Vadose Research Articles

The Influence of Rainfall and Evaporation Wetting–Drying Cycles on the Open-Pit Coal Mine Dumps in Cam Pha, Quang Ninh Region of Vietnam

Among the slope hazards caused by rainfall, not all of them occur directly during storm washout, and the wetting–drying cycles’ effect on the rainfall–evaporation process is an important cause of shallow slope instability. In this study, taking the slope of the open-pit coal mine dumps in Cam Pha, in the Quang Ninh region of Vietnam, as the research object, we carry out experiments on the physical properties of the rock body under different wetting–drying cycles, as well as numerical analyses. The results show that the wetting–drying cycles significantly affect the physical and mechanical parameters and permeability of the rock body. In the process of the wetting–drying cycle, a transient saturated zone occurs on the surface of the slope, and the range of the unsaturated zone inside the slope body decreases with the increase in the number of wetting–drying cycles. Moreover, the infiltration line keeps moving downward, but the rate of downward movement is slowed down by the decrease in the gradient of matrix suction affected by rainfall. Under the influence of the wetting–drying cycles, the slope displacement, plastic zone, and maximum shear strain increment range gradually approach the slope surface with the wetting–drying cycles, and the displacement peak gradually increases. A dump is a site for the centralized discharge of mining waste, formed by the crushing and stockpiling of the original rock formation. Bang Nau is the name of the dump considered in this study. After multiple rainfall events, the slope stability under five wetting–drying cycles decreases from 1.721 to 1.055, and the landslide mode changes from a whole landslide to a single-step shallow landslide, with a certain landslide risk. It is necessary to strengthen the slope stability as the landslide risk is very high, and it is necessary to strengthen the monitoring and inspection of the slope.

Three-Dimensional Model for Bioventing: Mathematical Solution, Calibration and Validation

Bioventing is an established technique extensively employed in the remediation of soil contaminated with petroleum hydrocarbons. In this study, the objective was to develop an improved foundational bioventing model that characterizes gas flow in vadose zones where aqueous and non-aqueous phase liquid (NAPL) are present and immobile, accounting for interphase mass transfer and first order biodegradation kinetics. By incorporating a correlation for the biodegradation rate constant, which is a function of soil properties including initial population of petroleum degrader microorganisms in soil, sand content, clay content, water content, and soil organic matter content, this model offers the ability to integrate a specific biodegradation rate constant tailored to the soil properties for each site. The governing equations were solved using the finite volume method in OpenFOAM employing the “porousMultiphaseFoam v2107” (PMF) toolbox. The equation describing gas flow in unsaturated soil was solved using a mixed pressure-saturation method, where calculated values were employed to solve the component transport equations. Calibration was done against a set of experimental data for a meso-scale reactor considering contaminant volatilization rate as the pre-calibration parameter and the mass transfer coefficient between aqueous and NAPL phase as the main calibration parameter. The calibrated model then was validated by simulating a large-scale reactor. The modelling results showed an error of 2.9% for calibrated case and 4.7% error for validation case which present the fitness to the experimental data, proving that the enhanced bioventing model holds the potential to improve predictions of bioventing and facilitate the development of efficient strategies to remediate soil contaminated with petroleum hydrocarbons.

Analysis of the spatiotemporal variation of groundwater storage in Ordos Basin based on GRACE gravity satellite data

Groundwater is the primary source for drinking, agriculture, irrigation, industrial, and municipal uses in Ordos Basin, a regional energy and heavy chemical industrial base in China. In recent decades, groundwater levels in the basin have declined due to climate change and anthropogenic activity. Analyses of the spatiotemporal variation of groundwater storage are crucial to regional sustainability. This study conducts the analysis utilizing GRACE gravity satellite data and GLDAS model data, employing methods that include the generalized three-cornered hat, Augmented Dickey-Fuller (ADF) test, and wavelet analysis to investigate the spatiotemporal variation of groundwater storage in the basin. The analysis results indicate that (1) before 2008, the climate had a significant influence on groundwater storage, with minimal impact from human activities, while after 2008, human activities have caused a noticeable decline in groundwater storage, particularly in the eastern region. (2) The eastern region of the basin experienced a decline in groundwater storage with a rate of −1.86 cm/yr, the middle region with a rate of −1.24 cm/yr, and the western region with a rate of −0.63 cm/yr. The extensive extraction of petroleum, natural gas, coal, and mineral resources in the basin has contributed to this pattern. (3) Human activities have altered the hydrological processes from precipitation infiltration, groundwater propagation, and groundwater distribution, leading to an increasingly complex groundwater system. (4) Human activities affect groundwater in the saturated zone more extensively than in the unsaturated zone. The research findings highlight that human activities are the main factor driving the variation in groundwater storage in the basin and provide crucial scientific evidence for protecting groundwater resources.

Enterococci pathways to coastal waters and implications of sea level rise

Highly urban coastal communities in low lying areas and with high water tables are vulnerable to sea-level rise and to corresponding increases in coastal groundwater levels. Stormwater conveyance systems are under increased risk. Rising groundwater levels affect the hydraulics of the stormwater system thereby increasing contaminant transport, for example the fecal indicator bacteria enterococci, to coastal waters. This study offers a unique opportunity to evaluate the impacts of increased contaminant transport on marine coastal environments. Here we assessed historic and recent coastal water quality, stormwater sampling data, groundwater monitoring and tidal elevations near the coastline, in the context of altered hydraulics within the system. Two pathways of enterococci to marine waters were identified. Direct discharge of contaminated stormwater runoff via the stormwater outfalls and tidally driven contaminated groundwater discharge. As sea level continues to rise, we hypothesize that a diminished unsaturated zone coupled with altered hydraulic conditions at the coastal groundwater zone will facilitate the transport of enterococci from urban sediments to the study site (Park View Waterway in Miami Beach, FL USA). We recommend improvements to the stormwater conveyance system, and maintenance of the sanitary sewer system to mitigate these impacts and minimize transport of enterococci, and other stormwater pollutants to coastal waters. The results of this study can be useful to interpret high enterococci levels in low lying coastal areas where groundwater is influenced by rising sea water levels.

Influencing Factors and Evaluation of Groundwater Ecological Function in Arid/Semiarid Regions of China: A Review

In arid and semi-arid areas, due to drought climate and shortage of water resources, groundwater is crucial for natural ecological protection and economic development. It serves a dual role as a resource function and an ecological function. However, with the continuous improvement of the exploitation and utilization of groundwater by human activities during rapid economic development, the phenomenon of groundwater overexploitation is becoming more and more serious, which has destroyed the natural balance of groundwater recharge and discharge. As a result, natural vegetation has lost the maintenance of the ecological function of groundwater, and a series of ecological and environmental problems have occurred, such as natural vegetation degradation, land desertification, sandstorms, and so on. In recent years, scholars have carried out research on groundwater resource management and optimization of water resource allocation, trying to solve the problem of water balance in arid regions. However, there is still a lack of comprehensive understanding and systematization regarding influencing factors and degeneration mechanisms related to groundwater’s ecological function. By summarizing and analyzing the previous research results, this paper summarizes the influencing factors, evaluation methods, existing problems and future directions of groundwater ecological function research in China to provide a reference for rational exploitation and utilization of groundwater and ecological protection. This paper is divided into four main contents. The first part introduces the definition of groundwater ecological function (GEF); the second part summarizes the research status of influencing factors of GEF, including the groundwater table depth, vegetation root system and lithologic structure of vadose zone, etc.; the third part analyzes the evaluation of groundwater ecological function; the fourth part discusses the existing problems in the study of groundwater ecological functions, and based on the above research the evaluation framework of GEF is proposed with the Shiyang River basin as a case study; and finally, it highlights the future research directions about GEF.

Variation of Soil Properties of Unsaturated Zone with Depth and Time at an Agricultural Site in Kuwait

Variation of Soil Properties of Unsaturated Zone with Depth and Time at an Agricultural Site in Kuwait

Responses of deep soil moisture to direct rainfall and groundwater in the red soil critical zone: A four-stage pattern

Deep soil moisture (DSM) plays a critical role in vadose zone hydrological processes. However, the recharge processes and their underlying mechanisms remain unclear due to the scarcity of comprehensive deep hydrological data, especially in regions characterized by active interactions between surface and subsurface hydrological processes. To address this knowledge gap, we performed an event-based study using a four-year hydrological monitoring dataset, encompassing rainfall, profile soil moisture, and groundwater along a hillslope at the Red Soil Critical Zone Observatory (CZO) in China. A total of 226 rainfall events were classified into four distinct types (I-IV) using a k-means clustering algorithm. The changes in DSM and groundwater table (GWT) were dependent on the rainfall type. The GWT (0.57–0.97) played a greater role in contributing to the DSM than the direct rainfall (0.48–0.64) based on a structural equation model, which was more pronounced from upper slope to foot slope. DSM recharge pattern can be described by a four-stage conceptual model, as indicated by the relationship between DSM and GWT: a slow and linear increase (stage 1), a small plateau (stage 2), a rapid linear rise (stage 3), and finally a great plateau (stage 4). DSM at the small and great plateau were closely related with the field capacity and saturation, respectively. Rainfall type, vadose zone features, and soil physical properties jointly shaped DSM recharge patterns. These findings can offer valuable insights into understanding the deep hydrological processes of the red soil region as well as regions with similar hydroclimatic conditions.

Discovery of modern living intertidal stromatolites on Sheybarah Island, Red Sea, Saudi Arabia

Abstract Microbial carbonates, and stromatolites in particular, represent the earliest geological record of life on Earth, which dominated the planet as the sole biotic carbonate factory for almost 3 b.y., from the Archean to the late Proterozoic. Rare and sparsely scattered across the globe in the present day, modern “living” stromatolites are typically relegated to extreme environmental niches, remaining as vestiges of a prodigious microbial past. Here, we report the first discovery of living shallow-marine stromatolites in the Middle East, on Sheybarah Island, Al Wajh carbonate platform, on the NE Red Sea shelf (Saudi Arabia). We detail their regional distribution and describe their environmental conditions, internal structures, and microbial diversity. We also report the first discovery of reticulated filaments in a photic setting, associated with these stromatolites. The Sheybarah stromatolites occur in the intertidal to shallow subtidal zones along the seaward-facing beach in three depth-dependent growth forms. Their inner layers were formed by microbially mediated accretion and differential lithification of sediment grains. Compositional microbial analysis revealed the presence of a wide range of microbial life forms.

Identification of Deep and Shallow Groundwater Potential Zones using GIS Techniques; Case Study: Monaragala District, Sri Lanka

One of the most crucial steps in the management of groundwater sources sustainably is the delineation of the zones with potential for groundwater. However, in addition to taking a lot of time and money, groundwater investigations can be difficult and complex in many locations. To get sufficient results, it needed to demarcate shallow and deep groundwater potentiality separately. Sri Lankan districts have various problems due to a lack of water. With population growth and urbanization, surface water is insufficient to meet the water requirement. This study focused on groundwater potential mapping in Monaragala district covered with the total are 5708 km2 in Sri Lanka. The fuzzy overlay and weighted overlay method integrated with GIS were mainly used to determine potential zones for deep and shallow groundwater. The final results from the two overlaying methods were compared to identify most accurate locations. Six parameters, namely aquifer type, soil depth, soil group, rainfall, proximity to surface water bodies, and slope, were evaluated for the shallow groundwater studies. Proximity to lineament, geology and shallow groundwater parameters were assessed for profound groundwater potentiality. The final output resulting maps were categorized into five main categories such as extremely low, low, moderate, high and extremely high by considering obtained potential values. The deep groundwater potential map demonstrates that the high groundwater potential areas are located around the lineaments, prominently areas having mountain ranges. Therefore the effect of the lineament is very high for deep groundwater availability. High shallow groundwater potential areas are located in smaller regions from Katharagama, Thanamalwila and Siyambalanduwa. Obtained results were validated using existing 220 tube well data and 100 dug well data. 
 Keywords: Fuzzy overlay, Geology, GIS, Groundwater, Weighted overlay

Spatial distribution of the diatoms <i>Dactyliosolen fragilissimus</i> and <i>Cerataulina pelagica</i> in the autumn phytoplankton of the South-Eastern Baltic in 2020–2021

The mass development of diatom Dactyliosolen fragilissimus and Cerataulina pelagica, which are atypical of the South-East Baltic Sea water area, were registered along the Sambia peninsula coastline in the mid of October 2020. Both species were found in the coastal zone of the western and northern coast of the Sambia peninsula to a depth of 32 m, from the Baltic Strait to port Pionerskiy. In early November 2021 a mass vegetation of C. pelagica was recorded –both in the shallow coastal zone of the northern coast of the Sambia peninsula and in the deep water zone of the South-Eastern Baltic Sea. The biomass of this species reached 2.8 g/m3. Both diatom species were abundant within the entire Russian Exclusive Economic Zone. The prevailing hydrological situation during the study period probably facilitated penetration of the species into the study area by surface transport from the Arkona Basin.

Paleozoic reef formation in the Pechora syneclise and the Caspian basin – a comparative analysis

In the two marginal depressions of the East European Platform, the Pechora syneclise and the Caspian depression, reef formations are widely represented, but the stratigraphic intervals of their development are far from equal. In the Pechora syneclise, reef formation began in the second half of the Llandoverian, reached its maximum in the Frasnian and was replaced by the development of reef hills in the Famennian. The structures are represented both as asymmetric reefs framing the shallow zones at their boundary with relatively deep paleobasins and in the form of single structures within the latter. The reefs of the next global maximums, the Late Visean-Serpukhovian and Lower Permian, are developed only marginally at the boundary with the Ural paleoocean and its relic, the Pre-Urals foreland basin. In the Caspian basin, reefs of all three global maxima of development are present, and there are both asymmetric reef systems framing the shelf edges and symmetric intra-basin isolated structures. Such difference is due to the different paleogeomorphological type of the basins. The Caspian basin was sharply differentiated in depth throughout the Middle and Late Paleozoic, which led to the formation of reefs rising above the bottom of these basins. In the Pechora syneclise, depth differentiation of the basins occurred only in the late Devonian. Generally weakly dissected shallow seas of the Visiean-Serpukhovian and early Permian did not provide conditions for the formation of powerful reefs protruding above the seafloor. The latter were formed only on the edge of the Ural paleoocean, and in the Permian ‒ on the edge of the Pre-Ural foreland basin.

Exploring the artistic dimensions of soils in the vadose zone

AbstractThe rise of industrialized agriculture, coupled with a global demographic shift toward urbanization, has marginalized every‐day connections between individuals and soils. This societal shift has led to a decline in the appreciation of and cultural identity with soils. Amid a broader movement aimed at fostering soil awareness and environmental action, many artists and designers have been instrumental in bringing soils to the cultural mainstream, figuring their esthetic, social, political, and ecological dimensions. Contemporary artists place great importance on the underlying idea of animating soils through artistic practice, often transcending the physical artifact itself to assign agency to soils and the myriad beings that occupy them. Artists harness a multitude of media to articulate human‐soil relationships. From the early environmental art movements of the 1960s and 1970s to contemporary works centered on urban and industrial brownfields, soils’ multifaceted roles in CO2 transformation, water and nutrient cycling, agriculture, and as living bodies buffering against pollution have become ground for public discourse. What could this mean for the vadose zone in terms of reflecting on material flows in porous media beyond understandings of soil physics? In this paper, we draw on over 20 years of experience in studying the portrayal of soil in various arts genres to deliberate the potential of creative thinking about and thinking with the vadose zone.

KarstNSim: A graph-based method for 3D geologically-driven simulation of karst networks

In karst aquifers, groundwater flow is highly influenced by the interconnected underground cavities and conduits that form the karst network. Modeling karst flows requires the use of spatially distributed approaches accounting for these networks. Their exploration is, however, often complex, and mapping them using indirect methods such as geophysical ones has proven challenging. To overcome these limitations, stochastically simulating discrete karst networks should account for the uncertainties on conduit position and geometry. Only a few existing methods can reproduce realistic and diverse karst morphologies. In this work, we propose a new algorithm, KarstNSim, for simulating discrete karst networks, that incorporates field data to generate a range of possible karst network geometries. It relies on the computation of the shortest path between the inlets and outlets of the network with the use of an anisotropic cost function defined on an n-nearest neighbor graph conformal to geological and structural heterogeneities. This cost function represents the physico-chemical processes that govern speleogenesis – such as erosion and chemical weathering – providing simplified control over the geometry of the generated networks. Our approach reproduces the vadose-phreatic partition visible in the karst networks, by generating sub-vertical conduits in the unsaturated zone and sub-horizontal ones in the saturated part. It encompasses geological parameters such as inception surfaces, fractures, permeability, and solubility of layers, along with considering the hydrological context of recharge by assigning relative weights to the inlets. We simulate various synthetic models to demonstrate the influence of different input parameters on the spatial organization of the past and present karst flows. We also apply KarstNSim to a real case study – the Ribeaucourt system (Meuse, France) – and use available data to generate realistic karst networks. The lack of knowledge on the Ribeaucourt network geometry is alleviated by the use of multiple scenarios corresponding to different sets of weights in the cost function, resulting in a variety of network morphologies which represent the uncertainty on the real geometry. The geometrical and topological metrics computed on the simulated networks generally overlap with those of real ones, suggesting the reliability of the method.

Transport of graphene oxide in the capillary fringe: Insights from sandbox experiments and numerical simulation

Studying contaminant transport in the capillary fringe (CF), a crucial part of the vadose zone, offers insights into the mechanisms controlling pollution in soils and groundwater aquifers. This paper investigated contaminant transport in the CF by continuously injecting a conservative tracer (NaCl) and graphene oxide nanoparticle (GONP), an adsorptive contaminant, into a sandbox. After entering the CF from the unsaturated zone, both NaCl and GONP underwent lateral transport. The breakthrough curves (BTCs) for NaCl and GONP were derived from water samples collected at predetermined sampling holes. Subsequently, contaminant transport in the CF was modeled using a one-dimensional–two-dimensional (1D-2D) coupled hydrodynamic model. This model incorporated lateral dispersivity (αL = 1.198 cm) and longitudinal dispersivity (αT = 0.286 cm), calculated using a point-by-point method. The hydrodynamic dispersion coefficients obtained were then applied to the Brooks and Corey (BC) and the van Genuchten (VG) parametric models. The BC model more accurately simulated the NaCl migration compared to the VG model, leading to its application in simulating GONP transport in the CF. However, the simulated BTCs for GONP showed a lag behind the measured data, especially at high ionic strengths. This discrepancy was attributed to the variable adsorption partition coefficient of GONP under different ionic conditions. During the experiment, GONP adsorption onto the porous media's surface altered the capillary dynamics, notably increasing capillary rise height, decreasing seepage velocity, and reducing GONP dispersion. Therefore, it is necessary to consider the adsorption capacity of the contaminants in order to accurately assess their transport within the vadose zone.

Extreme precipitation accelerates nitrate leaching in the intensive agricultural region with thick unsaturated zones

Nitrate accumulation in the soil profile in the intensive agricultural region has been widely concerned in the world. However, the changes in nitrate accumulation characteristics caused by climate change, such as extremely high precipitation, are not well quantified, particularly for the regions with thick unsaturated zones. Here, we resampled the soil profiles taken in normal year (2020) after extreme precipitation year (2021) (>800 cm) in three regions in the southern Loess Plateau (LP) with three different water managements including rainfed orchards (n = 10), well-irrigated orchards (n = 4) and canal-irrigated orchards (n = 8). The accumulation amounts, peak depths, and accumulation depths of nitrate soil profiles of the different regions of two years were compared. The results showed that average nitrate accumulation in normal year at the rainfed region (800-cm depth), well-irrigated region (800-cm depth) and canal-irrigated region (1400-cm depth) were 5995 kg N ha−1, 9765 kg N ha−1, and 19,608 kg N ha−1, respectively. Compared with 2020, extreme precipitation in 2021 led to 56–91% reductions (2060–3702 kg N ha−1) in nitrate accumulation in 0–200 cm soil layer, and average nitrate leaching into the aquifer was >1390 kg N ha−1 in the canal-irrigated region. Average migration depths of nitrate peak in rainfed, well-irrigated and canal-irrigated regions were 92 cm, 115 cm, and 188 cm, respectively; as for nitrate accumulation depths, they were 10 cm, 80 cm and 108 cm, respectively. Vertically, the dried soil layer and paleosol layer (high clay content) in the canal-irrigated region significantly hindered nitrate deep migration caused by the extreme precipitation. The result highlights that extreme precipitation significantly accelerated nitrate leaching in the deep soil profiles, and future vulnerability and risk assessment studies must account for the impacts of extreme precipitation on nitrate leaching.

Modeling 1-D aqueous film forming foam transport through the vadose zone under realistic site and release conditions

Aqueous film forming foams (AFFFs) have been used to extinguish fires since the 1960s, leading to widespread subsurface contamination by per- and polyfluoroalkyl substances (PFAS), an essential component of AFFF. This study presents 1-D simulations of PFAS migration in the vadose zone resulting from AFFF releases. Simulation scenarios used soil profiles from three US Air Force (USAF) installations, encompassing a range of climatic conditions and hydrogeologic environments. A three-component mixture, representative of major constituents of AFFF, facilitated the exploration of competitive and synergistic effects of co-constituents on PFAS migration. To accurately capture unsaturated transport of PFAS in porous media, the model considers (1) surfactant-induced flow, (2) non-linear sorption to the solid phase, (3) competitive accumulation at the air-water interface, and (4) the moisture-dependence of the air-water interfacial area. Defined PFAS releases were consistent with fire training exercises, emergency responses, and accidental spills of record. Simulation results illustrate the importance of hydrogeologic, climatic, geochemical, and AFFF release conditions on PFAS transport and retention. Comparison of field observations and model simulations for Ellsworth AFB indicate that much of the PFOA and PFOS mass is associated with the air-water interface and the solid phase, which limits their migration potential in the vadose zone. Results also show that rates of migration in the aqueous phase are largely controlled by hydrogeologic properties, including recharge rates and hydraulic conductivity. AFFF spill scenarios varying in volume, concentration, and frequency reveal the importance of release characteristics in determining rates of PFAS migration and concentration peaks. Variability is attributed to non-linear sorption processes, where, contrary to simple linear partitioning formulations, transport is strongly affected by the concentration of PFAS species. Simulations also demonstrate the importance of modeling the AFFF as a mixture since competitive interfacial accumulation effects are shown to enhance the mobility of less surface-active PFAS compounds.

Expanding Karst Groundwater Tracing Techniques: Incorporating Population Genetic and Isotopic Data to Enhance Flow-Path Characterization

Karst aquifers are unique among groundwater systems because of variable permeability and flow-path organization changes resulting from dissolution processes. Over time, changes in flow-path connectivity complicate interpretations of conduit network evolution in karst hydrogeology. Natural and artificial tracer techniques have long provided critical information for protecting karst aquifers and understanding the potential impacts on ecosystems and human populations. Conventional tracer methods are useful in karst hydrogeologic studies for delineating flow paths and defining recharge, storage, and discharge properties. However, these methods only provide snapshots of the current conditions and do not provide sufficient information to understand the changes in interconnection or larger-scale evolution of flow paths in the aquifer over time. With advances in population genetics, it is possible to assess population connectivity, which may provide greater insights into complex groundwater flow paths. To assess this potential, we combined the more traditional approaches collected in this and associated studies, including artificial (dye) and natural (geochemistry, isotopes, and discharge) tracers, with the population genetic data of a groundwater crustacean to determine whether these data can provide insights into seasonal or longer changes in connections between conduits. The data collected included dye trace, hydrographs, geochemistry, and asellid isopod (Caecidotea bicrenenta) population genetics in Fern Cave, AL, USA, a 25 km-long cave system. Combined, these data show the connections between two separate flow paths during flood events as the downstream populations of isopods belonging to the same subpopulation were measured in both systems. Additionally, the sub-populations found in higher elevations of the cave suggest a highly interconnected unsaturated zone that allows for genetic movement in the vadose zone. Although upstream populations show some similarities in genetics, hydrologic barriers, in the form of large waterfalls, likely separate populations within the same stream.

Modeling evaluation of the impact of residual source material on remedial time frame at a former uranium mill site

Groundwater contamination at legacy uranium processing sites is an ongoing global challenge. Plumes at many uranium-contaminated sites are more persistent than originally predicted by groundwater modeling. Previous investigations of uranium plume persistence identified residual and secondary sources that contribute to plume longevity, but there is a remaining need to revise forecasted cleanup times using information about these ongoing sources. The purpose of this study is to investigate the quantitative impact of residual vadose zone sources of uranium on groundwater remediation time frame. This objective was approached by applying numerical uranium transport simulations and uncertainty analysis to a former uranium mill site in the southwestern United States. Information from recent site investigations provided details about the distribution and release characteristics of uranium accumulations in the vadose zone. The residual uranium characteristics were incorporated as decaying source terms in the transport model. A stochastic approach using an iterative ensemble smoother was applied for history matching, and the transport model was used to assess the impact of multiple remedial alternatives on forecasted time frame. The forecasted time frame to achieve the groundwater remediation goal for uranium by monitored natural attenuation is on the order of thousands of years, and treatment of the dissolved plume does not reduce the projected time frame. The large proportion of residual uranium mass remaining in the vadose zone and the gradual leaching rate due to the site's semiarid climate create a long-lived source that can sustain a dissolved plume for thousands of years despite an estimated 99% mass removal achieved during mill tailings disposal. Residual uranium in vadose zone sediments beneath former tailings impoundments could present comparable uranium plume persistence and remediation challenges at other legacy uranium mill sites in semiarid climates. Other remaining uranium-impacted sites are similarly complex, and forecasted remedial time frames are needed to effectively achieve compliance, manage risk, assess the benefits of additional treatment, manage and project costs, and support beneficial site reuse.

Thermal conductivity in a vadose zone: A novel spectral solution and application by the implication of significant coherence of thermal condition in the shallow soil water layer

AbstractIn the context of the heterogeneity in the unsaturated or vadose zone, accurately representing the analytical mechanisms and in‐situ water content within the soil layer poses a significant challenge. Particularly in shallow layers, thermal conditions exhibit rapid changes in response to evolving surface temperatures. This study proposes a hypothesis suggesting that the in situ heat mechanism may notably impact the soil water layer. The research introduces an innovative approach to theoretically uncover thermal conditions, including soil temperature, soil temperature gradients, and heat flux, within the shallow Quaternary gravel layer at various depths through spectral analysis of temporal observations. The study presents a stochastic inverse solution to estimate thermal conductivity by leveraging spectral analysis of soil heat flux and temperature gradients. The findings reveal that thermal conditions exhibit the most prominent periodic fluctuations during the diurnal process over a 24‐hour cycle. The soil temperature gradients and heat flux measurements at depths of 0.1, 0.3, 0.6, and 1.2 m demonstrate their ability to capture changes in soil temperature and air temperature to a certain extent within the frequency domain. Furthermore, the analysis highlights the intrinsic uncertainty and sensitivity of estimating thermal conductivity in heterogeneous soil environments. The wide variability observed in thermal conductivity values, coupled with their dependence on soil type and environmental conditions, underscores the need for careful consideration of these factors in future studies and modeling efforts. Applying the derived inverse spectral solution allows for determining thermal conductivity throughout the soil‐water system across depths ranging from 0.1 to 1.2 m. As a result, this research demonstrates the feasibility and practicality of assessing the thermal conductivity of the soil layer in conjunction with heat flux and temperature gradients through spectral analysis.

A novel hybrid magnetic material based on three-phase saturated core fault current limiter

Installing a three-phase saturated core fault current limiter (TSFCL) is an effective method to limit the increasing short-circuit current in high-voltage alternating current (HVAC) systems. However, the traditional TSFCL uses silicon steels as its working material for the iron core, resulting in poor current-limiting effects, requiring a large DC excitation current, and having a slow response speed. Nanocrystalline alloys have advantages such as a lower saturation point, higher permeability in the unsaturated zone, and a steep B–H curve, making them highly suitable for TSFCL’s applications. However, their poor capability which withstands fault hindered their large-scale commercialization. Therefore, this paper proposes a novel hybrid magnetic material based on TSFCL (HMTFCL), where the materials of the working limbs are replaced by nanocrystalline alloys. Compared to TSFCL, the DC excitation current of HMTFCL decreases by 60.5%. And, the HMTFCL reduces the peak short-circuit current by 23%. Last, the magnetic flux intensity inside the working limb of HMTFCL is reduced to zero more quickly.