Impact of Past Mining Activity on the Quality of Water and Soil in the High Moulouya Valley (Morocco)

Physical and chemical properties and the total content of potentially toxic metals (PTMs) in waters and soils were studied from the High Moulouya Valley (Morocco) in order to assess the impact of the past mining activity on their quality and to lay the foundations of a potential reclamation of the area. Surface water and groundwater samples were collected from the Moulouya River and mine pit lakes; tailings and soils were sampled inside and outside the mine sites of Zeïda, Mibladen, and Aouli. Both waters and soils were alkaline, due to the limestone environment, and contained Pb and Zn as main metallic contaminants. Pollution levels were highest within the Mibladen mining site, and soil pollution was mainly restricted to the areas where activities of metal concentration were carried out. Tailings and soils from these areas besides Pb and Zn were also polluted by As, Cd, and Cu showing clay fraction highly enriched in metal contaminants. At the time of study, all soils and wastes (including the highly polluted tailings) were in advanced stage of spontaneous herbaceous and arbustive revegetation. It is concluded that, in the High Moulouya Valley, the processes governing PTM transfer from the element-rich sites to the nearby environment are strongly influenced by pH, carbonate content, and semi-arid climate reducing metal mobility from the mining waste impoundments by dissolution. The transfer by wind and water erosion of metal-enriched fine waste particles is likely to be a much more important vector for metal dispersion. In this perspective, among a range of land remediation techniques available, natural and oriented revegetation could represent a low-cost and possible permanent solution.