(R> 0.94), to estimate the concentration of chloride ions as a function of the electrical conductivity of water in the study area. A geophysical survey was conducted through 34 Vertical Electrical Soundings (VESs) to calculate the water electrical conductivity from the interpretation of the apparent resistivity data. Twenty-nine VESs were used to relate the resistivity of the saturated formation (Ro) with that for the groundwater (Rw) by the linear equation Rw = 0.427 Ro + 1.987. Then, EC was estimated as the inverse of Rw. Finally, the chloride ion concentration was determined by the equation mentioned above. Following the same procedure for the five remaining VESs, which were acquired in places where there are no wells, the chloride ion concentration and the electrical resistivity of the saturated formation (Ro) and groundwater (Rw and its inverse EC) were obtained without requiring a destructive technique.

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Se reporta en este estudio la caracterización de una zona contaminada por lixiviados, siguiendo una metodología que integra datos geofísicos y geohidrológicos para proponer un modelo hidrogeológico del fenómeno. La caracterización del sitio (la estructura del subsuelo, y las características del suelo) incluyó seis perfiles sísmicos de refracción, tres líneas electromagnéticas (FDEM), dos perfiles eléctricos (ERT), cinco sondeos eléctricos verticales (SEV), y una serie de pruebas geohidrológicas para delimitar la pluma contaminante. El área de estudio corresponde a la laguna de lixiviados del relleno sanitario de la ciudad de Oaxaca, sur de México. El modelo hidrogeológico que se presenta constituye un ejemplo del potencial de la integración de varios métodos aplicados con el mismo objetivo; reduciendo así la ambigüedad de la respuesta geofísica. Los resultados indican que los valores de baja resistividad (1.5 a 2.5 Ohm-m) se relacionan con un suelo contaminado subyaciendo a la laguna de lixiviados y al medio fracturado. También se detectó un desplazamiento de la pluma contaminante hacia el SW de la laguna. La calidad del agua es buena, pero la actividad humana en el área de estudio confiere un riesgo para el acuífero superficial de Zaachila.

A study of the fracture systems in the basement of the Matatlan urban waste dump of Guadalajara City, near the western edge of the Rio Grande de Santiago canyon (southwestern Mexico), is reported. The Matatlan dumpsite was developed on top of andesitic and rhyolitic rocks. Measurements at outcrops indicated that N–S (0°–15° and 165°–180°), N45–90E and N105–135E fracture systems affect the basement. Statistical analysis (micromagnetic method) of magnetic lineament azimuths indicated the presence of two lineament groups. The major one (N60–120E) has a maximum at N90–105E, and a secondary group (N120–165E). The gravity anomalies are featured by a major group (N60–120E, with maximums at N60–75E, and N105–120E) and a secondary group (N120–180E). Thus, a good to fair correlation exists between the measured fracture orientations and the lineaments featuring the gravity and magnetic anomalies. Horizontal derivative and tilt angle depicted horizontal limits of anomaly‐causative bodies. Results of the micromagnetic method are consistent with fracture orientations and with the limits established through edge‐detection techniques. Lineaments established by means of the gravity and magnetic Euler deconvolution are also consistent. Gravity and magnetic Euler deconvolution helped to estimate the depth extent of the limits of gravity and magnetic common sources. Euler deconvolution indicated the fault or contact nature of these lineaments. Furthermore, Euler deconvolution indicated slopes of the limits of gravity and magnetic sources. The fault or fracture nature of the major lineaments was finally confirmed by forward modelling (forward 2D cooperative modelling of gravity and magnetic profiles). For example, lineaments delimiting the northern depression could be characterized as normal faults. In general, this study indicates that it is possible, based on gravity and magnetic data, to characterize fractures affecting the basement of a dumpsite, a key parameter in hydrogeophysical studies. In particular, through this study, the inferred structures could be associated with regional tectonic faulting, which might provide migration paths to unhealthy lixiviate outside the dumpsite, giving rise to the contamination of the neighbouring environment. In particular, the study explains the presence of an unhealthy leachate waterfall to the northeast of the dumping site. Heavy metal contents in samples from this waterfall support that lixiviates originate at the dumpsite.

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