Sandstone Aquifer Research Articles

Assessing future climate trends and their impact on different fractured rock aquifers in Northern Togo

Abstract Water resources in the West African Sudan Savannah are concentrated in fractured crystalline and sedimentary rock aquifers. Due to their low storage, these aquifers are vulnerable to changes in climate. This study assesses future temperature and precipitation trends in the Koumfab watershed of northern Togo. The impact of these future climate trends on surface water and the two types of fractured rock aquifers is also investigated. A fully integrated hydrologic model of the Koumfab watershed in Northern Togo is used to study the impact of climate change on water resources. Bias-corrected temperature and precipitation from four regional climate models (RCMs) and two greenhouse emissions scenarios are used as climate forcings for the integrated model. Climate projections from the four RCMs indicate a rise (1.4 −5.5 °C) in average temperature, from the control (1971–2000) to the future period (2031–2060). Projected precipitation follows two contrasting trends with some RCMs predicting an increase (by up to 14%) in mean annual precipitation, while others predict a decline (by up to −14%). These changes in precipitation and temperature will have a noticeable effect on groundwater levels and stream flow. The hydrologic model indicates a decline in groundwater levels for all future climate projections by 1.4−5.7 m. The decline in groundwater levels is not uniformly distributed in the two types of aquifers. The decline in the fractured sandstone aquifer will be four times greater than that of the fractured granodiorite/migmatite aquifer. Projected stream flow at the watershed outlet shows increasing (59 -332%) and decreasing trends (−39 −100%).

Discussion on ‘Review of groundwater flow and contaminant transport modelling approaches for the Sherwood Sandstone aquifer, UK; insights from analogous successions worldwide’ by Medici and West ( QJEGH , 55, qjegh2021-176)

A thorough review paper on hydrogeology topics is challenging, as since the 1990s there has been a substantial increase in published papers and reports. It appears that Medici and West (2022), in keeping a reasonable length to their paper, have only reviewed selected parts of the sandstone stratigraphy comprising the principal sandstone aquifers of the UK. Much of the focus of their review is on the Triassic Sherwood Sandstone aquifers of the north-west of England.

Identification of shallow groundwater in arid lands using multi-sensor remote sensing data and machine learning algorithms

The focus of this study is to locate shallow groundwater (SGW) occurrences in arid lands using the Western Desert (WD; area: ∼680,000 km2) of Egypt as a test site. The SGW in the study area originated from paleo-precipitation during previous wet climatic periods. In wet periods, fossil groundwater was at higher levels, ascended along high-angle faults, and discharged at the surface. In contrast, at present, the water levels are lower, and the discharge occurs at near-surface elevations. Spring locations were identified as the dependent variable, while the independent variables included remote sensing–based variables and geomorphological features indicative of current or paleo discharge locations, including elevation, slope, curvature, distance to sapping features, soil moisture, NDVI, radar backscatter coefficient, and brightness temperature. Relationships between SGW occurrences (target) and their controlling factors (independent variables) were established using extreme gradient boosting (XGB), support vector machine (SVM), and logistic regression (LR) methods. The trained models were used to map SGW locations across the entire WD. Findings include the following: (1) the XGB yielded the most favorable result in identifying SGW locations (overall accuracy: 0.93) compared to SVM (overall accuracy: 0.88) and LR (overall accuracy: 0.87); (2) areas with a very high probability of SGW occurrences were found in lowlands and proximal to sapping features; (3) the overwhelming majority of the cultivated lands within the southern and central sections of the WD lie within areas identified as high and very high probability SGW locations; (4) our models identify-two previously unrecognized major SGW occurrences, an eastern zone (EZ; length: 800 km; width: 9 to 80 km; area: 43,000 km2) and an east–west trending northern zone (NZ) centered over the Qattara depression (length: 500 km; width: 200 km; area: 62,150 km2); (5) additional criteria were used to refine the modeled (XGB) SGW distribution (southern and central WD: 43,200 km2 to 23,400 km2; EZ: from 21,300 km2 to 17,400, and NZ: from 62,150 to 30,700 km2) including presence of shallow aquifers to accommodate rising Nubian waters, Nubian water salinity (fresh to brackish), and low to moderate thickness (<1 km) of post-Nubian successions that rising waters interact with. The techniques are cost-effective and efficient and could be readily applied to large sectors of Saharan Africa and Arabia, whose landscape and fossil aquifers bear many resemblances in their geologic, climatic, and geomorphic characteristics to the Nubian Sandstone Aquifer System.

Characteristics of Hydrogen and Oxygen Isotopes and Noble Gas Isotopes in the Groundwater of Weishan, Wudalianchi, Northeast China

AbstractAccording to the hydrochemical characteristics, hydrogen and oxygen isotope characteristics and the ratio of noble gas isotopes of the sandstone aquifer and basalt aquifer, this study calculated the recharge temperature and residence time of groundwater in the Weishan area of Wudalianchi, also calculating the contribution of noble gas components from different sources to the samples. Based on the characteristics of hydrogen and oxygen isotopes and noble gases Xe and Ne, the recharge altitude and recharge temperature of the two aquifers were estimated, and the recharge temperature fitting with the NGT model as verified, the results showing that the main recharge altitude of groundwater in the region was 500–600 m, the recharge temperature being 2–7°C. Heeq and Heea of the samples have been simulated using the OD model, the content of radioactive 4He in the crust being obtained, the groundwater ages under the two conditions (closed condition and open condition) both being simulated. The results show that groundwater from the sandstone layer water is older than groundwater from the basalt layer. Hydrochemical characteristics and noble gas isotope ratios indicate that in the basalt aquifer and sandstone aquifer in the Weishan area, in addition to atmospheric and crustal helium, there is also an input of mantle‐derived helium. The fault constitutes the uplift channel for groundwater containings mantle components, which results in the mantle source composition in water samples near the fault being much higher than those form non‐fault areas.

Iron isotope evidence for siderite precursors to iron oxide concretions from the Navajo Sandstone, Utah (USA)

The discovery of spherical accumulations of iron oxide mineralization on Mars has prompted renewed interest in widespread but enigmatic accumulations of iron oxide on Earth. The rinded iron oxide concretions found in the Navajo Sandstone (Utah, USA) have been among the most extensively studied of these occurrences. At least four different models have been proposed for the formation of iron oxide concretions in the Navajo Sandstone. These include 1) mixing of reduced Fe(II)-bearing and oxygenated groundwaters, 2) neutralization of oxidized, acidic waters by calcite concretions, 3) neutralization of reduced, acidic waters by calcite concretions, and 4) oxidation of siderite by microbes during invasion of the Navajo aquifer by oxygenated groundwaters. We measured δ56Fe values of iron-bearing minerals from whole-rock Navajo Sandstone, concretionary iron oxide cements, iron oxide stains that are oriented in the direction of paleo-groundwater flow, iron oxide stains on the interior of rinded concretions, and ferroan carbonate cements. We have then combined these data with published measurements to evaluate each of the four published models. Whole rock Navajo Sandstone from the Kolob Plateau has been interpreted to be unaltered by bleaching fluids and has a δ56Fe value of 0.21‰. Iron in the Kolob Plateau sample comprises a mixture of hematite grain coatings (δ56Fe = 0.12‰) and a magnetic mineral fraction (interpreted to comprise largely detrital magnetite) that has a higher δ56Fe value (0.45‰). Iron oxide cements have δ56Fe values that are typically negative and as low as −0.74‰. In contrast, iron oxide-stained Navajo Sandstone in close proximity to a rinded iron oxide concretion has δ56Fe values that are 0.9 to 1‰ greater than the δ56Fe value of the associated iron oxide concretion. Finally, ferroan carbonates from the Navajo Sandstone yield δ56Fe values as low as −0.86‰. These values are in good agreement with measurements published previously for lithologies for which comparable measurements have been made. The presence of ferroan carbonates with negative δ56Fe values is evidence that aqueous Fe(II) was transported through the Navajo Sandstone aquifer and produced carbonate mineralization with negative δ56Fe values. The difference in δ56Fe values between the iron oxide concretions and associated iron oxide staining is more consistent with equilibrium fractionation between aqueous Fe(II) and Fe(II) adsorbed on quartz grains than it is with equilibrium fractionation between aqueous Fe(II) and any reduced or oxidized iron oxide mineral species. The negative δ56Fe values of the iron oxide concretions are best explained by oxidation of a reduced iron phase in a closed system from which no aqueous Fe(II) could escape. We interpret the iron isotope data as evidence that iron was stripped from Navajo sand grains by reducing fluids, reprecipitated in the Navajo aquifer as siderite, and oxidized by groundwaters under closed conditions during incision of the Colorado Plateau.

Improved Combination Weighted Prediction Model of Aquifer Water Abundance Based on a Cloud Model.

The sandstone aquifer is an important underground water storage space, and the study of its water abundance is of great significance to ensure the safety of underground engineering and to explore the occurrence mechanism of groundwater sources. Based on the correlation between geological characteristics and aquifer water abundance, this paper proposed an aquifer water abundance prediction model based on a cloud model that improved combination weighting. The model took the roof sandstone aquifer of the Qingshuiying Coalfield as an example and selected five basic geological indicators that are closely related to the water-rich influence degree of the aquifer as evaluation indicators. The model was based on the idea of game theory, combined the analytic hierarchy process (AHP) and the entropy weight method, and introduced the cloud model evaluation method. The establishment of the model was based on the idea of game theory, combining the AHP and the entropy weight method and introducing the cloud model evaluation method. The results show that most of the study areas are located in weak or relatively weak water abundance areas; relatively strong water abundance areas are mainly distributed in the central, western, and southeastern parts of the study; strong water abundance areas are scattered in parts of the northeast, southwest, and southeast. The unit water inflow data of the actual pumping test is consistent with the water-rich prediction partition, which proves the accuracy and scientificity of the method. The model provides a new idea for the study of groundwater geology and a new method for predicting the water abundance of the roof aquifer in coal mines.

Lithostratigraphic identification using 3D geophysical/hydrogeological modeling for monitoring the aquifer’s vulnerability to contamination in El-Oweinat, Egypt

The integration between advanced techniques for groundwater vulnerability to contamination is necessary for groundwater management and risk assessment for aquifer systems. 3D geophysical/hydrogeological modeling has been developed for the delineation of lithostratigraphic layers of the Nubian Sandstone aquifer system based on geophysical and hydrogeological borehole data for 79 groundwater wells with a distance of 1 km between each well in the study area of El-Oweinat. Several parameters contributing to groundwater vulnerability have been selected and represented in 3D views as follows: surface elevation; water table; unsaturated and saturated thicknesses; laminar head losses; turbulent head losses; total drawdown; specific capacity; aquitard and aquifer thicknesses to monitor the aquifer vulnerability to contamination using Petrel software. This integration of lithostratigraphic layers and aquifer parameters (e.g. water depth) can significantly help to delineate and understand both the water pathway and attenuation processes caused by the aquitard layers, which serve as a protective layer for the underlying aquifer layers. 3D modeling of the aquifer system allows the decision-maker to visualize and deal with the issue of contamination as quickly as possible.

Integration of resistivity, neutron, and density logs for detecting, identifying, and calculating of groundwater over-pressuring phenomenon at Siwa Oasis Depression, Egypt

Along with Siwa Oasis depression, there are several ponds, lakes, and Sabkhas features resulted from the current flows through the springs due to the over-pressure of deep sandstone aquifer. The Nubia Sandstone aquifer (NSA) and Carbonate aquifer are the main two water-bearing units. They are separated by a huge thickness of shale and controlled by complicated structural faults. There are ten wells including gamma-ray, short and long resistivity, caliper, neutron, and density logs. These logs were used in identifying the lithology, calculating the porosities, water saturation percentages, and effective permeability. The long resistivity, neutron, and density logs were used to detect, identify, and calculate this over-pressure and its zones. The shale resistivity, porosity, and density of the Nubia Sandstone formation were used in determining the expected normal compaction trend. The top of over-pressuring, over-pressuring forewarning, over-pressuring transition, and over-pressuring zones were detected. The formation pressure and its gradient were calculated at the first depth in the over-pressuring zone. The piezometric heads and pressures were calculated and mapped. The depths to the top of over-pressures, formation pressures, and their gradient maps were constructed. The statistical analyses between the two pressures were carried out. Accordingly, the thickness and type of shale, the effective porosity, the compaction of the deep aquifer, the huge thickness of the overlaid formation and its porosities, and the complicated structural conditions are considered the main factors in generating the over-pressuring phenomenon at Siwa Oasis. Therefore, this study considers that the used logs are compatible powerful tools in studying this phenomenon.

Risk Assessment of Water Inrush from Coal Seam Roof Based on Combination Weighting-Set Pair Analysis

When exploiting Jurassic-era coal resources in Northwest China, there are risks of water inrush and sand burst disasters from coal seam roofs. To improve the safety of coal mining, it is imperative to accurately and objectively evaluate the water inrush risk of sandstone aquifers from coal seam roofs and to reasonably and effectively prevent and control water disasters. In this paper, the 221 mining area of the Shilawusu Coal Mine was considered. By combining the basic geological condition data, hydrogeological condition data, and drilling data in the area studied, four main control factors, including the equivalent thickness of sandstone, the lithology coefficient of sandstone, the interbedded coefficient of sand and mud, and the core recovery rate, were selected as evaluation indexes for predicting the water inrush risk from the coal seam roof. A hierarchical prediction and discrimination model of water inrush risk based on combination weighting-set pair analysis was established. The combination weighting method, which is based on the sum of squared deviations, was used to optimize the subjective and objective weight values obtained by the improved analytic hierarchy process and entropy weight methods. By applying set pair analysis theory, the comprehensive connection degree was determined using the set pair connection degree function that was constructed with 31 instances of drilling data in the study area. Then, the risk grade of each drilling data instance was evaluated by the confidence criterion of set pair analysis to calculate the water inrush risk evaluation index. Finally, the obtained index was combined with the borehole pumping test data and the discharging test data to partition the water inrush risk from the coal seam roof. The results indicated that most of the 221 mining area is safe, and the small transitional and dangerous areas are only in the central and northern regions. Based on the combination weighting-set pair analysis method, the water inrush risk from the coal seam roofs in the study area was accurately and objectively classified by a discrimination model.

Hydrogeochemical evolution induced by long-term mining activities in a multi-aquifer system in the mining area

The hydrogeochemical evolution of groundwater is related to and affected by long-term mining activities, which may deteriorate the quality of groundwater. The Fengfeng mine in Handan, North China has a 30-y history of coal mining with long-term mining activities and complex geological conditions, resulting in a complex hydrogeochemical environment in the mining region. In this study, the hydrogeochemical evolution mechanism of groundwater in a multi-aquifer system in the Fengfeng Mining Area was investigated using machine learning (self-organizing maps combined with K-means clustering) and sulfur and oxygen isotopes (δ34SSO4 and δ18OSO4). The hydrogeochemical characteristics of different aquifers in the mining area changed to different degrees after mining compared with the characteristics before mining. The spatiotemporal variations in groundwater components were found to be controlled by pyrite oxidation, gypsum dissolution, and carbonate dissolution, which are affected by mining activities. Pyrite oxidation primarily occurred in the Carboniferous thin-layer limestone aquifer (CLA) and Permian sandstone aquifer (PSA). The hydrogeochemical evolution in the Ordovician limestone aquifer (OLA), the main aquifer in the study area, was affected by leakage recharge from CLA and PSA caused by mining activities. The results showed that owing to the effects of long-term mining, the altered groundwater flow system affected the evolution of groundwater components in each aquifer, particularly the sulfate concentration. This study reveals a distinct hydrogeochemical evolution induced by mining activities, which can provide a basis for groundwater resource management in mining areas.

Quality and hydrochemical assessment of groundwater in geological transition zones: a case study from N.E. Nigeria.

Sustainable management of groundwater resources in geological transition zones (GTZ) is essential due to their complex geology, increasing population, industrialization, and climate change. Groundwater quality monitoring and assessment represent a viable panacea to this problem. Therefore, there is a great need to investigate groundwater resources in terms of their chemistry and pollution to ascertain their quality and implement robust pollution abatement strategies. This study focused on the characterization of groundwater in a typical geological transition zone in northeastern Nigeria. Eighty-seven (87) groundwater samples were collected from dug wells and boreholes during the 2017 dry season. pH, conductivity, and total dissolved solids (TDS) were measured in situ using a multiparameter probe, while major cations and anions were measured using atomic absorption spectrometry and ion chromatography, respectively. Data were analyzed using descriptive statistics, principal component analysis (PCA), water quality index, and standard hydrochemical plots. TDS ranged between 95 and 1154 mg L-1 in basement terrains and between 49 and 1105 in sedimentary areas. pH ranged between 6.8 and 7.7 mg L-1 in basement terrains and between 5.0 and 6.5 in sedimentary areas, suggesting a moderately acidic to alkaline low mineralized groundwater. Calcium (2.6-128.0 mg L-1) was the dominant cation in the basement areas, suggesting silicate weathering/dissolution, while sodium (1.9-106.0 mg L-1) dominated the sedimentary zones due to base exchange reactions. The PCA analysis suggests that mineral dissolution (mostly silicate weathering) controls the hydrochemistry of the basement aquifers, while ion exchange and albite weathering, with some influence of anthropogenic factor, control the sedimentary aquifers. The water quality index revealed that the basement setting was predominated by poor to unsuitable groundwater, while the sedimentary terrain was characterized by potable groundwater. The dominant hydrochemical facie in the basement areas was Ca2+-(Mg2+)-HCO3- characteristic of recharge meteoric water. The Na+- (K+)-HCO3- facie characterized the sedimentary zones, indicative of cation exchange reactions, while the mixed water facie typifies the geological contact zones. The shallow nature of the basement groundwaters makes them more susceptible to geogenic and anthropogenic pollution compared to the sandstone aquifers. However, the basement aquifers have better irrigation indices (Kelly ratio and soluble sodium percent) as compared to the sandstone aquifers, which exhibit poor Kelly ratios (< 1) and soluble sodium percent (> 50) ratings. Results from the study clearly highlight the poor-unsuitable groundwater quality in parts of the studied GTZ and can be very instrumental to the policymakers in implementing sustainable water treatment strategies and cleaner production technologies in GTZ to forestall the incidence of water-related diseases.

Large-scale paleo water-table rise in a deep desert aquifer recorded by dissolved noble gases

• Very high amounts of dissolved noble gases were identified in a deep desert aquifer. • Large water table fluctuations during past pluvial periods are reconstructed. • Hydrogeological settings highly affect the air entrapment and dissolution process. • Similar excess air dissolution patterns are identified in distinct desert aquifers. Illuminating past hydrological and climatological conditions in arid regions may provide insights into future trends in groundwater availability. The main objective of this study is to explore paleorecharge processes in the deep regional Nubian Sandstone Aquifer (NSA), which stretches below the hyperarid deserts of the Sinai Peninsula (Egypt) and the Negev (Israel), using dissolved noble gas data. Extremely high amounts of dissolved excess air (Ne concentrations up to 4 × solubility equilibrium) were observed in the ancient ( 81 Kr-depleted) groundwater that was recharged during past pluvial epochs in the basin. The observed unique excess air signal and the clear spatiotemporal structure of the noble gas compositions in the aquifer are hypothesized to reflect two major characteristics of the groundwater system: (a) large-scale, long-term rises in the water table that facilitate the entrapment and dissolution of air bubbles under increased hydrostatic pressure, and (b) the geological settings in the southern recharge area in Sinai, including an almost horizontal position of the layers and intercalation of low-permeability rock formations within the aquifer, which inefficiently reject air bubbles from groundwater, thereby allowing for substantial entrapment of bubbles that dissolve as the water table rises. Enhanced dissolution of entrapped air was also observed in other paleo-groundwater-containing regional sandstone aquifers across North Africa, which, together with the recent findings from the NSA, suggest that large-scale water table fluctuations have likely extensively occurred during past pluvial periods over these (and possibly other) arid regions. A preliminary assessment of noble gas recharge temperatures (NGTs) indicates an apparent decoupling of surface and water table temperatures in the case of deep aquifers with a thick (hundreds of m) unsaturated zone. This observed decoupling calls for a re-evaluation of previously obtained NGT records and a need for future work to consider the modification of NGTs due to soil air fractionation and geothermal heating of the underlying deep unsaturated zones.

Groundwater quality assessment for drinking and clean water in Bagelen and its surrounding area

Bagelen and its surrounding area are parts of the Kulon Progo Hills which have less water potential. However, groundwater can still be obtained from dug wells or several springs in the hills. This study aims to determine the quality of groundwater in the study area as clean water and drinking water. Hydrogeological surveys have been conducted to see the quality of this groundwater. Groundwater samples were taken from six dug wells and two springs. Groundwater can be found in sandstone, limestone and andesite breccias aquifers, through intergrains and cracks porosities. Groundwater usually has Ca-bicarbonate facies. The need for good quality groundwater for drinking and clean water has been investigated based on the WQI value. The WQI value is determined based on several physical parameters, including turbidity and TDS and chemical parameters such as pH, Fe, hardness, Mn, nitrate, Zn, sulfate, chloride and sodium. Based on the Minister of Health Regulation standard No. 492/2010 for drinking water and No. 32/2017 for clean water, the groundwater showed good - excellent value for drinking water and excellent value for clean water.

Geochemical modeling and geostatistical categorization of groundwater in Nubian Sandstone Aquifer, El Bahariya Oasis, Egypt

Geochemical modeling and geostatistical categorization of groundwater in Nubian Sandstone Aquifer, El Bahariya Oasis, Egypt

Using Geochemical and Environmental Isotopic Tracers to Evaluate Groundwater Recharge and Mineralization Processes in Qena Basin, Eastern Nile Valley, Egypt

The Qena basin (16,000 km2) represents one of the largest dry valleys located in the arid Eastern Desert of Egypt. Groundwater resources in this watershed are scarce due to limited recharge from annual precipitation. Hydrogeochemistry and environmentally stable isotopes were utilized to determine the main sources of recharge and geochemical processes affecting groundwater quality. The studied basin comprises three main groundwater aquifers: the Quaternary aquifer, the Post-Nubian aquifer (PNA) of the Paleocene-Eocene age, and the Nubian Sandstone aquifer (NSA) of the Lower Cretaceous age. Groundwater types vary from fresh to brackish groundwater. The groundwater salinity of the Quaternary aquifer ranges from 426 to 9975 mg/L with an average of 3191 mg/L, the PNA’s groundwater salinity ranges from 1134 to 6969 mg/L with an average of 3760 mg/L, and the NSA’s groundwater salinity ranges from 1663 to 1737 mg/L with an average of 1692 mg/L. The NSA’s groundwater is relatively depleted of stable isotopes’ signatures (ranges: δ18O from −9‰ to −4.81‰; δ2H from −71‰ to −33.22‰), whereas the Quaternary aquifer’s groundwater is relatively enriched (ranges: δ18O from −5.51 to +4.70‰; δ2H from −40.87 to +37.10‰). Geochemical and isotopic investigations reveal that the NSA groundwater is a paleo-water recharged in a cooler climate. In contrast, the upstream Quaternary groundwater receives considerable recharge from recent meteoric water and upward leakage from the artesian NSA. The downstream Quaternary aquifer in the delta of the Qena basin is composed of original groundwater mixed with recharge from the River Nile. Isotopic analysis confirms that the PNA’s groundwater recharge (ranges: δ18O from −5.90 to −0.10; δ2H −58.21 to −7.10‰) mainly originates from upward leakage from the NSA under the artesian condition and seepage from the upper unconfined Quaternary aquifer. NETPATH geochemical model results show that water–rock interaction, evaporation, and mixing are the main geochemical and physical processes controlling the groundwater quality. NSA groundwater has a significant regional extension and salinity suitable for use in expanding agricultural projects; it should be well managed for sustainable development.

An upscaling approach to predict mine water inflow from roof sandstone aquifers

Underground coal mining suffers from groundwater intrusion from the aquifers overlying coal seams. Therefore, developing methods for the accurate prediction of roof water inflow is urgently needed to design a safe drainage system. In this study, we developed a novel upscaling framework to predict roof water inflow by integrating the multiscale hydrogeological properties of roof aquifers. In this framework, we imaged rock samples via scanning electron microscopy and performed pore-scale analysis based on fractal theory. A fractal model of permeability was introduced to calculate the seepage capacity of the pore structure in the samples. The effect of fractures was further evaluated via core-scale pneumatic experiments. Subsequently, we derived an upscaling formula of hydraulic conductivity used for predicting roof water inflow at the field scale. The proposed upscaling approach was demonstrated using data from a coal mine in Northern China. The results indicate that the actual water inflow (21 m3/h) is within the predicted range of our upscaling framework (9.32–92.78 m3/h), and the initial line fracture rate dx is distributed between 0.02 % and 0.03 %. Therefore, these findings can guide the development of methods for considering micropores and fractures simultaneously and scaling them up to the field scale for effective prediction of water inflow from roof aquifers.

A revised hydrogeological conceptual model of the Fell Sandstone aquifer, Northumberland and its impact on the interpretation of long-term nitrate trends

Northumbrian Water abstract groundwater from the Fell Sandstone Formation (part of the Carboniferous Border Group) in north Northumberland, which is a groundwater-only water resource zone providing drinking water to Berwick-upon-Tweed and the surrounding area. Groundwater in observation and abstraction boreholes shows significant rising nitrate levels derived from agricultural land use, and are predicted to have an impact on groundwater quality by 2030. Northumbrian Water policy is to use catchment management techniques to mitigate rising nitrate levels through influencing land-use practices and reducing nitrate concentration in groundwater recharge. This paper demonstrates how a detailed geological and hydrogeological understanding of the area has been used to identify specific areas where appropriate catchment management techniques may be most effectively applied. Northumbrian Water and the Environment Agency jointly funded the British Geological Survey to develop a numerical groundwater model of the Fell Sandstone aquifer and to undertake a review of the geology of the Fell Sandstone Formation as part of a Water Industry National Environment Programme (WINEP). Combining the results of these two studies, supported by spatial and temporal field measurements of groundwater nitrate levels, an improved understanding of the potential fate and transport of nitrate in the Fell Sandstone aquifer has emerged. This allows a better prediction of the spatial and temporal impacts of nitrate losses from the soil zone to the aquifer in support of a catchment management approach to mitigating rising nitrate levels. Thematic collection: This article is part of the Hydrogeology of Sandstone collection available at: https://www.lyellcollection.org/cc/hydrogeology-of-sandstone

Inverse groundwater salinization modeling in a sandstone’s aquifer using stand-alone models with an improved non-linear ensemble machine learning technique

Groundwater (GW) salinization is among several hydro-environmental processes that essentially influence water resources management, freshwater supply, water scarcity and sustainability. Machine Learning (ML) is an effective and robust tool for GW monitoring, primarily when chaotic and interrelated parameters influence the system. The current study presents the first inverse modelling of GW salinization in sandstone aquifer using stand-alone (Elman NN, GRNN, BPNN, and ILR) models coupled with nonlinear ensemble ML (GPR-E, SVR-E, and ANFIS-E) techniques. For this purpose, 25 input parameters were imposed on data mining; subsequently, inversely correlated variables including bicarbonate (HCO3−), nitrate (NO3−), Temperature (Temp), Lithium (Li), and Manganese (Mn) were used for modelling the Electrical conductivity (EC). Neuro-sensitivity feature selection (NSFS) ranking was used to determine the input combinations. The Modeling schema was based on the actual field and experimental data. The results indicated the potential of GRNN-C1 with a value of NSE = 0.998, and 0.928 in both calibration and validation phases, respectively. The outcomes revealed weaknesses in all other stand-alone models with low efficiency ranged from 0 to 60%. The attained ensemble results proved promising for all, with ANFIS-E-C1 (RMSE = 2.993, MAE = 0.879, and NSE = 0.999) emerging best in the validation phase. The overall proposed ensemble learning proved the excellent capability of ML to handle complex GW processes and served as a reliable predictive tool for water resources management. The contribution-based methodologies explored in this study involved inverse modelling, nonlinear feature selection, and nonlinear ensemble techniques, which was the first study in GW salinization.

Noble gases in shallow aquifers preserve signatures of boiling events beneath Weishan volcano of Wudalianchi volcanic field, northeast China

The study on whether there is a magma chamber under Wudalianchi is a hot topic recently, as it holds great significances for the theory of plate tectonics, early warning of volcano eruption and geothermal exploration. There is no near surface geothermal abnormality reported in Weishan, the widely used and well-studied tool, geochemistry of geothermal fluids and geothermal gases, cannot be applied to this area. To reveal the thermal conditions under Weishan, we conducted a study about the abundances and isotope ratios of dissolved noble gases in shallow groundwater and springs of Weishan. The concentrations of noble gases display obvious Ne excesses and mass-dependent differentiation, the isotopic ratios indicate that Ne, Ar, Kr, and Xe are atmosphere-derived noble gases (ANGs). We apply the closed-system equilibrium (CE) model to process the data of noble gases, and indicate that the excess ANGs are not caused by the increased hydrostatic pressure or diffusive influx. Neither meltwater mixing nor oxygen consumption alone could generate sufficient noble gas excesses in our samples. Based on the reconstructed abundances of noble gases in vapor phases produced at different boiling temperatures, which are calculated according to the boiling model established on Henry's law, we conclude that the abundances of noble gases in these samples were influenced by vapor–liquid partition caused by underground boiling. The diagrams of 84Kr/36Ar, 20Ne/36Ar and 130Xe/36Ar confine the temperature range where the boiling events occur in ∼100 °C–300 °C. We argued that the excess ANGs in shallow groundwater are geochemical evidence of boiling events, which seems to be continuously happening during the time range confined by the young groundwater in basalt aquifer and old groundwater in sandstone aquifer. Our findings also corroborate the recent results of geophysical survey works that a potential magma chamber exists under Weishan area. We suggest that noble gases dissolved in shallow aquifers represent a reliable geochemical tool to unveil subsurface geothermal state, where no near-surface thermal anomaly occurs.

Fault-controlled hydrothermal dolomitization of Middle Permian in southeastern Sichuan Basin, SW China, and its temporal relationship with the Emeishan Large Igneous Province: New insights from multi-geochemical proxies and carbonate U–Pb dating

The mechanism of fault-controlled hydrothermal dolomitization has long been controversial due to its complicated tectonic and diagenetic conditions, especially for the source of dolomitizing fluids and its hydrological driving models. In the southeastern Sichuan Basin, fracture-related dolomite bodies are well developed in a Middle Permian carbonate succession, providing an example of dolomitization and its relationship with regional tectonic activities. Previously, many of the dolomites in the Sichuan Basin have been interpreted as of hydrothermal origin but are usually poorly defined since it is hard to determine the nature and timing of dolomitization. In the current study, new petrographic, geochemical, and chronological data of Middle Permian dolomites have been integrated and allowed the classification of those dolomites into two categories (replacive dolomites of D1–D2 and fracture-/vug-filling dolomites of D3–D5). Calcite (C1–C3) and other non‑carbonate cements have also been found. The near-micritic dolomite (D1) was formed at the near-surface to early burial stage, likely from modified seawaters, which was reflected by its similar δ18Ofluid estimates of the parent dolomitizing fluids and rare earth element patterns to matrix lime mudstone, as well as the fabric retentive texture. The fabric destructive (D2) and fracture-/vug-filling dolomites (D3–D5) are characterized by the high estimates of δ18Ofluid of their parent dolomitizing fluids, high 87Sr/86Sr ratios, high Fe and Mn concentrations, positive Eu anomalies, high Th values, and high salinity estimates, indicating a hydrothermal origin. However, the limestone-like δ13CVPDB and strongly negative Ce anomalies of D2–D5 suggest that these dolomites may have originally evolved from seawater-derived fluids which circulated in the basal clastic rocks and flowed upwards by thermal convection through fault systems. New U–Pb ages bracketed a time range of these dolomites from 251 ± 11 Ma to 264 ± 10 Ma, coinciding with the emplacement of the Emeishan Large Igneous Province (~257–260 Ma). This may imply that the contemporary basement faulting and associated abnormal thermal event in southeastern Sichuan Basin still remotely echoed with the activities of the Emeishan Large Igneous Province, although the study area was far away from its eruption center. It facilitated the fluid circulation through fault systems and underlying sandstone aquifers and thus drove fault-controlled hydrothermal dolomitization at shallow burial backgrounds.