Leaky Aquifer Research Articles

Salinization processes in a coastal leaky Aquifer system (Alt Empordà, NE Spain)

Water supply in the Alt Empordà area was obtained from ground water until 1987 when its high salinity contents forced managers to use surface water instead to satisfy the demand. In dry years, however, surface water may not suffice. In this paper, we study the hydrological behavior of this leaky aquifer system to finally estimate the feasibility bility of supplying low salinity ground water to complete local needs. We start on the hypothesis that squitard salt leaching is the main factor of salinity. Hydrogeological parameters of this leaky aquifer system are estimated using standard pumping tests, and fitting simulated drawdown using monthly withdrawal rates with head levels recorded from 1984 to 1987 in selected piezomaters. Based on a mass-balance approach, we conclude that the aquitard did not behave as the only cause of salinity. Seaintruded in the upper unconfined source bed leakedthe athrough the aquitard, and it represented the min origin of chloride.Moreover, sea water intrusion in the main aquifer was likely another source of salinity, as shown by simulated drawdowns.

Optimisation of aquifer parameters: a case study from Bheri Terai area, mid western Nepal

For the study of groundwater potential in any area, it is necessary to determine aquifer parameters as correctly as possible. The most effectively and popularly used tools in the field by groundwater geologists and engineers till today is old conventional curve techniques. A new approach is given to refine the aquifer characteristics by computer-assisted numerical techniques.
 The computer-assisted techniques were used in the Bheri Terai area (Banke/Bardiya), mid western Nepal with an objective of studying the aquifer parameters more accurately with reference to the prevailing hydrogeological condition. Keeping in view of the nature and types of aquifer, an optimisation based model developed by Jageshwar (1985) has been adopted for estimation of aquifer parameters. The aquifer parameters in the study area have been evaluated by using both curve procedure and computer assisted numerical techniques. Parameters are optimised by minimisation of sum of the square of residues between computed and observed drawdown. The starting values of parameter for optimisation were generally assigned as per the available graphical procedures. The applicability of the model to the field data has been demonstrated by using the existing test pumping data of Bheri Terai area (GWRDB, 1979). The purposed model for the analysis of test pumping data yields significantly better reproduction of time drawdowns. The results of analysis of test pumping data indicate confined and leaky confined nature of deep aquifer. Majority of leaky aquifers show a declining nature of piezometric head in the overlying aquifer while, some of the confined aquifer shows finite nature in areal extent due to the presence of barrier boundary (most probably impervious clay?).

Practical Approximations of the Well Function

AbstractComputation of the well function is required in the analysis of pumping test data for leaky or confined aquifers. Existing electronic dataloggers facilitate collection of hydraulic test data, which is commonly interpreted using computer programs. Approximate expressions have recently been proposed to compute the well function over the entire range of argument values. We propose approximations that, while providing reasonable accuracy, are less computationally intensive than previous approximations. A detailed comparative analysis of the execution times and the errors of these approximations is performed. The proposed expressions are generally accurate to within 1%, and result in a savings of computation time on the order of 15 to 87% for confined aquifers, and 29 to 76% for leaky aquifers.

Transport of Pb, U, and Sr in leaky aquifers in a contact metamorphic aureole

Transport of Pb, U, and Sr in leaky aquifers in a contact metamorphic aureole

Transport of Pb and Sr in leaky aquifers of the Bufa del Diente contact metamorphic aureole, north-east Mexico

The Sr and Pb isotopes from the 31.6 ± 0.3 Ma (2σ) old Diente del Bufa alkali syenite, northeastern Mexico, and marbles of its contact aureole were used to trace the sources and the mobility of these metals during hydrothermal activity. Chert layers form aquifers within the marbles. The marbles represent aquitards. During fluid-wallrock reaction, the chert layers developed wollastonite rims. Early wollastonite rims have Sr and Pb isotopic compositions similar to those of their immediate host marbles, which indicates that the isotopic composition of Sr and Pb is initially buffered by the marble. Later wollastonite and other replacement minerals rimming the aquifer have Sr and Pb isotopic compositions that carry with time increasingly larger contributions from the high-salinity magmatic brine. The Sr and Pb contributions from the alkali syenite can be traced isotopically for more than 90 m away from the contact of the intrusion. In contrast, Sr and Pb originating from the alkali syenite are traceable within the marbles only for 3 to 5 cm from the aquifer-marble boundary. This distance is comparable to the spatial distribution of isotopic alterations of C and O implying that Sr and Pb were transported into the marbles through a fluid phase. The isotopic variation of Sr, Pb, C, and O across the aquifer-marble profiles reflects infiltration as a transport mechanism rather than diffusion. Because Sr and Pb are minor components in both the infiltrating fluid and the rock and because their concentrations are strongly affected by the distribution coefficients among the solid phases present, there is little correlation between the isotopic compositions of the trace elements Sr and Pb and those of C and O, which are major components in fluid and rock. Very thin meta-argillite rinds at the outer margin of the aquifer represent residual material after the dissolution of calcite. They are distinctly enriched in Rb, Sr, and U. The Rb and Sr are to some extent residual from the original limestone mineralogy, whereas U is dominantly derived from the magmatic fluid and leaked from the aquifer with the escaping immiscible CO2-rich H2O-CO2 fluid that was produced by decarbonation. The 238U/204Pb values ranging from 100 to 250 and distinctly lowered Th/U in the meta-argillite rims (1) demonstrate that U was transported with the magmatic fluid along the aquifer and (2) imply that during unmixing of the highly saline magmatic fluid U fractionated into the CO2-rich H2O-CO2 fluid from which it precipitated selectively in the meta-argillite band across the aquifer. Radioautographs demonstrate that the upper meta-argillite rim has 20 to 40 times more U than the lower rim, which implies that 20 to 40 times more CO2-rich H2O-CO2 fluid has left through the upper aquifer contact.

Abstract: Identifying Underutilized Ground Water Resources in the Coastal Bend Region of Texas

ABSTRACT Water supply planning in the twelve-county region of Texas has focused on surface water sources, especially the Choke Canyon/Lake Corpus Christi reservoir system. Long term growth in water demand in the Coastal Bend region will require the development of additional dependable water supplies. Water from Lake Texana in Jackson County, northeast of the Coastal Bend region, will be conveyed to the Corpus Christi regional water supply system via the Texana Pipeline. This pipeline bisects Refugio County, creating opportunities for integrating ground water resources in the Gulf Coast Aquifer under Refugio County into the regional water supply system. This study uses the numerical ground water model MODFLOW (McDonald and Harbaugh, 1988) to simulate the effects of ground water withdrawals on aquifer conditions in Refugio County. The model is a regional-scale model of a two-layer, leaky aquifer system. The model was calibrated to accurately reflect water level conditions reported from a comprehensive series of water level measurements undertaken in the 1961-62 period. These steady-state conditions, which more recent measurements have confirmed, have developed in Refugio County as a result of relatively constant pumping rates from only a limited number of larger wells. Model calibration results indicate a good fit of computed versus observed water levels for target wells selected from available data. The calibrated simulation model was used to evaluate two different well placement scenarios: a linear arrangement of wells along the Texana Pipeline route, and a well field arrangement with two separate sets of wells arranged in groups in areas that have greater thicknesses of the Lissie/Goliad Sand and lower dissolved solids levels. Each well placement scenario was used to test the effects of withdrawals ranging from 10,000 to 60,000 acre-feet per year. Model results show that both well arrangements could produce up to 60,000 acre-feet per year without de-watering the aquifer. The well fields produced slightly lower drawdown levels at each pumping rate than the wells along the pipeline. Significant drawdown occurred in each case and the effects were evident over a large portion of Refugio County. At least 30,000 acre-feet per year of ground water could be withdrawn from the Lissie/Goliad Sand in Refugio County without causing serious water quality problems or excessive drawdown. This amount of ground water is on the order of ten times greater than the predicted long-term water demands in Refugio County.

More about the leaky aquifer function

The leaky aquifer function W(x, y) is an incomplete Bessel function which has had application in hydrology and more recently in electronic-structure calculations. This article presents an expansion which improves the efficiency of the calculation of W in the only part of its range not treated adequately by previously published methods, namely, the regime where x and y are both larger than unity but one is much larger than the other. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 623–626, 1998

Utilization of the Hantush Solution for the Simultaneous Determination of Aquifer Parameters

AbstractA method is presented to determine aquifer parameters simultaneously and uniquely based on time‐drawdown data collected from a single observation well in the vicinity of a pumping well partially penetrating a confined leaky aquifer. The Hantush solution is analyzed inversely for the identification of hydraulic properties using the Taylor series and a nonlinear least squares method. Aquifer parameters investigated include vertical and horizontal hydraulic conductivities, storage coefficient, and the leakage factor of the overlying aquitard. The developed method is verified using a hypothetical example and is applied to a field case. Error limits between the determined and true parameter values can be less than 0.1% depending on the quality of the field data.

Computer Determination of Aquifer Parameters Using Slope Matching

AbstractVarious numerical methods have been developed to solve aquifer tests and eliminate the subjectivity of traditional graphical type curve methods. The slope‐matching method, which matches the slope of the field data to the slope of the Theis type curve, can be used to numerically solve pump tests for both leaky and non leaky aquifers.The slope‐matching method was selected for implementation into a C/C++ computer program. The computerized version has the following advantages over the original hand calculator version: (1) it eliminates human error inherent in hand calculations; (2) it has the ability to quickly analyze large data sets and large numbers of data sets; and (3) it can be used on portable computers to analyze test data in the field.When performed by hand, the slope‐matching method requires the interpolation of values from tables for values of Theis curve slopes and the Bessel function Ko. For the computer implementation, an iterative “guess‐and‐correct” algorithm was developed to eliminate the need to interpolate from tables.The computer program shows a good correlation with results obtained by hand calculations for both leaky and no leaky aquifers, using the same method. Discrepancies with hand calculations are traced to rounding errors in the estimation of W (u) and elimination of the need to interpolate values from tables.

Effects of Unsaturated Zone on Aquifer Test Analysis in a Shallow‐Aquifer System

AbstractA comparison between two hypothetical flow models of an unconfined aquifer, one saturated and the other variably saturated, indicates that the variably saturated model which explicitly models drainage from the unsaturated zone provides a better conceptual framework for analyzing unconfined aquifer test data and better estimates of the lateral and vertical hydraulic conductivity in fine‐grained sands. Explicitly accounting for multiple aquifers, well‐bore storage, and the effects of delayed drainage from the unsaturated zone increases confidence in aquifer property estimates by removing some assumptions and allowing for the inclusion of early time data and water‐table observations in an aquifer test analysis. The inclusion of the unsaturated zone expands the number of parameters to be estimated, but reasonable estimates of lateral and vertical hydraulic conductivity and specific storage of the unconfined aquifer can be obtained. For the cases examined, only the van Genuchten parameter a needed to be determined by the test, because the parameters n and 9r had a minimal effect on the estimates of hydraulic conductivities, and literature values could be used for these parameters. Estimates of lateral and vertical hydraulic conductivity using MODFLOW were not as good as the VS2DT based estimates and differed from the known values by as much as 30 percent.The hydraulic properties of a surficial aquifer system were estimated through a series of aquifer tests conducted at Cecil Field Naval Air Station in Jacksonville, Florida. Aquifer test results were analyzed by calibrating a variably saturated, radial flow model to the measured drawdowns. Parameter estimation was performed by minimizing the difference between simulated and measured drawdowns with an optimization routine coupled to VS2DT and was constrained by assuming that the hydraulic properties of each aquifer or confining unit were homogeneous. Given the hydrogeologic conditions at the field site, estimating the hydraulic properties of the aquifers and confining units with analytically derived type curves would have been inappropriate. Estimates of the lateral hydraulic conductivity from the VS2DT solution were more consistent with the observed geology than estimates from Theis analyses, which ranged from 20 to 80 percent more than the final estimates. The unsaturated zone affected an aquifer test conducted in a leaky aquifer about 100 feet below land surface more than the other two aquifer tests because about half of the pumped water came from the overlying, unconfined aquifer.

Application of a Numerical Model in the Interpretation of a Leaky Aquifer Test

The potential use of numerical models in aquifer analysis is by no means a new concept; yet relatively few engineers and scientists are taking advantage of this powerful tool that is more convenient to use now than ever before. In this technical note the authors present an example of using a numerical model in an integrated analysis of data from a three-layer leaky aquifer system involving well-bore storage, skin effects, variable discharge, and observation wells in the pumped aquifer and in an unpumped aquifer. The modeling detail may differ for other cases. The intent is to show that interpretation can be achieved with reduced bias by reducing assumptions in regard to system geometry, flow rate, and other details. A multiwell aquifer test was carried out at a site on the western part of the Lawrence Livermore National Laboratory (LLNL), located about 60 kilometers east of San Francisco. The test was conducted to hydraulically characterize one part of the site and thus help develop remediation strategies to alleviate the ground-water contamination.

The Role of Bedding Fractures in the Hydrogeology of Sedimentary Bedrock—Evidence from the Newark Basin, New Jersey

AbstractBedding‐plane partings, particularly those enlarged by stress relief, tend to provide principal ground‐water flow pathways which are often overlooked. In order to identify them, the use of a proper conceptual model of the bedrock aquifer system and appropriate methods of hydrogeologic characterization are necessary. Several pervasive bedding partings were identified at a study site located within a dipping sequence of mudstone and shales, typical of the Passaic Formation in the Newark Basin of New Jersey. These bedding fractures constitute the discrete aquifer units of a multiunit, leaky bedrock aquifer system. One such unit of exceptional transmissivity (the “Raritan unit”) was identified and selected for a detailed characterization. Results of three short‐duration pumping tests verified the continuity and relatively uniform transmissivity of the Raritan unit over distances exceeding 1,500 feet. Significant hydrochemical differences between the various aquifer units at this 100‐acre site were found to be consistent with the multiunit structure of the bedrock aquifer system. A similar pattern can be observed in regional hydrochemical data recently published by others. The principal finding, that a few bedding fractures dominate ground‐water flow at many sites in the region, has a major implication on hydrogeologic characterization requirements for the water supply, well‐head protection, and aquifer remediation projects in the Newark Basin and similar areas of sedimentary bedrock.

Hydraulics of one- and two-dimensional flow fields in aquifers

New solutions in the Laplace and time domains are developed that describe the transient response of a leaky aquifer to constant and transient discharge into a fully or partially penetrating sink with storage, A parameter estimation procedure based on the Newton-Raphson algorithm is found to be robust in a synthetic example involving a pumping test of a large-diameter well situated in a leaky strip aquifer. The analytical solutions presented may find applications in describing water movement in strip aquifers, in aquifers discharging into channels or streams, or in thin laboratory tanks.

Well Hydraulics with the Weber–Goldstein Transforms

Two new integral transforms, ideally suited for solving boundary value problems in well hydraulics, are derived from one of the Goldstein identities which generalizes a corresponding Weber identity. The two transforms are, therefore, named the Weber–Goldstein transforms. Their properties are presented. For the first, second, and third type boundary conditions, the new transforms remove the radial portion of a Laplacian in the cylindrical coordinates. They are used to straightforwardly rederive known solutions to the problems of a fully penetrating flowing well and a fully penetrating pumped well. A novel solution for a fully penetrating flowing well with infinitesimal skin situated in a leaky aquifer is also found by means of one of the new transforms. This solution is validated by comparison to a numerical solution obtained via the finite-difference method and to a quasi-analytic solution obtained by numerical inversion of the corresponding solution in the Laplace domain. Based on the new solution, a flowing well test is proposed for estimating the hydraulic conductivity and specific storativity of the aquifer and the skin factor of the well. The test can also be used in a constant-head injection mode. A type-curve estimation procedure is developed and illustrated with an example. The effectiveness of the test in estimating the well skin factor and aquifer parameters depends on the availability of data on the sufficiently early well response.

On the Strategy of Estimating Regional‐Scale Transmissivity Fields

AbstractA case study of a leaky fluvioglacial aquifer concentrates on methods of estimating the zonated log10‐transmissivities of a regional‐scale ground‐water model covering 450 km2. Mainly three estimation methods are discussed: (a) kriging based on local measurements and predictions, (b) hydrologic inversion (i.e., nonlinear regression) based on head data, and (c) hydrologic inversion based on head data and on prior estimates from kriging. (a) Due to the shortage of data which is usual in heterogeneous aquifers, the present study questions the practical value of forming zonal kriging estimates from local data whenever estimates are to be used as an input to ground‐water models. In some parts of the homogeneous aquifers local data are sufficient to make such estimates, (b) In this study zonal hydrogeological parameters can be estimated by inversion based on head data. However, inaccuracies in head data may seriously damage the reliability of estimated parameters and, as a consequence, the ground‐water model, (c) Using zonal kriging estimates as prior information in the regression reduces the width of the confidence intervals of the parameters with prior information by up to 75%. The study indicates, however, that using prior information in the estimation of the hydrologic model parameters only minimally reduces the uncertainty of the predicted hydraulic heads.For this specific case, the results suggest that in order to parameterize and identify the parameters of the ground‐water model one should concentrate on qualitative mapping of the hydrogeology, on sampling accurate head data and on subsequent estimation of the zonal parameters by inversion (or manual calibration).

New approach to calculation of the leaky aquifer function

The leaky aquifer function W(x,y), an incomplete Bessel function which has had application in hydrology, is now also arising in electronic-structure calculations on periodic systems. This work presents an expansion which improves the efficiency of calculation of W in the range where x and y are comparable and both are larger than unity. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 913–916, 1997

New approach to calculation of the leaky aquifer function

New approach to calculation of the leaky aquifer function

A block iterative finite element model for nonlinear leaky aquifer systems: G. Gambolati & P. Teatini, Water Resources Research, 32(1), 1996, pp 199–204

A block iterative finite element model for nonlinear leaky aquifer systems: G. Gambolati & P. Teatini, Water Resources Research, 32(1), 1996, pp 199–204

A Graphical Method for Storage Coefficient Determination from Quasi-Steady State Flow Data

A simple, approximate but practical graphical method is proposed for estimating the storage coefficient independently from the transmissivity value, provided that quasi-steady state flow data are available from a pumping test. In the past, quasi-steady state flow distance-drawdown data have been used for the determination of transmissivity only. The method is applicable to confined and leaky aquifers. The application of the method has been performed for various aquifer test data available in the groundwater literature. The results are within the practical limits of approximation compared with the unsteady state flow solutions.

Volumetric Leaky-Aquifer Theory and Type Straight Lines

A new method based on the depression cone volume concept is presented for the identification of hydraulic parameters of leaky aquifers with additional elastic storage release from the unpumped aquifer. The solution deals with the flow system by first considering the continuity equation based on the unpumped and pumped aquifers and constant pump discharges. The elastic storage coefficients are taken into account individually by relating them to the depression cone volumes. In addition, the unpumped aquifer flow is assumed to be transmitted to the pumped aquifer through the aquitard according to a pseudo steady-state flow law. The resulting first-order ordinary differential equation in terms of the depression cone volume is solved, leading to time-variant unpumped and pumped aquifer discharge expressions. The pumped aquifer is then considered as a confined aquifer with variable discharge to the well. The results are presented as type curves, which reduce to the Theis and Hantush solutions if the storage coefficient of the unpumped aquifer is neglected. The type-straight-line method is developed for hydraulic parameter estimations based on late time-drawdown data. The method is general and includes the De Glee steady-state and Jacob straight-line solutions as special cases. A dimensionless time-drawdown plot is proposed to determine whether the aquifer is leaky or not. Necessary steps in the application of the methodology are presented with actual field data.