NewsDrop Winter 2022

In hydrology, the area between the ground surface and the water table of the aquifer is known as the unsaturated zone or vadose zone. Although the vadose zone isn’t saturated with water like the aquifer itself, it is still an important hydrological zone, supplying virtually all the water used by plants in the Edwards Aquifer region and contributing recharge to the aquifer through infiltration. Despite this importance, the vadose zone is complicated, and not well studied scientifically, especially in karst systems like the Edwards Aquifer. To combat this knowledge gap, EAA scientists will be using a cutting-edge method in vadose zone research known as nuclear magnetic resonance borehole logging. Nuclear magnetic resonance or “NMR” is one of only a very few methods capable of measuring the amount of water stored in rocks in the unsaturated zone. It does this by exploiting the behavior of atomic nuclei (specifically, the nuclei of hydrogen atoms, protons, in water molecules) in the presence of magnetic fields. The details are

technical, but the result is that NMR provides a direct estimate of the amount of water in the ground. This will allow EAA scientists to use NMR to monitor how much water is in the ground, and how that amount changes over time in response to rainfall, drought, and changes in land management. That capability alone is extremely valuable, but the NMR measurement also contains information about the flow properties of the material the water is held in. To get the NMR tool deep into the ground where it can measure the amount of water stored there, EAA scientists have installed eight 30-feet deep boreholes at the EAA Field Research Park specifically designed for NMR measurements. By collecting NMR measurements in the boreholes before and after rain events, scientists will be able to assess the potential water quantity benefits of land management and characterize other vadose zone environments typically found in the Edwards Aquifer Region.