Electromagnetic (EM) methods measure the bulk electrical conductance of the subsurface. Common configurations permit assessment of the top 18, 25, 50 and 100 feet of subsurface. Quality Geophysics frequently uses EM techniques to identify lithologic changes and soil thickness variations which may indicate potential karst-related sinkhole development. Quality Geophysics 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. Measurements are qualitative (not depth specific), but rapid to make. This makes EM a great tool for preliminary site assessment surveys.