Landfill Delineation and Characterization Using Electrical, Electromagnetic and Magnetic Methods

Abstract

Three geophysical techniques have been used to determine the boundaries and contents of a small composite landfill. Initially, widely spaced electrical resistivity soundings and profiles provided gross information on the distribution of electrical conductivity with depth and the approximate position of the landfill. Frequency‐domain electromagnetic data were then collected on a dense grid that encompassed the landfill and surrounding sediments. Using a simple new technique, these vertical‐ and horizontal‐mode data were inverted jointly to yield shallow electrical conductivities and approximate estimates of magnetic susceptibility. Finally, optically pumped Cesium‐vapor sensors were employed in the acquisition of total‐field and vertical‐gradient magnetic data over the same area as the electromagnetic data. Together, the resultant geophysical data sets revealed two distinct waste pits separated by a 20–40 m wide zone of undisturbed ground. One waste pit was distinguished by moderate to low‐amplitude geophysical anomalies. It was the likely dump for domestic garbage. Uniformly high‐amplitude anomalies suggest that the second pit was the main site for the disposal of industrial refuse, including steel containers of chemical waste. The irregular boundaries of the two waste pits were determined equally well on the electrical conductivity, magnetic susceptibility and vertical‐gradient magnetic maps. By comparing anomalies on these maps, it was possible to distinguish ferrous and non‐ferrous metallic objects outside of the landfill and to identify sand‐ and gravel‐rich units within the dominantly fine‐grain sediments of the region.