2 Hydrogeology of Thermal Springs

Monday, 31 March 2008
8:00 AM - 11:20 AM

INFLUENCE OF LOCALLY DERIVED RECHARGE ON THE WATER QUALITY AND TEMPERATURE OF SPRINGS IN HOT SPRINGS NATIONAL PARK, ARKANSAS

Paper number: 2-8
Program: THEME SESSIONS
Time: 10:20 AM – 10:40 AM

Authors

Abstract

The hot springs of Hot Springs National Park consist of a mixture of water from two recharge components. Abundant fractures present in the spring discharge area enable mixing of the predominant hot-water component with a local-recharge cold-water component. Urbanization in the area of Hot Springs National Park has increased the potential for degradation of the quality of surface-water runoff and local ground-water recharge to the hot springs. Water samples were collected during base-flow and storm-flow conditions at selected hot springs and cold-water springs and analyzed for a suite of water-quality parameters. Comparison of results with earlier studies dating back to the late 1800's indicates that little change in water chemistry has occurred and that the water continues to be of excellent quality.

Distinguishable differences in water chemistry of individual springs sampled during base-flow compared to storm-flow conditions were apparent, indicating changing input of cold-water recharge relative to hot-water recharge. Constituents that show statistically significant differences between base-flow and storm-flow conditions include silica, total dissolved solids, strontium, barium, and sulfate. While variations in these constituents do not degrade water quality, the differences do provide evidence of the influence of a locally derived, cold-water component of flow. Water temperature was measured continuously at nine hot springs for four to seven years (depending on the site). No indication of long-term change in water temperature was apparent; however, short time-scale water-temperature decreases occurred in response to mixing of hot water with locally derived recharge after storm events.

Water-quality and temperature data provide multiple lines of evidence supporting the importance of the contribution of cold-water recharge to hot springs. All the springs sampled showed some measure of influence from local recharge. Binary mixing models using silica and total dissolved solid concentrations indicate that cold-water recharge from storm-flow contributes an estimated 10 to 31 percent of the flow of the hot springs within 48 hours of the storm event. Models using water temperature indicate that cold-water recharge from storm-flow contributes an estimated 1 to 35 percent of total flow.