PEEKING INTO THE "GREY BOX": A MULTI-METHOD APPROACH TO STUDYING A KARST AQUIFER IN CENTRAL TEXAS

Understanding groundwater recharge and discharge are important when managing karst aquifers. However, these processes are difficult to characterize and quantify due to the inherent anisotropy and heterogeneity of karst. In the Northern Segment of the Edwards aquifer in Central Texas, managing groundwater-surface water interactions has been challenging during an epic drought, but is nevertheless important because the aquifer provides local drinking water, spring flow is a DFC (desired future condition) of the local groundwater district, and an endemic salamander that inhabits the springs is a candidate for the endangered species list.

Coupling physical and chemical sampling methods provided a better understanding of hydrogeological processes than using any one method alone. An approach using several physical and chemical sampling methods was applied to the Salado Springs area of the Northern Segment. Water levels from wells across the study area were measured to create a synoptic potentiometric surface for the Salado Creek basin in the Northern Segment under current conditions (low flow). This was compared to historical data to better understand how the aquifer has changed over several years. A multi-parameter datalogger was installed at one site to monitor water level, temperature, and specific conductance. Logging these parameters at a high sampling interval provided precision for comparison that would not be possible with less frequent sampling. Relating logging data to precipitation data during recharge events gave insight into aquifer response. Water from monitoring wells was analyzed for major ions and nutrients to characterize water chemistry, and dye tracing was conducted in a key location within the study area to confirm and reveal groundwater flowpaths between a cave and springs discharging along Salado Creek. Using a variety of physical and chemical methods that resulted in different but complementary data provided a greater understanding of groundwater recharge, storage, and flowpaths in the Northern Segment of the Edwards aquifer.