The Captain Jack Superfund site near Ward, Colorado hosts extensive interconnected underground mine workings, which drain via the Big Five Adit. Drainage from the adit has historically been acidic with elevated concentrations of metals. In 2018 the U.S. Environmental Protection Agency (EPA) utilized a subsurface remediation strategy consisting of the installation of a hydraulic bulkhead within the workings to preclude drainage out of the mine. To understand the processes occurring during water impoundment within the mine workings, the U.S. Geological Survey (USGS), in cooperation with EPA, completed water-quality sampling and analysis during 2020 as water was again impounded within the mine workings. The USGS sampling and analysis resulted in a diverse dataset including major and trace elements, rare earth elements (REE), stable isotopes, radiogenic isotopes, and environmental tracers. This diverse dataset aids in providing a complete hydrologic and geochemical conceptualization of the processes occurring in the mine workings and adjacent groundwater, and serves as an example of applications to other sites. This data release contains data pertaining to groundwater-level elevations and water-quality data furnished to USGS by EPA and collected by USGS. Also included are geochemical model input files to simulate aqueous speciation, mineral equilibrium, and groundwater age and mixing as well as output files. Data are provided in child item "Hydrologic and geochemical data" and model input and output files are provided in child item "Geochemical and environmental tracer models".