Groundwater Table Fluctuations Research Articles

Utilizing Data-Driven Approaches to Forecast Fluctuations in Groundwater Table

Accurate forecasting of fluctuations in groundwater table is crucial for the effective management of regional water resources. This study explores the potential of utilizing remotely sensed satellite data to predict and forecast water table variations. Specifically, two Artificial Neural Network (ANN) models were developed to simulate water table fluctuations at two distinct well sites, namely BA Ea 18 and FR Df 35 in Maryland. One model leveraged the relationship between variations in brightness temperature and water table depth, while the other model was founded on the association between changes in soil moisture and water table depth. These models were trained and validated using recorded water table depths from the aforementioned wells, brightness temperature data acquired from the Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR-E), and soil moisture information generated using the Land Data Assimilation System (LDAS). All models exhibited strong performance in predicting and forecasting water table fluctuations, with root mean square errors ranging from 0.043 m to 0.047 m for a 12-month forecasting horizon. Sensitivity tests revealed that the models displayed greater sensitivity to uncertainties in water table depth compared to uncertainties in both brightness temperature and soil moisture content. This underscores the feasibility of constructing an ANN-based water table prediction model, even in cases where high-resolution remotely sensed data is unavailable. In such situations, the model’s efficacy is contingent on the compatibility of the time series trends in data, such as brightness temperature or soil moisture, with those observed at the study site.

Active Anaerobic Methane Oxidation in the Groundwater Table Fluctuation Zone of Rice Paddies

Rice paddies are globally important sources of methane emissions and also active regions for methane consumption. However, the impact of fluctuating groundwater levels on methane cycling has received limited attention. In this study, we delved into the activity and microbial mechanisms underlying anaerobic oxidation of methane (AOM) in paddy fields. A comprehensive approach was employed, including 13C stable isotope assays, inhibition experiments, real-time quantitative reverse transcription PCR, metagenomic sequencing, and binning technology. Geochemical profiles revealed the abundant coexistence of both methane and electron acceptors in the groundwater table fluctuation (GTF) zone, at a depth of 40–60 cm. Notably, the GTF zone exhibited the highest rate of AOM, potentially linked to the reduction of iron oxides and nitrate. Within this zone, Candidatus Methanoperedens (belonging to the ANME-2d group) dominated the Archaea population, accounting for a remarkable 85.4%. Furthermore, our results from inhibition experiments, RT-qPCR, and metagenome-assembled genome (MAG) analysis highlighted the active role of Ca. Methanoperedens GTF50 in the GTF zone. This microorganism could independently mediate AOM process through the intriguing “reverse methanogenesis” pathway. Considering the similarity in geochemical conditions across different paddy fields, it is likely that Ca. Methanoperedens-mediated AOM is prevalent in the GTF zones.

Modeling water flow and volumetric water content in a degraded peat comparing unimodal with bimodal porosity and flux with pressure head boundary condition

AbstractDegraded peatlands release large amounts of greenhouse gases. The development of effective mitigation and management measures requires an understanding of relevant site‐specific biogeochemical and hydraulic processes. However, the simulation of water fluxes and vadose zone state variables of degrading peatlands relies on proper process description, parameterization of hydraulic functions, and representation of the boundary conditions. The objective of this study was to analyze the effects of unimodal versus bimodal soil hydraulic functions and pressure head versus flux‐type lower boundary conditions (LBCs) on the calculated hydraulic characteristics of a degraded peat profile. HYDRUS‐1D was used to study the hydraulic flow dynamics parameterized with data from a weighable groundwater lysimeter for the period from May 1 to December 31, 2019. Simulations comparing uni‐ and bimodal hydraulic functions showed only minor differences. Simulations of soil water pressure at a depth of 30 cm using a flux‐type LBC (RMSE: 27 cm, where RMSE is root mean square error) performed better than simulations using a pressure head LBC (RMSE: 48 cm). The pressure head LBC performed better at simulating volumetric water contents in 30‐cm depth than the flux LBC variant (RMSE: 0.05 vs. 0.09 cm3 cm−3). For specific site conditions with a shallow, fluctuating groundwater table and temporary air entrapment, the choice of LBC was important for a more accurate simulation of soil water fluxes and volumetric water content.

A multiphysics model for assessing the stability of cold region slope subjected to environmental dynamics

The stability of slopes in cold regions is governed by complex interactions between thermal, hydrological, and mechanical processes. This paper proposes a multiphysics model to investigate the effects of various environmental dynamics on cold region slope stability. These dynamics encompass ambient temperature, wind speed, solar radiation, precipitation, relative humidity, groundwater table fluctuations, and geothermal heat. The concept of the Local Factor of Safety (LFS) was introduced as an index to evaluate the slope safety. A case study was performed using the proposed model with data from a site in Norway. Through this simulation, a heat budget analysis was conducted to quantify environmental impacts on the freezing and thawing states of the slope. Subsequently, the influence of slope temperature and moisture distribution on LFS at moments before freezing, during freezing, and during partial thawing was investigated. A low-high-lower LFS transition pattern was found along the slope surface associated with pre-freezing/freezing/thawing processes. The potential surface-parallel sliding and water blocking effects, characteristics of slope in cold regions, were also captured by the model simulation results. With its comprehensive consideration of climatic factors, the model stands as a promising tool for adapting slope design to climate change. Its multiphysics analysis capability offers an insightful way to elucidate the intricate mechanisms underlying the failure of slopes consist of unsaturated frozen soil.

Characterizing large‐scale preferential flow across Continental United States

AbstractUnderstanding preferential flow (PF) at large scales is critical for improving land management and groundwater (GW) quality. However, limited knowledge of this process, due to soil surface heterogeneity and observational constraints, hampers progress. In this study, we propose estimating effective PF at remote sensing footprint scale (4–9 km) by examining its impact on soil moisture (SM) distribution and shallow groundwater (SGW) table fluctuations (depth 5 m). Effective PF encompasses macropore, funnel, and finger flow pathways influencing SGW table fluctuations. We compiled daily SGW observations (2019–2021) from 19 Continental United States (CONUS) sites through United States Geological Survey. Using inverse modeling in HYDRUS‐1D, SGW data, and climate hazards group infrared precipitation with station data precipitation, we inversely estimated soil hydraulic parameters of the dual‐porosity model (DPM) simulating vertical flow from soil surface to subsurface. Effective PF presence was inferred using three criteria: (1) daily precipitation equal to or exceeding the site‐specific average across multiple (calibration) years, (2) daily observed SGW table increase, and (3) daily difference between observed and DPM simulated SGW tables 50% of the site‐specific root mean square error. Leveraging optimized DPM parameters and associated soil texture, classified PF events, and soil moisture active passive (SMAP L3E) satellite‐based SM, a random forest algorithm with 10‐fold cross validation predicted large‐scale effective PF events. Results indicate seasonal dependence, with spring having the highest occurrence of PF events. The random forest model achieved 98% accuracy in predicting large‐scale PF events, with SMAP SM and saturated hydraulic conductivity (Ks) among the four most impactful variables. Our approach provides a soil hydraulic property, site characteristic, soil texture, and remote sensing‐based generalized tool to analyze large‐scale effective PF.

A multi-scenario multi-model analysis of regional climate projections in a Central–Eastern European agricultural region: assessing shallow groundwater table responses using an aggregated vertical hydrological model

The 2022 drought highlighted Hungary's vulnerability to climate change, especially the Great Hungarian Plain. Soil moisture, which is crucial for agriculture, depends on the position of the shallow groundwater table. This study investigated the effects of climate change on groundwater table fluctuations in more than 500 wells on the plain. An integrated vertical hydrological model, assuming negligible horizontal subsurface flows, employed the Dunay–Varga-Haszonits methodology for evaporation and Kovács approach for the water retention curve. Verified with two meteorological databases, the model was accepted for 463 wells based on NSE > 0.4 and RMSE < 0.5 m criteria. The FORESEE HUN v1.0 dataset proved suitable after spatial consistency tests. Examining 28 bias- and discontinuity-corrected climate model projections on these wells revealed a general decline in the groundwater table. Differences between trends to 2050 and 2100 suggested lower groundwater levels by mid-century. This research highlights climate change impacts in a crucial Central-European agricultural region in the Carpathian Basin and emphasizes the importance of modeling climate change-induced changes in shallow groundwater levels in water resources management.

Determination and assessment of the groundwater table and mineralization in irrigated areas (Xojeli district, Republic of Karakalpakstan)

Irrigated areas in the Aral Sea Basin are becoming highly saline due to the ascendant groundwater table and groundwater mineralization. This, in turn, leads to a decrease in soil fertility in agriculture and negatively affects the food security of basin countries. In the research work, seasonal changes in the groundwater table and mineralization during the periods of 2015 and 2023 were evaluated on the irrigated lands of the Xojeli district in the Republic of Karakalpakstan (Uzbekistan). Field monitoring was carried out on 142 observation wells using traditional methods of measuring the groundwater table and mineralization. Then, the obtained data was statistically analyzed, and maps based on the geoinformation system (GIS) were created by the inverse distance weighting (IDW) interpolation method for the study period. Furthermore, a correlation coefficient analysis was applied to find a relationship between climatic patterns, and groundwater table, and mineralization. Results based on statistical analysis present steady fluctuations in the groundwater table and wild fluctuations in mineralization over a period of nine years. The average water table below surface and mineralization in April was determined by 1.55 m and 2.94 g/l, in July by 1.78 m and 2.96 g/l, and in October by 2.18 m and 2.56 g/l. The visual maps created in accordance with the GIS-based method show that average values for the groundwater table in the irrigated areas were 1.5–2 m and 2–3 m (57.9% and 27.8%), and mineralization was 1-3 g/l and 3-5 g/l (62.4% and 36.5%). A correlation coefficient (r) shows a low relationship between the chosen variables.

PFAS release from the subsurface and capillary fringe during managed aquifer recharge

Managed aquifer recharge (MAR) is a sustainable way of harvesting groundwater in water-stressed urbanized areas, where reclaimed wastewater or stormwater is applied on a large basin to infiltrate water into the groundwater aquifer naturally. This process could rapidly fluctuate the water table and move the capillary fringe boundary, and the change in flow dynamic and associated geochemical changes could trigger the release of sequestered pollutants, including per- and polyfluoroalkyl substances (PFAS), also known as ‘forever chemicals’, from the subsurface and capillary fringe. Yet, the potential of PFAS release from the subsurface and capillary zone during recharge events when the water table rapidly fluctuates has not been evaluated. This study uses laboratory column experiments to simulate PFAS release from pre-contaminated subsurface and capillary fringe during groundwater table fluctuation. The results reveal that the groundwater level fluctuations during MAR increased the release of perfluorobutanesulfonic acid (PFBS) and perfluorooctanesulfonic acid (PFOS) from the capillary fringe, but the fraction released depended on PFAS type and their association with soil colloids. A higher proportion of PFOS in column effluent was found to be associated with particles, while a greater portion of released PFBS was in a free or dissolved state. The direction of water table fluctuation did not affect the release of PFAS in this study. A lack of change in the concentration of bromide, a conservative tracer, during flow interruption, indicates that diffusion of PFAS through reconnected pores during water table rise had an insignificant effect on PFAS release. Overall, this study provides insights into how PFAS can be released from the subsurface and capillary fringe during managed aquifer recharge when the groundwater level is expected to fluctuate quickly.

Assessing land use effects on ecohydrological partitioning in the critical zone through isotope‐aided modelling

AbstractStable water isotopes are naturally occurring conservative tracers that can ‘fingerprint’ water sources and track ecohydrological fluxes across the critical zone (CZ). Parsimonious, tracer‐aided models allow effective quantification of the ecohydrological partitioning of rainfall into different water fluxes. We incorporated stable water isotopes into a one‐dimensional, tracer‐aided model (EcoIsoPlot) to follow the pathway of precipitation through the CZ at a lowland catchment—the long‐term experimental Demnitzer Millcreek Catchment (DMC), Germany—with contrasting vegetation covers (forest, agroforestry, grassland and arable). Precipitation (amount and δ2H), potential evapotranspiration (PET), leaf area index (LAI), air temperature and relative humidity were used as input data for modelling the growing season of 2021. The year had relatively average overall wetness, but a dry, cold spring with snowfall, and an exceptionally large summer storm event (~60 mm precipitation). Multi‐criteria calibration of the model was conducted using depth‐specific soil moisture and soil water δ2H measurements as targets. The novel incorporation of isotopes into model calibration constrained process representation of the estimated water balance with reasonable simulations and uncertainty bounds for water partitioning. Throughout the soil profile, soil moisture dynamics and stable water isotope variations were captured reasonably well. Green water fluxes (evapotranspiration) were highest at the forest site and blue water fluxes (groundwater recharge) highest at the grassland. Comparing simulations with estimated potential evapotranspiration (ET) and measured groundwater table fluctuations added further confidence to the modelling result. Overall, these may suggest a slight underestimation of ET and slight overestimation of recharge, though the results are similar to previous findings. Our study demonstrated the potential of stable water isotope data to enhance relatively simple, transferrable approaches to ecohydrological modelling of water fluxes in the CZ and to help improve model consistency. Such low‐parameterised tracer‐aided models have major potential for evidence‐based applications to aid management and help stakeholder communication.

A new model for simulating root water uptake by vegetation under the impact of a dynamic groundwater table in arid regions

AbstractEcological water conveyance is an effective measure to mitigate or reverse vegetation ecosystem degradation in arid regions, which can lead to frequent fluctuations in the groundwater table. The depth of soil water that vegetation takes up varies in response to groundwater table fluctuations in arid environments. To better characterize the root water uptake process under dynamic changes in the groundwater table in arid regions, this study proposed a new model for simulating root water uptake. The model reduces the dominant effect of root density on water uptake by introducing a correction factor and accounts for the effect of changes in the water content profile on root water uptake in arid areas. The new model was incorporated into the HYDRUS code and tested against the monitoring data of typical vegetation in the arid region of northwestern China. The results demonstrated that the soil water content simulated by the new model matched well with the observed data, which was consistent with the water uptake process under the fluctuations of the groundwater table at the study site. Compared with other models, this model can flexibly alter water uptake layers according to soil moisture conditions in arid conditions, thus providing a new method to depict the dynamic process of water uptake influenced by fluctuations in the groundwater table.

The Migration Mechanism of BTEX in Single- and Double-Lithology Soil Columns under Groundwater Table Fluctuation.

The migration of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Groundwater table fluctuation can not only affect contaminant migration but also redox conditions, bacterial communities, and contaminant degradation. Understanding LNAPLs' (e.g., benzene, toluene, ethylbenzene, and xylene (BTEX)) behavior within porous media is critical for the high efficiency of most in situ remediation systems. A laboratory study of single- and double-lithology soil column investigation of the groundwater table fluctuation effect on BTEX transport, using benzene and toluene as typical compounds, in a typical representative model of aquifers subjected to water table fluctuation was undertaken in this study. The results show that benzene and toluene migration in single-lithology soil columns packed with sand was mainly affected by flushing due to the hydraulic force induced by water table fluctuations and that the double-lithology soil column packed with sand and silt was significantly affected by retention due to the higher adsorption induced by 10 cm of silt. The dissolution mainly correlated with the BTEX migration in saturated zones, and the contaminant concentration increased when the water table fell and decreased when the water table rose. For a contaminated site with a single-lithology structure consisting of sand, more attention should be paid to organic contaminant removal within the groundwater, and a double-lithology structure containing silt is more suited to the removal of organic contaminants from the silt layer. The difference in biodegradation kinetics between the groundwater table fluctuation (GTF) zone and the saturated zone should be better understood for the remediation of BTEX compounds.

Modeling BTEX Multiphase Partitioning with Soil Vapor Extraction under Groundwater Table Fluctuation Using the TMVOC Model

The effects of groundwater table fluctuation (GTF) on the remediation of a petrochemically polluted riverside using soil vapor extraction (SVE) were investigated. The migration and transformation of benzene, toluene, ethylbenzene, and o-xylene (BTEX) in cases of natural attenuation, SVE without GTF, and SVE with GTF were simulated using the TMVOC model. The results showed that the optimized extraction well pressure and influencing radius of the target site were 0.90 atm and 8 m, respectively. The removal rates of BTEX in cases of natural attenuation, SVE without GTF, and SVE with GTF were 11.49%, 85.16%, and 97.33%, respectively. The removal rate of BTEX was maximized in the case of SVE with a GTF amplitude of 0.5 m to 1 m. The removal rates of benzene (99.99%), toluene (99.74%), ethylbenzene (96.37%), and o-xylene (94.72%) were maximized in the case of SVE with GTF. For the cases of SVE without GTF and SVE with GTF, mass losses of BTEX in gaseous (0.05 kg, 0.05 kg, respectively) and aqueous phases (5.46 kg, 5.87 kg, respectively) were consistent. However, the mass loss of BTEX in the non-aqueous phase liquid (NAPL) phase in the case of SVE with GTF (155.13 kg) exceeded that in the case of SVE without GTF (135.41 kg). This is because GTF positively affected both the solubility and volatility of BTEX in the NAPL phase. With the groundwater table decreasing, flows of gas and gaseous pollutants increased by 25% along the vertical section. At this stage, the removal rates of volatile organic compounds can be further improved by increasing the flow of the extraction well.

Variation of some Water Quality Parameters with Fluctuation of Groundwater Table in Wana Sub-District Northern Iraq

This study aims to investigate the effect of groundwater fluctuation on some water quality characteristics in the Wana region of Northern Iraq. The fluctuations in water table levels in 18 tube wells were monitored to find out if there is a relationship between water table levels with some water quality factors. Groundwater samples were collected monthly from September 2020 to April 2021. Electric conductivity (EC), temperature, pH, water table level, total hardness (TH), sulfate and nitrate concentrations were all measured monthly for eight months. The results showed a wide range of water salinity variation ranging from 715 to 4420 µmohs/cm, with more than half of the examined samples exceeding 3000 µmohs/cm. Even in the same wells, water salinity varied during the monthly monitoring. The depth to the water table ranged from 3.39 to 37.56 m, depending on the topography, recharge rate, and aquifer conditions in the area. All of the wells produced very hard water as a result of the dissolution of gypsum and anhydrite bedrock, with about 84% having high sulphate concentrations of over 250 mg/l. More than a quarter of the samples tested showed pollution with nitrate at concentrations extremely close to or over 50 mg/l. It was found that there is no obvious correlation between groundwater quality properties and the fluctuation of the water table.

ASSESSMENT OF THE IMPACT OF GROUNDWATER TABLE FLUCTUATIONS ON THE TRANSFORMATION OF SUBSURFACE CONTAMINATION WITH PETROLEUM PRODUCTS

This paper describes the actual problem of groundwater contamination with petroleum products and its transformation under the influence of climatic factors. The global experience of studying the influence of groundwater table fluctuations on the transformation of petroleum contamination, in particular, the processes of redistribution of mobile petroleum products, dissolution, evaporation, and biodegradation of hydrocarbon compounds, as well as the difference between the actual thickness of a mobile petroleum product layer in porous media and the apparent thickness of a mobile petroleum product layer in a monitoring well was analyzed, which is important to plan remedial actions. The impact of groundwater table fluctuations on transformation of the petroleum contamination source within the warehouse of fuels and lubricants of the Boryspil airport was studied. As a result of groundwater table fluctuations, kerosene was “smeared” in the vadose zone, which led to an increase in the soil contamination area. During the observation period, a mobile kerosene layer almost disappeared when a groundwater table rose and restored when a groundwater table decreased, while the vadose zone was additionally contaminated since a new capillary zone was formed during each rise ofa groundwater table and kerosene. The long-term amplitude of groundwater table fluctuations was 2.4 m, and apetroleum contamination zone was also within these limits. During the observation period, the largest area of groundwater contamination with dissolved petroleum products was observed at the lowest groundwater table elevations in 2016. The highest concentration of dissolved hydrocarbons in groundwater (75.98 mg/dm3) wasfound within amobile kerosene lens. Beyond the mobile kerosene lens, spreading of groundwater contamination with dissolved hydrocarbons is limited. The analysis of the monitoring data of the petroleum contamination source within the warehouse of fuels and lubricants of the Boryspil airport indicates that at present subsurface contamination with petroleum products is localized, and its further spreading is not expected. It is recommended to continue in the future monitoring of the natural attenuation of subsurface contamination.

Does Microbial and Faunal Pattern Correspond to Dynamics in Hydrogeology and Hydrochemistry? Comparative Study of Two Isolated Groundwater Ecosystems in Münsterland, Germany

The objective of this study was to assess the temporal and spatial variability of aquatic invertebrates and microbial parameters (biomass and activity) with environmental data in springs, and to determine the impact of key parameters on the ecological situation of a groundwater system. Eight springs in the two study areas of Baumberge and Schöppinger Berg (W-NW of Münster, North Rhine Westphalia, Germany) were sampled at three sampling campaigns between 2018 and 2019. Physicochemical parameters of the spring samples and abundances of aquatic invertebrates were determined at each sampling event. Samples for hydro(geo)chemical and microbial analyses were collected during each sampling campaign in the springs. Spearman correlation and principal component analysis were used to identify the key parameters. The abundance of aquatic invertebrates and microbial activity were significantly positively correlated with groundwater table fluctuation. The abundance of stygobite individuals was significantly positively correlated with the Groundwater-Fauna-Index and phosphate in Baumberge, and negatively correlated with chloride in Schöppinger Berg. Most notably, the stable isotopes of water and microbial activity were significantly inversely correlated. The hydro(geo)chemical results showed no significant spatial differences in groundwater in both groundwater systems. Stable isotopes of water indicate a meteoric origin, with an effect of evaporation for two months, even though the downward percolation and groundwater recharge rates are high. The nitrate concentration was higher than 50 mg/L only in SB due to the agricultural activities. Nitrate input into groundwater comes from two sources in Baumberge, while it comes from one source in Schöppinger Berg. There was no evidence of denitrification in both areas. Secondary gypsum is assumed to be the source of sulfate in groundwater in Schöppinger Berg, but anaerobic oxidation of pyrite in the deeper part of the groundwater system as a source of sulfate cannot be excluded.

Groundwater table fluctuation: A driving force affecting nitrogen transformation in nitrate-contaminated groundwater

Groundwater table fluctuation alters the biochemical environment and nitrogen transformation, leading to periodic changes in groundwater nitrate concentration. A microcosm experiment of groundwater table fluctuation was designed to explore the underlying mechanism. The dissolved oxygen (DO), bacterial community, functional gene groups and associated nitrogen transformation were investigated based on field scenario. The results showed that groundwater rising reduced the average nitrate concentration, while falling aggravated it. Owing to the variations in groundwater table, the DO concentration underwent periodic changes. Furthermore, the abundance and diversity of soil bacteria were enriched and the structure of the microbial community was altered. Nitrogen transformation biomarkers such as Arthrobacter sp., Bacillus sp., Chloroflexi sp. and Acidobacteriota sp. as well as nitrogen transformation functional genes were identified. A structure equation model was established which demonstrated that groundwater table fluctuation altered DO and the dominant bacterial abundance, which in turn modified the functional gene groups and nitrogen transformation. This study broadens the understanding of how and to what extent groundwater table fluctuation affects nitrogen transformation and is vital for assessing and managing risks associated with groundwater nitrate contamination

Vertical Transportation Diversity of Petroleum Pollutants under Groundwater Fluctuations and the Instructions for Remediation Strategy

Based on the information from an actual petroleum-contaminated site, a one-dimensional soil column was used to examine the vertical transportation diversities of different petroleum components under the influence of water table fluctuations, and the results revealed the following: (1) There were two obvious pollution accumulation zones under the condition of water table fluctuations: (i) The pollution infiltration zone dominated by the residual phase was formed at the leakage position, and (ii) the floating zone dominated by the free phase was formed near the water table. Combined with the viscosity of the organic components, the concentrations of the residual phase were octanoic acid &gt; hexadecane &gt; cyclohexane &gt; toluene. Compared to coarse sand, clay can adsorb more components. (2) Different fluctuation frequencies had a great influence on the migration process of components. The free phase can transfer into the residual phase during the low groundwater table fluctuation. In the case of high-frequency groundwater fluctuations, there were more free phase components that can be carried by the water flow. However, due to the continuous flushing by the water, pollutants were finally spread to the whole underground system. (3) A cost-effectiveness remediation strategy is based on the difference in pollutant transportation. Therefore, the conclusions in this paper are fully applied in the actual contaminated sites. Specifically, the air-sparing (AS) and soil vapor extraction (SVE) devices were installed in the vadose zone to remove volatile substances (such as toluene). The permeable reactive barriers (PRBs) were set in the groundwater fluctuation zone to repair the residual pollutants (alkanes, cyclane, and asphaltenes hydrocarbons) that are continuously converted from the residual phase to the dissolved phase and free phase due to water level fluctuations. Hence, the results of this study provided a specific, targeted, and comprehensive strategy for petroleum pollution treatment.

Monitoring Methodology Study of a Reservoir Built on the Karst Depression: A Large Scale Laboratory Simulation Test.

The karst depression with a natural negative landform is favorable for reservoir construction with less excavation work. The underground air-water pressure would be complicated after the construction of a reservoir that blocks the natural air-water channel (sinkhole, karst channel, etc.). To develop a monitoring system for the reservoir, a large-scale laboratory simulation test was carried out to study the air-pressure evolution and water migration process during water table fluctuation after the blockage of the sinkhole in a karst depression. The results are as follows. (1) The positive pressure jacking effect and the negative pressure sucking effect were observed in the karst channel and inside the model during groundwater table fluctuation. (2) A water imbibition test on the rock-like material was carried out with layered resistivity and layered NMR measurement. The relationship of resistivity and water saturation was developed based on Archie's equation. (3) The resistivity evolution during the test was monitored using the high-density electronic resistivity imaging method. The resistivity of the measured profile was sensitive to the variation of the water level, and the water migration process was quantified by the resistivity to water saturation conversion. (4) The suitability of many techniques for monitoring a reservoir built on the karst depression was discussed. The resistivity monitoring technique combined with the air-water pressure monitoring technique could provide useful information for safety and reliability assessment.

Temporal moment-based approach to understand the dissolved-phase LNAPL recovery and associated characteristics in the porous system under dynamic groundwater table conditions

Abstract The dissolved-phase hydrocarbon recovery can be the first step in decontaminating the soil–water system if spilled with light/dense non-aqueous phase liquid (L/D-NAPL). This study proposes a temporal moment-based approach to investigate the effectiveness of groundwater table manipulations for recovering dissolved-phase byproducts of light non-aqueous phase liquid (LNAPL) from the subsurface system. Temporal moments were computed utilizing experimentally observed and HYDRUS-simulated dissolved-phase toluene concentration data, representative of LNAPL, under stable and dynamic groundwater table fluctuation (GWTF) scenarios. Zeroth temporal moment (ZTM) showed that the hydrocarbon mass recovery varied from 1,804 to 5,190.6 mg/L × h, with the highest variation for the rapid GWTF scenario. An increase in the ZTM of hydrocarbon was observed with an increase in the rate of change of magnitude of the water table and pore velocity fluctuation as in the case of a rapid GWTF as compared to a stable GWTF case. The value of mean residence time for the stable groundwater table case was highest for the entire experimental duration, followed by slow, general, and rapid cases. Temporal moment analysis revealed that the high dissolved-phase hydrocarbon recovery could be achieved by manipulating groundwater table conditions. The present study provides a powerful technique to improve dissolved hydrocarbon remediation in mineral aquifers using hydrological restorations.

Application of the electrical resistivity tomography in groundwater detection on loess plateau

Agricultural irrigation of the South Jingyang tableland in Shaanxi Province, China has led to a continuous rise of the groundwater level and has triggered a series of loess landslides, thereby seriously affecting the life and property safety of local residents. Research shows that the major cause of the landslide in the loess layer of the South Jingyang tableland is the rising groundwater level. Therefore, the research on the formation mechanism of landslide in this area should include the investigation of the stratigraphic structure and groundwater level distribution characteristics. On this basis, a series of approaches, such as electrical resistivity tomography (ERT), borehole, and laboratory tests, was carried out on the South Jingyang tableland, and the groundwater level distribution and stratigraphic structure in the study area were determined. The qualitative relationship between resistivity value and water content at different depths was detected using the inversion results of ERT and borehole data. Through laboratory tests, the quantitative relationship between resistivity values under different water contents was established. The precise depth of the groundwater level was inferred by connecting the qualitative relationship with the quantitative relationship, and then a detailed 3D geological model was established by linking the inversion results of ERT with the field borehole lithology data and geological survey data. The detection results show that when the qualitative and quantitative analyses of the ERT inversion results were combined, the distribution of the groundwater level was accurately judged. The ERT is effective in reflecting the stratigraphic structure and hydrological characteristics of the Loess Plateau, and its potential as a supplementary technology for detecting the groundwater level is reasonable. This study addresses the limitation and inaccuracy in determining the stratum structure and groundwater level by solely relying on borehole information or ERT. The established 3D geological model not only provides a basis for the study of groundwater table fluctuation, but also a technical guidance for the stability evaluation of loess slope, landslide prediction, and early warning in the study area.