Hydrologic and Geochemical Data and Models Supporting Integrated Evaluation of the Captain Jack Superfund Site, Boulder County, Colorado

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 impounded within the mine workings. The USGS sampling and analysis resulted [...]