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This study demonstrates the utilization of a multi-objective hybrid global/local optimization algorithm for solving managed aquifer recharge (MAR) design problems, in which the decision variables included spatial arrangement of water injection and abstraction wells and time-variant rates of pumping and injection. The objective of the optimization was to maximize the efficiency of the MAR scheme, which includes both quantitative and qualitative aspects. The case study used to demonstrate the capabilities of the proposed approach is based on a published report on designing a real MAR site with defined aquifer properties, chemical groundwater characteristics as well as quality and volumes of injected water. The demonstration problems include steady state and transient scenarios. The steady state scenario demonstrates optimization of spatial arrangement of multiple injection and recovery wells, whereas the transient scenario was developed with the purpose of finding optimal regimes of water injection and recovery at a single location. Both problems were defined as multi-objective problems. The scenarios were simulated by applying coupled numerical groundwater flow and solute transport models: MODFLOW-2005 and MT3D-USGS. The applied optimization method was a combination of global (the non-dominated sorting genetic algorithm [NSGA-2]) and local (the Nelder-Mead downhill simplex search algorithms). The analysis of the resulting Pareto optimal solutions led to the discovery of valuable patterns and dependencies between the decision variables, model properties, and problem objectives. Additionally, the performance of the traditional global and the hybrid optimization schemes were compared.

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.

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.

Nitrate in groundwater and surface water is among the most common contamination problems in the world. Efforts to reduce the loss of excess nutrients at the regional scale currently focus on Best Management Practices (BMPs) designed to facilitate the optimal use of fertilizers, adjusted for specific site conditions. Performance monitoring of regional BMPs has proven to be problematic owing to the large areal scales, the inherent heterogeneity of nutrient mobility on landscapes and in the subsurface, and the extended time lag between implementation and overall improvements in groundwater quality. In order to shorten the time for useful assessments of progress and for the beneficial results to be realized, a strategy is proposed here with specific application to unconsolidated granular aquifers. First, a novel approach for quantifying BMP performance in the short term is demonstrated involving the monitoring of transient nitrate storage in the unsaturated zone. Secondly, a temporary remediation method based on in situ denitrification is implemented for reducing nitrate levels in public supply wells in the interim period until the full influence of the regional nutrient management BMPs is realized. The remediation approach incorporates a passive component that necessitates enhanced site characterization methods including high definition assessments of aquifer properties and groundwater velocity. The preliminary findings from a series of field investigations conducted between 2004 and 2011 at a site in southern Ontario indicate that this combined two-step strategy may be capable of providing short-term quantifiable evidence of BMP performance and also of attenuating nitrate to desirable levels during the time lag period between implementation of the BMPs and the arrival of their desired beneficial effects on the quality of public well water supplies. This may avoid the need to construct permanent above-ground water treatment facilities that could eventually become redundant.

Climate change and sea-level rise will have severe impacts on coastal water resources around the world. However, whereas the influence of marine inundation is well documented in the literature, the impact of groundwater inundation on coastal communities is not well known. Here, core analysis, groundwater monitoring, and ground penetrating radar are utilized to assess the groundwater regime of the surficial aquifer on Bogue Banks Barrier Island (USA). Then, geospatial techniques are used to assess the relative roles and extents of groundwater and marine inundation on the dune-dominated barrier island under sea-level rise scenarios of 0.2, 0.5, and 1.0 m above current conditions by 2100. Additionally, the effects of rising water tables on onsite wastewater treatment systems (OWTS) are modelled using the projected sea-level rise scenarios. The results indicate that the surficial aquifer comprising fine to medium sands responds quickly to precipitation. Water-level measurements reveal varying thicknesses of the vadose zone (>3 to 0 m) and several groundwater mounds with radial flow patterns. Results from projected sea-level rise scenarios suggest that owing to aquifer properties and morphology of the island, groundwater inundation may occur at the same rate as marine inundation. Furthermore, the area inundated by groundwater may be as significant as that affected by marine inundation. The results also show that the proportion of land in the study area where OWTS may be perpetually compromised by rising water tables under worst case scenarios may range from ~43 to ~54% over an 86-year-period. Copyright © 2014 John Wiley & Sons, Ltd.

Pumping tests are one of the most commonly used in situ testing techniques for assessing aquifer hydraulic properties. Numerous researches have been conducted to predict the effects of aquifer heterogeneity on the groundwater levels during pumping tests. The objectives of the present work were as follows: (1) to predict drawdown conditions and to estimate aquifer properties during pumping tests undertaken in radially symmetric heterogeneous aquifers, and (2) to identify a method for assessing the transmissivity field along the radial coordinate in radially symmetric and fully heterogeneous transmissivity fields. The first objective was achieved by expanding an existing analytical drawdown formulation that was valid for a radially symmetric confined aquifer with two concentric zones around the pumping well to an N concentric zone confined aquifer having a constant transmissivity value within each zone. The formulation was evaluated for aquifers with three and four concentric zones to assess the effects of the transmissivity field on the drawdown conditions. The specific conditions under which aquifer properties could be identified using traditional methods of analysis were also evaluated. The second objective was achieved by implementing the inverse solution algorithm (ISA), which was developed for petroleum reservoirs to groundwater aquifer settings. The results showed that the drawdown values are influenced by a volumetric integral of a weighting function and the transmissivity field within the cone of depression. The weighting function migrates in tandem with the expanding cone of depression. The ability of the ISA to predict radially symmetric and log-normally distributed transmissivity fields was assessed against analytical and numerical benchmarks. The results of this investigation indicated that the ISA method is a viable technique for evaluating the radial transmissivity variations of heterogeneous aquifer settings. Copyright © 2013 John Wiley & Sons, Ltd.

The complexity of alluvial-pluvial fan depositional systems makes the detailed characterization of their heterogeneity difficult, yet such a detailed characterization is commonly needed for construction of reliable groundwater models. Traditional models mainly focus on using a single aquifer property to qualitatively or semi-quantitatively characterize the heterogeneity of aquifer, so that they are unable to quantitatively reflect the synthetic heterogeneity of all aquifer properties. In this paper, we propose the heterogeneity synthetic index (HSI) for quantitative characterization of synthetic heterogeneity of an aquifer. The proposed calculation process involves four steps: (1) estimation of the hydraulic conductivity of a sediment sample using the cloud-Markov model, (2) establishment of the sedimentary microfacies distribution model through the Markov chain, (3) characterization of the distribution model of hydrogeological parameters using the improved sequential simulation method according to the “facies-controlled modeling” technique, and (4) application of the entropy weight method to calculate the weight coefficient of the above aquifer properties. The HSI of an aquifer is calculated by superposition of these models according to the corresponding weight coefficient. This approach was applied to the Luancheng aquifer deposit in the southeast Hutuo River alluvial-pluvial fan in the North China Plain (NCP). The results have demonstrated that aquifer 3 which was formed in the middle Pleistocene has the strongest heterogeneity, with an HSI of 0.25–0.75. Aquifer 4 formed in the early Pleistocene shows an intermediate heterogeneity, with the HSI ranging 0.35–0.75. The weakest heterogeneity was found in aquifers 1 and 2 formed in the Holocene and late Pleistocene, with HSI values of 0.40–0.75 and 0.40–0.80, respectively. The heterogeneity of all the four aquifers is relatively strong in the radial direction of the Huai River alluvial-pluvial fan due to the abrupt change of microfacies. In contrast, in the radial direction of the Hutuo River alluvial-pluvial fan, the microfacies change mildly, and the continuity of hydrogeological parameters is better, which has resulted in weaker heterogeneity of the four aquifers in this direction. Findings suggest that the sedimentary environment has significant effects on the aquifer heterogeneity. Considering that there arc many aquifer properties, HSI can quantitatively characterize the synthetic heterogeneity of the aquifer and describe the influence of each aquifer property on the synthetic heterogeneity of the aquifer according to its weight coefficient. Thus the HSI approach can be successfully used to deal with the spatial heterogeneity of aquifer and provide a foundation for studies on contaminant transport.

This paper aims to contribute to understanding the importance of four factors on the determination of sustainable yields: (i) aquifer properties; (ii) temporal distribution of recharge; (iii) temporal distribution of groundwater pumping; and (iv) spatial distribution of pumping wells. It is important to comprehend how the present-day and future vulnerability of groundwater systems to pumping activities depend on these critical factors and what the risks are of considering sustainable yield as a fixed percentage of mean annual recharge (MAR). A numerical model of the Querenca–Silves aquifer in Portugal is used to develop hypothetical scenarios with which these factors are studied. Results demonstrate the aquifer properties, particularly the storage coefficient, have an important role in determining the resilience of an aquifer and therefore to which degree it is dependent on the spatial and temporal distribution of abstraction and recharge, as well as the occurrence of extreme events. Sustainable yields are determined for the developed scenarios based on specific criteria rather than a fraction of MAR. Under simplified current recharge and abstraction conditions, the sustainable yield was determined at approximately 73% of MAR or 76 million m3. When considering a concentration of rainfall in time, as predicted by climate scenarios for the region, sustainable yield could drop to ca 70% of MAR. However, a more even distribution of pumping volumes throughout the year could increase this value. The location of the pumping wells is seen to affect the distribution of hydraulic heads in the aquifer, albeit without significant changes in sustainable yield. Copyright © 2011 John Wiley & Sons, Ltd.

To determine specific storage and porosity, areally limited and time-consuming aquifer tests are frequently done. Hydrogeologic studies often do not have the resources to collect such data and rely on existing data sources for aquifer properties. An alternative tool for determining these aquifer properties is the analysis of earth tides. The objective of this study was to determine whether existing water-level and barometric-pressure data could be used to determine aquifer properties, such as porosity and specific storage, on a regional scale. In this study, national databases from the Great Lakes Region were queried for continuous records of groundwater-level and barometric-pressure data. Records from 37 selected wells were then analyzed for barometric efficiency and earth-tide responses. Specific-storage (S(s) ) and porosity values were determined, and the quality of the results were assessed with a measure of the "goodness of fit" (percent variance) of reconstruction of the response. Records from wells completed in several aquifer systems were analyzed with varying degrees of success. Aquifer S(s) values ranging from 5.9 × 10(-8) to 3.8 × 10(-6) /m were derived, with percent variance of reconstruction ranging from 1% to 78%. Comparisons with aquifer and laboratory testing of S(s) and porosity are favorable if the percent variance of reconstruction is above about 30%. Although the earth-tide-analysis method is not suitable for every situation, the S(s) and porosity of aquifers can, in many places, be estimated with existing water-level and barometric-pressure data or with data that are relatively inexpensive to collect.

Borehole flowmeters that measure horizontal flow velocity and direction of groundwater flow are being increasingly applied to a wide variety of environmental problems. This study was carried out to evaluate the measurement accuracy of several types of flowmeters in an unconsolidated aquifer simulator. Flowmeter response to hydraulic gradient, aquifer properties, and well-screen construction was measured during 2003 and 2005 at the U.S. Geological Survey Hydrologic Instrumentation Facility in Bay St. Louis, Mississippi. The flowmeters tested included a commercially available heat-pulse flowmeter, an acoustic Doppler flowmeter, a scanning colloidal borescope flowmeter, and a fluid-conductivity logging system. Results of the study indicated that at least one flowmeter was capable of measuring borehole flow velocity and direction in most simulated conditions. The mean error in direction measurements ranged from 15.1° to 23.5° and the directional accuracy of all tested flowmeters improved with increasing hydraulic gradient. The range of Darcy velocities examined in this study ranged 4.3 to 155 ft/d. For many plots comparing the simulated and measured Darcy velocity, the squared correlation coefficient (r2) exceeded 0.92. The accuracy of velocity measurements varied with well construction and velocity magnitude. The use of horizontal flowmeters in environmental studies appears promising but applications may require more than one type of flowmeter to span the range of conditions encountered in the field. Interpreting flowmeter data from field settings may be complicated by geologic heterogeneity, preferential flow, vertical flow, constricted screen openings, and nonoptimal screen orientation.

Water level fluctuations induced by tidal strains can be analyzed to estimate the elastic properties, porosity, and transmissivity of the surrounding aquifer material. We review underutilized methods for estimating aquifer properties from the confined response to earth tides. The earth tide analyses are applied to an open well penetrating a confined carbonate aquifer. The resulting range of elastic and hydraulic aquifer properties are in general agreement with that determined by other investigators for the area of the well. The analyses indicate that passive monitoring data from wells completed in sufficiently stiff, low porosity formations can provide useful information on the properties of the surrounding formation.

The measurements of nuclear magnetic resonance (NMR) parameters to investigate petrophysical properties related to fluid (e.g., water) storage and transport processes provide unique insights compared to other geophysical methods and have become a very useful tool for geophysicists during the last decades at the laboratory scale and as a borehole tool. We investigated, at a groundwater test site in the desert of Abu Dhabi, the reliability and limitation of surface NMR, a new but establishing technique that measures the NMR parameter from the surface by comparing its results to borehole NMR logs. Surface NMR or magnetic resonance sounding measurements (MRS) were conducted along a profile, close to several boreholes. The available borehole NMR logs were used to i) evaluate the potential of surface NMR derived results comparing them with borehole NMR measurements and to ii) extend the hydrogeological knowledge of the groundwater site. Firstly, we show how to carefully handle short relaxation signals of surface NMR data. The most significant steps during this process are: i) broad-band filtering to preserve the short decaying NMR signals, ii) correction for relaxation during pulse effects and iii) QT-inversion to extract reliable subsurface parameter distribution. By comparing surface NMR results with borehole NMR logs we found the following limitations: i) surface NMR is not able to detect borehole NMR measured water content related to T2 decay times lower than ≈80 ms T2 decay time. This reduced detectable water content of surface NMR is due to an instrumental dead time of 40 ms, measured T2* relaxation times and a lower Larmor frequency of 2 kHz and ii) borehole NMR has significantly higher vertical resolution. Taking this into account, surface NMR is in good agreement with borehole NMR. Secondly, on a profile of 1.3 km length 11 MRS measurements were carried out to map the lateral aquifer structure. The obtained results show that surface NMR provides unique lateral information of demanded aquifer properties complementary to e.g., transient electromagnetic.

Surface nuclear magnetic resonance (NMR) is a non-invasive geophysical method that can provide valuable information about aquifer properties related to groundwater flow and storage. Our ability to extract such information from surface NMR data, however, is limited by an insufficient understanding of the relaxation parameter T 2 * governing the decay rate of the surface NMR signal in Earth’s magnetic field. In this study, we use a combination of numerical and laboratory experiments to systematically explore the effect of two key geologic properties, pore size and magnetic susceptibility, on the T 2 * relaxation process. A one-dimensional numerical model is developed and parametrized to simulate the surface NMR response for a wide range of geologic materials. These simulations illuminate the processes controlling T 2 * relaxation and identify conditions under which T 2 * exhibits varied sensitivity to pore size. For materials with low magnetic susceptibility, T 2 * is highly sensitive to pore size; however, as susceptibility increases, this sensitivity diminishes and T 2 * becomes dominated by complex dephasing effects, particularly when pores are large. Laboratory Earth’s field NMR experiments complement the numerical simulations. Measurements on water-saturated quartz sands show that for weakly magnetic materials, T 2 * can be sensitive to pore size and thus could provide useful information about aquifer properties.

The paper focuses on analyses and correlations of flow dimensions in different dolomite aquifers in Slovenia. Flow dimensions are obtained through the reinterpretation of 72 pumping tests with the generalized radial flow model, based on the fractional flow dimension. The average value of flow dimensions is 2.16 for all dolomites. A study of flow dimensions in individual aquifers categorized according to their lithological properties shows that higher dimensions occur in massive late-diagenetic Cordevolian and Anisian dolomites compared with bedded Main, Baca, and especially Lower Triassic dolomites, which contain a greater proportion of noncarbonate minerals. Partially penetrating wells have higher flow dimensions than fully penetrating wells. Flow dimensions are poorly correlated with hydraulic conductivities of fractures. When comparing the quantities of major dissolved minerals, obtained by hydrogeochemical inverse modeling, with the values of flow dimensions, the Cordevolian and Anisian dolomites are found to exhibit the highest values of both dissolved dolomite and flow dimensions, indicating that greater dissolution occurs at higher flow dimensions. For other aquifers, data points are more scattered and the correlation is mostly poor. When compared with three-dimensional fractal dimensions of fracture networks, there is no correlation with flow dimensions. However, almost all the values of flow dimensions are lower than the corresponding fractal dimensions in dolomites (average D= 2.77), possibly indicating the channeling of flow within the available space of the fracture networks, consequently reducing the flow dimensions.

Despite its purported importance, previous studies of the influence of sea-level rise on coastal aquifers have focused on specific sites, and a generalized systematic analysis of the general case of the sea water intrusion response to sea-level rise has not been reported. In this study, a simple conceptual framework is used to provide a first-order assessment of sea water intrusion changes in coastal unconfined aquifers in response to sea-level rise. Two conceptual models are tested: (1) flux-controlled systems, in which ground water discharge to the sea is persistent despite changes in sea level, and (2) head-controlled systems, whereby ground water abstractions or surface features maintain the head condition in the aquifer despite sea-level changes. The conceptualization assumes steady-state conditions, a sharp interface sea water-fresh water transition zone, homogeneous and isotropic aquifer properties, and constant recharge. In the case of constant flux conditions, the upper limit for sea water intrusion due to sea-level rise (up to 1.5 m is tested) is no greater than 50 m for typical values of recharge, hydraulic conductivity, and aquifer depth. This is in striking contrast to the constant head cases, in which the magnitude of salt water toe migration is on the order of hundreds of meters to several kilometers for the same sea-level rise. This study has highlighted the importance of inland boundary conditions on the sea-level rise impact. It identifies combinations of hydrogeologic parameters that control whether large or small salt water toe migration will occur for any given change in a hydrogeologic variable.

In recent years the ground-water demand of the population of the island of Maui, Hawaii, has significantly increased. To ensure prudent management of the ground-water resources, an improved understanding of ground-water flow systems is needed. At present, large-scale estimations of aquifer properties are lacking for Maui. Seven analytical methods using constant-rate and variable-rate withdrawals for single wells provide an estimate of hydraulic conductivity and transmissivity for 103 wells in central Maui. Methods based on constant-rate tests, although not widely used on Maui, offer reasonable estimates. Step-drawdown tests, which are more abundantly used than other tests, provide similar estimates as constant-rate tests. A numerical model validates the suitability of analytical solutions for step-drawdown tests and additionally provides an estimate of storage parameters. The results show that hydraulic conductivity is log-normally distributed and that for dike-free volcanic rocks it ranges over several orders of magnitude from 1 to 2,500 m/d. The arithmetic mean, geometric mean, and median values of hydraulic conductivity are respectively 520, 280, and 370 m/d for basalt and 80, 50, and 30 m/d for sediment. A geostatistical approach using ordinary kriging yields a prediction of hydraulic conductivity on a larger scale. Overall, the results are in agreement with values published for other Hawaiian islands.

Twenty-nine Schlumberger electrical soundings were carried out in the Salamiyeh region in Syria using a maximum current electrode separation of 1 km. Three soundings were made at existing boreholes for comparison. Aquifer parameters of hydraulic conductivity and transmissivity were obtained by analysing pumping test data from the existing boreholes. An empirical relationship between hydraulic conductivity determined from the pumping test and both resistivity and thickness of the Neogene aquifer has been established for these boreholes in order to calculate the geophysical hydraulic conductivity. A close agreement has been obtained between the computed hydraulic conductivity and that determined from the pumping test. The relationship established has, therefore, been generalized in the study area in order to evaluate hydraulic conductivity and transmissivity at all the points where geoelectrical measurements have been carried out. This generalization allows one to derive maps of the hydraulic conductivity and transmissivity in the study area based on geoelectrical measurements. These maps are important in future modelling processes oriented towards better exploitation of the aquifers. Copyright © 2006 John Wiley & Sons, Ltd.

An experimental study was completed to assess the impact of sampling methods, contaminant levels, and subsurface temperatures on the quantification of tetrachloroethylene (PCE) and trichloroethylene (TCE) in source zones contaminated by dense non–aqueous phase liquids (DNAPLs). Intact cores of clean aquifer solids (fine-grained uniform sand with low foc) from a DNAPL site in Florida were spiked with neat PCE and TCE to yield concentrations such that DNAPL-phase contamination would be absent or present. Three methods characterized by different levels of media disaggregation and atmospheric exposure (MDE) were used to obtain samples from intact cores, which were at temperatures of 2� C, 20� C, and 38� C. The results of this study demonstrated that sampling of intact cores can yield negative bias, ranging from 0% to 98% or more, in the concentrations of PCE and TCE measured. Larger negative bias was correlated with higher MDE methods, presumably due to elevated volatilization losses during sample collection and containerization. Larger negative bias was also correlated with higher temperatures but only during sampling using higher MDE methods. The results of this study suggest that intact core sampling procedures may or may not lead to erroneous conclusions about a DNAPL source zone. For example, sampling data may lead to a conclusion that a potential source zone has no DNAPL-phase contamination present when in fact it is present, or that remediation has achieved source zone cleanup to a residual concentration goal, when in fact the goal was not met. Conversely, if a remediation goal is to achieve a specified mass depletion level (e.g., 90%), measurement bias may not result in an erroneous conclusion. Further research is planned to examine a wider range of aquifer properties and sampling conditions and to assess the impacts of measurement errors on DNAPL source zone characterization and assessment of remediation performance.

We deal in this paper with an ongoing development of the analytic element method. We present in outline new analytic line elements that are suitable to model general flow fields, i.e., flow fields that possess a continuously varying areal inflow or outflow. These elements are constructed specifically to model the leakage through leaky layers that separate aquifers in leaky systems and to model transient effects. The leakage or release from storage underneath linear features is modeled precisely by the new elements; the singularity in leakage is matched exactly by the approximate solution. Applications are given for a problem involving leakage and for a case of transient flow. We note that the analytic elements can be used also to reproduce the effect of continuously varying aquifer properties, e.g., the hydraulic conductivity or the elevation of the base of the aquifer. In the latter case, the elements would reproduce the rotation of the flow field caused by the variation in properties, rather than the divergence as for the case of leakage.

Before recent drilling and characterization efforts in the vicinity of Los Alamos National Laboratory (LANL), conceptual models had been developed for recharge and discharge in the regional aquifer on the basis of sparse data. By integrating site-wide data into a numerical model of the aquifer beneath the plateau we provide new insight into large-scale aquifer properties and fluxes. This model is useful for understanding hydrologic mechanisms, assessing the magnitudes of different terms in the overall water budget, and, through sampling, for interpreting contaminant migration velocities in the overlying vadose zone. Modeling results suggest that the majority of water produced in well fields on the plateau, extracted at rates approaching 70% of total annual recharge, is derived from storage. This result is insensitive to assumptions about the percentage of total recharge that occurs in the near vicinity of water supply wells, because of strong anisotropy in the aquifer that prevents fast transport of local recharge to deeper units from which production occurs. Robust estimates of fluxes in the shallow portion of the aquifer immediately down gradient of LANL are important for contaminant transport simulations. Our model calculations show that these fluxes have decreased in the past 50 years by approximately 10% because of production in water supply wells. To explore the role of parameter uncertainty in flux prediction, a predictive analysis method was applied. Results showed that predicted flux through older basalts in the aquifer can vary by a factor of three because of uncertainty in aquifer properties and total recharge. We explored the impact of model parameter uncertainty on these results; however, the true uncertainty of our predictions, including the impact of possible conceptual model errors, is likely to be larger and is difficult to quantify.

As part of its Wellhead Protection Program, the U.S. EPA mandates the delineation of "time-of-travel capture zones" as the basis for the definition of wellhead protection zones surrounding drinking water production wells. Depending on circumstances the capture zones may be determined using methods that range from simply drawing a circle around the well to sophisticated ground water flow and transport modeling. The simpler methods are attractive when faced with the delineation of hundreds or thousands of capture zones for small public drinking water supply wells. On the other hand, a circular capture zone may not be adequate in the presence of an ambient ground water flow regime. A dimensionless time-of-travel parameter T is used to determine when calculated fixed-radius capture zones can be used for drinking water production wells. The parameter incorporates aquifer properties, the magnitude of the ambient ground water flow field, and the travel time criterion for the time-of-travel capture zone. In the absence of interfering flow features, three different simple capture zones can be used depending on the value of T . A modified calculated fixed-radius capture zone proves protective when T0.1, while a more elongated capture zone must be used when T1. For values of T between 0.1 and 1, a circular capture zone can be used that is eccentric with respect to the well. Finally, calculating T allows for a quick assessment of the validity of circular capture zones without redoing the delineation with a computer model.

Groundwater studies are conducted to evaluate the occurrence, availability, and quality of groundwater. There are numerous practical applications like optimum development of groundwater basins, safe withdrawal, groundwater recharge, seepage from canals and reservoirs, and drainage that require knowledge of the hydraulic characteristics of aquifers. Two basic aquifer properties needed to make a quantitative assessment of such applications are transmissivity and storage coefficient which represent, in a general sense, its abilities to transmit and store water, respectively. The other hydraulic properties of an aquifer are hydraulic resistance, leakage factor, and drainage factor. Performing an aquifer test is an effective way of determining these hydraulic properties of aquifers. Steady-state flow aquifer tests are conducted to determine transmissivity, hydraulic conductivity, and hydraulic resistance; more detailed unsteady-state tests are conducted if other hydraulic properties are also to be evaluated. The objective of this article is to discuss steady-state methods of determining aquifer characteristics. Keywords: groundwater; well hydraulics; pumping test; drawdown; piezometric head; confined aquifer; unconfined aquifer; leaky aquifer; artesian aquifer; aquifer aquifer; artesian aquifer; aquifer constants; transmissivity; storage coefficient; hydraulic conductivity; hydraulic resistance; leakage factor; cylindrical flow; radial flow; spherical flow; steady-state flow; Darcy law; Dupuit–Thiem method; Logan's method; airline method

We examine the post-seismic change in the groundwater level following the 1999 (Mw = 7.5) Chi-Chi earthquake in central Taiwan, as recorded by a network of 70 evenly distributed hydrological stations over a large alluvial fan near the epicenter. Four types of post-seismic responses may be distinguished: In type 1, the groundwater level declined exponentially with time following a coseismic rise. This was the most common response in the study area and occurred in unconsolidated sediments on the Choshui River fan. In type 2, the groundwater level rose exponentially with time following a coseismic fall. This occurred in the deformed and fractured sedimentary rocks in the foothills near the Chelungpu fault that ruptured in the Chi-Chi earthquake. In type 3, the groundwater level continued to decline with time following a coseismic fall. This also occurred in the deformed and fractured sedimentary rocks near the ruptured fault. Finally, in type 4, the groundwater level, following a coseismic rise, stayed at the same level or even rose with time before it eventually declined. This occurred mostly in unconsolidated sediments along the coast of central Taiwan and along the Peikang Stream. We analyze these post-seismic responses by using a one-dimensional model. Together with the results from well test, the analysis show that the type 1 response may be explained by an aquifer model with coseismic recharge and post-seismic subhorizontal discharge across a length of 500-5,000 m; the type 2 response may be explained by a model of coseismic discharge and post-seismic recharge from surface water; the type 3 response may be explained by a model of coseismic discharge and post-seismic subhorizontal discharge across a length of 500-5,000 m; and the type 4 response may be explained by a model of coseismic recharge and sustained post-seismic recharge from surface water. The characteristic time for the post-seismic changes is similar to that for the groundwater-level decline during dry seasons before the earthquake, suggesting that there was no earthquake-induced changes in the aquifer properties (i.e., hydraulic conductivity), confirming the earlier results from recession analyses of the post-seismic streamflow elsewhere after several earthquakes.

Considerable advancements have been made in the development of analytical solutions for predicting the effects of pumping wells on adjacent streams and rivers. However, these solutions have not been sufficiently evaluated against field data. The objective of this research is to evaluate the predictive performance of recently proposed analytical solutions for unsteady stream depletion using field data collected during a stream/aquifer analysis test at the Tamarack State Wildlife Area in eastern Colorado. Two primary stream/aquifer interactions exist at the Tamarack site: (1) between the South Platte River and the alluvial aquifer and (2) between a backwater stream and the alluvial aquifer. A pumping test is performed next to the backwater stream channel. Drawdown measured in observation wells is matched to predictions by recently proposed analytical solutions to derive estimates of aquifer and streambed parameters. These estimates are compared to documented aquifer properties and field measured streambed conductivity. The analytical solutions are capable of estimating reasonable values of both aquifer and streambed parameters with one solution capable of simultaneously estimating delayed aquifer yield and stream flow recharge. However, for long term water management, it is reasonable to use simplified analytical solutions not concerned with early-time delayed yield effects. For this site, changes in the water level in the stream during the test and a varying water level profile at the beginning of the pumping test influence the application of the analytical solutions.

Recent research has shown that planting deep-rooted trees, such as poplar, can take up and degrade important ground water pollutants such as trichloroethylene (TCE) as they transpire water from the capillary fringe of shallow contaminated aquifers. The effect of hydrogeologic factors on the minimum plantation area needed to prevent downgradient migration of contaminated ground water is not well known. Accordingly, the objective of this research was to identify the hydrogeologic parameters that control phytoremediation effectiveness. We used a numerical ground water flow model to evaluate the effect that natural variations in hydrogeologic parameters and growing season duration have on the minimum plantation area required for capture. We found that the plantation area that was needed to completely capture a ground water contamination plume was directly proportional to aquifer horizontal hydraulic conductivity, saturated thickness, and ground water gradient. The plantation area needed for capture increased nonlinearly with increasing plume width, aquifer anisotropy, and decreasing growing season duration. The plantation area needed for capture was generally insensitive to aquifer-specific yield and storativity. Steady-state simulations can be used to predict the plantation area needed for capture in many applications. A particularly important finding of this work is that evapotranspiration fluxes through plantations appropriately sized to contain the plume substantially exceeded the ground water flux through the plume itself.

Groundwater temperature and electrical conductivity logs were applied in this study to gain an understanding of the hydrogeological behaviour of a complex system. This system, compartmentalized by a large number of fractures, which may even cause geothermal anomalies, is that of the Campo de Dalias in the south-east of the Iberian Peninsula. In addition to this complexity one must consider the different levels with aquifer properties and their varying lithologies, which in some cases are in direct contact with the sea. Vertical sections based upon the various logs allow lateral correlation to be made between the anomalies detected, and provide information on the existence of both ascending and descending vertical flows, and the inflow of sea water into the system. Analysis of environmental isotopes (18O and D) indicate the areas of recharge with the greatest flow velocity. No seasonal variation in the isotopes was observed, which suggests that the residence time of the groundwater in the aquifer is several years. Radiocarbon dating gave estimates of generally long residence times, although in some sectors it is possible to detect the current recharge based on its tritium content, from rainwater infiltration or seawater intrusion. Copyright © 2002 John Wiley & Sons, Ltd.

Laterite soils are widespread in tropical Africa and have a large impact on the hydrology of the areas they cover. The permeability of laterite helps determine the partitioning of runoff and interflow and regulates groundwater recharge to underlying bedrock. Groundwater within laterite also forms a widespread source of drinking water, typically from unimproved hang-dug-wells. Despite its importance, there is little published information on laterite aquifer properties. In this study, data from a 6 m deep well in Nigeria have been analysed to characterise the hydraulic conductivity of the laterite from repeated pumping tests. Transmissivity measurements from 40 tests spread out across a hydrological year varied from 0.1 to 1000 m2/d. Further interpretation of the data demonstrate a strong non-linear decrease in horizontal hydraulic conductivity with depth, characterised by an upper horizon of extreme permeability (400 m/d), and a much lower permeability profile beneath (

Over the last decade the dipole-flow test (DFT) evolved from the general idea of using recirculatory flow to evaluate aquifer properties, to the development of prototype instrumentation and feasibility studies, to a reliable tool for characterization of aquifer heterogeneity. The DFT involves the interpretation of head in recirculatory flow between injection and extraction sections (chambers) in a single well isolated from each other by a multipacker system. In this study, the steady-state dipole flow test (DFT) has been used to characterize the statistics of horizontal hydraulic conductivity (Kr) of the highly permeable, heterogeneous, and thin aquifer at the Horkheimer Insel site, Germany. In previous studies, Kr estimates were based on the steady-state head difference between chambers. A new by-chamber interpretation is proposed that is based on drawdown within each individual chamber. This interpretation yields more detailed information on structure of heterogeneity of the aquifer without introducing complexity into the analysis. The DFT results indicate that Kr ranges from 49 to 6000 m/day (mean ln Kr [(m/s)] approximately -4, and variance of ln Kr [(m/s)] approximately 1-2). Descriptive statistics from the DFT compare well with those from previous field and laboratory tests (pumping, borehole flowmeter, and permeameter tests and grain-size analysis) at this site. It is shown that the role of confining boundaries in the DFT interpretation is negligible even in this case of a thin (< 4 m thick) aquifer. This study demonstrates the flexibility of the DFT and expands the potential application of this method to a wide range of hydrogeologic settings.

Low-flow ground water sampling methodology can minimize well disturbance and aggravated colloid transport into samples obtained from monitoring wells. However, in low hydraulic conductivity formations, low-flow sampling methodology can cause excessive drawdown that can result in screen desaturation and high ground water velocities in the vicinity of the well, causing unwanted colloid and soil transport into ground water samples taken from the well. Ground water velocities may increase several fold above that of the natural setting. To examine the drawdown behavior of a monitoring well, mathematical relationships can be developed that allow prediction of the steady-state drawdown for constant low-flow pumping rates based on well geometry and aquifer properties. The equations also estimate the time necessary to reach drawdown equilibrium. These same equations can be used to estimate the relative contribution of water entering a sampling device from either the well standpipe or the aquifer. Such equations can be useful in planning a low-flow sampling program and may suggest when to collect a water sample. In low hydraulic conductivity formations, the equations suggest that drawdown may not stabilize for well depths, violating the minimal drawdown requirement of the low-flow technique. In such cases, it may be more appropriate to collectmore » a slug or passive sample from the well screen, under the assumption that the water in the well screen is in equilibrium with the surrounding aquifer.« less

The paper reviews the problems of uncertainty in the definition of aquifer properties and the scale-dependence of dispersion with specific regard to well-capture zones. Stochastic methods have been developed in response to the problems of characterizing aquifer properties for contaminant transport modelling, as they provide a formal framework for the treatment of uncertainty. Their use for well-capture zone analysis, however, has been neglected so far. In this paper a stochastic numerical modelling procedure is presented, based on conditional geostatistical simulation of fine-scale aquifer structure, which is shown to reproduce stochastic analytical properties. The methodological approach is applied to the analysis of uncertainty in well-protection zones, and implications of the results for groundwater management are discussed. Copyright © 2000 John Wiley & Sons, Ltd.

Over the past few decades, enormous effort has been expended on conducting traditional aquifer tests and model calibration for characterizing aquifers. Traditional aquifer tests generally involve pumping at one well and using the observed drawdown data at another well to estimate aquifer hydraulic properties. Analysis of the test is built upon Theis’ or Jacob’s approximate solution. These solutions assume aquifer homogeneity and uniform thickness despite the fact that aquifers are inherently heterogeneous at multiple scales and their thicknesses vary significantly spatially. These solutions at best predict an averaged drawdown over some volume of the aquifer (apples), which is likely different from the actual drawdown observed at a well, i.e., a single point in space (oranges). An application of these solutions to estimation of averaged aquifer properties based on a hydrograph from only one well is tantamount to comparing apples and oranges. Despite this inconsistency and impropriety, traditional aquifer tests continue to be widely adopted because the methods yield results, however questionable. Unfortunately, these results can significantly affect water resources management. For example, a recent study of traditional aquifer tests in heterogeneous aquifers by Wu et al. (2005) shows that the transmissivity estimate is a nonunique average of heterogeneity over the cone of depression, which evolves with time and depends on the location of the observation well. On the other hand, the estimated storage coefficient is mainly influenced by the geology between the pumping and the observation well. These findings suggest that ground water availability may have been either underestimated or overestimated, and our current management strategies of ground water resources as such are subject to great uncertainty. Likewise, calibrating a ground water model with spatially distributed parameters has been known as solving an ill-posed problem, which is often attributed to a lack of data. Despite of this fact, modelers have continued to search for magic algorithms to solve these problems that inherently have nonunique solutions and seldom have emphasized the need for collecting more data. Moreover, both modelers and practitioners rarely attempt to recognize the kinds of data (the necessary and sufficient conditions, see Yeh and Sim _ unek [2002]) that make an inverse problem well posed. As such, designs of laboratory and field experiments or monitoring networks often collect information irrelevant to resolve the ill-posed issue. Instead of collecting data to meet the necessary and sufficient conditions, which can be expensive and prohibitive for many large-scale field problems, a new technology, known as hydraulic tomography (HT), which collects data intelligently and analyzes data smartly, has recently been developed to provide high-resolution aquifer characterization (Gottlieb and Dietrich 1995; Renshaw 1996; Vasco et al. 2000; Yeh and Liu 2000; Bohling et al. 2002; Liu et al. 2002; Brauchler et al. 2003; McDermott et al. 2003; Zhu and Yeh 2005, 2006). In simple terms, HT is a sequential cross-hole hydraulic test followed by inversion of all the data to map the spatial distribution of aquifer hydraulic properties. Specifically, HT involves installation of multiple wells in an aquifer, which are partitioned into several intervals along the depth using packers. A sequential aquifer test at selected intervals is then conducted. During the test, water is injected or withdrawn (i.e., a pressure excitation) at a selected interval in a given well. Pressure responses of the subsurface are then monitored at other intervals at this well and other wells. This test produces a set of pressure excitation/response data of the subsurface. Once a test is completed, the pump is moved to another interval and the test is repeated to collect another set of data. The same procedure is then 1Corresponding author: Department of Hydrology and Water Resources, The University of Arizona, Tucson, AZ 85721; (520) 621-5943; fax (520) 621-1422; yeh@hwr.arizona.edu 2Department of Resources Engineering, National Cheng Kung University, Tainan, Taiwan, Republic of China. 3Department of Resources Engineering, National Cheng Kung University, Tainan, Taiwan, Republic of China; leech@mail.ncku. edu.tw Received November 2006, accepted November 2006. Copyright a 2007 The Author(s) Journal compilationa2007National GroundWaterAssociation. doi: 10.1111/j.1745-6584.2006.00292.x

A dipole probe (DP) for measuring vertical variations of hydraulic conductivity has been designed, constructed, and tested in field conditions. The variable-length device designed for the dipole flow test (DFT) consists of three packers separated by changeable spacer rods. The assembled DP is lowered into a well with a long screened interval. The packers are inflated, isolating two screened sections (chambers) between them. A small submersible pump, mounted on the central packer, transfers water from the upper (extraction) chamber into the lower (injection) chamber. This simultaneous injection and extraction creates a recirculatory flow within the aquifer. The chamber head responses are measured by two pressure transducers in the DP chambers. The DP can be used at discrete intervals along the entire well screen length. The DP has been successfully tested in a specially constructed well with a continuous screen in a highly conductive sand and gravel aquifer. During drilling, disturbed samples were collected using the split spoon method and the vertical profile of K was estimated from grain-size analysis. A total of 153 DFTs were performed with various DP geometries. Results indicate that the chamber head changes are sensitive to aquifer properties, reach steady state rapidly, vary linearly with redrculation pumping rate, and can be controlled by changes in DP dimensions. Vertical profiles of K compare well with grain-size analysis estimates.

In the analysis of pumping test data, the quality of the determined aquifer parameters can be greatly improved by using a proper model of the aquifer system. Moench (1995) provided an analytical solution for flow to a well partially penetrating an unconfined aquifer. His solution, in contrast to the Neuman solution (1974), accounts for the noninstantaneous decline of the water table (delayed yield). Consequently, the calculated drawdown in these two solutions is different under certain circumstances, and this difference may therefore affect the computation of aquifer properties from pumping test data. This paper uses an inverse computational method to calculate four aquifer parameters as well as a delayed yield parameter, α1 from pumping test data using both the Neuman (1974) and Moench (1995) solutions. Time-drawdown data sets from a pumping test in an unconfined alluvial aquifer near Grand Island, Nebraska, were analyzed. In single-well analyses, horizontal hydraulic conductivity values derived from the Moench solution are lower, but vertical hydraulic conductivity values are higher than those calculated from the Neuman solution. However, the hydraulic conductivity values in composite-well analyses from both solutions become very close. Furthermore, the Neuman solution produces similar hydraulic conductivity values in the single-well and composite-well analyses, but the Moench solution does not. While variable α1, seems to play a role in affecting the computation of aquifer parameters in the single-well analysis, a much smaller effect was observed in the composite-well analysis. In general, specific yield determined using the Moench solution could be slightly higher than the values from the Neuman solution; however, they are still lower than the realistic values for sand and gravel aquifers.

This study examines the near-field flow regime influencing the chemical composition of water samples collected form an irrigation well during short pumping periods. Data on the radial and vertical distribution of nitrate-nitrogen (NO{sub 3}-N) and on draw-down were collected from a closely spaced multi-level monitoring well network installed around an irrigation well. Aquifer properties were determined from grain-size analyses performed on samples collected from test holes drilled around the irrigation well and from drawdown data using the method of Neuman (1974). Grain-size characteristics were determined from cumulative distribution curves and used to construct vertical hydraulic conductivity (K) profiles based on frequently used empirical formulas applied to grain-size data for the determination of aquifer properties. Resultant vertical profiles show a general increase in K with depth. Results from the analysis of drawdown curves support the general trend of K determined form the grain-size data, drawdown-based K values, however, were 1.5 to 2 times greater than those determined form the empirical methods. Results from four pump-and-sample experiments at different times during the irrigation season indicate: (1) the distribution of NO{sub 3}-N around the irrigation well is complex and variable over time and space; (2) shapes of concentration-time curves for individual sample pointsmore » are governed by the initial contaminant distribution, and shapes of concentration-time curves for the pumping well are governed by variables such as well screen position and hydrogeologic properties; (3) irrigation well samples underestimate the highest, as well as the average NO{sub 3}-N concentrations within the aquifer; and (4) a sampling strategy based on the behavioral characteristics of the well as reflected in concentration-time curves can improve the interpretation of water quality data collected from high-capacity wells.« less

Based on aquifer performance tests, 13 out of 15 wells situated at the Mixed Waste Disposal (MWD) area located at the Savannah River site. South Carolina, exhibited high skin factors and low well efficiencies indicative of severely damaged wells. The use of damaged wells in aquifer testing can lead to inaccurate determinations of aquifer properties, and such wells are unusable in future remediation programs. Moreover, damaged wells can go dry during purging, thus compromising sample collection. Pump tests, chemical analyses, and biological investigations revealed that the poor well performance at MWD was attributable to calcite precipitation on the well screen and drilling mud in the filter pack. The calcite problem resulted from improper well installation, and the drilling mud in the filter pack was due to inadequate well development. Experimental rehabilitation procedures employed on two wells, MWD 5A and 1A, included acidification, swabbing, introduction of surfactants, and surging. Treatment of the wells substantially improved well yields, skin factors, and well efficiencies. Moreover, well rehabilitation was determined to be a reasonable alternative to drilling new wells at the MWD wellfield.

The Hilton Head Island Test Well {number_sign}1 was drilled to a depth of 3,833 feet to evaluate the upper Cretaceous section as a potential ground-water source for Hilton Head Island, South Carolina. The initial plan was to analyze continuous conventional cores. The interval to be analyzed extended from the top of the Eocene to the base of the Cretaceous (approximately 3,500 feet). However, due to the high cost ($400,000), the decision was made to evaluate aquifer potential using advanced geophysical logs with sidewall cores for calibration. The logging suite consisted of a dual induction resistivity, spontaneous potential, compensated neutron, density log, gamma ray, spectral gamma, multipole array acoustic log, caliper, high resolution dipmeter, and a circumferential borehole imaging log. In addition to the wireline logs, 239 sidewall cores and 12 Formation Multi-Test samples were obtained. The log, sidewall core, and FMT information were integrated into an interpretive package using computer generated logs and simple spreadsheets to calculate aquifer properties. Porosity, hydraulic conductivity, transmissivity, and lithologic data derived from this integrated analysis were then used to select screen zones. Water quality in relation to drinking water standards exceeded expectations. The information obtained from the integrated program allowed estimates to be mademore » about the well`s productivity without the expense of conventional coring, flow testing, and completion of the well.« less

Regional groundwater flow systems often contain both strong sinks and weak sinks. A strong sink extracts water from the entire aquifer depth, while a weak sink lets some water pass underneath or over the actual sink. The numerical groundwater flow model MODFLOW may allow a sink cell to act as a strong or weak sink, hence extracting all water that enters the cell or allowing some of that water to pass. A physical strong sink can be modeled by either a strong sink cell or a weak sink cell, with the latter generally occurring in low-resolution models. Likewise, a physical weak sink may also be represented by either type of sink cell. The representation of weak sinks in the particle tracing code MODPATH is more equivocal than in MODFLOW. With the appropriate parameterization of MODPATH, particle traces and their associated travel times to weak sink streams can be modeled with adequate accuracy, even in single layer models. Weak sink well cells, on the other hand, require special measures as proposed in the literature to generate correct particle traces and individual travel times and hence capture zones. We found that the transit time distributions for well water generally do not require special measures provided aquifer properties are locally homogeneous and the well draws water from the entire aquifer depth, an important observation for determining the response of a well to non-point contaminant inputs.

Analytical solutions for constant-rate pumping tests are widely used to infer aquifer properties. In this note, we implement a methodology that approximates the time-varying pumping record as a series of segments with linearly varying pumping rates. We validate our approach using an analytical solution for a sinusoidally varying pumping test. We also apply our methodology to analyze synthetic test data and compare the results with those from a commonly used method where rate variations are represented by a series of constant-rate steps.

Cylindrical (axasymmetric) flow to a well is an important specialized topic of ground-water hydraulics and has been applied by many investigators to determine aquifer properties and determine heads and flows in the vicinity of the well. A recent modification to the U.S. Geological Survey Modular Three-Dimensional Finite-Difference Ground-Water Flow Model provides the opportunity to simulate axisymmetric flow to a well. The theory involves the conceptualization of a system of concentric shells that are capable of reproducing the large variations in gradient in the vicinity of the well by decreasing their area in the direction of the well. The computer program presented serves as a preprocessor to the U.S. Geological Survey model by creating the input data file needed to implement the axisymmetric conceptualization. Data input requirements to this preprocessor are described, and a comparison with a known analytical solution indicates that the model functions appropriately.

Lincolns municipal wellfield consists of 44 wells developed in an alluvial aquifer adjacent to the Platte River near Ashland, Nebraska Induced recharge from the river is the primary source of water for the wellfield. Wafer samples were collected on a periodic basis from the Platte River arid two transects of monitoring wells. These samples were analyzed for the herbicide atrazine, which was used as a tracer of induced recharge in this stream-aquifer system. Atrazine concentrations in the river and aquifer were much less than 1.0 ppb during late fall and winter, but increased to as high as 18.9 ppb during spring and summer, associated with runoff from upgradient agricultural lands. There was approximately a 21-day lag time from the first detection of increasing atrazine concentration in the river to the first detection in monitoring wells immediately adjacent to the river. This lag time was relatively constant throughout the year and from one year to the next, even with major fluctuations of river stage and wellfield production. This consistency of lag time indicated that the travel times from the river to the first set of monitoring wells immediately adjacent to the river were fairly constant. Paths of preferential flow were identified in the aquifer at a depth of 25 to 35 feet below land surface. This aquifer zone appeared to play a significant role in movement of water from beneath the river into the wellfield. Aquifer dispersivity was calculated using a method described by Hoehn and Santschi (1987). Macrodispersivity (AL) was shown to increase linearly over the scale of the wellfield. Calculated values of AL were within limits of other reported values for this type of aquifer material and agreed well with values reported by Hoehn and Santschi (1987); These findings will be extremely beneficial for planning and management of the municipal wellfield.

A technique based on numerical ground-water flow modeling and unconstrained nonlinear optimization has been developed to provide guidance for protecting municipal ground-water supplies from contamination through capture zone management. The technique involves conventional finite-difference ground-water flow modeling and numerical flowpath/travel time calculation coupled with nonlinear mathematical programming. The objective of the technique is to specify pumping rates for wells in a wellfield such that the configuration of capture zones in relation to existing potential sources of contamination minimizes the risk of contamination while maintaining the required total water output from the wellfield. An important feature of the technique is its ability to incorporate realistic boundary conditions, complicated aquifer configurations, and spatially varying aquifer properties to whatever degree site-specific data are available. Also, the technique is implemented on a personal computer. This approach to ground-water supply protection enhances conventional wellhead protection area delineation because a greater level of protection can be achieved if potential contaminant sources are not even included in capture zones, rather than attempting to reduce the threat of those sources. The effectiveness of the technique was verified through application to a hypothetical ground-water system. Practical aspects were demonstrated with an application in Pekin, Illinois. These efforts demonstrate the utility of an innovative modeling technique in ground-water quality protection.

Step-drawdown tests may be used to evaluate the well loss component of the well drawdown and to obtain estimates of the aquifer properties. A procedure that analyzes step-drawdown tests with pumping stages of unequal time durations was formulated and developed into a computer program; the method is applicable to confined aquifers where the water-level drawdowns are governed by the Theis well function. A least-squares-fit error analysis is used in the determination of the aquifer properties and the well loss component of the drawdown.

In this study, nonlinear least-squares analysis of pump test data is used as a method for estimating aquifer parameters and choosing a conceptual model of the aquifer. The goal of this study is to investigate the potential advantages and disadvantages of using statistical algorithms for pump test analyses. Four different aquifer models were fitted to an extensive set of pump test data to characterize the aquifer at a single aquifer test site. These models were the Theis model, the equipotential boundary model, the confined leaky aquifer model, and the water-table aquitard model. For several of the data sets, more than one aquifer model was found to match the pump test response with the same residual least-squares error, and a review of the local hydrogeology was required to choose the leaky aquifer model as the most appropriate aquifer model. A few data sets, however, did not agree well with the leaky aquifer model. Using the fitting routine, the water-table aquitard model was found to significantly improve the fit to these data sets. Further analysis of hydrogeologic features at the site indicated that the duration of the pump tests which matched the leaky aquifer model was probably insufficient to exhibit deviation from the leaky aquifer model. The water-table aquitard model is, therefore, chosen as the most suitable model for this site, and parameters for the aquifer are estimated using the results from the fitting procedure. In comparison, an earlier graphical interpretation of these pump tests did not distinguish the improved fit which could be obtained with the water-table aquitard model. However, the graphical analyses were valuable as they did provide preliminary estimates of the aquifer transmissivity, aiding in accepting or rejecting the results of the fitting analysis. Thus, we found that nonlinear least-squares analysis can complement, but does not replace, graphical interpretation methods. The nonlinear least-squares analysis can provide a means for analyzing pump tests which may not have been easily interpreted using traditional techniques, as the nonlinear least-squares analysis attempts to match all the test data at both large and small values of time. However, this analysis also illustrates that fitting methods cannot be totally automated, but rather must be interpreted in light of other hydrogeologic data in order to arrive at a reasonable model for the aquifer.

A stochastic approach to steady-state time-related capture zone determination that is based on the conditional simulation of hydraulic conductivity is presented. Conditional simulation of hydraulic conductivity preserves the spatial correlation structure of the real hydraulic conductivity field as well as the measured, or known, values of hydraulic conductivity at sampling locations, thereby optimizing the use of available data and providing the most representative results possible. The stochastic analysis methodology utilizing conditional simulation is applied to a hypothetical ground-water system with a water supply well to estimate uncertainty in the 1-year and 10-year capture zones of the well. The results demonstrate the influence of known hydraulic conductivity values on the estimates of uncertainty, as well as the behavior of the “zone of uncertainty” of the capture zone as a function of travel time and orientation of regional flow. The results have significant implications regarding strategies for sampling aquifer properties (e.g., hydraulic conductivity) for capture zone delineation and for interpretation of the effects of hydraulic conductivity uncertainty on capture zones.

Two large-scale (9.5 m long, 4.7 m wide, 2.6 m deep), three-dimensional artificial aquifers were constructed to investigate the influence of spatial variations in aquifer properties on contaminant transport. One aquifer was uniformly filled with coarse sand media (0.6 to 2.0 mm) and the other was constructed as a heterogeneous aquifer using blocks of fine, medium, and coarse sands. The key features of these artificial aquifers are described. An innovative deaeration tower was constructed to overcome a problem of the aquifers becoming blocked with excess air from the ground water source. A series of tracer injection experiments were conducted to test the homogeneity of the first aquifer that was purposely built as a homogeneous aquifer and to calculate values of aquifer parameters. Experimental data show that the aquifer is slightly heterogeneous, and hydraulic conductivity values are significantly higher down one side of the aquifer compared to the mean value. There was very good agreement in estimated dispersivity values between the plume area ratio methods and the curve fitting of tracer breakthrough curves. Dispersivity estimates from a full areal source injection (12.2 m2) experiment using a 1D analytical model were higher than estimates from a limited source injection (0.2 m2) experiment using a 3D model, possibly because the 1D model does not take account of the heterogeneity of hydraulic conductivity in the aquifer, thus overestimating dispersivity. Transverse and vertical dispersivity values were about five times less than the longitudinal dispersivity. There was slight sorption of Rhodamine WT onto the aquifer media.

The objectives of an aquifer test are to identify the performance of a well (to estimate the yield capability) and to estimate aquifer properties. Accurate estimates of the hydraulic characteristics of aquifers depend on reliable aquifer test data. The tests are done on existing wells or a well drilled specifically for that purpose. An aquifer test is a controlled, field site experiment to determine hydraulic conductivity and aquifer storage. The test consists of measuring groundwater discharge and observing water level changes in the pumped well. Keywords: aquifertest; slugtest; specific capacity theis equations

In coastal confined aquifers, the extent of the salt-water wedge due to natural ground-water flow can be determined by available methods. If water is pumped by a discharge well, the quality of the water depends upon the rate and duration of pumping as well as the location of the well. A study has been made to find the extent of the progress of salt-water intrusion due to the operation of one discharge well taking into account various conditions of aquifer properties, pump capacities, natural flows, time effects, and well locations. Dimension-less solutions for specific conditions have been obtained by means of a simple computer program. Range of most common conditions is discussed. One of the main findings of this study was that salt water may be pumped out of a well even if it is located in an initially totally fresh-water zone beyond the natural salt/fresh-water interface.

The Edwards artesian aquifer occurs in cavernous limestones of Cretaceous (Albian) age within the Balcones fault zone in south-central Texas. The major recharge and discharge zones of the aquifer are contained within the upper reaches of three river systems: the Nueces, the San Antonio, and the Guadalupe. Within these watersheds, recharge dominates in the semiarid Nueces basin to the west while most discharge occurs farther east from wells in the subhumid San Antonio basin and from springs in the subhumid Guadalupe basin. This long-distance transfer of ground water (up to 240 km) is a result of several factors: depositional and early diagenetic history of the limestone host rock, geometry and magnitudes of fault displacement, and physiographic responses to faulting. The loci of greatest discharge from the aquifer occur in an area that was exposed subaerially with concomitant porosity enhancement due to dissolution of limestone during late Early Cretaceous time. This area also was subjected to the greatest fault displacement during Miocene time. Thus, faults and associated joints superimposed additional avenues for porosity and permeability development onto an area that already had considerable secondary porosity. Further determinants on aquifer properties resulted from late Tertiary and Quaternary drainage evolution in response to faulting along the Balcones trend. The strike of the fault zone lay at acute angles to the courses of the main trunk streams in the ancestral Guadalupe and San Antonio River systems, whereas in the Nueces basin the trend of the fault zone was normal to the courses of the main streams. Thus, as a fault-line scarp began to form in the eatern basins, scarp-normal streams were incised rapidly into northwest-trending canyons. These steep-gradient streams captured the eastward-flowing major streams in the easten watersheds. These pirate streams incised into the aquifer at the lowest topographic levels within the region because of: 1. The sudden acquisition of extensive catchment areas in a subhumid area; and 2. Steep stream gradients that reflected the larger fault displacement in the east. The low topographic points of discharge became the loci of major springs. Recharge is dominant in the Nueces basin mainly because streams cross permeable limestone units at higher topographic levels than in the San Antonio and Guadalupe basins. The topographic characteristics of the Nueces watershed resulted from a combination of diverse factors: lesser fault displacement, no major stream piracy, and less vigorous erosion because of a semiarid climate.

SYNOPSIS This study considers the groundwater conditions for the period 1948–82 in the Permo-Triassic Sandstone aquifer of the Liverpool area. During this period, significant changes have occurred in the abstraction patterns and a new railway tunnel has been constructed below sea level in Central Liverpool. To understand the flow conditions within the aquifer, detailed studies have been carried out into the aquifer properties, the influence of rivers and tunnels, and the estimation of recharge. It is found that conventional rainfall recharge accounts for only one-third of the total recharge. Numerical model solutions were used to check the adequacy of the understanding of the flow processes and the solutions have confirmed that the rising water levels in Central Liverpool result from high recharge and a reduction in abstraction. Having validated the model by comparisons with field data, the model was then used to predict the probable future water level changes.

Porous asphalt pavement is a storm-water management technique which reduces runoff and enhances ground-water recharge. Planned applications of this, or other ground-water recharge techniques, require that ground-water response to induced recharge be quantified. Here, we emphasize determination of the aquifer parameters hydraulic conductivity (K) and specific yield (Sy) at a porous asphalt ground-water recharge facility installed near Willow Grove, Pennsylvania. We compare values of these aquifer properties derived from conventional laboratory and field techniques to those derived using recharge event data collected at the site. By the comparisons, we illustrate the techniques of aquifer property determination apropos to the design of ground-water recharge installations. Because of the fractured nature of the aquifer, the K-values determined from pumping test and slug test analyses are about an order of magnitude greater than those of rock core samples, while the field-based specific yield values are about an order of magnitude less than effective porosities of the rock cores. Ratios of K/Sy derived from a chemical tracer test agree with the pumping test values. Finally, the K and Sy necessary to simulate facility response to recharge using a numerical model of ground-water flow correspond to those derived from field-oriented techniques rather than those of the rock cores. The results show that the design parameters K and Sy should be obtained from field-based techniques, such as the nonsteady pump test, which match the time and space scale in which the facility is expected to affect the aquifer.