USE OF RESISTIVITY SOUNDINGS TO DETERMINE LANDFILL STRUCTURE

Sixteen Wenner and Schlumberger array electrical soundings were made over portions of the Mallard North landfill in DuPage County, Illinois, to map the gross layered structure of a closed landfill. Sounding curves were fit to standard type curves and values inverted in a least‐squares procedure to yield multilayer geoelectrical models. Wood, newspaper, cloth, glass, plastic, and metal refuse interspersed with soil exhibited resistivities of 9–19 ohm‐m (unsaturated) and 2–7 ohm‐m (leachatesaturated). Mature unfractured clay‐till cover material exhibited a resistivity of about 30 ohm‐m, and its thickness was estimated to within 27% of its true thickness. Larger errors were encountered over fractured and freshly emplaced cover. Soundings were also inverted to yield accurate leachate levels and refuse thicknesses (errors for both averaged about 30%). While Schlumberger and Wenner soundings produced models with comparable accuracy, Schlumberger soundings were less sensitive to cover heterogeneities and easier to deploy. Moore's cumulative resistivity interpretation method was found to be unreliable in interpreting this type of resistivity data. Fractures present in the cover material, lateral changes in leachate level, and variations in cover thickness and resistivity contributed to errors in interpretation. Despite these limitations, models generated from electrical resistivity soundings are reasonably accurate in their depictions of internal conditions in this type of landfill. Such soundings could be used to map internal structure in other layered landfills that lack construction and operational records. Copyright © 1990, Wiley Blackwell. All rights reserved