Carolina Guardiola-Albert

Groundwater is a vitally important resource for humans. One of the main problems derived from the overexploitation ofaquifers is land subsidence, which in turn carries other associated natural risks. Advanced Differential satellite radarinterferometry (A-DInSAR) techniques provide valuable information on the surface displacements of the ground, whichserve to characterize both the deformational behaviour of the aquifer and its properties. RESERVOIR is a research projectbelonging to the European PRIMA programme, whose main objective is to design sustainable groundwater managementmodels through the study of four areas of the Mediterranean subjected to water stress. One of the main tasks of the projectis the integration of the terrain deformation data obtained with satellite remote sensing techniques in the hydrogeologicaland geomechanical models of the aquifers. In the present work, a first evaluation of the deformation of the ground in eachstudy area is carried out using the tools con...

La Vega Media del Segura (VMS) se localiza en el sector este de la Cordillera Bética. El valle está relleno por sedimentos recientes (Holoceno-Plioceno) potencialmente deformables que han sido depositados por la acción de los ríos Segura y Guadalentín. La extracción de agua subterránea de los niveles permeables que constituyen el acuífero conlleva la consolidación de los materiales deformables, dando lugar a asientos de la superficie del terreno. La Interferometría SAR diferencial (InSAR) es una técnica remota que permite monitorizar de forma efectiva y precisa amplias extensiones del territorio. En este trabajo se describe las diferentes experiencias llevadas a cabo por los autores en la VMS, que han permitido avanzar en el entendimiento del funcionamiento hidrogeológico del acuífero para la comprensión del comportamiento geomecánico del subsuelo, así como para monitorizar los desplazamientos del terreno desde el año 1994 usando imágenes ERS, ENVISAT y TerraSAR-X, contribuyendo de ...

<p>The bathymetry of the riverbed is essential in flood risk assessment at large rivers, and yet its acquisition is a slow process and endowed with a high budget economic. Moreover, recent research works have shown the importance of improving the geometrical characterization inside the riverbed, which is an issue due to the inability of light to penetrate water bodies. So, most of LiDAR techniques allow us for high resolution surface topography data but not for water occupied river channels. This, apart from making these jobs more difficult, sometimes generates the renouncement of it, using the topography of the water sheet as a riverbed, or the simplification of river channel configuration (trapezoidal transversal sections) which frequently generate an overestimation of flood zones. To overcome these deficiencies, a novel methodological approach has been developed to simulate this bathymetry using simplified models. The proposed approach is based upon the calibration of the flow roughness parameters (Manning´s n value) inside the riverbed. The use of abnormally low Manning´s n values has made it possible to reproduce both the extent of the flooded area and the water depth value within it in an acceptable manner: first results from hydrodynamic modelling of 500-year return period peak flow show the reduction of the water depth average error from 50-75 cm to only about 10 cm; and a direct economic flood damage differences reduction from 25-30% to values of about 5%.</p><p>The present work proposes to go further with these investigations and perform a robust geostatistical analysis of hydrodynamic modelling outputs obtained with modified Manning’s n values. The methodology scheme is to characterize the spatial distribution of the results and its spatial correlation with other variables, as the distance to the riverbank or flow rates (for different return periods), through variogram models. This quantitative statistical description of the floodable areas, depending on the Manning’s n value model used and the return period considered, could be used to perform geostatistical simulations that allow to quantify the spatial uncertainties associated to the studied models; as well as to calibrate the optimal spatial distribution of modified Manning’s n values inside the riverbed. These findings will be analysed as guidelines to construct more robust and reliable flood risk estimations; and can be applied to many other study cases around the world, saving analysis time and execution costs, but without losing its scientific rigour.</p>

<p>The problem of predicting terrain deformation time series from radar interferometry (InSAR) data is one of the biggest current challenges for the prevention and mitigation of the impact of geological risks (e.g. earthquakes, volcanoes, subsidence, slope landslides) that affect both urban (e.g. building movement) and non-urban areas. Generating spatio-temporal alert systems on the processes of deformation of the terrain based on predictive models is one of the great current challenges in the face of the prevention and management of geological risks. Within machine learning techniques, deep learning offers the possibility of applying prediction models of deformation time series on images using convolutional neural networks (Ma et al., 2020).</p><p>The objective of the present study is to develop a methodology to obtain predictive models of time series of terrain deformation from InSAR images using machine learning algorithms (e.g. deep convolutional neural networks). Data to train the algorithm will be time series of terrain deformation contained in InSAR images processed by the Geological Survey of Spain (IGME-CSIC). Different architectures and parameterizations of machine learning will be tested.</p><p>This work is performed within the framework of the SARAI Project PID2020-116540RB-C22 funded by MCIN/ AEI /10.13039/501100011033.</p><p>Reference:</p><p>Ma, P., Zhang, F., Lin, H. (2020). Prediction of InSAR time-series deformation using deep convolutional neural networks. Remote Sensing Letters, 11:2, 137-145.</p><p> </p>

Los modelos matematicos estocasticos para la simulacion de flujo multifase en medios porosos heterogeneos tienen un gran interes en ingenieria del petroleo e hidrologia subterranea. El entorno estocastico da la posibilidad de caracterizar la variabilidad espacial intrinseca de los parametros de flujo, asi como tomar decisiones con respecto al emplazamiento de los pozos o a los procedimientos asociados a los bombeos o las inyecciones. La teoria de modelizacion inversa da la posibilidad de integrar variables estaticas y dinamicas en la caracterizacion del yacimiento. La integracion de los datos de produccion en la modelizacion del yacimiento se realiza a traves de las tecnicas de modelizacion inversa porque los datos dinamicos estan relacionados de forma no lineal con las propiedades heterogeneas del yacimiento por las ecuaciones de flujo multifase. La permeabilidad absoluta es uno de los parametros que son tipicamente etimado spor medio de simulaciones inversa de flujo. En las ultima...

Accurate estimation of missing daily precipitation data remains a difficult task. A wide variety of methods exists for infilling missing values, but the percentage of gaps is one of the main factors limiting their applicability. The present study compares three techniques for filling in large amounts of missing daily precipitation data: spatio-temporal kriging (STK), multiple imputation by chained equations through predictive mean matching (PMM), and the random forest (RF) machine learning algorithm. To our knowledge, this is the first time that extreme missingness (>90%) has been considered. Different percentages of missing data and missing patterns are tested in a large dataset drawn from 112 rain gauges in the period 1975–2017. The results show that both STK and RF can handle extreme missingness, while PMM requires larger observed sample sizes. STK is the most robust method, suitable for chronological missing patterns. RF is efficient under random missing patterns. Model evalu...

Mathematical groundwater modelling with homogeneous permeability zones has been used for decades to manage water resources in the Almonte-Marismas aquifer (southwest Spain). This is a highly heterogeneous detrital aquifer which supports valuable ecological systems in the Doñana National Park. The present study demonstrates that it is possible to better characterize this heterogeneity by numerical discretization of the geophysical and lithological data available. We identified six hydrofacies whose spatial characteristics were quantified with indicator variogram modelling. Sequential Indicator Simulation then made it possible to construct a 3D geological model. Finally, this detailed model was included in MODFLOW through the Model Muse interface. This final process is still a challenge due to the difficulty of downscaling to a handy numerical modelling scale. New piezometric surfaces and water budgets were obtained. The classical model with zones and the model with 3D simulation were...

Karst depressions of decametric scale (dolines, uvalas, poljes, and other endorheic basins) play an important role in the hydrogeology of karst aquifers. They are traps of sediment and when their detritic filling has an important thickness they can retain a large amount of water delaying their percolation towards the water table or towards the networks of conduits. Many times the delineation of the depressions may be difficult because the study area may be very large, or inaccessible or hidden by vegetation. In those circumstances, it is of great help to have an automatic method of depression detection and delineation. The proposed procedure uses the digital elevation model, a geographical information system, an algorithm of pit removal and basic operations of map algebra. The method provides the depth of each detected depression measured from its rim. This fact can be used to detect the center of maximum depth as well as for calculating morphometric parameters using depth. The final map of depressions can be characterized by altitude in order to have morphometric parameters related with elevation. The algorithm has been extended for detection and delineation of karst hills. The methodology is illustrated with the Sierra de las Nieves karst aquifer in the province of Malaga, Southern Spain, where the depressions and hills show a strong structural control.

Karst aquifers are very complex and heterogeneous systems because of the presence of three kinds of porosity (matrix rock porosity, fracture porosity, and conduit porosity) that generally have a large spatial variability. In order to have realistic karst models the three kinds of porosity and their spatial variability must be taken into account. A quantitative model of a karst aquifer is proposed by integration of the three kinds of porosity in a three dimensional numeric model. Nevertheless, the main task of this work is restricted to the proposal of methods for their evaluation. Matrix rock porosity has been measured in the laboratory from samples collected in the field. Matrix rock porosity is well correlated with the lithology and with the structural position of the rock. Fracture porosity has been estimated from fracture mapping and field measurements. A geostatistical method is used to obtain a continuous field of fracture porosity. Conduit porosity has been calculated from a power model fitted to speleologic cave mapping data. However, because of the scarcity of conduit data, probabilistic models must be conjectured. The integration of the three kinds of porosity gives a three dimensional numerical model that can be used in vulnerability mapping, recharge estimation, and mathematical modeling of flow and transport in karst systems. The approach is illustrated with the Sierra de las Nieves karst aquifer in the province of Malaga in Southern Spain.

Three kinds of porosity and permeability, rock matrix porosity, fracture porosity and conduit porosity, must be considered when creating spatially distributed mathematical models of karst systems. These components are responsible for the two kinds of karst flows that can be observed in nature and that must be reproduced by the mathematical models: the slow flow that takes place through the matrix of porous and small fractures and the fast flow through large fractures and conduits. Although the three components present fractal characteristics, the aim of this work is the fractal behaviour of the karst conduits. Two aspects of the karst conduits are considered: their geometry and their topology. The geometry is defined by the sections of the conduits and their tortuosity while the topology is given by the network characteristics of the conduits (connectivity, spatial density and three-dimensional distribution in space). This work deals with the calculation of the fractal dimensions of the different characteristics and how the fractal dimension can be used for morphometric characterization of karst networks, for simulating three-dimensional networks of karst conduits and for calculating the volume of conduits and thus the total conduit porosity of the karst system. The karst system of Sierra de las Nieves in Malaga province (Southern Spain), a high relief karst where the endokarst is very well developed and has given birth to super-caves, is used to illustrate the methodology.

<p>Land subsidence produced from the exhaustive groundwater exploitation is a phenomenon that has critical effects in many areas around the world, especially in water-scarce areas. Among the objectives of the RESources managEment by integrating eaRth observation deriVed monitoring and flOw modelIng Results (RESERVOIR) project (GA nº 1924), one of them is the identification of the stakeholder requirements and groundwater conceptual model setup for several pilot sites. The present work is related with the Alto Guadalentín aquifer study case (SE Spain). To achieve the mentioned objective, a workshop was organized and a large number of potential stakeholders from local authorities, environmental agency, water supply companies, NGOs, insurance companies and regulatory institutions were summoned. During the workshop most important RESERVOIR activities were presented. Once the workshop was finished, a questionnaire that proposes the evaluation of the main problems in the area related to the groundwater management was sent to all participants. Results disclose that 55% of stakeholders consider that the principal problem in the Guadalentín aquifer is the overexploitation, and 50% of stakeholders regard that the lack of managerial, planning, and technical instruments are the most relevant issues to be addressed and solved. In more detail, the survey reveals that the monitoring coverage is inadequate in terms of: (a) groundwater levels monitoring (50%); (b) water quality measurement frequency (40%); and (c) water quality measurement points spatial distribution (55%) Even that area is reporting the highest subsidence rates in Europe, this problem is not considered as the most important, probably because affects agricultural areas and minimal damages were reported. Finally, 90% of the stakeholders have previous knowledge about groundwater modelling, but only 45% within them have information about the specific applications for which the model is employed in the Alto Guadalentín aquifer. Main conclusion leads to confirm that the measurements taken in the past have proved to be insufficient to reverse the state of the overexploitation of the aquifer. From this, some management measures must be strengthened, and several technical tools should be introduced to improve the groundwater management. On the other hand, improving the use of the numerical model of the Alto Guadalentín aquifer to support decision-making, as well as, updating the model by coupling it with the subsidence phenomenon through the definition of subsidence risk indexes would lead to a sustainable and holistic groundwater management.</p>

The accurate estimation of flood risk depends on, among other factors, a correct delineation of the floodable area and its associated hydrodynamic parameters. This characterization becomes fundamental in the flood hazard analyses that are carried out in urban areas. To achieve this objective, it is necessary to have a correct characterization of the topography, both inside the riverbed (bathymetry) and outside it. Outside the riverbed, the LiDAR data led to an important improvement, but not so inside the riverbed. To overcome these deficiencies, different models with simplified bathymetry or modified inflow hydrographs were used. Here, we present a model that is based upon the calibration of the Manning’s n value inside the riverbed. The use of abnormally low Manning’s n values made it possible to reproduce both the extent of the flooded area and the flow depth value within it (outside the riverbed) in an acceptable manner. The reduction in the average error in the flow depth value ...

Groundwater resources are regularly the principal water supply in semiarid and arid climate areas. However, groundwater levels (GWL) in semiarid aquifers are suffering a general decrease because of anthropic exploitation of aquifers and the repercussions of climate change. Effective groundwater management strategies require a deep characterization of GWL fluctuations, in order to identify individual behaviors and triggering factors. In September 2019, the Guadalquivir River Basin Authority (CHG) declared that there was over-exploitation in three of the five groundwater bodies of the Almonte-Marismas aquifer, Southwest Spain. For that reason, it is critical to understand GWL dynamics in this aquifer before the new Spanish Water Resources Management Plans (2021–2027) are developed. The application of GWL series clustering in hydrogeology has grown over the past few years, as it is an extraordinary tool that promptly provides a GWL classification; each group can be related to different...

<p>Almonte-Marismas is a coastal aquifer situated in Doñana Natural Park (Southwestern of Spain, Huelva). It supports one of the most important wetland areas in Europe due to its biodiversity, size and strategic location. Nowadays, the aquifer suffers serious threats due to the large amount of water extraction that takes place in the area due to the high demand for water that exists for the supply of tourism and irrigation.</p><p>There is a flow model of the regional aquifer which is used to support the water management Administration. However, this model does not take into account groundwater interactions with local ponds. Santa Olalla pond is a hypogenic wetland that, on a regional scale, it receives the discharge of the Almonte-Marismas aquifer. This fact allows it to maintain a permanent water regime without suffering a reduction in its volume of water. Despite of that, the intense pumping in the zone could affect it and be a risk in the future.</p><p>The objective of this study is the identification of an appropriate model structure to characterize and implement the Santa Olalla Pond in the current steady-state model of the regional aquifer of Doñana employing ModelMuse interface. For this purpose, different boundary conditions (LAKE and DRAIN packages) were contrasted to represent the pond, combined with different local grid refinement (LGR2 package). The contrast criteria to assess the goodness of the numerical representation have been the piezometric heads in the wells situated in the surroundings of the pond and the stage levels and water balance of the pond.</p>

In the current context of climate change, improving groundwater monitoring and management is an important issue for human communities in arid environments. The exploitation of groundwater resources can trigger land subsidence producing damage in urban structures and infrastructures. Alto Guadalentín aquifer system in SE Spain has been exploited since 1960 producing an average piezometric level drop of 150 m. This work presents a groundwater model that reproduces groundwater evolution during 52 years with an average error below 10%. The geometry of the model was improved introducing a layer of less permeable and deformable soft soils derived from InSAR deformation and borehole data. The resulting aquifer system history of the piezometric level has been compared with ENVISAT deformation data to calculate a first-order relationship between groundwater changes, soft soil thickness, and surface deformation. This relationship has been validated with the displacement data from ERS and Cosm...

Dune belts are crucial for the recharge of coastal aquifers. In spite of their hydrological relevance for the maintenance of precious natural wetland and wildlife environments and a range of other ecosystem services, only limited knowledge of soil water dynamics in dune belts is currently available. This study presents soil water balance components measured during one hydrological year using a high precision meteo-lysimeter with lower boundary control installed in a coastal dune belt under a dry subhumid climate in southern Spain close to the Atlantic Ocean. The site is equipped with a cylindrical lysimeter of 1 m surface and 1.50 m height (METER Group, Inc. USA) and a weighing resolution of 10 g, 2 SC650 soil moisture sensors (Campbell Scientific, Logan, UT) and 1 automatic meteorological station. The lower boundary condition at the bottom of the lysimeter is controlled at 1.4 m depth by a bidirectional peristaltic pump to maintain field conditions. Results show a recharge rate of 64% of the precipitation measured by the lysimeter. Diurnal oscillations of the measured upper boundary flow during days without rainfall represented vapor adsorption and real evaporation rates ranging between 0.3 and 0.4 mm/day and 0.4 and 0.6 mm/day, respectively throughout the whole year summing up an annual vapor adsorption of 77 mm. The measured precipitation of the lysimeter exceeded pluviometer data by 13% as a result of vapor adsorption. The presented results provide a precise balance of soil water components in a coastal dune belt including the relevant contribution of vapor flow.

Flood hazard analyses have been carried out traditionally with hydrologic and hydraulic methods and, to a lower extent, with palaeohydrologic, geologic and/or geomorphic methods. Among these, dendrogeomorphology has been demonstrated to be a valuable tool for palaeohydrologic investigations as it takes advantage of sources of information registered in roots, trunks and branches of trees and shrubs placed in settings where the complementing of systematic registries or paleohydrologic data of torrential floods are crucial. The systematic acquisition of dendrogeomorphic data is a tedious task and requires the destructive sampling and extraction of cores from trees. X-ray computed tomography (XRCT) scanning is a non-destructive measurement and allows the detection of internal density variations. Available 3D images of the tree samples from the Spanish Central System affected by flash floods are here processed to retrieve structural information with high accuracy. This paper presents a n...

La Rocina Creek, situated in a protected area bordering the Unesco Natural World Heritage site of the Doñana National Park, flows into the precious marshlands which constitute Europe's most important wetlands. In last two decades, strawberry farms have sprung up in the surroundings of La Rocina, one of the main water suppliers to the marshes in Doñana during the summer. The strawberry area in Doñana comprises about 6000 ha and constitutes more than the 60% of the Spanish production. Strawberries are a thirsty crop, and farmers have to extract massive quantities of groundwater, often illegally, to irrigate their plants. This has induced a severe decrease on the groundwater flows to wetlands and streams running into the Park; e.g. La Rocina has experienced the most important reduced flows. This has caused a series of environmental problems threatening the biodiversity in Doñana as well as the conservation of sensible species at present. This situation and the uncontrolled water us...

Acknowledgements The FEDER project UNCM08-1E-086 supported the X-band radar installation. This work is also part of the MARCoNI project (funded by the Spanish Ministry of Economy and Competitiveness, ref: CGL2013-42728-R), MIDHATO Venero project (funded by the Spanish Geological Survey, ref: IGME 2013/2313) and the project CGL2013-48367-P (funded by the Spanish Ministry of Economy and Competitiveness). 5. Conclusions  The improvement of this method in the study basin, highly dense instrumented but very small in extension, is the systematically generation of reliable rainfall maps based on X-band radar and rain gauge data.  In comparison with the classical Z-R relations, the method shows a greater capacity of distinction between wet and dry regions and minor errors.  Z-R relations underestimates rainfall, which is particularly dangerous when predicting flash floods.  These interpolations are suitable to be used as an input of hydrological models. * Contact: Carolina Guardiola Alb...

RESUMEN Los procesos de dilución en medios kársticos definen una doble permeabilidad, intergranular en la matriz y fracturas de poca apertura, y otra en la red de conductos, cavidades y fracturas de mayor apertura. En medios kársticos de doble permeabilidad el flujo subterráneo puede presentar un doble comportamiento: laminar sobre la matriz y/o turbulento en los conductos. Además existe un flujo de intercambio entre ambos medios (matriz y conductos), específico de cada caso, variable en el espacio y en el tiempo dentro del mismo acuífero y muy dependiente de las condiciones de contorno y de la conductancia entre la matriz y los conductos. Como resultado de todo ello, la respuesta hidrodinámica de los medios kársticos de doble permeabilidad es difícil de predecir y puede diferir mucho de la respuesta que daría un medio continuo de permeabilidad equivalente. La literatura sobre modelación matemática del agua subterránea en acuíferos kársticos pone de manifiesto que los códigos clásic...

ABSTRACT Researchers have been troubled with finding a reliable technique for estimating groundwater recharge in carbonate aquifers. Many studies have recognized the importance of preferential flow in karst systems. Despite this evidence, preferential infiltration has no effect on estimating recharge with a classical soil water budget. The present research aims to determine the significance of the correct location of preferential infiltration areas in estimating recharge with the APLIS method. The study was carried out in Sierra de las Nieves aquifer (Southern Spain). The effect of correctly estimating the preferential infiltration areas is studied through different levels of complexity in the geomorphological information: (i) a classical geomorphologic map with pothole databases available, (ii) a reviewed geomorphologic map, and (iii) fracture density and epikarst cartography obtained with field work and remote sensing interpretation. The obtained results provided a mean difference of more than 10 % of recharge in the whole aquifer, and up to 20 % when the pixel scale is considered at.

Indicator kriging is widely used for mapping spatial binary variables and for estimating the global and local spatial distributions of variables in geosciences. For continuous random variables, indicator kriging gives an estimate of the cumulative distribution function, for a given threshold, which is then the estimate of a probability. Like any other kriging procedure, indicator kriging provides an estimation variance

El conocimiento de los mecanismos de recarga y su cuantificación es fundamental tanto en la gestión de un acuífero, como para la protección de los recursos del agua subterránea. La recomendación común de que la recarga debe estimarse por múltiples métodos es sólida, pero las diferencias inherentes en los distintos métodos hacen difícil evaluar la exactitud de los diferentes resultados. En este estudio, se comparan cinco métodos para la estimación de la recarga subterránea: (i) Balance de agua, (ii) Balance de cloruros, (iii) APLIS, (iv) ZOODRM y (v) Estimación espacio-temporal para acuíferos kársticos. El área de estudio está ubicada en una zona de alta montaña y climáticamente semiárida de la provincia de Málaga. En concreto se ha trabajado en el sector occidental del acuífero kárstico de la Sierra de la Nieves, caracterizado por la falta de explotación y, en consecuencia, por un funcionamiento en régimen natural. Además, hay que tener en cuenta que en este tipo de acuíferos es cla...

ABSTRACT Knowledge of the spatial heterogeneity of wood is useful for industrial applications and improving dendrogeomorphic sampling, because it allows a better understanding of 3D wood density structure in tree stems damaged by geomorphic processes. X-ray computed tomography (XRCT) scanning as a means of non-destructive measurement has become an important technique in tree research as it allows the detection of internal variations in wood density. In this paper a new methodology for modelling spatial variations of relative wood density using variograms on XRCT images is developed. For each tree, XRCT images perpendicular to the stem axis were obtained with 1 mm spacing. In a first step, ImageJ software was used to process each image. Then, more than 30 one-dimensional variograms were studied for a selected number of cross-sections. The results show that there is a pattern in the diffusion of relative wood density linked to the attenuation of the geomorphic damage along the stem from the wounded area. Although the number of samples could be increased, these preliminary results demonstrated that variograms of XRCT are a useful tool to optimize dendrogeomorphic sampling, saving time and costs.

he presence of arsenic (As) in groundwater has become a public health priority because it limits the use of water resources for drinking water. Mapping probabilities that determines geographically the vulnerability of areas in relation to toxic trace elements as As in groundwaters (for As the limit is 10 mg/L, according with WHO recommendations) is often a preliminary step towards decision making. A straightforward approach consists of delimitation the spatial variability and definition areas with varying degrees of risk, especially those related with high levels of potentially harmful elements. During last decades Geostatistics has been commonly used to evaluate the probability that heavy metal concentrations exceed a location-specific environmental threshold, and different kriging methods have been developed. Though many works have been published applying and comparing existing methodologies, there is no agreement on which is the best. In this study seven kriging methods were used...

Arsenic levels in some spring waters collected in an area near the contact between metamorphic and igneous rocks of the Variscan basement, and Tertiary sediments of Duero Basin have been analyzed in relation to natural hydrogeotoxicity and its geographical distribution. The highest levels of arsenic HydroGeo- Toxicity (HGTAs >1) are recognized to depend on water-rock interaction processes and influence of deep flows with high temperature and negative values of Eh, which favor processes of sulfate reduction. Statistical and geostatistical analysis turn out to be an important tool to identify the affection of these factors on the distribution of HydroGeoToxicity by arsenic.

The geochemical risks in relation to geotoxic anomalies are being considered of great importance in the studies over environmental toxicology and public health. For the groundwater management in vulnerable areas with hydrogeotoxical risks it is critical to understand the spatial distribution of any Toxic Geogenic Trace Element (TGTE) -as As. Geostatistics has been used to evaluate the spatial variability of As in groundwater in the United States of America (Goovaerts et al. 2005) or Bangladesh (Karthik et al. 2001). Principal Component Analysis (PCA) has been also used as tool to support classical hydrogeochemical studies (Bhattacharya et al., 2006). This work presents a study of the spatial distribution of As concentration in spring waters of province of Ávila (Central Iberian Zone, Spain). The main objective of this study is to identify the factors and processes involved in the liberation and distribution of As using statistical and geostatistical tolos.