Steady-state Groundwater Flow Research Articles

Water and carbon fluxes from a supra-permafrost aquifer to a stream across hydrologic states

Supra-permafrost aquifers within the active layer are present in the Arctic during summer. Permafrost thawing due to Arctic warming can liberate previously frozen particulate organic matter (POM) in soils to leach into groundwater as dissolved organic carbon (DOC). DOC transport from groundwater to surface water is poorly understood because of the unquantified variability in subsurface properties and hydrological environments. These dynamics must be better characterized because DOC transport to surface waters is critical to predict the long-term fate of recently thawed carbon in permafrost environments. Here, we used distributed Darcy’s Law calculations to quantify groundwater and DOC fluxes into Imnavait Creek, Alaska, a representative headwater stream in a continuous permafrost watershed. We developed a statistical ensemble approach to model the parameter variability and range of potential contributions of steady-state groundwater flow to the creek. We quantified the model prediction uncertainty using statistical sampling of in-situ, active-layer soil hydro-stratigraphy (water table, ice table, and soil stratigraphy), high-resolution topography data, and DOC data. Moreover, the predicted groundwater discharge values representing all possible hydrologic conditions towards the end of the thawing season were also considered given the potential variability in saturation. The model predictions were similar to and span most of the observed range of Imnavait Creek streamflow, especially during recession periods, and also during saturation excess overland flow. As the Arctic warms and supra-permafrost aquifers deepen, groundwater flow is expected to increase. This increase is expected to impact stream, river, and lake biogeochemical processes by dissolving and mobilizing more soil constituents in continuous permafrost regions. This study highlights how quantifying the uncertainty of hydro-stratigraphical input parameters helps understand and predict supra-permafrost aquifer dynamics and connectivity to aquatic systems using a simple, but scalable, modeling approach.

Mathematical modelling for groundwater management for multilayers aquifers (Erbil basin)

This study addresses the pressing issues of groundwater depletion and drought problems in the Erbil basin, a vital resource region in the Middle East. Focused on an area of strategic importance due to its large size and critical water resources, the study employs the Groundwater Modeling System (GMS) software to create a detailed 3D hydrogeological model based on extensive borehole data. With over 240 boreholes analyzed, the study strategically selects 70 accurate wells drilled by the Groundwater Directorate. The construction of the 3D stratigraphic models for the Erbil basin relies on three main historical data including boreholes, geological formations and a comprehensive approach, incorporating deep well logging data and the definition of distinct geological layers. By discerning the presence of previous and impervious layers, the model effectively categorizes the aquifer types within the Erbil basin. The aquifer system is delineated based on stratigraphic units, designating materials with high conductivity (silt, sand, and gravel) as aquifers and clay (or claystone) as aquitards. A 3D steady-state groundwater flow model is successfully executed, employing PEST pilot point for automated parameter estimation. The model, validated with a coefficient of determination (R2) of 0.9998, reveals hydraulic conductivity values ranging from 0.000980705 to 100 m/day and a recharge value of 0.000976443 m/day. The study classifies Erbil's aquifer types as unconfined, confined, and semi-confined, providing a valuable foundation for groundwater management. The primary objective of this study is to construct a calibrated numerical groundwater model for the multi-aquifer system in the Erbil basin. The model aims to serve as a robust tool for analyzing the sustainability of diverse groundwater infrastructure development strategies within the region. The Erbil basin poses unique challenges for groundwater modeling, marked by a scarcity of critical data such as monitoring well information, pumping rates, recharge rates, and flow budgets. In response to these limitations, the study adopts an innovative approach by integrating in situ data with earth observation data. The integration of these datasets seeks to overcome data constraints and enhance the accuracy of the groundwater model. By achieving calibration and validation of the numerical model, this research strives to provide a valuable resource for decision-makers, planners, and stakeholders involved in groundwater management in the Erbil basin. Ultimately, the study aims to contribute to the development of sustainable and effective strategies for the utilization and preservation of groundwater resources in this vital region and also to enhance practical management strategies for the Erbil groundwater basin, ensuring sustainable utilization of the crucial sub-surface water resources, an objective successfully achieved through this research.

Mathematical Modeling of Transient and Steady-State Groundwater Flow in a Confined Aquifer

Groundwater flow problems can be expressed mathematically with the employ of partial differential equations and which could be solved analytically or numerically. The results obtained showed that the direction of flow of groundwater is from a region of higher hydraulic head to a lower hydraulic head, and that pumping groundwater from the well faster than it is recharged leads to dry wells. The numerical methods used for the analysis of Transient and steady-state groundwater flow produced efficient, effective and accurate solution and can be used for all real-life problems.

New particle tracking method for 2D steady-state groundwater flow around wells: A modified algorithm using the stream function

Particle tracking is an essential process in analyzing groundwater flow and solute transport in aquifers. A drawback of existing particle tracking methods, which are based on approximate estimations of the velocity in a time step, is the accumulative errors of numerous time steps would lead to deviation of particles away from the exact streamlines, especially when pumping and injecting wells exist. In this study, to improve the accuracy of particle tracking for the two-dimensional (2D) steady-state flow around wells, we propose a stream-function-based (SFB) particle tracking method in which a particle is traced along the exact streamline with a given value of the stream function, and the branch cut effect caused by the multivalued stream function around a well is eliminated. Three synthetic cases are used to demonstrate the advantages of the SFB method over the existing Pollock method and the fourth-order Runge-Kutta method. In the cases of a single pumping well and an injecting-pumping well pair, the Pollock and Runge-Kutta methods yield pathways that may be far away from the exact streamline, but the SFB method performs much better. In the case with a pumping well and two injecting wells, the SFB method successfully delineated a narrow capture zone of the pumping well, which requires a high accuracy particle tracking process. Moreover, the accuracy of particle positions obtained by the SFB method is insensitive to the step-travel distance. The study would be useful for accurate investigation of flow fields in aquifers disturbed by wells.

Groundwater Flow Modeling of A Microwatershed using Visual Modflow Flex

The present study attempts to make a simulation of groundwater flow modeling in Chikkodi micro-watershed Belagavi (District), Karnataka. A two-layer conceptualization and the three-dimensional groundwater flow model are primarily underlain by weathered basalt and fractured basalt. The first layer weathered zone is 30m from the ground surface and the second layer fractured zone is 80m below the ground surface spread over 20 rows and 20 columns. The cell height is 674m and the cell width is 440m. The work described here built a groundwater flow model in the micro-watershed using Visual MODFLOW Flex. The steady-state groundwater flow model was then numerically projected in April 2020 using seventeen observation wells using the present stress levels. The model aims to quantify input and output stresses and pinpoint the basin's overstressed regions. The water budget analysis estimates that evapotranspiration loss makes up 56.54% of the basin's total groundwater recharge while overall groundwater leaks from river systems are 28.72%. The findings indicated that the southern section of the basin is undergoing severe aquifer stress as a result of river overflow and evapotranspiration. To improve groundwater levels, it is suggested that artificial recharge structures should be developed in and near Chikkodi village at appropriate sites. The trial-and-error approach was used to assess the sensitivity of the calibrated model, and it was discovered that the model is extremely sensitive to changes in hydraulic conductivity and recharge levels. Model performance is excellent, with R2, RMSE, and NRMSE values of 0.97, 5.34, and 13.23% of the assessing criteria.

Assessing Vulnerability of Regional-Scale Aquifer-Aquitard Systems in East Gulf Coastal Plain of Alabama by Developing Groundwater Flow and Transport Models

Groundwater vulnerability assessment helps subsurface water resources management by providing scientific information for decision-makers. Rigorous, quantitative assessment of groundwater vulnerability usually requires process-based approaches such as groundwater flow and transport modeling, which have seldom been used for large aquifer-aquitard systems due to limited data and high model uncertainty. To quantify the vulnerability of regional-scale aquifer-aquitard systems in the East Gulf Coastal Plain of Alabama, a three-dimensional (3D) steady-state groundwater flow model was developed using MODFLOW, after applying detailed hydrogeologic information to characterize seven main aquifers bounded by aquitards. The velocity field calibrated by observed groundwater heads was then applied to calculate groundwater age and residence time for this 3D aquifer-aquitard system via backward/forward particle tracking. Radioactive isotope data (14C and 36Cl) were used to calibrate the backward particle tracking model. Results showed that shallow groundwater (<300 ft below the groundwater table) in southern Alabama is mainly the Anthropocene age (25–75 years) and hence susceptible to surface contamination, while the deep aquifer-aquitard systems (700 ft or deeper below the groundwater table) contain “fossil” waters and may be safe from modern contamination if there is no artificial recharge/discharge. Variable horizontal and vertical vulnerability maps for southern Alabama aquifer-aquitard systems reflect hydrologic conditions and intermediate-scale aquifer-aquitard architectures in the regional-scale models. These large-scale flow/transport models with coarse resolutions reasonably characterize the broad distribution and vertical fluctuation of groundwater ages, probably due to aquifer-aquitard structures being captured reliably in the geology model. Parameter sensitivity analysis, vadose zone percolation time, wavelet analysis, and a preliminary extension to transient flow were also discussed to support the aquifer vulnerability assessment indexed by groundwater ages for southern Alabama.

Hydrogeological modeling of the Roussillon coastal aquifer (France): stochastic inversion and analysis of future stresses

Global climate change-induced stresses on coastal water resources include water use restrictions, saline intrusions, and permanently modifying or damaging regional resources. Groundwater in coastal regions is often the only freshwater resource available, so an in-depth understanding of the aquifer, and the aquifer’s response to climate change, is essential for decision-makers. In this study, we focus on the coastal aquifer of Roussillon (southern France) by developing and investigating a steady-state groundwater flow model (MODFLOW 6) and calibrated with PEST++ on a Python interface (FloPy and PyEmu). Model input and boundary conditions are constrained by various scenarios of climate projections by 2080, with model results predicting the aquifer’s response (and associated uncertainty) to these external forcings. Using simple assumptions of intrusion estimates, model results highlight both strong climatic and anthropogenic impacts on the water table. These include aquifer drawdowns reaching several meters locally, and the seawater interface advancing locally several hundred meters inland and rising by several meters. Intrusions of this magnitude risk endangering exploited water wells and their sustainability. Our results demonstrate the critical importance of properly characterizing the geology and its heterogeneity for understanding aquifers at risk because poor predictions may lead to inappropriate decisions, putting critical resources at risk, particularly in coastal environments.

Quantifying Groundwater Infiltrations into Subway Lines and Underground Car Parks Using MODFLOW-USG

Urbanization is a worldwide process that recently has culminated in wider use of the subsurface, determining a significant interaction between groundwater and underground infrastructures. This can result in infiltrations, corrosion, and stability issues for the subsurface elements. Numerical models are the most applied tools to manage these situations. Using MODFLOW-USG and combining the use of Wall (HFB) and DRN packages, this study aimed at simulating underground infrastructures (i.e., subway lines and public car parks) and quantifying their infiltrations. This issue has been deeply investigated to evaluate water inrush during tunnel construction, but problems also occur with regard to the operation of tunnels. The methodology has involved developing a steady-state groundwater flow model, calibrated against a maximum groundwater condition, for the western portion of Milan city (Northern Italy, Lombardy Region). Overall findings pointed out that the most impacted areas are sections of subway tunnels already identified as submerged. This spatial coherence with historical information could act both as validation of the model and a step forward, as infiltrations resulting from an interaction with the water table were quantified. The methodology allowed for the improvement of the urban conceptual model and could support the stakeholders in adopting proper measures to manage the interactions between groundwater and the underground infrastructures.

Characterizing groundwater heat transport in a complex lowland aquifer using paleo-temperature reconstruction, satellite data, temperature–depth profiles, and numerical models

Abstract. Heat is a naturally occurring, widespread groundwater tracer that can be used to identify flow patterns in groundwater systems. Temperature measurements, being relatively inexpensive and effortless to gather, represent a valuable source of information which can be exploited to reduce uncertainties on groundwater flow, and, for example, support performance assessment studies on waste disposal sites. In a lowland setting, however, hydraulic gradients are typically small, and whether temperature measurements can be used to inform us about catchment-scale groundwater flow remains an open question. For the Neogene Aquifer in Flanders, groundwater flow and solute transport models have been developed in the framework of safety and feasibility studies for the underlying Boom Clay formation as a potential host rock for geological disposal of radioactive waste. However, the simulated fluxes by these models are still subject to large uncertainties as they are typically constrained by hydraulic heads only. In the current study, we use a state-of-the-art 3D steady-state groundwater flow model, calibrated against hydraulic head measurements, to build a 3D transient heat transport model, for assessing the use of heat as an additional state variable, in a lowland setting and at the catchment scale. We therefore use temperature–depth (TD) profiles as additional state variable observations for inverse conditioning. Furthermore, a Holocene paleo-temperature time curve was constructed based on paleo-temperature reconstructions in Europe from several sources in combination with land surface temperature (LST) remotely sensed monthly data from 2001 to 2019 (retrieved from NASA's Moderate Resolution Imaging Spectroradiometer, MODIS). The aim of the research is to understand the mechanisms of heat transport and to characterize the temperature distribution and dynamics in the Neogene Aquifer. The simulation results clearly underline advection/convection and conduction as the major heat transport mechanisms, with a reduced role of advection/convection in zones where flux magnitudes are low, which suggests that temperature is also a useful indicator in a lowland setting. Furthermore, the performed scenarios highlight the important roles of (i) surface hydrological features and withdrawals driving local groundwater flow systems and (ii) the inclusion of subsurface features like faults in the conceptualization and development of hydrogeological investigations. These findings serve as a proxy of the influence of advective transport and barrier/conduit role of faults, particularly for the Rauw fault in this case, and suggest that solutes released from the Boom Clay might be affected in similar ways.

Combining the Morris method and multiple error metrics to assess aquifer characteristics and recharge in the lower Ticino Basin, in Italy

Groundwater flow model accuracy is often limited by the uncertainty in model parameters that characterize aquifer properties and aquifer recharge. Aquifer properties such as hydraulic conductivity can have an uncertainty spanning orders of magnitude. Meanwhile, parameters used to configure model boundary conditions can introduce additional uncertainty. In this study, the Morris method of sensitivity analysis is performed on multiple quantities of interest to assess the sensitivity of a steady-state groundwater flow model to uncertain input parameters. The Morris method determines which of these parameters are less influential on model outputs. Uninfluential parameters can be set constant during subsequent parameter optimization to reduce computational expense. Combining multiple quantities of interest (e.g., RMSE, groundwater fluxes) when performing both the Morris method and parameter optimization offers a more complete assessment of groundwater models, providing a more reliable and physically consistent estimate of uncertain parameters. The parameter optimization procedure also provides an estimate of the residual uncertainty in the parameter values, resulting in a more complete estimate of the remaining uncertainty. By employing such techniques, the current study was able to estimate the aquifer hydraulic conductivity and recharge rate due to rice field irrigation in a groundwater basin in Northern Italy, revealing that a significant proportion of surficial aquifer recharge (approximately 81–94%) during late summer is due to the flood irrigation practices applied to these fields.

New semi-analytical solutions to the radial advection-dispersion equation for solute transport in a transient divergent radial flow

Solute transport through radial advection–dispersion is a common phenomenon in many applications, such as aquifer decontamination, heat exchange for geothermal exploration, and tracer testing. Numerous analytical solutions to the problem of tracer testing in a radially divergent flow field are available for fitting breakthrough curves. However, all of these analytical solutions assume non-uniform flow velocity based on Thiem's solution, which varies only spatially, not temporally. Although an injection well with a constant injection rate in a tracer test causes both spatial and temporal variability of the radial flow field, previous analytical studies have employed a steady-state groundwater flow solution, i.e. Thiem's solution, to derive analytical solutions for breakthrough curves or spatial concentration distribution curves. To the best of our knowledge, no analytical solution to the radial advection–dispersion equation under spatially and temporally variable flow conditions driven by injection at a constant rate is currently available.Here, we propose a novel semi-analytical solution for describing solute transport in spatially and temporally variable flow induced by an injection well with a constant injection rate. We find that, above certain threshold values of dimensionless parameters related to aquifer flow properties, solute transport parameters, and the injection rate, the differences between previous analytical strategies our proposed semi-analytical solution are negligible. These threshold values tend to increase more sharply with an instantaneous injection source than a continuous injection source. In other words, it is more difficult for an instantaneous injection source to reach the condition where the difference between our approach and previous ones is negligible than for a continuous injection source type. Our findings clarify when existing analytical solutions can be reasonably used for parameter estimation through fitting of the breakthrough curve to field data and when the proposed semi-analytical solution is a better alternative.

Aquifer-Peatland Hydrological Connectivity and Controlling Factors in Boreal Peatlands

The conditions in which groundwater inflow occurs in boreal peatlands and its contribution to peatland water balance are still poorly understood. The objectives of this research were to quantify the hydrological connectivity between a surficial aquifer and a peatland, and to identify the controlling factors in boreal peatlands of north-central Quebec (Canada). The peatlands were instrumented with piezometers and groundwater levels were monitored during two growing seasons. Hydraulic conductivities were measured on peat cores and in situ, groundwater inflows and outflows were calculated using the Darcy equation. The peatland water budgets were simulated for the two peatlands with a steady-state groundwater flow model to verify flow hypotheses, to quantify unmeasured flows and to explore recharge scenarios leading to changes in connectivity. The two peatlands have contrasted water budgets, with recharge representing the largest inflow (78%) and subsurface runoff representing the largest outflow (85%) the peatland with the smallest catchment area (Misask). The peatland with the largest catchment area (Cheinu) is also located downgradient within the regional watershed. Its inflows are dominated by groundwater (56%) and its outflows are mostly towards subsurface runoff (74%). The two peatlands are in conditions of precipitation excess and a recharge reduction would not affect their peatland heads markedly (<10 cm). However, recharge changes could induce larger modifications in groundwater inflows and outflows for the peatland with a larger catchment area. The dominating peatland hydrological functions are thus contrasted at the two sites, and it is hypothesized that the water table depths thresholds triggering changes between storage, transmission and runoff functions are also different. Although further studies remain to be done to understand how hydrological conditions change through time, and ultimately what are the long-term impacts of a changing climate on hydrology, vegetation and carbon accumulation, this work shows that understanding peatland hydrology requires to consider hydrological conditions beyond the peatland limits.

Stability of rectangular tunnel in anisotropic cohesionless soil under steady-state groundwater flow

The seepage force can cause failure of the underground excavations and openings that are lying below the groundwater table (GWT). The present research work aims to estimate the support pressure for peripheral stability of rectangular tunnel in anisotropic cohesionless soil below the GWT by using the lower bound finite element limit analysis and second-order conic programming. The seepage forces around the tunnel are computed from the total head distribution in the soil under steady-state seepage condition using finite element analysis. A uniform support pressure pi is applied at the tunnel periphery to resist the active state collapse of soil. The effects of various parameters on the magnitude of the normalized support pressure at the tunnel periphery are studied thoroughly. Design equations are provided by conducting regression analysis with present numerical results.

Numerical groundwater flow and nitrate transport assessment in alluvial aquifer of Varaždin region, NW Croatia

Study regionThe Varaždin alluvial aquifer located in the Drava River valley. Study focusThe study area is characterized by agricultural activity, which raised concerns due to the high nitrate concentration in groundwater. The present study aims to evaluate future nitrate concentrations in groundwater using the numerical groundwater flow and transport modeling. The regional model was generated in GMS software, using the MODFLOW code for steady-state groundwater flow model, and MT3DMS code for nitrate transport model. Advective-dispersive transport was simulated, without a chemical retardation process. The calibrated model was used to investigate the evolution of groundwater nitrate concentrations for the next 20 years under four scenarios: a) current nitrate input; b) zero input from wastewater; c) agricultural input reduced by 50%; d) input from natural vegetation and surface water New hydrological insights for the regionThe scenario analysis demonstrated that reducing the nitrate input from agricultural areas yields a considerable reduction of nitrate in groundwater, while the impact of wastewater is negligible. Neither of the scenarios reached concentrations below threshold value of 50 mg/L for the entire aquifer in the next 20 years. The nitrate concentration in the northern part of the aquifer will remain low, mainly due to the dilution from river. The central part of the aquifer is highly dependent on changing the on-ground nitrate concentration, showing inertia regarding the nitrate attenuation in groundwater.

Application of Meshless local Petrov-Galerkin approach for steady state groundwater flow modeling

Abstract The complicated behavior of groundwater system in an arid aquifer is generally studied by solving the governing equations using either analytical or numerical methods. In this regard, analytical methods are just for some aquifers with regular boundaries. Numerical methods used for this aim are finite difference (FDM) and finite element methods (FEM) which are engaged for some simple aquifers. Using them in the complex cases with irregular boundaries has some shortcomings, dependent on meshes. In this study, meshless local Petrov-Galerkin (MLPG) method based on the moving kriging (MK) approximation function is used to simulate groundwater flow in steady state over three aquifers, two standard and a real field aquifer. Moving kriging function known as new function which reduces the uncertain parameter. For the first aquifer, a simple rectangular aquifer, MLPG-MK indicates good agreement with analytical solutions. In the second one, aquifer conditions get more complicated. However, MLPG-MK reveals results more accurate than FDM. RMSE for MLPG-MK and FDM is 0.066 and 0.322 m respectively. In the third aquifer, Birjand unconfined aquifer located in Iran is investigated. In this aquifer, there are 190 extraction wells. The geometry of the aquifer is irregular as well. With this challenging issues, MLPG-MK again shows satisfactory accuracy. As the RMSE for MLPG-MK and FDM are 0.483 m and 0.566 m. therefore, planning for this aquifer based on the MLPG-MK is closer to reality.

Groundwater Recharge Assessment Using WetSpass and MODFLOW Coupling: The Case of Hormat-Golina Sub-basin, Northern Ethiopia

Water scarcity in northern Ethiopia, as well as its socio-economic relevance in terms of water demand for agriculture and domestic use, are at the root of the search for new groundwater resources and the development of groundwater models that can be used to control and manage the resource. The groundwater recharge of the Hormat-Golina sub basin was assessed using WetSpass-MODFLOW coupling. The goal of this paper is to assess the groundwater recharge in the Hormat-Golina sub-basin. These findings are then used to simulate the hydraulic head distribution using the MODFLOW groundwater flow simulation model. By comparing measured and simulated hydraulic heads, the steady state groundwater flow calibration was obtained. WetSpass calculated the mean annual evapotranspiration, surface runoff, and groundwater recharge to be 516.6, 204.9, and 35.6 mm, respectively. Groundwater recharge accounted for 4.7% of precipitation, while actual evapotranspiration and surface runoff accounted for 27% and 68% of precipitation, respectively. In such seasonal variations, the groundwater head distribution is 9.37 to 29.86 m in the winter (dry season), 9.53 to 29.89 m in the summer (wet season), and 9.58 to 30.17 m in the annual stress periods (recharges). For all stress periods, the estimated hydraulic heads in steady state fit well with the measured ones, with a correlation coefficient of 0.86 (summer, winter, and annual recharge). To preserve the resource's long-term viability, the balance between groundwater recharge and projected abstraction rates for agriculture and domestic water supply must be considered in future groundwater resource development plans in the valley.

Beneficial effects of dynamic groundwater flow and redox conditions on Natural Attenuation of mono-, poly-, and NSO-heterocyclic hydrocarbons

Natural Attenuation (NA) processes have been demonstrated to reduce pollutant loads at different contaminated groundwater sites world-wide and are increasingly considered in contaminated site management concepts. However, data are mainly available for steady state groundwater flow and stable redox conditions as well as pollutants listed in standard regulatory schemes. In this study, the influence of transient groundwater flow and redox conditions on NA was examined at a former gas works site near the river Rhine in Germany. The investigated 78 pollutants included 40 mono- and polyaromatic hydrocarbons (MAHs, PAHs) and 38 NSO-heterocyclic aromatic hydrocarbons (NSO-HET). In the highly polluted areas, the MAHs benzene, indene and indane, the PAHs naphthalene, acenaphthene, 1- and 2-methylnaphthalene and the NSO-HET 2-methylquinoline, carbazole, benzothiophene, dibenzofuran and benzofuran were predominant. Pollutant concentrations decreased with increasing distance from the sources of contamination. At the plume fringes, the MAHs benzene and indane, the PAH acenaphthene, the NSO-HET carbazole, 5-methylbenzothiophene, 2- and 3-methylbenzofuran and 2-methyldibenzofuran were predominant, indicating low retention and slow intrinsic biodegradation of these compounds. The influence of surface water on groundwater level, pollutant concentrations, and redox conditions in the monitoring wells was observed with a permanently installed groundwater sensor. The temporary availability of oxygen was observed at the plume fringes, resulting in aerobic and ferric iron reducing biodegradation processes. Field and laboratory data were used to set-up a groundwater flow and reactive transport model used for quantification of the field mass transfer rates. In conclusion, the study demonstrates that NA is effective under transient flow and redox conditions. A conceptual model and reactive transport simulation can facilitate the interpretation of pronounced fluctuations of pollutant concentration in monitoring wells. Based on the analysis of 78 pollutants, indane, indene and several NSO-HET like carbazole, benzothiophene and 2-methyldibenzofuran are recommended for monitoring at tar oil polluted sites, besides EPA-PAHs and BTEX.

Nonlinear Expression of Groundwater Head Interval Based on the Perturbation Method

An investigation of a groundwater system often requires the prediction of the spatiotemporal distribution of groundwater heads, which determine the groundwater flow direction and magnitude, among other applications. How to quantify the uncertainty of groundwater flow has been an important issue of concern to hydrogeologists for more than 40 years, and many methods based on stochastic and statistical approaches have been proposed to resolve this issue, with considerable progress being made. However, the statistical characteristics of parameters (e.g., hydrogeological parameters, boundaries, and sources/sinks) are often difficult to obtain precisely in practical applications. From a perspective of the interval uncertainty of groundwater, this study proposes a nonlinear expression of the groundwater head interval (GHI) using an interval uncertainty approach to quantify the uncertainty of numerical simulations in groundwater flow. This study uses a steady-state groundwater flow example to analyze the computational effectiveness of the acquired expression of GHI. A comparison of the results with the equal interval continuous sampling method (EICSM) shows that when the changing rate (which is the ratio of the absolute change in the numerical value to the numerical value itself) of a hydrogeological parameter is no more than 0.2, the relative discrepancy of the obtained GHI in this study and EICSM is no more than 5%. When the changing rate is no more than 0.3, such a relative discrepancy can be controlled within approximately 10%. In general, the proposed method is computationally efficient and robust for quantifying GHI. Finally, the method of this study is applied successfully to a real case.

Nonlinearity continuation method for steady-state groundwater flow modeling in variably saturated conditions

Application of nonlinearity continuation method to numerical solution of steady-state groundwater flow in variably saturated conditions is presented. In order to solve the system of nonlinear equations obtained by finite volume discretization of steady-state Richards equation, a series of problems with increasing nonlinearity are solved using the Newton method. This approach is compared to pseudo-transient method on several test cases, including real site problems and involving parallel computations.

Stability of rectangular tunnel in Hoek–Brown rocks under steady-state groundwater flow

This research study aims to determine the stability of a rectangular tunnel excavated in rock masses obeying Hoek–Brown yield criteria under steady-state groundwater flow using lower bound limit analysis. During tunnelling in the presence of groundwater table (GWT) seepage forces are generated, which causes a decrease in the stability of rock mass. The total head distribution due to seepage is obtained by using two-dimensional finite element software Optum G2. The stability has been presented by a non-dimensional number σci/γ′maxH obtained for various combinations of B/h, H/h, Hw/h, σci/γwh, mi, GSI and D where B and h are width and height of the tunnel, respectively, H is the depth of the tunnel from the ground surface and Hw is the height of GWT from the tunnel roof, respectively, σci and γ′ are uniaxial compressive strength and submerged unit weight of rock, respectively, γw is the unit weight of water and mi, GSI and D are the Hoek–Brown parameters.