Hydrochemistry and isotope compositions of groundwater from the Shihongtan sandstone-hosted uranium deposit, Xinjiang, NW China

Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO₃ type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ¹⁸O of − 8.3‰, δD of − 48.2‰,δ¹¹B of 1.5‰, and ⁸⁷Sr/⁸⁶Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO₄ type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ¹⁸O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ¹¹B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and ⁸⁷Sr/⁸⁶Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO₄ type water with the highest TDS (249.1 g/l, brine) and has δ¹⁸O of − 2.8‰, δD of − 45.8‰,δ¹¹B of 21.2‰, and ⁸⁷Sr/⁸⁶Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ¹¹B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.     

Hydrogeochemistry and isotope analyses used to determine groundwater recharge and flow in low-gradient catchments of the province of Buenos Aires,Argentina

The region known as Pampa Plain, in Argentina, is a vast area characterized by slopes of less than 0.05%. The surface sediment is silty sand, mainly Aeolian, referred to as Pampean Loess, which is a phreatic aquifer unit of utmost importance for the water supply of the region. On account of the slight gradient, hydrogeological analyses using only hydraulic measurements are difficult to perform, often leading to confusing results. Thus, the study presented relies on hydrochemical modeling and isotopic determinations as well. The study area comprises three catchments in the inter-mountainous area corresponding to El Moro, Tamangueyú and Seco creeks, and covering 2,570 km² in the province of Buenos Aires. Measurements of piezometric levels and samples of groundwater, surface water and rainwater were carried out between January and March 2005. Major ion results were analyzed by means of hydrochemical graphs and hydrogeochemical modelling using NETPATH. The resulting data show that it is possible to identify local changes in recharge, flow direction and stream/groundwater relationship by using hydrochemical and isotopic information, which may become a useful and more precise tool for the study of particularly flat landscapes.     

Recharge mechanism and hydrochemistry evaluation of groundwater in the Nuaimeh area, Jordan, using environmental isotope techniques

The relationship between the stable isotopic and chemical composition of precipitation and groundwater was studied in the Nuaimeh area of the Ajloun Highlands in Jordan. The isotopic composition values of precipitation and groundwater are almost identical. The spatial variation of stable isotopes in precipitation is mainly due to the effect of seasonal temperature, altitude and amount. The groundwater reveals identical variation in isotopic composition to the precipitation due to direct recharge and the karstic nature of the outcropping Turonian aquifer. Tritium levels in wells are high and their content is similar to the weighted mean value of tritium content in precipitation, indicating local recharge and low residence time. The ¹⁴C activity in the tritiated groundwater is found to be about half of the ¹⁴C activity of precipitation in the region. A geochemical evolution through dissolution of carbonate by water–carbonate rock interactions reduced the atmospheric ¹⁴C activity from 114 to 61 pmc in the groundwater. A ¹⁴C of around 61 pmc and 7.6 TU values are considered the initial concentration for the recharge in the shallow carbonate aquifer in the Yarmouk Basin. The large fluctuation of water level in observation wells during the rainy season indicates the sensitivity and direct response of the aquifer to the recharge. The chemical composition of the groundwater (Ca²⁺–HCO₃^–) gives emphasis to the short duration of water–rock interaction and indicates dissolution of the carbonate aquifer. The elevated concentrations of Cl^– and NO₃^– in groundwater are attributed to anthropogenic sources.

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Resumen Fue estudiada la relación entre la composición isotópica estable y la composición química, tanto de la precipitación como del agua subterránea, en el área de Nuaimeh en las montañas de Ajloun, en Jordania. Los valores de la composición isotópica de la precipitación y del agua subterránea son casi idénticos. La variación espacial de los isótopos estables en la precipitación, es debida principalmente al efecto de la temperatura estacional, a la altura y a la cantidad. El agua subterránea muestra una variación idéntica a la precipitación en cuanto a la composición isotópica, debido a la recarga directa y a la naturaleza cársica del acuífero Turoniano aflorante. Los niveles de tritio en los pozos son altos y su contenido es similar al valor medio ponderado del contenido de tritio en la precipitación, indicando una recarga local y un tiempo de residencia corto. Se ha encontrado que la actividad de ¹⁴C en el agua subterránea tritiada, es alrededor de la mitad de la actividad del ¹⁴C en la precipitación para la región. La evolución geoquímica ocurrida a partir de la disolución del carbonato, por las interacciones roca carbonatada–agua, redujeron la actividad atmosférica del ¹⁴C desde 114 en porcentaje de carbono moderno (pcm) hasta 61 pcm en el agua subterránea. Los valores del ¹⁴C cercanos a 61 pcm y de 7.6 unidades de tritio, se han considerado como las concentraciones originales para la recarga en el acuífero carbonatado somero de la Cuenca de Yarmouk. Una gran fluctuación en el nivel de agua de los pozos de observación, durante la estación lluviosa, indica la sensibilidad y la respuesta directa del acuífero frente a la recarga. La composición química del agua subterránea (Ca²⁺–HCO₃^–), enfatiza en la corta duración de la interacción de agua–roca, e indica disolución del acuífero carbonatado. La concentración elevada de Cl^– y NO₃^– en el agua subterránea, se atribuye a fuentes antropogénicas.

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Résumé Dans la région montagneuse dAjloun de Jordanie on a étudié la relation entre la composition chimique et isotopique des précipitations et des eaux souterraines. La composition isotopique est presque identique dans précipitations et les eaux souterraines. La variation spatiale de la teneur en isotopes stables dans les précipitations est déterminée en principal par les variations saisonnière de la température, laltitude ainsi que par la quantité des précipitations. A cause de la recharge directe et de la nature karstique des affleurements de laquifère dage touronienne, les eaux souterraines présentent la même composition isotopique que les précipitations. La teneur en ³H mesurée dans les forages présente des valeurs élevées, proches de la valeur moyenne des précipitations, ce quindique une recharge locale et un temps court de résidence. On a déterminé pour lactivité de ¹⁴C une valeur proche de la moitié trouvée dans les précipitations. Lévolution géochimique par dissolution des carbonates pendant linteraction entre leau et les roche a diminué lactivité du ¹⁴C, de la valeur de 114 pcm en atmosphère à 61 pcm dans les eaux souterraines. Dans laquifère calcaire de surface de bassin Yarmouk, on a considéré comme de concentrations initiales, les valeurs de 61 pcm pour ¹⁴C et 7.2 UT pour ³H. Les grandes fluctuations des niveaux des eaux souterraines observées dans les forages pendant les saisons pluvieux montrent la sensibilité ainsi que la réponse directe de laquifère au recharge. La composition chimique des eaux souterraines (Ca²⁺–HCO₃^–) montre de plus le temps court de linteraction entre leau et la roche, en indiquant aussi la dissolution de laquifère calcaire. Les taux élevées de la concentration en Cl^– et NO₃^– dans les eaux souterraines ont été attribuées aux sources humaines.

     

Deep groundwater flow and geochemical processes in limestone aquifers: evidence from thermal waters in Derbyshire, England, UK

Thermal waters potentially provide information on geochemical processes acting deep within aquifers. New isotopic data on groundwater sulphate, inorganic carbon and strontium in thermal and non-thermal waters of a major limestone aquifer system in Derbyshire, England, UK, are used to constrain sulphate sources and groundwater evolution. Shallow groundwaters gain sulphate from oxidation of sulphide minerals and have relatively ¹³C-depleted dissolved inorganic carbon (DIC). Thermal waters have relatively high Sr/Ca and more ¹³C-enriched DIC as a result of increased water–rock interaction. In other respects, the thermal waters define two distinct groups. Thermal waters rising at Buxton have higher Mg, Mn and ⁸⁷Sr/⁸⁶Sr and lower Ca and SO₄, indicating flow from deep sandstone aquifers via a high permeability pathway in the limestone. By contrast, Matlock-type waters (97% of the thermal flux) have elevated sulphate concentrations derived from interaction with buried evaporites, with no chemical evidence for flow below the limestone. About 5% of the limestone area's groundwater flows to the Matlock group springs via deep regional flow and the remainder flows via local shallow paths to many non-thermal springs. Gypsum dissolution has produced significant tertiary porosity and tertiary permeability in the carbonate aquifer and this is an essential precursor to the development of karstic drainage.

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Resumen Las aguas termales potencialmente proporcionan información sobre procesos geoquímicos que actúan a profundidad en acuíferos. Nuevos datos isotópicos de sulfatos, carbón inorgánico y estroncio en aguas termales y no-termales de un acuífero importante de caliza en Derbyshire, Inglaterra se utilizan para delinear las fuentes de sulfato y la evolución de aguas subterráneas.Las aguas subterráneas no muy profundas adquieren sulfato a través de la oxidación de minerales de sulfuro y poseen carbón inorgánico disuelto (DIC) relativamente deplatado de ¹³C. Las aguas termales muestran un ratio Sr/Ca relativamente alto y poseen (DIC) más enriquecido en¹³C, como resultado de la mayor interacción de roca-agua. En otros aspectos, los aguas termales definen dos grupos distintivos. Las aguas termales que ascienden en Buxton tienen mas Mg, Mn y ⁸⁷Sr/⁸⁶Sr y menos Ca and SO₄, indicando flujo de acuíferos de areniscas profundas por un sendero de alta permeabilidad en la caliza.En contraste el tipo de agua - Matlock (97% del flujo termal) posee altas concentraciones de sulfato, derivado por interacción con evaporitas enterradas, sin evidencia química de flujo debajo de la caliza. Aproximadamente 5% del agua del área de la caliza se fluye al grupo de manantiales de Matlock a través de un flujo regional profundo y el resto fluye por senderos locales poco profundos a muchos de los manantiales no-termales. La disolución de yeso ha producido porosidad terciaria importante así como permeabilidad en el acuífero de carbonato y este es un precursor esencial del desarrollo de drenaje kárstico.

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Résumé Les eaux thermales peuvent apporter des informations sur les processus géochimiques dans les aquifères profonds. De nouvelles données isotopiques sur les sulfates présents dans les eaux souterraines, le carbone inorganique et le strontium dans les eaux thermales et non thermales d'un système aquifère calcaire majeur dans le Derbyshire, Angleterre, Royaume Uni, sont utilisées pour comprendre les sources de sulfates et l'évolution des eaux souterraines. Les eaux souterraines phréatique s'enrichissent en sulfate via l'oxydation des minéraux sulfatés et ont un Carbone Inorganique Dissous (DIC) relativement appauvri en¹³C. Les eaux thermales ont un rapport Sr/Ca relativement plus élevé et un DIC plus enrichi en¹³C, du fait de l'interaction accrue des eaux avec les roches. En d'autres mots, les eaux thermales définissent deux groupes distincts. Les eaux thermales remontant à Buxton ont un Mg, un Mn et un rapport ⁸⁷Sr/⁸⁶Sr plus hauts, mais un Ca et SO₄ plus faible, indiquant un écoulement à travers les zones perméables des aquifers gréseux. Par contraste, les eaux du type de Matlock (97% du flux thermique), possèdent des concentrations élevées en sulfates, provenant de l'interaction des eaux avec les évaporites enfouies, tandis qu'il n'existe aucune évidence chimique d'un écoulement sous les calcaires. Sur environ 5% de la surface des calcaires, les eaux souterraines alimentent des sources non-thermales. La dissolution du Gypse a produit une porosité tertiaire significative et une perméabilité dans les aquifères calcaires, et ceci est un précurseur essentiel au développement du drainage karstique.

     

Use of hydrogeochemistry and environmental isotopes for evaluation of groundwater in Qingshuihe Basin,northwestern China

Hydrogeochemistry and environmental isotope data were utilized to understand origin, geochemical evolution, hydraulic interconnection, and renewability of groundwater in Qingshuihe Basin, northwestern China. There are four types of groundwater: (1) shallow groundwater in the mountain front pluvial fans, originating from recent recharge by precipitation, (2) deep paleo-groundwater of the lower alluvial plains, which was formed long ago, (3) shallow groundwater in the lower alluvial plains, which has undergone evaporation during the recharge process, and (4) mixed groundwater (shallow and deep groundwater in the plain). The main water types are Na–HCO₃, which dominates type (1), and Na–SO₄, which dominates types (2) and (3). Geochemical evolution in the upper pluvial fans is mainly the result of CO₂ gas dissolution, silicates weathering and cation exchange; in the lower alluvial plains, it is related to mineral dissolution. The evaporative enrichment only produces significant salinity increases in the shallow groundwater of the lower alluvial plains. Shallow groundwater age in the upper plain is 10 years or so, showing a strong renewability. Deep groundwater ages in the lower plain are more than 200 years, showing poor renewability. In the exploitation areas, the renewability of groundwater evidently increases and the circulation period is 70–100 years.     

Hydrogeochemical processes,mixing and isotope tracing in hard rock aquifers and surface waters from the Subarnarekha River Basin, (east Singhbhum District,Jharkhand State,India)

Geochemical observations, including major ion and trace element analysis, and isotopic tracing have been carried out in the Subarnarekha River system (northeastern India) during a surface-water- and groundwater-monitoring program aimed at evaluating impacts of mining. The aquifer is of fracture type. Groundwater flow conditions and pollutant transfer were observed through a network of 69 wells. δ¹⁸O and δ²H results suggest that transfer from rainfall towards groundwater storage through soils and the unsaturated zone is fast, without any major transformation like evaporation. The scatter of ⁸⁷Sr/⁸⁶Sr signatures in surface water and groundwater are explained by three end-members. One is compatible with rainwater inputs. The most mineralised end-member represents anthropogenic inputs (agricultural practices and ore processing). The third end-member, characterised by a high ⁸⁷Sr/⁸⁶Sr signature, is believed to be controlled by natural geochemical processes, although affected by human activities (e.g. drainage of mine waste). Potential flow paths, investigated north of the area, reveal that all groundwater types seem to evolve more in pockets than along a flow path. The limited extent of transfer and the predominance of natural phenomena help to explain the moderate level of groundwater contamination and the characteristics of surface water contamination by mining and the metallurgy industry.     

Environmental isotopic study on the recharge and residence time of groundwater in the Heihe River Basin, northwestern China

The recharge and origin of groundwater and its residence time were studied using environmental isotopic measurements in samples from the Heihe River Basin, China. δ¹⁸O and δD values of both river water and groundwater were within the same ranges as those found in the alluvial fan zone, and lay slightly above the local meteoric water line (δD=6.87δ¹⁸O+3.54). This finding indicated that mountain rivers substantially and rapidly contribute to the water resources in the southern and northern sub-basins. δ¹⁸O and δD values of groundwater in the unconfined aquifers of these sub-basins were close to each other. There was evidence of enrichment of heavy isotopes in groundwater due to evaporation. The most pronounced increase in the δ¹⁸O value occurred in agricultural areas, reflecting the admixture of irrigation return flow. Tritium results in groundwater samples from the unconfined aquifers gave evidence for ongoing recharge, with mean residence times of: less than 36 years in the alluvial fan zone; about 12–16 years in agricultural areas; and about 26 years in the Ejina oasis. In contrast, groundwater in the confined aquifers had ¹⁴C ages between 0 and 10 ka BP.     

Hydrochemistry of urban groundwater in Seoul, South Korea: effects of land-use and pollutant recharge

The ionic and isotopic compositions (δD, δ¹⁸O, and ³H) of urban groundwaters have been monitored in Seoul to examine the water quality in relation to land-use. High tritium contents (6.1–12.0 TU) and the absence of spatial/seasonal change of O–H isotope data indicate that groundwaters are well mixed within aquifers with recently recharged waters of high contamination susceptibility. Statistical analyses show a spatial variation of major ions in relation to land-use type. The major ion concentrations tend to increase with anthropogenic contamination, due to the local pollutants recharge. The TDS concentration appears to be a useful contamination indicator, as it generally increases by the order of forested green zone (average 151 mg/l), agricultural area, residential area, traffic area, and industrialized area (average 585 mg/l). With the increased anthropogenic contamination, the groundwater chemistry changes from a Ca–HCO₃ type toward a Ca–Cl(+NO₃) type. The source and behavior of major ions are discussed and the hydrochemical backgrounds are proposed as the basis of a groundwater management plan.     

Hydrogeological and mixing process of waters in aquifers in arid regions: a case study in San Luis Potosi Valley,Mexico

The climatic conditions of arid regions are characterized by high temperatures, low precipitation and high evapotranspiration rates that can explain the reduced recharge of aquifers. Thus, in these regions, there are some problems related to the groundwater quality and recharge that makes worse the problem of groundwater supply. A model, taking into account ternary mixtures, is presented and applied to a case study: the aquifer of San Luis Potosi valley located in the highlands of the central part of Mexico. In this valley, four hydrochemical facies were identified that correspond to the Ca–Na + K–HCO₃, Na + K–Ca–HCO₃, Ca–HCO₃ and Ca–SO₄ types. From this characterization, it was found out that the recharge area (known as Bledos Graben) is located at the SE of the valley; the deep water flow comes from there (Villa de Reyes and Alvarez Range) to the center of the valley. Mixture fractions were obtained by using chlorides and fluorides as conservative elements, from which it was possible to quantify the contribution of each member to the groundwater quality. According to these results, the contributions to the water extracted from this aquifer are as follows: shallow flows 50%, deep flows from Villa de Reyes 27%, and flows coming from the Alvarez Ranges about 15%.     

Groundwater flow and geochemistry in the lower reaches of the Yellow River: a case study in Shandang Province, China

Water samples were collected from the Yellow River and from wells for chemical and isotopic measurement in the counties of Yucheng and Qihe, to which 6–9×10⁸ m³ of water is diverted annually from the Yellow River. A zone of high electrical conductivity (EC) in groundwater corresponds well on the regional scale with a ridge in groundwater level, which is the main flow path through the region, but has a low gradient. The zone of highest EC along this ridge occurs at a position with the lowest ground altitude in the study area. The unique characteristic of the groundwater is the linear relationship among the principal anions as the result of mixing. The mixing effect is confirmed by its isotopic signature, which was then used to calculate the contributions from three sources: rainfall, old water, and diverted water with an average mixing rate of 18, 17, and 65%, respectively. As an indicator of water movement, Cl^– content varies across a wide range in the profile from 30–10 m with a maximum concentration at about 1.2 m depth. Concentrations are relatively stable at about 2 m, which is the average boundary of the saturated and unsaturated zone. The water from the Yellow River has proved to be dominant in mixing in the aquifer in terms of groundwater flow and geochemistry. Electronic Publication     

Geochemical heterogeneity and isotope geochemistry of natural attenuation processes in a gasoline-contaminated aquifer at the Hnevice site,Czech Republic

The geochemical processes, water–rock interactions and stable isotopes distribution (δ¹³C of DIC and δ¹⁸O and δ³⁴S of \({\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}} \)) were investigated in the gasoline-contaminated aquifer at the Hnevice site, 50  km northwest of Prague, Czech Republic. Diesel, gasoline and oil leaks originate from a large fuel storage area causing heavy contamination of the saturated and unsaturated zones in an area of about 0.7  km². Groundwater investigations were conducted using five multilevel sampler wells with emphasis on redox parameters and degradation by-products and a solid-phase study focused on iron speciation and determination of principal and secondary minerals. Based on the study of groundwater and solid-phase geochemistry, four different geochemical zones were described. Zone I is thought to be background consisting of an aerobic aquifer and the absence of reduced species in significant concentrations. Zone II is situated in the plume core with methanogenic, sulphate and iron-reducing conditions accompanied by ankerite and kutnahorite precipitates and significant depletion of the oxidation capacity of the aquifer. Zone III is a mixing (corona) zone, situated at the fringe of the plume with high biodegradation rates and Fe(III)-precipitants. In zone IV, reoxidation of Fe(II) minerals (with e.g. the occurrence of psilomelane and cornelite) is typical.     

Numerical simulation of groundwater flow for a coastal plain in Japan: data collection and model calibration

Using a three-dimensional finite element model, this study characterizes groundwater flow in a costal plain of the Seto Inland Sea, Japan. The model characterization involved taking field data describing the aquifer system and translating this information into input variables that the model code uses to solve governing equations of flow. Geological geometry and the number of aquifers have been analyzed based on a large amount of geological, hydrogeological and topographical data. Results of study demonstrate a high correlation between the ground surface elevation and the groundwater level in the shallow coastal aquifer. For calibrating the numerical groundwater model, the groundwater flow was simulated in steady state. In addition, the groundwater level and trend in the transient state has also been elucidated. The numerical result provides excellent visual representations of groundwater flow, presenting resource managers and decision makers with a clear understanding of the nature of the types of groundwater flow pathways. Results build a base for further analysis under different future scenarios.     

Geophysical and hydrogeologic investigation of groundwater in the Karoo stratigraphic sequence at Sawmills in northern Matabeleland,Zimbabwe: a case history

Geophysical and hydrogeological investigations have been carried out around Sawmills in Zimbabwe, Africa. The investigations are components of a larger investigation to assess the groundwater potential of the Karoo sedimentary basin with regards to supplying water to Bulawayo City. The Sawmills area was selected due to the availability of borehole logs indicating favourable stratigraphy for groundwater availability and due to the high yields from the aquifers measured from these boreholes. Data collected using two geophysical methods are presented here: transient electromagnetic (TEM) and continuous vertical electrical sounding (CVES) data. The data have also been processed using laterally constrained inversion (LCI). Because the CVES provides greater detail in the shallow subsurface, whereas TEM is more effective at depth, a more accurate image of the entire subsurface profile is provided based on using both methods. The results suggest that LCI of CVES and TEM data, in the subsurface at the required depths at Sawmills, is able to provide a substantially more accurate image of the subsurface than either method alone. The hydrogeological interpretation of the geophysical data is valuable for determining the depth to and thickness of the potential aquifer horizon(s) and for identifying the position of potential recharge zones.     

Palaeoenvironmental control on sediment composition and provenance in the late Quaternary deltaic successions: a case study from the Po delta area (Northern Italy)

Accumulation of continental, deltaic and shallow‐marine sediments in the Po River coastal plain preserves a record of the Late Quaternary sea‐level changes and shoreline migrations. The palaeoenvironmental evolution of this area and the changes in composition and provenance of sediments have been investigated through integrated sedimentological, micropalaeontological (mainly foraminifers) and geochemical analyses of core S1, from the southern part of the Po River delta, within a chronological framework supported by radiocarbon dating and correlations with adjacent core sequences. Eleven lithofacies, grouped into five facies associations, and four palaeontological assemblages provide the basis to define the palaeoenvironmental reconstruction of this succession consisting, from the base to the top, of: (i) continental sediments accumulated during the Late Pleistocene; (ii) back‐barrier sediments marking the onset of Holocene sea‐level rise; (iii) transgressive sands deposited during the rapid landward migration of a barrier‐lagoon system; (iv) shallow‐marine and prodelta sediments with faunal associations indicating a gradual approach to the Po River mouth; and (v) sub‐recent delta front sands that form a considerable portion of the present coastal plain. Bulk chemical composition of sediments shows remarkable relationships with palaeoenvironments and locally improves facies characterizations. For example, they reveal carbonate leaching that emphasizes the occurrence of palaeosols in continental deposits or record enrichments in loss on ignition, S and Br, diagnostic of organic‐rich layers in back‐shore sediments. Selected geochemical elements (e.g. Mg and Ni) are particularly effective for the recognition of sediment provenances from the three main source areas observed in the subsurface deposits of the Po River coastal plain (e.g. Apenninic rivers, North Adriatic rivers and Po River). An Apenninic provenance is observed in continental and back‐barrier sediments. A North Adriatic provenance characterizes the transgressive sands and the shallow‐marine deposits; a significant Po River provenance is recorded in sediments related to the onset of the prodelta environment, confirmed by foraminiferal assemblages indicating remarkable increase in fluvial influxes. Copyright © 2006 John Wiley & Sons, Ltd.     

Characteristics of groundwater in Northeast Qinghai-Tibet Plateau and its response to climate change and human activities: A case study of Delingha,Qaidam Basin

Delingha is located in the northeast margin of Qaidam Basin. Bayin River alluvial proluvial fan is the main aquifer of Delingha, in which groundwater generally flows from north to south. The hydrochemistry results showed that two different hydrochemical evolution paths formed along southeast and southwest directions, respectively. Cl-Na type groundwater was formed in front of Gahai Lake, and SO₄·HCO₃-Na·Ca type groundwater was formed in front of Keluke Lake. The results of deuterium (D) and ¹⁸O revealed that the groundwater mainly originated from the continuous accumulation of precipitation during geological history under cold and humid climate conditions. In addition, results of ¹⁴C indicated that the groundwater age was more than 1140 years, implying relatively poor renewal capability of regional groundwater. Moreover, our numerical modeling results showed that the regional groundwater level will continue to rise under the warm and humid climate conditions.© 2021 China Geology Editorial Office.     

Salinity mapping of coastal groundwater aquifers using hydrogeochemical and geophysical methods: a case study from north Kelantan,Malaysia

Integrated hydrogeochemical and geophysical methods were used to study the salinity of groundwater aquifers along the coastal area of north Kelantan. For the hydrogeochemical investigation, analysis of major ion contents of the groundwater was conducted, and other chemical parameters such as pH and total dissolved solids were also determined. For the geophysical study, both geoelectrical resistivity soundings and reflection seismic surveys were conducted to determine the characteristics of the subsurface and groundwater contained within the aquifers. The pH values range from 6.2 to 6.8, indicating that the groundwater in the study area is slightly acidic. Low content of chloride suggests that the groundwater in the first aquifer is fresh, with an average concentration of about 15.8 mg/l and high geoelectrical resistivity (>45 ohm m). On the other hand, the groundwater in the second aquifer is brackish, with chloride concentration ranging from 500 mg/l to 3,600 mg/l and very low geoelectrical resistivity (<45 ohm m) as well as high concentration of total dissolved solids (>1,000 mg/l). The groundwater in the third aquifer is fresh, with chloride concentrations generally ranging from 2 mg/l to 210 mg/l and geoelectrical resistivity of greater than 45 ohm m. Fresh and saltwater interface in the first aquifer is generally located directly in the area of the coast, but, for the second aquifer, both hydrogeochemical and geoelectrical resistivity results indicate that the fresh water and saltwater interface is located as far as 6 km from the beach. The considerable chloride ion content initially suggests that the salinity of the groundwater in the second aquifer is probably caused by the intrusion of seawater. However, continuous monitoring of the chloride content of the second aquifer indicated no significant changes with time, from which it can be inferred that the salinity of the groundwater is not affected by seasonal seawater intrusion. Schoeller diagrams illustrate that sulphate concentrations of the groundwater of the second aquifer are relatively low compared to those of the recent seawater. Therefore, this result suggests that the brackish water in the second aquifer is probably from ancient seawater that was trapped within the sediments for a long period of time, rather than due to direct seawater intrusion.     

Use of geochemical modeling to evaluate the hydraulic connection of aquifers: a case study from Chianan Plain, Taiwan

Aquifers are generally composed of highly permeable layers that can conduct a considerable amount of groundwater. Traditionally, aquifer units are correlated through the concept of lithostratigraphy. For low-permeable aquifers, it is difficult to define the spatial distribution of hydrogeological units, and this study attempts to use geochemical modeling to identify the groundwater flow paths in an area of Taiwan. Multiple geochemical analyses, including groundwater chemistry; stable isotopic compositions of hydrogen, oxygen and carbon; and radiocarbon contents were performed. Using these parameters as the constraints of geochemical models, the hydraulic connection was examined between pairs of possibly interlinked wells along four selected cross sections, and the conceptual groundwater model was accordingly established. The resultant model suggests that the hydraulic connection between aquifers should be correlated with the concept of chronological stratigraphy, especially for low-permeable, unconsolidated aquifers. Using Darcy’s law, the hydraulic conductivities of the fine-sand aquifers were estimated to be between 3.14 × 10⁻⁵ and 1.80 × 10⁻⁴ m/s, which are roughly one order of magnitude higher than those derived by in situ pumping tests. The substantial extraction of groundwater over a long period in the studied area could accelerate groundwater flow, leading to an overestimation of the aquifer permeability.

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Résumé En règle générale, les aquifères sont constitués de couches très perméables capables de conduire des quantités d’eau considérables. Les unités aquifères sont traditionnellement corrélées d’un point de vue lithostratigraphique. Dans le cas des aquifères à faible perméabilité, il s’avère difficile de définir une distribution spatiale des unités hydrogéologiques, et cette étude tente d’utiliser la modélisation géochimique pour identifier les cheminements des eaux souterraines dans un secteur de Taiwan. Plusieurs analyses géochimiques ont été réalisées ; elles incluent la chimie des eaux souterraines, les isotopes stables de l’hydrogène, de l’oxygène et du carbone et l’abondance en carbone 14. En utilisant ces paramètres comme contraintes pour les modèles géochimiques, les liaisons hydrauliques entre les puits potentiellement interconnectés ont été étudiées deux par deux, le long de quatre coupes présélectionnées, et le modèle conceptuel a été établi en conséquence. Ce modèle résultant suggère que les connexions hydrauliques inter-aquifères devraient être corrélées avec les concepts stratigraphiques, surtout pour les aquifères non consolidés à faible perméabilité. Les perméabilités dans les aquifères de sables fins ont été estimées par la loi de Darcy entre 3.14 × 10⁻⁵ et 1.80 × 10⁻⁴ m/s, soit environ un ordre de grandeur au-dessus de celles issues des tests de pompage sur site. L’exploitation substantielle des eaux souterraines sur une longue période dans la zone d’étude peut accélérer les écoulements souterrains, menant à une surestimation de la perméabilité de l’aquifère.

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Resumen Los acuíferos están generalmente compuestos de capas muy permeables que pueden conducir una cantidad considerable de agua subterránea. Tradicionalmente, se ponen en correlación las unidades acuíferas a través del concepto de litoestratigrafía. Para los acuíferos de baja-permeabilidad, es difícil de definir la distribución espacial de unidades hidrogeológicas y este estudio intenta usar modelamiento geoquímico para identificar las direcciones del flujo de agua subterránea en un área de Taiwán. Se realizó el análisis geoquímico múltiple, incluyendo la química del agua subterránea, la composición de isótopos estables de hidrógeno, oxígeno y carbono, y el contenido de radiocarbono. Usando estos parámetros como limitantes de modelos geoquímicos, la conexión hidráulica se examinó entre pares de pozos posiblemente interrelacionados, a lo largo de cuatro cortes transversales seleccionados y de acuerdo con esto se estableció el modelo conceptual del agua subterránea. El modelo resultante sugiere que la conexión hidráulica entre los acuíferos deba interrelacionarse con el concepto de estratigrafía cronológica, sobre todo para los acuíferos sin consolidar de baja permeabilidad. Usando la ley de Darcy, se estimaron las conductividades hidráulicas de los acuíferos de arena fina obteniendo valores entre 3.14 × 10⁻⁵ y 1.80 × 10⁻⁴ m/s, las cuales son aproximadamente un orden de magnitud mayor, que aquéllos obtenidos in situ por las pruebas de bombeo. La extracción considerable de agua subterránea durante un periodo largo en el área estudiada, podría acelerar el flujo de agua subterránea, llevando a una sobrestimación de la permeabilidad en los acuíferos.

     

Large reactivated landslides in weak rock masses: a case study from the Northern Apennines (Italy)

This case study paper is about a large rotational rock and earth slide—earth flow located in the Secchia River Valley, in the Northern Apennines of Italy, that has displayed multiple reactivation phases between 2002 and 2004. The main geological constraints of the mass movement are related to the overlap of flysch rock masses over clayey complexes that allows rock slides to take place in the source area. The disarrangement and weathering of rock masses following slope movements causes large amount of fine-grained debris to be accumulated on the slope and mobilised by earth sliding and flowing. Analysis of rainfall data at the onset of reactivation events has proved that they occurred after periods with cumulated values higher than the averages of the last 30 years. The quantification of the morphological modifications induced by these reactivations has been made possible by comparing pre- and post-event digital elevation models. Depletion and accumulation has been in the range of 30 m in different parts of the slope. In particular, an advancement of the landslide toe of more than 400 m, which caused a 30-m thick landslide tip to deposit, has been clearly seen. Monitoring data regarding subsurface movements and surface tension crack widening (tension cracks so large as to be properly described at trenches) has shown that sliding surfaces as deep as 43 m exist in the upper part of the landslide, while the accumulation lobe has moved by sliding and flowing over surfaces as deep as some 10 m. Velocities of cm/day have been recorded in the deep surfaces and in widening trenches of the source area, while the advancement of the accumulation lobe has been estimated as having velocities of up to 10 m/day. Groundwater in the landslide body has been observed at depths of 5–15 m in the upper areas, while it is estimated as being at the ground level in the toe. On this basis, it is concluded that the landslide still has a high potential for further development, both in the upper landslide zone and in the toe area.     

Determination of groundwater availability in shallow arid region aquifers utilizing GIS technology: a case study in Hada Al-Sham, Western Saudi Arabia

A simple, physically based method is developed in this paper to assist in the allocation of areas with high groundwater potential and for the determination of maximum allowed pumping rate to ensure proper groundwater management. This method utilizes the aquifer physical properties as well as GIS technology to accomplish this purpose. The design of this method was considered to be applicable in areas with little data, such as in most arid regions. This technique was applied to a catchment in an arid environment where qualitative as well as quantitative analyses of the results were undertaken. Locations of available groundwater and rates of maximum allowable pumping were compared with observations and experiments in the field and a good agreement was found. It was concluded that the best groundwater location was in the alluvial area, which represents only 16% of the total aquifer, which is a typical case in arid region catchments. The rate of maximum pumping was estimated to be 65 m³/h. However, to benefit 55% of the area, the maximum pumping rate should only be 40 m³/h with an average rate throughout the area (55%) of about 24 m³/h.This revised version was published online in December 2004 with corrections to the category.     

Prediction of inflow from overlying aquifers into coalmines: a case study in Jinggezhuang Coalmine,Kailuan, China

Aquifers overlying coal seams are common water sources in coalmines. The unexpected inflow of water can flood mines and threatens the mine safety. Mine flooding caused by the overlying aquifers has occurred more frequently in recent years in China. Proposed in this paper is a new method that involves three basic maps and two predictions to tackle this geo-hazard. This new approach is based on the water abundance in the overlying aquifer and risk analysis of the roof collapse. It couples groundwater flow models with rock mechanics analysis. The method was successfully applied to prediction of the water intrusion from the overlying aquifer at Jinggezhuang Coalmine in Kailuan, China. The areas with high risk of water intrusion were delineated. Visual Modflow (version 2.61) was used to simulate the inflows at two active working faces. The developed approach can predict the total inflow for a working face and the transient inflow as the working face advances.