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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 ...

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.

During the last few decades, the Grombalia shallow, an unconfined aquifer, had been under stress by groundwater pumping due to the increasing population and development of agricultural activity. Recently, the aquifer has displayed an important decline in the water level of boreholes and wells, and considerable deterioration of groundwater quality due to saltwater intrusion. A groundwater numerical model for the Grombalia aquifer has been developed based on the Visual Modflow 3.1 code to simulate the groundwater changes under steady state regime and transient conditions. The results of the model show reasonable agreement between observed and estimated groundwater levels in the observation wells. Sebkaht Soliman wetland aquifer connection has been identified. This paper presents the effect of different groundwater management scenarios and pumping discharge on groundwater resources in the Grombalia aquifer (Cap-Bon peninsula, Tunisia).

Assessing recharge in unconfined fractured rock aquifers is a challenging task due to the discontinuous nature of this medium. In this study, a methodology is proposed based on an analytical interpretation of the regional hydraulic head profiles of an unconfined fractured rock aquifer, to determine its recharge. This calculation is conducted for a regional groundwater system based on a one-dimensional Dupuit-Forchheimer model in steady-state conditions that yields the value of the ratio of the aquifer recharge to the aquifer hydraulic conductivity. The approach is tested on a crystalline bedrock aquifer (Kenogami Uplands) of the Canadian Shield located in the Province of Quebec in Canada. The results show an average hydraulic conductivity of the aquifer of 4.3 × 10−7 m/s and a recharge equivalent to approximately 0.4% (3.5 mm/year) of precipitation. These results are in agreement with other studies conducted on similar crystalline aquifers in the Canadian Shield. Editor D. Koutsoyiannis Citation ...

This paper focuses on a small back-barrier sand-island on the southeast coast of Queensland. The freshwater lens in the study area exhibits anomalously high short-range salinity gradients at shallow depths, which cannot be explained using a standard seawater intrusion model. The island groundwater system consists of two aquifers: a semiconfined aquifer hosting saline to hypersaline groundwater and an overlying unconfined freshwater aquifer. The deeper aquifer is semiconfined within an incised paleovalley, and groundwater flow is restricted to an east – west direction. Tidal response observations show that the tidal signal propagates far more rapidly and is of much higher magnitude in the semiconfined aquifer than the unconfined aquifer. The tidal wave-pulse amplitude is also subject to greater attenuation in the unconfined aquifer. A conceptual hydrogeological model illustrates how upwelling of hypersaline groundwater, induced by density-dependent flow and tidal pumping, has contaminated the shallow groun...

The State of Kuwait is located at the northwestern corner of the Arabian Gulf and covers an area of about ≈18,000 km2. The aquifer under investigation is the Eocene Dammam limestone aquifer. This paper discusses the hydrochemistry of the aquifer through the period 1972–2002 in order to identify the chemical and genetic types of groundwater, and to reveal the prevailing geochemical processes in the aquifer. Moreover, the spatial distribution of the brackish-brine groundwater is encountered to provide an overview of the regional scale hydrochemistry and to assess the possible factors controlling the aquifer quality. Accordingly, WATEQ4F program is used to compute the saturation indices of the minerals with respect to a state water composition. The Z- MAP and the STRATWORKS programs are used to construct the structural contour map and the subsurface geophysical logs of the Dammam Formation, respectively. The hydrochemical and geological investigations revealed that the Dammam limestone aquifer is oc...

Pumping tests in aquifers separated by semipervious layer are generally analyzed by using solutions for leafy aquifers that assume constant head distribution in the unpumped source bed. This may not be true under prolonged pumping. Hantush (1967) solutions take into account head decline in the unpumped source bed. The objective of this paper is to present procedures for pumping test analysis using some of these solutions. Both type curve matching and straight‐line methods have been presented. Procedures described in this paper can be used to analyze early‐time drawdown data of the pumped aquifer and the late late‐time drawdown data of the pumped and unpumped aquifer above the semipervious layer. The hydraulic properties for the pumped and unpumped aquifer and the semipervious layer estimated by different methods are quite comparable.

The contact between freshwater and seawater in coastal aquifers is studied using a relatively simple model for homogeneous aquifers. However, for real aquifers it is not so simple. The desalination plant built to supply water to the city of Almeria is situated over the aquifer in the southern part of the River Andarax Delta. Its design capacity is 1100 L s−1, and it is supplied from boreholes pumping water from beneath the freshwater—seawater contact in this aquifer. Well logs kept over a period of two years have allowed us to accurately define the interface geometry of the freshwater—seawater contact. Lithological data collected from 31 boreholes have also indicated the existence of strata with low hydraulic conductivity, within others of high conductivity. During a simultaneous pumping test of six wells with 690 L s−1 total discharge, electrical conductivity measurements showed the influx of seawater 6–10 m below sea level and a drawdown of the interface in the piezometers closest to the pumpin...

In this paper, a radial basis function network (RBFN) approach to the determination of aquifer parameters is developed. The approach is based on the combination of an RBFN and the Theis or the Hantuch‐Jacob solution. The proposed RBFN approach has advantages over the existing back‐propagation network (BPN) approach. It avoids inappropriate setting of a trained range. It also determines the aquifer parameters more accurately and needs less training time. Testing the BPN and RBFN approaches by synthetic data also demonstrates these advantages. As to the comparison between the RBFN approach and the type‐curve graphical method, two applications to actual time‐drawdown data show that the RBFN approach determines the aquifer parameters more precisely for both nonleaky‐confined and leaky‐confined aquifers. The RBFN approach is recommended as an alternative to the type‐curve graphical method and the existing BPN approach.

Pumping tests are often used to estimate effective values of the transmissivity and the storativity of the perturbed aquifer portion surrounding the pumping well and observation points. The interpretation of such pumping tests is based on analytic or semi-analytic methods that are normally developed under the assumption of homogeneity in the vicinity of the well. The purpose of this paper is to examine the impact of the local-scale heterogeneity of the transmissivity on the transient drawdown due to pumping. The log-transmissivity field is modeled as a multi-variate Gaussian random spatial function. Using Monte Carlo simulations, the aquifer response to a pumping test is simulated for various parameter values of the log-transmissivity variance and integral scale. The transient drawdown of the heterogeneous system is compared to the drawdown of an equivalent homogeneous aquifer with transmissivity equal to the effective transmissivity. The results of this study indicate that the impact of local heterogenei...

A combination of drilling, hydrogeochemical survey, geophysical survey, and the numerical modeling for the flow and transport of groundwater was performed to evaluate seawater intrusion in Baeksu-eup, Yeonggwang-gun, Korea. Twelve wells were drilled for the collection of geologic, hydrogeochemical, hydrologic, and geophysical logging data to characterize seawater intrusion. To evaluate the salinity distribution of a coastal aquifer, drilling, geophysical data such as vertical electrical soundings (VES), well logging, and hydrogeochemical results were used. Hydrogeochemical results were used to understand the origin of salt and the seawater mixing ratio of groundwater. Spatial layer interfaces derived from VES data, various in situ physical properties from geophysical well loggings, the estimated equivalent NaCl concentration, and aquifer test such as slug test and so on were used as useful input parameters for the numerical simulation with density-dependent flow. Our multidisciplinary approach fo...

Under field conditions the aquifer geometry rarely confirms to the concept of one aquifer system. In a borehole it is common to find number of aquifers. When the aquifers are separated by aquicludes, interaction between the aquifers is only through the well screens. However, when aquifer is separated by aquitards, the intersection between the aquifers takes place through the aquitards besides the well screens. In general, a tubewell has a strainer length of the aquifer depth. To curtail some cost of installation a partially penetrating well may be good provided the discharge does not drop down significantly due to partial penetration. But the hydraulics of a partially penetrating well in a leaky aquifer is different from that of confined aquifers. A well in a leaky aquifer withdraws water not only from the aquifer but also from the overlying semi- pervious layer. Steady case is possible in such case because o frecharge through the semi- pervious layer. During unsteady conditions the head varies w...

A simplified method has been developed for solving leaky aquifer non-Darcian flow hydraulics. The principle of volumetric approach is combined with the confined-aquifer, time-dependent drawdown equation in an observation well. The groundwater flow in the leaky aquifer is assumed to obey a non-Darcian flow law of exponential type. The results are obtained in the form of type-curve expressions from which the necessary bundles of curves are drawn for a set of selective non-Darcian flow aquifer parameters. Although application of the methodology appears as rather limited but it provides a scientific contribution and extension of leaky aquifer theory towards nonlinear flow conditions. The methodology developed herein is applied to some actual field data from the eastern sedimentary basin in the Kingdom of Saudi Arabia.

We study an homogeneous aquifer where fresh and salt water are separated by an interface T. The flow is governed by a nonlinear Darcy' law. Using suitable approximated problems, we prove existence of a solution and establish some properties.

Alluvial aquifers can often supply large quantities of water but if they are overlain by a low permeability zone, the recharge may be restricted with the result that the long term safe yield of the aquifer is greatly reduced. This paper describes a study of an alluvial aquifer in Bangladesh where there is a low permeability layer overlying the main aquifer. Pumping tests carried out in this aquifer were analysed using a numerical model which represents both the main aquifer and the overlying low permeability zone. Using the aquifer parameters deduced from the pumping test analysis, the numerical model was then used to represent five years of pumping. This long term simulation indicated that there would be a serious decline in the pumped levels and that a water table would develop in the main aquifer and would fall at a rate of almost five metres per year.

Since 1982 an operational well field consisting of a main well and 14 observation wells has served as an educational and research facility for students at South Dakota School of Mines and Technology. An alluvial aquifer 1.5 m thick is located at shallow depths near the Mineral Industries Building. Student projects include measurement of the static level, preparation of maps of the potentiometric surface, pumping, slug, and tracer tests, and flow and transport modeling. Drawdown during pumping tests follows the Theis nonequilibrium-type curve with transmissivity averaging 390 m2/d and a storage coefficient of 0.003. Tracer tests show the aquifer is more permeable in a NE-SW direction; this observation is supported by the spatial distribution of transmissivity values from the Theis analysis. Piezometer tests provide data about the variability of transmissivity and hydraulic conductivity within the aquifer. This information is useful in the development of digital models that are primarily used in graduate co...

A type-curve matching method is presented for the determination of aquifer parameters from water level observations in a finite confined aquifer and discharge measurements at a line sink where there is a constant drawdown. An existing solution in the literature (in the form of complementary error functions) to the one-dimensional nonsteady flow towards a line sink under constant drawdown in a confined aquifer of finite width has been used to define a drain function and to construct a family of type-curves. An application of the method is given.

This paper describes a study of groundwater flow in a coastal Miliolite limestone aquifer in western India. An examination of field information suggested that the transmissivity of the aquifer varies significantly between high and low groundwater heads. Pumping tests indicate that this is due to the development of major fissures in the upper part of the aquifer. A regional groundwater model with varying transmissivities is used to represent the field behaviour. The model is also used to examine the effect of artificial recharge on the alleviation of saline intrusion problems in the coastal area.

The presence of layers of different hydraulic conductivity can significantly affect the flow to a well in an unconfined aquifer. Model studies are described for homogeneous and layered aquifers using finite difference numerical solutions. The flow conditions at the phreatic surface and the approach velocities to the well face are calculated and compared for the different cases. The effect of the well penetration on the discharge is also observed. The adequacy of representing a layered aquifer as an equivalent anisotropic aquifer is discussed.

A pumping test was conducted along the Mullica River in the Wharton Tract, New Jersey as part of a water-resources investigation. Impermeable bog iron caps parts of the flood plain and channel so that ground-water recharge moves directly into the river. Observation wells on both sides of the river tapped water-bearing zones at 25 (shallow), 50 (medium), and 100 (deep) feet. A pumping well, screened in the medium zone, caused abrupt drawdowns which leveled off after a few minutes. Shape of the drawdown cone established early and changed little throughout the test. Piezometric surfaces were steepest on the southwest, indicating that most water came from there. Uninterrupted contour trends beneath the river show that here relatively little water entered the aquifer. Head differentials between the zones were greatest at the pumping well. Movement from the deep to medium zones was confined largely to the pumping-well vicinity. Pumping produced extensive reductions in the original areas of upward gradi...

The non-equilibrium formula of Theis has hitherto been found to be inadequate to analyse drawdown data from open wells, due to the influence of effects of well-storage on early drawdown data. Recently, a reliable type-curve method was proposed by Papadopulos and Cooper to analyse drawdowns in wells of large diameter. In order to study its practical validity, the Papadopulos-Cooper method was applied to drawdown data from six open wells, tapping the alluvial sands of the river Palar, near Madras city, India. The study has indicated that the method has considerable practical utility in analysing drawdown data from large diameter open wells. Besides, the method also offers an easy way of computing the duration over which the effects of well-storage are likely to influence drawdown data, in terms of aquifer transmissibility and well-radius. If a rough idea of aquifer trans-missibility is available from existing data, then, such a computation, to determine the duration over which wellstorage affects d...

By considering a conveniently chosen schematization of the flow regime in an unconfined coastal aquifer of large depth a generalization of the Ghyben-Herzberg formula, accounting for the discharge of fresh water towards the sea, is derived.