Ground Water Pollution With Chromium in Leon Valley, Mexico

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Abstract
Groundwater contamination by chromium has been detected in the Leon valley central Mexico. In order to determine the contaminant concentration levels and to find its source, a sampling and analysis program was developed. The analytical determinations of chromium and physico-chemical parameters, in a known hydrogeological framework, allowed the identification of three sources of chromium, two of them anthropogenic and one natural. The anthropogenic sources are: the inadequate solid wastes disposal by a chromate factory, which produces high localized concentrations (up to 50mg/l) in groundwaters to the southwest of the valley; and residual ashes produced in brick manufacturing which generates much lower concentrations (lower than 0.05 mg/l of hexavalent chromium) over a much wider area (about 180 km2) south of Leon city. The natural source is weathering of ultramafic rocks which produces detectable amounts (between 0.004 and 0.015 mg/l) of Cr (VI) in groundwaters to the Northeast of the valley. Although the city of Leon is one of the main shoe-manufacturing centers of the country, surprisingly tanneries did not add much chromium to groundwaters.