Recharge Areas Research Articles

Application of statistics to correlate groundwater chemistry with land use on O'ahu, Hawai'i.

This study compiles commonly available groundwater chemistry data from the Pearl Harbor Sole Source Aquifer (SSA), Hawai'i-O'ahu's primary drinking water source-and applies hierarchical clustering analysis (HCA), principal component analyses (PCA), piper diagrams, and box plots with geospatial analysis to better define groundwater regions and correlate groundwater chemistry in those regions with land use. Groundwater in this aquifer recharges and flows through chemically similar soil and rocks, such that anthropogenic activities are a primary influence on the chemical variability of the aquifer's differing regions. Our analyses link specific chemical species in groundwater to land use/cover categories: urban, agriculture, and natural and anthropogenically-induced saline water intrusion. To create distinct statistical groupings with different groundwater chemistry compositions, it was important that the suite of parameters used in the statistical analysis do not covary. In our case, Cl- covaried with several major ions; however, by including F-, alkalinity, and SiOx that do not covary with Cl- in the covariance matrix, we produced improved spatial grouping of HCA clusters and stronger affinities to land use designations. Results show that dominant groundwater chemistry changes with land use along flow paths. These results pertain to areas where groundwater flows from conservation land in high recharge areas of O'ahu's mountain ranges to urban and agricultural land use regions: groundwater retains its source characteristics until about 3-6km into agricultural and urban zoned lands. Ultimately, this study outlines a simple method for water quality regulators to use groundwater chemistry to identify risks of target contaminants based on land use.

Groundwater Dynamics near the Saltwater–Freshwater Interface in an Island of Seto Inland Sea

Groundwater dynamics near the saltwater–freshwater interface were investigated in an island of the Seto Inland Sea, using multiple tracers (δD, δ18O, Cl−, SF6, and 14C) at two coastal groundwater monitoring wells at depths of 10–40 m. The groundwater recharge area and age were also estimated using these tracers. Additionally, bedrock groundwater at a depth of 40 m at the 2.7 m altitude was brackish and considered to be near the saltwater–freshwater interface, and a mixture of seawater (2–3.5%) and fresh groundwater (97–98%) was estimated by the Cl− concentration. Based on the δ18O of fresh groundwater estimated from the seawater mixing ratio, the recharge area was estimated to range from near to above the summit; however, this region is unlikely to be the actual recharge area, as the groundwater may be old freshwater that was recharged during a previously colder period. Groundwater dating using SF6 and 14C suggests that the fresh groundwater originated during the last glacial period (assumed 20,000 years ago) and that the 40 m deep bedrock groundwater is a mixture of old water (0–28%), 30 m deep groundwater (76–100%), and stagnant seawater (1–3%).

GEOMORPHOLOGY AND THE FORMATION HISTORY OF GLACIAL MATERIALS OF THE EV’VAYAM RIVER VALLEY (KORYAK HIGHLANDS)<a href="#FN2"><sup>2</sup></a>

Based on the interpretation of satellite images and field observations, three moraines of different ages and morphology were identified in the valley of Ev’vayam River. The oldest, poorly preserved and significantly eroded moraines are located in the lower reaches of the Ev’vayam River near the Bering Sea coast. A well expressed in relief complex of younger moraines consisting of three better-preserved moraine ridges (45, 62–72 and 87–95 m a. s. l.) with thin soil cover is distinguished in the middle reaches of Ev’vayam River. The youngest moraines are found in the upper reaches of the Ev’vayam River Valley at elevations of 240–320 m a. s. l., where they form longitudinal ridges, or “tongues”. Based on the preservation degree, morphology and size of the investigated glacial complex, and published data on adjacent areas, the glaciation of the territory had a mountain-valley character. The glacier apparently reached its maximum size at the beginning of the Late Pleistocene, when it moved beyond the valley of the Ev’vayam River to the coast. The moraines in the central part of the valley and in its upper reaches were formed by much smaller glaciers during the end of Late Pleistocene. The recharge area of glaciers during this period was limited to a series of glacial cirques and kars in the central part of Pylgynskiy Range. Currently, small glaciers are present in cirques at elevations from 410 m to 720 m a. s. l., and continue to form modern moraines.

Development and Application of a Methodology for the Identification of Potential Groundwater Recharge Zones: A Case Study in the Virvini Micro-Basin, Tiraque, Bolivia

Groundwater plays a vital role in human consumption and irrigation in many parts of Bolivia; yet, the absence of policies to regulate its extraction and protect groundwater recharge areas has led to a decline in water tables and threatened food security. Some municipal initiatives have been implemented to develop regulations, but the lack of reliable hydrogeological data (such as aquifer geometry, groundwater level data, location of potential groundwater recharge zones, and flow dynamics) hinders their effective implementation. The case study presented herein focuses on a municipal policy in Tiraque, Bolivia, aimed at protecting groundwater recharge zones, in addition to the need for a reliable methodology for their technical identification. The EARLI approach (an acronym for “Enhanced Algorithm for Recharge based on the Rainfall and Land cover Inclusion”) is suggested as a participatory-simplified multi-criteria decision method to address the absence of hydrogeological data. This approach was adjusted to the basin’s specific conditions, including local vegetation communities and their influence on infiltration, and was applied as a pilot study in the Virvini micro-basin. The EARLI model emphasizes the spatial distribution of rainfall as an input indicator for potential recharge in addition to the biophysical characteristics of the catchment area. The methodology successfully mapped the degree of groundwater recharge potential and was validated by traditional hydrogeological models, field infiltration measurements, and the local community’s application of the tool. Therefore, the results of this study provide the necessary technical bases for groundwater-integrated management in Tiraque.

Using Artificial Intelligence to Identify Suitable Artificial Groundwater Recharge Areas for the Iranshahr Basin

A water supply is vital for preserving usual human living standards, industrial development, and agricultural growth. Scarce water supplies and unplanned urbanization are the primary impediments to results in dry environments. Locating suitable sites for artificial groundwater recharge (AGR) could be a strategic priority for countries to recharge groundwater. Recent advances in machine learning (ML) techniques provide valuable tools for producing an AGR site suitability map (AGRSSM). This research developed an ML algorithm to identify the most appropriate location for AGR in Iranshahr, one of the major districts in the East of Iran characterized by severe drought and excessive groundwater consumption. The area’s undue reliance on groundwater resources has resulted in aquifer depletion and socioeconomic problems. Nine digitized and georeferenced data layers have been considered for preparing the AGRSSM, including precipitation, slope, geology, unsaturated zone thickness, land use, distance from the main rivers, precipitation, water quality, and transmissivity of soil. The developed AGRSSM was trained and validated using 1000 randomly selected points across the study area with an accuracy of 97%. By comparing the results of the proposed sites with those of other methods, it was discovered that the artificial intelligence method could accurately determine artificial recharge sites. In summary, this study uses a novel approach to identify optimal AGR sites using machine learning algorithms. Our findings have practical implications for policymakers and water resource managers looking to address the problem of groundwater depletion in Iranshahr and other regions facing similar challenges. Future research in this area could explore the applicability of our approach to other regions and examine the potential economic benefits of using AGR to recharge groundwater.

Contamination Characteristics and Source Identification of Groundwater in Xishan Coal Mining Area of Taiyuan Based on Hydrochemistry and Sulfur–Oxygen Isotopes

Xishan mining area in Taiyuan is a typical coal industry cluster with a variety of coal-related industrial sites such as coal mines, power plants and coking plants, which seriously pollute the native ecological environment. Study of the hydrochemical characteristics and pollution sources of groundwater in the area can contribute to the ecological protection and remediation of regional groundwater resources. In this study, we collected surface water and groundwater samples from the Xishan mining area and measured and analyzed hydrochemical and sulfur–oxygen isotopes. Results showed that 64.7% of groundwater in the study area exceeded the sulfate standard due to the influence of the coal industry, with some karst groundwater up to 2000 mg/L. In the runoff and discharge area of karst groundwater, the proportion of anthropogenic input of SO42− increased, which led to the hydrochemical type of karst groundwater gradually changing from HCO3-Ca·Mg (recharge area) to SO4-Ca·Mg (discharge area). Results of sulfur–oxygen isotope tests indicated that the δ34SSO4 and δ18OSO4 values of samples were −10.01~24.42‰ and −4.90~12.40‰, respectively, and the sulfur–oxygen isotope values of some karst groundwater were close to the dissolved end of sulfide minerals, indicating their sulfate mainly came from the oxidation of pyrite. Sulfate sources in groundwater water were parsed using IsoSource model. Calculated results revealed that sulfate in pore groundwater mostly originated from pyrite oxidation, and karst groundwater in the recharge area was mainly influenced by atmosphere precipitation, while groundwater in the runoff and discharge areas were significantly affected by pyrite oxidation, accounting for up to 90% in some karst groundwater. Comparing the sulfur–oxygen isotope values of karst groundwater in 1989, 2016 and 2022, we found that the δ34SSO4 values in 2022 decreased significantly, which indicated the expansion of karst groundwater pollution in the Xishan mining area. This study highlights the pollution of regional groundwater by coal-related industrial agglomerations, and the groundwater pollution in the Xishan mining area requires urgent remediation and restoration.

Development of Groundwater Flow Models for the Integrated Management of the Alluvial Aquifer Systems of Dravsko polje and Ptujsko polje, Slovenia

With increasing exploitation of groundwater resources and implementation of various activities in their recharge areas, it is vital to conduct a comprehensive assessment of aquifers to ensure their conservation and sustainable management. In the present study, we used a comprehensive approach to conceptualise and identify the functioning of two connected aquifer systems in north-eastern Slovenia: the Quaternary porous aquifers Dravsko polje and Ptujsko polje. The study presents the conceptual models of both aquifers and their interconnectedness using separate mathematical-numerical models with the aim of ensuring an integrated management of these alluvial aquifer systems. It also highlights the importance of understanding connections between such systems for simulating groundwater flow and transport of different contaminants. To describe the entire aquifer system, the study defines its three essential elements: the geometry of the aquifers, their recharge by precipitation, and other boundary conditions. The geometry of the Quaternary aquifers was defined using Sequential Indicator Simulation (SIS) with the ESRI’s ArcMap software. Next, LIDAR was used for determining their surface geometry. The hydrogeologic model was designed using the Groundwater Modelling System (GMS) developed by AQUAVEO. We used the MODFLOW 2000 calculation method based on the finite difference method (FDM). The model was calibrated with the PEST module, which was used to calibrate hydraulic conductivity and hydraulic heads between the measured and modelled data. Finally, the model was validated using the Nash–Sutcliffe (NSE) efficiency coefficient. In addition, the model results estimated using the PEST tool were validated with the hydraulic conductivities determined at the pumping sites (pumping tests), each belonging to water protection zones that define the maximum travel time of the particles. This was performed using the MODPATH method. The paper also presents the possibility of modelling heterogeneous but interdependent aquifers in a groundwater body. Modelling the connection between the two aquifers, which are the most important ones in the region, is essential for a comprehensive management of the entire system of water resources. The models allow for a better understanding of groundwater flow in both aquifers. Moreover, their interconnectedness will be used for further studies in this field, as well as for integrated water management.

Groundwater characterization of the eastern Minesing Wetlands in support of the endangered Hine’s emerald dragonfly (Somatochlora hineana)

The Minesing Wetlands contain Canada’s only known population of Hine’s emerald dragonfly (HED), a species listed as endangered since 2011. The HED relies on groundwater discharge areas to complete its life cycle and therefore the population is potentially sensitive to changes in groundwater. The goals of this study were to, (1) characterize groundwater discharge to the eastern portion of the Minesing Wetlands, which corresponds to the HED habitat, (2) document any significant changes in groundwater chemistry since a 1998 study, and (3) establish a comprehensive baseline water quality data set to facilitate future comparisons. Consistent with HED habitats in the USA, the chemistry of Minesing Wetlands groundwater was dominated by calcium and bicarbonate. Low groundwater chloride and nitrate concentrations indicated minimal impact from activities such as road salt application and fertilizer use. Nitrate was generally only found at the wetland margin where groundwater springs emerged from the base of the uplands. The dominant form of inorganic nitrogen in wetland groundwater was ammonium (max = 1.5 mg N/L), and soluble reactive phosphorus concentrations were also relatively high (8 to 122 µg/L). The most consistent change in wetland groundwater chemistry between the 1998 study and samples collected in 2015–2017 was that chloride concentrations in 10 of 23 wells increased over time, however the maximum mean well chloride (11.6 mg/L) remained well below the guideline for the protection of aquatic life (120 mg/L). To preserve HED habitat, potential impacts to groundwater need to be considered during land use planning for the recharge area.

Environmental isotope constraints and hydrogeochemical evolution of groundwater in the semi-arid national capital environs of Delhi, India

Changes in hydrological regimes due to rapid urbanization and increasing anthropogenic stress on hydro-geological system creating an alarming condition for the management of ground water resources. Isotope and hydro-geochemical integrated approach has been used to determine the processes governing chemical composition of groundwater and the mechanism influencing the chemical composition of groundwater in National Capital Region (NCR), Delhi. The chemical evolution of groundwater has studied by using flow direction, hydro-chemical facies, bivariate plots of ionic ratios and saturation index. Stable isotopes and tritium are used to understand the recharge mechanism. Pollution index of groundwater (PIG) is also used to check the level of contamination in the groundwater. In total, 57 water samples were collected for water chemistry, 36 water samples for environmental isotopes and 13 samples for tritium measurement. The dominant water type is Ca-Mg-HCO3 and mixed water type. The dominant cation are Ca2+ > Na+ > Mg2+ > K+ and dominant anions are HCO3− > Cl− > SO42− > NO3−. The bicarbonate type water is dominant in quartzite, implies rapid and direct recharge through fracture and joints. Ionic ratios and saturation indices show that major processes controlling groundwater evolution are silicate hydrolysis and reverse cation exchange in the quartzite. Average values of δ2H and δ18O are −43.66 ‰ and −6.28‰. Stable isotopic ratio of groundwater of alluvium area falling on evaporation line, due to the prevailing semi-arid and arid climatic conditions, evaporation is the predominant factor affecting the chemistry of groundwater. The stable isotope shows that the groundwater in the quartzite is mostly meteoric in origin and acting as a recharge area for the nearby alluvium aquifer. Tritium results reveal that groundwater occurring in quartzite and alluvium aquifer in western parts are older than that of groundwater occurring in alluvium aquifer in the eastern parts.13% of groundwater samples are falling in very high pollution zone mainly occurring in alluvium aquifer that lies in the Eastern parts. It is inferred that alluvium aquifer (low lying) is having greater impact of anthropogenic activity than quartzite aquifer (high land).

Determination of groundwater recharge–discharge zone to support water resources in Galur–Lendah area, Indonesia

The impact of changes in regional development along with the construction of Yogyakarta International Airport in Kulon Progo Regency may affect land use changes as the activities of the surrounding population. Galur– Lendah area, which is located near the city of Yogyakarta and acts as the entrance to Kulon Progo, will also develop. Along with these developments, the determination of the groundwater recharge–discharge area is needed to ensure the availability of groundwater at this site. The purpose of this study was to determine the zonation of groundwater recharge–discharge areas to support the availability of groundwater. The method of research is a spatial analysis using a geographic information system (GIS) based on ratings and weighting values for six parameters, including slope, rainfall, groundwater table depth, soil type, rock permeability, and land use. The field hydrogeological was also conducted to find out rock permeability and groundwater quality (pH, EC, TDS). The results showed that areas with potential for groundwater recharge were in the central and northeastern parts of the study area and the discharge zones in the north and south were with potential infiltration values of 26–43 and 44–59, respectively. However, the recharge area can still function as a discharge zone.

Towards a better understanding of flow-related processes in the vertically distributed compartments of karst aquifers by combining natural tracers and stable isotopes

Understanding infiltration pathways throughout the different compartments of karst systems (soil-epikarst-unsaturated zone-saturated zone) is vital to assess recharge processes, vulnerability to pollution, and the general hydrogeological functioning of these kind of aquifers. To gain deeper insight into the soil-water-rock hydrogeochemical processes occurring throughout the vertically hierarchized compartments of the aquifer and to evaluate the applicability of different soil natural parameters as groundwater flow tracers, the present work analyzes the spatial and temporal evolution of total organic carbon -TOC-, intrinsic fluorescence related to organic matter, nitrates, δ13CTDIC, and the values of stable isotopes of δ2H and δ18O from water molecules and at different sampling points in a geologically complex karst aquifer in south Spain (Jarastepar carbonate massif). Over two years, rain and soil water (30 and 60 cm deep) samples were collected simultaneously at an experimental plot along with groundwater from the top of the saturated zone and a base-level spring. Results show that the variation in the concentration of natural soil tracers and the signal of water stable isotopes (δ2H and δ18O) smooth throughout the different compartments of the aquifer, with rapid variations in the unsaturated zone after recharge events and delayed effects in the saturated zone. At the same time, δ13CTDIC and nitrate values rise along the subsurface flow. While the carbon isotope evidences a shorter transit time between recharge areas and the top of the saturated zone than the subsequent path toward the permanent base springs, nitrate evolution is affected by pollution sources near discharge areas, so its applicability is questionable. Finally, organic matter (TOC and intrinsic fluorescence) mineralizes (or degrades) up to 90% from the first centimeters of soil to the permanent basal springs. An exponential decreasing trend defines the relationship between TOC and δ13CTDIC caused by organic matter attenuation along the groundwater flow path, while δ13CTDIC increases because of a higher residence time of water in contact with the host rock. These results, together with previous research based on other natural tracers (chemical, isotopes, and dating tools) and dye tracing experiences, permit to link TOC and δ13CTDIC values with a range of transit times, from hours-days to years-decades. Meanwhile, the attenuation of natural intrinsic fluorescence and TOC signal evidence the filter function of the aquifer from the soil to the saturated zone. All these findings highlight the usefulness of natural fluorescence and, particularly, TOC and δ13CTDIC, as tracers of groundwater flow and hydrogeochemical processes within the different compartments of complex karst aquifers.

The Significance of Groundwater Table Inclination for Nature-Based Replenishment of Groundwater-Dependent Ecosystems by Managed Aquifer Recharge

Managed aquifer recharge (MAR) is an increasingly popular technique; however, the significance of groundwater flow dynamics is rarely examined in detail regarding MAR systems. In general, a high hydraulic gradient is not favoured for MAR implementation, as it causes higher water loss and mixing of recharge water with native groundwater. However, during groundwater-dependent ecosystem (GDE) rehabilitation, these hydraulic gradient-driven flow processes can be taken advantage of. The aim of this research is to test this hypothesis by evaluating the effect of groundwater table inclination, topography, and other local characteristics on MAR efficiency from the perspective of GDE restoration. MAR efficiency was examined from recharge to discharge area in a simple half-basin based on theoretical flow simulations, using GeoStudio SEEP/W software. Different scenarios were compared to analyse the groundwater level increase and the infiltrated water volumes and to assess the efficiency of MAR based on these parameters in each scenario. The theoretical results were applied to a close-to-real situation of Lake Kondor, a GDE of the Danube-Tisza Interfluve (Hungary), which dried up in the past decades due to groundwater decline in the area. Based on the results, initial hydraulic head difference, model length, and hydraulic conductivity are the most critical parameters regarding water level increase at the discharge area. The water amount needed for increasing the water table is mainly influenced by the thickness of the unsaturated zone and the material properties of the aquifer. The findings can help better understand MAR efficiency in light of local groundwater flow processes and contribute to optimising MAR systems. The results of the study suggest that, if water is infiltrated at the local recharge area, the water table will also increase at the corresponding discharge area, which positively effects the connected GDEs. This approach can serve as a nature-based solution (NBS) to sustain sensitive ecosystems in changing climatic conditions.

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.

Use of GIS and R to estimate climate change impacts on groundwater recharge in Portoviejo River watershed, Ecuador

Future groundwater recharge estimations are helpful tools for water resources management. However, there is a need for more information about it in many parts of the world, including the Portoviejo River watershed (PRW) in the West of Ecuador, a semi-arid zone with a water deficit where climate change impacts could increase pressure on groundwater resources. Geographical Information Systems were used in this paper, owing to their simplicity of inputs and accuracy of outputs, to estimate current and future (2021–2070) groundwater recharge in the PRW. The study is divided into two stages: 1) a runoff map based on soil permeability, land use, and terrain slope, and 2) current and future recharge calculations using the Thornthwaite and Mather water balance method. Future precipitation and temperature data from an ensemble of four Global Circulation Models were used as inputs, along with a map of runoff spatial distribution. The representative concentration pathways (RCP) 4.5 and 8.5 were the climate change scenarios used in this study. The results showed that the location of the groundwater recharge zone would be impacted by future precipitation and temperature variability in both scenarios for the next fifty years. For the decade 2060–2070 and the scenario RCP 4.5, the highest recharge rate zones were located in the lowlands of the PRW surrounding Portoviejo city. In scenario RCP 8.5, the highest groundwater recharge areas increase considerably in the entire PRW. Currently, the highest groundwater recharge zones are in the highlands of the PRW. The future groundwater recharge scenarios provide information to decision-makers regarding land use, since the future groundwater recharge zones will be in the expansion areas of Portoviejo city.

The impact of livestock activities and geochemical processes on groundwater quality of fractured volcanic rock aquifer: Lake Çıldır watershed (NE Turkey)

This paper presents the impact of livestock activities and geochemical processes on the water quality of a fractured volcanic rock aquifer in the Lake Çıldır watershed, located at the northeastern part of Turkey. The existence of a high livestock population and animal grazing activities in meadow and pasturelands of the watershed during the short summer period poses serious stress on both surface and groundwater resources being the only drinking water supply for the local communities. Therefore, understanding the effect of grazing and livestock breeding activities occurring in the recharge areas of the fractured volcanic rock aquifer is vital to take precautions in order to protect limited water supplies at the watershed and vulnerable lake ecosystem as well. The mean nitrate content of the groundwater was measured at 6.4 ± 6.6 (std. dev) mg/L in the wet (before grazing) period and 7.1 ± 5.9mg/L in the dry (after grazing) period. Despite low nitrate concentration levels of groundwater, microbial contamination was observed in the spring waters at alarming levels especially after the animal grazing activities. 56%, 26%, and 11% of the groundwater samples showed bacterial contamination in terms of total coliform, fecal coliform, and fecal streptococci contents, respectively, prior to grazing activity, while in pursuit of intense livestock grazing at highland, these microbial indicators have been increased to 92%, 85%, and 77% in the dry period. A significant increase observed in fecal contamination indicates the negative impact of livestock activities on groundwater quality. Al (200-638µg/L) and Fe (66-218µg/L) enrichments locally observed in groundwater were related to advanced argillic alteration (kaolinization) and hematization zones in pyroclastic rocks.

Application of Geospatial Techniques for Artificial Recharge to Groundwater in Ratu Khola Watershed, Central Nepal

Water levels in many existing ponds and shallow tube wells are found lowering day by day in the Bhabar and Terai regions of Nepal. For the sustainable management of the groundwater, development of artificial recharge ponds is considered the best approach in this region. The suitable site selection for the artificial recharge ponds requires surface as well as sub-surface geological investigation along with other land use-related characteristics. The study area is a part of the Ratu Khola watershed in the Mahottari and Dhanusa districts and encompasses parts of the Siwalik, Bhabar, and Middle Terai regions from an aspect of the geological division. The present study has aimed to find suitable sites for the artificial recharge pond. For this purpose, extensive fieldwork was carried out to gather data related to geology, geomorphology, water table, and soil characteristics. However, slope and drainage density maps were developed from the Digital Elevation Model (DEM). The thematic layers of different parameters such as geology, geomorphology, slope, water table, drainage density, land use land cover, and soil type were prepared by using GIS and RS. Based on the field data and prepared maps the suitable sites for artificial recharge ponds were analyzed. The Analytic Hierarchy Process (AHP) method was adopted to assign rank and reclassify the prepared maps. The total area was differentiated into five classes to assess the suitable sites for artificial recharge ponds. These five classes are named as the most suitable, highly suitable, moderately suitable, low suitable, and unsuitable depending on the score of the suitability analysis. The most suitable, highly suitable, moderately suitable, low suitable, and unsuitable area for groundwater recharge is found at about 3%, 7%, 24%, 32%, and 34% respectively. Finally, the ROC/AUC curve was prepared using primary data (point data) collected from the field. An overall accuracy of 82.3% was achieved in this study and is considered satisfactory.

Geochemical investigation on the implications of fluid origin, subsurface processes and recharge on the Tangkuban Perahu geothermal conceptual model

Tangkuban Perahu and nearby volcano-hosted geothermal prospects are believed to be important for future power generation in West Java, Indonesia. Recharge areas of these prospects and geothermal fluid evolution are not yet fully understood. This study aims to describe the fluid origin, processes, and evolution of geothermal fluids concerning the recharge and the conceptual model of the Tangkuban Perahu Geothermal Systems (TPGS). Sampling and analyses of geothermal waters, rainwater, and gases collected in fumaroles and other manifestations were implemented in this study. Isotopic results of δ18O and δ2H collected from thermal and rainwater indicate deep-circulating meteoric origin, at an infiltration altitude range between 753 and 850 m in low terrain. Meanwhile, the high-standing terrain indicates the recharge zone to be within the wall of the Sunda Caldera and mountain slopes. Chondrite normalized patterns reveal an overall flat trendline that suggests the enrichment of Lower Rare Earth Elements (LREEs) in the central part of Tangkuban Perahu which is derived from the magmatic influx. The non-atmospheric gases origin was diagnosed by the lower N2/Ar (≤ 38) and is characterized by meteoric origin. The positive δ18O shifts from Ciater (CT), Batu Gede (BG), and Domas Crater (KwD) geothermal waters samples comparatively to the local meteoric lines are influenced by the interaction with wall rocks or magmatic influx. In these geothermal systems, the meteoric water infiltrated to the depth is heated, mixed with near-surface water, and followed by partial discharge as thermal springs along the faults. The resultant Tangkuban Perahu conceptual model has six distinct reservoirs with five geothermal systems hosted in the sedimentary (northern parts) and volcanic rock composition in the central and southern parts.

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.

Enrichment mechanism of fluoride in different aquifer systems of the Aksu area located in the Tarim Basin, Northwest China

In inland arid areas, the fluoride (F−) content of groundwater, which is an important source of drinking water, is often reported to exceed the standard. However, systematic comparative studies on the enrichment mechanism of F− in groundwater from different aquifer systems in the same area are lacking. In the present study, hydrogeochemistry, environmental isotopes, and hydrogeochemical reverse simulations were jointly employed to explore the distribution characteristics and enrichment mechanisms of F− in different aquifer systems of Aksu, Xinjiang. Our results showed that low-fluoride ((F−)<1.5 mg/L) groundwater was mainly distributed in the recharge area, whereas the high-fluoride ((F−)>1.5 mg/L) groundwater was mainly distributed in the runoff and discharge areas. The main enrichment mechanism of F− in the natural area of the Akotai shallow aquifer system may be the dissolution of fluorinated minerals (fluorite and biotite). The main enrichment mechanism of F− in the natural area of the Yi-A shallow aquifer system may be the dissolution of fluorinated minerals (fluorite) with cation exchange as the driving mechanism. The main enrichment mechanism of F− in the natural areas of deep aquifer system may also be the dissolution of fluorinated minerals (fluorite), with cation exchange and calcite precipitation as the driving mechanisms. The exchange between hydroxide (OH−) in groundwater and F− on the mineral surface may also contribute to the enrichment of F− in the natural areas of the Yi-A shallow aquifer system and the deep aquifer system. Recharge from irrigation water reduced the F− content of Akotai shallow groundwater in the irrigated area (Duolang Reservoir–Alar area) but did not reduce the F− content of the Yi-A shallow groundwater in the irrigated area (Wutuan area). The recharge from the deep groundwater originating from the direction of Awat outside the study area reduced the F− content of the deep groundwater in the Duolang Reservoir–Alar area. Evaporation had a weak effect on the enrichment of F− in groundwater. The results of the present study can provide a basis for the rational development of local water resources and would be helpful in understanding the common F− enrichment mechanisms in similar inland arid basins globally.

Hydrochemical evolution characteristics and mechanism of groundwater funnel areas under artificial governance in Hengshui City, North China

The largest groundwater funnel area is located in the North China Plain (NCP) due to long-term and large-scale overexploitation of groundwater from 1970s. Comprehensive control and management measures have been implemented both in national-scale and local-scale since 2015. This paper presented the evolution of hydrochemical characteristics and its mechanism before (2014) and during the artificial governance (2015–2020) in the center of the NCP funnels (Hengshui City) based on water level, water chemical (including concentrations of K+, Na+, Ca2+, Mg2+, Cl−, SO42−, HCO3−, TH and TDS) data. By using Piper diagrams, ion ratio relationships, geostatistical analysis, Gibbs diagrams, chlor-alkali index and inverse hydrogeochemical simulation (PHREEQC), the following conclusions can be drawn:(1)Temporally, the dominant cation and anion were Na+ and HCO3− both in shallow groundwater (SG) and deep groundwater (DG), respectively. Hydrochemical types both in SG and DG tend to be diverse, owing to the increase of SO42− and Cl− proportion after groundwater overdraft management. Spatially, ion concentrations (except for HCO3−) of discharge areas distributed higher due to shorter hydraulic retention time and flow path of recharge area. The impact of groundwater overdraft management on distribution characteristics of DG was lower than that in SG.(2)Compared with 2014 (before artificial management), SG and DG hydrochemical components had stronger correlation relationships with groundwater level. Hydrochemistry field was influenced by groundwater depth fluctuation and the rates of it at varying degree in recharge and discharge areas. Leakage from SG to DG can be deduced by similar alteration of ion concentrations.(3)In SG, the major water chemistry was controlled by evaporation and water–rock interaction, while dissolution of silicate and evaporate companied with ion exchange dominating the groundwater chemistry in DG from 2014 to 2020. Both in SG and DG simulation paths, dissolution/precipitation of mineral phases and artificial governance influence the hydrochemistry. DG also caused by SG leakage. During artificial management, human activities are a factor that cannot be ignored. Ion concentrations increased with the water–rock interaction enhanced, due to the rate of groundwater depth change decreasing.