Investigating Flow Paths and Mixing Relationships in a Shallow, Mantled-Karst Aquifer Using Chemical Analysis, Geophysical Well-Logs, and Continuous Monitoring of Temperatures and Water Levels at the Savoy Experimental Watershed

The Savoy Experimental Watershed (SEW) is a University of Arkansas property that encompasses about 1250 hectares in the mantled-karst of the Springfield Plateau in the southwestern Ozark Plateaus. SEW is a long-term, collaborative field research site that focuses on ground-water flow and transport in shallow, karstified carbonate aquifers. Previous studies at SEW established a three-component model consisting of the interface (soil) zone, interflow (epikarst) zone, and a focused flow (phreatic) zone. Permeability contrasts between these zones and within the aquifer are the primary control of ground-water flow, with structural features forming a secondary control. Hydrologic budget parameters needed to revise the existing conceptual model were identified in fall 2007. Four wells and three springs with weirs were selected to form two transects across the basin. In October 2007, data loggers were deployed at each of the selected stations and programmed to record absolute pressure and temperature at 15-minute intervals. These data are being used to identify flow paths and to describe mixing relationships in the aquifer. Geophysical well-logs were used for stratigraphic correlation to determine the hydrostratigraphy and to detect structural offset between stations. In June 2008, geochemical sampling was conducted to identify hydrochemical facies, which will further define flow patterns. Preliminary data from the period of record 10-23-07 to 06-01-08, suggests that the SEW ground-water system continues to evolve and dynamically change over short time scales. As more data are collected and as new technologies allow for higher resolution analysis, researchers are learning that the karst system is much more complex than initially envisioned. Recharge and ground-water flow occurs along discrete flow zones, some of which can be small and of limited extent. Nonetheless, these zones are capable of transmitting significant quantities of flow.