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Toxic elements in the groundwater of Budapest, Hungary
Authors: István Zsámbok, Anita Andó, László Kuti and András Sebők

The birth of urban geologic maps (which are considered environmental-geologic themed maps) and the progress in development of their content and design were driven by the growing importance of addressing environmental problems, and the increasing complex utilization of urban areas. Therefore, MÁFI and, since 2012, the MFGI Department of Environmental Geology, have prepared a series of maps for the local authorities of Budapest. These maps usually focus on the problems of urban planning from the viewpoint of geology, hydrogeology, and water chemistry, and as experience shows, they prove to be excellent tools in decision-making processes. This paper examines the chemical content of groundwater, which is one of the main indicators of the state of the environment. According to the everyday experience of the authors it is very useful to understand the state of both quality and quantity of subsurface and surface water. In a recent series of research work we measured the zinc, copper, boron and arsenic level of the groundwater in 10 districts of Budapest.

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Calibration process for groundwater flow model of a river influenced shallow aquifer
Authors: Andrea Kolencsik-Tóth and Balázs Kovács

Understanding and simulating the interaction of groundwater and surface water is essential to hydrologists. Water supply and water quality aspects are a few examples of common water-resource issues where understanding the interconnections of groundwater and surface water is fundamental to develop an effective water-resource management and policy. In our study a detailed investigation of a riverbank aquifer was performed to be able to simulate and predict the behavior of the flow system. The continuous hydraulic head measurements in the area of interest showed strong influence on the hydraulic head field caused by intensively changing river head at a distance from the river up to 3,500 m. Based on the results steady state and transient flow calculations were compared, and a great effort has been made to ensure that the model more precisely describe the time and space variable flow field. Beside fulfilling the standard calibration requirements, a multi-step calibration process was performed.

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The Euganean Geothermal Field (EGF) is the most important thermal field in northern Italy. It is located in the alluvial plain of the Veneto Region where approximately 17*106 m3 of thermal water with temperatures of 60–86 °C are exploited annually. A regional-scale conceptual model of the Euganean Geothermal System is proposed in this paper using the available hydrogeologic, geochemical and structural data for both the EGF and central Veneto. The thermal water is of meteoric origin and infiltrates approximately 80 km to the north of the EGF in the Veneto Prealps. The water flows to the south in a Mesozoic limestone and dolomite reservoir reaching a depth of approximately 3,000 m and a temperature of approximately 100 °C due to the normal geothermal gradient. The regional Schio-Vicenza fault system and its highly permeable damage zone act as a preferential path for fluid migration in the subsurface. In the EGF area, a geologic structure formed by the interaction of different segments of the fault system increases the local fracturing and the permeability favoring the upwelling of the thermal waters. Numerical simulations are performed to validate the proposed conceptual model using a finite difference code that simulates thermal energy transport in hydrothermal systems. A specific configuration of thermal conductivity and permeability for the formations involved in the thermal system is obtained after calibration of these parameters. This set of parameters is verified in a long-term simulation (55,100 years) obtaining a 60–70 °C plume in the EGF area. The modeled temperatures approach the measured temperatures of 60–86 °C, demonstrating that this conceptual model can be realistically simulated.

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A coupled geothermal model of the Alpokalja area, Hungary—Austria
Authors: Attila Kovács, Ágnes Rotár Szalkai, Zsolt Kercsmár and Tibor Cserny

A coupled groundwater flow and heat transport model was developed for a trans-boundary geothermal reservoir located in the Alpokalja area. The study area lies in the western part of the Pannonian Basin, at the border between Hungary and Austria. The study area contains several famous geothermal water utilizations on both sides of the border, which has an impact on natural groundwater conditions. The aim of the modeling study was to evaluate the natural-state and production-state groundwater conditions, and to make predictions on cross-boundary interferences. A three-dimensional finite element-type coupled geothermal model was constructed to provide a coherent quantitative representation of geothermal flow systems. The model described the hydraulic behavior of the flow system, the interaction between different reservoirs, and geothermal conditions.

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Gravity-driven groundwater flow systems function in topographic basins as subsurface conveyor belts. They pick up and move fluids, gases, solutes, colloids, particulate matter and heat from loading sites in recharge areas and/or on their way to the discharge areas and can deliver them “en route” or in discharge regions. Gravitational flow systems of various horizontal and vertical extents are organized into hierarchically nested complex patterns controlled by the configuration of the water table’s relief and modified by the rock framework’s heterogeneities of permeability. The systems are ubiquitous and act simultaneously on broad ranges of the spatial and temporal scales of measurement. Their universal geologic agency is manifest by numerous different, even disparate, natural processes and phenomena. Several of these are associated with geothermal heat flow. The understanding of geothermal phenomena in the context of basinal flow systems requires, therefore, an intimate familiarity with the overarching “Theory of regional groundwater flow” which, in turn, comprises two component theories: “The hydraulics of basin-scale groundwater flow systems” and “The geologic agency of basin-scale groundwater flow-systems”. The paper’s outline is based on this conceptual structure. The paper presents examples for geothermal effects of groundwater flow by means of the first theoretical models and some case studies of thermal springs and wells, and petroleum accumulations. The final section reflects the author’s conviction that geothermal studies cannot be complete without consideration and understanding of the area’s groundwater flow regime.

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Groundwater flow and geochemical modeling of the Acque Albule thermal basin (Central Italy): a conceptual model for evaluating influences of human exploitation on flowpath and thermal resource availability
Authors: Andrea Del Bon, Chiara Sbarbati, Elio Brunetti, Valentina Carucci, Alessandro Lacchini, Valentina Marinelli and Marco Petitta

Although the Acque Albule Basin has been studied since the middle of the 19th century, a comprehensive geologic conceptual model of the area has not yet been developed. The natural setting has been heavily modified by anthropic activities. Rapid evolution during the last 25 years has caused many interferences, which have led to a drastic increase of the hazards and linked risks, mainly related to water resource overexploitation and subsidence.

The implementation of an exhaustive framework has become mandatory for environmental and management purposes. Starting from a critical review of previous studies, hydrogeologic and hydrogeochemical surveys and related numerical modeling have been carried out in order to achieve a quantitative understanding of the active phenomena and processes.

Several hydrogeologic issues have been addressed concerning aquifer recharge areas and the different flowpaths of groundwater in respect to their division into a shallow and a deep circuit. Account has been taken of the groundwater chemistry as a function of water—rock interactions and mixing processes with uprising fluids. Different scenarios of groundwater flow in the Acque Albule aquifer have been built, using previously available piezometric measurements and the hydrodynamic parameters determined by in situ tests. These results led to the formulation of an updated hydrogeologic conceptual model to be further implemented, in which past, present and future anthropic instances and the potential of natural resources of the area have been included and taken into account. A sound conceptual model must rely on the design and development of a logical geo-database in which information is stored, updated and processed. This operational framework can result in a useful tool for land management, surveys planning and design, hazard and risk evaluation, identification of best practices and economic development of the area.

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A half century of reservoir property changes in the Szentes geothermal field, Hungary
Authors: András Bálint and János Szanyi

The general characterization of the Hungarian Szentes geothermal field is presented based on the review of previous research and is supplemented with the analysis of well hydraulic tests. Forty thermal wells were included in the study area, producing mainly from Upper Pannonian sandstone reservoirs. The intensive and long-term production of thermal water reservoirs without reinjection resulted in significant reservoir pressure decrease from natural conditions. By means of deep-well pressure build-up curves, deep-well capacity curves and surface pressure curves the reservoir condition changes were described in the last half century.

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Heat potential evaluation of effluent and used thermal waters in Budapest, Hungary
Authors: Anita Erőss, Ferenc Zsemle and Eszter Pulay

Europe’s largest thermal water system can be found in the capital of Hungary. The springs and wells that supply the famous baths of Budapest discharge mainly from a regional Triassic carbonate rock aquifer system. The springs have mostly been substituted by wells; only a few natural springs are known today, most of which are drained unused into the Danube.

In this study, first the heat potential of these unutilized spring waters in the three natural discharge areas was assessed. Secondly, the heat potential of used thermal waters of three baths was calculated. At the springs discharge and temperature measurements were carried out. In the case of the baths, water management data were evaluated. At the Boltív Spring at the foot of Rózsadomb, the heat potential calculation shows that cooling the spring water to 5 °C would provide 6 MWth thermal capacity, providing a stable energy source for heat pumps. From the overflowing water of the springs of Rudas Bath at the foot of Gellért Hill, a total of 107 kWth heat could be utilized when cooling it to 5 °C, possibly by heat pump system. However, the heat potential of the Bründl Spring is not sufficient for geothermal utilization, mainly due to lack of end users in the vicinity of the spring. Together with the wastewater of the thermal baths, the effluent springs and wastewaters of pools carry a total of 25 MWth waste heat, which is a considerable amount compared to the needs of a public institution. The importance of this study is in the assessment of such potential heat sources (unused lukewarm and thermal springs, wastewater of spa pools) which are present either naturally or artificially, and do not require further thermal water production for heating purposes.

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The heat content of shallow or deep aquifers can be used for space heating. Two innovative systems are described below in detail: a geothermal heat pump system based on a single well in China (= shallow), and a cascading use of tunnel waters (= deep) in Switzerland. The “Single Well System” (HYY SWS) was invented and developed by Beijing Ever Source Science & Technology Development Co., Ltd (HYY) to provide buildings with heating and cooling as well as with domestic hot water. The powerful system operates at about 500 kWth capacity. Unlike traditional groundwater heat pump systems, in which two wells are used (one for pumping groundwater out and the other to dispose of cooled water), the HYY SWS uses only one, specially designed well for production and reinjection. A borehole with a depth of about 70–80 m and a diameter of 0.5 m is drilled for HYY Single Well Systems. The necessary local geologic site condition is to have a shallow aquifer with a hydraulic conductivity of 10−3 m/sec or higher. Many such systems operate now in China, several of which, for instance, serve the 2008 Summer Olympic Facilities in Beijing. Switzerland has, in its mountainous parts, hundreds of deep tunnels. Tunnels drain the rock overburden and, depending on its thickness, water temperatures up to 50 °C can be encountered and utilized. The most straightforward and cheapest form of tunnel heat usage is to collect and transport inflowing waters via ducts to the portals, with as little temperature drop as possible. The thermal power depends on flow rate and temperature. At or near the portals the heat content of the waters can be used for various applications. When the temperature level of the tunnel water outflows is too low for direct applications (e.g. for district heating), heat pumps are employed. From Switzerland a whole suite of uses can be reported: space heating, greenhouses, balneology and wellness, fish farming. At the northern portal of the 35 km long Loetschberg base tunnel at Frutigen, the tunnel water is used subsequently (“cascading”) for space heating, greenhouse, and fish farming (incl. caviar production).

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New geothermal well-completion and rework technology by laser
Authors: Péter Bajcsi, Tamás Bozsó, Róbert Bozsó, Gábor Molnár, Viktor Tábor, Imre Czinkota, Tivadar M. Tóth, Balázs Kovács, Félix Schubert, Gábor Bozsó and János Szanyi

Our research team has developed a new well completion and rework technology involving lasers. The system is made up of a high-power laser generator and a custom-designed directional laser drilling head. The laser head is attached to a coiled tubing unit to maximize production and to carry out special downhole tasks. In this phase of the development effort, laser technology is particularly well suited to cost-efficiently drill short laterals from existing wells in a single work phase, drilling through the casing and cement as well as the formation. The technology, which is an extended perforation solution, enables a more intensive interaction with the downhole environment and supports cutting edge subsurface engineering scenarios such as barite removal. Laser-induced heat treatment appears to be a suitable alternative to effectively remove the almost immovable deposits and scales from thermal water-well pipes.

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