Assessment of the Potential Pollution of the Abidjan Unconfined Aquifer by Hydrocarbons

A study of the unconfined Continental Terminal aquifer in Abidjan District, located in a coastal sedimentary basin in Southern Côte d’Ivoire (West Africa), is conducted. This aquifer is the principal source of drinking water for the city of Abidjan. The water quality of the aquifer is affected by anthropogenic sources of pollution, such as scattered deposits of solid and liquid waste of all kinds. Additionally, the proliferation of gas stations, including potential tank leakage, must be considered in the event of an accident. To ensure the effective protection and management of the Abidjan groundwater, this work assesses the groundwater contamination risk of the Abidjan aquifer by hydrocarbons such as benzene. To achieve this objective, a numerical groundwater model that included the geological and hydrogeological data of the Abidjan aquifer was constructed with FEFLOW 7.1. A predictive simulation of groundwater flow coupled with the transport of dissolved benzene deposited on the soil surface at the N’Dotré and Anador gas stations was performed. The initial concentrations of dissolved benzene were 43.12 mg/L and 14.17 mg/L at the N’Dotré and Anador sites, respectively. The results revealed that a threshold concentration of 0.001 mg/L was reached after 44 years and two months at borehole ZE11, which is located four kilometers downgradient from the source. The maximum peak concentration of 0.011 mg/L was reached at this point after 47 years and two months. In this region, 14 other boreholes could be threatened by dissolved benzene pollution based on the simulation.