Springs Limestone Fractures
In March 2015, AGI, in partnership with The Jackson School of Geosciences at The University of Texas at Austin and Dr. Marcus Gary of the Edwards Aquifer Authority, conducted a hydrogeology workshop focused on groundwater exploration.
Why groundwater exploration?
This workshop’s purpose was important: As water—especially groundwater—becomes more and more scarce (and thus, valuable) knowing exactly where and how to find it will become more crucial. That’s where we come in.
Comal Springs, Texas, is home to the self-named springs, which flow from the Edwards Aquifer. The Edwards Aquifer is a karst aquifer that serves the agricultural, industrial, recreational, and domestic needs of almost two million users in south central Texas (source). The springs are also the starting point of the Comal River.
Underneath the fractured limestone of the springs are pathways for water. This is of importance for hydrogeology; because water flows here, we can draw conclusions about how limestones and aquifers mix. AGI’s instruments make finding this water flow simple: Instead of going the traditional route (installing electrodes in the ground and surveying), this method involved measuring resistivity via floating marine cables.
The purpose of this exploration was to use 3D imaging with floating marine cables and a small number of electrodes to demonstrate how AGI’s marine tools make it simple and fast to see the 3D volume of what’s happening below ground. In this case, we were training students and professional clients on how the instruments can map groundwater flow.
Instead of installing (think hammering down electrode spikes) into the ground, 28 electrodes spaced one meter apart on a floating graphite electrode cable were floated out on water and used to rapidly measure a 392-electrode 3D array over a spring to locate zones of higher seepage.
Observed gas bubbles were associated with seepage and were found to be rising up over karst features imaged in the 3D resistivity model.
Benefits For Our Clients
Ease of use: It’s easy to mobilize on water by floating a cable. Simply hold it still, then move it when it’s done measuring. You don’t have to install electrodes, which is important and time-saving when you’re surveying waterways, rivers, estuaries, etc.
Speed of data acquisition: The workshop highlights the system’s capability: Not only is it important to be able to move the cables quickly, it’s important to be able to gather data quickly.
Specially-designed tools: These rugged instruments are meant for marine work.
Detail: When you model in 3D, you can take into account any 3D artifacts below the ground, getting a more accurate look.
This is an easy way to do 3D imaging with a small amount of electrodes (which is affordable and efficient). It’s an ideal choice for groundwater exploration.