Feasibility of using electromagnetic geophysical methods to investigate landfills and disturbed areas as a threat to ground-water quality in Pima County, Arizona

Abstract

This project assessed the feasibility of using the electromagnetic geophysical technique (EM) in the Tucson basin to both (1) determine the boundaries of landfills and disturbed areas and 2) delineate and detect inorganic contaminant plumes which may threaten ground-water quality. Profiles of bulk electrical conductivity produced by the EM-34-3XL methods showed clearly the boundaries of landfills within the Tucson basin. Construction debris produced anomalies of about 10 mmhos/m, and municipal fill produced anomalies 20 to 50 mmhos/m greater than background variations. Horizontal-dipole configurations yielded profiles that were easier to read than from vertical-dipole configurations. The delineation of electrically conductive contaminant plumes in urban areas was impeded by metallic cultural artifacts. Although visual inspection of the graphed data did not yield evidence of a contaminant plume, a model from data collected north of the El Camino del Cerro Landfill showed a lower layer of greater conductivity than the lower layer west of the Santa Cruz River. Numerical modeling proved to be insensitive to the thickness of top layers.