Temperature and radon-222 as tracer of groundwater flow: application to El Hamma geothermal aquifer system, southeastern Tunisia (original) (raw)
Related papers
Hydrogeochemistry of Geothermal Resources in the Eastern Part of Turkey: A Case Study, Varto Region
Varto, in the eastern part of Turkey, is settled around the conjunction point of the East Anatolian (EAF) and North Anatolian (NAF) Fault zones. The border of these tectonic zones constitutes seismic belts marked by young volcanic associations and active faults, the latter allowing circulation of waters as well as heat. For this reason, there are various geothermal systems having several hot water springs in the region. The distribution of hot water springs in the Varto Region roughly parallels the distribution of the fault systems and young volcanism. Samples from five hot water and two mineral water springs together with cold (peripheral) waters were collected. Hot water samples were assessed through geothermometers in terms of geothermal usage opportunities. All water samples were measured and analyzed for physical, chemical and isotopic compositions. Physical parameters such as pH, electrical conductivity (EC; µS/cm) and temperature (T; ºC) were measured in field. Primary (major ions) and secondary constituents (trace elements and heavy metals) and Oxygen 18 ( 18 O), Deuterium (D), Tritium ( 3 H) isotopic compositions were determined by mass spectrometry. Average discharges of hot water springs in the study area are between 1 -5 L/sec. Surface temperatures of these springs vary 22.5 to 32ºC, electrical conductivity (EC) values 2100 to 5775µS/cm. Average discharges of mineral waters in that site are between 0.5 -2 L/sec. Surface temperatures of them were measured as 13.2 and 14.8ºC. Their electrical conductivity values are also in the range of 719 -751 µS/cm. The average discharges of cold water springs in the study area are between 1 -150 L/sec. Surface temperatures of these springs change between 4.9 -11.7ºC and electrical conductivity values 51 -199 µS/cm. Regarding pH values, water samples belonging to the site are entirely distinguished into the pH range of ~5.4 -~6.2 for hot and mineral waters, ~6.2 -~7.7 for cold waters. Hot water springs have acidic character, whereas pH values of cold water springs change from slightly acidic to neutral and slightly basic. In the vicinity of the study area, volcanic and volcaniclastic rocks crop out. Groundwater flow in the volcanic rocks is also controlled by the presence of structural features as suggested by the alignment of the springs. Their cooling fractures extend several meters in depth, providing a good avenue for deep penetration and circulation of groundwater. According to the Piper diagram, springs fall into Na-HCO 3 -Cl type for thermal waters and Ca-HCO 3 type for cold waters. Due to the fractures allowing deep circulation of groundwater and dominant Na-Cl component, the host rock is probably volcanic origin. Hot waters have the same recharge area with cold waters. The information on the fluid origin and the age of springs depicted by their 18 O-D and T contents shows that they are all meteoric origin and hot water springs are older than 50 years. Reliable reservoir temperature ranges for hot waters were obtained with Li-Mg geothermometer and β-Cristobalite geothermometer as 44 -66ºC and 54 -80ºC, respectively. These values are also checked with Saturation Indices (SI) vs T diagrams. Results of SI vs T diagrams point out equilibration with calcite and aragonite minerals which gives comparable results with Li-Mg and β-Cristobalite geothermometers. It is possible to get 80°C reservoir temperature by drilling in this area with the help of field observations and the data obtained. The geothermal potential of the study area have not been used up to now. This geothermal district might make a considerable contribution to tourism and agriculture usages.
The area of El Hamma, southeast of Tunisia, is characterized by warm groundwater. The aquifer in the city of El Hamma is considered the main source of water to meet the needs of agricultural, industrial, domestic, and traditional baths. Nowadays, groundwater flow in the aquifer system and the thermal origin have been not well explained. The objective of this study is to develop a conceptual model of the geothermal groundwater flow path based on the temperature distribution in the aquifer in the study area.The groundwater temperature data was collected from 130 wells and implemented into a database. The sampled wells depth range between 25 and 80 m below ground level at temperatures between 18 and 65 degrees Celsius. The temperature remains constant throughout the year, regardless of the external climatic conditions. The variographic analysis and ordinary kriging techniques were used to map the spatial distribution of temperature in the study area. The conceptual model, hydrodynamic,...
Euro-Mediterranean Journal for Environmental Integration
In southern Tunisia, the lack of permanent surface water, associated with drought conditions, leads to an endless abstraction from the limited low renewable multi-layered aquifer system of Système Aquifère du Sahara Septentrional containing two principal aquifers, the complex terminal and the Continental Intercalaire (CI) multi-layered systems. The deepest aquifer embodies the low-enthalpy thermal resources of Southern Tunisia. The thermo-mineral surface manifestations of the conductively heated waters reveal the complexity of the geotectonic history of the region and create oases systems in net contrast to the desertic landscape of the Chotts region. As agriculture constitutes the principal economic activity in the studied area and as it is currently threatened by thermal water quality degradation, the present hydrogeological investigation aims for a characterization of the CI thermal resources on the basis of a critical quality evaluation. Thus, different geothermometry approaches have been applied to characterize the low-enthalpy thermal field showing a temperature ranging from 27 to 72 °C. The application of cations geothermometers owns to different temperature estimations ranging from 28 to 202 °C. Based on Na +-Mg 2+-K + , K +-Mg 2+-Ca 2+ and HCO 3 −-Cl −-SO 4 2− geoindicators, the CI thermal resources refer to immature waters characterized by MI varying from − 0.5 to 0.19. The assessment of groundwater chemical composition based on a Durov diagram proves that CI thermal water is governed by mixing between different water bodies with relative abundance of Na + , Cl − , and SO 4 2− elements. According to D'Amore genetic diagram and meteoric genesis indices, the analyzed groundwater derived from deep circulation in sandy formations. The water quality can change along fluid migration pathways expressed by scattered isotopic and chemical data and a number of mixing ratios. Most changes in the background CI composition result from continuous pumping that modifies natural flows and increase quality degradation.
Environmental Science and Pollution Research, 2018
Assessing groundwater flow path in a thermal aquifer, such as El Hamma aquifer, southeastern Tunisia, and its lateral communication with the adjacent Jeffara-Gabes aquifers, is a very complex operation which requires the integration of several approaches to understand and explain the reality of phenomenon. In this study, geochemical and isotopic data, Kohonen selforganizing map, temperature cooling trend, and kriging techniques were used to assess groundwater flow path in hydrothermal aquifer of El Hamma-Gabes, Tunisia. For this objective, 32 sampled wells are analyzed for major ions, electric conductivity, pH, total dissolved solids, and stables isotopes (δ 2 H and δ 18 O). Geochemical diagrams reveal that groundwater chemistry was controlled by evaporation, and rock-water interaction with a dominant water facies was Cl•SO 4-Na•Ca-Mg. Kriging techniques were used to highlight groundwater flow path. Kohonen self-organizing map shows that the waters are clustered into three classes according to chemical and isotopic composition. These clusters represent a hydrothermal groundwater class from the Continental Intercalaire aquifer, a shallow groundwater class corresponding to Jeffara-Gabes aquifer and mixed water class. Groundwater cooling trend and stable isotopes indicate that groundwater flow is toward west to east part of study area, indicating a recharge of Jeffara aquifer from El Hamma thermal aquifer.
Environmental Earth Sciences, 2018
In this study, the Abgarm-Avaj geothermal system in Iran is investigated by analyzing hydrochemistry and stable environmental isotopes of water samples collected from cold and thermal water springs and the Khare-Rud River together with tectonic settings. The findings reveal that the geothermal system is associated with the deep fault zone of Hasanabad and can be categorized into a convection dominated and non-magmatic geothermal system in accordance with the catalog of geothermal play types presented by Moeck (Renew Sustain Energy Rev 37:867-882, 2014). In fact, local rainfall that is occurred over the Kuhe-Bozorg limestone highlands percolates into a high depth along the main active fault of Hasanabad and then heats and emerges finally at the lowest topographic elevation of the fault in the form of thermal springs characterized by temperature ranges from 30 to 52 °C. The water samples from the thermal springs are of a high electrical conductivity value (ranges from 6585 to 11265 µS/cm) with the chloride water type. The lower circulation depth of meteoric water in the geothermal system is estimated to be about 3000 m by considering the possible maximum geothermal gradient of about 46 °C/km. The stable isotopes ratios analysis suggests that thermal water originates predominantly from rainfall occurring over the higher elevations, since the oxygen-18 ratios of the thermal spring waters are depleted than that of the cold spring waters. The equilibrium temperatures of the geothermal system are estimated via using the Na-K (Truesdell, Summary of section III: geochemical techniques in exploration. In: Proceedings of the 2nd U.N. symposium on the development and use of geothermal resources, vol 1. U.S. Government Printing Office, Washington, DC, pp liii-lxxx, 1976) and Na-K (Tonani, Some remarks on the application of geochemical techniques in geothermal exploration. In: Proceedings of advances in European geothermal research, 2nd symposium, Strasbourg, pp 428-443, 1980) geothermometers are 142-148 and 146-153 °C, respectively, which fall within the temperature range suggested by the mineral saturation indices (137-160 °C) and by the warm spring mixing model (135-164 °C) for the thermal spring waters. Furthermore, the results show that geothermal hot water mixes predominantly with shallow cold groundwater during ascending, where the portion of the cold shallow and deep-hot waters is about 70 and 30%, respectively.
Hydrochemistry and geothermometry of thermal groundwater of southeastern Tunisia (Gabes region)
Arabian Journal of Geosciences, 2012
Given the vital importance of water and energy in desert regions, we undertook a study dealing with the deep reservoirs in Gabes area, which is located in the southeastern part of Tunisia. Geothermal resources are taken from the Intercalary Continental [or Continental Intercalaire (CI)], known as the largest deep aquifer in Tunisia and are used in a number of applications, mainly in agriculture. Previous investigations performed on the thermal waters of this area focused on the genesis of the deep waters with regard to the thermal features of geothermal reservoirs. A more detailed investigation has been carried out, considering both deep and shallow waters. In order to estimate the potential temperatures of deep reservoir in the Gabes area, we developed a synthetic study including chemical geothermometers, multiple mineral equilibrium approach, and other approaches. Chemical types of the thermal waters and effects of mixing between shallow cold waters with deep thermal waters were also discussed. In fact, the application of Na-K-Mg diagram relative to deep geothermal reservoir capitulate estimated temperatures (about 90°C). In addition, the multiple mineral equilibrium approach submits a similar estimated temperature ranging between 65 and 70°C, showing a disequilibrium status which indicates a possibly mixing with surface water. Indeed, wells exploiting the CI aquifer in the south part of the studied area showed the same characteristics, corroborating the reliability of the applied methods.
Geothermics, 2012
Geothermal waters originating from three aquifers in northwestern Romania have been analyzed for several physico-chemical parameters namely, pH, temperature, electrical conductivity, total dissolved solids, hardness, redox potential, and chemical oxygen demand. In addition, major dissolved ions and organic matter content and radium and radon occurrence have been analyzed. The three aquifers are the fissured Middle Triassic limestone/dolomite aquifer from Oradea, the Lower Cretaceous limestone aquifer from 1Mai-Felix Spa, and the Lower Pontian (Late Miocene) granular (sand) aquifer from Sȃcuieni. The first two aquifers belong to the Inner Dacides and the last to the Pannonian Basin. We have examined the relationships between the occurrence of radium and radon in the thermal waters and the hydrochemical and geothermal features of the aquifers, which may impart a secondary control on the activity of these radionuclides. According to their chemistry, the thermal waters were classified as sulfate-bicarbonate-calcium-magnesium (Oradea), bicarbonate-sulfate-calcium-magnesium (Felix-1Mai Spa), and bicarbonate-sodium-chloride (Sȃcuieni). The activities of radon and radium were higher in Sȃcuieni (up to 22.88 and 1.40 Bq/L) and Oradea (up to 34.82 and 1.82 Bq/L) than in Felix-1Mai Spa (up to 16.76 and 0.19 Bq/L). The data shows that the thermal processes may control the migration and distribution of radionuclides, and that the mobility of radionuclides may be influenced by several physico-chemical parameters, such as pH, total dissolved solids, and redox potential, or by some chemical processes, such as adsorption on humic acids or partitions into the organic (hydrocarbons) phase. The data illustrate no significant differences between the parameters analyzed from February to July 2009, proving that the production regime of the aquifers has a minor impact on their chemical and physical parameters.
Journal of Volcanology and Geothermal Research, 2011
The volcano-hydrothermal system of El Chichón volcano, Chiapas, Mexico, is characterized by numerous thermal manifestations including an acid lake, steam vents and boiling springs in the crater and acid and neutral hot springs and steaming ground on the flanks. Previous research on major element chemistry reveals that thermal waters of El Chichón can be divided in two groups: (1) neutral waters discharging in the crater and southern slopes of the volcano with chloride content ranging from 1500 to 2200 mg/l and (2) acid-toneutral waters with Cl up to 12,000 mg/l discharging at the western slopes. Our work supports the concept that each group of waters is derived from a separate aquifer (Aq. 1 and Aq. 2). In this study we apply Sr isotopes, Ca/Sr ratios and REE abundances along with the major and trace element water chemistry in order to discriminate and characterize these two aquifers. Waters derived from Aq. 1 are characterized by 87 Sr/ 86 Sr ratios ranging from 0.70407 to 0.70419, while Sr concentrations range from 0.1 to 4 mg/l and Ca/Sr weight ratios from 90 to 180, close to average values for the erupted rocks. Waters derived from Aq. 2 have 87 Sr/ 86 Sr between 0.70531 and 0.70542, high Sr concentrations up to 80 mg/l, and Ca/Sr ratio of 17-28. Aquifer 1 is most probably shallow, composed of volcanic rocks and situated beneath the crater, within the volcano edifice. Aquifer 2 may be situated at greater depth in sedimentary rocks and by some way connected to the regional oil-gas field brines. The relative water output (l/s) from both aquifers can be estimated as Aq. 1/Aq. 2-30. Both aquifers are not distinguishable by their REE patterns. The total concentration of REE, however, strongly depends on the acidity. All neutral waters including high-salinity waters from Aq. 2 have very low total REE concentrations (b 0.6 μg/l) and are characterized by a depletion in LREE relative to El Chichón volcanic rock, while acid waters from the crater lake (Aq. 1) and acid AS springs (Aq. 2) have parallel profile with total REE concentration from 9 to 98 μg/l. The highest REE concentration (207 μg/l) is observed in slightly acid shallow cold Ca-SO 4 ground waters draining fresh and old pyroclastic deposits rich in magmatic anhydrite. It is suggested that the main mechanism controlling the concentration of REE in waters of El Chichón is the acidity. As low pH results from the shallow oxidation of H 2 S contained in hydrothermal vapors, REE distribution in thermal waters reflects the dissolution of volcanic rocks close to the surface or lake sediments as is the case for the crater lake.
Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys
Journal of Earth Science
This study was conducted to identify the origin, hydrogeochemical processes and evolution of groundwater in a tectonic valley. This study was carried out with the aim of quantifying the proportions of groundwater flows contributing to the water chemistry abstracted in a zone of convergence favored by the presence of active faults. The study area is located in the Trans-Mexican Volcanic Belt. End members methodology was applied to identify the mixing of hydrothermal with fresh groundwater, where changes in the aquifer geology result in distinct groundwater chemical signatures. Ternary mixing was quantified using conservative elements. Moreover, other evolutionary processes, such as ion exchange and silicate weathering occur due to changes in the geology of the area. In ternary mixing, each of the end members is associated with the lithology through which it circulates. The local flow contributes 70% of the water to the system, the intermediate flow contributes 14%, and the regional flow contributes 16%. Three types of water are produced: Na-HCO3, due to the interaction of water with volcanic rocks of rhyolitic composition, Na-Mg-HCO3, due to the interaction of water with volcanic rocks of basaltic-andesite composition, and Ca-HCO3, due to the interaction of water with sedimentary calcareous rocks. KEY WORDS: hydrogeochemistry, ternary mixing, end members, conservative elements, local flow, Mexico. 0 INTRODUCTION Volcano-sedimentary aquifers in tectonic valleys are complex due to the interdigitation of sedimentary and volcanic materials as well as the presence of faults. The hydraulic conductivity is influenced by this heterogeneity; moreover, the infiltration rates through fractures may be extremely high (Cook et al., 2003). In general, these changes in geological conditions are reflected in the chemical characteristics of groundwater. Different studies have been investigated to understand these processes in tectonic valleys, some with the presence of active faults. These hydrogeochemical processes facilitate the mixing of thermal and cold groundwaters, as reported in a study to identify geothermal fields in the Xinzhou Basin, Shanxi Province, China (Han et al., 2010). Hydrogeochemical studies allowed to define the mixing processes of water with distinct temperatures at Pocheon, South Korea (Chae et al., 2006). In Romania, aquifers strongly influenced by hydro-geothermal phenomena acting within two main geological structures were identified (Povară et al., 2008). Studies in the valleys of central Italy showed that recent or active
Groundwater chemistry and radon-222 distribution in Jerba Island, Tunisia
Journal of Environmental Radioactivity, 2018
The present study integrates hydrogeological, hydrochemical and radiogenic data of groundwater samples taken from the Plio-Quaternary unconfined aquifer of Jerba Island, southeastern Tunisia, in order to interpret the spatial variations of the groundwater quality and identify the main hydrogeochemical factors responsible for the high ion concentrations and radon-222 content in the groundwater analysed. Thirty-nine groundwater samples were collected from open wells widespread on the island. Physical parameters (EC, pH, TDS and T°) were measured, major ions (Ca 2+ , Mg 2+ , Na + , K + , Cl − , SO 4 2− , NO 3 − and HCO 3 −) were analysed and 222 Rn concentrations were determined using a RAD7-H 2 O. Hydrogeochemical characterisation revealed that groundwater from the Jerba aquifer has several origins. Basically, two water types exist in the island. The first one, characterized by a low to moderate salinity with a chemical facies CaeMgeCleSO 4 , characterizes the central part of Jerba (a recharge area) due to carbonate and gypsum dissolution. The second water type with high salinities, dominated by NaeKeCl type, was observed in coastal areas and some parts having low topographic and piezometric levels. These areas seem to be affected by the seawater intrusion process. The 222 Rn concentrations in groundwater samples in Jerba varied from 0 Bq.L −1 to 2860 Bq.L −1 with an average of 867 Bq.L −1. The highest values were registered in the western coastal wells and near the fault of Guellala. However, the central and eastern wells showed low radon levels. Compared to 222 Rn activity in some countries with the same lithology, radon concentrations in the Jerba unconfined aquifer have higher values influenced by the structure of the aquifer and by seawater inflow enriched with 222 Rn resulting from the decay of uranium derived from phosphogypsum deposits in the gulf of Gabes. The EC and 222 Rn spatial variability in the study area were mapped using ARC Map 10.3 software. Hydrochemical results in addition to geological data and radon activities confirm the existence of vertical communication between the Miocene aquifer and the unconfined Plio-Quaternary aquifer through fault system and a lateral communication with the sea via seawater intrusion.