Hydrogeological System Research Articles

Evaluation of aquifer parameters through integrated approach of geophysical investigations, pumping test analysis and Dar-Zarrouk parameters in the central part of Bari Doab, Punjab, Pakistan.

In the central part of Bari Doab in Punjab Province of Pakistan, the factors such as sporadic rainfall pattern, decrement of water in rivers, subsurface salinity and excessive mining of groundwater have badly affected the hydrogeology and recharge system of aquifer. The present research work is an endeavour to evaluate the characteristics and potential of aquifer for its future sustainable availability within the study area of central part of Bari Doab. The geophysical studies, pumping tests data, borehole logs and Dar-Zarrouk parameters were used integrally to evaluate the aquifer hydraulic and hydrologic parameters in the study area. VES technique of geophysical investigations using Schlumberger electrodes configuration was carried out at sparsely distributed 435 locations. Litho-logs and VES results altogether decipher that the subsurface alluvial succession is primarily composed of intermixed layers of sand, gravel, clay, silt and some kankar inclusions. The VES data allied with pumping test analysis of test wells in the study area were used to evaluate the aquifer hydraulic properties. Comparatively low values of discharge rate, hydraulic conductivity and transmissivity were evaluated in two wells whilst relatively higher values of these parameters were evaluated in rest of six wells. The results of hydrologic parameters also confirm the results of hydraulic parameters in the wells. Finally, the Dar-Zarrouk parameters were used for the estimation of hydraulic parameters for whole study area and the aquifer zones of relatively high and low potential were delineated.

Characterization and classification of lakes based on geospatial analyses in the karst hydrogeological system of the Bambuí group, Lagoa Santa, Minas Gerais, Brazil

The karst of Lagoa Santa is a protected area located near the city of Belo Horizonte, in Minas Gerais state (Brazil), namely Lagoa Santa Karst Environmental Protection Area (EPA), one of the main research areas related to archeology, paleontology, speleology and hydrogeology in the Brazilian territory. The region is comprised by several lakes, because of its complex water system due to karst evolution. In addition, the karstic nature of the rocks in the region allows the existence of several other typical dissolution morphologies, such as: caves, speleothems, sinkholes, uvalas, among others. The morpho-structural characteristics, combined with the local geology, can provide important information about the behavior of lakes in view of the cycles of expansion and retraction of the water surface. Thus, this work aims to understand the water dynamics of the lakes present in the Karst of Lagoa Santa through analysis of spatial data between the years 1984 and 2020. Based on the surveys, 153 lakes were identified in the study region in the last 35 years: 40 perennial lakes, 89 intermittent lakes, 19 new lakes and 5 lakes that dried up completely. Also, this study compares the relationship of each lake with the type of relief depressions (Sinkhole or Uvala), rock masses and the main negative structural lineaments. The data obtained allowed the identification of which characteristics are diagnostic for perenniality or intermittence of existing lakes in the region, as well as the grouping of existing lakes into subgroups with similar geological and morpho-structural characteristics. The most important characteristics to define the water dynamics on lakes are the evolutionary state in karst depressions and the presence of structural lineaments, in which in more evolved depressions (uvalas) the lakes tend to be intermittent and in less evolved depressions (sinkholes) the lakes tend to be perennial. Finally, the water bodies associated with structural lineaments may be the condition for the permanence of water in some depressions, mainly in lakes over non-carbonate formations existing in the region.

Uranium migration lengths in Opalinus Clay depend on geochemical gradients, radionuclide source term concentration and pore water composition

Abstract. Safety assessments of highly radioactive waste disposal sites are done based on simulation of radionuclide migration lengths through the containment providing rock zone. For a close to real case situation, the present model concept established for uranium is derived from the hydrogeological evolution and geochemical and mineralogical data measured at the deep geothermal borehole Schlattingen including the effect of geo-engineered barriers on the source term. In the Schlattingen area, the Opalinus Clay is tectonically undeformed compared to the Mont Terri anticline and represents the geochemical and temperature conditions at the favoured disposal depth. The geochemical conditions are more or less constant with slightly decreasing concentrations of pore water components towards the footwall aquifer. Uranium migrates less compared to the Opalinus Clay system at Mont Terri, where gradients of pore water geochemistry towards the embedding aquifers are more pronounced. This means, stable geochemical conditions with no or low concentration gradients are to be favoured for a safe disposal since migration lengths strongly depend on spatial and temporal variation of the hydrogeological and geochemical conditions within the host formation. The engineered barriers reduce the source term concentration what, in turn, is associated with a decrease in uranium migration. Stable geochemical conditions further enable the application of the Kd approach to estimate the impact of the barriers. The hydrogeological system must always be considered when quantifying radionuclide migration.

Conceptual model of groundwater flow in a volcanic-sedimentary aquifer system of the Andean region of Chimborazo, Ecuador

The Chimborazo volcano is located in Ecuador's northern Andes and is one of the world's tallest mountains. The central valley of Riobamba's morphology, structure, and groundwater flow networks are all influenced by the evolution of this stratovolcano. Both the urban and rural populations in this area rely on groundwater extracted from volcano-sedimentary aquifers. This study presents a conceptual model of the groundwater flow system in the lower Chambo River basin (LCRB) based on the interpretation of geological, hydrogeological, hydrochemical, and stable isotope (δ18O and δ2H) data from 23 wells, 10 springs, two sources of surface water, and rainwater. The Tertiary-Quaternary volcanic-sedimentary infill of the Inter-Andean Valley, that overlies the Jurassic-Cretaceous metamorphic bedrock of the Eastern and Western cordilleras, gave rise to three multilayer aquifers (Llo-Guano, Riobamba, and Yaruques). In these aquifers, groundwater flows from the recharge of Chimborazo glaciers to deep circulation zones of low-elevation lands in Riobamba. In this pathway, groundwater evolves from acidic - low temperature - low electric conductivity bicarbonate waters to alkaline - high temperature - high electric conductivity sulfate waters discharged in the Chambo River. The stable isotope data confirmed the hypothesis of different types of water changing and interacting in the flow direction, demonstrating a dynamic hydrogeological system that evolves from the recharge area in Chimborazo, Igualata, and Altar volcanoes to the discharge area in the Chambo River.

Steady-state simulation of groundwater flow in Khartoum state, Sudan

AbstractThe multi-aquifer system of the Nubian aquifer in central Sudan hydrogeological system was simulated using a three-dimensional steady-state model. The goal of the study is to detect the effect of pumping on the groundwater flow and thus, the aquifer productivity. The conceptual model of the study area was built based on the available geological and hydrogeological data guided by geophysical survey. Processing MODFLOW numerical code was used to calculate the hydraulic head and water balance under the existing boundary conditions. The model accurately simulated the hydraulic head with a determination coefficient of 0.88. The calibrated model indicated that the change in storage is 0.56 m3/day indicating the study area constitutes highly productive zone and is recommended for groundwater developments.

Sub-surface configuration in the northern part of Lembang groundwater basin recharge area

Lembang groundwater basin has an area of 209 km2. Increased tourism activities in the Lembang Groundwater Basin require sufficient groundwater resources to support the sustainability of these tourism activities. The purpose of this study was to analyze the hydrostratigraphy of the groundwater recharge zone of the Lembang groundwater basin in the Cikole-Lembang. Electrical Resistivity Tomography (ERT) with dipole–dipole electrode array and seismic refraction was used to analyze the hydrostratigraphy. The results of ERT and seismic refraction inversion show that Tangkubanparahu Pyroclastic Fall 2 can be characterized as aquifers. This layer consists of low (123–292 Omega m) and intermediate (293–700 Omega m) resistivity value and also has low (300–1350 m/s) to medium (2700–1350 m/s) velocity. Tangkubanparahu lava (Tl) layer has a high resistivity value (701–3875 Omega m) and high (1350–2999 m/s) velocity. The Tangkubanparahu Pyroclastic Fall 1 has a resistivity of 300–700 ohms. Tangkubanparahu (Tl) lava deposits can be characterized as fracture aquifer and impermeable layers in the Tangkubanparahu volcanic hydrogeological system depend on the historical structural geology event.

Enhancing estimation accuracy of nonstationary hydrogeological fields via geodesic kernel-based Gaussian process regression

In this study, the combined application of the geodesic kernel and Gaussian process regression was explored to estimate nonstationary hydraulic conductivity fields in two-dimensional hydrogeological systems. Specifically, a semianalytical form of the geodesic distance based on the intrinsic geometry of the manifold was derived and used to define positive definite geodesic covariance matrices that were used for the Gaussian process regression. Furthermore, the proposed approach was applied to a series of synthetic hydraulic conductivity estimation problems. The results show that the incorporation of secondary information, such as interpretations of geophysical explorations or geological surveys, can considerably improve the accuracy of the estimation, especially in nonstationary fields. In addition, groundwater flow and solute transport simulations based on estimated hydraulic conductivity fields reveal that the accuracy of the simulation is strongly affected by the inclusion of secondary information. These results suggest that incorporating secondary information into manifold geometry can remarkably improve the accuracy of the estimation and provide new insights into the underlying structure of geological data. This proposed approach has critical implications for hydrogeological applications, such as groundwater resource management, safety assessments, and risk management strategies related to groundwater contamination.

Soil Conservation Service-Curve Number method-based historical analysis of long-term (1936-2016) temporal evolution of city-scale potential natural groundwater recharge from precipitation: case study Algiers (Algeria).

Managing groundwater resources in urban areas requires an adequate understanding and assessment of urban hydrogeological systems (structure, components, connections, and imposed conditions) as a part of a larger, dynamically evolving environment. Urbanization and climate change are amongst the widely recognized signs of such a continuous evolution. Within this context, the present study gives a quantitative assessment of the impact of these two factors threatening water resources in urban environments. The Soil Conservation Service-Curve Number (SCS-CN) method is used to conduct a long-term quantitative analysis of the temporal evolution of the potential natural groundwater recharge from precipitation at the scale of Algiers city for an 80-year-long period (1936-2016). The length of the study period allowed us to account for and analyze important changes in urban settings and climatic conditions within the study zone. Overall, two trend shifts over three distinct periods were found to characterize the temporal evolution of precipitation, several climate change indicators defined for the study, and the potential natural aquifer recharge. A strong, approximately 1:4, linear correlation between the estimated city-scale potential natural aquifer recharge and precipitation was observed for the studied period (R2 = 0.748). Moreover, even though the urban area has known a rapid (2nd order polynomial) increase from 1936 to 2016, climate change (accounted for via the changes in precipitation regime) impacted the city-scale potential natural groundwater recharge with higher magnitudes than urbanization. Finally, the computed climate change indicators show that starting in the mid-1980s, Algiers has started receiving less precipitations, with fewer heavy rain events and longer dry condition periods.

Hydrogeochemical impact of Opalinus Clay system shown in migration lengths of uranium

Abstract. Models and simulations allow a prognosis of how processes in the geosphere might occur in the future by considering physical and chemical processes. They are the only way to test future scenarios and hypotheses and to evaluate how a repository site will develop over a period of a million years, e.g. by quantifying potential radionuclide migration in the hydrogeological system of the containment providing rock unit. An example is used to demonstrate the extent to which simulated migration lengths can vary for a million years, depending on the model concept and on the underlying data and parameters. In the case of uranium in the potential host rock Opalinus Clay (Switzerland), the range extends from 5 m, by applying experimentally determined transport parameters, over 50 m, using process-based approaches and taking hydrogeology into account, and up to 80 m, depending on the thermodynamic data set used. The degree of reliability of the models is derived from comparison with laboratory tests, data from boreholes and underground laboratories or natural analogues. This is the only way to assess the simulation results. In addition, indications can be provided regarding where new data need to be collected. So our task is to find an answer to the following question: how accurate do the models for the repository site search have to be in order to produce resilient and robust forecasts? To reduce the uncertainty related to the migration length of uranium in the Opalinus Clay, the calcite carbonate ion and the hydrogeological system at a potential disposal site need to be known, whereas the quantity of clay minerals plays a subordinate role, as long as it is enough, which is the case in argillaceous formations.

Geostatistical based optimization of groundwater monitoring well network design

Monitoring groundwater quality in economically important and other aquifers is carried out regularly as part of regulatory processes for water and other resource development. Many water quality parameters are measured as part of baseline monitoring around mining and onshore gas resource development regions to develop improved understanding of the hydrogeological system as well as to inform managerial decisions to assess and manage contamination risks and health hazards. Water quality distribution in an aquifer is most often inferred from point measurements from limited number of bores drilled at arbitrary locations. Estimating the distribution of water quality parameters in the aquifer based on these point measurements is often a challenging task and results in high uncertainty in the estimates due to limited data availability. Minimizing uncertainty can be achieved by drilling more bores to collect water quality data and several approaches are available to identify optimal bore hole locations to minimize estimation uncertainty. However, optimization of borehole locations is difficult when multiple water quality parameters are of interest and have different spatial distributions in the aquifer. In this study we use geostatistical kriging to interpolate a large number of groundwater quality parameters. Then we integrate these predicted values and use the Differential Evolution algorithm to determine optimal locations for bores that would simultaneously reduce spatial prediction uncertainty of all parameters. The method is applied for designing a groundwater monitoring network in the Namoi region of Australia for monitoring groundwater quality in an economically important aquifer of the Great Artesian Basin. Optimal locations for 10 new monitoring bores are identified using this approach.

AREHS: effects of changing boundary conditions on the development of hydrogeological systems: numerical long-term modelling considering thermal–hydraulic–mechanical (–chemical) coupled effects

Abstract. The objective of the AREHS project, funded by BASE (FKZ 4719F10402), is to model the effects of changing external boundary conditions on the hydrogeologically relevant parameters and effects (e.g. hydraulic permeability, porosity, migration pathways, fluid availability, hydraulic gradients) of a generic geological repository in Germany in all three potential host rocks (clay, salt, and crystalline rocks) in its hydrogeological setting. Special attention is paid to the cyclic mechanical loading due to glaciation events. This results in stress changes (M – mechanical processes) as well as induced temperature effects (T – thermal processes) due to permafrost and warm periods. Since the thermal, hydraulic (H – hydraulic processes), and mechanical processes are strongly coupled, they have to be covered by state-of-the-art coupled thermal–hydraulic–mechanical (THM) (C) modelling. The presentation consists of a (a) presentation of important findings for all three host rock types and a (b) presentation of the overall workflow. Complex, time-varying boundary conditions have been formulated for modelling glacial cycles. Investigating the effects of these boundary conditions with THM simulation reveals a variety of coupling effects. To conduct the complex modelling workflow for claystone and salt rock effectively, an automated workflow was developed and tested. It handles the transformation from a simulator-independent geological model to a numerical model specific to the simulator. This contains a suitable finite-element mesh and a parameterization of the fully coupled or optionally isolated thermal–hydraulic–mechanical processes, which are implemented and executed in the OpenGeoSys simulator. Simulation results are presented for selected physical quantities at characteristic local and temporal points with respect to the position of a migrating glacier. The investigation results are reproducible through full automation, container deployment, and a continuous integration process running on a GitLab instance (see Fig. 1a). To simulate the response of a fractured crystalline rock mass to THM impacts, the explicit integration of the fracture network in numerical models is necessary. The workflow couples the distinct element method (DEM) software “3DEC” and the discrete fracture network (DFN) software “DFN.Lab” automatically (Fig. 1b).

Effects of the 2021 La Palma volcanic eruption on groundwater resources (part I): Hydraulic impacts

The 2021 volcanic eruption in the Cumbre Vieja mountain range on La Palma Island (Canary Islands, Spain) raised concerns regarding the potential impact on groundwater resources. This study is the first part of a series of papers investigating those impacts, and focuses on the hydraulic impacts of the eruption, while subsequent papers will explore the geochemical consequences. Three boreholes equipped with sensors to measure hydraulic head, temperature, and electrical conductivity of groundwater were installed near the volcano. Monitoring started during the eruption and continued a year after it. Statistical analysis were performed to assess the relationship between the measured variables and real-time seismic-amplitude measurements (RSAM). In addition, the possibility of groundwater vaporization due to magma emergence was assessed with a groundwater flow numerical modelling of the island. Correlation coefficients were computed to assess the linear relationship between groundwater parameters and seismic signals, observing a statistically significant association, and suggesting near-instantaneous variations in parameters such as groundwater levels and EC. Different response patterns of groundwater levels were observed in recharging areas in highlands compared to discharge areas, showing an opposite correlation direction. Deduction of natural trends from the linear regression models of head and RSAM two months after the eruption revealed a more predictable impact on the groundwater system, as the hydrogeological system adjusts to the volcanic activity and its effects on the aquifer. The hydrogeological simulation of the "magma pumping effect" suggested that groundwater extraction was possible, but the absence of an appropriate groundwater monitoring network made it impossible to determine the amount of water extracted from the aquifer. The uncertainty analysis showed values up to 2000 m3·day−1. These findings have important implications for understanding the negative impacts of volcanic eruptions on groundwater resources, highlighting the need for regular monitoring and assessment by hydrogeologists and water management professionals.

Geo-Appraisal of groundwater resource for sustainable exploitation and management in Ibulesoro, Southwestern Nigeria

Groundwater exploitation requires better understanding of the resource availability and quality/vulnerability. Geophysical techniques, pumping test, hydraulic measurement, borehole logging and quality test analysis have been used in Ibulesoro, southwestern Nigeria, to understanding the hydrogeological system in terms of groundwater availability, aquifer delineation, and evaluate the groundwater physico-chemical and biological contents. The study utilized multi-criteria evaluation techniques (GWPIV) to assess the overall aquifer potential/vulnerability. The geology of the area comprises granite, migmatite, migmatite gneiss, biotitic granite, and gneiss. The main water-bearing unit was the weathered layer and fractured basement, which are usually unconfined aquifer. The hydraulic conductivity and formation factor is related by y = 0.239e0.0519x with correlation coefficient of 0.0961. The average hydraulic conductivity and transmissivity are 0.52 m/d and 5.78 m2/d respectively. The hydrogeological parameters viability increases southwardly, just as groundwater movement/flow is due south. The average thickness of the weathered layer and overburden are 8.6 m and 16.1 m respectively, with dominant resistivity in the range of 80 – 200 ohm-m. The best drilling points (migmatite/gneiss geologic units) are where the fractured basement underlies the weathered layer which most not necessarily exceed 30 - 35 m. The average depth to basement rock is 16.1 m. The obtained GWPIV varied from 1.12 to 1.71, with an average of 1.30 suggesting low potential but good for drinking and irrigation uses in its present state, however highly vulnerability to contamination, as the vadose zone thickness (5.68 m avg.), AVI (0.57 avg.), and LC (0.0818 mhos avg.) all point to the low protective capability. The water types is mixed Ca-Mg-Cl. The mechanism controlling the groundwater quality falls in the mixed zone, which indicates contribution from soil/rock-water interaction, precipitation, and evaporation; while carbonic weathering is more active than the silicate weathering process.

Data‐Driven Estimation of Groundwater Level Time‐Series at Unmonitored Sites Using Comparative Regional Analysis

AbstractA new method is presented to efficiently estimate daily groundwater level time series at unmonitored sites by linking groundwater dynamics to local hydrogeological system controls. The proposed approach is based on the concept of comparative regional analysis, an approach widely used in surface water hydrology, but uncommon in hydrogeology. Using physiographic and climatic site descriptors, the method utilizes regression analysis to estimate cumulative frequency distributions of groundwater levels (groundwater head duration curves, HDC) at unmonitored locations. The HDC is then used to construct a groundwater hydrograph using time series from distance‐weighted neighboring monitored (donor) locations. For estimating times series at unmonitored sites, in essence, spatio‐temporal interpolation, stepwise multiple linear regression (MLR), extreme gradient boosting (XGB), and nearest neighbors are compared. The methods were applied to 10‐year daily groundwater level time series at 157 sites in unconfined alluvial aquifers in Southern Germany. Models of HDCs were physically plausible and showed that physiographic and climatic controls on groundwater level fluctuations are nonlinear and dynamic, varying in significance from “wet” to “dry” aquifer conditions. XGB yielded a significantly higher predictive skill than nearest neighbor and MLR. However, donor site selection is of key importance. The study presents a novel approach for regionalization and infilling of groundwater level time series that also aids conceptual understanding of controls on groundwater dynamics, both central tasks for water resources managers.

Unravelling geological controls on groundwater flow and surface water-groundwater interaction in mountain systems: A multi-disciplinary approach

Mountain water resources are considered to be the world’s water towers. Still, despite their importance for downstream societies and ecosystems and their vulnerability to climate change, they remain poorly understood – It is the case in particular of mountain groundwater systems. Their complexity makes them difficult to conceptualize, while their remoteness makes them difficult to study, both observationally and instrumentally. Understanding mountain hydrogeological systems is mostly limited by the lack of characterization of the subsurface geologic framework and by the limited understanding of the role of geological structures on groundwater flow and on surface water-groundwater interaction. Removing methodological barriers is therefore a necessary step for improving the understanding of mountain hydrogeological systems.To tackle this problem, we develop a comprehensive multi-disciplinary approach to gain insights into the hydrogeological role of geological structures in ungauged mountain catchments. The methodology consists of several complementary methods: (1) geological mapping at multiple scales; (2) a geophysical study including on-ground Electrical Resistivity Tomography (ERT) and, gravimetry transects, and a UAV-based magnetic survey; (3) hydraulic data, including a 9 km long transect of streamflow measurements in the recession period, the long-term Normalized Difference Vegetation Index (NDVI), and varied hydric markers (e.g., a thermal spring and a puddle). The methodology is tested in the Parque Nacional del Río Clarillo, an ungauged catchment in the Andes Mountains (≈130 km2) that is illustrative of the complexity of mountain hydrosystems featuring fault zones, weathered zones, intrusive rocks, and volcano-sedimentary successions.An increase of approximately 50% in the streamflow is observed over a short distance of 1 km. Such a localized and significant increase in the baseflow is not related to any superficial supply and can only be explained by groundwater exfiltration. Based on the multiscale geological mapping and geophysical survey, a regional N-S fault and a secondary set of E-W local faults are identified in the vicinity of the resurgence area, which conjointly are likely to export groundwater from a neighbouring subcatchment up to the resurgence area. Downstream of the resurgence area, no significant change in the baseflow is observed, corresponding to the presence of an impermeable granitic pluton identified by the geological and geophysical mapping. Finally, a fractured zone in the Andean foothills is identified in the volcanic unit, which coincides with a perennial thermal spring, indicating upwelling flow and hydrogeological connectivity between the mountain block and the alluvial basin.The results strongly support the ability of the proposed methodology to identify geological structures that substantially impact the evolution of the baseflow through the catchment. The complementary multi-disciplinary methods are used innovatively to infer the link between geological and hydrogeological structures. The methodology does not aim to fully characterize the geological framework of the catchment but pragmatically focuses on hydrogeologically pertinent structures that may impact baseflow and consequently catchment management.

A clay-coal fly ash based dual hydraulic-reactive liner for controlling acid mine drainage.

Hydraulic liners are used to restrict hazardous leachates such as acid mine drainage (AMD) from entering the hydrogeological system. In this study, we hypothesized that: (1) a compacted mix ratio of natural clay and coal fly ash with a hydraulic conductivity of at most 1 × 10- 8 ms- 1 can be achieved, and (2) mixing clay and coal fly ash in the right proportion can result in increased contaminant removal efficiency of a liner system. The effects of adding coal fly ash to clay on the mechanical behavior, contaminant removal efficiency, and saturated hydraulic conductivity of the liner were investigated. All clay:coal fly ash specimen liners with less than 30% coal fly ash had significantly (p < 0.05) lower cohesion stress values, and were discarded without further tests. Saturated hydraulic conductivity values showed no significant effect (p > 0.05) on the results of clay:coal fly ash (7:3) specimen liners and compacted clay liner. The clay:coal fly ash mix ratios of 8:2 and 7:3 significantly (p < 0.05) reduced the leachate concentration of Cu, Ni, and Mn. The pH of AMD increased from an average of 2.14 to 6.80 after permeating through a compacted specimen of mix ratio 7:3. Overall, the 7:3 clay to coal fly ash liner showed superior pollutant removal capacity and its mechanical and hydraulic properties were comparable to compacted clay liners. This laboratory scale investigation emphasizes potential limitations with column scale evaluation of liners and provides new information on the application of dual hydraulic reactive liners for engineered hazardous waste disposal systems.

Hydrogeochemistry of productive Lower Jurassic deposits of the Talinskoye oil field in Western Siberia

The aim of the study is to determine, in terms of the prevalence of influence of natural or technogenic factors, the factors of formation of the hydrogeochemical composition of productive Lower Jurassic deposits of the Talinskoye oil field. During the study, the authors of the article evaluated the effects of sedimentogenesis, elutriation, neotectonic processes and oilfield water injection on the chemical composition of the waters studied. Water injection is known to cause changes in the hydrogeochemical balance and the formation of technogenic hydrogeological systems. Formation water salinities currently range from 3.7 to 15.3 g/dm3. More than 8960.3 thou-sand m3 of water was injected from overlying sediments into productive formations to maintain reservoir pressure (2014-2021). The authors analysed the genetic coefficients of different types of water (including injected water). Then they compared the coefficients. It was concluded that injected water currently doesn't have a significant impact on the hydrogeochemical appearance of the productive Lower Jurassic reservoirs of the Talinskoye oil field.

Pesticides in the hydrogeo-environment: a review of contaminant prevalence, source and mobilisation in India.

Chemical pesticides in the hydrogeological system are a global concern as they pose a severe threat to humans and other organisms. In agriculture, around 4.12 million tonnes of pesticides were used globally in 2018, which is 50% more than in the 1990s. Various pesticides detected in the hydrogeological system of India since the 1990s have been documented and reviewed to understand the prevalence, source, history and degradation pathways. This review contributes to a better understanding of existing pesticide pollution and the state of hydrogeological resource deterioration. Small to excess levels of pesticide residues were detected in groundwater, surface water, soil, and sediments. Pesticides that were most commonly and predominantly found in the hydrogeological system were HCHs, DDTs, endosulfan, heptachlor, drins (aldrin, dieldrin, endrin), chlordane etc. β and γ-HCH isomers among HCHs, whereas p,p'-DDT and p,p'-DDE among the DDTs were detected most prevalently. In many regions, pesticide residue levels in water have exceeded the maximum residue limits of WHO and BIS, while those in soils and sediments have exceeded the threshold effect level and probable effect level. Higher pesticide residues were detected in the water resources of rural agricultural areas compared to peri-urban or urban areas. A positive correlation of pesticide residues between water resources and soil has been observed in some regions, suggesting a similar contamination source. Diagnostic ratios of pesticides reveal their source, history and degradation pathways. Diagnostic ratios observed in various studies conducted in India suggest historical as well as recent use of banned pesticides. Strengthening current policies and regulations, monitoring pesticide use, changes in pesticide application practices, awareness among farmers, and the use of prominent removal techniques are necessary to tackle pesticide contamination in India.

Contribution of Gravity Data for Structural Characterization of the Ifni Inlier, Western Anti-Atlas, Morocco: Hydrogeological Implications

The Sidi Ifni region in southwest Morocco is mainly composed of crystalline rocks with limited groundwater storage capacity. These water resources drain in particular fault zones with high fracture permeability. The main objective of this study is to describe the geological structure of the region to optimize future drilling locations. The gravity data were processed using various techniques, such as total horizontal gradient, tilt derivative, and Euler deconvolution, in conjunction with the interpretation of the geological data, to create a new structural map. This map confirms the presence of many previously identified or inferred faults and identifies significant new faults with their respective trends and depths. Analysis of this map shows that major faults are oriented NNE-SSW and NE-SW, while minor faults are oriented E-W, NW-SE, and NNW-SSE. The superposition of the hydrogeological data and the structural map reveals that the high groundwater flow values in the boreholes are located in the vicinity of the major faults and talwegs. The structures deduced from the filtering and interpretation of the gravity data suggest that the hydrogeological system of the Ifni Inlier is controlled by its structures. To confirm this impact, a high-resolution electrical resistivity map (7200 Hz) was used, with penetration depths ranging from 84 to 187 m. Negative boreholes, located in high resistivity ranges corresponding to sound basement formations without fault crossings, showed high resistivity values. The positive holes, located in anomalies with low linear resistivity, revealed the impact of fault crossings, which drain water and tend to decrease the resistivity values of the formations. Therefore, these new structural maps will assist in planning future hydrogeological studies in this area.

Hydrogeological spatial modelling: A comparison between frequentist and Bayesian statistics

Abstract Traditional and modern spatial prediction techniques are applied in the analysis of water quality, evidencing a new approach that allows the modeling of a hydrogeological system in the central area of Boyacá, Colombia. The objective is to determine the quality status of groundwater for human consumption. In the process, spatial predictions were made based on frequentist methods (kriging, cokriging) and Bayesian methods (R-INLA stochastic partial differential equation) as an alternative to Markov chain Monte Carlo methods that require a large computational cost. From the application of these methods, a comparison is made by statistical tests that determine the goodness of adjustment of the predictions. Our interest here is in the implementation of future more robust, economic and scientific solutions, particularly for hydrogeological data, and the proper management of water resources. Finally, the vulnerability of aquifers is analyzed with the DRASTIC method, which takes into account the surrounding media of the aquifers through the variables depth (D), net recharge (R), type of aquifer (A), soil (S), topography (T), impact of the vadose zone (I) and hydraulic conductivity (C).