Groundwater Flow Field Research Articles

Multiphase Flow Fields in In-situ Air Sparging and its Effect on Remediation

In-situ air sparging (IAS) is used for the clean-up of soil and groundwater that are contaminated with volatile organic compounds in relatively permeable subsurface environments. In this study, we investigated the secondary groundwater and gas flow fields that develop in the vicinity of single and multiple air sparging wells. The purpose is to evaluate their effects on contaminant plume migration and thus, remediation. Governing equations describing multiphase flow and contaminant transport in a three-dimensional domain were formulated and solved using the Galerkin finite element technique. Trichloroethylene was selected as a target contaminant. The increase in air injection contributed to an increase in the size of the IAS cone of influence and the gas saturation levels within the cone. This reduced the groundwater velocity within the cone and increased the zone of detour of groundwater around the air sparging wells. This outcome was quantified and compared under several IAS operations. Different soil permeability characteristics also affected the groundwater and gas flow patterns, and this impacted the remedial performance of the IAS system. Under high ambient groundwater velocity, an air sparging system that uses a single injection well caused the detour of contaminant plumes around injection wells, regardless of air injection rates, and failed to meet the remedial goal specified here. This system was successful for relatively low ambient groundwater velocity environments used here. An IAS system with multiple injection wells was effective in capturing and remediating the detoured contaminant plume, and showed superior performance when compared to a single injection well IAS system. Using IAS simulation, we also analyzed the impact of injection rates on site remediation using single or multiple wells. Design criteria that are based on the results of this study would be useful in enhancing the performance of the IAS systems.

Volume-based inverse model (VINMOD): innovative approach to quantify groundwater pollution in heterogeneous aquifers

The inversion method of pumped concentration can be used as an alternative or complementary method to the conventional methods for groundwater pollution evaluation and quantification. This method is useful even when the monitoring wells are few and also when the contamination source is unknown. In a homogeneous-isotropic case, with radially dominated groundwater flow field, this method of inversion can be performed analytically. However, in many cases, the real aquifer systems are heterogeneous. A novel volume-based inverse model (VINMOD) is developed for numerical inversion of pumped concentration under heterogeneous conditions. VINMOD helps us to determine the mean concentration and mass flow rate of an “undisturbed” contaminant plume at a predefined imaginary control plane (ICP). Model verification and preliminary tests are presented using a hypothetical single-layer aquifer. It is noticed that VINMOD is highly sensitive to the groundwater flow velocity and the well capture zone geometry, which in fact influences the determination of total mass flow rate of a pollutant in the groundwater.

Long-term ground penetrating radar monitoring of a small volume DNAPL release in a natural groundwater flow field

An earlier field experiment at Canadian Forces Base Borden by Brewster and Annan [Geophysics 59 (1994) 1211] clearly demonstrated the capability of ground penetrating radar (GPR) reflection profiling to detect and monitor the formation of DNAPL layers in the subsurface. Their experiment involved a large volume release (770 L) of tetrachloroethylene into a portion of the sand aquifer that was hydraulically isolated from groundwater flow by sheet pile walls. In this study, we evaluated the ability of GPR profiling to detect and monitor much smaller volume releases (50 L). No subsurface confining structure was used in this experiment; hence, the DNAPL impacted zone was subjected to the natural groundwater flow regime. This condition allowed us to geophysically monitor the DNAPL mass loss over a 66 month period. Reflectivity variations on the GPR profiles were used to infer the presence and evolution of the solvent layers. GPR imaging found significant reflectivity increases due to solvent layer formation during the two week period immediately after the release. These results demonstrated the capacity of GPR profiling for the detection and monitoring of lesser volume DNAPL releases that are more representative of small-scale industrial spills. The GPR imaged solvent layers subsequently reduced in both areal extent and reflectivity after 29 months and almost completely disappeared by the end of the 66 month monitoring period. Total DNAPL mass estimates based on GPR profiling data indicated that the solvent mass was reduced to 34%–36% of its maximum value after 29 months; only 4%–9% of the solvent mass remained in the study area after 66 months. These results are consistent with independent hydrogeological estimates of remaining DNAPL mass based on the downgradient monitoring of the dissolved solvent phase. Hence, we have concluded that the long-term GPR reflectivity changes of the DNAPL layers are likely the result from the dissolution of chlorinated solvents residing in those layers. The long-term monitoring results demonstrated that GPR profiling is a promising non-invasive method for use at DNAPL contaminated sites in sandy aquifers where temporal information about immiscible contaminant mass depletion due to either natural flow or remediation is needed. However, our results also indicated that the GPR signature of older DNAPL impacted zones may not differ greatly from the uncontaminated background if significant mass reduction due to dissolution has occurred.

Modelling study on the impact of deep building foundations on the groundwater system

AbstractCoastal areas are usually the preferred place of habitation for human beings. Anthropogenic activities such as the construction of high‐rise buildings and underground transport systems usually require extensive deep foundations and ground engineering works, which may unintentionally modify the coastal groundwater system because the construction materials of foundations are usually of low hydraulic conductivity. In this paper, the impact of these building foundations on the groundwater regime is studied using hypothetical flow and transport models. Various possible realizations of foundation distributions are generated using stochastic parameters derived from a topographical map of an actual coastal area in Hong Kong. The effective hydraulic conductivity is first calculated for different realizations and the results show that the effective hydraulic conductivity can be reduced significantly. Then a hypothetical numerical model based on FEFLOW is set up to study the change of hydraulic head, groundwater discharge, and saltwater‐fresh water interface. The groundwater level and flow are modified to various degrees, depending on the foundations percentage and the distribution pattern of the buildings. When the foundations percentage is high and the building foundations are aggregated, the hydraulic head is raised significantly and the originally one‐dimensional groundwater flow field becomes complicated. Seaward groundwater discharge will be reduced and some groundwater may become seepage through the ground surface. The transport model shows that, after foundations are added, overall the seawater and fresh groundwater interface moves landward, so extensive foundations may induce seawater intrusion. It is believed that the modification of the coastal groundwater system by building foundations may have engineering and environmental implications, such as submarine groundwater discharge, foundation corrosion, and slope stability. Copyright © 2007 John Wiley & Sons, Ltd.

Upscaling of mass transfer rate coefficient for the numerical simulation of dense nonaqueous phase liquid dissolution in heterogeneous aquifers

Mass transfer from entrapped dense nonaqueous phase liquids (DNAPLs) in heterogeneous aquifers takes place in natural, three‐dimensional groundwater flow fields. However, mass transfer processes are characterized in the laboratory in columns or flow cells under conditions of one‐dimensional or two‐dimensional water flow. Dissolution data generated in these test systems are used to determine empirical parameters of correlations that relate a dimensionless form of a mass transfer coefficient (Sherwood number) to other dimensionless groups that capture the basic processes contributing to mass transfer (e.g., Reynolds and Schmidt numbers). These phenomologically based empirical correlations, which are referred to as Gilland‐Sherwood models, are not directly applicable in predicting the dissolution of DNAPLs in the field as they do not capture the effects of aquifer heterogeneity and DNAPL entrapment morphology (referred to as DNAPL entrapment architecture). Numerical simulation of DNAPL dissolution requires the discretization of the problem domain into computational grid blocks and assignment of an effective mass transfer coefficient to each of these blocks containing DNAPL. A methodology for upscaling is needed to determine the grid‐scale effective mass transfer coefficient from the laboratory‐determined empirical correlations. It is our hypothesis that the upscaled effective mass transfer coefficient needs to contain information on the field‐scale heterogeneity and DNAPL entrapment architecture. This hypothesis was tested through a Monte‐Carlo‐based numerical experiment using a laboratory‐validated dissolution model with the goal of developing and testing an upscaling method. The developed upscaling method involves the use of geostatistical parameters that capture the aquifer heterogeneity and the DNAPL entrapment architecture. These parameters were determined to be the variance of log hydraulic conductivity, correlation lengths, and the normalized second moments of DNAPL mass distribution in the entrapment zone. Monte Carlo numerical simulation experiments combined with inverse modeling were used in this theoretical development and to determine parameters of the proposed upscaled Gilland‐Sherwood mass transfer correlation. Through these numerical modeling studies, the upscaled mass transfer correlation was successfully verified. Sensitivity analyses indicate that the normalized second moment, which describes the spreading of DNAPL mass in the vertical directions, was the most sensitive parameter in simulating the mass transfer at large scales.

Mass balance simulation and its application to refining flow field in Binchang area, China

Groundwater flow fields in aquifers are often determined by water level data measured in monitoring wells. The flow field can be further refined by mass balance simulations, especially when groundwater level data is limited. The mass balance simulation is based on the principle of mass conservation and relies on water quality data in the same aquifer. The approach is applied to the Luohe aquifer in the Binchang area, China. The water-rock interactions and the hydrogeochemical evolution were studied along four typical flow paths. The study indicates that groundwater in the Luohe formation flows from the southern border to the interior of the Ordos Basin. The southern border, approximately 1,400 km2, is a recharge zone, where the Luohe formation outcrops. The total dissolved solids of the groundwater in the southern boarder are less than 1 g/l, and the hydrochemistry type is HCO3–Na. This new finding refines the flow field of the water-bearing formation, and an additional 1,400 km2 is included in the water resource planning of the area.

Deduction of groundwater flow regime in a basaltic aquifer using geochemical and isotopic data: The Golan Heights, Israel case study

Summary Groundwater flow-paths through shallow-perch and deep-regional basaltic aquifers at the Golan Heights, Israel, are reconstructed by using groundwater chemical and isotopic compositions. Groundwater chemical composition, which changes gradually along flow-paths due to mineral dissolution and water–rock interaction, is used to distinguish between shallow-perched and deep-regional aquifers. Groundwater replenishment areas of several springs are identified based on the regional depletion in rainwater δ 18 O values as a function of elevation (−0.25‰ per 100 m). Tritium concentrations assist in distinguishing between pre-bomb and post-bomb recharged rainwater. It was found that waters emerging through the larger springs are lower in δ 18 O than surrounding meteoric water and poor in tritium; thus, they are inferred to originate in high-elevation regions up to 20 km away from their discharge points and at least several decades ago. These results verify the numerically simulated groundwater flow field proposed in a previous study, which considered the geological configuration, water mass balance and hydraulic head spatial distribution.

GIS assisted inverse geochemical modeling for plausible phase transfers in aquifers

A geographical information system (GIS) assisted approach that couples a groundwater flow model and an inverse geochemical model is presented to quantify the phase mole transfers between two points on the flow path within a groundwater system. It is used to investigate the plausible phase transfers in the unconfined aquifer of Mehsana district of Gujarat State, India. X-ray diffraction analysis of soil samples is carried out for mineral characterization. The groundwater flow field is simulated using MODFLOW and flow paths used for inverse geochemical modeling are traced using PMPATH, a particle tracking algorithm. The plausible phase mole transfers in the flow path are quantified using PHREEQC geochemical code. The different scenarios generated by inverse modeling routine are used as input to the geochemical model and simulation runs are taken as forward models. The obtained results are compared to the target solution chemistry by using the square of the Pearson product moment correlation coefficient. Results reveal that the groundwater is undersaturated with anhydrite, carbon dioxide (gas), fluorite, gypsum, halite, jarosite-K, and siderite. It is oversaturated with aragonite, calcite, dolomite, ferrihydrite, goethite, and hematite. Results further reveal that calcite is precipitating, while dolomite, gypsum, carbon dioxide, and fluorite are dissolving together with ion exchange in the flow path.

Karst groundwater management by defining protection zones based on regional geological structures and groundwater flow fields

In a semiarid region, the karst aquifer generally forms a large groundwater reservoir that can play an important role in regional water supply. But because of the specific physical properties of karst aquifers, they are vulnerable to pollution and anthropogenic impacts. Karst groundwater management strategies are vital. As representative of karst springs in a semiarid area, Niangziguan Springs is located in the east of Shanxi Province, China with an annual average rate of discharge of 10.34 m3/s (1956–2003) (Y. Liang, unpublished data). The Niangziguan Spring Basin covers an area of 7,394 km2 with an annual average precipitation of 535 mm (1958–2003) (Hao et al. in Carsologica Sinica 23(1):43–47, 2004). Over the past three decades, accelerated groundwater exploitation has caused water-table decline in the aquifer, reduction of the spring discharge, and deterioration of water quality. In this study, three protection zones were defined to ensure the quality and capacity of this resource. The confluence of the 11 spring systems and the discharge areas were defined as I protection zone, the recharge basin was II protection zone, and the slack water area where there is little surface recharge was the III protection zone. Management strategies for each zone were suggested and evaluated to provide a scientific foundation for sustainable utilization.

Field-Scale Evaluation of the Passive Flux Meter for Simultaneous Measurement of Groundwater and Contaminant Fluxes

A new method, passive flux meter (PFM), has been developed and field-tested for simultaneously measuring contaminant and groundwater fluxes in the saturated zone at hazardous waste sites. The PFM approach uses a sorptive permeable medium placed in either a borehole or monitoring well to intercept contaminated groundwater and release "resident" tracers. The sorbent pack is placed in a groundwater flow field for a specified exposure time and then recovered for extraction and analysis. By quantifying the mass fraction of resident tracers lost and the mass of contaminant sorbed, groundwater and contaminant fluxes are calculated. Here, we assessed the performance of PFMs at the Canadian Forces Base Borden field site in Ontario, Canada. Two field tests were conducted under imposed groundwater flow fields: (1) radial flow to a well and (2) linear flow in a test channel confined by sheet pile walls on three sides. Both tests demonstrate that the local fluxes measured by PFM and averaged overthe screen interval were within 15% of imposed groundwaterflow and within 30% of measured contaminant mass flux. Patterns in depth variations in groundwater and contaminant fluxes, determined by the PFM approach, allow for site characterization at a higher spatial resolution. These results support the PMF method as a potential innovative alternative for measuring groundwater and contaminant fluxes in screened wells.

The effects of vertical barrier walls on the hydraulic control of contaminated groundwater

We present explicit analytic solutions describing the hydraulic head and discharge vector for two-dimensional, steady groundwater flow past an impermeable barrier embedded in a regional flow field. We use the solution to investigate the effects of open vertical barriers on the flow field; in particular, we examine the hydraulic containment of contaminant plumes or source zones by combination of a vertical barrier wall and extraction wells. We quantify the local reduction in discharge rates due to the barrier wall and the local increase in the size of the capture zone of an extraction well near an open, up-gradient barrier. We find that the combination of an open vertical barrier with down-gradient extraction wells can be very effective in decreasing the well discharge rate necessary to control a contaminant plume or source area. Design charts are presented for quantifying the effects of the barrier wall on the hydraulic control of the groundwater flow field and for estimating the jump in head across a barrier. The charts are appropriate for use in the preliminary design and cost estimating of remedial systems, and for the design of dewatering systems.

The southeastern border of the Upper Rhine Graben: a 3D geological model and its importance for tectonics and groundwater flow

A 3D geological model of the area east of Basel on the southeastern border of the Upper Rhine Graben, consisting of 47 faults and six stratigraphic horizons relevant for groundwater flow, was developed using borehole data, geological maps, geological cross sections, and outcrop data. This model provides new insight into the discussions about the kinematics of the area between the southeastern border of the Upper Rhine Graben and the Tabular Jura east of Basel. A 3D analysis showed that both thin-skinned and thick-skinned tectonic elements occur in the modeled area and that the Anticline and a series of narrow graben structures developed simultaneously during an extensional stress-field varying from E–W to SSE–NNW, which lasted from the Middle Eocene to Late Oligocene. In a new approach the faults and horizons of the 3D geological model were transferred into discrete elements with distributed hydrogeological properties in order to simulate the 3D groundwater flow regime within the modeled aquifers. A three-layer approach with a horizontal regularly spaced grid combined with an irregular property distribution of transmissivity in depth permitted the piezometric head of the steady-state model to be automatically calibrated to corresponding measurements using more than 200 piezometers. Groundwater modeling results demonstrated that large-scale industrial pumping affected the groundwater flow field in the Upper Muschelkalk aquifer at distances of up to 2 km to the south. The results of this research will act as the basis for further model developments, including salt dissolution and solute transport in the area, and may ultimately help to provide predictions for widespread land subsidence risks.

On using simple time‐of‐travel capture zone delineation methods

As part of its Wellhead Protection Program, the U.S. EPA mandates the delineation of "time-of-travel capture zones" as the basis for the definition of wellhead protection zones surrounding drinking water production wells. Depending on circumstances the capture zones may be determined using methods that range from simply drawing a circle around the well to sophisticated ground water flow and transport modeling. The simpler methods are attractive when faced with the delineation of hundreds or thousands of capture zones for small public drinking water supply wells. On the other hand, a circular capture zone may not be adequate in the presence of an ambient ground water flow regime. A dimensionless time-of-travel parameter T is used to determine when calculated fixed-radius capture zones can be used for drinking water production wells. The parameter incorporates aquifer properties, the magnitude of the ambient ground water flow field, and the travel time criterion for the time-of-travel capture zone. In the absence of interfering flow features, three different simple capture zones can be used depending on the value of T . A modified calculated fixed-radius capture zone proves protective when T < 0.1, while a more elongated capture zone must be used when T > 1. For values of T between 0.1 and 1, a circular capture zone can be used that is eccentric with respect to the well. Finally, calculating T allows for a quick assessment of the validity of circular capture zones without redoing the delineation with a computer model.

Three‐dimensional numerical simulation of fully coupled groundwater flow and land deformation in unsaturated true anisotropic aquifers due to groundwater pumping

A hydrogeomechanical numerical model is presented to evaluate three‐dimensional groundwater flow and land deformation in unsaturated true anisotropic aquifers due to groundwater pumping. This multidimensional numerical model is developed on the basis of the fully coupled poroelastic governing equations for saturated‐unsaturated groundwater flow in deforming true anisotropic geologic media and the Galerkin finite element method. A series of true anisotropic aquifers, which comprise variously tilting layers, respectively, and a corresponding isotropic aquifer, which is composed of a geometrically averaged equivalent isotropic material, are simulated for the purpose of comparison. The numerical simulation results show that true anisotropy has significant effects on the spatial distributions and temporal changes of hydraulic head and displacement vector. Such effects of true anisotropy are caused by the uneven partitioning of the hydraulic pumping stress between the vertical and horizontal directions in both groundwater flow and solid skeleton deformation fields. This directionally uneven partitioning of the hydraulic pumping stress results from both the differences in hydraulic and mechanical properties among the principal axes and the discordance between the global coordinate axes and the principal axes.

Temporal and spatial variations of shallow subsurface temperature as a record of lateral variations in groundwater flow

In the present paper it is shown how profiles consisting of closely spaced (≤10 m) temperature measurements at shallow depth, obtained at several instances during one season, provide a detailed record of lateral variations in vertical groundwater flow. This is illustrated by a field study around the Peel Boundary Fault zone that cuts through the unconsolidated, siliciclastic deposits that occur in the southeastern part of Netherlands. This regionally important fault forms at many locations a strong barrier to horizontal groundwater flow and therefore induces complex groundwater flow patterns. Temperature anomalies (over 2°C) are observed over short distances. These anomalies reverse over the season. Numerical modeling of coupled groundwater flow and heat transport demonstrates how the temporal and spatial variations of subsurface temperature are the result of the interaction between seasonal fluctuations in surface temperature and spatial variations in groundwater flow. In addition to the horizontal profiles, temperature‐depth profiles obtained in groundwater observation wells were used to constrain the larger‐scale characteristics of the groundwater flow system. In order to simulate the observed geothermal patterns it appeared to be essential to account for the long‐term changes in surface temperature. Although groundwater temperature data are commonly used to constrain groundwater flow fields on regional scale or to calculate vertical groundwater velocities at point locations beneath small streams, the present study is one of the first to integrate these different scales and incorporate the impact of recent climate change.

Research on the conversion relationships between the river and groundwater in the Yellow River drainage area

Conversion relationships between the river and groundwater in the Yellow River drainage area are studied in this paper based on the geologic and physiognomy conditions and the data of the groundwater regime, isotope, groundwater flow field and field survey. Then eight recharge and discharge modes on the relationships are put forward and the hydraulic characteristics of the modes are analysed, which provides a scientific basis for quantitatively simulating and assessing the conversion relationships, maintenance mechanism of the Yellow River and the regeneration ability of the groundwater in the area.

On the Nonlocality of Reversible-Time Particle Tracking Methods

This article presents a novel methodology for time reversal in groundwater transport simulations. A variance minimization procedure leads to a stochastic method, analogous to the Random Walk Particle Tracking Method (RWPTM), capable of tracking groundwater solute concentration profiles over time. This method, called the Reversible-Time Particle Tracking Method (RTPTM), can backtrack in time a certain solute plume, of arbitrary shape, and identify the most probable spill location. The correspondence to the "classical" RWPTM is established for forward-time simulations, and the method is applied to one-dimensional transport of both conservative and nonconservative solutes in spatially invariant and variant groundwater flow fields with great success.

Fluid-potential patterns and hydrocarbon deposits in groundwater flow-fields induced by gravity and tectonic compression, Hungarian Great Plain, Pannonian Basin

In the course of a petroleum hydrogeological research project in the Pannonian sedimentary basin, spatial coincidence has been observed between dozens of known hydrocarbon pools and mapped fluid-potential anomalies based on more than 16,000 pore-pressure measurements over an area of approx. 40,000 km 2. The anomalies were identified on vertical pressure profiles at 8 sites, 4 hydraulic cross sections totalling 850 km in length, and a stack of 13 tomographic fluid-potential maps reaching to depths of over 3 km. The perturbations have been attributed to hydraulic windows formed by conducting faults and sedimentological discontinuities in a subsurface flow domain comprising a lower, tectonically driven, overpressured regime and an upper, gravity-drive zone. Because these types of geologic features can also be pathways and traps for hydrocarbons, their attendant potentiometric disturbances may be indicative of the presence of petroleum accumulations.

Conformal mapping of groundwater flow fields with internal boundaries

An analytical approach is presented for solving problems of steady, two-dimensional groundwater flow with inhomogeneity boundaries. A common approach for such problems is to separate the problem domain into two homogeneous domains, search for solutions in each domain, and then attempt to match conditions, either exactly or approximately, along the inhomogeneity boundary. Here, we use classical solutions to problems with inhomogeneity boundaries with simple geometries, and map conformally the entire domain onto a new one. In this way, existing solutions are used to solve problems with more complex, and more practical, boundary geometries. The approach is general, but subject to some restrictions on the mapping functions that may be used. Using this approach, we develop explicit analytical solutions for two problems of practical interest. The first problem addresses aquifer interaction across a gap in an impermeable separating layer; flow regimes are defined and the interaction is quantified. The second solution represents flow in the vertical plane to a partially clogged stream bed that is partially penetrating the aquifer; the stream bed is modeled as a thin layer of low-permeability silt. Flow regimes for groundwater surface–water interaction are quantified analytically.

特異域のある領域における地下水流動解析のための流れ関数モデル

A new method, which makes use of stream function models together with potential models, is proposed to draw stream lines for groundwater flow fields with anomalous zones. The anomalous zones within analytical domains include impermeable zones, prescribed head zones, and discharge and/or recharge wells. All boundary conditions for stream function models are precisely evaluated by using calculated results of potential models. Elimination of anomalous zones from analytical domains can be achieved by a branch cut at a location of any prescribed stream line or at an arbitrary location. Simulated examples are shown for each case of anomalous types and the results obtained by the stream function models are compared with the results by the counterpart potential models. The comparison shows sufficient accuracy of the proposed stream function models.