Flow Potential Between Stacked Karst Aquifers in Central Texas, USA

Abstract

The Cretaceous-age Middle Trinity Aquifer in central Texas exhibits significant karst features where it is exposed at the surface.Where these units are overlain by the karstic Upper Trinity and Edwards Aquifers, the degree of karstification is not known, but groundwater in certain units of the Middle Trinity Aquifer is chemically similar to shallow groundwater in this area. Geochemical, potentiometric, and hydraulic conductivity data suggest that this deep groundwater is following pathways from the recharge areas that allow for rapid flow compared to other deep units that contain waters of significantly different chemistry. A 340-m deep multiport monitor well was installed in the Edwards (shallowest), and Upper and Middle Trinity Aquifers to better understand the vertical and horizontal relationships of these aquifers. The well was completed with 14 monitor zones allowing for groundwater sampling, hydraulic conductivity testing, and pressure measurements (potentiometric levels) in each zone. Data from this well suggest that karstification processes are active at depths of 300 m below land surface in a confined aquifer at least 25 km from the closest recharge areas.