Mapping the extent of groundwater contamination beneath landfills and hazardous waste sites is a major environmental challenge, particularly in developing countries.  Monitoring wells are scarce, expensive, and commonly fail to define the full extent of contamination and its three-dimensional character.  Geophysical methods offer a powerful noninvasive tool for identifying subsurface contamination in these situations, especially when combined with other hydrogeological and remote sensing data within a Geographic Information System (GIS) framework. 

This study examines a mine waste contaminated area near Maoming in Guangdong Province, southern China. Oil shale mining and retorting northwest of Maoming have produced 50 million tons of waste that were dumped in two huge landfills averaging 6-7 km long, 1-2 km wide and 5-6 m high.  Rainfall and surface water percolating through the waste has led to pollution of adjacent shallow aquifers by landfill leachate containing heavy metals and organic compounds.  The immense size of these landfills, and the surrounding contaminated area, has led to the use of both GIS and remote sensing data to identify and characterize potential contaminant pathways.  Landsat and surface reflectance imagery were combined with structural and regional hydrogeological maps to identify lineaments that probably represent fracture zones and preferential contaminant pathways beneath the landfills. Reconnaissance surface geophysical measurements were also made at the site.  One resistivity sounding identified a very low-resistivity layer (less than 10 ohm-m) at 5-6 m depth in a village about 1 km southwest of the north landfill – this may represent leachate contamination of a shallow confined aquifer. Other electrically conductive zones, also possibly indicating leachate contamination, were identified near village wells approximately 1 km east of this landfill. All of this information is presently being assembled into a conceptual hydrogeological model of the landfills and their vicinity.