Definition: The non-invasive investigation of subsurface conditions in the Earth through measuring, analyzing and interpreting physical fields at the surface. Some studies are used to determine what is directly below the surface (the upper meter or so); other investigations extend to depths of 10's of meters or more.

Methods Employed: Ground penetrating radar (GPR), seismic reflection and refraction, DC resistivity, electromagnetic induction, gravity and magnetics. Data from the field are interpreted using mathematical models generated using in-house and commercial desktop computer algorithms.

Applications to Groundwater and Hydrogeology: Surface geophysics is often used to characterize subsurface conditions for engineering, geologic and hydrogeologic investigations - a favorite application is determining the depth to bedrock beneath unconsolidated soils. Geophysics can also detect and quantify the presence of water in the subsurface, from partially saturated conditions near the surface (essential information for agriculture) to fully saturated conditions beneath the watertable (essential for detecting and delineating groundwater aquifers or reservoirs). Once groundwater aquifers are detected, geophysics can be used for designing the engineering plan to optimize their development, such as providing predrilling estimates of their hydraulic characteristics, and for defining geologic features that control their recharge or discharge.

Applications to Environmental Assessment & Remediation: Surface geophysics is used to assess the presence and potential impact of subsurface hazardous materials and chemical contamination. "Base-line" information is essential for a preliminary assessment of a potential or designated hazardous waste site. Geophysical studies can remotely detect buried drums, pipelines, underground storage tanks, and, in some cases, remotely delineate the distribution of contaminant plumes. When used early in such investigations, these studies can optimize (or modify) plans for investigatory test coring, test pits and trenching excavations.

Applications of Non-Invasive Geophysical Field Methods to Environmental Investigations
Noninvasive Geophysics: Matching the Technology at the Surface to the Geology of the Substrate
Elements of Geophysical Methods Relevant to Environmental and Groundwater Investigations