Introduction to October Focus: Hydrogeophysics: The Past, Present & Future

The ability to detect and image things that are hidden from our sight has always been a fascination of humans. This applies to geoscience as much as any other field. With the ability to sense objects and materials beneath the earth’s surface, the discipline of exploration geophysics has been instrumental in the development of natural resources around the globe. Originally developed for oil, gas, and mineral exploration, the application of geophysical reconnaissance methods to map, develop, and protect our groundwater resources has been evolving over the last few decades. Today, a number of techniques are commonly employed help to reveal the groundwater secrets of the earth in both remote and water-stressed regions of our planet. The application of “hydrogeophysics”, as it is called, to real world challenges regarding the sustainable development of groundwater resources provides hope and prosperity to those requiring access to its life-sustaining and economic-generating properties.

Many of the traditional techniques used today have a basis in detecting perturbations in the earth’s magnetic field, or subtle changes in its gravitational pull. Others use the propagation of acoustic energy sent into the subsurface and responses back (i.e. seismic), or electrical stimulations to resolve subsurface materials and structures (i.e. resistivity soundings and electromagnetic imaging). Although useful in their application, the challenge with these “traditional” techniques has always been one of non-uniqueness, and the need for inference regarding the geologic setting. These indirect methods of detection are also challenged by the degree of resolution and interpolation required. Yet, when confronted with simple, layer-cake systems, these applications have proven their merit time and time again. However, in more complex settings (e.g. folded, faulted), the challenges and limitations associated with current, traditional approaches have revealed themselves.

The field of exploration geophysics is an ever-evolving one, where methods are developed and integrated into the discipline as their abilities are understood, tested, and validated. This is true today as new technologies are being brought to the forefront – some based on measurements of dielectric permittivity and spectral energy, and others on the detection of material resonant frequency and the resulting perturbations to the near-earth electric field. Whether collected by ground-based surveys or derived from multi-spectral data collected by low-earth orbit satellites, these new technologies are poised to broaden the application of subsurface imaging by the direct detection of target substances based on their unique quantum properties, including groundwater of varying qualities.

Although some of these newer technologies may sound less like science, and more like science fiction, the introduction and acceptance of geophysical methods into the community of practice has faced similar challenges in the past. As our detection, data analytics, and imaging capabilities continue to develop in our accelerating digital-age, acceptance and adoption of new technologies is required for this aspect of the geosciences to stay at the cutting edge.

This edition of the RECORDER has been designed to acknowledge the traditional approaches to geophysics, as they are applied to the field of groundwater exploration, and introduce some of the emerging technologies that are blazing a trail in the ever-evolving realm of hydrogeophysics. From finding water for needy refugees to mapping complex aquifer systems, we hope the examples provided will capture your imagination and demonstrate the importance of this field of science.

Emergency Response Groundwater Exploration at Rohingya Refugee Camps in Bangladesh
ALASTAIR MCCLYMONT, PAUL BAUMAN, COLIN MIAZGA, ERIC JOHNSON, AND CHRIS SLATER

Extending the Reach of Radio Waves for Subsurface Water Detection
GORDON D.C. STOVE

Advances in the Realm of Hydrogeophysics: The Emerging Role of Quantum Geoelectrophysics in Aquifer Exploration
RICHARD HATALA, JON FENNELL, AND GERALD GURBA