Geoelectrical characterization of the Hydrogeological System in the part west of the Potiguar Basin applying the Vertical Electric Sounding method

This work presents a the results of a research project that it had as motivation to obtain a better knowledge of the Hydrogeological System of the Chapada do Apodi, which is an area in the which the federal and state governments are implementing important irrigation projects whose the viability and success are directly related with the considerable volumes exploitation warranty of physicalchemistry good quality groundwater. It has been intensive the increasing of drinking water supply coming from the regional aquifers Alluvium, Jandaira and Açu, This continuous withdraw has resulted in such problems as the decline of the groundwater levels in the regional aquifers. It is known based on previous hydrogeological studies in the Potiguar Basin that the Açu Formation presents outstanding lithologic and hydrologic heterogeneities that should be taken in account in groundwater exploitation for domestic, agricultural or industrial uses. Previous geophysical studies in others areas of the Potiguar Basin used the Electrical Resistivity method, however in the area studied in this work that corresponds to the Medio-Baixo Jaguaribe where the Açu Formation recovers an area of 1.100 km2 they were not still accomplished geophysical studies and consequently one doesn't know your thickness. Due to this fact the research project had as objective to obtain a geoelectrical model of the subsurface that describes in depth the stratigraphic sequence and its lateral variation along some profiles, identifying the Açu and Jandaira Formation’s thickness in the Medio-Baixo Jaguaribe's central portion that is localized in the west part of the Potiguar Basin. As it intended to map in depth the stratigraphic sequence the electrical resistivity survey was carried out using the Schlumberger configuration array. In the study area the crystalline basement is at the depth that varies from -100 m to –300 m in relation to the sea level, consequently the 23 vertical electric soundings (VES) stations were made and interpreted using the array of current electrode up to a maximum spacing AB/2 of 1 km. For the computational processing of the field data it was applied “ridge regression” inversion outline and used as priore information a lithostratigraphic log profile of a 250 m deep well. The results obtained by the geophysical investigation are analyzed and interpreted in terms of a hydrogeologic model of the deep regional Açu Aquifer.