Preliminary study on vulnerability to water pollution in the cobalt-nickel ore treatment area of the Ambatovy project, Toamasina Madagascar

This work is part of the global study on the vulnerability of the water resources to industrial pollution from the cobalt-nickel treatment carried out in the East coast zone of Madagascar, province of Toamasina. This paper shows the first chemical and physical field work result in 2015. The main purpose of the study is to characterize the groundwater and surface water flow, to identify the origin of the pollution due to the industrial activity process that could lead to the water quality degradation with respect to the hydrological aspect, the relationship between surface water and groundwater interaction. The chemical results show that around the cobalt-nickel treatment area (ITACN), in the southern part of the site, the groundwater has the highest concentration of sulphate ion, 300mg.L^-1, compared to that of North ITACN of which concentration is 60mg.L^-1. On the opposite the sulphate ion concentration is lower in the tailings, 45mg.L^-1. The respective electrical conductivity reinforces the latter results, since it is evaluated to 800μS.cm^-1 in the south ITACN and 70μS.cm^-1 in North ITACN, whereas it varies from 50 to 400μS.cm^-1 in the tailings. The Piper Diagram shows that groundwater and surface water have four facies. Firstly, most of the water samples have the calcium bicarbonate type (Ca-HCO₃) facies, particularly those collected downstream the tailings, those in the eastern part of the site and downstream the ITACN area. Secondly, one sample has the calcium and sodium bicarbonate type (Na-Ca-HCO₃) facies, upstream the south-west part of the ITACN. Thirdly, in the western part area of the ITACN, the groundwater sample has the sodium chloride type (Na-Cl) facies. And finally, the sulphated calcium chloride type (Ca-Cl-SO₄) facies is observed downstream the south of the ITACN and in the tailings. The relation between the major ions and electrical conductivity show that the sulphate ion controls the water mineralization around the ITACN in both surface water and groundwater. The natural purification system seems to work properly since the groundwater mineralization is decreasing along the direction of water flow from the ITACN treatment area towards the tailings area.