Person: Martínez Santos, Pedro
Universidad Complutense de Madrid
Faculty / Institute
Geodinámica, Estratigrafía y Paleontología
Now showing 1 - 10 of 55
PublicationFree-product plume distribution and recovery modeling prediction in a diesel-contaminated volcanic aquifer(Elsevier, 2012) Hernández Espriú, Antonio; Martínez Santos, Pedro; Sánchez León, Emilio; Marín, Luis E.Light non-aqueous phase liquids (LNAPL) represent one of the most serious problems in aquifers contaminated with petroleum hydrocarbons liquids. To design an appropriate remediation strategy it is essential to understand the behavior of the plume. The aim of this paper is threefold: (1) to characterize the fluid distribution of an LNAPL plume detected in a volcanic low-conductivity aquifer (∼0.4 m/day from slug tests interpretation), (2) to simulate the recovery processes of the free-product contamination and (3) to evaluate the primary recovery efficiency of the following alternatives: skimming, dual-phase extraction, Bioslurping and multi-phase extraction wells. The API/Charbeneau analytical model was used to investigate the recovery feasibility based on the geological properties and hydrogeological conditions with a multi-phase (water, air, LNAPL) transport approach in the vadose zone. The modeling performed in this research, in terms of LNAPL distribution in the subsurface, show that oil saturation is 7% in the air–oil interface, with a maximum value of 70% in the capillary fringe. Equilibrium between water and LNAPL phases is reached at a depth of 1.80 m from the air–oil interface. On the other hand, the LNAPL recovery model results suggest a remarkable enhancement of the free-product recovery when simultaneous extra-phase extraction was simulated from wells, in addition to the LNAPL lens. Recovery efficiencies were 27%, 65%, 66% and 67% for skimming, dual-phase extraction, Bioslurping and multi-phase extraction, respectively. During a 3-year simulation, skimmer wells and multi-phase extraction showed the lowest and highest LNAPL recovery rates, with expected values from 207 to 163 and 2305 to 707 l-LNAPL/day, respectively. At a field level we are proposing a well distribution arrangement that alternates pairs of dual-phase well-Bioslurping well. This not only improves the recovery of the free-product plume, but also pumps the dissolve plume and enhances in situ biodegradation in the vadose zone. Thus, aquifer and soil remediation can be achieved at a shorter time. Rough calculations suggest that LNAPL can be recovered at an approximate cost of $6–$10/l. PublicationAssessment of the transferred water infiltration in the management of a Mediterranean man-maintained wetland: las Tablas de Daimiel national park (Spain)(Polish Geological Institute, 2005) Castaño Castaño, Silvino; Martínez Alfaro, Pedro Emilio; Martínez Santos, Pedro; Mediavilla López, Ros; Santisteban Navarro, Juan Ignacio; López Pamo, EnriqueLas Tablas de Daimiel National Park wetlands (Central Spain) have had their main origin in the West La Macha aquifer discharges. Inflows into these wetlands ceased due to the intensive aquifer exploitation. A progresive deterioration of the wetland brought about several attempts of remedial actions by means of building several small dams and pumping groundwater to the Las Tablas basin. The main attempt to preserve these wetlands has been made by means of the inter-basins tranfers. However, a part of these water transfers is lost within the wetland basin due to the infiltration into the underlying aquifer. Infilitration becomes an essential parameter in any study related to the attempts at keemping some water in the basin and, therefore, in the integrated managmeent of the water resources systems related to the wetland. The actual extent of these losses is difficult to quantify due to the poor quality of existing data as well as to the lack of determination of various important parameters. A methodology based on dailiy water balance in the wetland basin allows to assess that losses and can be used for the National Park water management. PublicationManual Borehole Drilling as a Cost-Effective Solution for Drinking Water Access in Low-Income Contexts(MDPI, 2020) Martínez Santos, Pedro; Martín Loeches, Miguel Martín; Díaz Alcaide, Silvia; Danert, KerstinWater access remains a challenge in rural areas of low-income countries. Manual drilling technologies have the potential to enhance water access by providing a low cost drinking water alternative for communities in low and middle income countries. This paper provides an overview of the main successes and challenges experienced by manual boreholes in the last two decades. A review of the existing methods is provided, discussing their advantages and disadvantages and comparing their potential against alternatives such as excavated wells and mechanized boreholes. Manual boreholes are found to be a competitive solution in relatively soft rocks, such as unconsolidated sediments and weathered materials, as well as and in hydrogeological settings characterized by moderately shallow water tables. Ensuring professional workmanship, the development of regulatory frameworks, protection against groundwater pollution and standards for quality assurance rank among the main challenges for the future. PublicationModelling the effects of climate change and population growth in four intensively exploited Mediterranean aquifers. The Mijas range, southern Spain(Elsevier, 2020-05-15) Martín Arias, Javier; Martínez Santos, Pedro; Andreo, BartoloméGroundwater is key to economic growth in the Mediterranean region. This is particularly true of areas such as southern Spain, where aquifers underpin social development by supplying water to a booming tourist industry. Intensive groundwater use raises sustainability concerns, as pumping often exceeds the long-term recharge rate. Climate change and population growth are likely to exacerbate the water supply challenge in the coming years, due to the expected decrease in rainfall and to increasing competition among users. This paper examines some of the main aquifers in the Costa del Sol region, one of Spain's leading tourist destinations, where intensive groundwater extraction has led to water table drawdowns and the desiccation of all major springs. A numerical model was developed and calibrated for the purpose of evaluating the likely evolution of the system in the future. Downscaled scenarios from global circulation models were coupled with population growth forecasts to establish a range of plausible water management scenarios. Given the relatively small size of the aquifers and the limited recharge rate, the current pumping patterns appear unsustainable. Results suggest that drawdowns in excess of 150 m could take place within the next decade, thus compromising domestic supplies. PublicationMulticlass spatial predictions of borehole yield in southern Mali by means of machine learning classifiers(Elsevier, 2022) Gómez Escalonilla, Víctor; Diancoumba, Oumou; Traoré, D.Y.; Montero González, Esperanza; Martín Loeches, Miguel Martín; Martínez Santos, PedroStudy region: Regions of Bamako, Kati and Kangaba, southwestern Mali Study focus: Machine learning-based mapping of borehole yield. Three algorithms were trained on an imbalanced multiclass database of boreholes, while twenty variables were used as predictors for borehole yield. All models returned balanced and geometric scores in the order of 0.80, with area under the receiver operating characteristic curve up to 0.87. Three main methodological conclusions are drawn: (a) The evaluation of different machine learning classifiers and various resampling strategies and the subsequent selection of the best performing ones is shown to be a good strategy in this type of studies; (b) ad hoc calibration tools, such as data on borehole success rates, provide an apt complement to standard machine learning metrics; and (c) a multiclass approach with an unbalanced database represents a greater challenge than predicting a bivariate outcome, but potentially results in a finer depiction of field conditions. New hydrological insights for the region: Alluvial sediments were found to be the most productive areas, while the Mandingue Plateau has the lowest groundwater potential. The piedmont areas showcase an intermediate groundwater prospect. Elevation, basement depth, slope and geology rank among the most important variables. Lower values of clay content, slopes and elevations, and higher values of basement depth and saturated thickness were linked to the most productive class. PublicationIncorporating the water footprint and virtual water into policy: Reflections from the Mancha Occidental region, Spain(Springer, 2010) Aldaya, Maite M.; Martínez Santos, Pedro; Llamas, M. RamónWater resource management is often a controversial issue in semiarid regions. Most water resources experts admit that water conflicts are not caused by the physical water scarcity but they are mainly due to inadequate water management. The virtual water concept (the volume of water used in the production of a commodity, good or service) together with the water footprint (indicator of water consumption that looks at both direct and indirect water use of a consumer or producer), links a large range of sectors and issues, thus providing a potentially appropriate framework to support more optimal water management practices by informing production and trade decisions. This paper provides an analysis of these two concepts within the context of the Mancha Occidental region, Spain, exploring the hydrological and economic aspects of agricultural production. In doing so, this work not only distinguishes between green and blue water but also between surface and groundwater. We conclude by discussing the practical implications of the results, as well as their potential limitations from the policy standpoint. PublicationResources assessment of a small karstic mediterranean aquifer (South-Eastern, Spain)(Springer, 2010) Andreu, J.M.; Martínez Santos, Pedro; Pulido Bosch, A.; García Sánchez, ErnestoGroundwater from small aquifer systems is frequently used for urban supply in southeastern Spain. Aquifers such as the Ventos system, located in Mediterranean semiarid environments, are sensitive to climatic and anthropogenic changes. Many of them have been severely depleted due to intensive pumping. Drawdowns in the Ventos aquifer amount to approximately 80m over the last three decades. Adequate knowledge of groundwater resources is necessary for water planners and managers to guarantee suitable abstraction. This paper presents a methodology to estimate groundwater recharge in these kinds of quick-response semiarid karst aquifers. A distributed model has been used to evaluate the fraction of rainfall that ultimately results in aquifer recharge, as well as the correlation between the magnitude of rainfall events and infiltration rates. Modelling results are then compared with direct observations of the recharge processes and discussed to evaluate the implications of time scales. PublicationMapping groundwater-dependent ecosystems by means of multi-layer supervised classification(Elsevier, 2021-12-26) Martínez Santos, Pedro; Díaz Alcaide, Silvia; Hera Portillo, África de la; Gómez-Escalonilla Canales, VíctorIdentifying groundwater-dependent ecosystems is the first step towards their protection. This paper presents a machine learning approach that maps groundwater-dependent ecosystems by extrapolating from the characteristics of a small sample of known wetland and non-wetland areas to find other areas with similar geological, hydrological and biotic markers. Explanatory variables for wetland occurrence include topographic elevation, lithology, vegetation vigor, and slope-related variables, among others. Supervised classification algorithms are trained based on the ground truth sample, and their outcomes are checked against an official inventory of groundwater-dependent ecosystems for calibration. This method is illustrated through its application to a UNESCO Biosphere Reserve in central Spain. Support vector machines, tree-based classifiers, logistic regression and k-neighbors classification predicted the presence of groundwater-dependent ecosystems adequately (>96% test and AUC scores). The ensemble mean of the best five classifiers rendered a 90% success rate when computed per surface area. This method can optimize fieldwork during the characterization stage of groundwater-dependent ecosystems, thus contributing to integrate wetland protection in land use planning. PublicationReview: Advances in groundwater potential mapping(Springer, 2019) Díaz Alcaide, Silvia; Martínez Santos, PedroGroundwater resources can be expected to be increasingly relied upon in the near future, as a consequence of rapid population growth and global environmental change. Cost-effective and efficient techniques for groundwater exploration are gaining recognition as tools to underpin hydrogeological surveys in mid- and low-income regions. This paper provides a state of the art on groundwater potential mapping, an explorative technique based on remote sensing and geographical databases that has experienced major developments in recent years. A systematic review of over 200 directly relevant papers is presented. Twenty variables were found to be frequently involved in groundwater potential investigations, of which eight are almost always present: geology, lineaments, landforms, soil, land use/land cover, rainfall, drainage density, and slope. The more innovative approaches draw from satellite images to develop indicators related to vegetation, evapotranspiration, soil moisture and thermal anomalies, among others. Data integration is carried out either through expert judgement or through machine-learning techniques, the latter being less common. Three main conclusions were reached: (1) for optimal results, groundwater mapping must be used as a tool to complement field work, rather than a low-cost substitute; (2) the potential of remote-sensing techniques in groundwater exploration is enormous, particularly when the power of machine learning is harnessed by involving human judgement; (3) quality assurance remains the main challenge ahead, as exemplified by the fact that a majority of the existing studies in the literature lack adequate validation. PublicationVulnerability assessment of groundwater resources: A modelling-based approach to the Mancha Occidental aquifer, Spain(Elsevier, 2008-09) Martínez Santos, Pedro; Llamas, M. Ramón; Martínez Alfaro, Pedro E.The semiarid Mancha Occidental aquifer represents a paradigmatic case of intensive groundwater use for agriculture. Irrigation has proven a catalyst for welfare in the area over the last three decades, if at a significant environmental cost and while raising concerns as to its mid-term sustainability. This paper describes an interdisciplinary exercise of scenario design and modelling, providing a methodology to couple hard-science numerical modelling approaches with the involvement of key water actors. Given the long-standing conflicts in the area, modelling work largely focuses on carrying out a vulnerability assessment rather than on trying to find solutions. The system's most resilient aspects and its drivers for change are identified, while their potential implications for aquifer sustainability are assessed under the light of the mandatory objectives established by the European Union Water Framework Directive for all Member States. Whereas modelling results imply that such objectives are unlikely to be met, a vulnerability assessment suggests that even adverse scenario pumping patterns could be sustained in the mid- to long-term (two to four decades).