f Waste disposal site mapping using the CVES method

ctions were constructed using Res2Dinv software, which is a computer program for rapid 2D resistivity inversion using the least-squares method by Loke and Barker (1996)1. The waste disposal site is 300x500m and consists of non-organic materials (mostly building waste), layered alternately with thin, sandy-loamy layers and underlain by a thick layer of dune sands. Visual inspection of the site revealed that, apart from bricks, wood and concrete fragments, there was also a substantial number of metallic objects randomly distributed throughout the waste volume. The sandy-loamy layers retain moisture whereas the sand is drained, thus there is a significant difference in electrical resistivity between the waste and the natural sandy base layer. At the northern and eastern sides of the site, the waste layer is higher than the sandy basement, while at the southern and western sides, both the waste and the basement are at the same level. It was, therefore, possible to correct the thickness of the waste layers using a forward calibration measured at the waste outcrops. Five CVES lines, totaling 1500 meters in length, were carried out in the waste disposal area. Fig. 1 shows a typical geoelectric cross-section of Line 2. Two layers are clearly observed: the upper layer (waste) is characterized by resistivities of 5-50 ohm-m, while the lower sandy layer has resistivities of 100-500 ohm-m. The corresponding interfaces are shown by dashed lines. The field between these interfaces may be interpreted as a “transition” zone, i.e. a sandy layer with different electrical properties. The results of the survey are shown in Fig. 2 as an lateral changes of the thickness of the waste layer. The map shows that the thickness of the waste layer varies from 0-30 m. The thickest part (more than 32 m) is located in the center of the map. An example of waste disposal site mapping using the CVES method with 2D inversion technique is given. This is one of the few geophysical methods that can be used successfully to map such heavily heterogeneous structures.