Natural Vulnerability Assessment to Contamination of Unconfined Aquifers by Longitudinal Conductance – (S) Method

Given the importance of the groundwater for diverse uses, particularly the public supply, and considering the increasing impacts on underground reserves as a result of overexploitations, as well as the degradation of the water quality by anthropogenic activities, it becomes essential to establish tools for planning and management of the use of groundwater resources. For this reason, the aim this paper is to assess the natural vulnerability to contamination of the Bauru Aquifer System, in the South-Central region of the State of São Paulo, Brazil. Therefore, a vulnerability map was generated by using the (S) method, a new proposal developed to estimate the vulnerability by means of the Dar Zarrouk parameter - longitudinal conductance (electrical resistivity method). The vulnerability classes were defined using values ranges of longitudinal conductance: from very low (> 2.5 siemens) to extreme (< 0.1 siemens). In applying this methodology in the unsaturated zone, the electrical resistivity of the first layer of the saturated zone was used, seeing that the materials of both zones are similar in the study area. The application of the (S) method produced good outcomes, generating a more detailed map, with greater classes variability that indicate the sensitivity of this method, predominating regions with low vulnerability, and secondly, moderately vulnerable areas.