Contaminación de un acuífero por metales pesados de origen geogénicoimportancia del control hidrogeológico de los sondeos de captación de aguas

Zusammenfassung

This paper presents a problem of domestic water supply contamination. The water comes from drilled holes in a terrigenous aquifer located above a marly and carbonate formation, with black shale levels. Water contains an abnormally high quantity of suspended solids whose chemical composition is characterized by high concentrations of heavy metals. The water also presents some dissolved metals with concentrations slightly higher than the maximum admissible for drinking water. Since the boreholes, drilled without hydrogeological criteria, crossed not only the aquifer formation but also part of the underlying one, it is suggested that the materials in suspension in the water have their origin he black shale levels. Therefore, in addition to the particles in suspension, samples of the black shales outcropping in nearby areas were analyzed, as well as the cuttings from one of the wells. The analytical results show a very similar pattern in the composition of all solid materials although the concentration of metals in the material in suspension is much higher than in the other samples.