The purpose of this report is to describe the results of an investigation that was initiated in 2007 to characterize the water chemistry and groundwater flow-paths of the Madison aquifer in the vicinity of the park. Water chemistry data sampled from various locations in an aquifer provide information about the movement of water from recharge areas where water first percolates into the aquifer to discharge areas where water discharges through springs or by wells drilled into the aquifer. The report includes a description of major ion chemistry, stable isotope chemistry, age of groundwater, and a discussion of both regional and local flow-paths.