Search

This paper presents an analytical model for describing the tidal effects in a two-dimensional leaky confined aquifer system in an estuarine delta where ocean and river meet. This system has an unconfined aquifer on top and a confined aquifer on the bottom with an aquitard in between the two. The unconfined and confined aquifers interact with each other through leakage. It was assumed that the aquitard storage was negligible and that the leakage was linearly proportional to the head difference between the unconfined and confined aquifers. This model's solution was based on the separation of variables method. Two existing solutions that deal with the head fluctuation in one-dimensional or two-dimensional leaky confined aquifers are shown as special cases in the present solution. Based on this new solution, the dynamic effect of the water table's fluctuations can be clearly explored, as well as the influence of leakage on the behaviour of fluctuations in groundwater levels in the leaky aquifer system. Copyright © 2015 John Wiley & Sons, Ltd.

Short-Term Low Volume (STLV) Sea Water Desalination Plant of 6000 m3/d is under construction in the middle area of Gaza Strip. The plant will provide desalinated water for 75,000 inhabitants in regions in Khanyounis and Rafah. The intake of desalination plant will be indirectly from four beach wells. This article aims at providing the environmental impacts of these wells on the aquifer and the mitigation measures in case of negative impacts. In order to study the impacts of beach wells on the aquifer, a prediction groundwater three-dimensional model for the beach wells area, starting from the year 2000 until year 2030, was used. MODFLOW software was used for modeling the groundwater flow and SEAWAT software was used to model the seawater intrusion effect. The aquifer parameters were set as if they were in the transient model. The long term seasonal recharge rate for the summer and winter is considered to represent the seasonal differences in recharge through each year. The study showed that the steady four-meter drawdown in the beach wells will force the flow from the eastern direction to the sea. This will have positive impacts on the aquifer since it will decrease the seawater intrusion to the aquifer. The beach wells will pump water with Cl concentration equal to 18,000 mg/l. This means that the beach wells will accelerate the flow from the aquifer to the sea direction but still the pumped water is considered as seawater. This indicates the positive impacts on the groundwater aquifer since it will decrease the seawater intrusion in the beach wells area (Gaza Strip Middle area). In conclusion, these beach wells in this desalination plant (small capacity) are safe for the groundwater aquifer and it will decrease the effect of seawater intrusion on the aquifer.

Summary A semi-analytical solution considering the vertical unsaturated flow is developed for groundwater flow in response to a slug test in an unconfined aquifer in Laplace space. The new solution incorporates the effects of partial penetrating, anisotropy, vertical unsaturated flow, and a moving water table boundary. Compared to the Kansas Geological Survey (KGS) model, the new solution can significantly improve the fittings of the modeled to the measured hydraulic heads at the late stage of slug tests in an unconfined aquifer, particularly when the slug well has a partially submerged screen and moisture drainage above the water table is significant. The radial hydraulic conductivities estimated with the new solution are comparable to those from the KGS, Bouwer and Rice, and Hvorslev methods. In addition, the new solution also can be used to examine the vertical conductivity, specific storage, specific yield, and the moisture retention parameters in an unconfined aquifer based on slug test data.

Pumping tests are routinely performed to characterize aquifers. In particular, recovery tests involve analyzing the residual drawdown after the termination of pumping. Evaluating the radius of investigation of pumping tests is important for test design and interpretation. However, the radius of investigation during the recovery phase has rarely been discussed in the literature. Here, we derive exact (semi-analytical) and approximate (fully analytical) solutions for the radius of investigation during the recovery phase, and present a sensitivity analysis for typical parameter values. During recovery, the radius of investigation shows non-monotonic behavior: it first increases, then decreases, and eventually vanishes. The maximum radius can be up to five times larger than that at the end of the pumping phase in the investigated range of parameter values. However, the conditions yielding a large radius of investigation are such that the time at which the maximum occurs is relatively large: up to one hundred times the pumping duration, depending on the parameters. Thus, in practice, one may need to find a compromise between the size of the investigated area and the time required for the test. In addition to the aquifer parameters, we observe that the pumping rate and duration, and the apparent measurement resolution are key parameters controlling the radius of investigation during recovery. Finally, the approach is applied to a field example. This study provides fundamental insight on the radius of investigation of recovery tests as well as practical solutions, thereby facilitating the design and interpretation of recovery tests in practice.

Finding large volume of saline water to support oil field developments in an arid region of the Barmer Basin, Rajasthan, India, was a challenge. Prior to this study, very limited information was available about aquifers deeper below 150 m below ground level (bgl). The present paper describes the characterization of a deep aquifer system using oil field data acquired during hydrocarbon exploration and development. The objective of the study was aimed to identify saline water that has no practical use for domestic or irrigation purposes at economically viable cost without any adverse effect on freshwater system. Detailed regional hydrogeological study has been carried out using oil exploration data, i.e. seismic, geophysical logs, etc. followed by aquifer well drilling and testing to understand the hydrogeology of the southern part of the Barmer Basin. It has been found that extensive confined multiaquifer systems exist between 150 and 1000 mbgl. Aquifers were identified by using oil field well logs and cores of exploration and development wells. Four distinct groups of permeable granular zones separated by impermeable zones have been identified. The spatial extent of the aquifer has also been mapped with the help of seismic reflection data. Finally, geometry and thickness of the aquifer have been defined of each layer with reasonable accuracy. The salinity data of drilled wells indicate that groundwater salinity increases with depth. Brackish (2500 mg/L) groundwater occurs at the top and becomes highly saline (~17,500 mg/L) at the bottom. An extensive deep confined saline aquifer has been identified in Jagadia (Miocene) formation. Aquifer test has been conducted to understand the hydraulic characteristics and water quality of this aquifer. The results indicate that hydraulic conductivity is in range of 20–25 m/day in the Jagadia formation. Salinity of groundwater is ~17,500 mg/L. The aquifer is shallower in the north and gradually deepens southwards where aquifer top is ~1500 mbgl. The gross thickness of sand in the Jagadia formation varies from 25 m to a maximum of 600 m (south-east). The total gross calculated volume of the aquifer is ~2.6 × 109 m3. The aquifer contains unconsolidated to poorly consolidated, medium- to coarse-grained, moderate to well-sorted, subrounded sands. Quartzose with carbonaceous claystone and clay interbeds and minor lignite are also present. Grain size analyses indicate a mostly uniform formation with the majority of samples having a uniformity coefficient of 4 or less. The effective porosity has also been derived from petrophysical logs, and it is ~20% in the northeast and increases to ~30% in the southeastern boundary. This large static groundwater resource within the Jagadia formation below ~250 m depth has been identified as suitable aquifer for saline water abstraction to meet the long-term saline water requirement of oil fields in the southern area of the Barmer Basin. This aquifer is not in use for domestic and irrigation purposes due to salinity and its depth of occurrence. Saline water abstraction is not likely to deplete the limited dynamic shallow groundwater resources.

The aim of this work was to develop the exact groundwater flow model within a confined aquifer. We argued that, the Theis groundwater flow model is an approximation of the real formulation of the model as Theis removed some components of the equation to have a simple model. Initially, we derived an exact groundwater flow equation for a confined aquifer so as to include all high order terms that were removed by Theis and also to take into account the assumptions that were used during the derivation of the groundwater flow by Theis. Thereafter, we proved that the new groundwater flow equation has a unique solution. We then derived a new numerical scheme for a singular partial differential equation that combines the Mellin transform and the Lagrange approximation of a continuous function. The Mellin transform was used to remove the singularity in the newly developed exact groundwater flow equation for a confined aquifer. The equation became ordinary, wherein we used the Adam Bashforth method to the ordinary differential equation in the Mellin space. The inverse of Mellin was then used to get the exact numerical scheme in real space. We present the stability analysis of the new numerical scheme using the von Neumann method. Lastly, numerical simulations using experimental field data are presented. Our solution is compared to that of Theis. Our simulations show the importance of the scaling factor which was removed from the Theis groundwater flow equation. The simulations also show that the change in drawdown dependdepends on the scaling factor.

The present study is focused on an examination of the correlation relationships for hydraulic permeability and transmissivity with electrical resistivity in a range of fractured and alluvial aquifers. The observed permeability data for fractured rock aquifers at some locations is correlated nonlinearly with electrical resistivity of the aquifers estimated from resistivity sounding data and it is found that the permeability of the aquifer in this region exponentially decreases with increase in resistivity. Permeability of the hard rock aquifer within the weathered zone and alluvium aquifers increases exponentially with increase in resistivity, and transmissivity decreases exponentially. However, in case of fracture rock and sandwiched aquifers, transmissivity increases exponentially with increase in resistivity. An attempt has been made to find general functional relationship between hydraulic parameters and resistivity of the aquifer, and therefore, published and observed data from India and other parts of the world has been taken under consideration. It is found that for fracture rock and alluvium aquifers, permeability and the transmissivity are best defined as the exponential functions of aquifer resistivity. The application of electrical parameters obtained from resistivity data for evaluation of hydraulic parameters has been demonstrated in detail within the Osmania University Campus, Hyderabad (India). The empirical relations between aquifer parameters and resistivity are established for transforming resistivity distribution into permeability and transmissivity of the aquifer. The information thus obtained from resistivity data on permeability of the aquifer and transmissivity distribution in the study area can be used for optimal use and assessment of water resources.

A pumping test is a field experiment in which a well is pumped at a controlled rate and water-level response (drawdown) is measured in one or more surrounding observation wells and optionally in the pumped well (control well) itself. Response data from pumping tests are used to estimate the hydraulic properties of aquifers, evaluate well performance and identify aquifer boundaries. Aquifer test and aquifer performance test (APT) are alternate designations for a pumping test.

A new method of testing anisotropic, inhomogeneous multiple aquifer systems developed by the author makes use of small diameter bore construction techniques and enables simultaneous testing of superposed aquifers and aquitards (aquicludes). Because of the low cost of the method the hydraulic properties of the multiple aquifer system can be determined at many sites distributed throughout the area of interest, enabling simulation of the local and regional ground-water flow conditions and other hydrological characteristics of the system. Since its development in 1964 the technique improved and was employed in ground-water investigations. Data and results from the inhomogeneous, anisotropic multiple aquifer system west of Melbourne are given.

This research modeled geological and hydrogeological controls on groundwater occurrence in Oban Massif and environs southeastern Nigeria. Topographical, hydrogeological, and structural maps, including lithology samples from drilled bores, well completion, and pumping test data in the study area were procured. Collection of coordinates of rock sample locations and structural data on strike and dip of rock exposures was collected. Geological and structural information collected was overlaid on the topographical, hydrogeological and structural map and digitized to produce the geological map of the study area. Thematic map on geological groundwater prospect map of the study was prepared using multicriteria evaluation. Relative weights were assigned to various rock types based on their relative contribution to groundwater occurrence and the map was reclassified using geographic information system (ArcGIS10.1) analysis. Depth ranges of the various lithologic units from drilled boreholes were used to construct lithologic correlation section of the boreholes across the study area using RockWorks16 Program software. Hydrogeological parameters such as storativity, specific capacity, transmissivity, drawdown, pumping rate, static water level, total depth, and well yield were computed from well completion reports and aquifer test. Results shows that the geologic groundwater prospect map was categorized into very good (28.73 m2), good (9.66 m2), moderate (35.08 m2), fair (49.38 m2), and poor (77.63 m2) zones. Aquifer parameters showed ranges such as (specific capacity (1.81–31.16 m2/day/m), transmissivity (0.0033–12 m2/day), storativity (9.4 × 10−3–2.3), drawdown (2.2–17.65 m), pumping rate (0.75–3.57 l/s), static water level (0–20.5 m), and total depth (3.3–61 m). Borehole depths obtained in the basement are shallower than those in the sedimentary area. Aquifer test parameters obtained from boreholes across the study indicate better correspondence with zones identified as good water prospect in the study. It was evident that well yield is not a very reliable aquifer performance indicator, because it depends largely on the efficiency of the pump installed. Therefore, other aquifer parameters must be employed in aquifer performance assessment. The geologic formation is paramount in determining aquifer performance. The result of this groundwater occurrence is useful as a guide for groundwater developers, which engineers in water resource management and land-use planners to select suitable areas to implement development schemes and also government agencies.

Coastal Aquifer System of Jakarta consist of unconfined aquifer layers, confined aquifer I and confined aquifer II. Resources of groundwater is very important for Jakarta City, for drinking water, industry, hotel, government offices and various other facility. Important considering of groundwater resources of Jakarta hence needed an effort to preserve the groundwater and awake its continuity by conducting a system management of groundwater. Model used for the management of groundwater system of aquifer coastal referred as Groundwater Model Simulation and Optimization of Quasi Three Dimension ( OPT-Q3D). Model simulation and optimization represent computer model of quasi-three dimensions with method of finite difference used for the operation of infiltration of sea water. This model can conduct current simulation of groundwater flow, head of fresh water and brine, and describe the movement of interface fresh water and sea water. The model can also make optimization of system aquifer with single or multi layers. Jakarta Groundwater Basin assumed consist three layers of aquifer separated by impermeable layer. Applying of groundwater simulation model in Jakarta can give information regarding balance of groundwater, head of freshwater, head of brine, interface brine and freshwater, map of brine distribution and bargain in each; every aquifer. Herein after model optimization will yield various information able to wear upon which consideration to manage the amount of pumping of optimal ground water every area in each layer of aquifer, amount of optimal pumping, optimal freshwater head, head of optimal brine and map of infiltration. Kata Kunci : Air Tanah, Pengelolaan, Intrusi Air Laut, Modeling

The paper aims to evaluate the impacts of the average hydraulic conductivity of the heterogeneous aquifer on the estimated hydraulic conductivity using the observations from pumping tests. The results of aquifer tests conducted at a karst aquifer are first introduced. A MODFLOW groundwater flow model was developed to perform numerical pumping tests, and the heterogeneous hydraulic conductivity (K) field was generated using the Monte Carlo method. The K was estimated by the Theis solution for an unconfined aquifer. The effective hydraulic conductivity (Ke) was calculated to represent the hydraulic conductivity of a heterogeneous aquifer. The results of numerical simulations demonstrate that Ke increase with the mean of hydraulic conductivity (EK), and decrease with the coefficient of variation of the hydraulic conductivity (Cv). The impact of spatial variability of K on the estimated Ke at two observation wells with smaller EK is less significant compared to the cases with larger EK.

Groundwater management authorities usually use groundwater budget calculations to evaluate the sustainability of withdrawals for different purposes. The groundwater budget calculation does not always provide reliable information, and it must often be supported by further aquifer monitoring in the case of hydraulic connections between neighboring aquifers. The Riardo Plain aquifer is a strategic drinking resource for more than 100,000 people, water storage for 60 km2 of irrigated land, and the source of a mineral water bottling plant. Over a long period, the comparison between the direct recharge and the estimated natural outflow and withdrawals highlights a severe water deficit of approximately 40% of the total groundwater outflow. A groundwater budget deficit should be a clue to the aquifer depletion, but the results of long-term water level monitoring allowed the observation of the good condition of this aquifer. In fact, in the Riardo Plain, the calculated deficit is not comparable to the aquifer monitoring data acquired in the same period (1992–2014). The small oscillations of the groundwater level and the almost stable streambed spring discharge allows the presumption of an additional aquifer recharge source. The confined carbonate aquifer locally mixes with the above volcanic aquifer, providing an externally stable recharge that reduces the effects of the local rainfall variability. The combined approach of the groundwater budget results and long-term aquifer monitoring (spring discharge and/or hydraulic head oscillation) provides information about significant external groundwater exchanges, even if unidentified by field measurements, and supports the stakeholders in groundwater resource management.

Recovery pumping tests are still one of the most commonly preferred preliminary design steps in the assessment of aquifer hydraulics. The use of the existing methods would be insufficient under non-ideal aquifer conditions (i.e. heterogeneity, measurement errors, and boundary effect, etc.) which violate the Theis model assumptions developed for recovery test analysis. In this study, a new parameter estimation methodology based on the Radial Basis Collocation Method (RBFCM) was formulated to access the hydraulic parameters in a reliable, robust and accurate manner using recovery pump test. The suggested approach was established on the idea that the dimensionless time value at the pump-cessation which serves as a matching value is obtained by means of RFBCM. The proposed approach is straightforward to implement; which requires no data refinement, additional parameter, and visual match. The performance of the proposed method was tested with several aquifer conditions including homogeneous synthetic data, heterogeneous aquifer simulation and real field applications. The results confirm that the proposed method has a parameter estimation capacity as high as the available techniques in the literature and provides the practitioners to understand a more accurate portrayal of the effects of heterogeneity on the hydraulic parameters during the test process. In addition, the suggested methodology for the interpretation of aquifer recovery test can be evaluated to be employed as a diagnostic tool to identify non-ideal conditions. The potential use of RBFCM in this study was also presented as the supplement of aquifer test interpretation assessment.

We used numerical modeling to study self-potential (SP) signals associated with a pumping test in a layered aquifer containing the main aquifer, a thin aquitard, and a shallow aquifer. The results revealed an unusual behavior of SP signals, which were not linearly correlated with the hydraulic head distributions. We explained this behavior by a vertical downward groundwater flow, from the shallow aquifer to the main aquifer, in the course of the pumping test. However, when plotted as a function of time, the SP signals and hydraulic heads displayed coherent behavior. In both distributions, three stages of the pumping test were determined: at early times, only the main aquifer and the aquitard responded to the pumping; at intermediate times, the downward flow from the shallow aquifer occurred; and at late times, the layered aquifer responded to the pumping as a whole. The SP signals reacted to the sequence of these stages much faster than the hydraulic head distributions. In principle, this might allow reducing the duration of the pumping tests without losing valuable information.

The paper presents hydrogeologic properties for a leaky till–mantled fractured bedrock aquifer system based on geophysical and hydraulic tests performed at a drumlin located in northeastern Massachusetts, USA. The site profile consists of a fractured bedrock aquifer overlain by a 30 m thick unweathered, coarse-grained till aquitard. Steady state, decadal scale, hydraulics varied little until seasonal irrigation pumping was initiated in recent years, causing a substantial annual drawdown in the aquifer and leakage from the overlying till. High frequency hydraulic head data sets collected in monitoring wells record the hydraulic response to the irrigation pumping. These data sets, together with results from small scale slug and purge tests performed in monitoring wells, are used to characterize the hydrogeologic behavior of this groundwater system. Geophysical logging performed in bedrock wells confirmed the presence of numerous flowing fractures. The large-scale continuum analysis of the fractured bedrock aquifer response to the irrigation pumping yields transmissivity values consistent with those determined from the small-scale, short-term purge test results. The low hydraulic conductivity till has a significant impact on the drawdown behavior of the fractured bedrock aquifer. Calibrated values from the collective data sets and analyses result in the following properties for the 30 m thick unweathered till: hydraulic conductivity K′ = 7.2 × 10−9m/s, transmissivity T′ = 2.3 × 10−8m2/s, and storativity S′ = 2.7 × 10−4, and for the underlying fractured bedrock aquifer: T = 6.5 × 10−6m2/s with an average fracture aperture of 46 μm and hydraulic conductivity Kf= 1.3 × 10−3m/s. These results should describe similar unweathered coarse-grained till–mantled fractured bedrock aquifer systems and provide useful data for preliminary analyses prior to any site-specific investigations.

The standard subsidence package for MODFLOW, MODFLOW-SUB simulates aquifer-system compaction and subsidence assuming that only 1-D-vertical displacement of the aquifer system occurs in response to applied stresses such as drawdowns accompanying groundwater extraction. In the present paper, 3-D movement of an aquifer system in responses to one or more pumping wells is considered using the new aquifer-system deformation package for MODFLOW, NDIS. The simulation of aquifer- system 3-D movement using NDIS was conducted with a stress or hydraulic head dependent specific storage coefficient to simulate nonlinear deformation behavior of aquifer-system sedimentary materials. NDIS's numerical simulation for aquifer horizontal movement is consistent with an analytic solution for horizontal motion in response to pumping from a leaky confined aquifer (Li, 2007). For purposes of comparison, vertical subsidence of the aquifer system in response to groundwater pumping is simulated by the both the NDIS and MODFLOW-SUB models. The results of the simulations show that land subsidence simulated by MODFLOW-SUB is significantly larger and less sensitive to pumping rate and time than that simulated by NDIS. The NDIS simulations also suggest that if the total pumpage is the same, pumping from a single well may induce more land subsidence than pumping from multiple wells.

In this study, we use a finite difference method to solve low velocity non-Darcian flow to a well in the first kind of leaky aquifer system. Flow in the confined aquifer is assumed to be Darcian and horizontal, whereas flow in the aquitard is assumed to be non-Darcian and vertical. The threshold hydraulic gradient existence of non-Darcian flow in low permeability porous media is employed to describe the non-Darcian flow in the aquitard. A numerical solution has been obtained by using a finite difference method. This solution is compared with the previous solution for Darcian flow case in leaky aquifer system. The error has been analyzed. The comparison of this study and Darcian flow case (Hantush and Jacob, 1955) in leaky aquifer system indicates that the error is very small and can be neglected. However, the hydrogeological parameter calculation of leaky aquifer system is remarkably influenced by low velocity non-Darcian flow in aquitard. For the inflection point method (Hantush, 1956), the absolute values of estimated errors for coefficient of transmissibility of confined aquifer and vertical hydraulic conductivity of aquitard show negative relationship with the pumping rate. For the type curve-fitting method (Walton, 1962), the estimated errors for coefficient of transmissibility and elastic drainable porosity of confined aquifer are very small under small pumping rate. In general, the estimated errors for coefficient of transmissibility and elastic drainable porosity of confined aquifer can be controlled under certain level through adjusting pumping rate. The estimated error of vertical hydraulic conductivity of aquitard is quite large no matter which method is used, even up to nearly 300%.

We present a distributed-order fractional diffusion-wave equation (dofDWE) to describe radial groundwater flow to or from a well, and three sets of solutions of the dofDWE for flow from a well for aquifer tests: one for pumping tests, and two for slug tests. The dofDWE is featured by two temporal orders of fractional derivatives, b1 and b2, which characterise small and large pores, respectively. By fitting the approximate solutions of the dofDWE to data from slug tests in the field, we determined the effective saturated hydraulic conductivity, Ke, transmissivity, Tf, and the order of fractional derivatives, b2 in one test and b2 and b1 in the second test. We found that the patterns of groundwater flow from a well during the slug tests at this site belong to the class of sub-diffusion with b2 < 1 and b1 < 1 using both the short-time and large-time solutions. We introduce the concept of the critical time to link Ke as a function of b2 and b1. The importance of the orders of fractional derivatives is obvious in the approximate solutions: for short time slug tests only the parameter b2 for flow in large pores is present while for long time slug tests the parameters b2 and b1 are present indicating both large and small pores are functioning.

The streamflow depletion due to groundwater pumping from deep aquifer near the Juksan stream has been simulated, in this study, by using the surface water and groundwater integrated model, SWAT-ODFLOW in order to analyze the relationship between the stream depletion and hydraulic properties of aquifer and streambed, and to spatially assess the streamflow depletion. The simulated results showed that the streamflow depletion rate divided by the pumping rate for each well location ranges from 10% to 90% with reflecting the various well-stream distance, transmissivity, storativity, and streambed hydraulic conductance. In particular, the streamflow depletion exceeds about 50% of pumping rate for conditions with transmissivity higher than or storage coefficient lower than 0.1. The simulated results in the form of spatial maps indicated that the spatially averaged percent depletion of streamflow is about 53.6% for five years of pumping which is lower than that for shallow aquifer pumping by 12.9%. From the spatially distributed stream depletion, it was found that higher and more rapid stream depletion to pumping occurs near middle-downstream reach.

A karst analog model has been developed for simulating karst aquifer systems with fracture and conduit domains in the laboratory. In this study, sixty-four experiments under different recharging and discharging conditions were carried out with the analog setup to study flow in the karst analog model. The experiments did not only provide hydraulic head data but spring discharge process as well. The experimental results were used to obtain empirical models of water hydraulic head under different hydrological conditions, which together with the spring discharge analysis aided in developing a water hydraulic head prediction model for the analog model. The results showed that water hydraulic head increased with logarithm of time and declined in step-shaped style, which can be used in karst aquifer systems research. Consequently, the study provides useful information for a better understanding of flow in karst aquifer systems.

Water level time series from groundwater production wells offer a transient dataset that can be used to estimate aquifer properties in areas with active groundwater development. This article describes a new parameter estimation method to infer aquifer properties from such datasets. Specifically, the method analyzes long-term water level measurements from multiple, interacting groundwater production wells and relies on temporal water level derivatives to estimate the aquifer transmissivity and storativity. Analytically modeled derivatives are compared to derivatives calculated directly from the observed water level data; an optimization technique is used to identify best-fitting transmissivity and storativity values that minimize the difference between modeled and observed derivatives. We demonstrate how the consideration of derivative (slope) behavior eliminates uncertainty associated with static water levels and well-loss coefficients, enabling effective use of water level data from groundwater production wells. The method is applied to time-series data collected over a period of 6 years from a municipal well field operating in the Denver Basin, Colorado (USA). The estimated aquifer properties are shown to be consistent with previously published values. The parameter estimation method is further tested using synthetic water level time series generated with a numerical model that incorporates the style of heterogeneity that occurs in the Denver Basin sandstone aquifers.

Semi-analytical solutions of flow to a well in an unconfined single porosity aquifer underlain by a fractured double porosity aquifer, both of infinite radial extent, are obtained. The upper aquifer is pumped at a constant rate from a pumping well of infinitesimal radius. The solutions are obtained via Laplace and Hankel transforms and are then numerically inverted to time domain solutions using the de Hoog et al. algorithm and Gaussian quadrature. The results are presented in the form of dimensionless type curves. The solution takes into account the effects of pumping well partial penetration, water table with instantaneous drainage, leakage with storage in the lower aquifer into the upper aquifer, and storativity and hydraulic conductivity of both fractures and matrix blocks. Both spheres and slab-shaped matrix blocks are considered. The effects of the underlying fractured aquifer hydraulic parameters on the dimensionless drawdown produced by the pumping well in the overlying unconfined aquifer are examined. The presented solution can be used to estimate hydraulic parameters of the unconfined and the underlying fractured aquifer by type curve matching techniques or with automated optimization algorithms. Errors arising from ignoring the underlying fractured aquifer in the drawdown distribution in the unconfined aquifer are also investigated.

This paper presents an innovative technology referred to as Dual Function Well (DFW), which has been developed in order to reduce the construction costs of dewatering when excavation is conducted in an aquitard over a confined aquifer. DFW technology is a method to lower both shallow groundwater and deep groundwater, either separately or simultaneously, using one well. The DFW includes two or more independent screens corresponding to each aquifer, and a valve is located between the screens inside a steel pipe. When the valve is closed, groundwater is pumped from the upper screen in the shallow aquifer. When the valve is open, groundwater is pumped from the screens in both the shallow and deep aquifers. DFW technology is used to replace the traditional method involving two sets of wells, in which the first set of wells pumps groundwater from the shallow aquifer, and a second set pumps groundwater from the deep aquifer. To investigate the effectiveness of DFW, field pumping tests using a DFW were conducted, and both groundwater head and settlement were monitored. Numerical simulation was adopted to simulate the results of the pumping tests. Comparison between the results from the DFW and from an ordinary mixing well indicates that the use of a DFW with the valve closed can reduce the pumping time from a deep aquifer and can reduce the ground settlement caused by dewatering. The results indicate the DFW technology is feasible and effective.

We present the comprehensive discharge potential for steady three-dimensional flow in horizontally stratified coastal aquifers with a horizontal base and a vertical coastline. The gradient of this comprehensive potential gives the vertically integrated discharge throughout the aquifer, i.e., the specific discharge vector as a function of three-dimensional space integrated over the saturated portion of the aquifer. The boundary values of the comprehensive potential along the coast can be computed precisely, given the geometry of the aquifer: the hydraulic conductivities of the strata, the elevations of the horizontal planes that separate the strata, and the elevation of the impermeable base of the aquifer relative to sea level. Boundary conditions of the comprehensive potential may either be given in terms of its gradient, or computed from given heads along the boundaries. The governing equation of the comprehensive potential is the Poisson equation in areas of infiltration and the Laplace equation elsewhere. The computation of interface elevations, piezometric heads, and the vertical distribution of flow, requires that an assumption be made regarding the relation between the comprehensive potential and piezometric heads. We adopt the Dupuit-Forchheimer approximation for this purpose and make use of the Ghyben-Herzberg equation. We present several applications of the approach, and find that the stratification may have a significant effect on the boundary value of the comprehensive potential, and thus on the flow rates in the aquifer. This article is protected by copyright. All rights reserved.

Hard-rock aquifers, which constitute a water supply source in many countries, are highly heterogeneous and defining a realistic model of an aquifer can be extremely complex. The objective of this study was to hydraulically characterize a metamorphic aquifer in a representative area of Italy and to identify the most appropriate approach for tapping of groundwater in this challenging environment. The results of surface fracture surveys, injection tests, pumping tests, and a simplified numerical model were compared. From the surface fracture survey, a model of the rock mass characterized by a well-developed discontinuity network and by a high frequency of discontinuities resulted. The injection tests showed the extreme heterogeneity and the lower hydraulic conductivity of the rock mass in comparison with the results of the pumping tests. The independent estimate of the hydraulic parameter resulting from numerical model highlighted a range of values higher than those resulting from the pumping tests. The study demonstrated that the continuum medium approach can be used in the case of hard-rock aquifers with a dense network of discontinuities. The multi-scale approach is recommended for investigating hydraulic heterogeneity and significantly helps to identify the most promising areas for well locations and their characteristics in relation to the style of fracturing.

Aquifers within the Columbia River Basalt Group (CRBG) provide a critical water supply throughout much of the Pacific Northwest of the United States. Increased pumping has resulted in water level declines in this region. Recharge into this aquifer system is generally not well understood. Recent suggestions of probable decades-long droughts in the 21st century add to this problem. We show that geophysical methods can provide useful parameters for improved modeling of aquifers in a primary CRBG aquifer located on the eastern edge of the Columbia Plateau. Groundwater models depend in part on the area, thickness, porosity, storativity, and nature of confinement of this aquifer, most of which are poorly constrained by existing well information and previous stress tests. We have made use of surface gravity measurements, borehole gravity measurements, barometric efficiency estimates, earth tidal response, and earthquake seismology observations to constrain these parameters. We show that the aquifer, despite its persistent drawdown, receives a great deal of recharge annually. Much of the recharge to the aquifer is due to leakage from overlying flows, ultimately tied to precipitation, an important result for future aquifer management in times of sustained drought.

Estimation of aquifer hydraulic properties is essential for predicting the response of an aquifer to extractions and hence estimating the availability of the groundwater resources. Aquifer tests are commonly used for the estimation of aquifer properties; however, they can be expensive and often only characterize the short-term response of the aquifer. This paper presents a time series modelling approach to estimating aquifer hydraulic properties. It is applied to 42 bores monitoring an unconfined aquifer within an irrigation region of south-eastern Australia, and the resulting probabilistic estimate of hydraulic properties are evaluated against pumping test estimates. It is demonstrated that the time series modelling can provide a reliable estimate of the hydraulic properties that are typical of a very long-term pumping test. Furthermore, the application of the time series modelling to 42 bores provided novel insights into the aquifer heterogeneity. We encourage others to further test the approach and the source code is available from: http://www.mathworks.com/matlabcentral/fileexchange/48546-peterson-tim-j-groundwater-statistics-toolbox Copyright © 2015 John Wiley & Sons, Ltd.

This paper presents a case history of behaviour during a series of pumping tests in an alternated multi-aquifer-aquitard system in a foundation pit in Tianjin, China. The test site is located at Tianjin Railway Station, which is in the downtown area and is surrounded by many buildings. The groundwater system at the test site is composed of a phreatic aquifer and three confined aquifers. Four groups of single well pumping tests were conducted in each aquifer to obtain the hydrogeological parameters of the aquifers and investigate the hydraulic connection among the aquifers. Test results show that there is hydraulic connection among the upper 3 aquifers. Moreover, both analytical and numerical methods were employed to analyse the hydrogeological parameters. The analytical solution was obtained for the phreatic aquifer using the Dupuit equation, and the Cooper–Jacob method was conducted for the confined aquifers. The numerical simulation was performed using a finite element method (FEM). The results illustrate that the numerical method gives more reliable results than the analytical method does. The numerical simulation considers the anisotropic characteristic of soils, and the hydrogeological parameters of all of the soils can be calculated. The analytical solution, however, may be influenced by wellbore storage or by the leakage effect of the aquitards, and it only gives the parameters of the aquifer where the pumping tests were performed.

This study deals with protection of springs, which are fed by aquifers susceptible to contamination by anthropogenic activities. Krokos aquifer, located in Western Macedonia, Greece, whose springs provide water to Krokos town, is used as a case study. In this aquifer, concentrations of nitrates, exceeding the legislation limits, had been occasionally detected. First, some additional water quality measurements have been conducted, covering more than one calendar year, which confirmed rather high concentrations of nitrates, close, but not exceeding the World Health Organization guideline limit of 50 mg/L. Then, numerical simulation of groundwater flow in Krokos aquifer took place. Groundwater modeling system, which allows for construction of a three-dimensional flow model, has been used in this task. First, the boundaries of the aquifer and the respective boundary conditions have been defined, based on available field data. Then, the required hydraulic head and groundwater velocity values have been ...

Coastal aquifers are always under threat of seawater intrusion due to over-extraction of groundwater. The objective here is to assess aquifer response to variation in pumping and rainfall recharge due to projected climate change by groundwater modelling in a heavily exploited aquifer. Finite element groundwater flow modelling was carried out from March 1988 to December 2030 using FEFLOW software. Steady state calibration was done to match observed and simulated groundwater head by varying aquifer parameters within the allowable range. Transient state calibration was carried out during the period March 1988 to December 2002. The calibrated model was validated by comparing the simulated and observed groundwater head from January 2003 to December 2012. Groundwater head was predicted for a period until 2030 under eight different scenarios of changes in pumping and rainfall recharge. This prediction indicated that 10% increase of recharge and 10% decrease of pumping causes 3 m and 6 m increase in groundwater head in upper and lower aquifers, respectively, by the end of 2030. Groundwater recharge can be increased by rejuvenation of existing surface water bodies, check dams and construction of proposed check dams. Thus, increase of groundwater recharge and decrease in well field pumping is achievable to restore this heavily exploited coastal aquifer in another 20 years.

This paper describes the development of a methodology that can be used for determining the spatial and temporal distribution of additional water volumes required to meet a defined groundwater target, such as an historical peizometric surface. The methodology is demonstrated on a case study concerned with mitigating declining groundwater levels in an alluvial aquifer intensively used for agriculture in the Lockyer Valley, Queensland, Australia. The proposed mitigation measure is the importing of large volumes of purified recycled water (PRW) from a large scale indirect potable reuse scheme into the aquifer system. The developed methodology employs both a groundwater flow model together with linear uncertainty analysis. Therefore for the case study, a distributed parameter numerical groundwater flow model was developed for the Lockyer valley alluvial aquifer system using MODFLOW, calibrated to observed groundwater levels, and further constrained by estimates of diffuse and river recharge from water balance studies. The model was used to simulate groundwater levels in the aquifer over a 20-year period. Optimal spatial and temporal distribution of volumes of imported water required to mitigate declining groundwater levels over that period were then estimated, using a modified version of the MODFLOW General Head Boundary (GHB) package. Uncertainty in the predicted import volumes was estimated using linear bayesian analysis principles. The relative worth of data from each observation bore within the groundwater monitoring network was also assessed in terms of the extent to which predictions of import water volumes were made more reliable when furnished with that data. Application of the methodology to the Lockyer alluvial aquifer system illustrated the suitability of the developed methodology for estimating the additional water volumes required for managed aquifer recharge or groundwater substitution schemes in similarly over-exploited aquifers.

Due to the pollution of shallow groundwater and the rapid development of society and economy which consume more freshwater, the exploitation of confined groundwater is steadily increasing in north China. Therefore, the rapid decline of the confined groundwater head increases the risk of confined aquifer pollution by leaky recharge from shallow aquifers. In this paper, a quantitative method for assessing confined aquifer vulnerability to contamination due to pumping has been developed. This method is based on the shallow and confined groundwater flow model and the advection and dispersion in the aquitard, including sorption. The cumulative time for the pollutant concentration at the top boundary of confined aquifer exceeding the maximum allowable level is defined as the confined aquifer vulnerability index, which can be obtained by numerically solving the solute transport equation. A hypothetical example is chosen as a case study to illustrate the whole process. The results indicate that the proposed method is a practical and reasonable assessment method of confined aquifer vulnerability.

To take into account the variability of the medium through which the groundwater flow takes place, we presented the groundwater flow equation within a confined aquifer with prolate coordinates. The new equation is a perturbed singular equation. The perturbed parameters is introduced and can be used as accurately replicate the variability of the aquifer from one point to another. When the perturbed parameter tends to zero, we recover the Theis equation. We solved analytically and iteratively the new equation. We compared the obtained solution with experimental observed data together with existing solutions. The comparison shows that the modified equation predicts more accurately the physical problem than the existing model. Copyright © 2015 John Wiley & Sons, Ltd.

In this study, 50 Vertical Electrical Soundings (VES) were carried out in the region, including 14 near existing boreholes for comparison. Aquifer parameters of hydraulic conductivity and transmissivity were obtained by analyzing pumping test data from existing boreholes. An empirical relationship between hydraulic conductivity (K) obtained from pumping test and both resistivity and thickness of the Pan-African aquifer has been established for these boreholes in order to calculate the geophysical hydraulic conductivity. The geoelectrical interpretation shows that almost all aquifers are made of the fractured portion of the granitic bedrock located at a depth ranging between 7 and 84 m. The hydraulic conductivity varies between 0.012 and 1.677 m/day, the resistivity between 3 and 825 Ωm, the thickness between 1 and 101 m, the transmissivity between 0.46 and 46.02 m2/day, the product K σ between 2.1 × 10 −4 and 4.2 × 10 −4.

Groundwater is ubiquitous and immensely important for human uses but there is inadequate supply especially in the basement complex terrain as most boreholes are either abortive or can’t yield sustainable water to wells. This research tends to delineate into the subsurface in order to understand the aquifer pattern in Ogbagba area. A geophysical survey involving twelve vertical electrical sounding (VES) was carried out at some selected locations in Ogbagba. Resistivity meter was used to acquire the geophysical field data. Conventional partial curve matching and WinResist software was used for the data processing. 75% of the aquifers in the study area are confined aquifers while the remaining 25% are unconfined aquifers. Also, three probable aquifer units were delineated where clayey sand has 75%, sandy clay constitutes 16.7% and fractured bedrock shares the remaining 8.3%. The study revealed that insufficiency of groundwater exploitation in the study area is due to the geologic formation of the aquifers and the depth to which groundwater is been abstracted. If these mistakes are corrected, Ogbagba will henceforth start to enjoy groundwater exploitation adequately

This paper presents an investigation into increased deformation of Aquifer II caused by groundwater pumping from the aquifer in Changzhou, China. As groundwater levels of aquifers have been decreasing in recent decades due to uncontrolled water pumping, land subsidence is becoming a serious geohazard in Changzhou. Based on recently reported field data, the compression of aquitards has not increased compared to that of aquifers with the same scale of layer thickness. The Cosserat continuum model was adopted to analyse the observed phenomenon in this study. A classic Cauchy continuum model is also used for comparison. The comparison between these two models indicates that the proposed approach can interpret the increased deformation well, and the classic Cauchy continuum model underestimates the aquifer deformation as it does not consider shear displacement and macro-rotation. A discussion on the relationship between the groundwater level in the aquifer and subsidence is then undertaken. The results show that the severity of the annual subsidence is correlated with the variation in groundwater level in Aquifer II. To mitigate the subsidence hazards, countermeasures should be adopted to avoid the shear stress in aquifers which results from the high hydraulic gradient, by the appropriate allocation of pumping wells and by restricting groundwater withdrawal volume from each pumping operation.

A new type of vertical circulation well (VCW) is used for groundwater dewatering at construction sites. This type of VCW consists of an abstraction screen in the upper part and an injection screen in the lower part of a borehole, whereby drawdown is achieved without net withdrawal of groundwater from the aquifer. The objective of this study is to evaluate the operation of such wells including the identification of relevant factors and parameters based on field data of a test site and comprehensive numerical simulations. The numerical model is able to delineate the drawdown of groundwater table, defined as free-surface, by coupling the arbitrary Lagrangian-Eulerian algorithm with the groundwater flow equation. Model validation is achieved by comparing the field observations with the model results. Eventually, the influences of selected well operation and aquifer parameters on drawdown and on the groundwater flow field are investigated by means of parameter sensitivity analysis. The results show that the drawdown is proportional to the flow rate, inversely proportional to the aquifer conductivity, and almost independent of the aquifer anisotropy in the direct vicinity of the well. The position of the abstraction screen has a stronger effect on drawdown than the position of the injection screen. The streamline pattern depends strongly on the separation length of the screens and on the aquifer anisotropy, but not on the flow rate and the horizontal hydraulic conductivity.

An artificial recharge test aimed at investigating transport characteristics of the injected water plume in a fractured rock aquifer was conducted. The test used an injection well for injecting tap water whose temperature and electrical conductivity were different from the groundwater. Temporal and depth-wise variation of temperature and electrical conductivity was monitored in both the injection well and a nearby observation well. A highly permeable fracture zone acting as the major pathway of groundwater flow was distinctively revealed in the monitoring data. A finite element subsurface flow and transport simulator (FEFLOW) was used to investigate sensitivity of the transport process to associated aquifer parameters. Simulated results showed that aperture thickness of the fracture and the hydraulic gradient of groundwater highly affected spatio-temporal variation of temperature and electrical conductivity of the injected water plume. The study suggests that artificial recharge of colder water in a fractured rock aquifer could create a thermal plume persistent over a long period of time depending on hydro-thermal properties of the aquifer as well as the amount of injected water.

Summary A mathematical model for describing groundwater flow to a partially penetrating pumping well of a finite diameter in an anisotropic leaky confined aquifer is developed. The model accounts for the jointed effects of aquitard storage, aquifer anisotropy, and wellbore storage by treating the aquitard leakage as a boundary condition at the aquitard–aquifer interface rather than a volumetric source/sink term in the governing equation, which has never developed before. A new semi-analytical solution for the model is obtained by the Laplace transform in conjunction with separation of variables. Specific attention was paid on the flow across the aquitard–aquifer interface, which is of concern if aquitard and aquifer have different pore water chemistry. Moreover, Laplace-domain and steady-state solutions are obtained to calculate the rate and volume of (total) leakage through the aquitard–aquifer interface due to pump in a partially penetrating well, which is also useful for engineers to manager water resources. The sensitivity analyses for the drawdown illustrate that the drawdown is most sensitive to the well partial penetration. It is apparently sensitive to the aquifer anisotropic ratio over the entire time of pumping. It is moderately sensitive to the aquitard/aquifer specific storage ratio at the intermediate times only. It is moderately sensitive to the aquitard/aquifer vertical hydraulic conductivity ratio and the aquitard/aquifer thickness ratio with the identical influence at late times.

An electrical resistivity survey, down-hole logging and pumping test were conducted in Delta Central District of Nigeria to determine the groundwater potential and aquifer characteristics of the study area. Twenty vertical electrical soundings of the Schlumberger configuration were performed with an ABEM SAS 1000 Terrameter. The geoelectric data obtained were interpreted with partial curve matching and computer iteration using RESIST software. The results showed the presence of four geoelectric layers comprising loamy–sandy topsoil, clay, fine sand and coarse sand. The investigation also revealed the presence of a confined aquifer in the area, with resistivity values of 869.1–8704.1 Ωm, while the depth of the aquifer ranged between 20.2 and 25.4 m. The average values of the groundwater characteristics obtained were 0.026 mS/m for electrical conductivity, 25.75 mg/m3 for total dissolved solids, 0.022 m2/min for transmissivity and 0.000133 for storativity. Comparison of these values with international standards indicated that the water in the aquifer is of good quality and that the yield could withstand heavy pumping. It is therefore recommended that a good water scheme be established to serve the people of the area, including its surrounding towns.

A grid based variable density numerical model, SEAWAT-2000 is used to conceptually simulate groundwater flow and transport for a coastal stretch in Karnataka state, India. SEAWAT is a coupled version of MODFLOW and MT3DMS designed to simulate three-dimensional, variable density groundwater flow and multi-species transport. The variable density flow process uses the familiar and well established MODFLOW methodology to solve the variable density groundwater flow equation. The aquifer considered for the present study is bounded by Arabian sea on the west, the ridge line along the east andShambhaviand Pavanjerivers along the northern and southern sides respectively. The study has its focus on managing the available data in the most efficient manner to develop a reliable and sophisticated simulation model. The aquifer parameters are estimated by calibrating the model for two year period with daily time step. The aquifer can be categorized as unconfined having good groundwater potential with aquifer transmissivity and specific yield ranging from 10 to 810 m2/day and 0.0008 to 0.0122 respectively. The model evaluation in terms of the accuracy is carried out bycomparingwith the measured data on seasonal basis.From this, the model is found to be scientifically sound for further management applications. The model so developed can be applied in predicting the saltwater intrusion in coastal aquifers for various developmental and climate change scenarios like sea level rise.

The Ogallala-High Plains aquifer is an important resource for irrigated agriculture in a semi-arid region of the United States. Steep declines in groundwater levels are putting increasing strain on the viability of the aquifer for irrigation, necessitating improved estimates of recharge rates and sources to the aquifer. This study uses a combined approach to obtain high resolution geochemical and isotopic composition of the vadose zone and aquifer pore fluids to better understand recharge dynamics to the aquifer. Significant differences between the shallow, intermediate and deep vadose zone and shallow and deep aquifer indicate modern precipitation is not providing a significant source of recharge to the aquifer across a large area (diffuse recharge). Rather, recharge to the aquifer is a result of either focused recharge or long-term, delayed drainage from the portion of the vadose zone which was saturated before irrigation development.

In the process of groundwater recharge, surface water usually enters an aquifer by passing an overlying unsaturated zone. Little attention has been given to the development of analytical solutions to a coupled unsaturated–saturated flow model due to localized recharge up to now. This paper develops a mathematical model to depict three-dimensional transient unsaturated–saturated flow in an unconfined aquifer with localized recharge on the ground surface. The model contains Richards' equation for unsaturated flow, a flow equation for saturated formation, and the Gardner constitutive model describing the behavior of unsaturated soil properties. Both flow equations are coupled through the continuity conditions of the head and flux at the water table. The semi-analytical solution to the coupled flow model is derived by the methods of Laplace transform and Fourier cosine transform. A sensitivity analysis is performed to explore the head response to the change in each of the aquifer parameters. A quantitative tool is presented to assess the recharge efficiency signifying the percentage of the water from the recharge to the aquifer. We found that the effect of unsaturated flow on the saturated hydraulic head is negligible if two criteria associated with the unsaturated soil properties and initial aquifer thickness are satisfied. The head distributions predicted from the present solution match well with those from finite-difference simulations. The predictions of the present solution also agree well with the observed data from a field experiment at an artificial recharge pond in Fresno County, California.

International audience; Crystalline aquifers of semi-arid southern India represent a vital water resource for farming communities. A field study is described that characterizes the hydrodynamic functioning of intensively exploited crystalline aquifers at local scale based on detailed well monitoring during one hydrological year. The main results show large water-table fluctuations caused by monsoon recharge and pumping, high spatial variability in well discharges, and a decrease of well yields as the water table decreases. Groundwater chemistry is also spatially variable with the existence of aquifer compartments within which mixing occurs. The observed variability and compartmentalization is explained by geological heterogeneities which play a major role in controlling groundwater flow and connectivity in the aquifer. The position of the water table within the fracture network will determine the degree of connectivity between aquifer compartments and well discharge. The presented aquifer conceptual model suggests several consequences: (1) over-exploitation leads to a drop in well discharge, (2) intensive pumping may contribute to the hydraulic containment of contaminants, (3) groundwater quality is highly variable even at local scale, (4) geological discontinuities may be used to assist in the location of drinking-supply wells, (5) modeling should integrate threshold effects due to water-table fluctuations.