Abstract

A large number of old landfills, and chemical- and industrial-waste disposal sites have been located in alluvial and Bonneville lakebed deposits of northern Utah. Fine-grained silts and clay layers within these deposits are important as aquitards to the vertical migration of waste fluids and as low-permeability zones which channel the subsurface movement of ground water and fluid contaminants. Dipole-dipole resistivity surveys are a cost-effective technique for mapping the configuration of underlying clay layers as well as the near-surface discontinuities of landfills and buried disposal trenches.

Dipole-dipole profiles were completed over two large landfills and three waste-disposal pits at Hill Air Force Base, Utah, in 1982 as part of a Phase II hydrogeologic survey within the U. S. Air Force Installation Restoration Program. Apparent resistivities observed with 9-meter dipoles varied from more than 700 ohm-meters to less than 10 ohm-meters on several profiles. This range of apparent resistivities indicates the heterogeneous nature of the alluvial material, variation in the degree of saturation, and the presence of, or depth to, clay layers.

Numerical modeling of selected profiles aided in mapping the top of clay layers at depths of 3 to 20 meters, the prefill surface of a large landfill, and the morphology of a slump block at one chemical-waste disposal pit. The resistivity data, supplemented by ground magnetic and self-potential profiles, provided guidance for a drilling and sampling program and continuity for understanding the sampling results.