R. Lovera

Use of electrical tomography methods to determinate the extension and main migration routes of uncontrolled landfill leachates in fractured areas.

This study focuses on the uses of the electrical tomography and its relationship with hydrochemical data in order to characterize contaminated groundwater flows in fractured aquifers. The studied area is contaminated with different hazardous substances like lyndanes, organochlorinated compounds and benzenes coming from the old non-controlled Sardas landfill. The enormous volumes of wastes filling the landfill have generated a convoluted mixture of leachates. Due to the lack of a landfill liner, the leachates have migrated through the fractured Eocene marls towards the Gallego River. The striking correlation between high concentrations of polluted groundwater and low electrical resistivity of the subsurface (<8Ω·m) allows defining the principal contaminant migration route thanks to the distribution of these conductive anomalies. This mapping verifies that there is intense tectonical-structural control of the leachate migration, because the deep migration presents the same direction as the geological axis fold.

Geophysical exploration on the subsurface geology of La Garrotxa monogenetic volcanic field (NE Iberian Peninsula)

We applied self-potential (SP) and electrical resistivity tomography (ERT) to the exploration of the uppermost part of the substrate geology and shallow structure of La Garrotxa monogenetic volcanic field, part of the European Neogene–Quaternary volcanic province. The aim of the study was to improve knowledge of the shallowest part of the feeding system of these monogenetic volcanoes and of its relationship with the subsurface geology. This study complements previous geophysical studies carried out at a less detailed scale and aimed at identifying deeper structures, and together will constitute the basis to establish volcanic susceptibility in La Garrotxa. SP study complemented previous smaller-scale studies and targeted key areas where ERT could be conducted. The main new results include the generation of resistivity models identifying dykes and faults associated with several monogenetic cones. The combined results confirm that shallow tectonics controlling the distribution of the foci of eruptive activity in this volcanic zone mainly correspond to NNW–SSE and accessorily by NNE–SSW Neogene extensional fissures and faults and concretely show the associated magmatic intrusions. These structures coincide with the deeper ones identified in previous studies, and show that previous Alpine tectonic structures played no apparent role in controlling the loci of this volcanism. Moreover, the results obtained show that the changes in eruption dynamics occurring at different vents located at relatively short distances in this volcanic area are controlled by shallow stratigraphical, structural and hydrogeological differences underneath these monogenetic volcanoes.

Hydrogeological and geophysical characterization of fractured aquifer of Òdena (Barcelona, Catalunya)

Summary The results of the geophysical survey reflects the presence of heterogeneity distribution of electrical resistivity values. This allowed to delimit the geometry of the three layers, as indicated by borehole logging. At the same time, it has been possible to highlight several zones with low electrical resistivity values in the central part of some profiles. These have been considered as fractured areas. In many cases, these areas of low resistivity fractures coincide with areas where the wells have registered low values of the electrical conductivity. This fact reveals the effect as preferential flow areas that have these fractures throughout the circulation system of the contaminant.

Conceptual Model for Exploring Geothermal Resources in La Seva Basin (NE Spain) from Integrated Geophysical Data

An integrated geophysical interpretation has been conducted around La Selva basin that show strong geochemical and geologic evidences of hydrothermal with the intent of define a conceptual model for exploration of low and intermediate enthalpy geothermal resources. The geophysical data involved in this study consist of gravity, magnetic and geoelectrical, supplemented by geological and hydrogeochemical information. The interpretation of gravity anomalies has been useful for defining the main structural discontinuities, magnetic map show the existence of several anomalies related to mafic intrusions while geoelectrical prospecting let delineate more conductive areas which could correspond to an increase in thermal fluid circulation. The results obtained by the different geophysical methods are in good agreement and allows defining a reliable geostructural model of the subsurface of the studied area.

Geophysical Evaluation of the Volume of a Mine Tailing Dump (Osor,Girona,NE Spain) Using ERT

Mine tailing ponds are environmentally hazardous because of high susceptibility to leaching and erosion by water and wind. In this study we demonstrates the usefulness of electrical resistivity tomography for assessing volume and internal structure of mine tailing ponds in abandoned Osor mine as significant information for decision-making measures of environmental protection.

ERT monitoring the effects of irrigation with a blend of desalinated/brackish groundwater on an instrumental plot

Desalinated brackish groundwater is becoming a new source of water supply to comply with growing water demands, especially in (semi) arid countries. Irrigation with desalinated or a blend of desalinated and ground/surface water, presents associated impacts on plants, soil and aquifer media. Mixed waters with different salinities can lead to the formation of unexpected chemical precipitates. The use of desalted groundwater for irrigation counts with potential drawbacks, among them: changes of hydraulic properties of soil-aquifer systems (e.g. hydraulic conductivity, porosity) as a consequence of mineral precipitation; root growth blockage and plant uptake of pollutants; as well as leaching of contaminants to groundwater. An experimental plot located at SE Spain, covered by grass and irrigated by sprinklers with a blend of desalted and groundwater from a brackish aquifer has been monitored in order to characterize at field scale the possible impacts on soil hydraulic properties.

Structure of the Pliocene Camp dels Ninots maar-diatreme(Catalan Volcanic Zone, NE Spain)

Maar volcanoes expose shallower or deeper levels of their internal structure as a function of the degree of erosion. In El Camp dels Ninots maar-diatreme (Catalan Volcanic Zone, Spain), the tephra ring has been largely eroded, and the remaining volcanic deposits infilling the diatreme are hidden under a lacustrine sedimentary infill of the crater. The volcano shows hardly any exposure, so its study needs the application of direct (e.g., boreholes) and indirect (shallow geophysics) subsurface exploration techniques. Additionally, this maar-diatreme was built astride two different substrates (i.e., mixed setting) as a result of its location in a normal fault separating Neogene sediments from Paleozoic granites. In order to characterize the internal structure and post-eruption stratigraphy of the maar-diatreme, we did geological studies (mapping, continuous core logging, and description of the tephra ring outcrops) and near-surface geophysics, including nine transects of electric resistivity tomography and a gravity survey. Results show that the deeper part of the diatreme is excavated into granites and is relatively steep and symmetrical. The uppermost diatreme is asymmetrical because of mechanical contrast between granites and Pliocene sands. The maar crater contained a lake permanently isolated from the surrounding relief and was deep enough to host anoxic bottom waters while its margins had shallower waters. These lake conditions preserved the remarkable Pliocene fossil record found in the lacustrine sediments.