Monitoring Network collected by the U.S. Geological Survey (USGS) in Pennsylvania, 2015-2019. The quality-control data (such as blanks and replicates) were collected at a subset of sites to ensure that the data meets specific data-quality objectives of this program. Also included in this data release are the supplemental tables for the accompanying USGS publication “Characterization of Ambient Groundwater Quality within a State-wide, Fixed Station Monitoring Network in Pennsylvania, 2015-2019.” The supplemental tables consist of: 1) a correlation matrix using results from principal components analysis (PCA) and 2) individual contributions of each sample to the PCA results are also included.