Ana Copat Mindrisz

The contamination of underground waters by hydrocarbons originated from gas stations has been object of increasing preoccupation in environmental organization all over the world. The organic compounds Benzene, Toluene, Ethylbenzene and Xylene (BTEX), present in these fuels, are extremely toxic to human health and could make impracticable the exploration of these contaminated waters by these kinds of pollutants and consequently the gasoline wells used for this purpose. In this work, it was carried out a diagnosis of the water quality with information and analyses, with the goals to snap shot the situation of the wells destinated to domestic and commercial supply of water in the urban area of Santo André city, São Paulo state. There have been evaluated the presence of micron pollutants BTEX, after contamination due to leaks in fuel storage tanks close to the wells, in different places of the city. The physical chemistry parameters like color, turbidity and residual chlorine were also evaluated as well as trace elements, metals, anions like fluorine, sulphates, chlorine, nitrates and phosphates and bacteriological (total coliphorms, themostable coliphorms, heterotrophic bacterias). On definition of the sampling area, it was sought, at first, the evaluation of environmental contaminations historical series by gas stations, evaluating the set of information available at government environmental organizations and spacial representativety of the problem. For administration of the underground water quality it was adopted the methodology used by Companhia de Tecnologia de Saneamento Ambiental (CETESB), being accomplished a previous identification of contamined potencial areas and organizing a data base on landfills disposal and negleted places; registration of gas station services and, wells used by the population, industrial inventory with active and negleted maps taking into consideration the size and residues generation (such as SEMASA), prioritizing in this way the monitoring places. It was made registrations of places and preliminary investigation of suspicious areas was accomplished. The sampling and monitoring were carried out and the results were compared with the standard values for underground water that are established by CETESB. The results showed that in the twelve wells evaluated were not found values of BTEX above the recommended by Law 518/2004 of the Health Ministry in which the allowed value for benzene is 5 µg L-1. It was observed that three of the twelve wells studied were contamined with nitrate, which is responsible for Methemoglobinemia induction. They were appraised also the processes or mechanisms of natural (biodegradation) or induced remediation.

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