Na-HCO3 Type Research Articles

Hydro-geochemistry and Related Processes Controlling the Composition of Thermal Waters in the Lake Natron Basin, Northern Tanzania

Lake Natron Basin (LNB) forms part of the eastern branch of the East African Rift System (EARS) in Tanzania. The basin is endowed with thermal springs flowing towards the lake from the western, northwestern, southwestern and eastern parts. The western, northwestern and south-western thermal springs emanate from fractures in the basaltic rocks while in the east, they originate from the western flank of the Gelai volcano. There are limited studies on these springs, thus their geochemical differences and distributions of physicochemical parameters are not well understood. A hydrogeochemical study was conducted to interpret available geochemical data from the LNB springs, including cold and thermal water to allow their geochemical characterization. Results have shown that LNB water is dominated by sodium (Na+), chloride (Cl-) and bicarbonate (HCO3-) ions. Three hydro-chemical facies have been identified forming Na-Cl, Na-HCO3 and Ca-HCO3 water types. This study has also revealed that thermal water in the north-western part of the basin is highly mineralised and gradually becomes diluted toward south-west and south due to groundwater incursion. Water-CO2-rock interaction affects the overall chemistry of thermal water leading to HCO3- water, particularly in the east of the basin. While few springs from the western side of the basin indicated maturity of the thermal waters, other springs indicated mixed Cl-HCO3/peripheral water; while the cold waters are HCO3 type. It is recommended to take precautions when planning geothermal projects to avoid corrosion and scaling of production facilities. Similarly, mixing or dilution of thermal water with shallow groundwater can affect the temperature and the composition of Cl-.

Extricating hydrogeochemical evolution of geothermal fluids of an unexplored section in North-Eastern Himalayas, Arunachal geothermal province, India

The thermal springs of the study area are situated in North-eastern Arunachal Himalayas, India along Subansiri and Siang River valleys with surface temperature ranging between 20 and 57 °C. The pH of thermal springs varies from 7.69 to 9.31, indicating near neutral to alkaline nature of thermal and non-thermal waters. The major geochemical processes influencing hydrochemistry are demonstrated using conventional graphical plots, geochemical modelling by PHREEQC and multivariate statistical analysis. The thermal waters of Chetu and Taksing in Subansiri valley are primarily Na–Cl and Na–HCO3 type, while, thermal water of Yangte in Siang valley is also mixed water-type and others of Ca–Mg–HCO3 type. The geochemically distinct type of waters is obvious from dendrogram derived from hierarchical cluster analysis. Quartz geothermometer predicts reservoir temperatures of thermal springs of 88 ± 13 °C; while, Na–K Giggenbach geothermometer predicts 182 °C and 176 °C for Chetu and Taksing hot springs. Thermal waters are immature and highly prone to mixing with meteoric waters as evident from enthalpy-chloride modelling. Evaporite dissolution, silicate weathering and ion exchange processes are found to contribute to total ion budget in geothermal waters. The saturation indices studies depict oversaturation of all thermal waters with calcite and dolomite. Considering all geochemical features, a conceptual hydrological model resembling geomorphology and origin of thermal springs of North-Eastern Arunachal Himalaya has been proposed. The thermal waters of Subansiri valley display very high Sr and F− content which prohibit them from drinking and utilization purposes. High concentration of toxic elements is addressed to geogenic causes over anthropogenic contributions due to lesser accessibilities at hot spring spots.

Identifying interactions of linked irrigated lake-groundwater system by combining hydrodynamic and hydrochemical method.

During the irrigation period, the interactions between the linked lake-groundwater systems are complicated and change. This is because natural and human activities are happening at the same time, which makes it harder to identify the interactions. This study uses data on water level, hydrochemistry, and hydrogen-oxygen stable isotopes to analyze the hydrodynamics, electrical conductivity (EC), isotopic characteristics, and spatial distribution of lake water and groundwater to reveal lake-groundwater interactions. The results indicate that the hydrochemical type of Chagan Lake and groundwater is dominated by the HCO3-Na type. The key hydrochemical indicator EC obtained by principal component analysis (PCA) can be used to reveal the lake-groundwater interaction, and the interaction should be identified by location according to the significant correlation between hierarchical clustering results and regional distribution. The lake body's geographic coefficient of variation for EC and δ18O is small, and irrigation return flow is one factor in the region's surface water's significant spatial variation for EC and δ18O. The three study methods indicate that the groundwater supplies the lake in the vicinity of the Huoling River-Hongzi Pool, while in other sections, the lake water leaks and replenishes the groundwater, exhibiting geographic inconsistency. The isotope method was employed as a support tool to determine that groundwater might recharge the lake at Xinmiao Pool. According to the calculations of the Mix SIAR model, the groundwater recharge contribution rate in the Xinmiao Pool section is approximately 51%, while in the remaining sections, the contribution rate of lake water to groundwater ranges from approximately 25% to 52%. Therefore, the identification of the interaction is crucial for the linked irrigated lake-groundwater system where water sources are scarce and threatened by agricultural pollution.

Water quality assessment and pollution of Akarçay River, Türkiye

River water is a vital source of agricultural activities and ecology in the Akarçay basin. This study aims to determine the water quality of the Akarçay River. According to this purpose, 12 water samples that were thought to be affected by different polluting sources were taken through the flow path of the river and physicochemical analyses were performed. The water quality index (WQI) was used for drinking purposes, and the analysis results were compared with World Health Organization and Turkish drinking water standards. Irrigation quality parameters like sodium absorption ratio, residual sodium carbonate, and magnesium hazard were also calculated, showing that most samples are unsuitable for irrigation. The river water is of the Ca–Mg–HCO3, Na–Cl and Na–HCO3 types. It has been determined that the river water is unsuitable for irrigation and drinking water due to its high EC, Na+, Cl−, SO42−, As, B, F−, Fe, and Mn content. According to the WQI results, river water has different classifications from excellent to unsuitable. Geothermal water mixture and industrial, domestic and agricultural activities are the primary pollution sources. At the same time, the evaporation that the river is exposed to indicates the solute concentration and changes the usage characteristics.

Deciphering Hydrochemistry and Fluid-Mineral Equilibria from Characteristic Low-Enthalpy Geothermal Waters of Himalaya and Eastern India

Geothermal energy, with associated low-carbon emissions compared to conventional fossil fuels, is presently one of the potential renewable energy sources. The decryption of the chemistry of thermal manifestations of geothermal systems, in terms of relative abundances of various chemical facies, is mandatory before launching systematic geothermal exploration in a given area as it provides valuable information on the basic characteristics of the geothermal reservoir. For the present study, three clusters of hot springs have been selected -1) Shyok-Nubra valleys geothermal prospect in NW Himalaya, 2) Subansiri valley geothermal areas in NE Himalaya and 3) the hot spring system occurring along Munger-Saharsa Ridge Fault Zone (MSRF) in the Eastern part of India. The study of these geothermal systems with low to moderately high temperatures of 35−75°C, has been carried out with two main objectives. The first objective is to estimate reservoir temperature and other characteristics in the three above-mentioned hot spring groups using conventional chemical geothermometry techniques for the first-hand assessment of the quality of the geothermal resource and postulating its possible application. The second objective of the study is to understand the distribution of stable isotopes (δ2H and δ18O) in the studied geothermal systems to reveal reservoir-related hydrological aspects of the geothermal system. The three groups of hot springs show large variations in total dissolved solids (TDS) from <150 to about 1800 mg/L. Enigmatic and inexplicably low TDS values of 126 to 150 mg/Lare reported from the three Bhimband hot springs along MSRF Zone. These springs discharge Ca−Mg−HCO3 type water. The dearth of dissolved ionic species in these springs indicates lack of water-rock interaction in Bhimband area. Silica is the most abundant solute species and corresponds to a reservoir temperature of about 75°C. It may be inferred that relatively inert lithology in the reservoir and very high water-to-rock ratio might have rendered the observed chemical signatures to Bhimband hot springs. Shyok-Nubra springs at Changlung and Panamik are predominantly Na-HCO3 type with TDS values of about 1700 and 550 mg/L, respectively. These hot springs give an indication of water-rock interaction in different types of lithology at temperatures of 120 to >150°C resulting in the observed chemical differences between the two. Thermal water at Taksing in NE Himalaya is also Na−HCO3 type. Chetu hot spring with TDS of >1100 mg/Lis anomalous in two ways. First, it has a very high SO4 content of 358 mg/Land second, it has the lowest silica value. There is a possibility that the Chetu hot spring has its chemistry influenced by the dissolution of sulfates of Ca and Na. Preliminary stable isotope study indicates that the geothermal fluid is derived from meteoric sources. The lack of any indication for positive δ18O-shift suggests that reservoir temperatures of the springs are generally low. Keywords: Thermal Waters, Hydrogeochemistry, Reservoir Temperature, Stable Isotopes, Himalayas, Bihar

Structural control effects on hot springs’ hydrochemistry in the northern Red River Fault Zone: Implications for geothermal systems in fault zones

Hot springs in fault zones play a critical role in studying the structural effects on the evolution of geothermal systems. The northern Red River Fault Zone lies in the western part of Yunnan, southwest China, with hot springs ranging from low-medium to high temperatures. From 2013 to 2019, thirty water samples were collected to analyze hydrochemical characteristics and structural effects. The hydrochemical compositions of hot springs mainly come from the weathering or dissolution of the carbonate, evaporite, and silicate minerals, and the cation exchange. High contents of F and Si in the hot springs of high temperature enhance water–rock interactions. For hot springs along faults, there is a positive correlation between TDS and circulation depth. Li/Cl ratios show that geothermal waters have three reservoir sources of different depths. Hot spring waters from shallower reservoirs are mainly Ca-SO4 or Ca-HCO3 type, and those from deeper reservoirs are Na-HCO3 type. Hydrochemical compositions of the hot springs are controlled by faults in terms of circulation depth and geothermal reservoirs. Hot spring waters are mixed, with the proportions of cold water ranging from 60% to 90%. The hot springs with varying mixing ratios may indicate the heterogeneity of fault networks and different reservoir sources. This study underlines the hydrochemical evolution of geothermal water along faults, with key implications for the understanding and exploitation of geothermal systems in the fault zone and similar regions.

Hydrochemical, D–O–Sr isotopic and electromagnetic characteristics of geothermal waters from the Erdaoqiao area, SW China: Insights into genetic mechanism and scaling potential

The Erdaoqiao area has been the hot area of geothermal resource prospecting in southwestern China. Significance difference of scaling potential has been found between left and right riverbanks of the Erdaoqiao area. However, there still has no interpretation for the scaling difference since the genetic mechanism of geothermal waters remains unclear. In this study, hydrochemical, D–O–Sr isotopic and electromagnetic (EM) approaches were integrated to clarify the genetic mechanism and quantitively evaluate scaling potential of geothermal waters. All geothermal waters belonged to Ca–Na–HCO3 type and were determined by the weathering and/or dissolution of carbonates (66.87%) and silicates (31.53%) with cation exchange based on hydrochemical and Sr isotopic analyses. Na–K–Mg triangle diagram indicated they were immature water mixed by shallow cold water. Quartz geothermometer indicated the shallow reservoir temperatures (after cold–water mixing) of left riverbank (88.46 °C–90.51 °C) were higher than those of right riverbank (61.20 °C–87.89 °C). Silica – Enthalpy methods revealed the initial geothermal reservoir temperatures and cold-water mixing ratio were 102.03 °C–138.93 °C and 65.24%–85.87% in the right riverbank, 144.11 °C–146.76 °C and 73.08%–74.79% in the left riverbank of the Erdaoqiao area. D-O isotopes proposed the geothermal waters were recharged by atmospheric precipitation in the elevation of 4957 m to 5118 m. Therefore, the genetic model of geothermal waters in the Erdaoqiao area can be constructed. Stronger calcite scaling in left riverbank was attributed to deeper circulation identified by higher reservoir temperature and electromagnetic exploration. Quantitively evaluation demonstrated that the weight of scaling during 48 h in left riverbank (2968 kg) was four times higher than that in right riverbank (748 kg). The achievements of this study contribute to geothermal exploration in the Erdaoqiao and other similar areas worldwide.

Hydrogeochemical processes and groundwater evolution in complex volcanic highlands and alluvio-lacustrine deposits (Upper Blue Nile), Ethiopia.

Lake Tana basin encompasses a wide regional volcanic aquifer system, in the northwestern highlands of Ethiopia. It has significant water resource potential for water supply and irrigation purposes. The objective of this study was to assess the physiochemical characteristics of the surface water-groundwater and investigate the processes controlling groundwater chemistry. A total of 273 water samples were collected from different water points for major ions and stable isotope analysis, representing different physiographic and hydrogeologic regions. Multivariate statistical, graphical methods, saturation and speciation modelling were used jointly to characterize water chemistry and to define hydrogeochemical processes. The Piper plots in combination with cluster analysis and isotope hydrological data indicate that, generally, the groundwater chemistry of the basin can be classified into (1) low TDS Ca-HCO3, Ca-Mg-HCO3, and Ca-Na-Mg-HCO3 type water which is relatively enriched in δ18O-δ2H and depleted in δ13C. These are recharge waters, which are characterized by low rock-water interaction; (2) brackish Mg-Na-Ca-HCO3 type water which is relatively depleted in δ18O-δ2H and enriched in δ13C; and (3) low TDS Na-(Ca)-HCO3 and Na-HCO3 type water which varies from less to more depleted in δ18O-δ2H and is characterized by relatively enriched δ13C. The cross-plots of the major cations vs. HCO3- and stability diagrams show that the primary processes controlling the groundwater evolution in the Lake Tana basin are alumino-silicate weathering and dissolution. Studying the hydrogeochemical characteristics of a complex geologic system with integrated approach helps to understand the complex groundwater flow system and flow dynamics, which in turn helps for proper groundwater utilization and future management.

Hydro-chemical Characteristics of Melt Water Draining from Glaciers of Rongdo Basin, Shyok Valley, Ladakh

Abstract Physico-chemical parameters of meltwater of 20 water samples from glaciers of Rongdo basin, Shyok valley are presented here. The concentration of cations and anions of the two valleys were found in the order Ca>Mg>Na>K and HCO3>SO4>Cl>NO3 respectively. Significant altitudinal variation was found in major ions as indicated by the increase of TDS of glacial melt and stream water samples downstream. Gibbs plot shows chemical weathering of the rock forming minerals as the main cause for contributing ions to the melt water. The dominant order of hydrogeochemical water types identified is Ca-HCO3, is due to the water rock interaction which leads to the easy dissolution of carbonate and silicate minerals. However, few glacial melt and stream water have the influence of precipitation and meltwater runoff on chemistry. The hot spring falls in Na-HCO3 type, a typical of deeper groundwater influenced by ion exchange processes. Scatter plots of HCO3+SO4 vs. Ca/Na Plot and Ca/Na vs. HCO3/Na clearly indicates that the weathering of carbonate and silicate play a dominant role on groundwater chemistry. Two chloro-alkaline indices indicate reverse exchange reaction between Na+, K+, Mg2+and Ca2+. The physical parameters and major ions are within the permissible concentrations as per WHO and BIS indicating water is good for drinking and domestic purposes. The groundwater is suitable for irrigation as per the quality parameters and plots including EC, sodium percent (Na%) and sodium adsorption ratio (SAR).

Geochemical Signatures of Bara Basin Aquifers, Kordofan State, Sudan

Purpose: In this paper, geochemical investigation has been carried out to study the concentrations of major cations; Sodium (Na+), Potassium (K+), Magnesium (Mg2+), and Calcium (Ca2+), and major anions; Chloride (Cl-), Bicarbonate (HCO3-), Nitrate (NO3-) and Sulphate (SO42-), other parameters such as (pH), Electric conductivity and T.D.S were also studied in all water samples taken from wells in Bara basin.
 Methodology: Forty five (45) water samples have been collected from wells. Lab works were done at Groundwater and Wadis Directorate (GWD), Khartoum State according to Sudanese Standards and Metrology Organization, (2002), to study the major cations and major anions.
 Findings: The results revealed that the average value of pH was (7.9) E.C values were (843.4 μS/cm) and T.D.S values were (59 mg/l). The average concentrations of the major cations obtained were; Na+ (126.3), K+ (5.22), Mg2+ (28.30), Ca2+(66.41) and the major anions (mg/l) were; Cl- (159.00), HCO3- (165.30), NO3- (156.70) and SO42- (164.70). The (Na/Cl) ratio is (2.47) is also high which reflects the abundance of (Na+) ions relative to the Chloride (Cl-) ions which confirmed the light-salty nature of groundwater. Geochemical mass balance calculations indicate that upper aquifer is mainly affected by the dissolution and dolomitization processes of major anions.
 Unique Contribution to Theory, Policy and Practice: This process is highly developed in the central west part of the basin due to the abundance of Sulphate (SO42-), Bicarbonate (HCO3-), Magnesium (Mg2+), and Calcium (Ca2+) ions. High values of E.C, T.D.S, Ca2+, and SO42- are mainly presents as a saline water resource in some villages. Two types of water are classified here these are : i). Na-HCO3 type and ii). Ca- Cl -SO4 type. The study concluded that water samples from Almakser, Hamdan-2, Um-Zeeraga-2, and Al-Zareeba-2 villages have very high concentrations of E.C, T.D.S Ca2-, Cl-, NO3- and SO42-, which may suggest that water samples are not fit for human consumption, according to guidelins by W.H.O (1984). This paper recommends further study on water quality.

Geochemistry of thermal fluids and the genesis of granite-hosted Huangshadong geothermal system, Southeast China

The geochemistry of the thermal waters in the granite-hosted Huangshadong geothermal system was studied to characterize the hydrogeology of the system and potential geothermal energy prospects. In recent years, interest in geothermal energy utilization as an alternative and non-fossil fuel energy source has grown in China. The thermal waters have temperatures of 48–99 °C at the surface and are classified as of HCO3-Na type with low total dissolved solids (TDS) content (192–727 mg/L) and neutral pH (7.12–8.15). Based on the isotope (δ2H, δ18O, 87Sr/86Sr) and chemical (Li, Cl, and Sr) compositions, the thermal waters were sourced from local meteoric water, followed by water-rock interaction with the granite host rocks and mixing with non-thermal water upon water ascent to the surface. Applying geothermometry and mixing models, the chemical composition (SiO2, B, Li, Na, K, Rb, Ca, Mg, Sr, Al, F, Cl, Br, HCO3, and SO4) of deep thermal water was assessed and the reservoir temperature was predicted as approximately 150–165 °C. The corresponding thermal water elemental composition was in equilibrium with common secondary minerals. Based on noble gas isotope systematics (3He, 4He, and 20Ne), He is a crustal source (>95%) being accompanied by radiogenic heat, which is presumably the principal source of induced heat observed in the geothermal systems. Other volatiles (CO2, N2, and Ar) were also of crustal and/or atmospheric origin. Based on chemical and isotopic systematics, it was concluded that the Huangshadong geothermal field is a medium-enthalpy geothermal system with thermal water circulated to a depth of approximately 3.5 km, corresponding to a power density of 4.4 MW/km2. Such geothermal systems are potentially suitable for deep drilling (>2–3 km), followed by energy production and the direct use of thermal water. These findings reveal the genesis mechanism of hydrothermal systems in the granite-hosted area of Southeast China and indicate that high-enthalpy geothermal fluids can hardly be expected within a drilling depth of 4 km.

Hydrogeochemistry and Strontium Isotopic Signatures of Mineral Waters from Furnas and Fogo Volcanoes (São Miguel, Azores)

This study focused on 13 water samples collected from two of the main active volcanoes (Furnas and Fogo) at São Miguel, Azores. Based on the major element composition, the waters are classified into Na-HCO3 and Na-Cl types. While the concentrations of chloride seem to reflect the contribution of sea salt aerosols, the behavior of the main cationic species and Sr in the analyzed waters appear to have been largely controlled by the interaction between meteoric waters and the underlying bedrock. The temperature and input of CO2 from the secondary volcanic activity are enhancing the silicate leaching. The stable isotopic data show that these waters have a meteoric origin (δ18O = −2.03 to −4.29‰; δ2H = −7.6 to −17.4‰) and are influenced by a deep hydrothermal/volcanic carbon source (δ13C = −4.36 to −7.04‰). The values of δ34S (0.13 to 12.76‰) reflects a juvenile sulfur source derived from the leaching of volcanic rocks. The Sr isotopic ratios show a slight difference between the values from Furnas (87Sr/86Sr = 0.705235–0.705432) and Fogo (87Sr/86Sr = 0.705509–0.707307) whereas the Furnas waters are less radiogenic. The Sr isotope also shows that the hydrochemical signatures of the groundwater was controlled by the rock leaching, and the samples Furnas reached water-rock isotopic equilibrium.

Deep groundwater flow in the Kamikita Plain, Japan, inferred from geochemical tracers including 36Cl

Long-term changes in deep groundwater flow in a coastal sedimentary plain affected by sea-level changes were investigated using a paleohydrological approach with 36Cl. The 36Cl/Cl ratios of the saline component in the Na-Cl type deep saline/brackish waters extensively distributed inland were found to be comparable to the secular equilibrium value of the aquifer. On the other hand, younger saline/brackish waters with low 36Cl/Cl are distributed in coastal areas, particularly in the deep aquifer. Deep freshwaters of the Na-Cl to Na-HCO3 type found at slightly shallower depth than −1000 m a.s.l. have δD values ∼10 ‰ lower than recent precipitation, suggesting that they were recharged during a colder period than present. The presence of low-δD deep freshwaters inland and the distribution of relatively young saline/brackish waters in coastal areas both indicate that older saline water was flushed out by meteoric water during the glacial period, but to a limited extent and area.

Groundwater Quality and Potential Pollution in the Southern Shimabara Peninsula, Japan

Nitrate pollution in groundwater is a severe problem in Shimabara Peninsula, Nagasaki Prefecture, Japan. Previous studies have investigated water quality characteristics in the northern part of the peninsula and shown serious effects of nitrate pollution in the groundwater. The present study aimed to investigate the groundwater quality in the southern areas of the peninsula for improved understanding of the water quality status for the entire peninsula. Groundwater samples were collected at 56 locations in Minami-Shimabara City from 28 July to 4 August 2021. The spatial distribution of water quality constituents was assessed by Piper-trilinear and Stiff diagrams for major ion concentrations. One agricultural area in the western parts exceeded Japanese recommended standards for water. According to the Piper-trilinear diagram, 44 sampling sites (78.6%) were classified as alkaline earth carbonate type, nine sites (16.1%) as alkaline earth non-carbonate type, and three sites (5.3%) as alkaline carbonate type. Stiff diagrams displayed Ca-HCO3 water type for most of the sites. Na-HCO3 and Mg-HCO3 types were found in coastal areas. Principal component analyses showed that the first component corresponded to dissolved constituents in groundwater and denitrification, the second effects of ion exchange and low nitrate pollution, and the third effects of severe nitrate pollution. Hierarchical cluster analysis was used to classify the groundwater into five groups. The first group included sites with relatively high nitrate concentration. The second group had relatively low ion concentration, distributed from center to eastern parts. The third group included intermediate ion concentration, distributed at lower altitudes along the coastal line. The fourth and fifth groups had a higher ion concentration, especially characterized by high sodium and bicarbonate concentration.

Hydrogeochemical evolution and assessment of groundwater quality for drinking and irrigation purposes in the Gushegu Municipality and some parts of East Mamprusi District, Ghana

The Gushegu Municipality and the East Mamprusi District in Ghana are dominated by the Oti/Pendjari Group within the Voltaian Supergroup. The major rock types found in the area are quartzites, siltstones, conglomerates, and shales with minor occurrences of tillites, silexites, limestones, and barite-rich dolomites. The inhabitants of the area are mainly peasant farmers, and their activities might be influencing the groundwater chemistry, but little is known about the quality of the groundwater. Therefore, this study evaluated the suitability of groundwater resources in the Gushegu Municipality, and some parts of the East Mamprusi District in Ghana for domestic and irrigation uses, employing hydrogeochemical graphing, geochemical modelling, multivariate statistical analysis, and computation of water quality indices. Sodium (Na+), with concentrations ranging from 4.93 to 323 mg/L and a mean of 169 mg/L, is found to be the major cation in the groundwater, while bicarbonate (HCO3-), with concentrations ranging from 19.9 to 685 mg/L and a mean of 397 mg/L, is the major anion in the area. The dominant hydrochemical facies is the Na-HCO3 type, accounting for about 72.7% of the study area's groundwater and is influenced by silicate weathering, carbonate mineral dissolution, and ion exchange reactions. Other factors accounting for this dominance may be anthropogenic activities, including the dissolution and leaching of fertilizers from farmlands. Overall, this study reveals that the groundwater in the area is suitable for drinking based on the WQI classification. There are localized contaminations with respect to B and F-, making the water in those areas unsuitable for drinking. Also, the groundwater in the area is unsuitable for irrigation purposes due to the high Na% values (43 to 99% with a mean of 86%), magnesium hazard values (1 to 312 with a mean of 88), and sodium adsorption ratio (0.57 to 42.4 with a mean of 12.7). All these indices exceed their respective standards for irrigation purposes.

Identification of water–rock interaction of surface thermal water in Songwe medium temperature geothermal area, Tanzania

The Songwe geothermal prospect is situated in western Tanzania in the Rukwa Rift of the western branch of the East African Rift System. Thermal springs discharge along NW–SE oriented fracture zones in two separate areas: in the main Songwe graben (Iyola, Main springs, Rambo and Kaguri) and eastern Songwe graben (Ikumbi). Lithologies forming and filling the Songwe graben are metamorphic gneiss and shist as basement rocks, overlain by the Karoo sandstones, and Red sandstones, both silt- and sandstones with a carbonatic matrix. In some areas of the graben, volcanic rocks intruded these formations forming basalt outflows. The discharge temperatures of springs are between 37 and 85 °C with Na-HCO3 type fluids. Carbonate deposits surround most of the springs. Using previous geophysical, geological studies and historical fluid geochemical data and mineral data, the Songwe geothermal system interpretation was updated, including new reservoir fluid temperature, fluid flow pathway and water–rock interaction models. The classical geothermometers of K-Mg and Na-K-Ca (Mg correction) were used to predict the reservoir fluid temperature and show that fluid emerging in the Songwe area reaches temperatures between 125 and 148 °C. Reservoir fluid characteristics are reconstructed based on the geothermometer calculation and a PHREEQC model in which the deep fluid reacts with certain lithologies. Minerals precipitating at the surface and reservoir depth were used to calibrate the models. The models run at surface temperature were calibrated with minerals precipitating around the springs and suggest that Songwe thermal fluids interact with Red sandstone only, while Ikumbi spring water is the only spring that interacts with all lithologies (simplified referred to as: metamorphic rocks, Karoo and Red sandstone). The model run at reservoir temperature indicates that rising water is also in contact with Karoo sandstones and Ikumbi spring water composition is again influenced by the contact with all lithologies in the graben. Our conceptual model summarizes all data showing the meteoric origin of the fluids, the travel through the basement, rising along the Mbeya fault and the main reaction with sandstones through a lateral travel towards the hot springs. The proposed models reinforce the idea that carbonate dissolution from the sandstone layers is the most common water–rock interaction. Our model is supported by carbonate deposition observed in all springs, dominated by HCO3 and Na.

Geochemical fingerprint and spatial pattern of mine water quality in the Shaanxi-Inner Mongolia Coal Mine Base, Northwest China

The spatial distribution of mine water quality and geochemical controls must be investigated for water safety and ecosystem protection in Shaanxi-Inner Mongolian Coal Mine Base (SICMB). Based on 122 mine water samples collected from 14 mining areas, self-organizing maps (SOM) combining with principal component analysis (PCA) derived that the mine water samples were classified into seven clusters. Clusters 1 and 3 (C1 and C3) samples were dominant by HCO3-Ca and mixed types, which were distributed in the recharge area of the middle SICMB. In this area, the active groundwater circulation contributed to the good water quality. Cluster 2 (C2) samples were characterized by HCO3-Na type, mainly distributed in the discharge area of the middle SICMB. These samples were threatened by heavy fluorine contamination and high residual sodium carbonate (RSC) because of slow groundwater flow in this area. Clusters 4 and 5 (C4 and C5) samples, distributed in the northeast and middle SICMB, were characterized by high Cl− concentration and light fluorine contamination. They were influenced by anthropogenic input through faults or underground mining. In contrast, Clusters 6 and 7 (C6 and C7) samples with high salinity and sulfate were distributed in the southwest SICMB. The deep groundwater circulation enhanced water-rock interaction and contributed to poor water quality. These findings are beneficial to the management of mine water resources in the SICMB and provide an insight to investigate the mine water quality in large spatial scale.

Statistical analyses of hydrochemistry in multi-aquifers of the Pansan coalmine, Huainan coalfield, China: implications for water-rock interaction and hydraulic connection

Understanding the groundwater hydrogeochemical processes and aquifer hydraulic connections are essential for effective prevention of water inrush in concealed coal mines. In this study, 40 groundwater samples were collected from the loose layer aquifer (LA), coal measure aquifer (CA), and limestone aquifer (LA) in the Pansan coal mine, Huanan coalfield, China, and the major ion concentrations were analyzed by bivariate diagrams (Na+ + K+ - Cl− versus Ca2+ + Mg2+ - SO42− - HCO3− and CAI-I versus CAI-II), multivariate statistical methods, and receptor model in order to identify the water-rock interactions and aquifer hydraulic connections. Piper diagram showed that groundwater in LA and TA was dominated by the Na–Cl type, while groundwater in CA was mainly of the Na–HCO3 type. Based on the results of bivariate diagrams and PCA/FA, weathering of silicate minerals and cation exchange (source 1), sulfate dissolution (source 2) and chloride dissolution (source 3) were the main processes controlling the groundwater chemistry. Unmix model revealed that the mean contribution of source 1 to CA samples was 74%, while LA and TA samples have higher contributions from evaporite dissolution (source 2 and source 3) relative to CA samples. Moreover, both clustering analysis methods (Q-type hierarchical and K-means cluster) confirmed the existence of a hydraulic connection between LA and TA in the northeastern part of the study area. It is concluded that the application of multivariate statistical analysis to interpret groundwater chemistry can provide useful guidance to prevent water inrush in coal mines.

Geogenic enrichment of fluoride in groundwater of hard rock aquifer in fluorosis prevalent area of Balangir district, Odisha, India

Hydrogeochemical characterization of groundwater has been carried out in a hard rock aquifer from Balangir district, a fluorosis-affected area of Odisha, India with the aim of understanding the sources and processes controlling fluoride (F−) enrichment. A total of 37 groundwater (tube wells) and 7 surface water (pond) samples were collected during the pre-monsoon period. Groundwaters are mostly categorized as moderate to very hard water types with alkaline nature. The enhanced Na+ and HCO3− concentration in groundwater is mostly a result of silicate weathering. The F− concentration in groundwater ranged from 0.4 to 4.29 mg/l, with 38% of samples exceeded the drinking water limit (1.5 mg/l; as prescribed by the World Health Organization, 2011), in contrast to very low F− (<0.9 mg/l) in surface water. High F− concentrations in underlying granitic bedrocks (up to 700 mg/kg), which spatially corresponds to F− rich groundwater, suggest that lithological composition is the main control of F−. Fluoride-rich waters are mostly Na–HCO3 type, followed by mixed Na–Ca–HCO3 (Cl) type with Na+/Ca2+ ratio >1. The significant positive correlations of F− with Na+, HCO3−, and pH indicate that the weathering of sodium-rich silicate minerals and increase of pH mobilizes F− ion. Geochemical modeling indicates that the activity of F− in groundwater increased by precipitation of calcite, dolomite, and aragonite. Fluoride risk assessment indicates that 38% of groundwater samples can cause a high prevalence of dental fluorosis with children being at greater risk than adults. Henceforth, it is advisable to treat this contaminated groundwater before consumption or provide alternative drinking water to avoid further fluorosis risks in the concerned area.

Hydrogeochemical characteristics and evaluation of the geothermal fluids in the Gazlıgöl geothermal field (Afyonkarahisar), Western Anatolia, Turkey

The Gazlıgöl geothermal field located in 20 km northern of Afyonkarahisar in Western Anatolia region of Turkey is one of the most important geothermal areas in the Afyon-Akşehir Graben on the basis of potential. The present study has been performed to investigate the hydrogeochemical and isotopic characteristics and evaluate the origin, reservoir temperature and processes controlling the chemical composition of thermal waters of the Gazlıgöl geothermal field. Discharge temperature, electrical conductivity and pH of the thermal waters vary from 58.5 to 74 °C, 3910 µS/cm to 4050 µS/cm and, 7.05 to 7.54, respectively. The Gazlıgöl thermal waters are chemically of Na-HCO3 type, with high salinity, while the cold waters have mainly Ca-Mg-HCO3, Ca-Na-HCO3 and Ca-Mg-HCO3-SO4 types, with low salinity. Geochemical processes controlling chemical composition of the thermal waters are mainly water-rock interactions including dissolution and/or weathering of mostly silicates and partially carbonates and ion-exchange reactions. Besides, the bacterial sulfate reduction is another main process leading to the depletion of SO4 in the thermal water. Higher contents of some minor elements in the thermal waters, such as F, B, Li, As and Sr, are probably derived from enhanced water-rock interaction, and the minor elements can be regarded as indicator of residence times and flow paths.Geothermometer applications including quartz geothermometers and SiO2-K2/Mg, mineral saturation state and silica enthalpy mixing models provide the most reliable estimations of reservoir temperature in the varying of 100-150 °C for the Gazlıgöl thermal waters. Accordingly, the Gazlıgöl geothermal system can be classified as a low-moderate geothermal resource. The isotope data (δ18O, δ2H and 3H) of the thermal waters point to their deep circulating meteoric origin, and let estimating of recharge elevation varying from 1300 to 1400 m.a.s.l. These elevations suggest the mountainous region in the north-northeastern of the study area as the recharge area of the geothermal system. Long-term circulation of meteoric waters within the aquifer is confirmed by low tritium ratios (< 1 TU) of the thermal waters although the fluids do not achieve thermodynamic equilibrium. Based on the all gathering data, a conceptual model of the functioning of geothermal system has been constructed. Accordingly, geothermal fluid is heating at deep zones due to the high geothermal gradient caused by active fault systems and heated waters rise toward the shallow levels through faults and fractures. During moving to the surface, they undergo conductive cooling by mixing with the cold groundwater at shallow depths and during contacting with the colder rocks.