GEOELECTRIC EVALUATION OF SUBSURFACE CONTAMINATION AT A GAS AND SERVICE STATION, ALAGOINHAS, BA, BRAZIL

Abstract

This work contains the results of geoelectrical soundings performed around the Lubrijau Gas and Service Station, in Alagoinhas County, Bahia State, Brazil. A total of 56 vertical electrical soundings (VES) were conducted along five parallel lines using a Schlumberger electrode array with a maximum AB/2 spacing of 300 m. The aim was to define the structure of the Marizal-São Sebastião aquifer system found below the area, as well as to evaluate the status of eventual contamination, caused either by fuel leaks or improper sewage disposal practices. Data were interpreted as one-dimensional sounding curves and as two-dimensional resistivity sections using both public domain (RESIST 1.0 and RES1D) and commercial (RES2DINV) softwares. The interpreted results have shown that: (i) the groundwater flow under the area is directed from NW to SE; (ii) the static water table lies from 30 to 45 m in depth; (iii) the depth to the contact between the Marizal and SËœao SebastiËœao formations exceed 45 m; and (iv) there is a conductive plume (Ï < 300.m) in the subsurface, outlined as an ellipsoidal body extending to SE, having a length of about 850 m and a width of 600 m along its maximum spread. This plume has not yet reached the water well situated about 550 m from the gas station.