Mapeamento da vulnerabilidade e análise de risco de contaminação como instrumentos de proteção das águas subterrâneas em áreas industriais: caso ALBRAS, Barcarena-PA.

Abstract

This work was made in the Solid Waste Disposal Site (SWDS) at the Alumínio Brasileiro S.A. Industry (ALBRAS)., in the town Barcarena, State of Pará; Northern Brazil. The principal objective was to find the main physical properties of the unconfined aquifer its natural vulnerability to contamination and the risk of contamination of the studied aquifer. To know and understand the local hydrogeology, were made manual bore holes, grain size analyses and a pumping test, were made as well as interpretation of geotechnical bores profiles. The natural vulnerability of the unconfined aquifer was determined by the GOD and DRASTIC methods, based basically on water depth, type of aquifer, lithology, characteristics of non-saturated zone, hydraulic conductivity, topography and aquifer recharge. The local assessment of contamination risk considered the risks to environmental resources and public health. The studied aquifer is unconfined, and the vadose zone consists of unconsolidated silty-sand, silty-sand-clay sediments, with creamy yellow and orange till light gray colors, badly sorted and sub-angled. The hydraulic conductivity is approximately 10“cm/s. In the rainy season the water level reached from O to 5,1 meters depth. The transmissivity, obtained by pumping test of short time, is estimated in 43.92 mí/day. The net recharge showed an infiltration rate of 115.58 mm/year. The unconfined aquifer vulnerability, obtained through the GOD method, ranged between high and moderated levels; and by the DRASTIC model, the vulnerability index ranged between 118 and 141. Although these numbers do not imply an intrinsic value, they could be extrapolated by the comparison with DRASTIC index of others regions. The index of all hydrogeologic environments studied by the method authors in the United States range between 65 and 223. Therefore we can consider the index of the current study area moderated (128) until high (151), considering the environment constituted by unconsolidated sediments. The natural groundwater vulnerability assessment in areas with small extension as in SWDS was better 4 applied throughout the GOD Method than by the DRASTIC Indexes. Mainly because the first one apply less parameters than the second one; e.g. litology of non-saturated zone, recharge net and hydraulic conductivity, which show little or any difference in its values in an area with 5 km”, presenting not very important for the final vulnerability indexes. The final value obtained for the risk contamination was bellows the critic index of 200.