in Central Texas
An accurate conceptual model of a complex aquifer system is critical to constructing a groundwater model. The prior creation of a 3-D stratigraphic model may provide the necessary hydrogeological information to build a groundwater model of a complex system.
The Llano Uplift in Central Texas is one of the most complex areas in Texas with regards to structure and stratigraphy. The Llano Uplift covers more than 14,000 square miles and consists of a large Precambrian granite stock which formed the base for the deposition of Cambrian through Cretaceous limestones, shales, and sandstones. Three minor aquifer systems are found within the stratigraphy overlying the Llano Uplift, ranging in age from Pennsylvanian to Cambrian (Marble Falls, Ellenburger-San Saba, and Hickory aquifers). These aquifers supply groundwater to over twenty cities and towns in the study area, which depend totally on the groundwater from these aquifers for all of their municipal, irrigation, ranching and industrial needs. The purpose of this project was to provide a stratigraphic framework of this aquifer system for the future construction of a groundwater model.
The stratigraphy and structure of the three aquifers were investigated. These three aquifers are part of a stratigraphic/aquifer sequence which was intensely faulted during Pennsylvanian aged Ouachita tectonism. Faulting offsets ranging between 100 and 5,000 feet, created numerous, independent fault blocks resulting in local compartamentalization of the aquifers. The stratigraphic interpretation of this sequence was further complicated by Pre-Cambrian paleo-topography, unconformities, nonconformities, thickness and facies changes.
Over 1,100 geophysical logs and driller’s reports were used to interpret and correlate ten stratigraphic surfaces (Cambrian through Pennsylvanian). ESRI’s ArcGIS 9.2 software was used to create a geodatabase and gridded stratigraphic surfaces which were ultimately imported into CTECH's MVS 3-D software for visualization of this complex aquifer system.