Use of Geophysics, SRTM and Remote Sensing to Characterize Groundwater Contamination from Oil Shale Wastes in South China

Carpenter, Philip J.¹; Ding, Aizhong ²; Cheng, Lirong ²; Sturnfield, Emily ¹; Liu, Puxin ³; Chu, Fulu ^4
1 Geology and Environmental Geosciences, Northern Illinois University, DeKalb, IL.
² College of Water Sciences, Beijing Normal University, Beijing, China.
³ Maoming Environmental Protection Bureau, Maoming, China.
⁴ Hebei Institute of Geophysics, Langfang, China.

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. Remote sensing observations from Earth orbit, as well as geophysical methods operating at the Earth’s surface, offer innovative and noninvasive tools for identifying subsurface contamination in these situations, as illustrated by this study of the Maoming oil shale landfills.

Between the 1950s and 1990s oil shale mining and retorting northwest of Maoming City, southern China, 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 aquifers by landfill leachate containing heavy metals and organic compounds. Values of pH as low as 3.0 have been measured in some residential and village municipal wells adjacent to the landfills. Resistivity soundings and profiles were made over and adjacent to the north landfill in 2001, in conjunction with sampling water quality in village wells surrounding the landfill. Soundings identified a very low-resistivity layer (less than 10 ohm-m) at 5-6 m depth in a village with contaminated wells about 1 km southwest of the north landfill -- this conductive zone may represent leachate contamination of a shallow confined aquifer. Resistivity models, combined with groundwater specific conductance values, suggest an apparent formation factor of 10.6+2.8 for the oil shale waste and formation factors of 1.7- 3.9 for the Laohuling Formation aquifer that surrounds the landfill. This information, and other electrical properties of these formations, will be used to design and model future 2D resistivity and EM surveys. In addition, Shuttle Radar Topography Mission (SRTM) data provide excellent constraints on elevation of the north landfill and may be used to infer water table elevations, based on elevation of surface water bodies. Landsat Thematic Mapper, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data have also proven useful in defining the extent of waste areas and their degree of vegetation. Remote sensing the extent and type of vegetation will be useful in planning and monitoring phytoremediation at this site.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009