Vulnerabilidade e risco à poluição do sistema aqüífero – entre Crato e Missão Velha, bacia do Araripe, Ceará

Abstract

It is increasing in the entire globe, the preoccupation with the environment, where we emphasize in this work the preoccupation with the vulnerability and risk to pollution of Medium Aquifer System in the region between Crato and Missão Velha towns, Cariri Valley, Araripe Basin, Ceará. The studied area is located at the south portion of Ceará State, in the basis of Araripe Plateau, which influences very much its weather. The access, from Fortaleza, can be done by terrestrial through the BR-116 or CE-060 highway, known as cotton road, and by aerial way. The objective of the work is to evaluate the vulnerability and risk to pollution of Medium Aquifer System. The methodology adopted is basic, divided in six stages: literature revision, elaboration of a well archive of the area, confection of preliminary maps, field stages, treatment and integration of data. The water supply on the area is in almost entirely done by groundwater. In the southern region of Ceará is situated one of the best Aquifer Systems that is the Medium Aquifer System, target of the research. The formation of Araripe Basin began at the Paleozoic going until the Mesozoic, where it has from the bottom to the top the following geologic formations: Mauriti, Brejo Santo, Missão Velha, Abaiara, Rio da Batateira, Santana, Arajara and Exu. Starting by the characterization of the geologic formations, the inaccurate description of most part of the geologic sections of the drilled wells and the shallow depth reached by the wells, it was adopted the following hydrogeologic division in Araripe Sedimentary Basin: Superior Aquifer System (Exu and Arajara Formations); Santana Aquiclude; Medium Aquifer System (Rio da Batateira, Abaiara and Missão Velha Formations); Brejo Santo Aquiclude; and Inferior Aquifer System (Mauriti Formation and bottom part of Brejo Santo Formation).The methodology adopted to the elaboration of the vulnerability and natural risk map of the Medium Aquifer System was the GOD, where is used three basic parameters: “G” aquifer condition (free, semi-confined, confined or there is no aquifer); “O” global characterization of the aquifer in relation to consolidation degree and lithologic nature (of the unsaturated zone); and “D” depth until the freatic level or confined aquifer top (unsaturated zone). The indices of the vulnerability of Medium Aquifer System had varied of Negligível the Extremity of vulnerability, being in the generality of Negligível and Baixa, explained for the occurrence of argillaceous layers giving a bigger natural protection to the system. The elaboration of the map of natural vulnerability the contamination facilitated the identification of the areas more or less susceptíveis to the contamination. The polluting load risk was taken in consideration to the number of some potential activities of pollution, not taking in consideration the amount of polluting loads, being possible to make a comparative degree of risk between the cities. The area of the city of Juazeiro do Norte is the one that presents a bigger risk of contamination for presenting zones of High vulnerability and raised loads of pollutants, followed of Barbalha, Crato and Missão Velha.