Abstract: Ribeirão Preto Dumpsite: Environmental Problems and Solutions

Ferreira, Justo Camejo - Petrobras/Cenpes; João Álvares da Costa - University of Ribeirão Preto

Ribeirão Preto City, in the State of São Paulo, Brazil, is entirely dependent on the water stored in sands of the Botucatu Formation of the Paraná Basin. Despite this, a large dumpsite (sanitary landfill), now abandoned, was located near the city, in the recharge area of the aquifer, as shown in the illustration. It is estimated that 600,000 tons of domestic, industrial and hospital refuses were dumped there in a large pit left by the exploitation of sand and clay.

The purpose of this investigation was to appraise the environmental problems caused by the dumpsite and to propose solutions. The project was performed jointly by the Center of Excellence in Geochemistry (CEGEQ) of Petrobras' Research Center (CENPES) and the University of Ribeirão Preto (UNAERP).

Besides conventional hydrogeologic studies, about 60 physical and chemical parameters were determined in the water of each of the 18 monitoring wells and 10 water supply wells. New techniques were devised and employed.

The pit was excavated in low permeability Cenozoic sediments. However, it was deep enough to open a small "window" in the underlying Botucatu Formation, thus providing a preferential site for leachate percolation.

The water table of the aquifer is 40m deep in the dumpsite area. Upon reaching it, the leachate migrates S50°W, away from the supply wells.

The contamination is restricted to a short distance from the dumpsite, due to the relatively small speed of the water flow (10m/year).

It was concluded that the danger of contamination of the aquifer, particularly in the area of the supply wells, is extremely remote, since (1) the leachate is poor in contaminants; (2) the water is flowing in the opposite direction; (3) the leachate reaches the aquifer highly diluted by meteoric waters; and (4) the dilution increases in the aquifer by diffusion.

It was recommended (1) to pump and treat the more concentrated leachate from a few pockets in the dumpsite; (2) to drill an additional monitoring well; and (3) to reforest the area in order to create a public recreational park.

The recommended well was already drilled in the area of the anticipated plume of contamination. This well fully corroborated the interpretations. The aquifer water was found contaminated by the leachate. Besides several inorganic contaminants, a series of organic compounds was identified, inclusive drugs certainly sourced in hospital refuses.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil