A local case study for the environmental impact of landfill leachate on groundwater quality along and across the Mediouna landfill is presented, based on physicochemical and statistical approaches. The landfill has been operational since 1986 and it receives municipal solid wastes produced by the city of Casablanca, whose the daily waste output exceeds 4000 t. This waste is stockpiled in old sandstone quarries; the site has never been sealed before its opening. The aim of this study is to update the knowledge about groundwater quality around the landfill, to determine the factors controlling the extent of groundwater contamination and compare the results with those of 1989 and 2001. To evaluate groundwater pollution due to this landfill, piezometric level and geochemical analyses have been carried out on 19 wells. The physicochemical data of groundwater down-gradient of the landfill site is showing a deterioration of its quality, to the point that the wells have become unusable. The statistical treatment of physicochemical data by principal components analysis allowed the mapping of three areas downstream of the landfill. The first is hardly polluted, the second is moderately polluted and the third is characterized by mineralization through their waters and the almost absence of organic matter. The extent of groundwater contamination from an area with a radius of 200 m in 1989, to an area with a radius of about 1 km in 2001 to more 2 km as of today. This extension is controlled by the structural factor of faults, by the lithology of aquiferous and the intensity of water pumping; the wells equipped with pumps exert pressure against the advanced front of the pollution.
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