HYDROGEOLOGY: THE DEMAND FOR WATER


Figure 4 - Cross-Section.


it takes a locally experienced hydrologist to best identify the proper location of new wells. However, the opportunity for sustainable large production levels exists with proper well siting.


Recharge, Water Levels and Discharge


The Middle Trinity aquifer in Bexar and Comal counties is primarily under artesian or leaky-artesian conditions. Even in areas near the outcrop, stratification and karst conditions tend to cause the aquifer to behave as if it were confined or semi-confined. The aqui- fers in the Bexar and Comal County area are much more sensitive to climate (i.e., wet- dry cycles) than the primary aquifers in the Panhandle, Permian Basin, Trans- Pecos, and (especially) those aquifers located south and east of Interstate 35.


Like that of the Edwards aquifer, the overall small storage capacity of the Middle Trinity aquifer and the confined conditions result in water levels in local production wells fluc- tuating through wet-dry cycles. Seasonal fluctuations also have been recorded. Additionally, water-levels respond relatively rapidly to significant rainfall events indicating that substantial recharge occurs through





stream losses where the Middle Trinity is exposed in stream- beds. It is likely that recharged water migrates along faults and fracture planes from the overlying Upper Trinity aquifer (i.e., Upper Glen Rose Limestone) to the Middle Trinity (5). Figure 5 shows the relationship between historical rainfall and local water levels in the Middle Trinity aquifer. Groundwater flow and stream flow modeling indicate that pumping from the local Trinity aquifer will cause very small reductions


Figure 5 - Relationship between Precipitation and Middle Trinity Ground Water Levels. 


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