Assessment of the impact of lithology on the watertightness of aerated lagoon systems in a Sub-Saharan Africa environment: the case study of an oil factory company in two councils in the Littoral region of Cameroon

This study aimed to assess the impact of soil lithology in the watertightness of aerated lagoon systems in oil factory company in two councils (Dibombari and Edea 1st ) in the Littoral region of Cameroon. Primary data were obtained through sampling and analysing wastewater in the first basin, soils at various depths (3 m, 7 m, 15 m and 21 m) and groundwater after piezometers’ construction. Data processing involved several steps. Firstly, wastewater parameters were compared to soil parameters at three meters. Secondly, the evolution of soil parameters was analysed for each site by calculating pollutant reductions based on lithological sections. Finally, groundwater parameters from both sites were compared. The results showed that the lagoons systems with geotextile membrane, although quite effective, have shortcomings concerning in particular total nitrogen and phosphates. Due to its lithology, the Dibombari site provided better watertightness (final reductions ranging from 99.84% for total organic matter to 27.20% for sulphates) than that of Edéa (final reductions ranging from 97.25% for total nitrogen to 36.40% for sulphates). Laterites, clayed sands, and clays were the soil types with purifying and filtering qualities associated particularly to these reductions of nitrates and phosphates concentrations. Comparing the piezometers’ groundwater highlighted the superior water quality at the Dibombari site, whose characteristics are closer to natural raw water than those at the Edéa site. Combining these soil types with geotextile membranes during the construction of local lagoon basins could enhance water retention, directly protecting groundwater and indirectly offering opportunities for optimizing waterproofing technology.