On July 26, 2017, a solution containing approximately 200 kilograms of dissolved sodium bromide was added to the the flooded underground shaft of the Minnesota Mine, near Empire, Colorado. This addition was conducted as part of an effort to determine the degree to which the mine shaft is hydrologically connected to a series of downgradient seeps and springs. These seeps and springs discharge from the hillside and enter Lion Creek, an acidic, metal-rich stream that lies immediately to the west of the Minnesota Mine. A water quality sonde and pressure transducer deployed within the shaft recorded temperature, specific conductance, and stage before, during, and after the addition. The downgradient seeps and springs were also monitored during this time to check for increases in bromide concentration that result from the shaft addition. Monitoring consisted of logged data from bromide specific electrodes, and discrete samples collected from the seeps and springs. This data release consists of 5 tables: Table 1, Locations of the Minnesota Mine shaft and the monitored seeps and springs Table 2, Bromide concentration data from the seeps and springs Table 3, logged data from the bromide specific electrode Table 4, Temperature and specific conductance of the shaft water Table 5, Water level (stage) within the mine shaft