Search

Interdisciplinary and comprehensive field work combining hydraulic and geophysical experiments yielded an improved understanding of the fractured and partly karstified Kohlenkalk aquifer in the Hastenrather Graben near Aachen, Germany. The aquifer is used for drinking water production and located in a geologically and tectonically complex area shaped by various tectonic events. A workflow which combines implicit 3D structural modeling with hydrogeological conceptual model building enabled determining hydrogeological boundary conditions at specific boundary cross sections, calculating the aquifer volume, and analyzing the hydraulic influence of faults on the aquifer system. Electrical resistivity tomography, seismic refraction tomography, well logging, and a coring campaign combined with available maps and additional literature research served as basis for the setup of the 3D structural model. This 3D model comprises all important structural elements, including the fault system, deep folded structures, and thrusts in the graben center. Integration of geological structure and hydraulic studies yielded a conceptual model of the hydrogeology, describing the Kohlenkalk aquifer and neighboring layers. Hydraulic conductivity of the aquifer system varies between 6.0 × 10−7 and 6.4 × 10−4 m s−1 with a decreasing trend from the NE graben shoulder to the graben center. Analysis of piezometric heads and resulting groundwater contour maps indicated four hydrogeological units which are partly limited by faults. Data on groundwater recharge as well as anthropogenic influences on the groundwater resources are part of the conceptual model.

Groundwater is an important resource in the Adansi mining area as some communities in the area are not connected to the Ghana national water network. These communities therefore utilise groundwater for potable water supply. The hydrogeological properties of an aquifer coupled with climatic conditions and geomorphology determines how much groundwater exists in that location. A hydrogeological study of the rocks in the Adansi area was carried out to obtain the aquifer hydraulic properties. Drilling and pumping test analysis information were used to assess these properties. The average borehole depth in the area was 44.3 m whilst the average static water level is 10.75 m. There is a general decrease in yield with an increase in borehole total depth. There is also no strong correlation between aquifer saturated thickness, yield and drawdown. Transmissivity of the aquifer decreases from the phyllite, argillitc sediments, granites to sandstone. Three hydrogeological regimes (> 0.9 m/day, 0.9 – 0.09 m/day and < 0.09 m/day) were also realised based on the hydraulic conductivity. The spatial distribution of the hydraulic properties suggests the influence of geological structures on the occurrence of groundwater in the area. Keywords : Hydrogeological Properties, Mining, Hydraulic, Drilling, Groundwater

In this paper, new analytical solutions are presented to quantify interaction of water between a sloping aquifer and stream of varying heads in presence of a thin vertical sedimentary layer. The initial hydrogeological setting consist of an unconfined sloping aquifer of semi-infinite extent, a fully penetrating stream of varying water level, and a vertical layer of streambank deposits that acts as an interface between stream and aquifer. Unsteady groundwater flow is characterized by a nonlinear Boussinesq equation subject to Robin boundary condition (also referred to as third kind and Cauchy boundary condition). Unlike existing results, which focus only on step changes in stream stage, the current study accounts for gradual rise and decline in stream level. A closed-form analytical solution for water head distribution, discharge rate, and net volumetric exchange of water between stream and aquifer are developed from the solution of a linearized advection-diffusion equation. Performance of the anal...

A groundwater flow and mass transport model simulated the remediation capability of non-pumped wells with filter media placed in backfilled trenches in homogeneous and heterogeneous aquifers. For each of five homogeneous and heterogeneous aquifer settings, the model identified a base configuration of wells for a backfill hydraulic conductivity equal to the mean of the aquifer (1.5 m/d). Base configurations comprised the least number of wells necessary to contain and remove a contaminant plume. For each setting, the model also simulated base configurations with backfill hydraulic conductivity one and two orders of magnitude lower and one and two orders of magnitude higher than the mean of the aquifer. In general, backfill with a hydraulic conductivity equal to the mean of the aquifer, or slightly higher, outperformed other scenarios.

Aquifer parameters transmissivity ‘T’ and storage coefficient ‘S’ are very important parameters to assess the groundwater potential either through mathematical modeling or any conventional methods. In early days, these parameters are estimated either by means of in situ test or performing test on aquifer samples brought in the laboratory. In recent times, the pumping test has become an important method to estimate these parameters. This is the only method that provides simultaneous information on the hydraulic behavior of the well (borehole), the reservoir and the reservoir boundaries, which are essential for efficient aquifer and well field management. The applicability of the result from the laboratory test has limitations while in situ tests give representative aquifer parameters. The most common in situ test is pumping test performed on wells, which involves the measurement of the fall and rise of water level with respect to time. Theis (American Geophysics Union Transcripts, 16th annual meeting, part 2, pp 519–524, 1935) was first to propose method to evaluate aquifer parameters from the pumping test on a bore well in a confined aquifer. Since then, several methods have been developed to analyze the pumping test data (time-drawdown) under different conditions. For the characterization of the aquifer parameters in Man River basin area, it is essential to know the Transmissivity (T = Kb where, b is the aquifer thickness: pumping flow rate, Q = TW (dh/dl) flow through an aquifer) and Storativity (confined aquifer, S = bSs, unconfined, S = Sy) so as to predict the rate of drawdown of the water table/potentiometric surface during the pumping of an aquifer. The determination of aquifer’s parameters is an important basis for groundwater resources evaluation, numerical simulation, development and protection as well as scientific management. Pumping test is a main method for determining aquifer’s parameters. A study area shows that this method has rapid speed and high accuracy. The results of parameter’s determination are optimized so that it has important practical value for scientific research and engineering practice.

Two single-well injection–extraction (“push–pull”) tracer tests were performed in a groundwater monitoring well located in the Horonobe coastal sedimentary basin, Japan. The aim of the experiment was to investigate the in situ behavior of groundwater constituents when different mineralized fluids intrude into the aquifer (e.g., through a dynamic saltwater–freshwater interface). Artificially produced brackish water was used as the test fluid in the first experiment and deionized water in the second. Results from mixing models strongly suggest rapid mobilization and demobilization of ions within the aquifer as a reaction to the intruding fluids. Hydraulic modeling of the conservative chloride ions yielded effective porosities of about 1 %. These results show that the transport of ions is dependent on the composition and mineralization of the fluid. The refreshening of an aquifer leads to increased mobilization of ions and, in addition, to an increase of dispersivity due to clay swelling. This has consequences not only for dynamic saltwater–freshwater systems (aquifers in coastal areas and aquifer storage and recovery systems), but also for all systems in which chemically altered fluids come into contact within an aquifer (as, for example, can occur during geothermal heat/energy generation, or during CO2 storage).

This study is aimed to investigate the principal aquifer in the northern part of Paris (Beauvais region) which is materialized by the Senonian chalk deposits. This aquifer supplies water to the principal region in the north and in particular the Picardie and Artois region. In order to characterize the chalk aquifer of this area, a wide pluridisciplinary research program based on the well logging and near surface geophysics surveys (seismic refraction and electrical resistivity tomography) is in progress. These surveys were carried out within the experimental site of the LaSalle Beauvais Polytechnic Institute and its hydrogeological boreholes. The heterogeneous distribution of the seismic velocities in the complex aquifer and of the physico-chemical properties (conductivity, temperature and gamma-ray) of the chalk aquifer were revealed by the analysis and the interpretation of the seismic lines and data logging, which are linked to changes in lithology and water properties at the place of the hydrogeological wells. The fracturation investigation identified during this work makes it possible to consider the relationship between the degree of the fracturation and the variation of the hydrogeological parameters (hydraulic conductivity, porosity) and physico-chemical parameters (electrical conductivity and temperature). The interface between vadose and saturated zones was assessed by the measurement of the water conductivity, the variation of the average temperature and by the cuttings analysis in particular at the level of the capillary fringe of the chalk aquifer. The presence of the saturated depth is confirmed by the piezometric investigation. The interpretation of the well logging by using gamma-ray is consistent with the seismic and electrical analysis: the three principal layers are composed of silt and clay with cherts, soft chalk, as well as hard chalk.

Data on aquifer storage properties (storativity and specific yield) are required for transient groundwater models. Storativity is usually determined from aquifer pumping tests using the Theis method or variations thereof. Quantification of specific yield is much more challenging because of the long time required (especially in fine-grained sediments) for gravity drainage to occur to completion. Evaluation of the properties of aquitards (semi-confining units) may also be a key element of aquifer characterization and modeling investigations. Heterogeneity, particularly a strong scale effect, and very slow groundwater flow rates are the main challenges associated with aquitard characterization. Multiple methods should be employed to evaluate aquifer storage and aquitard properties with the values subject to adjustment during the model calibration process.

Aquifer characterization is broadly defined as processes by which the three-dimensional structure, hydraulic and transport properties, and chemistry of aquifers are evaluated. Aquifer characterization provides the foundation for groundwater modeling, which is ubiquitously used to evaluate sedimentary aquifers. Detailed aquifer characterization is particularly important where solute transport is a concern, as aquifer heterogeneity has a much greater impact on groundwater flow direction and rates than it does on aquifer heads. An introduction to aquifer hydraulic and transport parameters and basic aquifer heterogeneity concepts is provided. Aquifer heterogeneity includes layered, lateral, and multiple-porosity systems. Aquifer characterization starts with an initial conceptual geological model development, followed by evaluations of the type and scale of aquifer heterogeneity and the values of petrophysical and hydraulic parameters, and finally, data analysis and synthesis, and groundwater flow and solute-transport modeling.

The quantification of the hydraulic parameters is important to support decision making in environmental impact assessment, water resources evaluation or groundwater contamination remediation, among others. These kind of parameters derived from aquifer tests usually encompasses a vast amount of data (spatial and non-spatial) for management and analysis. To achieve this in a clear and understandable manner, the GIS environment is a useful instrument. Development of innovative software to analyze pumping tests in a GIS platform environment to support the hydraulic parameterization of groundwater flow and transport models is presented in this paper. This new platform provides three interconnected modules to improve (a) pumping test interpretation code through a user-friendly interface, (b) pumping test data visualization supported by a set of tools that perform spatiotemporal queries in a GIS environment and (c) the storage and management of hydrogeological information. Additionally, within the GIS platform, it is possible to process the hydraulic parameters obtained from the pumping test and to create spatial distribution maps, perform geostatistical analysis and export the information to an external software platform. Finally, a real-world application in the area of Barcelona (Spain) has shown the usefulness of the tools developed in support of hydrogeological analysis., This work was supported by the Catalan Industrial Doctorates Plan of the Secretariat for Universities and Research, Ministry of Economy and Knowledge of the Generalitat de Catalunya. The authors would like to thank J. Hidalgo, A. Medina and A. Nardi for their support during the work’s development. R. Criollo gratefully acknowledges the financial support from the Grup d’Hidrologia Subterrània, SGR: 2014 SGR 1377.

International audience; Karst aquifers are characterized by a strong heterogeneity in their physical properties. The purpose of the study is the spatial variability of water transfers in a carbonated karstic aquifer. To this end, a high spatial density of information about the water transfer is needed. The characteristics of the site, a topographic hill of 13 km2 with eight boreholes, which was monitored hourly over four years, allows the study of the spatial variability of water transfers. The variability of the impulse response of the system is studied using autocorrelation and cross-correlation analysis between the rainfall and piezometric level time series. The shapes of the autocorrelation and cross-correlation functions vary according to the geographical location of the boreholes, that proves a spatial organization of the groundwater transfer. The response time varies depending on the thickness of the unsaturated zone by an unusual inverse correlation. In this case, the water level signal spatially integrates the signal transfer of the unsaturated zone and the signal transfer of the saturated part of the aquifer. Consequently, inertia and response time increased with the distance between the borehole and the top of piezometric dome. This description supports highly organized fast transfers in this karst aquifer and a highly connected fracture network.

Simulated transmissivities are constrained poorly by assigning permissible ranges of hydraulic conductivities from aquifer-test results to hydrogeologic units in groundwater-flow models. These wide ranges are derived from interpretations of many aquifer tests that are categorized by hydrogeologic unit. Uncertainty is added where contributing thicknesses differ between field estimates and numerical models. Wide ranges of hydraulic conductivities and discordant thicknesses result in simulated transmissivities that frequently are much greater than aquifer-test results. Multiple orders of magnitude differences frequently occur between simulated and observed transmissivities where observed transmissivities are less than 1,000 feet squared per day. Transmissivity observations from individual aquifer tests can constrain model calibration as head and flow observations do. This approach is superior to diluting aquifer-test results into generalized ranges of hydraulic conductivities. Observed and simulated transmissivities can be compared directly with T-COMP, a suite of three FORTRAN programs. Transmissivity observations require that simulated hydraulic conductivities and thicknesses in the volume investigated by an aquifer test be extracted and integrated into a simulated transmissivity. Transmissivities of MODFLOW model cells are sampled within the volume affected by an aquifer test as defined by a well-specific, radial-flow model of each aquifer test. Sampled transmissivities of model cells are averaged within a layer and summed across layers. Accuracy of the approach was tested with hypothetical, multiple-aquifer models where specified transmissivities ranged between 250 and 20,000 feet squared per day. More than 90 percent of simulated transmissivities were within a factor of 2 of specified transmissivities.

Open-loop groundwater geothermal heat pumps (GWHP) represent an interesting technology that is expected to contribute significantly to the reduction of primary energy use for buildings heating and cooling needs especially in urban context. In the GWHP's design phases the geological and hydrogeological parameters must be accurately determined in order to maximize efficiency and minimize installation costs.Physical properties of the aquifer such as the porosity and the thermal parameters of the aquifer framework have been usually obtained through field and laboratory geotechnical testing. Hydrogeological and hydraulic parameters of the exploited aquifer such as hydraulic conductivity and the storativity are usually obtained through pumping test.As reported in literature, the prevailing component of the heat transfer in the aquifer induced by the water re-injection is related to the advection and therefore the determination of the real field groundwater velocity in transient and steady conditions is fundamental in the modelling of the thermal plume especially in the GWHP plant design phases. To this aim the pumping tests appear to be among the most useful field hydrogeological investigations to be performed in most cases. Such tests can also provide suitable information related to the aquifer productivity (specific discharge rate) and therefore can permit to assess if the GWHP plant requirement can be satisfied in terms of groundwater sustainable withdrawals. A real field pilot plant aimed to supply energy needs to the Architecture Faculty building of the Politecnico di Torino (NW Italy) is presented and discussed.

The terms hydraulic conductivity (K), transmissibility (T) and storage coefficient (S) are useful for computation of yield. The hydraulic conductivity of an aquifer is its capacity to transmit and to yield it. The transmitting capacity for the entire thickness is known as transmissibility (T), and storage coefficient (S) of an aquifer is the volume of water discharged through unit prismatic volume. During pumping test, a time–drawdown curve is generated. From this curve, T and S values are calculated by different methods. As the drilling and pumping tests are expensive, time-taking and laborious geoelectrical measurements are used for alternate approach to estimate the aquifer characteristics. In this process, a few drillings are carried out in the area of investigation. The T and K are calculated in these boreholes with the help of pump test. Vertical electrical sounding (VES) is carried out near the boreholes. Transverse resistance (T′) and formation factors (F) are calculated from all the VES results. Then, a straight-line relation between transmissibility and transverse resistance and hydraulic conductivity and formation factor is brought out. Now, if the entire area is surveyed by VES and the T′ and F are calculated for each point, the hydraulic conductivity (K) and transmissibility (T) can be found out using the relations for the entire area of investigation. A contour can also be drawn for hydraulic conductivity and transmissibility for the area.

Aquifer pumping tests are an integral component of aquifer characterization because they provide quantitative data on large-scale aquifer hydraulic properties such as aquifer transmissivity, storativity, and the vertical hydraulic conductivity (leakance) of confining strata. Aquifer performance tests (APTs), also referred to as aquifer pumping tests, involve the pumping of an aquifer at a known rate and the measurement of the corresponding changes in water levels in the pumped and observation wells. Aquifer hydraulic testing may also be performed by injecting water into a well. APTs can provide important information on well yields, well efficiency, and the stability of water quality. Successful aquifer hydraulic testing requires attention to detail and careful consideration of the underlying assumptions of the various methods used to interpret the data.

Electrical resistivity imaging approaches were integrated with hydrogeochemical and geological analysis to assess saltwater intrusion and aquifer condition in the Langat Basin. A major issue in water policy is groundwater preservation. Approaching this problem can be provided by comprehensive understanding of the aquifer systems. Geoelectrical surveying and modeling tools have been used to determine the thickness and resistivity of aquifer. In addition, geochemical analyses are used to describe the groundwater quality in the Langat Basin. Chemical analyses of groundwater samples collected from thirteen wells and 75 Wenner array resistivity surveys along five lines have been undertaken successfully. A Wenner array was selected because of its sensitivity in detecting vertical changes in subsurface resistivity. According to the resulting models, the aquifer depth varies from 10 to 25 m and the layer thickness changes from 10 to 44 m, respectively, from east to west across the study area. The useful information which is supplied in this research can be applied to improve a wider knowledge of groundwater quality in the area and their relationship with the local geology. Refereed/Peer-reviewed

International audience; In semi-arid regions with high seasonal variability of water availability, adaptive management strategies and technical measures are required to ensure the sustainable use of water resources. In this study, managed recharge of storm water into a karst aquifer and the water level fluctuations related to pumping in a nearby wellfield were simulated at Wadi Wala, Jordan. We used a numerical equivalent porous medium (EPM) approach with specific adaptations to account for the heterogeneity and anisotropy of the karst aquifer. The model domain was vertically projected along the wadi course, resulting in a 2-dimensional model, and subdivided into hydraulic zones representing the karst-specific flow pattern of fast flow and slow depletion. Results show satisfying agreement of measured and simulated groundwater tables from 2002 to 2012 and predict a lowering of the average groundwater table until 2022 of around 2.7m in the immediate surroundings of the reservoir and an increased depletion towards the wellfield, mainly caused by sedimentation in the reservoir and an associated decrease in infiltration. Abstraction at the wellfield changed considerably over the regarded time period and strongly influences the groundwater fluctuations, which shows the need of improved pumping management and monitoring. The results can serve as a basis for decision makers regarding an optimization of water management at the reservoir and wellfield. Furthermore, the presented numerical approach can be transferred to karst regions with similar physio-geographical conditions to assess managed aquifer recharge.

Monitored groundwater level data, well logs, and aquifer data as well as the relevant surface hydrological data were used to conceptualise the hydrogeological system of the Densu Basin in Southern Ghana. The objective was to numerically derive the hydraulic conductivity field for better characterization of the aquifer system and for simulating the effects of increasing groundwater abstraction on the aquifer system in the basin. The hydraulic conductivity field has been generated in this study through model calibration. This study finds that hydraulic conductivity ranges between a low of 2 m/d in the middle sections of the basin and about 40 m/d in the south. Clear differences in the underlying geology have been indicated in the distribution of aquifer hydraulic conductivities. This is in consonance with the general assertion that the hydrogeological properties of the aquifers in the crystalline basement terrains are controlled by the degree of fracturing and/or weathering of the country rock. The transient model suggest aquifer specific storage values to range between 6.0 × 10−5 m−1 and 2.1 × 10−4 m−1 which are within acceptable range of values normally quoted for similar lithologies in the literature. There is an apparent subtle decrease in groundwater recharge from about 13% of the annual precipitation in 2005 to about 10.3% of the precipitation in 2008. The transient model was used to simulate responses of the system to annual increment of groundwater abstraction by 20% at the 2008 recharge rates for the period 2009 – 2024. The results suggest that the system will not be able to sustain this level of abstraction as it would lead to a basin wide drawdown in the hydraulic head by 4 m by the end of the prediction period. It further suggests a safe annual increment in groundwater abstraction by 5% under business as usual recharge conditions. Identification and protection of groundwater recharge areas in the basin are recommended in order to safeguard the integrity of the resource under the scenario of increased abstraction for commercial activities in the basin. Copyright © 2012 John Wiley & Sons, Ltd.

Aquifers may have alluvium deposits, weathered layers, fractured zones, and karstic formations separately or in mixture forms. Such geological configurations do not allow classical aquifer test applicability, due to a set of underlying assumptions that are not usually valid in nature. In practice, the Jacob straight line method is the most commonly used approach for aquifer parameter determinations. Constant transmissivity and storativity estimations depend on large time-drawdown plots on semilogarithmic paper as a straight line. A common mistake is that the appearance of a general trend as a straight line on semilogarithmic paper is taken as guaranteed for the application of Jacob method. Since Jacob straight line is the large time extension of Theis type curve, there is only one straight line on the semilogarithmic paper that can represent Jacob method, which is based on the assumption that the aquifer is porous and homogeneous. In such a case, the Jacob method slope should equal to 2.3, which shows its validity. Otherwise, a modification of Jacob method is suggested in this paper. The basis of the methodology is a dimensionless type straight line approach for the aquifer parameter assessment. Its application is presented for aquifer test data from Oude Korendjik porous medium aquifer data. The application results indicate that the classical Jacob straight line method might not be valid without a preliminary check. The dimensionless reevaluation of existing data helps to check the validity. The necessary formulations for the modification of the classical straight line method are derived, which reduce to classical Jacob method for a specific set of parameters.

Wadi Zerka Ma’in catchment area is located to the north east of the Dead Sea. It has two types of aquifers: (a) an upper unconfined aquifer and (b) a lower confined aquifer. The two aquifers are separated by a marl aquiclude. A major strike slip fault passes perpendicularly through the two aquifers and the aquiclude layer with embedded normal faults. The aim of the study was to specify the effect of the major strike slip fault on the groundwater chemistry. The spatial variability of the hydrochemical compositions and physiochemical parameters of the groundwater were investigated. It was found that the embedded normal faults, of the strike slip fault, form conduits that allow groundwater to flow from the lower aquifer to the upper aquifer, resulting in mixed groundwater. The ratio of mixing was estimated to be 94 % groundwater from the upper aquifer and 6 % from the lower aquifer. Since groundwater in the lower aquifer is around three times more saline than the upper aquifer, water mixing into the upper water aquifer generates a salinity hazard.

This study proposes a reservoir model for evaluation of aquifer parameters from a long duration pumping test conducted with a radial collector pumping well and nine observation wells in an unconfined aquifer in the Tailan River basin of China. The proposed model, based on the concept of double continuum, was used to conceptualize the pumping test site into conduit and porous reservoirs coupled by a linear flow exchange for simulating flow during the pumping test. The set of model equations developed from the concept were solved by an iterative method. The model-simulated hydraulic heads agree reasonably well with the observation heads in both the pumping and observation wells at an average normalized root mean square error of 10.99 and 8.06%, respectively, during pumping but were weaker in the recovery period. This notwithstanding, the specific yield estimates compare well with the range obtained for a numerical modeling of the entire aquifer basin. Significantly, the model was applied successfull...

The structure of groundwater flow system is the core of study of groundwater system and the base of evaluation of groundwater resources. The control role of aquifer system to groundwater flow system is a key of study of the structure of groundwater flow system. The groundwater systems of the Ordos basin are analyzed as a case study. The control role of aquifer system to groundwater flow system is studied by comparison of groundwater flow systems under the control of different aquifer structures in 2-D profile numerical model. The research shows that the groundwater flow systems of the Ordos basin have the multilayer structure characteristics. The groundwater flow systems in the north of the Ordos basin show a cross-formational multi-hierarchy nested flow pattern in the northern aquifer systems without regional impermeable layer where the hydraulic connection between aquifer layers is closely. While, the hydraulic connection is discontinuous in the southern aquifer systems because there are regional impermeable layers in the aquifer systems. The groundwater flow systems in the south of the Ordos basin show a follow-formational flow pattern.

Aquifer parameter determination in practical hydrogeological studies exposes one of the most significant steps in groundwater resources assessment and management. Successful parameter estimation necessitates both a reliable methodology and field data. Different analytical solutions in the forms of type curves depend on well and aquifer configuration such as porous or fractured media; confined, unconfined, and leaky conditions; and small- and large-diameter wells. Most often Cooper-Jacob (CJ) straight line is used for aquifer parameter estimations from late time-drawdown data in cases of confined and unconfined aquifers. This straight-line method is attractive because of its simplicity and straightforward calculations without tedious and dubious type-curve matching procedure. The warranty of the CJ method application depends on the fact that the late time-drawdown measurements fall along the final portion of the Theis type curve. The main purpose of this paper is to present a general type straight-...

The vertical variation of drawdown around pumping wells generates an induced flow in the observation wells. A set of governing equations is presented to couple the drawdown variation and the vertical flux distribution in observation wells. A numerical example is performed to justify the governing equations and to verify the solution methods used by the simulation software WT. The example analyzes the effect of skin loss, wellbore storage, and vertical segmentation on the drawdown and induced flow in observation well during pumping. The evaluation of the Fairborn pumping test involves a vertically homogeneous and anisotropic water table aquifer, uniform well-face drawdown conditions in the pumping well and simulation of the drawdown evolution in the observation well with and without the effect of induced flow. The computer calibrations resulted in small differences between the measured and simulated drawdown curves.

Tidal drainage effect of confined aquifer is important to well tide interesting many relevant researchers. Through tidal analysis of water level monitoring in Chuan06 well, this paper explored the tidal drainage effect of the confined aquifer and its influence on the well tide. It indicated that: the changes in phase shift (η) and amplitude response (A) were attributed to the changes in transmissivity (T) rather than that in storativity (S), and the tidal drainage effect of isotropic aquifer could be effectively described by Hsieh model.

Summary Interpretation of pumping tests in unconfined aquifers has largely been based on analytical solutions that disregard aquifer heterogeneity. In this study, we investigate whether the prediction of drawdown responses in a heterogeneous unconfined aquifer and the unsaturated zone above it with a variably saturated groundwater flow model can be improved by including information on hydraulic conductivity ( K ) and specific storage ( S s ) from transient hydraulic tomography (THT). We also investigate whether these predictions are affected by the use of unsaturated flow parameters estimated through laboratory hanging column experiments or calibration of in situ drainage curves. To investigate these issues, we designed and conducted laboratory sandbox experiments to characterize the saturated and unsaturated properties of a heterogeneous unconfined aquifer. Specifically, we conducted pumping tests under fully saturated conditions and interpreted the drawdown responses by treating the medium to be either homogeneous or heterogeneous. We then conducted another pumping test and allowed the water table to drop, similar to a pumping test in an unconfined aquifer. Simulations conducted using a variably saturated flow model revealed: (1) homogeneous parameters in the saturated and unsaturated zones have a difficult time predicting the responses of the heterogeneous unconfined aquifer; (2) heterogeneous saturated hydraulic parameter distributions obtained via THT yielded significantly improved drawdown predictions in the saturated zone of the unconfined aquifer; and (3) considering heterogeneity of unsaturated zone parameters produced a minor improvement in predictions in the unsaturated zone, but not the saturated zone. These results seem to support the finding by Mao et al. (2011) that spatial variability in the unsaturated zone plays a minor role in the formation of the S-shape drawdown-time curve observed during pumping in an unconfined aquifer.

Mathematical models play a key role in assessing the future behavior of a groundwater system in response to various schemes of ground water resources development such as artificial recharging and in selecting an appropriate one out of many proposed schemes for its sustainable development. This paper presents an analytical solution of groundwater flow equation for unconfined, anisotropic, 2-D rectangular aquifer under the Boussinesq approximation to predict water table fluctuations in the aquifer in response to general time-varying intermittent recharge from multiple rectangular infiltration basins of different spatial dimensions. The horizontal anisotropy incorporated in the model is such that the principal axes of the hydraulic conductivity tensor are oriented parallel to the rectangular sides of the aquifer. The time-varying recharge rate is approximated by a series of line elements of different lengths and slopes depending on the nature of variation of recharge rate. The solution is obtained by using extended finite Fourier sine transform. Application of the solution is demonstrated with the help of synthetic examples. Numerical results of the analytical solutions are verified by comparison with the results obtained from MODFLOW. Numerical results indicate significant effect of anisotropy in hydraulic conductivity on the nature of water table variation.

This study is aimed at quantifying the difference in aquifer's response to recharge between some different locations in a fan aquifer and a delta aquifer for a preliminary study of revealing mechanisms of water transport in alluvial aquifer. The aquifer's response to recharge is statistically quantified with the two viewpoints: (1) timing and volume of recharge and (2) time length of aquifer's holding water. For the first point, a statistical model that links precipitation and groundwater level is introduced, and its parameters are identified using correlation analysis. Our results show that the recharge rate at the toe is higher than that at the apex and at the delta. For the second point, the concept of ‘memory effect’ of aquifer is adopted and quantified using the autocorrelation and spectral analyses. Our results show that the memory effect is longer at the toe of fan than at the apex, and thus, a temporary increase of water level has about five times as long-term influence on subsequent water levels at the toe of the fan as at the apex. This study demonstrates that the statistical analyses and modeling of hydrological data are useful for characterizing aquifer's hydrodynamics. Copyright © 2012 John Wiley & Sons, Ltd.

Natural or artificial hydraulic connections between a granular aquifer in contact with a fractured-rock aquifer can have significant physical and chemical impacts at both a local and a regional scale. In this study, numerical simulations are conducted in order to illustrate the hydrogeological consequences of such hydraulic relationships. The numerical investigation, based on a conceptual model, focuses on the effects of the hydraulic connections when conducting a pumping test in a well that is set into a granular confined aquifer overlying a fractured-rock aquifer which presents a few fractures directly connected to the granular aquifer. It is illustrated that when interpreting the pumping test with the conventional methods consisting of plotting the drawdown versus time, a bias is introduced on the estimation of the transmissivity of the granular aquifer due to groundwater flowing from the fractured-rock aquifer via connecting fractures. However, it is underlined that plotting drawdown log-derivative versus time helps to diagnose the existence of these hydraulic relationships and therefore avoids committing a bias on the transmissivity estimation of the granular aquifer. Numerical simulation results also illustrate that hydraulic connections between the two aquifers can have significant impacts on the hydrogeochemical signature of the granular aquifer under investigation.

Management of groundwater resources can be improved by using groundwater models to perform risk analyses and to improve development strategies, but a lack of extensive basic data often limits the implementation of sophisticated models. Dar es Salaam in Tanzania is an example of a city where increasing groundwater use in a Pleistocene aquifer is causing groundwater-related problems such as saline intrusion along the coastline, lowering of water-table levels, and contamination of pumping wells. The lack of a water-level monitoring network introduces a problem for basic data collection and model calibration and validation. As a replacement, local water-supply wells were used for measuring groundwater depth, and well-top heights were estimated from a regional digital elevation model to recalculate water depths to hydraulic heads. These were used to draw a regional piezometric map. Hydraulic parameters were estimated from short-time pumping tests in the local wells, but variation in hydraulic conductivity was attributed to uncertainty in well characteristics (information often unavailable) and not to aquifer heterogeneity. A MODFLOW model was calibrated with a homogeneous hydraulic conductivity field and a sensitivity analysis between the conductivity and aquifer recharge showed that average annual recharge will likely be in the range 80–100 mm/year.

The effect of tidal fluctuation on groundwater flow is an important issue from many aspects in coastal areas. This paper develops a new analytical solution to describe the groundwater fluctuation in a sloping coastal aquifer system which comprises an upper unconfined aquifer, a lower confined aquifer, and an aquitard in between. The solution is allowed to investigate the effects of bottom slope and leakage as well as aquifer parameters on head fluctuations in both unconfined and confined aquifers. The research result indicates that the effect of the bottom angle on the groundwater fluctuation and time lag is significant in the unconfined aquifer and not negligible if the leakage in the confined aquifer is large. In addition, the joint effects of aquifer parameters and bottom angle on groundwater fluctuation and time lag are also discussed.

Effective evaluation, management and abstraction of groundwater resources of any aquifer require accurate and reliable estimates of its hydraulic parameters. This study, therefore, looks at the determination of hydraulic parameters of an unconfined aquifer using both analytical and numerical approaches. A long-duration pumping test data obtained from an unconfined aquifer system within the Tailan River basin in Xinjiang Autonomous Region in the northwest of China is used, in this study, to investigate the best method for estimating the parameters of the aquifer. The pumping test was conducted by pumping from a radial collector well and measuring the response in nine observation wells; all the wells used in the test were partially penetrating. Using two well-known tools, namely AquiferTest and MODFLOW, as an aid for the analytical and numerical approaches, respectively, the parameters of the aquifer were determined and their outputs compared. The estimated horizontal hydraulic conductivity, vertical hydraulic conductivity, and specific yield for the analytical approach are 38.1–50.30 m/day, 3.02–9.05 m/day and 0.204–0.339, respectively, while the corresponding numerical estimates are 20.50–35.24 m/day, 0.10–3.40 m/day, and 0.27–0.31, respectively. Comparing the two, the numerical estimates were found to be more representative of the aquifer in the study area since it simulated the groundwater flow conditions of the pumping test in the aquifer system better than the analytical solution.

A mathematical model is presented that describes small, periodic, water level perturbations in a fully screened observation well penetrating a homogeneous, isotropic, confined aquifer system. The analytical solution is formulated in terms of frequency and phase response functions that are controlled by aquifer transmissivity (T) and storage coefficient (S). Well casing storage effects are considered; however, well screen entrance losses associated with turbulence are neglected because piezometric head differences inside and outside the well are small. As the ratio of well casing radius to well screen radius (r"c/r"w) changes, these theoretical response functions are systematically altered. When r"c/r"w 0 and system responses associated with differences in T and S are accentuated. For (r"c/r"w)>=1, however, distinguishing between system responses is more complicated because well casing storage effects gradually dominate water level perturbations as r"c/r"w grows. Finally, in practical applications for any r"c/r"w value, obtaining unique estimates for T and S can be difficult in the presence of noise without the improved Levenberg-Marquardt (LM) optimization scheme developed here. Initially, a sigmoidal curve fitting algorithm and observed frequency and phase response functions are used to identify a starting estimate for T. This value is then used in the LM procedure and facilitates convergence to optimal system parameters while minimizing uncertainty. Without this approach, however, the LM scheme will not yield unique estimates. This methodology yields smaller aquifer parameters than traditional specific capacity tests, suggesting either a well bore skin effect or a scaling phenomenon similar to that reported in the literature for slug and aquifer test comparisons. Hence, this technique is probably best suited for monitoring wells where conventional aquifer test methods are impractical. This approach is documented in several MATLAB m-files and illustrated by several examples using observed data.

Due to increases in water demand, the City of Kenedy, TX, USA must expand their small drinking water supply in the Gulf Coast aquifer system. Groundwater wells owned by the City of Kenedy, Karnes County, TX were examined to estimate properties for the Jasper aquifer. Conditions of four wells were assessed, after which two wells were rehabilitated and used as pumping wells in aquifer tests. Aquifer tests show that recovery in observation wells was not coincident with the cessation of pumping. Post-pumping data were selectively excluded so that only recovery data were used for analyses. Transmissivity for the Jasper aquifer ranges from 102 to 242 m2 d−1, and storativity ranges from 6.9E−05 to 3.3E−04. Transmissivity computed from recovery data was approximately 25 % higher than transmissivity computed from time-drawdown data. Field measured specific capacities and drawdowns were compared to theoretical specific capacities and drawdowns to calculate pumping well efficiencies in the range of 52.2–99.4 %. This study indicates that water demand for the City of Kenedy could be met by incorporating the tested wells into the water supply system. Future studies should be designed to estimate groundwater recharge rates and a complete water balance for computing a sustainable maximum annual yield.

Underground structures that penetrate into aquifers can cause groundwater-level drawdown and land subsidence. Numerical analyses, based on a three-dimensional (3-D) groundwater flow model incorporated with a 1-D consolidation model, have been conducted to assess the behaviour of seepage and effect on subsidence by considering underground structures in the multi-aquifer–aquitard system of Shanghai, China. Two extreme scenarios were examined: (1) distributed underground structures, and (2) concentrated underground structures around the heavily urbanized area. In the first scenario, the aquifer with underground structures was substituted with another material that possessed a lower hydraulic conductivity, established using the effective-medium theory; when the ratio of the volume of the underground structures to that of selected aquifer layers—(1) low-pressure partially-confined aquifer (Aq02), (2) the first confined aquifer (AqI), and (3) the second confined aquifer (AqII)—increases by 10 %, subsidence increases by about 3, 3 and 32 %, respectively. In the second scenario, part of the aquifer material was directly replaced by the structure material (very low hydraulic conductivity). In this situation, when the ratio of the volume of the underground structure to the volume of aquifers Aq02, AqI or AqII increases by 10 %, subsidence increases by about 5, 8 or 20 %, respectively.

Summary Drawdowns generated by extracting water from large diameter (e.g. water supply) well are affected by wellbore storage. We present an analytical solution in Laplace transformed space for drawdown in a uniform anisotropic aquifer caused by withdrawing water at a constant rate from partially penetrating well with storage. The solution is back transformed into the time domain numerically. When the pumping well is fully penetrating our solution reduces to that of Papadopulos and Cooper (1967); Hantush (1964) when the pumping well has no wellbore storage; Theis (1935) when both conditions are fulfilled and Yang (2006) when the pumping well is partially penetrating, has finite radius but lacks storage. Newly developed solution is then used to explore graphically the effects of partial penetration, wellbore storage and anisotropy on time evolutions of drawdown in the pumping well and in observation wells. We concluded after validating the developed analytical solution using synthetic pumping test.

Summary We analyze numerically the impact of key assumptions which are usually adopted to interpret borehole flowmeter test data. We base our work on a set of detailed numerical simulations of transient and pseudo-steady state convergent flow to a fully penetrating well that pumps at a constant total flow rate in a confined three-dimensional system formed by well demarcated facies. Our results allow identifying the effects of (i) the presence of a skin zone around the well, (ii) the contrast of hydraulic conductivities of the aquifer facies and the gravel pack, and (iii) the dynamics of the flow regime on the ability to characterize the local aquifer conductivities of a stratified system through the typical interpretation of downhole flowmeter tests. Vertical intervals along the wellbore, where reliable estimates of the aquifer conductivities can be obtained through classical formulations are identified in terms of a set of dimensionless parameters. These parameters involve the thickness of the facies constituting the stratified aquifer and the contrast of conductivities amongst different facies and between them and the skin zone.

Summary Head response to sea level fluctuations has been extensively used for characterizing coastal aquifers. When the aquifer is semiconfined and extends for a certain distance D under the sea, head response results from the superposition of two types of effects: hydraulic (i.e., ground water flow connection through aquifer and aquitard) and mechanical (induced by tidal loading onto the sea floor). Solutions are available for this problem that has been analyzed before, but only for D zero or infinity. These solutions do not allow analyzing aquifer systems that extends for a finite D, or identifying them, which is critical for coastal aquifer management. We derive an exact analytical solution that describes separately the mechanical and hydraulic effects. The proposed analytical solution is a generalization of most of existing analytical solutions. A simpler approximate analytical solution is also obtained for soft aquitards with low permeabilities. We find that the impact of the hydraulic component of the aquitard and the mechanical effects in the total head fluctuation at the shoreline is significant, but not very sensitive to the properties of the aquitard. The amplitude of these fluctuations relative to that of the sea tide ranges approximately between 1 (small D) and 0.5 (large D). This implies that aquifer penetration under the sea can indeed be identified if it is below a certain threshold, beyond which the system responds as if D was infinity. Surprisingly, the time lag is close to zero regardless of hydraulic parameters of the aquifer system.

This paper analyses the classical problem of transient surface–groundwater interaction in a stream–aquifer system under rather realistic conditions. The downward sloping unconfined aquifer is in contact with a constant water level at one end, and a fully penetrating stream at the other end whose water level is rising at a uniform speed. Furthermore, the aquifer is replenished by a vertical time-varying recharge. Closed form analytical expressions for hydraulic head and flow rate in the aquifer are obtained by solving the linearized Boussinesq equation using Laplace transform method. Effects of aquifer parameters on transient water table and flow rate are illustrated with a numerical example. To assess the efficiency of the linearization method, analytical solutions are compared with numerical solutions of the corresponding non-linear equation.

The standard practice for assessing aquifer parameters is to match groundwater drawdown data obtained during pumping tests against theoretical well function curves specific to the aquifer system being tested. The shape of the curve derived from the logarithmic time derivative of the drawdown data is also very frequently used as a diagnostic tool to identify the aquifer system in which the pumping test is being conducted. The present study investigates the incremental area method (IAM) to serve as an alternative diagnostic tool for the aquifer system identification as well as a supplement to the aquifer parameter estimation procedure. The IAM based diagnostic curves for ideal confined, leaky, bounded and unconfined aquifers have been derived as part of this study, and individual features of the plots have been identified. These features were noted to be unique to each aquifer setting, which could be used for rapid evaluation of the aquifer system. The effectiveness of the IAM methodology was investigated by analyzing field data for various aquifer settings including leaky, unconfined, bounded and heterogeneous conditions. The results showed that the proposed approach is a viable method for use as a diagnostic tool to identify the aquifer system characteristics as well as to support the estimation of the hydraulic parameters obtained from standard curve matching procedures. Copyright © 2012 John Wiley & Sons, Ltd.

Previous studies showed that the values of the representative parameters of an aquifer, such as the hydraulic conductivity (k), increase with the scale, that is, with the aquifer volume involved in the measurement. The main cause of this behavior is commonly ascribed to the heterogeneity of the porous media. Heterogeneity influences the scaling behavior differently for laboratory or field measurement, but the scale dependence of hydraulic conductivity is not dependent on the specific measurement method. In the present study, the scaling law of this parameter was determined on a real confined aquifer, using measurements obtained, both in the laboratory (flow cells) and the field (slug tests and aquifer tests). The corresponding data were statistically analyzed. A scaling law was proposed for both the laboratory and field scale, using the data obtained from flow cells, slug tests, and aquifer tests. Afterward, the scaling law was estimated at just the field scale, first using the slug tests and aquifer tests and then using only the aquifer test data.The scale dependence of the storativity was also investigated for all field measurements and then using only the aquifer test data. In conclusion, for both hydraulic conductivity and storativity, the trend to reach an upper bound increasing the scale parameter was investigated in the scale ranges of 67 and 99 m, respectively, examining only the data set relative to aquifer test measurements. Copyright © 2012 by Lippincott Williams & Wilkins.

Wells in aquifers of loose collapsible sediment are cased so that they have a blind wall and gain water only from the bottom. The hydraulic gradient established at the bottom of these wells during pumping brings the aquifer materials in a quicksand state, which may cause abrasion of pipes and pumps and even the destruction of well structure. To examine the quicksand occurrence, an analytical solution for the steady flow to a partially penetrating blind-wall well in a confined aquifer is developed. The validity of the proposed solution is evaluated numerically. The sensitivity of maximum vertical gradient along the well bottom in response to aquifer and well parameters is examined. The solution is presented in the form of dimensionless-type curves and equations that can be easily used to design the safe pumping rate and optimum well geometry to protect the well against sand production. The solution incorporates the anisotropy of aquifer materials and can also be used to determine the hydraulic conductivity of the aquifer. Copyright © 2012 John Wiley & Sons, Ltd.

The karstic upper Floridan aquifer in north-central Florida (USA) is recharged by both diffuse and allogenic recharge. To understand how recharged water moves within the aquifer, water levels and specific conductivities were monitored and slug tests were conducted in wells installed in the aquifer surrounding the Santa Fe River Sink and Rise. Results indicate that diffuse recharge does not mix rapidly within the aquifer but instead flows horizontally. Stratification may be aided by the high matrix porosity of the eogenetic karst aquifer. Purging wells for sample collection perturbed conductivity for several days, reflecting mixing of the stratified water and rendering collection of representative samples difficult. Interpretive numerical simulations suggest that diffuse recharge impacts the intrusion of allogenic water from the conduit by increasing hydraulic head in the surrounding aquifer and thereby reducing influx to the aquifer from the conduit. In turn, the increase of head within the conduits affects flow paths of diffuse recharge by moving newly recharged water vertically as the water table rises and falls. This movement may result in a broad vertical zone of dissolution at the water table above the conduit system, with thinner and more focused water-table dissolution at greater distance from the conduit.

Karst aquifers can have a complex flow as a result of the formation of large conduits from dissolution features. As a result, a three-dimensional finite-difference groundwater flow model (equivalent porous media) may not apply as the dual porosity nature of karst features and the effects of turbulent flow cannot be directly simulated. Statistical analysis of karst hydrographs of the Trifilia aquifer in Greece showed the existence of a slightly karstified mass with high primary porosity that regulates the flow. An equivalent porous media model was developed to simulate the Trifilia karst aquifer using MODFLOW. Steady state and transient state calibration gave encouraging results for the equivalent porous media approach, which does not consider pipe flow or turbulence. Detailed hydrogeological research conducted in the area helped define the aquifer hydraulic conductivity zones and extent; and flux to/from the aquifer. Only hydraulic conductivity and specific yield were adjusted during calibration, as the flux to/from the system was considered known and applied as boundary conditions. Small mean absolute and RMS piezometric head error of the model under both steady and transient state conditions were achieved.

Determining aquifer type, unconfined, semi-confined, or confined, by drilling or performing pumping tests has inherent problems (i.e., cost and complex field issues) while sometimes yielding inconclusive results. An improved method to cost-effectively determine aquifer type would be beneficial for hydraulic mapping of complex aquifer systems like fractured rock aquifers. Earth tides are known to influence water levels in wells penetrating confined aquifers or unconfined thick, low-porosity aquifers. Water-level fluctuations in wells tapping confined and unconfined aquifers are also influenced by changes in barometric pressure. Harmonic analyses of water-level fluctuations of a thick (~1000 m) carbonate aquifer located in south-central Oklahoma (Arbuckle-Simpson aquifer) were utilized in nine wells to identify aquifer type by evaluating the influence of earth tides and barometric-pressure variations using signal identification. On the basis of the results, portions of the aquifer responded hydraulically as each type of aquifer even though there was no significant variation in lithostratigraphy. The aquifer type was depth dependent with confined conditions becoming more prevalent with depth. The results demonstrate that harmonic analysis is an accurate and low-cost method to determine aquifer type.

Summary This paper presents new analytical solutions of a linearized Boussinesq equation characterizing groundwater flow in a stream–unconfined aquifer system due to transient seepage. The aquifer is underlain by a horizontal leaky bed, and interacts with an adjoining stream of varying water level through a semipervious vertical stream bank. Close form analytical expressions are derived to predict water head distribution, flow rate and volumetric exchange of water in response to time dependent rise or drop in the stream water level. Comparison between analytical and numerical results shows satisfactory agreement. The effects of the finite and semi-infinite lengths of the domain are considered in detail. Certain asymptotic situations such as sudden rise or drop in the stream water level, no flow condition at the aquifer’s base and absence of vertical stream bank can be dealt with as limiting cases of main results. An illustration of the new analytical approach is used to quantify the accretion/recession of the bank storage due to variation in various aquifer parameters.