Introduction to December Focus: Developments in Groundwater Geophysics

Issues related to groundwater continue to grow in importance throughout the world, and geoscience techniques to deal with these issues are developing rapidly. Methods are needed to map the extent and quality of groundwater resources, water depletion and pollution, and subsurface flow related to engineering projects such as dams. Increasingly, airborne electromagnetic (AEM) surveys are used in combination with well data and surface measurements to provide regional maps of water resources and aquifer quality and structure. In this issue, we present four papers on the use of geophysics to solve problems related to groundwater mapping and subsurface flow.

In the article “Interpreted Water Quality Calculated from Borehole Resistivity Measurements in the Gulf Coast Aquifer, Lower Rio Grande Valley, Texas, U.S.A.”, by John Meyer and Andrea Croskey of the Texas Water Development Board, the authors describe the use of borehole resistivity logs to map the volume of brackish water available for desalinization projects in the Rio Grande Valley. Combining water quality samples with log analysis, the authors interpreted over 40 million acre-feet of slightly saline water and 112 million acre-feet of moderately saline water in 9 geological formations of the Gulf Coast Aquifer.

In the article “The Application of Airborne Geophysics for Water Exploration”, by Bill Brown and Dr. Flemming Effersø, of SkyTEM Canada Inc. and SkyTEM ApS, respectively, the authors describe the dual-moment SkyTEM helicopter-borne time-domain EM (TEM) system and its use in groundwater studies. They present three groundwater case histories illustrating its use. The first was a project in the Peace Region of Northeastern British Columbia conducted to map shallow aquifers for domestic, industrial and First Nations use. The second was a project to delineate aquifers, aquicludes, recharge areas, and fresh water in the Lower Platte Area of Eastern Nebraska. The third was a project in Sudan related to a gold prospect. The project found a source of processing water for a potential mine which greatly improved its economics.

In the article “Hydrogeophysical Investigations of Earthen Dams – Two California Case Studies”, by Bethany Burton, Paul Bedrosian, Burke Minsley, Scott Ikard, and Michael Powers of the U.S. Geological Survey, the authors describe the use of resistivity tomography, time-domain electromagnetic soundings, seismic, and self-potential to map subsurface conditions, aquifers, and buried channels under two earthen dams in California which exhibit seepage. The study provided a solid geoscience basis for future remedial engineering.

In the article “Integrating Airborne Electromagnetic and Gamma Log Data for Regional Aquifer Mapping: Montney Play Area, NE British Columbia”, by M. Best (Bemex Consulting International), V. Levson (Quaternary Geosciences Inc.), and C. Salas (Geoscience BC), the authors present the results of a project to integrate well data, gamma log interpretation, and a resistivity inversion of an airborne TDEM survey to map Quaternary geology and aquifers in the Peace Region of NE British Columbia. The results were in good agreement with a follow-up drilling and logging program.