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• Intermittent freshwater extraction and cold-water recharge can reduce the total salt mass. • Intermittent and continuous methods achieve comparable effectiveness in mitigating SWI. • Total salt mass exhibits a delayed and prolonged response to heat storage reduction. • A far recharge distance and low permeability delay thermal impacts of cold-water recharge. Decreasing groundwater temperature by freshwater extraction and cold-water recharge can mitigate seawater intrusion in coastal aquifers. However, the impact of frequently employed and easily executed intermittent well operations on this has been overlooked. This study numerically examines temperature and salinity distributions in coastal aquifers subject to intermittent freshwater extraction and cold-water recharge (IER) at an equal rate. Results show that IER maintains an equivalent effect on inhibiting seawater intrusion as the continuous method, while IER during cold seasons reduces operational time and cooling heat consumption. For instance, numerical test on a realistic aquifer shows that 90 d of IER could lead to a 75% decrease in operational time and a 29% reduction in cooling energy usage compared to the continuous method. The mitigation effectiveness depends on the averaged seaward hydraulic gradient, which is affected by heat storage reduction above the saltwater wedge. The cold-water plume from IER is convergently transported and discharged, creating a pronounced fluctuation of heat storage reduction and thereby resulting in a delayed periodic variation of the hydraulic gradient. As salt efflux is an integrated result of periodically changing hydraulic gradients, total salt mass exhibits a delayed and prolonged response to the variation of heat storage reduction. Sensitivity analyses show that a far recharge distance and reduced aquifer permeability increase the delay between heat storage reduction and total salt mass, and low recharge temperature facilitates seawater intrusion mitigation. This study demonstrates the importance of the intermittent method in inhibiting seawater intrusion and has implications for sustainable management of coastal groundwater resources. [ABSTRACT FROM AUTHOR]

Microbial reductive dechlorination is a key process in aquifers contaminated with chlorinated ethenes and results in a net mass reduction of organic pollutants. Biodegradation rates in the subsurface are temperature-dependent and may be enhanced by increased groundwater temperatures. This study explores the potential of combining the temperature increase from low-temperature Aquifer Thermal Energy Storage with In Situ Bioremediation (ATES-ISB). The effects of highly dynamic groundwater flow and heat transport on microbial degradation rates were examined in a contaminated aquifer based on a pilot-scale experiment and a comprehensive process-based modeling analysis. The low-temperature ATES-ISB pilot test was carried out in Birkerød (Denmark), in an aquifer contaminated with trichloroethene by implementing a groundwater flow dipole, injecting heated groundwater, biostimulating the system with lactate and bioaugmenting it with a Dehalococcoides containing culture. Solute concentrations were monitored in four observation wells over the course of the test and a non-isothermal reactive transport model, solved in a two-dimensional heterogeneous domain, was developed to quantitatively interpret the experimental observations. The process-based numerical model also allowed evaluating the evolution of chlorinated ethenes concentrations considering different hydraulic, thermal, and operational scenarios. The results demonstrate the beneficial combination of ATES with in situ contaminant bioremediation, showing enhancement of contaminant mass reduction and more complete reductive dechlorination. The developed process-based model can be instrumental for the design and parameterization of pilot and full scale low-temperature ATES-ISB remediation in shallow aquifer systems. • Pilot test of ATES combined with in situ bioremediation in a contaminated aquifer • Numerical model coupling non-isothermal flow, heat and reactive transport • Simulation of pilot test operations and model-based analysis of observations • Temperature-dependent flow, transport and degradation rates of chlorinated ethenes • Scenario simulations to assess the effects of different remediation approaches [ABSTRACT FROM AUTHOR]

Campi Flegrei is a volcanic field located west of Naples (Italy) in a densely populated area. Since 2005, its ground has been rising steadily due to the accumulation of fluids at shallow depths. The inflation of volcanic edifices is a possible precursor of an impending eruption. The uplift is accompanied by increasing seismic activity. This raises concerns about the possibility that the volcano may be on the verge of an eruption. To track the fluid movement, it is possible to monitor subtle changes of velocities of seismic waves by exploring ambient seismic noise. By examining different frequency bands, we can observe velocity changes at different depths. We interpret these changes as a monitoring of depth-dependent deformation in addition to the standard monitoring of surface deformation. We observe a velocity decrease in the long-term trend, presumably due to the extension of the hydrothermal system at shallow depths. To explain the long-term changes, we model a spherical pressure source to simulate volumetric strain changes induced by recent fluid activity. The model explains both, surface and subsurface deformation which leads to the opening of microcracks and pores, resulting in the observed velocity decrease. The short-term velocity changes are mainly driven by temperature or groundwater level changes. Once velocity changes are corrected for seasonal effects, remaining short term velocity changes can be associated with volcanic activity and earthquake swarms. • Monitoring of seismic velocity variations using passive image interferometry. • Long-term velocity change due to volumetric changes of microcracks and pores. • Short-term velocity change due to seasonal temperature and groundwater fluctuations. • Removing seasonal effects reveals short-term velocity changes from volcanic activity. [ABSTRACT FROM AUTHOR]

In this study, a Trnsys simulation prediction model for multistage utilization solar-assisted groundwater source heat pump system and a new year-round operation control strategy are proposed. A new dual-interface solar and groundwater heat storage module Type299 was created, which was imported into Trnsys transient simulation model for simulation. A one-year experiment was conducted to test the accuracy of the new model Type299 and Trnsys transient simulation prediction model, taking a case system in the Shenyang area as an example. When the proposed new system and control strategy was applied to the case system, the results showed that the maximum comprehensive performance coefficient of the new system is approximately 4.54, which is 23.8% higher than that of the original system. The annual solar energy utilization of the new system increased by approximately 4.68 × 105 MJ compared with the original system. After 10 years of simulation operation, it was found that the groundwater temperature under the action of the new system was approximately 3.1 °C higher than that of the original system. This effectively alleviates the underground water temperature decrease year by year caused by the operation of the original system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe2+ in groundwater serves as a sustained catalyst to drive the removal of NH 4 +-N. • High selectivity of NH 4 +-N conversion to N 2 by PMS- Fe 3 O 4 /Cl– system. • Ammonia removed by Cl• − mediated AOPs even under microtherm conditions. • Reliability assessment of NH 4 +-N in-situ removal by PMS-Fe 3 O 4 /Cl– system. The conventional ammonia in-situ treatment technology fails to achieve complete NH 4 +-N degradation, while the high concentration of native iron in groundwater further complicates its removal process, potentially leading to adverse environmental consequences. This study investigates the introduction of peroxymonosulfate (PMS) into groundwater containing high concentrations Fe2+ (Fe 3 O 4 as a ferrous source), which can act as persistent catalysts, and Cl-, causing the degradation of ammonia through chlorine free radical-based advanced oxidation processes (PMS- Fe 3 O 4 /Cl-), and evaluates the advantages and limitations of employing the PMS- Fe 3 O 4 /Cl- system for ammonia treatment. The rapid reaction between SO 4 •- and Cl- resulted in the formation of Cl• as primary products. Cl• initiates a cascade of subsequent reactions with pH-dependent secondary active products. Under optimal conditions, the ammonia removal efficiency reached 97.44 % using the PMS- Fe 3 O 4 /Cl- system within 120 min of operation, which can be attributed to the selective oxidation of ammonia by chlorine reactive species. And this finding was substantiated by observations from experiments involving free radical quenching and EPR spectra coupled with DMPO. The HCO 3 – and humic acid (HA) in water can significantly affect the removal of ammonia, owing to their capability of quenching SO 4 •- and Cl•. Meanwhile, the levels of generated toxic chlorates in our system remain within acceptable limits. The PMS- Fe 3 O 4 /Cl- system exhibited outstanding transport capacity and stability in simulated columns, demonstrating excellent ammonia oxidation efficiency in natural groundwater, thereby confirming its promising practical potential. All experiments were executed at a temperature of 12 ℃, thereby verifying the remarkable efficacy of the PMS- Fe 3 O 4 /Cl- system in removing ammonia even under microtherm conditions. [ABSTRACT FROM AUTHOR]

The production of freshwater represents a prominent global challenge nowadays. One eco-friendly technology to provide clean water even in an adverse environment, with extreme temperatures and scarce groundwater resources is solar-driven water evaporation or solar-to-steam generation. Besides, freshwater can be also extracted from polluted soil or water, purifying the water in the process at the same time. The champion solar-driven water evaporation efficiency is achieved at over 100%. The advancements in photothermal evaporation predominantly prioritize material modification and interfacial heating, with a significant emphasis on optimizing vapor generation efficiency, often neglecting the practical aspect of water collection. By using the right materials, the system can be cost-effective and have a low environmental impact. In this progress report, the latest advancements in natural materials, carbonization of natural materials, hybrid natural materials, and nature-inspired materials are presented. We will delve into their effectiveness in evaporation and their energy efficiency. The review provides suggestions about the compatibility of natural materials for this application and reports on insights into the advancements already accomplished, as well as the remaining opportunities for enhancing the performance of these cost-effective, environmentally friendly, high-performance systems. [Display omitted] • Recent developments of nature-inspired design for solar vapor have been reviewed. • The effectiveness of evaporation and its energy efficiency are discussed. • The suggestions about the compatibility of natural materials are highlighted. • This work reports on insights into the advancements already accomplished. • The crucial challenges in this field are emphasized. [ABSTRACT FROM AUTHOR]

[Display omitted] • Models consider groundwater (GW) inflow, conduction, shading, and other heat fluxes. • Equilibrium temperature deficit concept is used as scenario comparative benchmark. • GW inflow and riparian shading most strongly drive changes in temperature signals. • These scenarios support process-based interpretation of paired air–water metrics. • GW source depth and inflow magnitude affect climate change thermal resilience. Headwater stream temperature often exhibits spatial variation at the kilometer-scale, but the relative importance of the underlying hydrogeological processes and riverine perturbations remains poorly understood. In this study, we investigated the relative importance of groundwater (GW) and other processes on downstream annual stream temperature signal characteristics using deterministic heat budget model (HFLUX) scenarios within an idealized stream reach representative of mountainous forested conditions. We summarized annual stream thermal regimes from the relationship of paired sinusoidal air and water temperature signals (amplitude ratio, phase lag, and mean ratio). Results showed that downstream changes in annual temperature depended on the thermal gradient between water and the hypothetical equilibrium temperature (where all heat fluxes sum to zero). GW inflow, riparian shading, and the boundary input signal were the most significant factors affecting downstream annual water temperature signals, while flow volume and channel dimensions impacted how quickly annual temperature signals changed. Effects of GW were dominated by advective rather than conductive heat exchange processes, but conduction played a larger role when GW input was more spatially diffuse. Our results indicated several mechanisms by which local processes may affect stream thermal resilience to disturbances and can help guide management of wildfire and climate change. [ABSTRACT FROM AUTHOR]

• Coastal algal bloom is jointly regulated by physical and chemical controls. • Coastal phosphate is significantly originated from coastal groundwater. • The fluctuation of groundwater phosphate is governed by temperature. • Groundwater phosphate along with submarine groundwater discharge enters coasts. Algal blooms have been identified as one major threat to coastal safety and marine ecosystem functioning, but the dominant mechanism regulating the formation of algal blooms remains controversial, ranging from physical control (via water column stability), the chemical control (via coastal nutrients) to joint control. Here we leveraged the unique data collected in the Hong Kong water over the annual cycle and past three decades, including direct observations of algal blooms and coastal nutrients and process model output of water column stability, and evaluated the differential competing hypotheses in regulating algal blooms. Our results demonstrate that the joint mechanism rather than the single mechanism effectively predicts all algal blooms. Meanwhile, we observed that the adequate nutrients (phosphate, PO 4 3−) significantly originate from coastal groundwater. The production and fluctuation of PO 4 3− in beach aquifers are primarily governed by groundwater temperature, leading to a sustained and sufficient supply of PO 4 3− in a low groundwater temperature environment. Furthermore, along with submarine groundwater discharge (SGD), the ongoing release of PO 4 3− in groundwater enters coastal waters and serves as sufficient nourishment for promoting algal blooms in coastal areas. These results highlight the importance of both physical and chemical mechanisms, as well as SGD, in regulating coastal algal blooms. These findings have practical implications for the prevention of coastal algal blooms and provide insights into mariculture, water security, and the sustainability of coastal ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

The Linta Basin, located in the Southwestern Madagascar, is a semi-arid area where groundwater in fractured media bedrock aquifer constitutes the main source of water supply. In the last two decades, highly mineralized groundwater was identified in this area; however, the origin of the salinity was not clear. The purpose of the study was to clarify the origin of salinity and to identify hotspots with groundwater unsuitable for water supply. Groundwater quality in this basin was investigated by hydrogeochemical and isotopic methods accompanied by mineralogical study. In total, 32 groundwater samples were collected and analyzed. The results showed that groundwater temperature varied from 25.2 °C to 31.7 °C. Values of pH and TDS varied from 6.55 to 8.24 and 221 to 5612 mg/L, respectively. The aquifer, which is mainly fractured, showed 7 groundwater types, namely Mg–HCO 3 ,Na–HCO 3 and also Na–C1, Mg–Cl, Na–Cl–HCO 3 , Mg–Cl–HCO 3 -, and Ca–Mg–HCO 3. Two groups of variables have been identified by factor analysis; the factor F1 comprises EC, Ca2+, Mg2+, SO 4 2−, and Cl− whereas the factor F2 comprises HCO 3 −, K+, and Na+, and they were interpreted in terms of hydrogeochemical processes. Values of saturation indices (SI) for carbonate minerals were generally positive, indicating their possible precipitation. Based on the Gibbs diagram and factor analysis, groundwater mineralization is affected by water-rock interactions and evaporation, respectively. The important role of evaporation is confirmed by enrichment of stable isotopes with δ18O values up to 1.2 ‰. Processes such as base ionic exchange process and reverse ionic exchange process may also be important locally. The main origin of groundwater mineralization is the hydrolysis of silicate minerals such as feldspars and micas coupled with evaporation. In several wells, salinity is too high for water supply and nitrate concentration is above the WHO limit for drinking water. Results of the study highlighted groundwater chemistry formation processes and are applicable in other African countries with bedrock aquifers. • Groundwater chemistry in bedrock aquifer in SW Madagascar was investigated. • Mineralization increases in flow direction and dominant groundwater types are Mg– HCO 3 and Na–HCO 3. • Principal processes affecting groundwater chemistry are dissolution of silicates and evaporation. • Hotspots with high salinity and nitrate concentration were identified. [ABSTRACT FROM AUTHOR]

[Display omitted] • Groundwater levels in the province of Quebec show a slight downward trend. • In cold and humid climates, hydrogeological systems undergo an annual reset due to the cold period, keeping droughts short. • 10- to 20-year time series are sufficient for analyses of trends and determining the role of precipitation and temperature on groundwater variability. • Standardized indexes are extremely useful to assess how groundwater levels are affected by meteorological conditions. Understanding the fluctuations in groundwater levels in response to meteorological conditions is challenging, especially given the slow transit time associated with groundwater reservoirs and the short duration of time series for groundwater levels. Nevertheless, this knowledge is crucial for water resource management, especially given that global warming will drastically impact the hydrological dynamics in cold and humid climates. The objective of this work was to quantify how standardized indexes contribute to understanding groundwater level fluctuations in response to meteorological conditions in cold and humid climates and with short time series (10 to 23 years). The relationships between the standardized precipitation index (SPI), standardized temperature index (STI), global climate indexes, and standardized groundwater index (SGI) were analyzed. The reactivity of groundwater levels was examined between 2000 and 2022 using groundwater level measurements from 152 wells located between 46 °N and 52 °N in the province of Quebec (Canada). The results showed that the available time series were sufficient to provide new insights into the role of precipitation and temperature on groundwater fluctuations, demonstrating the usefulness of the indexes. One of the main contributions of this study was that hydrogeological systems in cold and humid climates go through an annual reset due to the prolonged freezing period. This annual reset was one of the drivers isolating year-to-year hydrogeological conditions, contributing to short-duration droughts. [ABSTRACT FROM AUTHOR]

Geothermal waters are featured in many locations in Aakkar district north of Lebanon. Among which, the town of Semmaquiyeh is home to a geothermal well, drilled back in the seventies. To this date this geothermal source remains unexploited. To investigate the potential use of this site, it is imperative to define the subsurface geology and groundwater flow. The geological information of the area was reviewed, and a geophysical investigation was carried out on site with measurements of the Multi-Channel Analysis of Surface Waves (MASW). The horizontal-to-vertical spectral ratio (HVSR) method was also used to estimate the resonant frequency of sedimentary layers on top of bedrock, and the Audio-frequency Magnetotelluric probing (AMT) was applied for groundwater true resistivity. The results of the MASW investigation showed conformity with the geologic formations of fluvio-marine deposits with a thick layer of clayey limonite soil. The Audio-frequency Magnetotelluric probing profile indicated that the groundwater table is very shallow, and the gradient is flat mimicking the surface topography. The study gave insights into some potential economic exploitations. Further detailed geological studies of the subsoil from boreholes, laboratory soil testing, detailed geochemical water analysis and determination of the groundwater temperature gradient with depth are recommended to be able to determine future geothermal applications. [ABSTRACT FROM AUTHOR]

Thermal performance of the ground source heat pump (GSHP) system can be significantly affected by the complex geological substructures (such as ground stratification and groundwater advection). This study installed a seepage box inside the two-layered laboratory device to investigate the heat transfer processes of the unsaturated, saturated and infiltrated ground. Various operational and geological conditions were designed to study the temperature distributions at various locations and time experimentally and numerically. The groundwater effect on ground heat exchanger (GHE) thermal performance depends on the thermal properties, flow advection and the relationship between temperatures of the groundwater and ground. If the ground was partially saturated during the heat injection period, the cooling seepage will efficiently remove the heat of GHEs in upper-stream rather than those located in the bottom-stream. Meanwhile, the heat transfer can be enhanced if two legs of the U-tube vertical to the direction of groundwater seepage. The groundwater flow can redistribute the heat within the ground and showed a better recovery performance which advance an even temperature distribution by 3 h. The temperature and carried heat load of the cooler groundwater will increase during the heat injection experiment, and further contributed to various temperature distributions of ground at different locations and time. • A laboratory box with two-layered subsurface and groundwater was introduced. • Experiments with various operational and geological conditions were conducted. • Detailed thermal distributions of partially saturated ground were analysed. • Cooling seepage can only efficiently remove the heat accumulated in upper stream. • Heat redistribution brought by groundwater flow gave a better recovery performance. [ABSTRACT FROM AUTHOR]

Groundwater heat pump (GWHP) system directly uses a stable temperature of groundwater for cooling and heating of buildings or districts. In this study, a simulation-optimization model for the sustainable operation of GWHP system was developed. The simulation model computed the coupled groundwater flow and heat transport with considering thermal recycling. As an optimization technique, genetic algorithm was linked with the simulation model. The developed model can determine the optimal extraction and injection rates of GWHP system to maximize system performance and efficiency, to maintain stable operation, and to minimize costs and environmental impacts. Assuming a 2D hypothetical aquifer, it was demonstrated how the optimal operation of GWHP system obtained from the model can be changed according to several operational and hydrogeological conditions, including well distance, regulation on injection water temperature, hydraulic conductivity, and regional hydraulic gradient. The results highlighted a necessity to determine an operational strategy of GWHP system through the optimization able to consider site-specific condition. In addition, the performance and capability of the developed model were demonstrated by obtaining the optimal strategy for the cooling operation of a research-oriented GWHP facility installed in Korea. • A simulation-optimization model for optimal operation of GWHP system is developed. • It can consider operational efficiency, stability, cost, and environmental impacts. • Results show that the optimum can be different depending on site-specific condition. • It implies the usefulness of this model that can consider site-specific condition. • The applicability of this model is shown on a real-scale GWHP facility in Korea. [ABSTRACT FROM AUTHOR]

• Multiple methane cycling processes in shallow groundwater are evidenced by multiple methods. • CO 2 reduction, acetate fermentation and methane oxidation all occurred in groundwater. • CO 2 reduction dominated acetate-fermentation in two methanogenic pathways in groundwater. • Various factors may lead to contrasting groundwater methane cycling in different settings. Groundwater rich in dissolved methane is often overlooked in the global or regional carbon cycle. Considering the knowledge gap in understanding the biogeochemical behavior of methane in shallow aquifers, particularly those in humid alluvial-lacustrine plains with high organic carbon content, we investigated methane sources and cycling pathways in groundwater systems at the central Yangtze River basins. Composition of multiple stable isotopes (2H/18O in water, 13C in dissolved inorganic carbon, 13C/2H in methane, and 13C in carbon dioxide) was combined with the characteristics of microbes and dissolved organic matter (DOM) in the study. The results revealed significant concentrations of biogenic methane reaching up to 13.05 mg/L in anaerobic groundwater environments with abundant organic matter. Different pathways for methane cycling (methanogenic CO 2 -reduction and acetate-fermentation, and methane oxidation) were identified. CO 2 -reduction dominated acetate-fermentation in the two methanogenic pathways primarily associated with humic DOM, while methane oxidation was more closely associated with microbially derived DOM. The abundance of obligate CO 2 -reduction microorganisms (Methanobacterium and Methanoregula) was higher in samples with substantial CO 2 -reduction, as indicated by isotopic composition. The obligate acetate-fermentation microorganism (Methanosaeta) was more abundant in samples exhibiting evident acetate-fermentation. Additionally, a high abundance of Candidatus Methanoperedens was identified in samples with apparent methane oxidation. Comparing our findings with those in other areas, we found that various factors, such as groundwater temperature, DOM abundance and types, and hydrogeological conditions, may lead to differences in groundwater methane cycling. This study offered a new perspective and understanding of methane cycling in worldwide shallow alluvial-lacustrine aquifer systems without geothermal disturbance. [ABSTRACT FROM AUTHOR]

• Play Fairway Analysis is adapted for use in geothermal exploration. • An example is developed for Snake River Plain volcanic province in southern Idaho. • Risk maps produced for heat, permeability, and seal using new and published data. • Play Fairway method is shown to be effective paradigm for discovering new resources. The Snake River Plain (SRP) volcanic province overlies the track of the Yellowstone hotspot, a thermal anomaly that extends deep into the mantle. Most of the area is underlain by a basaltic volcanic province that overlies a mid-crustal intrusive complex, which in turn provides the long-term heat flux needed to sustain geothermal systems. Previous studies have identified several known geothermal resource areas within the SRP. For the geothermal study presented herein, our goals were to: (1) adapt the methodology of Play Fairway Analysis (PFA) for geothermal exploration to create a formal basis for its application to geothermal systems, (2) assemble relevant data for the SRP from publicly available and private sources, and (3) build a geothermal PFA model for the SRP and identify the most promising plays, using GIS-based software tools that are standard in the petroleum industry. The study focused on identifying three critical resource parameters for exploitable hydrothermal systems in the SRP: heat source, reservoir and recharge permeability, and cap or seal. Data included in the compilation for heat source were heat flow, distribution and ages of volcanic vents, groundwater temperatures, thermal springs and wells, helium isotope anomalies, and reservoir temperatures estimated using geothermometry. Reservoir and recharge permeability was inferred from the analysis of stress orientations and magnitudes, post-Miocene faults, and subsurface structural lineaments based on magnetics and gravity data. Data for cap or seal included the distribution of impermeable lake sediments and clay-seal associated with hydrothermal alteration below the regional aquifer. These data were used to compile Common Risk Segment maps for heat, permeability, and seal , which were combined to create a Composite Common Risk Segment map for all southern Idaho that reflects the risk associated with geothermal resource exploration and identifies favorable resource tracks. Our regional assessment indicated that undiscovered geothermal resources may be located in several areas of the SRP. Two of these areas, the western SRP and Camas Prairie, were selected for more detailed assessment, during which heat, permeability, and seal were evaluated using newly collected field data and smaller grid parameters to refine the location of potential resources. These higher resolution assessments illustrate the flexibility of our approach over a range of scales. [Display omitted] [ABSTRACT FROM AUTHOR]

• Three neural networks are used to assess groundwater resources under climate change. • An ensemble of RCM projections defines the inputs of the trained networks. • RCP4.5 and RCP8.5 are used to evaluate the groundwater changes on this century. • LSTMs outperform CNNs and NARXs to handle time series long dependencies. This study develops three different artificial intelligence (AI) models in order to investigate the effects of climate change on groundwater resources using historical records of precipitation, temperature and groundwater levels together with regional climate projections. In particular, the Non-linear Autoregressive Neural Network (NARX), the Long-Short Term Memory Neural Network (LSTM) and the Convolutional Neural Network (CNN) were compared. Considering an aquifer located in northern Italy as a case study, the neural networks were trained to replicate observed groundwater levels by taking as input precipitation and temperature records, and in the case of the NARX also antecedent groundwater levels, on a monthly scale. The trained networks were used to infer groundwater levels until the end of the century based on precipitation and temperature projections provided by an ensemble of 13 Regional Climate Models (RCMs) from the EURO-CORDEX initiative. Two emission pathways were considered: the RCP4.5 and RCP8.5. All the AI models show good performance metrics during the training phase, but NARXs perform poorly compared to the other models during validation and testing. For the future, the NARX and LSTM models predict a decline in groundwater levels, especially for the RCP8.5 scenario, while slight changes are expected using the CNN. As NARXs are not deep learning techniques and CNNs may not be able to extrapolate values outside the training range, LSTMs appear to be better suited for climate change impact evaluations. [ABSTRACT FROM AUTHOR]

• A relation between groundwater temperature and quality is established. • Soil and groundwater are warming in the studied area. • Warming is associated with changes in groundwater quality. Climate change and urbanization are currently leading to a warming of the subsurface worldwide with yet unforeseen consequences for groundwater quality. The temperature-sensitivity of chemical and biological processes suggests that small temperature changes driven by current warming should have a detectable effect on the ecology of aquifers and the composition of groundwater itself, but field observations covering temperatures that are environmentally relevant are sparse. The analysis of a large data set provides field-scale evidence that, within the naturally occurring temperature range between 5 and 20 °C, temperature affects the quality of groundwater. A difference in temperature of +1 K is linked to a 4% decline in oxygen saturation and a pH drop of 0.02 due to the accumulation of carbon dioxide. Further, warmer groundwater shows signs of enhanced mineral weathering and higher concentrations of drinking water-relevant elements such as manganese. The observed trends in groundwater quality are consistent with a temperature-associated intensification of microbial metabolic rates and enhanced organic matter mineralization at warmer temperatures either within the aquifers or in the overlying soils. A times series analysis reveals that soil and groundwater temperatures in the studied area have been increasing at a rate of 0.1–0.4 K per decade -comparable to recent global warming- driving subtle, but distinct changes in groundwater pH and oxygen concentrations. The results confirm, that certain but central aspects of groundwater quality (pH, O 2 , p CO 2 , Mn, DOC) change due to warming, which may increase the costs for purification when drinking water is produced from groundwater resources and may turn some aquifers uninhabitable for groundwater biota. [ABSTRACT FROM AUTHOR]

Abstract High-temperature thermal energy storage in shallow aquifers can potentially increase ambient groundwater temperatures up to 70 °C or even more. Since an increase in temperature is expected to influence contaminant mass flux into groundwater monitoring the spreading of organic contaminants located in the subsurface is crucial. In numerous former studies, the NAPL solubility, one major parameter controlling mass flux on field scale, was measured at temperatures up to 70 °C for a broad spectrum of organic substances. However, quantitative calculations of solubilities as a function of temperature considering a compiled database are largely missing. Aiming to examine the reliability of existing solubility-temperature relationships, to describe them functionally and further to identify knowledge gaps, previously published data on solubilities of 42 different organic groundwater contaminants were evaluated in this study. By using a common temperature regression function, the calculated solubility curves from compiled solubility data for 5–70 °C show relative changes between a few percent (CHCs and BTEX) and up to 2000% (PAHs). As published temperature-dependent solubilities for chlorinated ethylenes are contradictory in parts, solubilities of tetrachloroethylene, trichloroethylene, 1,2-cis-dichloroethylene and 1,2-trans-dichloroethylene were additionally investigated in more detail using batch experiments between 5 and 70 °C. The results show distinctive solubility minima at medium temperatures (20–40 °C) with concentrations decreasing from 5 °C to the minimum by 10–20%. The measured and calculated temperature-dependent solubilities enable a more reliable assessment of thermal energy storage at contaminated sites, of existing thermal remediation approaches and of combinations of underground heat storage with groundwater remediation. Highlights • Revised solubility data of 42 organic compounds as a function of temperature. • NAPLs solubility in water as a function of temperature is strongly compound specific. • Chlorinated ethenes have a distinctive minimum at medium temperatures (20–40 °C). • Data basis for evaluation of thermal energy storage in contaminated aquifers. [ABSTRACT FROM AUTHOR]

Abstract In metropolitan areas, shallow groundwater temperatures are affected by anthropogenic heat sources. The resulting thermal conditions in the subsurface are highly site-specific, and spatial and temporal trends have only been revealed for a few cities. In this study, the anthropogenic heat input is quantified for 15 locations in Osaka, Japan using an analytical, one-dimensional conductive heat transport model. Mean anthropogenic fluxes into the subsurface are determined annually between 2003 and 2011. The model depicts fluxes from buildings and from different land cover types separately. The main objective is to compare the predicted annual mean heat input to heat storage increase, and to identify site-specific factors relevant for the thermal evolution of the underground at each well location. Our results indicate that mean fluxes from asphalt covered areas (0.28 ± 0.07 W/m2) and from buildings (0.32 ± 0.18 W/m2) are significantly higher than fluxes from unpaved (0.06 ± 0.06 W/m2) and grass-covered (−0.04 ± 0.06 W/m2) areas. Furthermore, the temporal variation of mean fluxes from buildings is stable over the studied time period, while annual mean fluxes from asphalt, grass and unpaved areas vary as much as 0.8 MJ/m2. Still, the uncertainty associated with the combined annual heat input of all heat sources is slightly higher than the changes between the years. Overall, the predicted cumulative heat input (2003 to 2011) at the wells ranges from 4 MJ/m2 to 60 MJ/m2. Comparing these results to heat storage increase, additional local heat fluxes, such as from construction work or a sewage treatment plant, have to be considered for about 1/3 of the wells. In addition, it becomes apparent that a significant percentage of determined anthropogenic heat input is not stored in the urban aquifer and heat input is predicted to be considerably higher than heat storage increase. Graphical abstract Unlabelled Image Highlights • Heat flux into the underground is quantified for 4 heat sources and 15 wells. • Heat flux in Osaka is considerably lower than previously determined flux in Europe. • Sealed surfaces and buildings contribute equally to urban subsurface warming. • Temporal analysis reveals little variation in annual heat input. • For undisturbed wells heat accumulation correlates to heat input, but is lower. [ABSTRACT FROM AUTHOR]

Characterizing the temporal variation of microbial community is essential to better understand the biogeochemical cycles in groundwater systems. So far, the roles of microbial metabolisms in affecting the seasonal variation of shallow groundwater biogeochemistry remains largely unknown. In this study, shallow groundwater was sampled during rainy season (RS) and dry season (DS) at Yuncheng Basin, a semi-arid region in northern China. Based on results of hydrogeochemical, environmental isotopic (δ18O, δ2H and δ13C) and high-throughput sequencing analysis, we found that 1) the seasonal variation of groundwater geochemistry is closely related to the stronger evaporation, mineral dissolution, and anthropogenic activities in DS and enhanced cation exchange and stronger recharge in RS; 2) the seasonal dynamics of microbial community were mostly driven by groundwater temperature (T) and total organic carbon (TOC); 3) potential functional consequences indicated stronger microbial carbon fixation and denitrification in RS; 4) the microbial contribution to SO 4 2− in groundwater may increase when gypsum dissolution was weaker while sulfur oxidation was stronger during RS. Our findings suggest that the seasonal variation of microbial metabolisms play important roles in the dynamic characteristics of groundwater geochemistry. [Display omitted] • Water-rock interaction and microbial activity drive groundwater chemistry variation. • The microbial community shows significant variation between rainy and dry seasons. • Temperature and TOC affect the seasonal dynamics of microorganisms in groundwater. • Carbon fixation, denitrification and sulfur oxidation were stronger in rainy season. [ABSTRACT FROM AUTHOR]

This study examined the influence of thermal forcing on saltwater intrusion into nearshore aquifers (SWI) in the context of sea level rise due to climate change and continued groundwater withdrawal due to increasing demand. The study used the SEAWAT code to test two case studies: the Henry problem as a benchmark and the Biscayne Aquifer, Florida, USA, as a real case. Simulations were performed for the base case, sea level rise (SLR), and inland groundwater recharge reductions. A new management method was proposed for mitigating SWI in nearshore aquifers using the Abstraction of saline water, Desalination, Cooling the desalinated water, and Injection into the aquifer (ADCI) strategy. The method was tested with different freshwater temperatures of 25, 20, 15, 10, and 5 °C. The results showed that freshwater recharge in coastal regions is sensitive to the thermal regime, resulting in the attenuation of SWI. The results of this study are important for the sustainable management of groundwater resources in coastal areas to meet increasing water demands. The Biscayne salt repulsion reached +9.80 %, +10 %, +10.20 %, +10.30 %, and + 10.50 % for changing the injection recharge by 25, 20, 15, 10, and 5 °C. Future planning, design, and development of SWI mitigation measures should consider thermal regime effects. In addition, a cost–benefit analysis for this method using 3D models is needed to determine the feasibility and economic aspect of cooling water supply compared to current techniques. [Display omitted] • Sea level rise and overpumping accelerated saltwater intrusion (SWI). • Decreasing groundwater temperature affecting coastal aquifers hydrodynamics. • SWI is mitigated using a new technique ADCI. • Injection or Irrigation at night by the low freshwater temperatures could protect the coastal freshwater resources. [ABSTRACT FROM AUTHOR]

We report on the potential of elevated groundwater temperatures and zero-valent iron permeable reactive barriers (ZVI PRBs), for example, through a combination with underground thermal energy storage (UTES), to achieve enhanced remediation of chlorinated hydrocarbon (CHC) contaminated groundwater. Building on earlier findings concerning deionized solutions, we created a database for mineralized groundwater based on temperature dependence of tetrachloroethylene (PCE) degradation using two popular ZVIs (i.e., Gotthart–Maier cast iron [GM] and ISPAT sponge iron [IS]) in column experiments at 25 °C–70 °C to establish a temperature-dependent ZVI PRB dimensioning approach. Scenario analysis revealed that a heated ZVI PRB system in a moderate temperature range up to 40 °C showed the greatest efficiency, with potential material savings of ~55% to 75%, compared to 10 °C, considering manageability and longevity. With a 25 °C–70 °C temperature increase, rate coefficients of PCE degradation increased from 0.4 ± 0.0 h−1 to 2.9 ± 2.2 h−1 (GM) and 0.1 ± 0.1 h−1 to 1.8 ± 0.0 h−1 (IS), while TCE rate coefficients increased from 0.6 ± 0.1 h−1 to 5.1 ± 3.9 h−1 at GM. Activation energies for PCE degradation yielded 32 kJ mol−1 (GM) and 56 kJ mol−1 (IS). Temperature-dependent anaerobic iron corrosion was key in regulating mineral precipitation and passivation of the iron surface as well as porosity reduction due to gas production. • Sophisticated analysis of temperature dependent CHC degradation and side reactions at ZVI in groundwater conditions. • Evaluation of CHC degradation kinetics considering the influence of mineral precipitates and H 2 gas formation. • Presentation of a dimensioning approach for temperature-dependent scaling of ZVI PRB approaches. • Scenario analysis for the evaluation of the main factors influencing the temperature-dependent dimensioning of ZVI-PRBs. [ABSTRACT FROM AUTHOR]

Groundwater vulnerability assessment is a measure of potential groundwater contamination for areas of interest. The main objective of this study is to modify original DRASTIC model using four objective methods, Weights-of-Evidence (WOE), Shannon Entropy (SE), Logistic Model Tree (LMT), and Bootstrap Aggregating (BA) to create a map of groundwater vulnerability for the Sari-Behshahr plain, Iran. The study also investigated impact of addition of eight additional factors (distance to fault, fault density, distance to river, river density, land-use, soil order, geological time scale, and altitude) to improve groundwater vulnerability assessment. A total of 109 nitrate concentration data points were used for modeling and validation purposes. The efficacy of the four methods was evaluated quantitatively using the Area Under the Receiver Operating Characteristic (ROC) Curve (AUC). AUC value for original DRASTIC model without any modification of weights and rates was 0.50. Modification of weights and rates resulted in better performance with AUC values of 0.64, 0.65, 0.75, and 0.81 for BA, SE, LMT, and WOE methods, respectively. This indicates that performance of WOE is the best in assessing groundwater vulnerability for DRASTIC model with 7 factors. The results also show more improvement in predictability of the WOE model by introducing 8 additional factors to the DRASTIC as AUC value increased to 0.91. The most effective contributing factor for ground water vulnerability in the study area is the net recharge. The least effective factors are the impact of vadose zone and hydraulic conductivity. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate heavy metal contamination in four major vegetable bases and determine the health risks of residents in the vicinity of the highly urbanized city Urumqi in Xinjiang, China. In this paper, we determined the contents of six heavy metals (i.e., As, Zn, Cd, Cr, Hg, and Pb) in surface soil and groundwater to evaluate the levels of heavy metal pollution and human health risks using the pollution index (PI), the Nemerow integrated pollution index (NIPI), the ecological risk factor (E i r ), risk index (RI) and the health risk assessment model. The results showed that (1) The PI, NIPI, the ecological risk factor and risk index indicated that Cd and Hg were the primary pollutants in Sishihu village. These indices suggested moderate to slightly heavy potential ecological risks. In Anningqu town, Hg and Cd led to high levels of pollution and posed slightly heavy potential ecological risks. In Qinggedahu village, it was concluded that the metals Zn, Cr, Cd, Hg, and Pb caused moderate to heavy pollution. In Liushihu village, the pollution trends in the area were low. The results of the pollution level of the irrigation well water (i.e., groundwater) indicated that the well water was considerably safer than the soil, but Cr posed a slight pollution risk. (2) The non-carcinogenic risks for adults based on the HI values of these four vegetable bases were <1. However, when considering the non-carcinogenic risks for children, the HI values were larger than 1 in all areas, indicating the local children have a higher potential non-carcinogenic risk. In addition, CR (Carcinogenic risk) from dermal contact with the vegetables bases did not pose a high risk for residents. However, for adults, the carcinogenic risk posed by Arsenic (As) through trough inhalation was the primary pathway of exposure in three of the vegetable bases, generally in the order of Qinggedahu village > Sishihu village > Anningqu town. For children, the carcinogenic risks posed by As through trough inhalation and ingestion were the main exposure pathways. From the TCR results, it can be seen that in Sishihu village, Anningqu town, and Qinggedahu village, the TCR values for adults and children were >1 × 10 −4 (unitless), and this degree of carcinogenic risk is unacceptable. (3) The identification of risk sources determined the main pollution sources affecting the vegetable bases were human activities and natural sources. Anthropogenic activities were most often related to traffic pollution sources and agricultural pollution sources, such as the irrational use of pesticides and fertilizers and stock farming. The results are important for designing remediation scenarios to control the spread of contamination as well as for serving as a reference point for soil environmental protection efforts in this region. [ABSTRACT FROM AUTHOR]

Abstract Ground source heat pump (GSHP) systems have been considered to be a low-carbon technology to provide heating and cooling for buildings in urban environments. This study focuses on the short-and long-term evolution of groundwater temperature induced by high-density GSHP installations in an urban residential area in Cologne, Germany. Specifically, a 2D heat transport model considering both thermal convection and conduction has been constructed using the finite element simulator OpenGeoSys. The simulated temperature changes within the initial few years were compared to the monitored dataset, while the GSHP heating load and thermal conductivity were calibrated. Subsequently, the validated model was run for 25 years to evaluate the long-term trend of the subsurface temperature. Also, effects of model uncertainties were explored with different simulated scenarios. Results indicate that sufficiently large groundwater flow and a high cooling ratio can effectively mitigate ground cooling. Based on these findings, best and worst-case scenarios were formulated for the studied case and the sustainability of GSHP operation were evaluated accordingly. As an outcome, specific design and operation criteria were proposed for the sustainable utilization of shallow geothermal energy for the heating and cooling of buildings in urban areas. [ABSTRACT FROM AUTHOR]

Highlights • Mathematical model of DCMD system integrated with PT plant was developed and solved in MATLAB software. • Effect of feed water temperature on permeate flux and freshwater production has been presented. • Performance of PT solar power plant has been evaluated in terms of capacity factor and gross-to-net conversion factor. • Performance of DCMD system has been assessed in terms of evaporation efficiency and specific energy consumption. Abstract This paper investigates performance and economic evaluation of integrating 50 MWe parabolic-trough (PT) plant with direct-contact membrane distillation (DCMD) system for electricity and freshwater production in Abu Dhabi, United Arab Emirates. The evaluations of PT plant were performed utilizing SAM software. Maximum and minimum electrical energy generation was estimated to be 13.5 GWh and 7.71 GWh in May and December, respectively. Similarly, the cooling water requirement fluctuated from 856 m3/day to 1440 m3/day in December and May, respectively. The economic evaluation showed that the nominal and real levelized electricity cost was 24.54 cents per kWh and 19.3833 cents per kWh, respectively. The performance evaluation of DCMD system was performed by solving DCMD mathematical model in MATLAB® Software. An increase in feed temperature from 30 °C to 45 °C increased the permeate flux from 5.19 kg/m2 h to 20.01 kg/m2 h, and evaporation efficiency from 39.2% to 54.98%, respectively. Furthermore, it was assessed that proposed PT plant integrated with DCMD system could produce up to 14.33 m3 of freshwater per day with a water production cost of $0.64/m3. It was revealed that the integration of DCMD system with PT plant could be a sustainable and economical approach to cope with increasing demand of freshwater and electricity. [ABSTRACT FROM AUTHOR]

Highlights • Karst features in coastal areas are easy targets for water extraction. • Urban coastal springs are vulnerable to salt water intrusion. • Extraction of water directly from springs increases the rate of saltwater intrusion. • These activities impact the increasingly urban coastal karst regions worldwide. Abstract Sulphur Springs Cave is an extensive phreatic cavity that produces a large, historic spring in the middle of metropolitan Tampa, Florida, USA. The city of Tampa extracts groundwater from the spring to supplement municipal water supply and to support low-salinity habitat in the estuarine Hillsborough River. Extraction at this site has occurred for many decades, but has intensified since the early 2000s, rapidly increasing the salinity of the spring and cave water. The purpose of this study was to address the potential sources and mechanisms of saltwater intrusion at this site using historical and current hydrochemical data published in the literature and online by government agencies. We also explored the cave to identify point-sources of intrusion, and collected water and biological samples from inside the cave to identify potential ecosystem impacts of increasing cave salinity. From 1946 to present, Sulphur Springs water shifted from being fresh (specific conductance <500 µS cm−1) and of calcium-sulfate type to being brackish (specific conductance ∼5000 µS cm−1 and higher) and of sodium-chloride type. We found numerous vents in the cave that issue saline, thermal, sulfidic water and host distinct microbial mat communities. These vents are likely connected to bedrock fractures that provide preferential flow-paths along which confined, deep-sourced saline water enters the freshwater portion of the aquifer, probably originating from the coastal mixing zone. Salinity increased at the spring during dry-season pumping activity and after wet-season recharge events, which likely increased artesian pressure in confined saline aquifer units. Salinization of Sulphur Springs may disrupt the cave microbe and stygobite communities and eventually make the spring unsuitable to maintain low-salinity habitat in the Hillsborough River. [ABSTRACT FROM AUTHOR]

Highlights • Provides a history of the development of the concept of the leakance coefficient to estimate surface groundwater interaction. • Shows the empirical nature of the leakance coefficient. • Provides as simple practical way to give back to the coefficient an exact scientific nature physical meaning. • Demonstrates that the degree of penetration of the river cannot be ignored. • Demonstrates that the leakance coefficient cannot be calibrated as a constant value in time. Abstract Due to the dynamic flow exchange between a stream and a connected water- table aquifer, a physically based hydrologic model is an important tool for the design of conjunctive use of surface and ground waters. It is needed to develop sound plans for sustainable use of the groundwater with minimal undesirable effects. This article reports an investigation of the component (module) that describes the stream-aquifer flow exchange in several groundwater simulators. The study indicates that the module may not have a solid physical basis when used in large-scale regional studies to estimate the stream-aquifer flow exchange. The component relies upon an empirical parameter known as the leakance coefficient. It is demonstrated that neglecting river penetration of the aquifer can lead to non-negligible errors in estimation of seepage. In addition the leakance coefficient (dimension inverse of a time) is not constant in time but varies with the conditions in the river and in the surrounding aquifer. A potential, practical and simple alternative is presented. [ABSTRACT FROM AUTHOR]

Highlights • Optimizing the conjunctive use of surface water and groundwater at the regional scale. • Promoting the economic benefits of water resource systems while considering the penalties and risks. • Reflecting uncertainties expressed as discrete intervals and probability distributions. • Obtaining various water planning alternatives under different climate change scenarios. Abstract The shortage of water resources and the increasing competition among water users have highlighted the importance of the water allocation problem. Water availability is crucial for water resource allocation and changes frequently, leading to the necessity to predict available water. This paper develops a framework aimed to plan regional water allocations under different representative concentration pathways (RCP) scenarios using an interval parameter conditional value-at-risk (CVaR) two-stage stochastic programming model. This framework combines prediction and optimization to reflect climate change, the uncertainty of water system and the coordination between water resources allocation and risk. The feasibility and practicality of the framework are demonstrated by its application in a real-world case study in the Lower Songhua River Basin in northeast China. Comparison between the results of the developed model and actual conditions show that 11.61 × 108 m3 volume of water supply can be saved after optimization, indicating that the developed model tends to allocate water in a more efficient way. The ratio of surface water to groundwater is reduced from 2:1 to 1.62:1. The proposed model has practical relevance for saving water and alleviating groundwater overexploitation. The approach is applicable to most areas with severe water shortages and groundwater overexploitation, and decision makers can determine the appropriate options for water resources allocation based on risk preferences and actual conditions. [ABSTRACT FROM AUTHOR]

Highlights • The FAO Irrigation and Drainage Paper 56 can be adapted for bare soil evaporation. • Lysimeters were simulated by a water balance model based on FAO 56. • The reduction in bare soil evaporation compared to cropped areas is quantified. Abstract Unlike evaporation from open water, the magnitude of evaporation from bare soil decreases as the water table falls. Bare soil evaporation studies have included field and laboratory experiments, mathematical formulations and semi-empirical models. However, there is only limited field information, especially concerning evaporation from bare sand. The semi-empirical approach of the FAO 1 ETo – Evapotranspiation; FAO – Food and Agriculture Organisation; REW – Readily Evaporable Water; TEW – Total Evaporable Water. 1 Irrigation and Drainage Paper 56, which contains guidelines for computing crop water requirements, can be adapted for bare soil evaporation with a three stage process. The suitability of the FAO 56 approach for bare sand evaporation is investigated by installing lysimeters in sand dams. Sand dams are shallow groundwater storage systems, which are designed on the assumption of reduced evaporation as the water table falls. The field results from the lysimeters are simulated adequately by a water balance model based on FAO 56 with an additional component to represent both the difference between the variable saturation with depth, which occurs in practice, and the assumption in standard water balance models of a sudden change from dry to fully-saturated conditions at the water table. This study demonstrates and quantifies the reduction in bare soil evaporation compared to open water or cropped areas and confirms the validity of the three stage FAO semi-empirical approach. [ABSTRACT FROM AUTHOR]

Over the last century, the vast majority of peatlands in Europe have experienced substantial transformation as a result of drainage works that led to an imbalance in the natural hydrologic regime as well as changes in vegetation composition. The ongoing study aims to reconstruct the natural hydrologic regime of peatlands and restore their typical vegetation communities. In this study, we examine the variability of groundwater levels and groundwater temperature in raised bogs located in the Bieszczady Mts. in southern Poland. Both groundwater table levels and groundwater temperature serve to characterise the hydrology of peatlands, which in turn is critical for plant growth and rates of relevant biochemical processes. Our objective is to determine the predominant scale of intra-annual variability in time series and identify their potential sources by assessing the adaptive response of peat bogs to key changes in weather conditions. For this purpose, data obtained from 9 monitoring wells located in peat bogs, with a varying degree of degradation, were used. Fluctuations in time series and potential linkages between selected variables were analysed in the frequency domain using the continuous wavelet transform. The results show that peat bogs exhibit a relatively high stability of groundwater table levels and groundwater temperature despite meaningful changes in weather conditions. The most visible response of peat bogs to weather conditions was observed in summer and autumn. Our study demonstrates that degraded peat bogs experience the largest decrease in groundwater table levels and more frequent fluctuations. In contrast, groundwater temperature remained stable throughout the year at all the studied bog sites. [ABSTRACT FROM AUTHOR]

It is essential to research the technology for effective remediation of petroleum hydrocarbon-contaminated groundwater because the petroleum hydrocarbon contamination of groundwater is becoming more and more serious. The petroleum hydrocarbon-degrading bacteria screened in this experiment were identified as Pseudomonas spp. by 16 S rDNA sequencing. Using wheat straw biochar as the carrier, a highly stable immobilized bacteria integrating adsorption and degradation was prepared by microbial immobilization technology. The results of scanning electron microscopy and Fourier transform infrared spectroscopy analysis showed that the microorganisms were adsorbed on the biochar. Degradation of petroleum hydrocarbon by immobilized bacteria conformed to the second-order kinetic model. For the manufacture of immobilized bacteria, the following immobilization parameters worked best: immobilization pH of 7 and immobilization time of 24 h. Finally, the produced immobilized bacteria were added to four groundwater samples with various initial concentrations of petroleum hydrocarbon, and it was found that all of the petroleum hydrocarbon degradations were above 95%. The study can serve as a useful resource for groundwater petroleum hydrocarbon remediation technology since the immobilized bacteria can successfully adapt to the groundwater petroleum hydrocarbon environment and significantly reduce the concentration of petroleum hydrocarbon. • Effective bioremediation of petroleum-contaminated groundwater by immobilized bacteria. • Biochar can act as a good protective barrier for microorganisms in bioremediation. • Immobilized bacteria can adapt to the low temperature environment of groundwater. [ABSTRACT FROM AUTHOR]

Groundwater is a crucial resource for humans and the environment, but its global human demand currently exceeds available volumes by 3.5 times. Climate change is expected to exacerbate this situation by increasing the frequency of droughts along with human impacts on groundwater ecosystems. Despite prior research on the quantitative effects of climate change on groundwater, the direct impacts on groundwater biodiversity, especially obligate groundwater species, remain largely unexplored. Therefore, investigating the potential impacts of climate change, including groundwater temperature changes, is crucial for the survival of obligate groundwater species. This study aimed to determine the thermal niche breadth of the crustacean amphipod species Niphargus longicaudatus by using the chronic method. We found that N. longicaudatus has a wide thermal niche with a natural performance range of 7–9 °C, which corresponds to the thermal regime this species experiences within its distribution range in Italy. The observed range of preferred temperature (PT) was different from the mean annual temperature of the sites from which the species has been collected, challenging the idea that groundwater species are only adapted to narrow temperature ranges. Considering the significant threats of climate change to groundwater ecosystems, these findings provide crucial information for the conservation of obligate groundwater species, suggesting that some of them may be more resilient to temperature changes than previously thought. Understanding the fundamental thermal niche of these species can inform conservation efforts and management strategies to protect groundwater ecosystems and their communities. [Display omitted] • Niphargus longicaudatus has a wide thermal range of 7–9 °C. • The preferred thermal range of N. longicaudatus matches with its Italian distribution. • Niphargus species may be more resilient to temperature changes than previously thought. [ABSTRACT FROM AUTHOR]

• An analytical solution of heat transfer in karst conduit was proposed. • Conduit structure and flow properties determine thermal equilibrium depth. • Insufficiently heat exchange results in temperature fluctuations in karst springs. • Event thermal response was verified by heat exchange and mixing function. Thermal responses of groundwater are useful signatures to reveal the recharge-discharge process and characterize aquifer structure in karst groundwater. Four karst springs with varying circulation depths ranging from ∼ 60 to 820 m in South China, were used to decipher the mechanism of heat exchange between recharge water and surrounding rock formations. An analytical solution of heat transfer in karst conduit was proposed to simulate the peak or trough temperatures of pulse flow. Hydraulic diameter, flow velocity, input temperature and circulation depth in karst aquifer, mainly depending on the recharge water volume after rainfall events, are important transport factors to control the thermal equilibrium depth and the efficiency of heat exchange that directly controls the behavior of warm peaks or cold troughs in groundwater temperature. In shallow karst aquifers wherein the circulation depth is less than its theoretical thermal equilibrium depth, the recharge water does not sufficiently exchange heat with the surrounding rocks, resulting in clear event-scale warm peaks in summer and cold troughs in winter. Otherwise, the recharge water will firstly reach a thermal equilibrium state and then mix with the warmer base flow at deeper location, which is verified in a karst spring with anomalous event-scale temperature drops after rainfall events all year around. The thermal response simulations obtained from this work provide new ways and insights to characterize geographic structure of karst aquifer and elucidate heat transfer mechanism in karst aquifer systems. [ABSTRACT FROM AUTHOR]

We develop a new geostatistical method to combine evidence provided by diverse geological data sets and produce maps of geothermal resource probability. The application is to the State of Hawaii, and the data sets include the locations and ages of mapped volcanic centers, gravity and magnetotelluric measurements, groundwater temperature and geochemistry, ground surface deformation, seismicity, water table elevation, and groundwater recharge. Using the basic principles of Bayesian statistics, these data and expert knowledge about the effects and importance of the data are used to compute the probabilities of the primary resource qualities of elevated subsurface heat, reservoir permeability, and reservoir fluid content. The product of these marginal probabilities estimates the joint probability of all three qualities and hence the probability of a successful geothermal prospect at each map point. An analogous set of algorithms is used to quantify the confidence in the probability at each point. Not surprisingly, we find that successful geothermal prospects are most probable on the active volcanoes of Hawaii Island, including the area of Hawaii’s single geothermal energy plant. Probability decreases primarily with shield volcano age, being relatively moderate in select locations on Maui and Lanai, relatively low on Oahu, and minimal on Kauai. Future exploration efforts should consider these results as well as the practical, societal, and economic conditions that influence development viability. The difficulties of interisland power transmission mean that even areas with moderate to low probabilities are worth investigating on islands with population centers. [ABSTRACT FROM AUTHOR]

On-site sanitation is generally advocated as a means to eradicate the health hazards associated with open defecation. While this has provided a welcome upgrade to the livelihoods of millions of people in low-income countries, improved sanitation facilities are increasingly becoming a threat to domestic groundwater-based supplies. Within this context, a survey of pit latrines, domestic wells and improved water sources was carried out in a large rural village of southern Mali. All households were surveyed for water, sanitation and hygiene habits. Domestic wells and improved water sources were georeferenced and sampled for water quality (pH, electric conductivity, temperature, turbidity, total dissolved solids, thermotolerant coliforms, chloride and nitrate) and groundwater level, while all latrines were inspected and georeferenced. A GIS database was then used to evaluate the proportion of water points within the influence area of latrines, as well as to underpin multiple regression models to establish the determinants for fecal contamination in drinking supplies. Moreover, an appraisal of domestic water treatment practices was carried out. This revealed that nearly two-thirds of the population uses bleach to purify drinking supplies, but also that domestic-scale treatment as currently implemented by the population is far from effective. It is thus concluded that existing habits could be enhanced as a means to make water supplies safer. Furthermore, population, well and latrine density were all identified as statistically significant predictors for fecal pollution at different spatial scales. These findings are policy-relevant in the context of groundwater-dependent human settlements, since many countries in the developing world currently pursue the objective of eliminating open defecation. [ABSTRACT FROM AUTHOR]

Computational requirements sometimes discourage using mathematical optimization for groundwater management. To dramatically reduce computation time, the presented hybrid response matrix method (RMM), Coefficient Generation and Use method 4 (CGU4), prepares surrogate simulators used during optimization. CGU4 reduces numerical model simulations needed to populate the surrogates (linearized convolution equations, LCEs). LCEs often represent flow and head constraints within groundwater flow optimization problems. CGU4 reduces computations for problems having: varying time period sizes; eras of sequential time periods of equal duration; and system (non)linearity. For a situation having: linear, piece-wise, and nonlinear groundwater flows; 20 periods of varying and sequentially constant durations; and optimization problems employing (non)linear objective functions and linear head and aquifer-surface seepage constraints, CGU4 requires 22–61% fewer simulations to compute optimal objective function values within 0.001–0.003% of the best alternative RMM. For hypothetical (non)linear dynamic stream-aquifer problems, CGU4 required the same or 63–89% less time than previous RMMs. [ABSTRACT FROM AUTHOR]

Different land uses exert a strong spatially distributed and temporal varying signal of heat fluxes from the surface in or out of the ground. In this paper we show an approach to quantify the heat fluxes into a groundwater body differentiating between near surface soil temperatures under grass, forest, asphalt, agriculture and surface water bodies and heat fluxes from subsurface structures like heated basements or sewage pipes. Based on observed time series of near surface soil temperatures we establish individual parameters (e.g. shift, moving average) of a simple empirical function that relates air temperature to soil temperature. This procedure is useful since air temperature time series are readily available and the complex energy flux processes at the soil atmosphere interface do not need to be described in detail. To quantify the heat flux from heated subsurface structures that have lesser depths to the groundwater table the 1D heat conduction module SoilTemp is developed. Based on soil temperature time series observed at different depths in a research lysimeter heat conduction and heat storage capacity values are calibrated disregarding their dependence on the water content. With SoilTemp the strong interaction between time series of groundwater temperature and groundwater level, near surface soil temperatures and the basement temperatures in heated buildings could be evaluated showing the dynamic nature of thermal gradients. The heat fluxes from urban areas are calculated considering the land use patterns within a spatial unit by mixing the heat fluxes from basements with those under grass and asphalt. The heat fluxes from sewage pipes and of sewage leakage are shown to be negligible for evaluated pipe diameters and sewage discharges. The developed methodology will allow to parameterize the upper boundary of heat transport models and to differentiate between the heat fluxes from different surface usages and their dynamics into the subsurface. [ABSTRACT FROM AUTHOR]

Human activity directly influences ambient air, surface and groundwater temperatures. The most prominent phenomenon is the urban heat island effect, which has been investigated particularly in large and densely populated cities. This study explores the anthropogenic impact on the thermal regime not only in selected urban areas, but on a countrywide scale for mean annual temperature datasets in Germany in three different compartments: measured surface air temperature, measured groundwater temperature, and satellite-derived land surface temperature. Taking nighttime lights as an indicator of rural areas, the anthropogenic heat intensity is introduced. It is applicable to each data set and provides the difference between measured local temperature and median rural background temperature. This concept is analogous to the well-established urban heat island intensity, but applicable to each measurement point or pixel of a large, even global, study area. For all three analyzed temperature datasets, anthropogenic heat intensity grows with increasing nighttime lights and declines with increasing vegetation, whereas population density has only minor effects. While surface anthropogenic heat intensity cannot be linked to specific land cover types in the studied resolution (1 km × 1 km) and classification system, both air and groundwater show increased heat intensities for artificial surfaces. Overall, groundwater temperature appears most vulnerable to human activity, albeit the different compartments are partially influenced through unrelated processes; unlike land surface temperature and surface air temperature, groundwater temperatures are elevated in cultivated areas as well. At the surface of Germany, the highest anthropogenic heat intensity with 4.5 K is found at an open-pit lignite mine near Jülich, followed by three large cities (Munich, Düsseldorf and Nuremberg) with annual mean anthropogenic heat intensities > 4 K. Overall, surface anthropogenic heat intensities > 0 K and therefore urban heat islands are observed in communities down to a population of 5000. [ABSTRACT FROM AUTHOR]

Nitrate contamination in ground and surface water is a persistent problem in agricultural countries. The transition zone between rivers and riparian aquifers plays an important role in mediating riverine nitrate export, as it promotes intensive denitrification, resulting in permanent nitrate removal from aquatic systems. However, the underlying mechanisms controlling riparian denitrification are not well understood. In this study, we present an assessment of water chemistry and isotope data from a two-year river and groundwater sampling period along a coastal watershed in Southeast China. The results showed that the highest oxygen depletion and denitrification rates in the riparian aquifer occurred in the infiltrated river proportions with higher groundwater temperatures. Heterotrophic microbial responses in the riparian zone may have been driven by bioavailable organic carbon from the river water in the riparian aquifer. For the underlying processes of NO 3 - removal efficiency from riparian groundwater, the additional processes substantially surpassed denitrification (mean of 12.1% vs. 6.6%), particularly at the furthest distance from the river in winter. The mean proportional contribution of manure and sewage (54.5%) was the highest for nitrate contamination, followed by soil N fertilizer (23.7%), chemical fertilization (18.5%), and atmospheric deposition (3.3%). This study provides valuable guidance for agricultural water management based on the key finding that high connectivity between rivers and groundwater might improve the NO 3 - removal potential. • We assessed the nitrogen removal efficiency in riparian groundwater. • We identified the key factors controlling nitrogen removal in riparian groundwater. • Nitrate removal rate by additional processes surpassed denitrification. • Infiltrating river water in riparian groundwater promoted denitrification activity. [ABSTRACT FROM AUTHOR]

This research has allowed to provide new information about the geochemical groundwater composition in the Central Pacific of Costa Rica, a place with an important commercial, touristic, and real estate development with a continues water resource demand. Previous reports of iron and manganese elevated concentrations, and flow water rate decrease in production wells, turn the area into an object of hydrogeological studies as the resource demand increases. The main objective of this research was to provide information about the quality and composition of the groundwater, and to understand the relationship with the geological and structural context. A total of 25 groundwater samples were collected, subsequently hierarchical clustering method were applied to analyze chemical concentrations and characterized the groundwater. Results showed some samples with atypical trace elements concentrations such as Al, Mn, and Fe, which are above the water quality limits. After applied the hierarchical clustering, results evidence the presence of two main clusters, which one cluster have samples with high temperatures and mineralized waters in common. The groups are distributed between three major neotectonics faults Barranca, Jesús María, and Tárcoles that creates a complex structural context that provides pathways movement for the contribution of thermal waters which can strongly dissolve the rocks, and provide a certain water chemical composition related with the presence of volcanic rocks with high concentrations of K, Mg, Mo, P, Rb, Si, Fe, Mn, F and U, and sedimentary rocks with high concentrations of B, Ba, Ca, Cu, Fe, Ge, Li, Na, S, SO4 and Zn. • Hierarchical clustering evidenced the presence of two clusters which groundwater composition are correlated with the lithological units. • High temperature values in groundwater evidenced the presence of a structural graben. • High concentrations of Al, Fe and Mn in groundwater are related to the dissolution of hydrothermalized volcanic rocks. • High groundwater temperatures may indicate the presence of blind faults. [ABSTRACT FROM AUTHOR]

• Paired air and stream water temperature metrics can provide an alternate or complementary method for assessing post-fire hydrologic change. • Results suggest increases in the magnitude of shallow groundwater discharge post-fire for sites with minimal pre-fire groundwater influence. • Watershed pre-fire stream-groundwater connectivity influences post-fire vulnerability to subsurface hydrologic change. Within the western United States, increasingly severe and frequent wildfires may alter the magnitude, timing, and quality of water exported from burned areas by streams. Post-fire hydrologic studies often focus on peak stream flow responses to shifts in runoff generation or on annual streamflow yield response to changes in evapotranspiration following fire. However, the magnitude and duration of wildfire effects on groundwater recharge, changes in subsurface routing, and consequences for stream low flows sourced predominately by baseflow are poorly understood. Here, we demonstrate an approach using the amplitude and phase of paired annual air and stream water temperature signals to broadly identify changes in watershed subsurface flow contributions after fire. Watersheds were classified using pre-fire temperature data, as having air-coupled (i.e., reduced apparent groundwater signature), deep groundwater, or shallow groundwater stream temperature signals. Changes in pre- and post-fire paired air and stream water temperature metrics were compared for locations (n = 17) spanning a large range of physiographic and climatic conditions across the western United States. Pre- and post-fire comparisons were computed by quantile using bootstrapped confidence intervals (ci = 95), as well as in aggregate using Kruskal-Wallis and post-hoc Dunn tests. Statistical comparisons of pre- and post-fire temperature metrics suggest that overall, watersheds classified as having minimal groundwater influence are the most likely to experience fire-induced subsurface hydrologic change. More specifically, watersheds classified as having air-coupled or shallow groundwater signals experienced increases in the magnitude of groundwater discharge, with more stable annual thermal regimes post-fire that are less-coupled to ambient air temperature. These findings form the basis of a conceptual framework for watershed resistance to subsurface hydrologic change following fire that can be broadly applied as a first approximation for water management, impacts on aquatic habitat, and post-wildfire response planning. [ABSTRACT FROM AUTHOR]

The increasing application of minor elements such as REE, Ti, Fe in zircon as petrogenetic indicators depends on zircon remaining a closed chemical system over a history that can include metamorphic events, erosion, transport, and sedimentation. Whereas examples have been described of U Pb loss and element exchange during metamorphic reactions, for over 50 years there have been reports of the accumulation of a range of non-formula elements such as Ca, Al, Fe, in zircons with no metamorphic history that have been tentatively related to hydrothermal action or some other process such as weathering. This open system behaviour of zircons needs further explanation and in this contribution we present data from three zircons from a late Archaean granite from Western Australia that confirm previous observations on the distribution of non-formula elements in radiation damaged zircon and support our earlier conclusion that elements are added from percolating low temperature weathering solutions and provide new insights into the mechanisms and processes controlling access of weathering fluids into the zircon. These include radiation damage accumulation over time from the decay of U and Th to produce domains of porous amorphous material that vary in porosity and the presence of weaknesses along the boundaries of oscillatory zones which allow the penetration of low temperature groundwater fluids carrying solute elements. Also important is the size of particles of the solute elements such as Al and Ca, which depends on Eh - pH of the groundwater and porous domains within the zircon structure. This low temperature fluid interaction is distinguished from hydrothermal activity by a lack of any reaction fronts or annealing of the radiation damage and a lack of any modification of existing zircon structures. Capillary action is proposed as the mechanism driving the penetration of weathering solutions into radiation damage expansion fractures and the radiation damaged zonal structure. The susceptibility of radiation damaged zircon to infusion by low temperature fluids and deposition of accompanying solute elements has implications for the application of zircon trace element chemistry as a petrogenetic and temperature indicator as well as a geochronometer and host for nuclear waste. [ABSTRACT FROM AUTHOR]

• Heat-transfer properties were analyzed to see how changes in hydraulic velocity and recharge rate allocation affected them. • The GWHP system's heat-transfer efficiency is evaluated by controlled physical studies in a lab setting. • A variety of pumping and recharge well layout schemes, and their effects on heat transfer efficiency, are analyzed. A groundwater heat pump (GWHP) is a form of ground-source heat pump that utilizes groundwater as its heat source and offers great efficiency, significant energy savings, and little pollution. As a GWHP system runs, thermal breakthrough is a crucial feature of system design that can result in a progressive shift in pumping water temperature and negatively impact GWHP performance. Variation in the groundwater flow field is crucial for heat transfer in terms of pumping and recharging well groups, especially when high porosity and permeability aquifers are taken into account, as this has a direct impact on the development of the groundwater temperature field. The primary goal of this study was to evaluate the impact of groundwater flow field variation due to groundwater velocity and recharge rate allocation changes on heat-transfer characteristics using laboratory physical experiments, to study the evolution trends of the groundwater flow field and groundwater temperature field, and to compare and determine various pumping and recharge well-group layout schemes to improve GWHP operation efficiency. The test results showed that the rise rate of pumping water temperature and the thermal breakthrough occurrence time increase with the increase of groundwater velocity, and when the groundwater velocity is the same, the thermal breakthrough occurrence time and the rise rate of pumping water temperature in the vertical well layout scheme are 0.48–0.76 times and 1.36–4.0 times that of the parallel well layout scheme, respectively. In addition, the recharge rate allocation has a greater impact on the parallel well layout scheme but a smaller impact on the vertical well layout scheme. The physical test results can provide a scientific basis for future research. [ABSTRACT FROM AUTHOR]

• The sources and paths of a leakage are identified with an integrated approach. • The clogging-induced permeability variation is quantified by inverse modelling. • The amount and its variation of leakage rate from each source are evaluated. The Xiluodu arch dam is one of the highest dams in the world. A noticeable leakage having a maximum rate of 192 L/s and accounting for 46 ∼ 75 % of the total discharge at the site has been observed in the plunge pool area since impoundment. For long-term safety of the dam, an integrated approach of groundwater temperature analysis, hydrochemical data clustering, cross-correlation function and inverse modelling is presented to detect the sources and flow paths of the leakage. It is found that the leakage is originated from three major sources, i.e., the confined limestone aquifer (underlain by the unconfined basalt aquifer), the reservoir and the downstream river. The vertical leakage from the limestone aquifer occurs through unplugged boreholes drilled during site investigation. Inverse modelling shows that induced by particle filling, clogging and rock deformation, the effective permeability of the unplugged boreholes follows the same exponential decay with the near-field basalt rocks upstream the impervious system. Consequently, the amount of the vertical leakage decreases annually, which leads to an annual decrease of the discharge in the plunge pool area. The leakage from the reservoir and the downstream river is dynamically stable in magnitude, which occurs through the basalt aquifer by bypassing the grout curtains in the dam and subsidiary dam foundations, respectively. During the past seven years of operation, the proportions of leakage from the above three sources account for, on average, 44 %, 31 % and 25 %, respectively. [ABSTRACT FROM AUTHOR]

This investigation evaluates spatial relationships between summer (July) groundwater temperatures and Fe(II)/Fe(III) biogeochemical cycling over a five year period in a shallow pristine sand aquifer at Meilleurs Bay near Deep River, Ontario, Canada. A warm subsurface thermal island of 12.5–16.1 °C, compared to background conditions of 10–11 °C, was manifest in contour maps of average groundwater temperature over the study period. The warm zone coincided with an area of convergent groundwater flow, implicating horizontal heat transfer by advective convection as the reason for elevated temperatures. Additionally, high concentrations of dissolved Fe(II) and Fe(III) overlapped the warm thermal island, indicative of increased rates of bacterial Fe(II)-oxidation and Fe(III)-reduction. A depletion in the modal abundance of Fe(II)-bearing minerals, notably amphibole and biotite, inside the area of the warm thermal island was also observed, suggesting enhanced mineral dissolution owing to chemoautotrophic Fe(II)-oxidation coupled to the reduction and fixation of dissolved inorganic carbon as biomass. Throughout the aquifer, redox conditions were poised in terms of Eh and pH close to equilibrium with respect to the Fe(II)/Fe(OH) 3 couple, feasibly enabling simultaneous bacterial Fe(II)-oxidation and Fe(III)-reduction with an adequate supply of electron acceptors and donors, respectively. The significance of higher groundwater temperature as a determinant of elevated dissolved Fe(II) and Fe(III) concentrations induced by thermal intensification of microbial biogeochemical activities yielded Pearson product-moment correlations in which temperature alone, as a single independent variable, explains almost 30 to nearly 60 percent of the variation in the measured dissolved Fe(II) and Fe(III) concentrations in the groundwater. These results emphasize the important influence of thermal conditions on biogeochemical processes in aquifers coupled to the development of steep gradients in groundwater quality over short distances in shallow unconfined groundwater systems. [ABSTRACT FROM AUTHOR]

Underground structures have a major influence on groundwater temperature and have a major contribution on the anthropogenic heat fluxes into urban aquifers. Groundwater temperature is crucial for resource management as it can provide operational sustainability indicators for groundwater quality and geothermal energy. Here, a three dimensional heat transport modeling approach was conducted to quantify the thermally affected zone (TAZ, i.e. increase in temperature of more than + 0.5 °C) caused by two common underground structures: (1) an impervious structure and (2) a draining structure. These design techniques consist in (1) ballasting the underground structure in order to resist hydrostatic pressure, or (2) draining the groundwater under the structure in order to remove the hydrostatic pressure. The volume of the TAZ caused by these underground structures was shown to range from 14 to 20 times the volume of the underground structure. Additionally, the cumulative impact of underground structures was assessed under average thermal conditions at the scale of the greater Lyon area (France). The heat island effect caused by underground structures was highlighted in the business center of the city. Increase in temperature of more than + 4.5 °C were locally put in evidence. The annual heat flow from underground structures to the urban aquifer was computed deterministically and represents 4.5 GW · h. Considering these impacts, the TAZ of deep underground structures should be taken into account in the geothermal potential mapping. Finally, the amount of heat energy provided should be used as an indicator of heating potential in these areas. [ABSTRACT FROM AUTHOR]

• Freezing-induced groundwater recharge is the water source of frozen soil. • Groundwater recharged to the frozen layer is redistributed during the thawing period. • Groundwater temperature dynamics are controlled by the soil accumulated heat storage. • In field freeze–thaw characteristic curve can consider water migration between soil layers. Understanding the mechanisms of water migration and heat transfer in frozen soil is essential for the selection of water resource management measures and determination of irrigation schemes for winters. However, the dynamics of the groundwater level and temperature caused by freezing and thawing and their impact on soil water redistribution remain unclear. In this field study, the mechanisms of water migration and heat transfer in the soil during the freeze–thaw period under the combined action of the surface temperature change (upper boundary) and groundwater level fluctuation (lower boundary) were comprehensively considered with the theory and method of heat transfer, freeze–thaw characteristic curves of soil, and water balance model. The results showed that: (1) The soil temperature distribution and groundwater temperature dynamics can be interpreted intuitively by the soil temperature gradient and accumulated heat storage. (2) The freeze–thaw characteristic curves of soil indicated that the soil temperature dynamics caused a phase transition of the soil water. This further changed the soil water potential and permeability by 1–2 magnitudes and 1–5 magnitudes, respectively, which affected the direction and quantity of water migration. (3) The water balance quantitatively revealed the controlling effect of groundwater level changes caused by freezing and thawing on soil moisture dynamics. About 20% of the ice in the frozen layer was formed by the upward recharge of the groundwater during the freezing period. In the thawing period, most of this water returned to the groundwater (84%), while the rest (16%) increased the soil water content. These results systematically explain the mechanisms of heat transfer and water migration between the soil water and the groundwater during the freeze–thaw period, providing a theoretical reference for agricultural water management in seasonally frozen regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Full-scale energy retaining walls have been numerically investigated thoroughly. • Reliable hydrogeological information is vital for the system performance evaluation. • The significance of groundwater flow on the system performance is revealed. • The λ ground plays an important role on performance when groundwater flow is minimal. • The pipe flow rate has a rather small effect on the system thermal performance. A ground source heat pump (GSHP) system provides efficient space heating and cooling and thus is regarded as a contributor to achieve net-zero emissions targets. This study focuses on an economical type of GSHP system – energy walls where earth retaining walls are equipped with pipes to act as geothermal heat exchangers in addition to being geotechnical structures. A detailed numerical investigation is performed to study the long-term heat exchange mechanism between the walls and the surrounding ground. The work highlights the significance of the existence and magnitude of groundwater flow on the temperature distribution of the ground and the thermal performance of energy walls. Compared to the case when there is no subsurface flow, the energy retaining wall can offer up to a 6 % better coefficient of performance (COP) or provide up to 1.3 times higher thermal yield for relatively slow groundwater flow velocities of 0.013 m/d. The COP can improve up to 93 % and thermal yield up to 23 times for high velocities of 2 m/d, even in extremely cooling-dominant thermal demand cases. The study also shows that the ground thermal conductivity plays a crucial role on performance when groundwater flow is minimal, however, as the convective heat transfer resulting from the groundwater flow becomes more dominant, the influence of thermal conductivity gradually diminishes. It is also found that the absorber pipe flow rate has a rather small effect on the system thermal performance, of less than a 10 % COP difference in all studied cases. This suggests that obtaining reliable hydrogeological information specifically on the groundwater flow velocity and direction are crucial for accurate predictions and optimal design for energy retaining walls and large scale GSHP installations. The insights from this study can improve the design and enhance the uptake of retaining walls for efficient heating and cooling of above/underground spaces - critical components in achieving a clean energy future. [ABSTRACT FROM AUTHOR]