ACCESSIBLE GEOPHYSICAL METHODS TO INFER SUBSURFACE FLUID SATURATION: AN EXAMPLE FROM NORTHERN ECUADOR

Geoelectrical and electromagnetic methods enable investigation of subsurface structures and their physical parameters. Equipment for these methods are often costly and hard to access. This study points out collaborative access to and ground-up implementation of equipment used to study underground fluid saturation. The set-up consists of an electrical resistivity-meter (ERM) and a ground-penetrating radar (GPR) with which we surveyed the surroundings of a septic pool within a recent public development zone in northern Ecuador. The ERM vertical electrical sounding results were translated to two two-dimensional electrical resistivity tomography pseudosections using constant separation traversing and inversion models. Each pseudosection belonged to a location around the pool, upslope or downslope. These results were later compared to the GPR radargrams in the same locations, surface vegetation patch observations and the inferred position of pipelines draining into the pool. We found that zones of high electromagnetic reflectivity matched the surface observations of vegetation and were portrayed with precision by the ERM as zones of high electrical conductivity. We infer that these zones are characterized by a generalized subaerial leak leading to fluid saturation. The surveys showed that saturation areas follow a downslope path surrounding the pool, matching spatially with areas where vegetation is more prominent.