CALCULATING THE AGE OF THE WATER IN HOT SPRINGS NATIONAL PARK, AR BY USE OF CARBON-14 ISOTOPES

Mean water age for spring discharge in Hot Springs National Park was calculated as approximately 4,400 years by Bedinger et al (1978) using carbon-14. Their analysis indicated that the water was a mixture of a small portion of cold water that was less than twenty years old with a preponderance of hot water. However, this result includes some error due to Bedinger et al using general isotopic values for soil dissolved in-organic carbon and mineral carbon instead of obtaining actual values from the study area. Additionally, the study did not account for the potential loss of carbon that can occur as water travels along its flowpath. As precipitation falls from the atmosphere it collects atmospheric carbon dioxide, soil-gas carbon dioxide from plant decay, and inorganic carbon from soil and bedrock during infiltration and recharge. A more accurate age calculation for the springs has been made possible by additional geological and geochemical data collected (Bell and Hays 2007; Kresse and Hays, 2010). An improved age model will be developed using the USGS soft-ware NetpathXL; this program models the isotopic compositions and net geochemical mass-balance reactions along the flowpath. NetpathXL is capable of calculating every possible combination of mass transfers. Rayleigh distillation calculations can also be applied to each model to predict carbon and radiocarbon dates at the end path. Initial testing of the NetpathXL software has yielded younger ages than were previously calculated by Bedinger.