Groundwater Mixing Research Articles

Assessment of the groundwater recharge processes of a shallow and deep aquifer system (Maggiore Valley, Northwest Italy): a hydrogeochemical and isotopic approach

The Maggiore Valley well field plays a fundamental role in supplying drinking water to a large territory of the Piedmont Region (northwestern Italy) and has been intensively exploited since the early twentieth century. This water resource is hosted in a deep, multilayered aquifer system. The main purpose of this study was to characterize the recharge processes of the deep aquifer through hydrochemical and isotopic assessments, as well as the water quality in the recharge and drainage areas. For this purpose, 128 physical–chemical analyses (major ions) and 50 isotopic analyses (δ18O and δ2H) were carried out on samples collected in shallow and deep aquifer complexes in two sampling campaigns in 2021. From the results, a hydrogeological conceptual model of recharge processes was developed. The chemical data confirm the presence of bicarbonate–calcium facies in most samples of the shallow and deep aquifer complexes. Clear hydrochemical differences were observed among the investigated sectors. The recharge areas were identified as (1) far zones, namely the shallow aquifer complex of the Cuneo Plain, and (2) the shallow and deep aquifer complexes with groundwater mixing in the riverside sector of Po Plain in the Turin area. The mixing of waters from the Cuneo Plain and Turin Plain was verified in the well field area. The isotopic values of the artesian well water also confirmed contributions from the Turin and Cuneo Alps. This study clarified the recharge processes, thereby defining potential pollutant pathways, and the results provide additional support for groundwater resource management and protection.

Application of radium isotopes to estimate seawater intrusion rate in coastal aquifers

Coastal aquifers, as the interface zone between ocean and land, are highly sensitive and vulnerable to seawater intrusion. This study presents the behavior of radium isotopes and their application to estimate the rate of seawater intrusion in a typical coastal city (Qinhuangdao, China). The hydrochemical results indicated that the coastal aquifers have Na–Cl type water with the lower Na/Cl ratios. The analysis revealed that the formation process of the chemical composition of groundwater was mainly the mixing of seawater and groundwater, while that of inland groundwater was dominated by mineral dissolution and cation exchange and adsorption. Groundwater of intruded aquifers contain significantly higher activities of radium than those of nearshore seawater and inland groundwater. The rates of seawater intrusion were estimated by using equation of the fate and transport of radium in 1–D transient groundwater flow system. In the calculation process, we ignored dissolution and co-precipitation and mainly considered mixing, alpha recoil and decay contribution for radium activity as sources and sinks terms of radium in coastal groundwater based on the characteristics of radium activity and 224Ra/228Ra ratio in groundwater. The recoil (P) was determined by the activity ratio of 224Ra to Th (232Th/230Th), while the retardation (Rf) was calculated from the steady-state radium equilibrium equation. The seawater intrusion rates were obtained by integrating 224Ra and 228Ra activities under different thorium ratios (232Th/230Th). The results show that the rate of seawater intrusion varies in a wide range at different locations, which are 0.17–1.03 (232Th/230Th = 0.67) and 0.11–1.01 (232Th/230Th = 1.25) m/d. The method of calculating seawater intrusion rate with radium isotope can obtain the rate of different parts of heterogeneous anisotropic aquifer, which also extends the application of radium isotope in hydrogeology.

Unraveling the Complexities of Groundwater Salinization in Coastal Environments: Insights from Laizhou Bay’s Eastern Coast, China

Coastal areas have made substantial contributions to global economic development but are plagued by challenges such as groundwater salinization. Groundwater serves as the primary source for drinking, industrial, and domestic purposes in these coastal areas. Therefore, understanding the causes and processes of groundwater salinization holds paramount significance for effective groundwater management. The coastal area of Laizhou Bay in northern China serves as a quintessential example of such a scenario. With substantial groundwater extraction and severe groundwater salinization issues, it exacerbates the disparity between water-resource supply and demand. Currently, our understanding of the processes and influencing factors related to groundwater salinization in this region remains limited. In this study, employing hydrochemical and stable chlorine isotope analyses on 35 groundwater and seawater samples, an in-depth investigation into the complex mechanisms underlying groundwater salinization in the Quaternary aquifers of the eastern coastal plain of Laizhou Bay was conducted. The test results of the samples indicate that brine and saline groundwater are primarily of the Na-Cl type, exhibiting a hydrochemical composition similar to that of seawater. Brackish groundwater exhibits a diverse hydrochemical composition. The hydrogen and oxygen isotope characteristics of brackish and fresh groundwater resemble atmospheric precipitation, while brine, seawater, and saline groundwater show hydrogen and oxygen isotope depletion. Compared to seawater, brine exhibits significant δ37Cl depletion. The analysis of the test results reveals that the formation of brine aquifers results from a complex interplay of climate change, tectonic movements, and sea–land evolution, involving lagoon development during seawater regression, salt concentration through evaporation, and subsequent water–rock interactions. The genesis of saline groundwater involves a complex interplay of brine–seawater mixing, significant evaporation, and potential input of fresh groundwater from atmospheric precipitation and river sources. The formation of brackish groundwater is predominantly influenced by atmospheric precipitation, and agricultural activities, with significant variations in NO3− concentrations attributed to varying intensities of fertilizer application in the northern plain area. These insights contribute to a deeper understanding of the origins of groundwater and can inform the development of policies for groundwater protection in this area.

Isotopic identification of groundwater circulation and mixing in the Legnica-Głogów Copper District mines

Identification of the conditions of circulation, mixing, origin and age of groundwater in the area of underground mining plants is necessary for the correct design of drainage systems, directions of mining exploitation and intensity of mining works. For this purpose, isotopic studies were carried out in the mines of the Legnica-Głogów Copper District (LGCD) in Poland, characterized by complex hydrogeological conditions. The observed values of δ2H, δ18O and concentrations of tritium, as well as chlorides, sulfates and main cations in 29 water samples taken from different lithostratigraphic levels (and a few historical results) were used to explain the spatial variability of the origin of groundwater flowing into the mines. A model of groundwater mixing in the mining area of the LGCD was developed. The results of the research indicate that, depending on the region, the LGCD mines contain Holocene and/or interglacial waters, pre-Quaternary waters as well as older waters, recharged in period of very warm climate - flowing into the mining workings from deeper geological strata. Isotopic studies together with the chloride content measurements confirmed the correctness of the conceptual model of groundwater circulation within the mines. Their results will be useful in further elaboration of the strategy related to dewatering and designing further mining activities.

Groundwater Quality and Suitability Assessment for Irrigation Using Hydrogeochemical Characteristics and Pollution Indices: A Case Study of North Al-Quwayiyah Governorate, Central Saudi Arabia

The present work focuses on a comprehensive hydrochemical assessment of groundwater within a shallow aquifer located in the central region of Saudi Arabia. This aquifer serves as the principal source of groundwater supply for agricultural irrigation purposes. A total of twelve groundwater samples were systematically collected and subjected to thorough analysis to determine various physicochemical parameters. These parameters encompassed electrical conductivity (EC), pH, temperature, total dissolved solids (TDS), as well as concentrations of major ions. Analysis of major ion analysis was employed to elucidate the chemical attributes of groundwater within the research area. This approach facilitated an understanding of the geochemical evolution and the potential suitability of the groundwater for agriculture irrigation. The recorded range of electrical conductivity (EC) for the groundwater in this region falls between 3283 and 11,000 µS/cm, with an average value of 6709.4 µS/cm. The pH levels of the groundwater exhibited a slightly alkaline nature, ranging from 7.8 to 8.6. All sampled wells exhibited brackish water conditions (TDS > 1000 mg/L) based on TDS concentrations. The findings of this investigation demonstrated that the average ion concentration followed the order: Na+ > Ca+ > Mg2+ > K+ and Cl− > SO42− > HCO3− > NO32−. Applying Piper’s classification system, the groundwater samples were classified into two predominant categories: Ca-Cl and mix-Ca-Mg-Cl. The predominance of Ca2+ and Mg2+ over alkalis indicated mixed groundwater facies influenced by processes of reverse ion exchange and extensive interactions between water and rock formations. The distinct chemical characteristics of the groundwater were attributed to a combination of factors, including the percolation of irrigation-returned water, chemical transformations within the vadose zone, and extensive interactions with subsurface lithology. Despite major ion concentrations surpassing the permissible limits outlined by the World Health Organization (WHO) for drinking water, the assessment of quality indices was conducted to ascertain the suitability of the groundwater for irrigation purposes. These quality indices encompassed the permeability index (PI), magnesium hazard (MH), Kelly’s ratio (KR), sodium-adsorption ratio (SAR), residual sodium carbonate (RSC), sodium percentage (Na%), and magnesium ratio (MR). A meticulous evaluation of groundwater quality for agricultural utilization indicated that all sampled groundwater sources were deemed suitable for irrigation purposes.

Assessment of the hydrogeochemical and isotopic characterization and hydraulic behavior of the Izeh complex karstic area, Khuzestan province, southwest Iran

Proper water resources management requires recognizing and evaluating the factors that affect the quantity and quality of water resources. The Ilam-Sarvak (Upper Cretaceous) and Asmari (Oligocene to Miocene) limestone- dolomite formations in the Zagros structural belt have formed a promising karst groundwater horizon. In the present study, the hydraulic relationship between the karst structures of the Izeh territory in the northeast of Khuzestan province was investigated using hydrogeochemical and isotopic information of springs and wells. The results enabled to understand various components influencing the recharge of water resources. In this study, samples were collected from the karst springs and wells of Mongasht, Shavish-Tanosh and Kamarderaz anticlines and Naal-e-Asbi (Horseshoe) syncline and meteoric water to understand the hydrochemical and isotopic characterization, and hydrogeological and hydraulic behavior of the Izeh karst system. The meteoric and groundwater samples were analyzed to determine major and minor ion concentrations and δ18O and δ2H isotope ratios. Isotopic content ranged from -31.6 to -2.9‰ and from -6.32 to -1.87‰ for δ2H and δ18O, respectively, and d-excess values were high and positive. The study of the isotopic content of water samples of springs and wells in the region shows three groups of water sources. The first group, related to the Mongasht anticline springs, has lower isotopic values, indicating that it is recharged by rainfall at high altitudes and snow melting. The isotopic value of the second group is richer than that of the first group, indicating rainfall recharge as well as groundwater mixing (ex­amples of Naal-e-Asbi syncline and Shavish-Tanosh anticline). The highest value in the third group (samples of Kamarderaz anticline) is attributed to evaporation and longer distance from the recharge site to the discharge point, as well as to the diffu­sion system. The trend of decrease in Sr+2 and increase in Ba+2 in the samples of dolomitic limestone formations (Shavish Ta­nosh and Mongasht anticlines) compared to the water samples of Kamarderaz anticline and Naal-e-Asbi syncline indicates the possibility that karst aquifers of the region are recharged from the Mongasht anticline and that there is a hydraulic relation­ship between these structures. D-excess and δ18O show a linear trend, illustrating the effect of altitude difference on isotopic content and recharge sources. The major and minor changes in the concentration of ions, the isotopic content of groundwa­ter and the relationship between TDS and δ18O and d-excess and δ18O indicate the mixing and recharging of karst aquifers (Shavish-Tanosh, Kamarderaz and Naal-e-Asbi aquifers) from the Mongasht karst aquifer and their hydraulic connection.

The genesis of acid alteration in the Luohe IOA-type deposit, Eastern China and its constraints on mineralization

Luohe is the largest IOA-type deposit in the Middle and Lower reaches of the Yangtze Metallogenic belt. The iron ore body is hosted in thick volcanic rocks, and widespread acidic alteration (secondary quartzite) developed at shallow depths, providing an excellent opportunity to study the genesis of acidic alteration rocks and the genetic links with the IOA mineralization. In this study, detailed mineralogy, in situ sulfur isotopes, and trace element analyses were performed on pyrite from a shallow drill hole in the Luohe deposit. The results indicate that the formation time of acidic alteration is between magnetite (stage II) and anhydrite-pyrite (stage IV), with pyrite sulfur isotopes ranging from −14 to 4‰, which is significantly different from those in stage IV (7-9‰). The anomaly negative sulfur isotope suggests the existence of SO2 disproportionation reaction, and the δ34S of pyrite increases with depth decrease, ultimately falling within the mantle sulfur range. This indicates that the sulfur origin of acidic alteration pyrite is a single magma sulfur source, which is significantly different from the deep iron mineralization system (magmatic + evaporite). The trace elements Co, Ni, As, Ti, Cu, Sb, Tl in pyrite indicate that the acidic alteration fluid has the characteristics of low temperature, low pH, and is rich in F and Cl. Combined with the sulfur isotope results, it is believed that pyrite in the acidic alteration rock of the Luohe was formed by the mixing of gaseous SO2 and shallow groundwater, which is a part of the Luohe magmatic-hydrothermal mineralization system and an important indication for regional exploration of similar deposits.

Mechanisms of water-rock interaction and implications for remediating flooded mine workings elucidated from environmental tracers, stable isotopes, and rare earth elements

Contamination from acid mine drainage affects ecosystems and usability of groundwater for domestic and municipal purposes. The Captain Jack Superfund Site outside of Ward, Boulder County, Colorado, USA, hosts a draining mine adit that was remediated through emplacement of a hydraulic bulkhead to preclude acid mine drainage from entering nearby Lefthand Creek. During impoundment of water within the mine workings in 2020, a diverse and novel dataset of stable isotopes of water, sulfate, and carbon (δ2H, δ18OH2O, δ18OSO4, δ34S, δ13CDIC), rare earth elements, and environmental tracers (noble gases and tritium) were collected to understand groundwater recharge and mixing, mechanisms of sulfide oxidation and water-rock interaction, and the influence of remediation on the hydrologic and geochemical system. Water isotopes indicate that groundwater distal from the mine workings has seasonally variable recharge sources whereas water within the workings has a distinctive composition with minimal temporal variability. Sulfate isotopes indicate that sulfide oxidation occurs both within the mine workings and in adjacent igneous dikes, and that sulfide oxidation may occur under suboxic conditions with ferric iron as the oxidant. Carbon isotopes track the neutralization of acidic waters and the carbon mass budget of the system. Rare earth elements corroborate stable isotopes in indicating groundwater compartmentalization, and additionally illustrate enhanced mineral weathering in the mine workings. Environmental tracers indicate mixing of modern and pre-modern groundwater and inform timelines that active remediation may be needed. Together these datasets provide a useful template for similar investigations of abandoned mine sites where physical mixing processes, sources of solute loading, or remediation timeframes are of importance.

Spatial and seasonal controls on dissolved organic matter composition in shallow aquifers under the rapidly developing city of Patna, India

The distribution and composition of dissolved organic matter (DOM) affects numerous (bio)geochemical processes in environmental matrices including groundwater. This study reports the spatial and seasonal controls on the distribution of groundwater DOM under the rapidly developing city of Patna, Bihar (India). Major DOM constituents were determined from river and groundwater samples taken in both pre- and post-monsoon seasons in 2019, using excitation-emission matrix (EEM) fluorescence spectroscopy. We compared aqueous fluorescent DOM (fDOM) composition to satellite-derived land use data across the field area, testing the hypothesis that the composition of groundwater DOM, and particularly the components associated with surface-derived ingress, may be controlled, in part, by land use. In the pre-monsoon season, the prominence of tryptophan-like components likely generated from recent biological activity overwhelmed the humic-like and tyrosine-like fluorescence signals. Evidence from fluorescence data suggest groundwater in the post-monsoon season is composed of predominantly i) plant-derived matter and ii) anthropogenically influenced DOM (e.g. tryptophan-like components). Organic tracers, as well as Eh and Cl−, suggest monsoonal events mobilise surface-derived material from the unsaturated zone, causing dissolved organic carbon (DOC) of more microbial nature to infiltrate to >100 m depth. A correlation between higher protein:humic-like fluorescence and lower vegetation index (NDVI), determined from satellite-based land use data, in the post-monsoon season, indicates the ingression of wastewater-derived OM in groundwater under the urban area. Attenuated protein:humic-like fluorescence in groundwater close to the river points towards the mixing of groundwater and river water. This ingress of surface-derived OM is plausibly exacerbated by intensive groundwater pumping under these areas. Our approach to link the composition of aqueous organics with land use could easily be adapted for similar hydrogeochemical settings to determine the factors controlling groundwater DOM composition in various contexts.

Anatomy of the convective geothermal system from geophysical and hydrochemical data: A case study from the Changshou geothermal field, South China

There are abundant low-medium temperature geothermal resources in southern China; however, a lack of research into their properties restricts the utilization of the geothermal energy. To expand the geothermal energy potential in southern China, it is vital to clarify the nonvolcanic geothermal system mechanisms. This study aimed to elucidate the mechanisms for the Changshou geothermal field, as a representative structurally controlled convective geothermal system, by analyzing the geophysical and hydrochemical data. The surface-to-subsurface (400 m depth) electrical resistivity structure of the geothermal field was obtained by 2D inversion of two intersecting controlled-source audio-frequency magnetotellurics and electrical resistivity tomography geophysical profiles. We identified the cap rock, reservoir, and fluid pathways of the geothermal system and verified them via drilling results. The cap was composed of Quaternary sediments and Cretaceous sandstone with moderate resistivity (10–50 Ωm), and the geothermal reservoir and fluid pathways were composed of dolomites and fracture zones with low resistivity (less than 5 Ωm), respectively. The hydrochemical results showed that the geothermal water was of the type HCO3·SO4−Ca·Mg, with low values of total dissolved solids resulting from shallow groundwater mixing. Isotope analyses indicated that the geothermal water was derived from precipitation in the Dahong Mountains, southeast of the geothermal field. The average temperature of the geothermal reservoir, as estimated by chalcedony and K-Mg geothermometers, was 53°C. Based on the geothermal gradient calculation, the circulation depth of the groundwater was 1500 m, with the circulation process driven by heat flows originating deep within the earth. The Changshou geothermal field was identified as a potential source of energy for residential heating in winter, owing to the large flow (2700 m3/d) and high permeability (24.03 m/d) of the geothermal reservoir.

An approach combining chlorine isotopes and hydrochemistry for identification of magmatic fluid-affected hydrothermal systems

Identification of hydrothermal systems affected by magmatic fluid input is relevant for geothermal energy development. Thus, an approach for identifying such systems based on chlorine isotope composition and auxiliary hydrochemical indices was proposed. The approach enabled us to distinguish Rehai, a magmatic hydrothermal area in the Tengchong volcanic region of China, from several other typical non-magmatic hydrothermal areas in Tengchong: Menglian, Shiqiang, and Jietou. The hot springs in the non-Rehai areas featured high δ37Cl values, reflecting an exclusive contribution of chlorine from hostrock leaching. By contrast, some hot springs with much lower δ37Cl values occurred in Rehai, all of which were nearly fully equilibrated waters with respect to reservoir hostrocks, rich in chloride and bromide. These springs should have the closest relationship with the fluids released from the underlying magma chamber. Notably, the potential reservoir processes that geothermal waters may undergo after receiving an input of magmatic fluids can further alter their chlorine isotope compositions to various degrees. Therefore, a deep understanding of these processes would help improve the use of the proposed approach based primarily on chlorine isotopes. Regarding Rehai, all the neutral to alkaline hot springs with δ37Cl values ranging from −0.44 ‰ to 0.31 ‰ evolved from a parent geothermal fluid that received an input of magmatic fluids—via adiabatic cooling, conductive cooling, mixing with low-temperature shallow groundwaters, or a combination of some of these processes. By contrast, the acidic Rehai hot springs with the highest δ37Cl values (up to 1.12 ‰) were essentially locally perched groundwaters heated by geothermal steam separated from underlying geothermal fluids upon their adiabatic cooling; thus, they were much less to do with the parent geothermal fluid than the neutral to alkaline springs were. Hence, only the neutral to alkaline Rehai hot springs not strongly affected by the mixing of shallow groundwaters and adiabatic cooling can reflect the chlorine isotope characteristics of intrusive magmatic fluids. Overall, chlorine isotope composition in combination with hydrochemistry has proven to be a robust tool for identifying a magmatic fluid-affected hydrothermal system.

δ18O and δ2H isotopes, trace metals and major ions in groundwater around uranium and fluoride contaminated Indus valley Quaternary alluvial plain, SW Punjab, India: Implications on hydrogeochemical processes, irrigation use and source

Uranium and fluoride enrichment in groundwater along alluvial plains pose a severe threat to living beings like cancer, fluorosis and crop yield as witnessed around semi-arid southwest Punjab, India. In-situ groundwater was examined for major ions, stable isotopes and trace metals to understand the hydrogeochemical processes, contaminant origin and health risks around SW Punjab, India. Groundwater from a freshly drilled bore well is found to be hard, alkaline, and saline with total dissolved solids and salinity up to 1300 and 1500 mg L−1, respectively. Fluoride (up to 4 mg L−1) and uranium (up to 90.07 μg L−1) contents exceed permissible limits in most samples and originated from fertilizer inputs and aquifer leaching. Uranium contents decline with depth, while fluoride remains invariable. Decreased U contents are inferred to be caused by U(VI) reduction to U(IV) as evidenced by an increase in Fe2+ vs. Fe3+, S2− vs. S6+ and N3− vs. N5+ with depth. NaHCO3, NaCl + NaHCO3 and NaCl are the dominant water types for shallow (<38 m), intermediate (49–83 m) and deeper groundwater (105–128 m) with Na+ and HCO3− as the dominant cations and anions, respectively. Silicate weathering majorly controlled the groundwater geochemistry together with a partial contribution from cation exchange processes. Unsuitability for drinking and irrigation use is envisaged for all depths, while deeper groundwater is safe in regard to radiological risk. δ18O and δD variations are suggestive of evaporation dominance in shallow groundwater, while intermediate groundwater witness canal and groundwater mixing and deeper groundwater are recharged through higher altitude.

Analysis of the interaction between surface water and groundwater using gaseous tracers in a dynamic test at a riverbank filtration intake

AbstractWe discuss a study designed to elucidate the genesis and inflow conditions at riverbank filtration wells located on a mountain river. This article seeks to identify the most important drivers of spatio‐temporal dynamics of water flow in the hyporheic exchange zone, in natural conditions and conditions disturbed by the water abstraction. In our study we try to contribute to further understanding the dynamics of groundwater mixing with river water in the hyporheic exchange zone. We focus on understanding river/aquifer interactions at the scale of reach of an intake, especially the unidirectional water flows induced by water abstraction. To understand these issues, a two‐day field hydrogeological experiment was conducted based on a pumping test of increasing intensity. At each pumping stage, groundwater and river samples were collected to determine the concentration of noble gases, CFCs, SF6, stable isotope content, and the chemical composition of the water. The study results indicate a short pressure propagation time (of the order of several hours) between the intake and the river, which already results in the inflow of water from the river–aquifer mixing zone at low rates of water abstraction by the intake. As pumping rates increase, the conditions of mixing and inflow of water to individual wells stabilize or approach stabilized conditions in less than 1–2 days. The share of river water in the water flux flowing into the intake does not exceed 12%, whereas the ratio of river water to groundwater in the mixing zone is estimated at 1 to 7 or more. The range of the river‐aquifer mixing zone may reach up to 170 m from the river and this range can be identified with a good approximation as coinciding with the range of the zone of hyporheic exchange in the study area.

Exploring the reliability of 222Rn as a tracer of groundwater age in alluvial aquifers: Insights from the explicit simulation of variable 222Rn production

Knowledge of groundwater residence times (GRT; the time elapsed since surface water infiltration) between losing rivers and pumping wells is crucial for management of water resources in alluvial aquifers. The radioactive noble gas radon-222 (222Rn) has been used for decades as a natural indicator of surface water infiltration, as it can provide quantitative information on GRT. However, models using 222Rn as a tracer of GRT are often based on a set of highly simplifying assumptions, including spatially homogenous 222Rn production and exclusively advective mass transport within the aquifer. In this paper, we use the integrated surface-subsurface hydrological model HydroGeoSphere (HGS) to simulate 222Rn transport, production, and decay in a bank filtration context. Spatially variable 222Rn production, based on experimental data, is explicitly considered. We show that variable 222Rn production rates, coupled with hydrodispersive mixing of groundwater, may lead to large biases in GRT estimates. Under certain transient conditions however, changes in tracer-derived GRTs correlate well with changes in mean groundwater age. Whereas 222Rn-derived GRTs may only be reliable under a narrow range of field conditions, 222Rn may serve as a powerful tracer of changes in mean GRT even in complex and heterogenous environments.

Hydrogeochemical characterization and geochemical modeling for the evaluation of groundwater quality and health risk assessment in the Varuna River basin, India.

This study focuses on determining significant controlling factors of chemical consequences, inverse geochemical modeling, water quality, and human health risk in the Varuna River basin of India. The study interprets that according to pH, total dissolved solids, and total hardness, the maximum number of groundwater samples are alkaline, fresh, and have substantial hardness. The abundance of major ions follows a pattern: Na > Ca > Mg > K, and HCO3 > Cl > SO4 > NO3 > F. Piper diagram shows that Ca-Mg-HCO3 facies are predominant during both seasons. Na-normalized molar ratios of HCO3/Na, Mg/Na, and Ca/Na are 0.62, 0.95, and 1.82 (pre-monsoon) and 0.69, 0.91, and 1.71 (post-monsoon), respectively, elucidating the coupled silicate and carbonate weathering (dolomite dissolution) sources. The Na/Cl molar ratio is 5.3 (pre-monsoon) and 3.2 (post-monsoon), indicating silicate alteration as the primary process rather than halite dissolution. The chloro-alkaline indices confirm the presence of reverse ion- exchange. Geochemical modeling using PHREEQC identifies the formation of secondary kaolinite minerals. The inverse geochemical modeling categorizes the groundwaters along the flow path from recharge area waters (Group I: Na-HCO3-Cl), transitional area waters (Group II: Na-Ca-HCO3), and discharge area waters (Group III: Na-Mg-HCO3). The model demonstrates the prepotency of water-rock interactions in pre-monsoon justified by the precipitation of Chalcedony and Ca-montmorillonite. The mixing analysis shows that in the alluvial plains, groundwater mixing is a significant hydrogeochemical process that affects groundwater quality. The Entropy Water Quality Index ranks 45% (pre-monsoon) and 50% (post-monsoon) of samples as an excellent category. However, the non-carcinogenic health risk assessment shows that children are more susceptible to fluoride and nitrate contamination.

Hydrogeological origin of the CO2-rich mineral water of Vilajuïga in the Eastern Pyrenees (NE Catalonia, Spain)

The mineral water of Vilajuïga village in Alt Empordà (NE Catalonia, Spain) owes its uniqueness to an emanation of geogenic CO2 that modifies groundwater hydrochemistry to produce a differentiated HCO3–Na- and CO2-rich groundwater among the usual Ca–HCO3 type found in this region. A hydrogeological conceptual model attributes its occurrence to the intersection of two faults: La Valleta and Garriguella-Roses. The former provides a thrust of metamorphic over igneous rocks, formed during the Paleozoic, over a layer of ampelitic shale that, from a hydrogeological perspective, acts as a confining layer. The Garriguella-Roses normal fault, which originated during the Neogene, permits the degassing of geogenic CO2 that is attributed to volcanic activity occurring in the Neogene. Groundwater mixing from the metamorphic and igneous rock units plus the local occurrence of CO2 creates a HCO3–Na water that still holds free-CO2 in solution. Interaction with the gas phase is restricted at the intersection of the two faults. Radiocarbon dating, after correcting for geogenic dead carbon, estimates an age of 8,000 years BP. The low tritium content (0.7 TU) indicates that Vilajuïga water is a mix of “older” groundwater recharged in the metamorphic rocks of the Albera range and “younger” groundwater from the igneous rocks of the Rodes range, over a recharge area of 45 km2 and a maximum elevation of 600 m. Given its origin as rare groundwater in the southern slope of the Eastern Pyrenees, purposeful monitoring is necessary to evaluate the groundwater vulnerability and anticipate impacts from nearby wells and climate-change effects.

Physico-Chemical Analysis of Drinking Water of District, Chindwara (M.P.)

Human health benefits from drinking clean, fresh water. Surface water is the source of clean, drinkable water. Contaminated drinking water is harmful to human health and can lead to conditions like lung irritation, cancer, paralysis, disorder, neurological, nerve damage, thyroid issues, kidney issues, liver issues, and many more conditions that are also severe issues noted in this study. The ratio of ions and dissolved oxygen, which is fictitiously present in both ground water and surface water, changes abruptly as a result of the mixing of ground water and industrial waste, posing a major threat to human health in the form of water-borne diseases. For this investigation, fifteen locations out of a total of sixty were chosen. Investigations into physico-chemical analyses of ground and surface water in Chindwara were conducted, including measurements of dissolved oxygen (DO), total dissolved solids, COD, BOD, total alkalinity, temperature, and pH. (TDS). All data were compared to industry standards, and our goal is to educate the local population about the water quality they are consuming and encourage them to take the necessary steps to improve it as needed.

Hydrochemical and stable isotopes (δ2H and δ18O) changes of groundwater from a spring induced by local earthquakes, Northwest China

It has been well reported that earthquakes can cause changes in groundwater chemistry and isotopes, and much of those changes were occurred in wells or hot springs; however, changes in cold spring caused by local small earthquakes have received less attention. Here, we collected continuous monitoring of the X10 spring (September 2018 to December 2019), investigated the hydrogeochemical characteristics of the spring by using water chemistry analysis and isotope methods. We compared the changes in water chemical ion concentrations and hydrogen-oxygen isotope ratios with the surrounding seismic activity, and the results show that 1) major chemical ion concentrations in X10 springs have an annual dynamic pattern of being high in winter and low in summer, and this change may be related to the seasonal effect of snowmelt; 2) the spring water originates from long-distant meteoric water, snowmelt, and bedrock fissure water and is affected by rock weathering and evaporation; 3) the hydrogen and oxygen stable isotope ratios and HCO3− concentration in groundwater are sensitive to local small seismic activity. We considered that small earthquakes can change the permeability in fault zones or aquifers, leading to mixing of groundwater with different chemical composition and isotopes. Our study demonstrates that the hydrogen and oxygen stable isotopes are more sensitive to seismic activity than the commonly used chemical constitutents, and that the sensitive constitutents vary in different observation wells or springs; therefore, combined monitoring of isotopes and water chemistry should be considered in the future to capture hydrogeochemical precursor signals caused by earthquakes.

Effect of groundwater residence time on geogenic fluoride release into groundwater in the Mt. Meru slope area, Tanzania, the Great Rift Valley, East Africa

People living in the Great Rift Valley in East Africa suffer from fluorosis resulting from their consumption of groundwater. This paper shows that geogenic fluoride contamination in a natural water system has changed in the last two decades in the Mt. Meru slope area of northern Tanzania based on water quality, dating of the residence time, and stable isotopes of groundwater. The results demonstrate that 1) the average recharge altitude of groundwater with a high geogenic fluoride concentration is estimated to range from 1900 m to 3000 m on the southern slope of Mt. Meru, and the fluoride concentration tends to increase with an increase in the recharge altitude, 2) the fluoride concentration increases with increasing groundwater residence time for groundwater with a residence time of 20 years or longer, suggesting that water-rock interaction processes (weathering, dissolution, and ion exchange), which depend on the contact time between the volcanic aquifer and groundwater, have predominated for approximately 20 years or longer, and 3) the mixing of aerobic young water and old groundwater has been active for approximately 20 years, and the fluoride concentration is increasing in some shallower well waters. The mixing of fluoride-contaminated groundwater with aerobic water infiltrating the aquifer through pumping groundwater in the last two decades may increase the spread of groundwater contaminated with fluoride due to increased water demand caused by rapid population growth, and urbanization, industrial growth, and the expansion of irrigated agriculture.

Radon-rich waters of the Tulinka aquifers, Novosibirsk, Russia

The first integrated isotope and chemical data on radon-rich waters of the Tulinka aquifers (Novosibirsk, West Siberia) are presented. The Tulinka radon waters are fresh, with neutral to moderately alkaline рН (7.3–7.7), SO4–HCO3 Na–Mg–Ca major-ion chemistry. The amount of total dissolved solids is 720–910 mg/L, Si content 6.41–9.02 mg/L. Eh is within +169.1 – +250.0 mV, corresponding to oxidized conditions. The concentration of dissolved oxygen is 2.86–7.37 mg/L. Radon activity (222Rn) varies from 173 to 276 Bq/L. The concentrations of U, Th, and Ra isotopes are 0.015–0.017 mg/L238U, 9.59∙10−7 to 1.58∙10−5232Th, and up to 4.93∙10−10226Ra; the 232Th/238U ratio is in the range 5.81∙10−5 to 9.42∙10−4. Total α activity is not higher than 891 mBq/L, and β activity is 80 mBq/L. The compositions of stable isotopes are −15.4 to −15.1‰ δ18O, −114.2 to −112.8‰ δD, and −13.9 to −9.9‰ δ13C. The isotope signatures and recharge patterns of the Tulinka waters are insensitive to seasonal effects, which suggests the slow water exchange. Substantial seasonal variations of the content of dissolved inorganic carbon (DIC) are detected. The range of δ13CDIC in the analyzed samples (from −14.3 to −9.0‰) corresponds to a mixed CO2 origin: diffusion of soil CO2 approaching the atmospheric δ13CCO2 values, and biogenic CO2 released by decaying plant residues. The measured isotope characteristics provide evidence that the waters recharge by infiltration from meteoric sources. The approximate radiocarbon age of DIC in the Tulinka waters, determined for the first time, is 2663 ± 144 years. However, this age may be underestimated due to groundwater mixing with the present-day surface waters.