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Ground water exchange affects the ecology of surface water by sustaining stream base flow and moderating water-level fluctuations of ground water-fed lakes. It also provides stable-temperature habitats and supplies nutrients and inorganic ions. Ground water input of nutrients can even determine the trophic status of lakes and the distribution of macrophytes. In streams the mixing of ground water and surface water in shallow channel and bankside sediments creates a unique environment called the hyporheic zone, an important component of the lotic ecosystem. Localized areas of high ground water discharge in streams provide thermal refugia for fish. Ground water also provides moisture to riparian vegetation, which in turn supplies organic matter to streams and enhances bank resistance to erosion. As hydrologists and ecologists interact to understand the impact of ground water on aquatic ecology, a new research field called 'ecohydrology' is emerging., Editor's note: This paper is reprinted with slight modification from the Japanese Journal of Groundwater Hydrology 43, 327-341, published by the Japanese Association of Groundwater Hydrology, 2001. Introduction Surface water [...]

This paper comments on the current state of knowledge in the field of hydrogeology and claims that fundamental understandings must be developed if creative research is to have maximum impact. Problems of great importance to society include water development and quality, waste disposal, and global cycling of resources. These problems cannot be addressed effectively unless significant advances are made in understanding of a range of challenging scientific issues including fundamental physics, the importance of scale, modeling, and chemical and biological processes. Meaningful advances in hydrogeologic research will require an increased emphasis on fundamental understanding, interdisciplinary approaches, educational reforms, and the attraction of excellent researchers to the field., Introduction Our experiences as educators, researchers, editors, reviewers, and advisors active in water resources have provided us with a perspective on the general state of knowledge in hydrogeological research. Our [...]

The beginning of the 21st century has coincided with our recognition that Ute-sustaining earth cycles are remarkably fine-tuned, and that humans have developed technological abilities to perturb these cycles. Also, inspired by the gifts of freedom and democracy, humans have given themselves laws to exploit nature for profit. The upshot is that nature's balance, governed by immutable physical laws, is being confronted by social laws driven by human aspirations. This conflict and its implications to the human relevance of the earth sciences are explored in the context of an extraordinary tradition of European culture known as public trust. Introduction, Most earth scientists agree that the earth is a bounded natural system. Although this finiteness of the earth was recognized by 19th century naturalists, its potential implications to human society [...]

Remediation of ground water and soil contamination at the Wells G & H Superfund Site, Woburn, Massachusetts, uses technologies that reflect differences in hydrogeologic settings, concentrations of volatile organic compounds (VOCs), and costs of treatment. The poorly permeable glacial materials that overlie fractured bedrock at the W.R. Grace property necessitate use of closely spaced recovery wells. Contaminated ground water is treated with hydrogen peroxide and ultraviolet (UV) oxidation. At UniFirst, a deep well completed in fractured bedrock removes contaminated ground water, which is treated by hydrogen peroxide, UV oxidation, and granular activated carbon (GAC). The remediation system at Wildwood integrates air sparging, soil-vapor extraction, and ground water pumping. Air stripping and GAG are used to treat contaminated water; GAG is used to treat contaminated air. New England Plastics (NEP) uses air sparging and soil-vapor extraction to remove VOCs from the unsaturated zone and shallow ground water. Contaminated air and water are treated using separate GAG systems. After nine years of operation at W.R. Grace and UniFirst, 30 and 786 kg, respectively, of VOCs have been removed. In three years of operation, 866 kg of VOCs have been removed at Wildwood. In 15 months of operation, 36 kg of VOCs were removed at NEP. Characterization work continues at the Olympia Nominee Trust, Whitney Barrel, Murphy Waste Oil, and Aberjona Auto Parts properties. Risk assessments are being finalized that address heavy metals in the floodplain sediments along the Aberjona River that are mobilized from the Industri-Plex Superfund Site located a few miles upstream., Introduction The Wells G & H Superfund Site in Woburn, Massachusetts, has been in the scientific spotlight since publication of the award-winning book A Civil Action (Harr 1995). The book [...]

Study of ground water in the Southern High Plains is central to an understanding of the geomorphology, deposition of economic minerals, and climate change record in the area. Ground water has controlled the course of the Canadian and Pecos rivers that isolated the Southern High Plains from the Great Plains and has contributed significantly to the continuing retreat of the westward escarpment. Evaporative and dissolution processes are responsible for current plateau topography and the development of the signature 20,000 small playa basins and 40 to 50 large saline lake basins in the area. In conjunction with eolian processes, ground water transport controls the mineralogy of commercially valuable mineral deposits and sets up the distribution of fine efflorescent salts that adversely affect water quality. As the water table rises and retreats, lunette and tufa formation provides valuable paleoclimate data for the Southern High Plains. In all these cases, an understanding of ground water processes contributes va luable information to a broad range of geological topics, well beyond traditional interest in water supply and environmental issues., Introduction Ground water is one of society's most valuable resources and an important geologic agent in the transport of mass and energy within the earth. Most introductory geology textbooks, however, [...]

Within the ground water community, the idea persists that if one can estimate the recharge to a ground water system, one then can determine the size of a sustainable development. Theis addressed this idea in 1940 and showed it to be wrong--yet the myth continues. The size of a sustainable ground water development usually depends on how much of the discharge from the system can be 'captured' by the development. Capture is independent of the recharge; it depends on the dynamic response of the aquifer system to the development. Ground water models were created to study the response dynamics of ground water systems; it is one of the principal reasons hydrogeologists model., Introduction The idea persists within the ground water community that if one can determine the recharge to an aquifer system then one can determine the maximum magnitude of a sustainable [...]

'Coefficient of Permeability Determined by Measurable Parameters,' by D,W, Barr, May-June 2001 issue, v. 39, no. 3:356-361. Discussion by Robert K. Niven, School of Civil Engineering, University College, The University [...]

'Hydrogeological Research: Beginning of the End or End of the Beginning?' by F.W. Schwartz, and M. Ibaraki. 2001. Ground Water 39, no. 4: 492-498. DISCUSSION by Miller and Gray appears [...]

I. General Comments The topic of the recent manuscript by Heron et al. (1997) is timely and we applaud the authors' attention to analytical details. We argue that there are [...]

Yin and Brook defends their position by citing certain issues which seems to have been misinterpreted by their critics. Their study is not the only one that has ever questioned the validity of the topographic approach to well siting. They did not dispute the findings nor question the important role of earlier studies. They maintain the the need for mapping the fracture traces with remote sensing imagery based on their experience.

'Dipole Probe: Design and Field Application of a Single-Borehole Device for Measurements of Vertical Variations of Hydraulic Conductivity' by Vitaly A. Zlotnik and Brian R. Zurbuchen, November-December 1998 issue, v. [...]

'Relationship Between Pumping-Test and Slug-Test Parameters: Scale Effect or Artifact?' by J.J. Butler Jr. and J.M. Healey, March-April 1998 issue, v. 36 no. 2: 305-313. Discussion by Charles W. Rovey [...]

'A Stream Depletion Field Experiment,' by Bruce Hunt, Julian Weir, and Bente Clausen, March-April 2001 issue, v. 39, no. 2: 283-289. Discussion by SJ. Kollet and V.A. Zlotnik, both from [...]

'Anomalous Fresh Water Lens Morphology on a Strip Barrier Island' by C. Ruppel, G. Schultz, and S. Kruse, November--December 2000 issue, v. 38, no. 6: 872-881. DISCUSSION by William P. [...]

'A Conceptual Model for DNAPL Transport in Karst Ground Water Basins' by Caroline M. Loop and William B. White. Ground Water 39, no. 1: 119-127. DISCUSSION by Tom Aley, Ozark [...]

The criticisms which were generated by Tsang's paper are interpreted as a misunderstanding and misreading of its points. The first clarification is on the linkage of model calibration to model validation. The second is on the consensus necessary for validation. On the first point, it is asserted that model calibration was even deemphasized. On the second point, his emphasis was the need for peer review and open discussions at every step of the modeling process. Two other points of contention regarding the choice of performance criteria and the definition of model validation are discussed.

A reply to the evaluation made by D.I. Siegel is presented. It is argued that the variation in chloride/sulfate ratios and the different causes of elevated chloride/sulfate ratios were significant enough to merit an independent study. While the groundwater flow model proposed by Siegel can be deemed as relevant as it may apply over the aquifer as a whole, the model used in the study is defended by indicating that other processes affect the flow regime in this aquifer on a local scale.

'Generating Two-Dimensional Fields of Autocorrelated, Normally Distributed Parameters by the Matrix Decomposition Technique' by A.I. El-Kadi and S.A. Williams, July-August 2000 issue, v. 38, no.4:530-532. The authors of El-Kadi and [...]

Discussion by Bhaskar Joshi, Department of Agricultural & Bioresource Engineering, University of Saskatchewan, Saskatoon, Canada O'Brien et al. have argued on page 678 that the reason for low recharge flux [...]

The intensity of global groundwater use rose from 124 m3 per capita in 1950 to 152 m3 in 2021, for a 22.6% rise in the annual per capita use. This rise in global per capita water use reflects rising consumption patterns. The global use of groundwater, which provides between 21% and 30% of the total freshwater annual consumption, will continue to expand due to the sustained population growth projected through most of the 21st century and the important role that groundwater plays in the water-food-energy nexus. The rise in groundwater use, on the other hand, has inflicted adverse impacts in many aquifers, such as land subsidence, sea water intrusion, stream depletion, and deterioration of groundwater-dependent ecosystems, groundwater-quality degradation, and aridification. This paper projects global groundwater use between 2025 and 2050. The projected global annual groundwater withdrawal in 2050 is 1535 km3 (1 km3 = 109 m3 = 810,713 acre-feet). The projected global groundwater depletion, that is, the excess of withdrawal over recharge, in 2050 equals 887 km3, which is about 61% larger than in 2021. This projection signals probable exacerbation of adverse groundwater-withdrawal impacts, which are worsened by climatic trends and the environmental requirement of groundwater flow unless concerted national and international efforts achieve groundwater sustainability.

In this issue paper, the authors refine the definition of water sustainability to account for temporal dynamics and spatial variability, identify specific challenges that must be resolved in the very near future to avoid catastrophic outcomes on levels ranging from economic disruption to survival of mankind, discuss related policy changes and potential effectiveness, and describe several technologies available to achieve water security and sustainability. While water quality certainly poses formidable challenges, in this piece we emphasize and address challenges associated with dynamic water supply availability. Our future as a society will depend upon how well and how rapidly we navigate these challenges in the coming years. As such, the main objective is to encourage private and public sector practitioners to consider revising existing programs, and to update current industry business models in a manner that promotes expedited solutions, alignment of beneficial goals, and motivates the biggest consumers of water to adopt modern data collection and decision support technologies.

Methods for calculating the safe yield are evaluated in this paper using a high-quality and long historical data set of groundwater recharge, discharge, extraction, and precipitation in a karst aquifer. Consideration is given to the role that climatic variability has on the determination of a climatically representative period with which to evaluate the safe yield. The methods employed to estimate the safe yield are consistent with its definition as a long-term average extraction rate that avoids adverse impacts on groundwater. The safe yield is a useful baseline for groundwater planning; yet, it is herein shown that it is not an operational rule that works well under all climatic conditions. This paper shows that due to the nature of dynamic groundwater processes it may be most appropriate to use an adaptive groundwater management strategy that links groundwater extraction rates to groundwater discharge rates, thus achieving a safe yield that represents an estimated long-term sustainable yield. An example of the calculation of the safe yield of the Edwards Aquifer (Texas) demonstrates that it is about one-half of the average annual recharge.

As Edmond Halley (Figure 1) himself noted, over the course of recorded human history "the sea has not sensibly decreased by the loss in vapor; nor yet abounded by the immense quantity of fresh water it receives continually from the rivers" (Halley 1691, 469). Halley published a paper on the history of the city of Palmyra (Halley 1695) and attempted to reconstruct the time and place at which Julius Caesar first landed in Britain (Halley 1686). Halley concluded that cumulative river flow into the Mediterranean Sea was "little more than one-third of what is proved to be raised in vapour out of the Mediterranean in 12 hours time" (Halley 1687, 369). Halley concluded that his hypothesis of condensation at high altitudes "is more reasonable than that of those who derive all springs from the rain-waters" (Halley 1691, 472). [Extracted from the article]

In her review of Benchmark Papers in Hydrogeology, Mary Anderson ([1]) presented 35 of what she considered to be the most impactful papers written during the past 150 years from Darcy to Gorelick. Of these, more than a third were authored by staff from the National Research Program (NRP) of the U.S. Geological Survey (USGS) Water Resources Division (WRD; now the "Water Mission Area"). The termination of the USGS's National Research Program in the Water Mission Area is a serious loss to the USGS and the global water science community. [Extracted from the article]

Heat carried by ground water serves as a tracer to identify surface water infiltration, flow through fractures, and flow patterns in ground water basins. Temperature measurements can be analyzed for recharge and discharge rates, the effects of surface warming, interchange with surface water, hydraulic conductivity of streambed sediments, and basin-scale permeability. Temperature data are also used in formal solutions of the inverse problem to estimate ground water flow and hydraulic conductivity. The fundamentals of using heat as a ground water tracer were published in the 1960s, but recent work has significantly expanded the application to a variety of hydrogeological settings. In recent work, temperature is used to delineate flows in the hyporheic zone, estimate submarine ground water discharge and depth to the salt-water interface, and in parameter estimation with coupled ground water and heat-flow models. While short reviews of selected work on heat as a ground water tracer can be found in a number of research papers, there is no critical synthesis of the larger body of work found in the hydrogeological literature. The purpose of this review paper is to fill that void and to show that ground water temperature data and associated analytical tools are currently underused and have not yet realized their full potential., Introduction Heat-flow theory has been important in the development of the science of ground water hydrology; yet, the body of literature on heat as a ground water tracer is relatively [...]

This paper describes a methodology for resolving transboundary water disputes that arise when people/states/nations sharing a resource that crosses legal/political jurisdictions disagree about the use of the resource. Laws and treaties written in an attempt to settle disputes are frequently neither enforced nor effective, and disagreements continue. Crises, arising through resource overuse or shortages, worsen the conflict and typically result in further discord, lawsuits, depletion of the resource, and even open-armed hostility. Many water management experts call for either private/market-based or state/command-and-control resource management systems, but these eventually break down during crisis. The crises therefore necessitate the adoption of a more effective institutional arrangement to address and resolve present and future problems. A better alternative to management by private or state entities and the resolution of conflicts by the mere application of law is a cooperative approach. The Rowland-Ostrom Framework, introduced in this paper, incorporates Ostrom's eight design principles for sustainable common pool resource management within the context of crisis that involves an urgent threat to the quantity or quality of a resource such as water, as described by the author. This paper demonstrates that although established 15 years ago, Ostrom's design principles remain applicable today for effective, sustainable transboundary water management, and the Rowland-Ostrom Framework is a model for the equitable use of shared water resources throughout the world., Introduction Few would disagree that the world's supply of water is under stress from increasing usage. Nearly half of the world's population shares water from river basins that traverse national [...]

Ground water plays an important role in water supply and the ecology of arid to semiarid areas such as Northwest China, where the landscape is fragile due to frequent drought in the past few decades. This paper discusses the role of ground water in these ecosystems, including the effect of condensation water and water table depth on the growth of plants and degree of soil salinity. The paper also discusses the controlling process for land desertification and soil salinization in Northwest China. Water table depth is a key factor controlling the water balance, ground water flow, and salt transport in the vadose zone. The suitable water table depth for vegetation growth, which can prevent land desertification and soil salinization, is within a range of 2 to 4 m; the optimal depth is ~3 m. As examples, changes in ecosystems owing to water resources development in Tarim and Manas basins, Xinjiang, China, are discussed., Editor's Note: The following four papers are part of a series of seven papers on 'Ground Water Research in China'. The first three papers in the series were published in [...]

In this paper we present a hydrologic application of a new statistical learning methodology called support vector machines (SVMs). SVMs are based on minimization of a bound on the generalized error (risk) model, rather than just the mean square error over a training set. Due to Mercer's conditions on the kernels, the corresponding optimization problems are convex and hence have no local minima. In this paper, SVMs are illustratively used to reproduce the behavior of Monte Carlo-based flow and transport models that are in turn used in the design of a ground water contamination detection monitoring system. The traditional approach, which is based on solving transient transport equations for each new configuration of a conductivity field, is too time consuming in practical applications. Thus, there is a need to capture the behavior of the transport phenomenon in random media in a relatively simple manner. The objective of the exercise is to maximize the probability of detecting contaminants that exceed some regulatory standard before they reach a compliance boundary, while minimizing cost (i.e., number of monitoring wells). Application of the method at a generic site showed a rather promising performance, which leads us to believe that SVMs could be successfully employed in other areas of hydrology. The SVM was trained using 510 monitoring configuration samples generated from 200 Monte Carlo flow and transport realizations. The best configurations of well networks selected by the SVM were identical with the ones obtained from the physical model, but the reliabilities provided by the respective networks differ slightly., Background The design of ground water pollution monitoring networks entails the selection of sampling points (spatial) and sampling frequency (temporal) to determine physical, chemical, and biological characteristics of ground water [...]

A typical fractured rock mass is intersected by several sets of discontinuities, which provide the main flowpath for ground water. Due to the limitations of data obtained by conventional field measurements, it is often difficult to estimate the anisotropic permeability tensor associated with the joints existing in the rock mass. For that reason, determining permeability tensors for fractured rocks is an important topic in rock mass hydraulics. Based on field surveys, joint parameters can be analyzed by using probabilistic and statistical tools, and three-dimensional mapping of the jointed rock mass. Through analysis of a single joint's hydraulic characteristics, the principal value of the permeability tensor for the jointed rock mass can be determined by using Monte Carlo methods and the searching percolation trace method, which is developed in this paper. The study reports on practical examples demonstrating that results from the methods discussed in this paper are in agreement with those from field hydrogeological surveys and measurements., Introduction A typical fractured rock mass is intersected by several sets of discontinuities whose geometry exhibits a random behavior. In some cases these discontinuities, or joints, are the main paths [...]

Ground water validation is one of the most challenging issues facing modelers and hydrogeologists. Increased complexity in ground water models has created a gap between model predictions and the ability to validate or build confidence in predictions. Specific procedures and tests that can be easily adapted and applied to determine the validity of site-specific ground water models do not exist. This is true for both deterministic and stochastic models, with stochastic models posing the more difficult validation problem. The objective of this paper is to propose a general validation approach that addresses important issues recognized in previous validation studies, conferences, and symposia. The proposed method links the processes for building, calibrating, evaluating, and validating models in an iterative loop. The approach focuses on using collected validation data to reduce uncertainty in the model and narrow the range of possible outcomes. This method is designed for stochastic numerical models utilizing Monte Carlo simulation approaches, but it can be easily adapted for deterministic models. The proposed methodology relies on the premise that absolute validity is not theoretically possible, nor is it a regulatory requirement. Rather, the proposed methodology highlights the importance of testing various aspects of the model and using diverse statistical tools for rigorous checking and confidence building in the model and its predictions. It is this confidence that will encourage regulators and the public to accept decisions based on the model predictions. This validation approach will be applied to a model, described in this paper, dealing with an underground nuclear test site in rural Nevada., Introduction During the past two decades, stochastic studies have shown that inadequate and insufficient data limit the ability of ground water models to predict system behavior without substantial uncertainty (Pohll [...]

When using monitoring wells for investigation of contaminant sources in clayey till, there is a high risk that fractures may cause mobile contaminants to bypass the monitoring wells. This paper indicates that the probability of interception between monitoring wells and hydraulic conductive fractures is often significantly less than 50%. Based on a field experiment and application of a calibrated discrete fracture matrix diffusion numerical model (FRAC3Dvs), the paper also evaluates pesticide-monitoring results for different positions of monitoring well screen relative to fractures. For well screens situated 0.25 and 2 m from a conductive fracture, the first concentrations of the pesticide metabolite (2,6 dichlorobenzamide, 'BAM') would be measured two years and 18 years, respectively, after the contaminant had been transported into an underlying aquifer. In this way, underlying aquifers may be subjected to contamination by downward moving contamination without being observed in monitoring wells in the till., Introduction Among the very large number of monitoring and water supply wells that are annually analyzed for pollution in Denmark, short wells play an important role in mapping contamination sources [...]

Investigation techniques for karst flow systems are based mainly on the study of different signals leaving the system caused by natural or induced external influences. Each signal represents one of the systems outputs (e.g., hydraulic, chemical, physical, or isotopic responses) that reflect the characteristics of the entire system. In this paper, we present a method to infer information about the structure of karst systems. It is based on a simultaneous analysis of chemical and hydraulic responses. Beside the classical piston flow at the beginning of a flood pulse, we define a chemically based recession flow phase. During this phase, field data show that the concentration of total dissolved solids can be considered as an exponential function of the logarithm of flow. This relationship allows two parameters to be defined, one of which is dependent on the structure and degree of development of the karst conduit network, the other is dependent mainly on bioclimatic factors. Data collected from seven karst springs are used to support ideas introduced in the paper., Introduction From a hydrogeological point of view, a karst system can be schematically represented as an ensemble of conduits--the karst network--with a high hydraulic conductivity (K > [10.sup.-1] mlsec) embedded [...]

This paper uses citation data to assess whether articles published in key ground water journals such as Ground Water (GW) and Water Resources Research (WRR) are impacting research. Citation information was obtained from SCI Journal Citation Reports and The Web of Science--databases maintained by the Institute for Scientific Information (ISI). Information extracted from The Web of Science was processed further to remove corrections to papers, discussion/replies, and book reviews. Generally, there are many ground water papers published, but citations of these papers are limited. Approximately 10% to 15% of WRR articles, and 2% to 3% of GW articles attract more than 50 citations in their lifetimes. In both GW and WRR, the top 10% of papers eventually will contribute nearly half of the total yearly citations. Another emerging trend is a diminishing emphasis on citations to new work as compared to work more than 10 years in age. When articles in Ground Water or Journal of Hydrology cite papers in Water Resources R esearch, those papers cite work 10 or more years old half of the time. If one believes that citations are a measure of science impact, then there is cause for concern. Research is inefficient with much produced for little gain. On a typical industrial life-cycle curve, ground water research is likely ranked as mature and close to aging. At this stage, much work will have been completed and the number of truly impactful problems will have dwindled to just a few., Introduction This paper is motivated in part by a book by Horgan (1997) titled The End of Science. He provides a thought-provoking discussion as to whether science in general is [...]

The introduction concerning particle tracking algorithms and velocity estimation methods on unstructured grids is limited to methods developed by Cordes and Kinzelbach ([1]). By using the absolute coordinate system, the authors unfortunately provide the estimation of the path deviation depending on the coordinate system itself. The artifact on the path calculation observed in the simple rectangular grid block is present and amplified in the other presented case studies - Figures 5 and 6 of the paper. [Extracted from the article]

Abstract The first paper in this series (Rautman and Istok, 1996) presented a geostatistical framework for obtaining a probabilistic assessment of ground-water contamination. This paper presents the results of a [...]

Introduction This paper is the second in a series of two that examine the applicability of slug interference testing within unconfined aquifers. In the first paper, the procedure for generating [...]

Carbon dioxide (CO(2)) capture and geologic storage has been postulated as one possible method to stabilize the atmospheric concentration of CO(2) by injecting and storing it in deep geologic formations. This issue paper analyzes the viability of capture and geologic storage of becoming an effective method to aid in stabilizing the atmospheric concentration of CO(2). It is herein shown that such viability is contingent on overcoming major obstacles that are hydrogeological, technical, and economic in nature. Our analysis indicates that capture and geologic storage is likely to have negligible success in reducing the atmospheric buildup of CO(2) in the coming decades. The magnitude of the anthropogenic emissions of CO(2) indicates that a transition of the world economy away from reliance on fossil fuels might be the only path to stabilize its atmospheric concentration.

Issue and Review Papers--Two New Features in Ground Water In this issue of Ground Water we introduce two types of papers that we hope will become regular features in the [...]

We are well on our way to providing full and complete online access to all papers published in Ground Water. NGWA members can access papers published in the March-April, May-June [...]

We acknowledge the similarity between our paper and a portion of Agarwal (1980). We compiled our paper on the basis of several informal and unpublished essays prepared through the years [...]

The most appropriate definition of flux, as related to ground water, is the one that is used in the field of transport phenomena, and is a vector at each point in space, since it is defined with respect to a direction. It is proposed that the transport definition of flux be used consistently in technical presentations, published papers and books, the consistent usage of which would teach the following generation of hydrogeologists that flux has a definite meaning in science.

One of the challenges in characterizing fractured-rock aquifers is determining whether the equivalent porous medium approximation is valid at the problem scale. Detailed hydrogeologic characterization completed at a small study site in a densely fractured dolomite has yielded an extensive data set that was used to evaluate the utility of the continuum and discrete-fracture approaches to aquifer characterization. There are two near-vertical sets of fractures at the site; near-horizontal bedding-plane partings constitute a third fracture set. Eighteen boreholes, including five coreholes, were drilled to a depth of ~10.6 m. Borehole geophysical logs revealed several laterally extensive horizontal fractures and dissolution zones. Flowmeter and short-interval packer testing identified which of these features were hydraulically important. A monitoring system, consisting of short-interval piezometers and multilevel samplers, was designed to monitor four horizontal fractures and two dissolution zones. The resulting network consisted of >70 sampling points and allowed detailed monitoring of head distributions in three dimensions. Comparison of distributions of hydraulic head and hydraulic conductivity determined by these two approaches suggests that even in a densely fractured-carbonate aquifer, a characterization approach using traditional long-interval monitoring wells is inadequate to characterize ground water movement for the purposes of regulatory monitoring or site remediation. In addition, traditional multiwell pumping tests yield an average or bulk hydraulic conductivity that is not adequate for predicting rapid ground water travel times through the fracture network, and the pumping test response does not appear to be an adequate tool for assessing whether the porous medium approximation is valid., Introduction The purpose of this paper is to compare and contrast continuum and discrete-fracture approaches for hydrogeologic characterization in a fractured-carbonate aquifer. Carbonate rocks, which underlie 40% of the United [...]

More than one-half of the world's population is dependent on ground water for everyday uses such as drinking, cooking, and hygiene. In fact, it is the most extracted natural resource in the world. As a result of growing populations and expanding economies, many aquifers today are being depleted while others are being contaminated. Notwithstanding the world's considerable reliance on this resource, ground water resources have long received only secondary attention as compared to surface water, especially among legislatures and policymakers. Today, while there are hundreds of treaties governing transboundary rivers and lakes, there is only one international agreement that directly addresses a transboundary aquifer. Given that many of the aquifers on which humanity so heavily relies cross international borders, there is a considerable gap in the sound management, allocation, and protection of such resources. In order to prevent future disputes over transboundary aquifers and to maximize the beneficial use of this resource, international law must be clarified as it applies to transboundary ground water resources. Moreover, it must be defined with a firm basis in sound scientific understanding. In this paper we offer six conceptual models is which ground water resources can have transboudary consequences. The models are intended to help in assessing the applicability and scientific soundness of existing and proposed rules governing transboundary ground water resources. In addition, we consider the development of international law as it applies to ground water resources and make recommendations based on the models and principles of hydrogeology. The objective is the development of clear, logical, and science-based norms of state conducts as they relate to aquifers that traverse political boundaries., Introduction Over the past half-century, ground water has emerged as a vital source of water for millions of people worldwide (McCaffrey 1991). More than one-half of the world's population today [...]

Ground water is a vital, but underappreciated, natural resource in the Great Lakes basin. It meets many human needs and contributes significantly to the hydrology of the Great Lakes and the health of ecosystems. This paper provides an overview of ground water in the Great Lakes and the institutional and legal setting that governs the use, protection, diversion, and removal of water from the basin and proposes a citizen-centered vision for management of ground water in the 21st century., The Great Lakes and Ground Water Ground water is now and will remain a vital component of the Great Lakes ecosystem. Its condition and the management of this resource should [...]

This paper presents a general model of optimal water management for a transboundary aquifer under three different management approaches: cooperative, noncooperative, and myopic. Comparing the results from the approaches, we find the cooperative solution, where a single management plan is executed for all parts of the aquifer, results in the highest level of net social welfare, followed by the noncooperative and then the myopic. The trade-offs we find for the higher levels of welfare are lower use levels in the earlier periods. We present a short discussion of factors that can increase the inefficiencies of the models and suggest directions for future research., Introduction Water is becoming increasingly scarce. Efficient use requires improved analytic models that simultaneously consider physical, economic, and institutional aspects of the problem. This is especially true for ground water, [...]

Historically, specific capacity information has been used to calculate aquifer transmissivity when pumping test data are unavailable. This paper presents a simple computer program written in the MATLAB programming language that estimates transmissivity from specific capacity data while correcting for aquifer partial penetration and well efficiency. The program graphically plots transmissivity as a function of these factors so that the user can visually estimate their relative importance in a particular application. The program is compatible with any computer operating system running MATLAB, including Windows, Macintosh OS, Linux, and Unix. Two simple examples illustrate program usage., Introduction A computer technique for estimating transmissivity from specific capacity data is currently available (Bradbury and Rothschild 1985). However, it is written in BASIC and does not graphically display results. [...]

This paper presents a critical review of model-input parameters for transport of on-site wastewater treatment system (OWS) pollutants. Approximately 25% of the U.S. population relies on soil-based OWS for effective treatment and protection of public health and environmental quality. Mathematical models are useful tools for understanding and predicting the transport and fate of wastewater pollutants and for addressing water-budget issues related to wastewater reclamation from site to watershed scales. However, input parameters for models that simulate fate and transport of OWS pollutants are not readily obtained. The purpose of this analysis is to illustrate an objective, statistically supported method for choosing model-input parameters related to nitrogen (N) and phosphorus (P). Data were gathered from existing studies reported in the literature. Cumulative frequency distributions (CFDs) are provided for OWS effluent concentrations of N and P, nitrification and denitrification rates, and linear sorption isotherm constants for P. When CFDs are not presented, ranges and median values are provided. Median values for model-input parameters are as follows: total N concentration (44 mg/L), nitrate-N (0.2 mg/L), ammonium (60 mg/L), phosphate-P (9 mg/L), organic N (14 mg/L), zero-order nitrification rate (264 mg/L/d), first-order nitrification (2.9/d), first-order dentrification (0.025/d), maximum soil capacity for P uptake (237 mg/kg), linear sorption isotherm constant for P (15.1 L/kg), and OWS effluent flow rates (260 L/person/d)., Introduction The standard of practice for wastewater management in the United States and many developed countries has evolved to include large, centralized wastewater treatment plants fed by networks of sewer [...]

This paper describes reactive transport simulations conducted to assess the impact of mineral fouling on the hydraulic behavior of continuous-wall permeable reactive barriers (PRBs) employing granular zero-valent iron (ZVI) in carbonate-rich alluvial aquifers. The reactive transport model included a geochemical algorithm for simulating corrosion and mineral precipitation reactions that have been observed in ZVI PRBs. Results of simulations show that porosity and hydraulic conductivity of the ZVI decrease over time and that flows are redistributed throughout the PRB in response to fouling of the pore space. Under typical conditions, only subtle changes occur within the first 10 years (i.e., duration of the current field experience record with PRBs), and the most significant changes do not occur until the PRB has operated for at least 30 years. However, changes can occur sooner (or later) if the rate at which mineral-forming ions are delivered to the PRB is higher (or lower) than that expected under typical conditions (i.e., due to higher/lower flow rate or inflowing ground water that has higher/lower ionic strength). When the PRB is more permeable than the aquifer, the median Darcy flux in the PRB does not change appreciably over time because the aquifer controls the rate of flow through the PRB. However, seepage velocities in the PRB increase, and residence times decrease, due to porosity reductions caused by accumulation of minerals in the pore space. When fouling becomes extensive, bypassing and reductions in flow rate in the PRB occur., Introduction The permeable reactive barrier (PRB) is a passive treatment technology used to remove contaminants from ground water. As contaminated ground water flows through a PRB, contaminants are degraded, transformed, [...]

While the discussion of model uncertainty has centered on spatial heterogeneity, it is possible that ground water models have not enjoyed much success as predictive tools often because the sources that were eventually imposed in the field differed from those represented in the simulations. This is because deterministic prediction of future conditions is often inaccurate due to the random nature of contaminant sources, in terms of their timing, location, and magnitude. This paper presents a stochastic framework for accommodating random contaminant sources in conventional, deterministic advection-dispersion transport models. The contaminant sources are first classified into two types: those occurring continuously with a deterministic component and random variations and those occurring randomly at instantaneous discrete-time intervals. For the first type, the governing partial differential equation (PDE) is replaced by a stochastic PDE. The random variations are modeled by Gaussian noise or Brownian motion, and the solution is obtained by using Ito's integration technique. For the second type, Markovian analysis is used for discrete-time contamination events. Both approaches use a deterministic transport model to generate response functions at any observation location and time. The response functions are then integrated to yield probabilistic description of contaminant transport, from which key statistical properties such as mean, standard deviation, and confidence interval can be drawn., Introduction Contaminant transport modeling is an essential component of any risk assessment and risk management pertinent to ground water quality. However, it is recognized that contaminant transport modeling is associated [...]

The calculation of the discharge to a constant drawdown well or tunnel in the presence of an infinite linear constant head boundary in an ideal confined aquifer usually relies on the numerical inversion of a Laplace transform solution. Such a solution is used to interpret constant head tests in wells or to roughly estimate ground water inflow into tunnels. In this paper, a simple approximate solution is proposed. Its maximum relative error is on the order of 2% as compared to the exact analytical solution. The approximation is a weighted mean between the early-time and late-time asymptotes., Introduction Constant head tests offer an interesting alternative to the more standard constant rate pumping tests. They are naturally applicable in artesian wells, where it is sufficient to open the [...]