Application of Electrical Resistivity and DRASTIC Models in the Study of Groundwater Contamination Risk in the Surroundings of the Hulene - B Waste Dump, Maputo, Mozambique

Abstract The contamination of groundwater by leachate migration around waste dumps is a growing challenge for maintaining the quality of water resources in urban centers. In this study the electrical resistivity method was applied, where six 400 m profiles were executed around the Hulene - B waste dump and then an inversion was performed by RES2D. The application of the electrical resistivity method allowed us to characterize in detail some of the fundamental aspects of the DRASTIC risk (estimating groundwater depth, characterizing the vadose zone and understand soil permeability) and to identify anomalous zones of possible fundamental contamination, which we grouped into two (i) anomalous lithological surfaces that we considered permeable and migrating leachate from the waste dump and (ii) anomalous zones in the subsoil and groundwater possibly contaminated. The computed DRASTIC index is very high for the area covered by profiles 2 and 6 (156 - 165) given the proximity of groundwater to the contaminating surface and the surrounding area consisting of very conductive materials. On profile 5 area the index is very low (96) due to the strong resistivity of the surface layers and the high depth at which groundwater was detected (> 40m). The area of profile 3 (further north of the dump) has also a low index (105) due to its distance from the contamination source (dump) and the strong resistivity of the lithological layers, indicating low permeability, in addition to the great depth (> 40m) at which groundwater were detected. Concerning profiles 1 and 4, despite presenting permeable materials at the surface (low resistivities), groundwater level was recognized at greater depth (> 40m), DRASTIC risk index was lower (115 - 125) than expected. The overall value of the DRASTIC index for the surrounding area of Hulene - B dump was estimated at 127, which represents a low overall vulnerability. However, the high vulnerability index values for the area covered by profiles 2 and 6, and given their relatively higher surficial altitude, suggest a strong groundwater contamination by horizontal dilution of leachates from the whole area surrounding of the Hulene - B waste dump.