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

The water that feed springs of Hot Springs National Park are meteoric in origin. precipitation enters the highly fractured Bigfork Chert and Arkansas Novaculite in the anticlinal valley west, north, and northeast of the discharge area for the hot springs. The hot water component travels down with a geothermal gradient warming the water until the flow path reaches the conduits formed from faults and fractures in the shales belonging to the Polk Creek and Missouri Mountain Shale. After reaching the main thrust faults the hot waters resurface through the Hot Springs Sandstone while the cold water component mixes near the springs’ discharge area due to the widespread distribution of fractures. Bedinger et al calculated the mean residence time of the spring discharge using carbon-14 isotopes. The 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 about 4,400 years old. However, this result is flawed due to Bedinger et al using general isotopic values for soil dissolved inorganic 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 is running along its flowpath. As precipitation falls from the atmosphere it collects atmospheric carbon from carbon dioxide, organic carbon from plants and inorganic carbon from soil as it enters the soil and mineral carbon as it enters through the bedrock. A more accurate age calculation of the springs can be performed by using the USGS software 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 was previously calculated by Bedinger with an age determination of 3,638 years.