In 2015-16, the U.S. Geological Survey (USGS), in cooperation with the Muskingum Watershed Conservancy District, conducted a study to assess baseline (2015-16) surface-water quality in six lake basins within the Muskingum River watershed that are in the early years of shale-gas development. Six samples were collected at each of 30 sites to characterize surface-water chemistry over a range of hydrologic conditions. Quality-control (QC) samples collected before and during sampling included blanks and replicates. Blank samples were used to check for contamination during sample collection, processing, equipment cleaning, and/or analysis. Replicate samples were used to determine the reproducibility/variability in the collection and analysis of environmental samples. All QC samples were collected and processed according to protocols described in the USGS National Field Manual for the Collection of Water-Quality Data (U.S. Geological Survey, variously dated). Major ion, nutrient, organic, volatile organic compound (VOC), and radiological results of quality-control analyses for 12 equipment blanks, 22 field blanks, and 19 replicate samples from Muskingum River Watershed, Ohio, 2015-2016. This data set includes one table of Non-Volatile Organic Compounds equipment blank samples, one table of Non-Volatile Organic Compounds field blank samples, one table of Non-Volatile Organic Compounds field replicate samples, one table of Volatile Organic Compounds equipment blank samples, one table of Volatile Organic Compounds field blank samples, and one table of Volatile Organic Compounds field replicate samples. U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chaps. A1-A10, available online at http://pubs.water.usgs.gov/twri9A.