Assessing Karst Groundwater Resources in a Complex Region of Structural Confinement

This investigation focuses on the connection between the Uvalde pool (west) and the San Antonio pool (east) of the Edwards aquifer. This area lies within and is affected by uplift relating to the Uvalde salient and proximate igneous intrusive plugs to the south.  Aspects of the hydrogeology relating to the separation of these pools has been a topic of interest among researchers in this area for numerous years; however, the exact location and nature of boundaries remain undefined, and the discharge through this area is not accurately known.  It is hoped results from this investigation will aid in refining our understanding of a water budget for the San Antonio Pool of the Edwards aquifer, and in the determination of accurate flow boundaries and budgets for Uvalde County. This investigation was limited to the transmissive (karstified) part of the Edwards aquifer within the study area, and is based on previous work supplemented with newly collected data. The newly collected data include: 1) compilation of a complete table of wells within the study area;  2) redefined placement of flow boundaries (faults), most of which appear to be structurally controlled; 3) hydrostratigraphic analysis of the Knippa Gap area based on drilling and wireline logs; 4) characterization of the depth of karstification within the Knippa Gap; 5) creation of water quality maps within and contiguous to the study area; and 6) assessment of groundwater flow velocities and directionality based on dye tracing within the study area.  These data constrain a revised conceptual model of the flow and karstification in this critical area of recharge to the Edwards aquifer, and provide specific lateral boundaries and vertical karstification zones which can be tested quantitatively.