Correlation of Boreholes through Well Logs: Application to the Western Sector of Madrid.

This study correlates the results obtained from the resistivity and spontaneous potential well logs in six boreholes for water extraction, located in the multilayer siliciclastic basin in the Madrid region, in the center of the Iberian Peninsula. Given the small lateral continuity that the layers considered in isolation show in this type of multilayer aquifer, geophysical stretches, with their corresponding average lithological assignments, have been established to achieve this objective from the well logs. These stretches allow for mapping the internal lithology in the studied area, obtaining a correlation of greater geological scope than that provided by the correlation between layers. Subsequently, the possible correlation of the lithological stretches selected in each of the boreholes was analyzed, verifying their lateral continuity and establishing an NNW-SSE section in the study area. In this work, the transcendence of the correlation of wells up to great distances (about 8 km in total, and average distance of 1.5 km between wells) is focused on the fact that, if there is a presence of pollutant in certain aquifer stretches in a part of the studied area, overexploitation in the Madrid basin will cause the mobilization of this pollutant to the whole basin, with a possible impact on non-polluted areas.

A Different Processing of Time-Domain Induced Polarisation: Application for Investigating the Marine Intrusion in a Coastal Aquifer in the SE Iberian Peninsula.

This study presents the developments regarding the time-domain induced polarisation method as a supporting tool for resistivity soundings during investigations of coastal detrital aquifers that are salinized by marine intrusion. The interpretation of resistivity measurements in such aquifers, which have variable hydrochemistry and lithology, involves uncertainties owing to the presence of low-resistivity lithologies, such as clays. To reduce these uncertainties, the use of other geophysical parameters is necessary; hence, this study focuses on induced polarisation since it can be measured simultaneously with resistivity. In detail, we propose the determination of induced polarisation using 1D techniques while developing a different algorithm for processing the induced polarisation data. The aim is to extend the results of this phenomenon, using, instead of chargeability, the concepts of polarisability and decay time, which are extracted from the decay curve, given that they represent more intrinsic properties of the various analyzed subsurface media. Results were obtained by applying this methodology to a Quaternary aquifer of the Costa del Sol in the SE Iberian Peninsula (in the province of Almería) during two different campaigns, one in mid-autumn and one late winter (i.e., in October and February, respectively) are presented. The results reveal the position of the saline front during each campaign while reflecting the seasonal movement of the marine intrusion.

Optimization of Dominant Frequency and Bandwidth Analysis in Multi-Frequency 3D GPR Signals to Identify Contaminated Areas.

Ground-penetrating radar (GPR) has been widely used in investigations of contaminated areas because of its sensitivity to variations associated with the nature of pore fluids. However, most of the studies were usually based on the visual interpretation of radargrams or on a time domain amplitude analysis. In this work, we propose a methodology that consists of analyzing the spectral content of the signal recorded in multi-frequency 3D GPR profiles. A remarkable advantage of this type of antenna is its step-frequency system, which provides a much wider emission spectrum than the one corresponding to conventional single-frequency antennas. From the data in the frequency domain, the dominant frequency and bandwidth were calculated as parameters whose variation could be related to the presence of light non-aqueous phase liquid (LNAPL) in the subsurface. By analyzing the variations of these two parameters simultaneously, we were able to delimit the contaminated zones in a case study, associating them with a significant shift of the frequency spectrum with respect to the average of the study area. Finally, as a validation method of the proposed methodology, the results of the frequency analysis were compared with resistivity data obtained with an electromagnetic conductivity meter, showing a very good correlation between the results.

Fuzzy Logic Tools Application to the Characterization of Stress-Strain Processes in Waste Construction Dam Geopolymers: A New Circular Mining.

The ceramics industry dedicated to the manufacture of building materials is a very significant cause of environmental pollution, and various research projects are being carried out to reduce the associated environmental impact. One of the most important research lines is the generation and development of new materials, from waste, through more sustainable production processes. All of this is framed in circular mining. In this research study, geopolymers were developed with biomass bottom ashes and brick dust in order to replace the traditional ceramics used to construct bricks. For this, different families of test tubes were formed with different percentages of both residues, and their physical and mechanical properties were studied. In this way, the properties of geopolymers could be compared with traditional ceramics. In addition, in order to determine the cause-effect relationships between physical properties and compressive strength, data were processed using fuzzy logic and data mining techniques. The results showed the feasibility of geopolymers generation with biomass bottom ashes and brick dust with acceptable properties to replace conventional ceramics. In addition, the fuzzy logic analysis allowed for establishing clear and objective relationships between the physical properties and the compressive strength of the geopolymers, with the aim of developing the highest quality geopolymer.

Acid Mine Drainage as Energizing Microbial Niches for the Formation of Iron Stromatolites: The Tintillo River in Southwest Spain.

The Iberian Pyrite Belt in southwest Spain hosts some of the largest and diverse extreme acidic environments with textural variation across rapidly changing biogeochemical gradients at multiple scales. After almost three decades of studies, mostly focused on molecular evolution and metagenomics, there is an increasing awareness of the multidisciplinary potential of these types of settings, especially for astrobiology. Since modern automatized exploration on extraterrestrial surfaces is essentially based on the morphological recognition of biosignatures, a macroscopic characterization of such sedimentary extreme environments and how they look is crucial to identify life properties, but it is a perspective that most molecular approaches frequently miss. Although acid mine drainage (AMD) systems are toxic and contaminated, they offer at the same time the bioengineering tools for natural remediation strategies. This work presents a biosedimentological characterization of the clastic iron stromatolites in the Tintillo river. They occur as laminated terraced iron formations that are the most distinctive sedimentary facies at the Tintillo river, which is polluted by AMD. Iron stromatolites originate from fluvial abiotic factors that interact with biological zonation. The authigenic precipitation of schwertmannite and jarosite results from microbial-mineral interactions between mineral and organic matrices. The Tintillo iron stromatolites are composed of bacterial filaments and diatoms as Nitzschia aurariae, Pinnularia aljustrelica, Stauroneis kriegeri, and Fragilaria sp. Furthermore, the active biosorption and bioleaching of sulfur are suggested by the black and white coloration of microbial filaments inside stromatolites. AMD systems are hazardous due to physical, chemical, and biological agents, but they also provide biogeochemical sources with which to infer past geochemical conditions on Earth and inform exploration efforts on extraterrestrial surfaces in the future.

Extremely Acidic Eukaryotic (Micro) Organisms: Life in Acid Mine Drainage Polluted Environments-Mini-Review.

Acid Mine Drainage (AMD) results from sulfide oxidation, which incorporates hydrogen ions, sulfate, and metals/metalloids into the aquatic environment, allowing fixation, bioaccumulation and biomagnification of pollutants in the aquatic food chain. Acidic leachates from waste rock dams from pyritic and (to a lesser extent) coal mining are the main foci of Acid Mine Drainage (AMD) production. When AMD is incorporated into rivers, notable changes in water hydro-geochemistry and biota are observed. There is a high interest in the biodiversity of this type of extreme environments for several reasons. Studies indicate that extreme acid environments may reflect early Earth conditions, and are thus, suitable for astrobiological experiments as acidophilic microorganisms survive on the sulfates and iron oxides in AMD-contaminated waters/sediments, an analogous environment to Mars; other reasons are related to the biotechnological potential of extremophiles. In addition, AMD is responsible for decreasing the diversity and abundance of different taxa, as well as for selecting the most well-adapted species to these toxic conditions. Acidophilic and acidotolerant eukaryotic microorganisms are mostly composed by algae (diatoms and unicellular and filamentous algae), protozoa, fungi and fungi-like protists, and unsegmented pseudocoelomata animals such as Rotifera and micro-macroinvertebrates. In this work, a literature review summarizing the most recent studies on eukaryotic organisms and micro-organisms in Acid Mine Drainage-affected environments is elaborated.

Application and limitations of time domain-induced polarization tomography for the detection of hydrocarbon pollutants in soils with electro-metallic components: a case study.

Nowadays, the growing concern about the environmental problems affecting the subsoil has focussed efforts on the detection and characterization of contaminated sites through geophysical prospecting methods. In the present study, a case of a contaminated site by hydrocarbons and their study by means of time domain-induced polarization tomography is presented. The response in chargeability of porous media due to this kind of pollutant allows its delimitation using this method. However, one of the limitations for the application of this technique is the presence of lithologies that contain electro-metallic salts. These salts can produce anomalies of chargeability and mask those due to nonaqueous phase liquids. The studies were conducted in an area contaminated by fuel leaks from supply tanks within a train maintenance facility. Those leaks occurred while the tanks were in use, but since their dismantling, the leak stopped. The geology of the area presented strong heterogeneities and the access was limited by train tracks. In order to locate and characterize the contaminant plume, measurements of resistivity and chargeability were carried out. A grid of monitoring wells in this area was also available from which information about free-phase pollutants was obtained, and a new drilling was carried out to verify an unexpected anomaly. The results obtained show that the location of the plume by the geophysical techniques employed can lead to ambiguity, as an anomaly that does not correspond to contaminated areas appeared but to the presence of clays rich in electro-metallic components such as Mg, Fe, Mn and Al.

Physico-Chemical Influence of Surface Water Contaminated by Acid Mine Drainage on the Populations of Diatoms in Dams (Iberian Pyrite Belt, SW Spain).

Twenty-three water dams located in the Iberian Pyrite Belt were studied during March 2012 (early spring) in order to carry out an environmental assessment based on diatom communities and to define the relationships between these biological communities and the physico-chemical characteristics of the dam surface water. This is the first time that a diatom inventory has been done for dams affected by acid mine drainage (AMD) in the Spanish part of the Iberian Pyrite Belt (IPB). It was found that the pH was the main factor influencing the behaviour of the diatom communities. Then, using a dbRDA approach it was possible to organize the aggrupation of diatoms into four groups in response to the physico-chemical conditions of the ecosystem, especially pH: (1) Maris, Aac, Gos, Cmora (pH 2-3); (2) Andc, San, And, Dpin (pH 3-4.5); (3) Gran, Pleon, Oliv, Lagu, Chan, SilI, SilII, Joya, Gar, Agrio, Camp, Corum (pH 4.5-6); (4) Herr, Diq I, Diq II (pH 6-7). The obtained results confirmed the response of benthic diatom communities to changes in the physico-chemical characteristics of surface water, and helped to understand the role of diatoms as indicators of the degree of AMD contamination in those 23 dams. Special attention was given to those that have an acidophilic or acid-tolerant profile (pH 2-3 and pH 3-4.5) such as Pinnularia aljustrelica, Pinnularia acidophila, Pinnularia acoricola and Eunotia exigua, which are the two groups found in the most AMD contaminated dams.

The UNESCO national biosphere reserve (Marismas del Odiel, SW Spain): an area of 18,875 ha affected by mining waste.

At the mouth of the Odiel River, within the Natural Area "Marismas del Odiel", there has been for years a collection of waste from different mining sites. In the present work, an approach has been made to the problem that this supposes, quantifying the pollutants that are poured into the estuary from the mineral collection located on the banks of the river. The study carried out has been able to determine high metal concentrations, comparable with any rubble from the upstream mines, with pH value of 1.66, lower than many other areas affected by acid mine drainage in the same river, and even with concentrations of Fe and As higher than those provided by the rest of the mining facilities of the Odiel basin. This can make us understand the serious situation of the Natural Park, where a great variety of birds and plants of special ecological interest are located.

Negative pH values in an open-air radical environment affected by acid mine drainage. Characterization and proposal of a hydrogeochemical model.

This paper presents the finding of a singular environment polluted by acid mine drainage in the Iberian Pyrite Belt. This situation is regulated by particular conditions, thus the analysed values can be considered as extreme, not only because of the high concentrations of toxic elements, but also due to the extreme low pH, reaching an average negative pH of -1.56, never found before in open-air environments contaminated by acid mine drainage. Concentrations up to 59 g/L of Fe, 2.4 g/L of Al, 740 mg/L of As, 4.3 mg/L of Co, 5.3 mg/L of Ge, 4.8 mg/L of Sb, inter alia, can be found dissolved in these polluted waters. The main aims of the present work are the physicochemical characterization and the toxicity assessment of these radical polluted waters. In addition, a hydrogeochemical model of the system will be proposed, which justifies the extreme pH value and the extraordinarily high concentrations of toxic elements, even for acid mine drainage polluted environments. Extreme acidity and metal and sulphate concentrations in the Radical Environment are due to several processes of different nature, mainly driven by the geochemistry of the minerals presents in the endorheic character of the basin. The extremely acidic nature of these waters control the Fe species present in them, being FeHSO4+ the mainly Fe specie representing 94% of total. High toxicity of these waters has been detected due to the absence of any diatoms species.