The management of wastewater issued from olive oil extraction (locally named margine), continues to cause enormous problems due to the great quantities annually produced, and the contamination risks related to their high level of pollution and toxicity. The nearness of Agareb zone to the main olive oil production zone of Sfax and the existence of clayey outcrops are the main factors influencing the choice of this zone for the implantation of a site for the margine evaporation. The investigation and sampling works developed on the site have established the geological, hydrogeological, geotechnical and environmental characteristics. The permeable silty and sandy layers in the site favorized the infiltration of margine through and below the storage basins. This infiltration is particularly observed in the south part of the site where it has reached a depth of 4m at a distance of 20 m laterally. The chemical analysis of the substratum and infiltrated margine showed that the latter constituted a polluting source, its acidity may affect physical and geotechnical clay layer properties and causes pollutant migration in the subsoil. The wastewater infiltration in the underlying layers has caused the dissolution of salts and the modification of pH, nutrients contents and phenolic compound concentrations. The geotechnical investigations conducted on the site showed the instability of the embankments slopes separating the margine storage basins and the presence of sliding which may cause margine flow out from the storage basins and consequently the spreading of pollution on great areas.

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Olive mill wastewater (OMW) is the most significant source of environmental pollution in Sfax, the main olive oil producing region of Tunisia. The management of OMW presents enormous problems due to the great quantities produced annually, its high organic content and toxicity. Storage of OMW in evaporation ponds has been used as a solution, but these ponds induce soil and groundwater contamination. This paper reports on an optimal approach to environmental management of OMW to selected disposal sites in the Agareb region of Sfax. The approach is based on the use of a geographic information system (GIS) and multi-criteria analysis. The GIS manages information describing the study area and offers spatial analysis operators for different environmental, social and economical factors. These multiple layers of information can be integrated in different combinations. Multi-criteria analysis methods are used to determine possible locations for OMW disposal sites (using an analytical hierarchy process) and eventually to select the best options.

In Tunisia, olive mill wastewater (OMWW) locally named ‘margine’ constitutes a serious problem due to its huge amount, of about one million ton per year, and the high pollutant load resulting in the excessive chemical oxygen demand (COD) values and the presence of phytotoxic and antibacterial polyphenols. The most common treatment of OMWW was storage in evaporation ponds which are authorized but uncontrolled. Thus, it represents a potential contamination source of natural resources (air, soil and water) via infiltration. This study aims at a critically analysing the OMWW storage management on the site of Agareb in Sfax, Tunisia. The data relating to the OMWW production highlights that it exceeds its storage capacity due to the uncomplete OMWW evaporation. The geotechnical investigations confirmed the spread of OMWW through and below the storage basins. Furthermore, multiple slope sliding has been observed within embankments separating the OMWW storage basins. Faced with this alarming situation, the assessment of the incorporation of geomembrane is analysed in order to ensure the sustainability of OMWW landfilling. The slope stability analysis based on limit-equilibrium method (LEM) using Midas-Soil works software was investigated. The use of geomembrane can secure the slope stability and limit OMWW infiltrations in the landfill body and sub-soils in the studied site.