Barton Springs/Edwards Aquifer Hydrogeology and Groundwater Quality

This study examines hydrogeologic and water-quality data of the Barton Springs segment of the Edwards Aquifer collected by the Barton Springs/Edwards Aquifer Conservation District from 1990 to 1994. Ten water-level stations are continuously monitored by the District. The water-level changes in the ten monitor wells varied in response to recharge and drawdown events. Monitor wells 58-57-9A (Miller), 58-50-801 (Dowell), 58-58-123 (Porter), 58-58-4CM (Centex) and 58- 50-216 (Target) have shown rapid responses to some recharge events, indicating a good hydraulicconnection to areas of recharge during certain flow conditions. We1158-50-301 (Lovelady) shows a very gradual response to recharge events, indicating that it is fed by diffuse flow. Two areas of concentrated groundwater flow are hypothesized, the Manchaca and Sunset Valley flow routes, primarily based on potentiometric surface configurations, and supported with supplemental geologic and water-quality information. These areas are probably water-saturated conduits or transmissive zones that approximately correspond to major fault locations where more rapid groundwater movement is anticipated to occur. The two areas of concentrated flow may be connected as part of a single major route of flow to Barton Springs, or may be two separate routes of groundwater flow. Further delineation and verification of the hydrologic characteristics of these areas should be performed using additional water-level measurements and groundwater tracing techniques. Thirty-seven wells and springs were sampled in this study. Twenty-two wells were sampled during drought conditions in May through October, 1990. Twenty of the same wells were resampled during high water-level conditions in March 1993. Two wells and springs were added in March 1993, and 13 different wells and springs were sampled in March 1994. One well sampled in the bad-water zone showed high levels of dissolved solids, sodium, chloride, magnesium, gross alpha, and boron. Ten wells showed significant contributions from th