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Natural aquifers usually exhibit complex physical and chemical heterogeneities, which are key factors complicating kinetic processes, such as contaminant transport and transformation, posing a great challenge in the remediation of contaminated groundwater. Aquifer heterogeneity usually leads to a distinct feature, the so-called “anomalous transport” in groundwater, which deviates from the phenomenon described by the classical advection-dispersion equation (ADE) based on Fick’s Law. Anomalous transport, also known as non-Fickian dispersion or “anomalous dispersion” in a broad sense, can explain the hydrogeological mechanism that leads to the temporally continuous deterioration of water quality and rapid spatial expansion of pollutant plumes. Contaminants enter and then are retained in the low-permeability matrix from the high-permeability zone via molecular diffusion, chemical adsorption, and other mass exchange effects. This process can be reversed when the concentration of pollutants in high-permeability zones is relatively low. The contaminants slowly return to the high-permeability zones through reverse molecular diffusion, resulting in sub-dispersive anomalous transport leading to the chronic gradual deterioration of water quality. Meanwhile, some contaminants are rapidly transported along the interconnected preferential flow paths, resulting in super-dispersive anomalous transport, which leads to the rapid spread of contaminants. Aquifer heterogeneity is also an important factor that constrains the efficacy of groundwater remediation, while the development, application, and evaluation of groundwater remediation technologies are usually based on the Fickian dispersion process predicted by the ADE equation. Comprehensive studies of the impacts of non-Fickian dispersion on contaminant transport and remediation are still needed. This article reviews the non-Fickian dispersion phenomenon caused by the heterogeneity of geological media, summarizes the processes and current understanding of contaminant migration and transformation in highly heterogeneous aquifers, and evaluates mathematical methods describing the main non-Fickian dispersion features. This critical review also discusses the limitations of existing research and outlines potential future research areas to advance the understanding of mechanisms and modeling of non-Fickian dispersion in heterogeneous media.

Grouting has been commonly used for structure controlling in mining engineering. To investigate the mechanism of fracturing grouting, an experiment was conducted under constant flowing conditions. Through the real-time gathering of main parameters and reconstruction of the slurry distribution, the complete grouting process and pressure spread of the high-pressure slurry were revealed. An identification method of fracturing diffusion based on acoustic emission (AE) signals was proposed and verified. The results indicated that the intact rock showed fracturing response with a mutated pressure in a short time. For fractured ones, the grouting process can be divided into five stages: seepage flow, pressure holding, fracturing diffusion, steady flow, and pressure relief. Influenced by the hydraulic fracture and slurry infiltration, there were three states: cement diffusion, water seepage, and the unaffected zone. A calculation method of whole stages for the grouting pressure was proposed based on the Hoek–Brown strength criterion and flow model in a fracture. In addition, AE ring counting occurred during the entire slurry process but was relatively concentrated in pressure holding and fracturing diffusion stages. Considering the zonal distribution characteristics, the AE method was used to characterize the slurry diffusion range and flow paths. The slurry distribution was obtained by the three-dimensional cutting and reconstruction method to verify its feasibility. This study is expected to further clarify the grouting mechanism, and guide engineering practices.HighlightsHigh-pressure grouting experiment of fractured rock based on acoustic emission was carried out.The whole process of fracturing grouting shows five responses in fractured rock.The pressure calculation model for revealed whole injection process was established in inclined fracture.AE monitoring can be used to identify the splitting-diffusion range and path for fracturing grouting.

Coastal groundwater dynamics and solute transport were influenced by multiple factors including aquitards, tides, evaporation, and slope breaks in coastal aquifers. However, quantification of the impacts of these factors on groundwater flow and salinity distribution remains a challenge. In this study, both field observations and numerical modeling were applied to investigate hydraulic heads and groundwater salinity in a tidal flat with large‐scale seepage faces at Laizhou Bay, China. Results showed that seepage‐face evaporation increased groundwater salinity landward and promoted groundwater and salt exchange within the intertidal zone significantly in comparison to the case without evaporation. Seawater infiltrated the aquifer on the left of the slope break and discharged on the right, forming a groundwater circulation cell, which notably influenced leakage flow between unconfined and confined aquifers through the aquitard. The aquitard prevented approximately 85% of inland freshwater discharge near the slope break, resulting in the formation of two atypical freshwater discharge tubes in the upper and middle intertidal zones. Two additional groundwater circulation cells developed in the lower intertidal zone due to the spring‐neap tidal cycle. The outflow and inflow fluxes over a spring‐neap tidal cycle were numerically estimated to be 1.46 and 1.27 m2/d, respectively, with evaporation accounting for 45% of the outflow flux. These findings provide significant insights for further investigations on groundwater dynamics and solute transport in multi‐layered coastal aquifers, and have strong implications for biogeochemical processes within the intertidal zone. Plain Language Summary The coastal aquifer serves as a crucial connection between terrestrial and marine systems, with groundwater flow and salt transport in coastal regions influenced by factors such as topographic variations (e.g., slope break), tides, aquitards (low‐permeability layers among permeable layers), and evaporation. Quantification of these complex processes is a challenge. Here, we combined field observations and numerical simulations to quantify the effects of slope break, tides, aquitard, and evaporation on groundwater flow paths and salinity distribution beneath a tidal flat. It was found that evaporation may significantly increase groundwater salinity landward, and promoted the mass exchange between groundwater and seawater on the tidal flat surface. The combined effects of slope break, spring‐neap tidal cycle, and aquitard notably altered the pathways of groundwater flow and solute transport in coastal aquifers. These may profoundly influence the biogeochemical conditions in multi‐layered coastal aquifers, with important implications for coastal management and environmental protection. Key Points Seepage‐face evaporation significantly increases groundwater salinity and promotes groundwater/salt exchange within the intertidal zone Two new freshwater discharge tubes and three groundwater circulation cells develop due to the aquitard, spring‐neap tidal cycle, slope break Significant exchanges of groundwater and solutes occur between unconfined and confined aquifers via leakage under the slope break

Seasonal patterns of dissolved organic matter (DOM) were evaluated for multiple watershed sources and stream water during baseflow and stormflow to investigate the influence of hydrologic flow paths and key phenological events. Watershed sources sampled were throughfall, litter leachate, soil water, and deep groundwater. DOM data for a 4-year period (2008–2011) included: DOC concentrations and spectrofluorometric indices such as a₂₅₄, humification index, protein-like and humic-like DOM. Seasons were defined as—winter (December–February), spring (March–May), summer (June–September) and autumn (October and November). Seasonal differences in DOM were most pronounced for surficial flow paths (e.g., stormflow, litter leachate, throughfall and soil water) but muted or absent for groundwater and baseflow. This was attributed to the loss of DOM by sorption on mineral soil surfaces and/or microbial breakdown. DOM in summer stormflow had higher DOC concentrations and was more humic in character versus DOM in spring and winter runoff. Storm events in early autumn produced a sharp increase in DOC concentrations and % protein-like DOM for stream waters and litter leachate. Elevated DOC concentrations for early spring throughfall were attributed to leaching of organic exudates associated with leaf emergence. Our results underscore that watershed and ecosystem studies need to pay a greater attention to surficial flow paths and runoff sources (including stormflow) for understanding seasonal patterns of DOM. Understanding the influence of phenological episodes such as autumn leaf-fall for DOM is important considering that these transitional events may be especially affected by climate change.

Carbonate rock aquifers are an important resource in the face of water scarcity. However, groundwater recharge processes are not fully understood in the heterogeneous matrix and fracture system. The shallow epikarst zone is important for drainage, transport and storage and needs to be investigated. Geophysical techniques are promising, particularly ground penetrating radar (GPR) due to its sensitivity to water saturation. To test the potential of GPR, hydrogeological structures were investigated in the Lower Muschelkalk of the Rüdersdorf limestone quarry near Berlin, Germany. A survey field was monitored under three different moisture conditions and the experiments included densely spaced zero offset GPR and common midpoint (CMP) profiles. The analysis focused on EM wave velocities as a proxy for water saturation, which were used for a relative comparison of the results from different methods. The more generic CMP results were significantly higher than the velocities from diffraction hyperbolas, which only represent the very local position. Structural observations from picked reflectors throughout the monitoring contributed to the interpretation. While the matrix appears to be unaffected by water variability, preferential flow paths can be identified. Diffraction hyperbolas may occur at fractured porous zones that preferentially store water and drain towards the bedding planes. Their spatial characteristics suggest that they may be precursors of potential sinkholes. The survey shows how GPR can help to understand hydrological processes in carbonate rock and locate relevant structures for further investigation. The collected dataset provides opportunities for further analysis.

Purpose This study aim to use the finite volume method to solve differential equations related to three-dimensional simulation of a solar collector. Modeling is done using ANSYS-fluent software program. The investigation is done for a photovoltaic (PV) solar cell, with the dimension of 394 × 84 mm2, which is the aluminum type and receives the constant heat flux of 800 W.m−2. Water is also used as the working fluid, and the Reynolds number is 500. Design/methodology/approach In the present study, the effect of fluid flow path on the thermal, electrical and fluid flow characteristics of a PV thermal (PVT) collector is investigated. Three alternatives for flow paths, namely, direct, curved and spiral for coolant flow, are considered, and a numerical model to simulate the system performance is developed. Findings The results show that the highest efficiency is achieved by the solar cell with a curved fluid flow path. Additionally, it is found that the curved path’s efficiency is 0.8% and 0.5% higher than that of direct and spiral paths, respectively. Moreover, the highest pressure drop occurs in the curved microchannel route, with around 260 kPa, which is 2% and 5% more than the pressure drop of spiral and direct. Originality/value To the best of the authors’ knowledge, there has been no study that investigates numerically heat transfer, fluid flow and electrical performance of a PV solar thermal cell, simultaneously. Moreover, the effect of the microchannel routes which are considered for water flow has not been considered by researchers so far. Taking all the mentioned points into account, in this study, numerical analysis on the effect of different microchannel paths on the performance of a PVT solar collector is carried. The investigation is conducted for the Reynolds number of 500.

Utility trenches are an integral part of a sewer system. When situated in an aquitard, their coarse granular bedding material potentially forms a preferential flow path. The hydrologic functioning of the utility trenches and their bedding has been analyzed using water level data from a unique district-wide investigation of the interaction between a storm sewer system, the associated utility trench network and an aquitard. Utility trench water level recessions have been examined using analytical results based on recession analysis with the one-dimensional (1-D) Boussinesq equation, as well as deterministic 1-D and 2-D numerical groundwater models of utility trenches. The results show that water level rises occur after cessation of exfiltration recharge. These rises are associated with nonequilibrium recharge and occur when branch utility trench flows exceed the downslope trunk utility trench flows. A near-linear recession occurs when the branch utility trenches transition into a quasi-exponential recession on cessation of these water level rises. The magnitude of water level rises and duration of the near-linear recession are increased by the convergence of flow from branch utility trenches to the trunk utility trench. A utility trench network situated in an aquitard could be considered an analog for some natural aquifers with preferential flow paths. It is proposed that significant post-recharge storage increases associated with nonequilibrium recharge events could occur in such aquifers, which may be indicated by near-linear recessions preceding quasi-exponential recessions.

The infiltration of liquid water in a seasonal snowpack is a complex process that consists of two primary mechanisms: a semi-uniform melting front, or matrix flow, and heterogeneous preferential flow paths. Distinguishing between these two mechanisms is important for monitoring snow melt progression, which is relevant for hydrology and avalanche forecasting. It has been demonstrated that a single co-polarized upward-looking radar can be used to track matrix flow, whereas preferential flow paths have yet to be detected. Here, from within a controlled laboratory environment, a continuous polarimetric upward-looking C-band radar was used to monitor melting snow samples to determine if cross-polarized radar returns are sensitive to the presence and development of preferential flow paths. The experimental dataset consisted of six samples, for which the melting process was interrupted at increasing stages of preferential flow path development. Using a new serial-section hyperspectral imaging method, polarimetric radar returns were compared against the three-dimensional liquid water content distribution and preferential flow path morphology. It was observed that the cross-polarized signal increased by 13.1 dB across these experiments. This comparison showed that the metrics used to characterize the flow path morphology are related to the increase in cross-polarized radar returns spanning the six samples, indicating that the upward-looking polarimetric radar has potential to identify preferential flow paths.

This study empirically evaluates whether the conventional Water Supply Ecosystem Service (ES) assessment framework in South Korea adequately reflects actual water supply processes, and proposes a methodological framework for its improvement. Using the nationwide distribution of water sources, we divided the study area into three regions and inferred potential groundwater contribution pathways (flow paths) through terrain-based analysis. A sensitivity analysis identified a 500 m grid as the optimal resolution, and a grid-based scoring approach was applied to compare the conventional and enhanced ES frameworks. The results indicate that the conventional scores broadly correspond to regional patterns of water source distribution, suggesting partial representation of potential water supply capacity. However, flow-path-based evaluation revealed that scores along inferred supply pathways were not consistently concentrated in the higher range of the overall distribution, highlighting limitations in capturing actual supply processes. In contrast, the enhanced framework, incorporating hydrologically relevant indicators such as soil properties, topographic conditions, and slope morphology, significantly improved the percentile ranks of flow-path grids, with regionally varying effects. By evaluating and refining Water Supply ES assessments using actual water source locations rather than watershed-scale proxies, this study provides a process-oriented framework for more realistic evaluation and management of forest-based water supply ES.

This paper proposes a flow-path-network-based (FPN-based) algorithm, constructed from a square-grid digital elevation model (DEM) to improve the simulation of the flow path curvature (C). First, the flow-path network model was utilized to obtain an FPN. Then, a flow-path-network-flow-path-curvature (FPN-C) algorithm was proposed to estimate C from the FPN. The experiments consisted of two sections: (1) quantitatively evaluating the accuracy using 5 m DEMs generated from the mathematical ellipsoid and Gauss models, and (2) qualitatively assessing the accuracy using a 30 m DEM of a real-world complex region. The three algorithms proposed by Evans (1980), Zevenbergen and Throne (1987), and Shary (1995) were used to validate the accuracy of the new algorithm. The results demonstrate that the C value of the proposed algorithm was generally closer to the theoretical C value derived from two mathematical surfaces. The root mean standard error (RMSE) and mean absolute error (MAE) of the new method are 0.0014 and 0.0002 m, reduced by 42% and 82% of that of the third algorithm on the ellipsoid surface, respectively. The RMSE and MAE of the presented method are 0.0043 and 0.0025 m at best, reduced by up to 35% and 14% of that of the former two algorithms on the Gauss surface, respectively. The proposed algorithm generally produces better spatial distributions of C on different terrain surfaces.