The main landfill in the city of Rabat (Morocco) is based on sandy material containing the shallow Mio-Pliocene aquifer. The presence of a pollution plume is likely, but its extent is not known. Measurements of spontaneous potential (SP) from the soil surface were cross-referenced with direct measurements of the water table and leachates (pH, redox potential, electrical conductivity) according to the available accesses, as well as with an analysis of the landscape and the water table flows. With a few precautions during data acquisition on this resistive terrain, the results made it possible to separate the electrokinetic (~30%) and electrochemical (~70%) components responsible for the range of potentials observed (70 mV). The plume is detected in the hydrogeological downstream of the discharge, but is captured by the natural drainage network and does not extend further under the hills.

In many parts of the world, the impact of open landfills on soils, biosphere, and groundwater has become a major concern. These landfills frequently generate pollution plumes, the contours of which can be delineated by non-intrusive geophysical measurements, but in arid environments, the high soils resistivity is usually an obstacle, which results in the low number of studies that have been carried out there. In addition, such prospecting using geophysical techniques do not provide information on the intensity of the processes occurring in the water table. This study was carried out on an uncontrolled landfill in the arid Tadla plain, Morocco’s main agricultural region. A survey based on geo-referenced spontaneous potential measurements was combined with measurements of anoxic conditions (Eh-pH and O₂ equilibrating partial pressure) in the groundwater and leachates, in order to highlight a pollution plume and its geometry. The range of spontaneous potential measurement is wide, reaching 155 mV. Ponds of leachate with high electrical conductivity (20 to 40 mS cm⁻¹) form within the landfill, and present very reducing conditions down to sulphate reduction and methanisation. The plume is slowly but continuously supplied with these highly reducing and organic carbon-rich leachates from the landfill. Its direction is towards N-NW, stable throughout the season, and consistent with local knowledge of groundwater flow. The fast flow of the water table suggests pollution over long distances that should be monitored in the future. The results obtained are spatially contrasting and stable, and show that such techniques can be used on a resistive medium of arid environments.

The delineation of pollution plumes generated by household waste landfills is not easy, particularly in the case of discontinuous or intricately extending water tables, such as those developed in a fractured crystalline bedrock context. In Ouagadougou (Burkina Faso), there are many uncontrolled landfills throughout the urban area. The water table, generally located between 3 and 10 m deep, is likely to be contaminated by the leachate from these landfills. More than 1000 measurements of spontaneous potential (self-potential), referenced by GPS, have been carried out on a landfill and its immediate surroundings to the south of the urban area. The geostatistical processing by analysis of variograms and correlograms highlights an adapted prospecting technique and reliable cartography. The response seems to be mainly due to the electrochemical component with hot spots within the landfill and a plume heading towards the North-East. The distribution of the spontaneous potential seems to be controlled, not by the topography of the site, but by the fracturing of the mother rock of dominant direction 15° N, and by the mother rock/saprolite contact. Thus, the plume does not flow to the market gardening just below the landfill but rather to a residential area where monitoring of the quality of the borehole water is required.

Un vertedero de 110 ha, ubicado sobre el acuífero superficial de Akrach en Marruecos, ha sido estudiado para caracterizar la calidad de las aguas subterráneas alrededor del vertedero, conocer la extensión del área contaminada y estudiar los factores involucrados en esta contaminación. El vertedero se emplazó en la ciudad de Um Azza (15 km al sur de Rabat), entre el rio Akrach, al oeste, y la represa Sidi Mohaed Ben Abdallah, al este. Un control piezómetro y análisis químicos se hicieron sobre 22 pozos para estudiar esta contaminación. La calidad del agua es afectada por una contaminación importante, especialmente en las áreas al contacto cercano del vertedero, y aguas abajo de este mismo. En las zonas afectadas la conductividad eléctrica de las aguas supera 1100 µS.cm-1, los bicarbonatos superan 508 mg.L-1 , los cloruros, sulfatos y nitratos superan 850,200 y 1 mg.L-1. Además se consiguió alto contenido en cadmio (50-100 µg.L-1) y cromo (40-230 µg.L-1). En definitiva, se superaron olgadamente los valores estipulados en las normas de la OMS para el agua potable y de riego. Un análisis en componentes principales se llevó a cabo sobre el conjunto de datos. No aparece un eje factorial consistente, sino más bien muchos ejes de importancia similar, lo que muestra un conjunto de mecanismos de la misma fuerza involucrados en la calidad química de las aguas contaminadas. Una clasificación jerárquica ascendente da tres grupos de muestras, cada grupo corresponde a un nivel de contaminación.