This new, highly automated, highly efficient version of electrical resistivity will revolutionize the way many geophysical problems are approached. SAIC has used Electrical Imaging (EI) for karst investigations, lithologic investigations, and to aid in siting wells.
Electrical resistivity measures the bulk electrical resistance of the subsurface by inducing a current between two electrodes implanted in the subsurface. Electrical resistivity is used by SAIC to characterize subsurface stratigraphy, water table depth, conductive plumes, and buried wastes.
With advances in technology, data collection and inversion methods have been advanced to the point that electrical resistivity is sometimes referred to as electrical imaging.
Electromagnetic (EM) methods measure the bulk electrical conductance of the subsurface. SAIC uses EM techniques to identify lithologic changes and soil thickness variations which may indicate potential karst-related sinkhole development. SAIC also uses EM techniques to detect and map conductive or nonconductive contaminant plumes, layering and lateral variations in stratigraphy, fractures zones, and waste disposal areas.
Gravity measurements detect changes in the earth's gravitational field caused by variations in the density of the soil or rock or engineered structures. SAIC uses gravity surveys to locate and characterize buried bedrock channels and bedrock structural features. Other applications are to detect voids, caves, and abandoned mines or tunnels.
Ground Penetrating Radar (GPR) is used to measure changes in the dielectric properties of subsurface materials. SAIC uses GPR to delineate subsurface features such as underground storage tanks, buried drums, and utilities. GPR is also used to locate karst-related voids in the subsurface. Other applications include mapping landfilled and excavated areas and site stratigraphy.
Metal detectors can range from the treasure-hunter variety that can be seen on the beach or park. However, for environmental investigations significantly deeper penetrating metal detectors are required, requiring special coil configurations. Specialty time domain high sensitivity metal detectors are frequently used for sites with unexploded ordnance (UXO) concerns.
Magnetic surveying measures the perturbations in the earth's magnetic field caused by changes in concentrations of natural ferrous minerals or by ferrous metals. SAIC uses magnetics to locate buried ferrous metals such as wastes, drums, or utilities. Other applications include characterizing geologic structures and mineral exploration.
Classical seismic surveys can be conducted between boreholes to measure shear and compressional seismic wave velocities. This information can be used to compute Poisson's Ration, the Shear Modulus, Bulk Modulus, or Young's Modulus for engineering applications. Elaborate measurements can allow a tomographic reconstruction of the velocities between two boreholes.
Seismic refraction and reflection methods measure the transmission of sound waves through the subsurface generated using a hammer blow or explosive energy source. Individual subsurface layer depths and thickness can be calculated based on the analysis of sonic wave arrival times. SAIC uses seismic methods to obtain the depth to bedrock surfaces and the water table; to characterize rock type and degree of weathering; and to locate fractures, faults, and buried channels.
Underground pipes and utilities are mapped by SAIC by inducing a signal onto a subsurface utility and tracing the signal as it moves along or within the utility. Inductive locating is a one-person operation used for locating a particular object or several points along a buried pipeline or utility cable. It is a method for locating unknown or lost conductors. Conductive tracing is a one-person operation used for tracing an individual pipe or cable (conductor) or for use when other conductors or metal objects are nearby. In addition, this method may also be used to trace nonmetallic pipe by connecting to a wire, plumber's snake, or electrical fish tape. SAIC also screens for loaded (active) underground power lines.