The Marcellus Shale Energy and Environment Laboratory (MSEEL) is a long-term field site and laboratory at the Northeast Natural Energy LLC (NNE) production facility, adjacent to the Monongahela River, located in western Monongalia County, West Virginia, USA. NNE began drilling two horizontal production wells, MIP (Morgantown Industrial Park) -5H and MIP-3H, in the Marcellus Shale in 2014. The wells were completed in December 2015. Large volumes of wastewater are generated with natural gas production. These wastewaters contain organic and inorganic chemical constituents from fracturing fluids used during drilling and stimulation of gas in host rocks/shale, as well as chemical compounds that are derived from formation water and the solid shale. Many of the organic and inorganic substances in the wastewater are potentially toxic and could pose an environmental risk if released due to spills, leaks, or unsafe disposal practices. An on-site storage tank and a separator tank (MIP-5H), both containing produced wastewater, were sampled from 2015 through 2019. The storage tank received wastewater from multiple wells (not just MIP-5H). The data associated with the chemical conditions of these two tanks, at the time of sampling, have been previously published in a companion data release (https://doi.org/10.5066/P9Q3Y16S). The current data release reports on a sub-set of produced water samples co-collected from the above-mentioned storage and separator tanks during the 2016-2019 period, which were reserved for explicit experiments and analyses associated with detailed geochemical characterization of both the solid phase and dissolved fractions. The eleven machine readable data files (*.csv format) provided herein, and the description of the data contained in each, are described in the Entity and Attribute section (xml tag 'eainfo') of this metadata file.