Surface geophysical methods have been used for decades to explore for groundwater resources. For depths on the order of 100 meters or less, the Electrical Resistivity Tomography (ERT) and seismic refraction methods are generally useful and economic.
Near-surface geophysics for groundwater investigations is usually restricted to depths less than 500m below the surface. Groundwater applications of near-surface geophysics include mapping the depth and thickness of aquifers, mapping aquitards or confining units, locating preferential fluid migration paths such as fractures and fault zones and mapping contamination to the groundwater such as that from saltwater intrusion.
Many geophysical techniques have been applied to groundwater investigations with some showing more success than others. In the past, geophysics has either been used as a tool for groundwater resource mapping or as tool for groundwater character discrimination. For groundwater resource mapping potential field methods, gravity and magnetics, have been used to map regional aquifers and large-scale basin features. Seismic methods have been used to delineate bedrock aquifers and fractured rock systems. Electrical and electromagnetic methods have proved particularly applicable to groundwater studies as many of the geological formation properties that are critical to hydrogeology such as the porosity and permeability of rocks can be correlated with electrical conductivity signatures.
Most geophysical techniques have been used for groundwater characterization, but electrical and electromagnetic methods have provided the greatest success in directly mapping and monitoring contaminated and clean groundwater.