bluuebunny/crossref_metadata_2025 huggingface dataset:
Sources of Salinity in Ground Water from Jericho Area, Jordan Valley
Authors: Marie Amer , Vengosh Avner
Published: December 2005

One of the major problems in the lower Jordan Valley is the increasing salinization (i.e., chloride content) of local ground water. The high levels of salinity limit the utilization of ground water for both domestic and agriculture applications. This joint collaborative study evaluates the sources and mechanisms for salinization in the Jericho area. We employ diagnostic geochemical fingerprinting methods to trace the potential sources of the salinity in (1) the deep confined subaquifer system (K2) of Lower Cenomanian age; (2) the upper subaquifer system (K1) of Upper Cenomanian and Turanian ages; and (3) the shallow aquifer system (Q) of Plio‐Pleistocene ages.

The chemical composition of the saline ground water from the two Cenomanian subaquifers (K1 and K2) point to a single saline source with Na/CI ∼0.5 and Br/CI∼7 × 10−3. This composition is similar to that of thermal hypersaline springs that are found along the western shore of the Dead Sea (e.g., En Gedi thermal spring). We suggest that the increasing salinity in both K1 and K2 subaquifers is derived from mixing with deep‐seated brines that flow through the Rift fault system. The salinization rate depends on the discharge volume of the fresh meteoric water in the Cenomanian Aquifer. In contrast, the chemical composition of ground water from the Plio‐Pleistocene Aquifer shows a wide range of CI (100–2000 mg/L), Na/CI (0.4–1.0), Br/Cl (2–6 ×10−3), and SO4/CI (0.01–0.4) ratios. These variations, together with the high SO42‐, K+, and NO3− concentrations, suggest that the salinity in the shallow aquifer is derived from the combination of (1) upconing of deep brines as reflected by low Na/Cl and high Br/Cl ratios; (2) leaching of salts from the Lisan Formation within the Plio‐Pleistocene Aquifer, as suggested by the high SO42 concentrations; and (3) anthropogenic contamination of agriculture return flow and sewage effluents with distinctive high K+ (80 mg/L) and NO3−(80 mg/1) contents and low Br/Cl ratios (2 ×10−3). Our data demonstrates that the chemical composition of salinized ground water can be used to delineate the sources of salinity and hence to establish the conceptual model for explaining salinization processes.
Extension of Vedernikov's Graph for Seepage from Canals
Authors: Chahar Bhagu R.
Published: December 2005

In this investigation, using previously derived equations by Vedernikov and Morel‐Seytoux, closed‐form solutions have been obtained to compute the seepage from a slit and a strip. Also, a graphical solution as an extension of Vedernikov's graph has been presented for computing quantity of seepage from triangular, rectangular, and trapezoidal canals. The solution replaces approximately the cumbersome evaluation of improper integrals with unknown implicit transformation variables.
Influence of Transient Flow on Contaminant Biodegradation
Authors: Schirmer Mario , Durrant Graham C. , Molson John W. , Frind Emil O.
Published: December 2005

The rate of biodegradation in contaminated aquifers depends to a large extent on dispersive mixing processes that are now generally accepted to result from spatial variations in the velocity field. It has been shown, however, that transient flow fields can also contribute to dispersive mixing. The influence of transient flow on biodegrading contaminants is particularly important since it can enhance mixing with electron acceptors, further promoting the reactive process. Using numerical simulations, the effect of transient flow on the behavior of a biodegradable contaminant is evaluated here both with respect to the development of apparently large horizontal transverse dispersion and also with respect to enhanced mixing between the substrate (electron donor) and electron acceptor. The numerical model BIO3D, which solves for advective‐dispersive transport coupled with Monod‐type biodegradation of substrates in the presence of an electron acceptor, was used for the simulations. The model was applied in a two‐dimensional plan view mode considering a single substrate. Transient flow fields were found to yield larger apparent transverse dispersion because the longitudinal dispersivity also acts transverse to the mean flow direction. In the reactive case, the transient flow field increases substrate‐oxygen mixing, which in turn enhances the overall rate of biodegradation. The results suggest that in the case of moderate changes of flow directions, a steady‐state flow field can be justified, thereby avoiding the higher computational costs of a fully transient simulation. The use of a higher transverse horizontal dispersivity in a steady flow field can, under these conditions, adequately forecast plume development.
In Situ Determination of Subsurface Microbial Enzyme Kinetics
Authors: Istok J.D. , Field J.A. , Schroth M.H.
Published: December 2005

The single‐well, push‐pull test has been used in previous field studies to measure in situ zero‐ and first‐order rates for aerobic and anaerobic microbial respiration in the saturated zone. In this paper we demonstrate that the test can also be used to obtain more generalized descriptions of the kinetics of microbially mediated enzymatic reactions. Laboratory and field tests were performed with the model enzyme substrate p‐nitrophenyl‐β‐D‐glucopyranoside (PNG). During a push‐pull test, injected PNG is hydrolyzed in situ to p‐nitrophenol (PNP); the rate of PNP production is taken as a measure of the β‐glucosidase activity expressed by indigenous microorganisms. Laboratory tests were performed in physical aquifer models packed with natural aquifer sediment; field tests were performed in a shallow unconfined alluvial aquifer at a petroleum contaminated site. The laboratory and field tests demonstrate that it is possible to compute the in situ rate of PNP production as a function of PNG concentration using only data from a single push‐pull test. These data can then be used to estimate the Michaelis‐Menton kinetic parameters Vmax and Km for the hydrolysis reaction. This approach potentially extends the range of applicability of the push‐pull test approach for use in determining kinetic parameters for a wide range of microbial processes in situ. These could include the broad class of substituted nitrophenyl substrates used to assay other enzyme systems, as well as microbially mediated redox reactions that occur during contaminant transformations.
A Variable‐Volume, Head‐Dependent Mine Water Filling Model
Authors: Banks David
Published: December 2005

Current simple mine water filling models suffer from two drawbacks: (1) they often do not account for variations in mine void volume with depth; and (2) they assume that recharge to the mine is approximately constant. The Mine Water Filling Model (MIFIM) presented here rectifies these drawbacks by presenting the concept of effective area (Ea) in a lookup table and assigning deep ground water inflows a conductance whereby inflow varies in inverse proportion to mine water head, once the mine water level exceeds the level of the water inflow. The MIFIM concept may be readily programmed in a computer spreadsheet environment, with simple graphical output. The approach is particularly suited to mines in low permeability rock, with a limited number of discrete inflow features.
Analytical Procedure for Simultaneous Use of Seven Fluorobenzoates in Multitracer Tests
Authors: Dalian Ofer , Ronen Zeev
Published: December 2005

An analytical procedure allowing simultaneous use of seven fluorobenzoate (FBA) isomers was developed and examined through column and field tracer experiments. The analytical method, based on high performance liquid chromatography (HPLC), included a reverse‐phase separation method. This method was found to be very efficient for the FBA analysis, allowing accurate determination of seven FBAs in a single HPLC run, while avoiding analytical interference of other natural water constituents or pollutants. Consequently, this separation method allows the simultaneous use of seven isomers in multitracer tests in highly saline or contaminated environments. The mobility properties of the FBAs were examined in percolation experiments through a column filled with a mixture of crushed chalk and common fracture filling and coating material. The FBAs behaved conservatively as compared to bromid. All seven FBA isomers were successfully used in a multitracer test in a field percolation experiment designed to identify flowpath along a fracture plane.
Comparison of Upscaling Methods to Estimate Hydraulic Conductivity
Authors: Vidstrand Patrik
Published: December 2005

A hydraulic field test program was performed at a hard rock laboratory (Aspo HRL) on the Swedish east coast to test upscaling theories. The test program investigated the rock volume around a borehole located at a depth of approximately 340 m below sea level. Hydraulic packer tests were performed at various scales, from 2 m to the entire borehole length of 296 m. From this set of data the predictive ability of different upscaling methods could be evaluated.

The comparison of the evaluated “true” field scale hydraulic conductivity with the upscaled hydraulic conductivity yielded that the majority of the upscaling methods tested in this paper predict the large scale values with significant accuracy. However, the ability to predict rapidly decreases when the variance of the natural logarithm of hydraulic conductivity of the subsamples is larger than one. Such a variance is consistently found in the crystalline rocks at the tested site at the 2 m scale. However, at scales of 10 m and larger, a variance larger than one is uncommon. Therefore, it is concluded that there exists a smallest possible scale for use of hydraulic pumping test results for estimating the effective hydraulic conductivity at scales typical for regional flow.
A First Estimate of Ground Water Ages for the Deep Aquifer of the Kathmandu Basin, Nepal, Using the Radioisotope Chlorine‐36
Authors: Cresswell Richard G. , Bauld John , Jacobson Gerry , Khadka Mohan Singh , Jha Mani Gopal , Shrestha Minesh Prasad , Regmi Sushila
Published: December 2005

The Kathmandu Basin in Nepal contains up to 550 m of Pliocene‐Quaternary fluvio‐lacustrine sediments which have formed a dual aquifer system. The unconfined sand and gravel aquifer is separated by a clay aquitard, up to 200 m thick, from the deeper, confined aquifer, comprised of Pliocene sand and gravel beds, intercalated with clay, peat, and lignite. The confined aquifer currently provides an important water supply to the central urban area but there are increasing concerns about its sus‐tainability due to overexploitation.

A limited number of determinations of the radioisotope 36Cl have been made on bore waters in the basin, allowing us to postulate on the age of ground water in the deeper, confined aquifer. Ground water evolution scenarios based on radioisotope decay, gradual dissolution of formational salts as the ground waters move downgradient, and flow velocity estimations produce comparable ground water ages for the deep waters, ranging from 200,000 to 400,000 years. From these ages, we deduce a mean ground water flow velocity of only 45 mm/year from recharge in the northeast to the main extraction region 15 km to the southwest. We thus estimate current recharge at about 5 to 15 mm/year, contributing 40,000 to 1.2 million m3/year to the ground water system. Current ground water extraction is estimated to be 20 times this amount. The low specific discharge confirms that the resource is being mined, and, based on current projections, reserves will be used up within 100 years.
Hydrogeological Research: Beginning of the End or End of the Beginning?
Authors: Schwartz Franklin W. , Ibaraki Motomu
Published: December 2005

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 Research, 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.
Riverbed Permeabilities: Information from Pooled Data
Authors: Calver Ann
Published: December 2005

Numerical values of hydraulic conductivities of river channel‐lining materials are assembled from published and unpublished sources. These are found to cover a range from below 1.0×10−9 to above 1.0×10−2 m sec1 and to be concentrated in the region 1.0×10−7 to 1.0 ×10−3 m sec−1. Variability within a site can be large. Assessment of the values in relation to sediment, scale, and method of determination presents a complex picture, and generalization is not straightforward. Hydraulic conductivity determinations from numerical modeling, which tends to be associated with averaging at larger spatial scales, are associated with a more conservative range of values than those derived from field and laboratory analyses. The sample of determinations provides a guideline basis of representative values for hydrological and hydrogeological assessment where specific investigation is not possible.
A Numerical Model and Spreadsheet Interface for Pumping Test Analysis
Authors: Johnson Gary S. , Cosgrove Donna M. , Frederick David B.
Published: December 2005

Curve‐matching techniques have been the standard method of aquifer test analysis for several decades. A variety of techniques provide the capability of evaluating test data from confined, unconfined, leaky aquitard, and other conditions. Each technique, however, is accompanied by a set of assumptions, and evaluation of a combination of conditions can be complicated or impossible due to intractable mathematics or nonuniqueness of the solution.

Numerical modeling of pumping tests provides two major advantages: (1) the user can choose which properties to calibrate and what assumptions to make; and (2) in the calibration process the user is gaining insights into the conceptual model of the flow system and uncertainties in the analysis. Routine numerical modeling of pumping tests is now practical due to computer hardware and software advances of the last decade.

The RADFLOW model and spreadsheet interface presented in this paper is an easy‐to‐use numerical model for estimation of aquifer properties from pumping test data. Layered conceptual models and their properties are evaluated in a trial‐and‐error estimation procedure. The RADFLOW model can treat most combinations of confined, unconfined, leaky aquitard, partial penetration, and borehole storage conditions. RADFLOW is especially useful in stratified aquifer systems with no identifiable lateral boundaries. It has been verified to several analytical solutions and has been applied in the Snake River Plain Aquifer to develop and test conceptual models and provide estimates of aquifer properties. Because the model assumes axially symmetrical flow, it is limited to representing multiple aquifer layers that are laterally continuous.
Application of Continuous Time Random Walk Theory to Tracer Test Measurements in Fractured and Heterogeneous Porous Media
Authors: Berkowitz Brian , Kosakowski Georg , Margolin Gennady , Scher Harvey
Published: December 2005

We examine a set of analytical solutions based on the continuous time random walk (CTRW) approach, which can be evaluated numerically and used to analyze breakthrough data from tracer tests. Practical application of these solutions, with discussion of the physical meaning of the relevant model parameters, is emphasized. The CTRW theory accounts for the often observed non‐Fickian (or scale‐dependent) dispersion behavior that cannot be properly quantified by using the advection‐dispersion equation. The solutions given here, valid for a wide range of dispersive behaviors of conservative tracers, and useful for both characterization and prediction, have been integrated into a library of external functions for use with the GRACE graphical display and analysis package. Example applications of these solutions are presented. The library and graphics software are freely accessible from a Web site.
Comparison of Continuous and Cyclic Pumping from a Well
Authors: Kawecki M. Wojciech
Published: December 2005

Two practically applicable pumping patterns for wells are: (1) continuous pumping at a sustainable constant rate; and (2) pumping at a sustainable constant rate for a fixed period every day (cyclic pumping). Theoretical analysis shows that with the cyclic pumping pattern the pump can be run at a higher rate than with continuous pumping. However continuous pumping at the maximum continuously sustainable constant rate produces considerably more water. If the objective is to produce as much water as possible, it is important to use a pump designed for running at the maximum continuously sustainable rate.
Turbulent Flow Through Porous Media
Authors: Barr Douglas W.
Published: December 2005

The pressure driving flow through porous media must be equal to the viscous resistance plus the inertial resistance. Formulas are developed for both the viscous resistance and the inertial resistance. The expression for the coefficient of permeability consists of parameters which describe the characteristics of the porous medium and the permeating fluid and which, for unconsolidated isotropic granular media, are all measurable. A procedure is proposed for testing for the occurrence of turbulence and calculating the effective permeability when it occurs. The formulas are applied to a set of data from 588 permeameter runs ranging from laminar to highly turbulent. The equations fit the data from the permeameter closely through the laminar flow conditions and quite closely through the turbulent conditions. In the turbulent range, the plotting of the data separates into three distinct lines for each of the three shapes of particles used in the tests. For the porous medium and fluid of these tests, turbulence begins at a head gradient of about 0.1.
Influence of Natural Heterogeneity on the Efficiency of Chemical Floods in Source Zones
Authors: Ibaraki Motomu , Schwartz Franklin W.
Published: December 2005

Several technologies for cleaning up DNAPLs in source zones rely on solubilizing contaminants or destroying them in situ. Typically, these approaches employ an injection/withdrawal system to recirculate this treatment fluids. Our interest is in examining factors that influence delivery efficiency. Although many factors can affect this efficiency, this study looks at the combined influence of density‐driven flow and porous media heterogeneities. The analysis is based on a series of numerical simulations of hypothetical chemical floods (e.g., potassium permanganate), which are highly resolved in space and time with a scale that is typical of field installations. Results indicate that the characteristics of convective mixing, i.e., natural, forced, and mixed convection, greatly affect delivery efficiency and patterns of mass transport. The ratio of the Grashof number (Gr) and Reynolds number (Re) proved useful in interpreting the patterns of flooding in a homogeneous porous medium. When higher‐permeability layers are included in the domain, they act as conduits, effectively expediting the transport of treatment chemicals from injection to recovery wells. These large fluxes of chemicals in the high‐permeability layers produce significant flooding inefficiencies. The problem is less severe in heterogeneous mediun where the connectivity through the treatment zone is less well developed. Overall, this paper illustrates that density effects and high‐permeability pathways need to be considered in designing chemical floods.
Hydraulic Head Applications of Flow Logs in the Study of Heterogeneous Aquifers
Authors: Paillet Frederick L.
Published: December 2005

Permeability profiles derived from high‐resolution flow logs in heterogeneous aquifers provide a limited sample of the most permeable beds or fractures determining the hydraulic properties of those aquifers. This paper demonstrates that flow logs can also be used to infer the large‐scale properties of aquifers surrounding boreholes. The analysis is based on the interpretation of the hydraulic head values estimated from the flow log analysis. Pairs of quasi‐steady flow profiles obtained under ambient conditions and while either pumping or injecting are used to estimate the hydraulic head in each water‐producing zone. Although the analysis yields localized estimates of transmissivity for a few water‐producing zones, the hydraulic head estimates apply to the far‐field aquifers to which these zones are connected. The hydraulic head data are combined with information from other sources to identify the large‐scale structure of heterogeneous aquifers. More complicated cross‐borehole flow experiments are used to characterize the pattern of connection between large‐scale aquifer units inferred from the hydraulic head estimates. The interpretation of hydraulic heads in situ under steady and transient conditions is illustrated by several case studies, including an example with heterogeneous permeable beds in an unconsolidated aquifer, and four examples with heterogeneous distributions of bedding planes and/or fractures in bedrock aquifers.
Initial Yield to Depth Relation for Water Wells Drilled into Crystalline Bedrock—Pinardville Quadrangle, New Hampshire
Authors: Drew Lawrence J. , Schuenemeyer John H. , Armstrong Thomas R. , Sutphin David M.
Published: December 2005

A model is proposed to explain the statistical relations between the mean initial water well yields from eight time increments from 1984 to 1998 for wells drilled into the crystalline bedrock aquifer system in the Pinardville area of southern New Hampshire and the type of bedrock, mean well depth, and mean well elevation. Statistical analyses show that the mean total yield of drilling increments is positively correlated with mean total well depth and mean well elevation. In addition, the mean total well yield varies with rock type from a minimum of 46.9 L/min (12.4 gpm) in the Damon Pond granite to a maximum of 74.5 L/min (19.7 gpm) in the Permian pegmatite and granite unit. Across the eight drilling increments that comprise 211 wells each, the percentages of very low‐yield wells (1.9 L/min [0.5 gpm] or less) and high‐yield wells (151.4 L/min [40 gpm] or more) increased, and those of intermediate‐yield wells decreased. As housing development progressed during the 1984 to 1998 interval, the mean depth of the wells and their elevations increased, and the mix of percentages of the bedrock types drilled changed markedly.

The proposed model uses a feed‐forward mechanism to explain the interaction between the increasing mean elevation, mean well depth, and percentages of very low‐yielding wells and the mean well yield. The increasing percentages of very low‐yielding wells through time and the economics of the housing market may control the system that forces the mean well depths, percentages of high‐yield wells, and mean well yields to increase. The reason for the increasing percentages of very low‐yield wells is uncertain, but the explanation is believed to involve the complex structural geology and tectonic history of the Pinardville quadrangle.
Delineating Depth to Bedrock Beneath Shallow Unconfined Aquifers: A Gravity Transect Across the Palmer River Basin
Authors: Bohidar Rabi N. , Sullivan Jeffrey P. , Hermance John F.
Published: December 2005

In view of the increasing demand on ground water supplies in the northeastern United States, it is imperative to develop appropriate methods to geophysically characterize the most widely used sources of ground water in the region: shallow unconfined aquifers consisting of well‐sorted, stratified glacial deposits laid down in bedrock valleys and channels. The gravity method, despite its proven value in delineating buried bedrock valleys elsewhere, is seldom used by geophysical contractors in this region. To demonstrate the method's effectiveness for evaluating such aquifers, a pilot study was undertaken in the Palmer River Basin in southeastern Massachusetts.

Because bedrock is so shallow beneath this aquifer (maximum depth is 30 m), the depth‐integrated mass deficiency of the overlying unconsolidated material was small, so that the observed gravity anomaly was on the order of 1 milligal (mGal) or less. Thus data uncertainties were significant. Moreover, unlike previous gravity studies elsewhere, we had no a priori information on the density of the sediment. Under such circumstances, it is essential to include model constraints and weighted least‐squares in the inversion procedure. Among the model constraints were water table configuration, bedrock outcrops, and depth to bedrock from five water wells. Our procedure allowed us to delineate depth to bedrock along a 3.5 km profile with a confidence interval of 1.8 m at a nominal depth of 17 m. Moreover, we obtained a porosity estimate in the range of 39% to 44%. Thus the gravity method, with appropriate refinements, is an effective tool for the reconnaissance of shallow unconfined aquifers.
A Nested Rediscretization Method to Improve Pathline Resolution by Eliminating Weak Sinks Representing Wells
Authors: Spitz Frederick J. , Nicholson Robert S. , Pope Daryll A.
Published: December 2005

This paper discusses a method for overcoming the problem of weak sinks representing wells that result from spatial discretization effects when using MODPATH, the particle‐tracking postprocessor for the ground water low model MODFLQW. Weak sink cells are model cells that represent a well that does not discharge at a sufficiently large rate to capture all of the flow entering the cell; therefore, flowpaths within these cells cannot be uniquely defined because it is impossible to know whether a given water particle discharges to the well or passes through the cell. Creating a submodel of the well cell by using the nested rediscretization method can eliminate this ambiguity by converting the weak sink cell into a strong sink cell. The method is designed to be run manually for each well and for steady‐state conditions. Other advantages, disadvantages, technical considerations, and limitations of the method are presented. Software created for the method consists of five Fortran programs that are operated using a set of instructions. A practical application of the method is presented by using an example wellhead‐protection problem that demonstrates that nested rediscretization can provide more accurate particle‐tracking results than those obtained by using a coarsely discretized model alone.
Hydraulic Tests with Direct‐Push Equipment
Authors: Butler James J. , Healey John M. , McCall G. Wesley , Garnett Elizabeth J. , Loheide Steven P.
Published: December 2005

The potential of direct‐push technology for hydraulic characterization of saturated flow systems was investigated at a field site with a considerable degree of subsurface control. Direct‐push installations were emplaced by attaching short lengths of screen (shielded and unshielded) to the bottom end of a tool string that was then advanced into the unconsolidated sediments. A series of constant‐rate pumping tests were performed in a coarse sand and gravel aquifer using direct‐push tool strings as observation wells. Very good agreement (within 4%) was found between hydraulic conductivity (K) estimates from direct‐push installations and those from conventional wells. A program of slug tests was performed in direct‐push installations using small‐diameter adaptations of solid‐slug and pneumatic methods. In a sandy silt interval of moderate hydraulic conductivity, K values from tests in a shielded screen tool were in excellent agreement (within 2%) with those from tests in a nearby well. In the coarse sand and gravel aquifer, K values were within 12% of those from multilevel slug tests at a nearby well. However, in the more permeable portions of the aquifer (K > 70 m/day), the smaller‐diameter direct‐push rods (0.016 m inner diameter [I.D.]) attenuated test responses, leading to an underprediction of K. In those conditions, use of larger‐diameter rods (e.g., 0.038 m I.D.) is necessary to obtain K values representative of the formation. This investigation demonstrates that much valuable information can be obtained from hydraulic tests in direct‐push installations. As with any type of hydraulic test, K estimates are critically dependent on use of appropriate emplacement and development procedures. In particular, driving an unshielded screen through a heterogeneous sequence will often lead to a buildup of low‐K material that can be difficult to remove with standard development procedures.
Probabilistic Capture Zone Delineation Based on an Analytic Solution
Authors: Jacobson Elizabeth , Andricevic Roko , Morrice Joseph
Published: December 2005

A major tool used in the design of wellhead protection areas is the delineation of a capture zone for a pumping well by use of a simple, steady‐state analytic solution. This simple approach has been useful for many small municipalities because of the high costs associated with obtaining the hydrogeologic information needed for detailed numerical modeling. This analytic solution, however, is deterministic, and uncertainty in the mean value estimates of the hydraulic parameters used in this model can be a major source of error in predicting capture zones. To address this problem, a statistical theory was developed for including the uncertainty in the transmissivity and the magnitude and direction of the hydraulic head gradient in the analytic solution for both the ultimate and time‐dependent capture zone for an arbitrary reliability level. To demonstrate the method and investigate the effect of varying magnitudes of uncertainty on time‐dependent capture zones, the method is applied to three synthetic data sets based on data from the Borden Aquifer in Ontario, Canada. In general, the results show that uncertainty in the length of the time‐dependent capture zone at a given reliability level is dependent on the uncertainty in the magnitude of the mean regional flow, which is equal to the transmissivity multiplied by the hydraulic head gradient; uncertainty in the maximum width of the capture zone is dependent primarily on the uncertainty in the mean direction of the regional flow.
Using High Hydraulic Conductivity Nodes to Simulate Seepage Lakes
Authors: Anderson Mary P. , Hunt Randall J. , Krohelski James T. , Chung Kuopo
Published: December 2005

In a typical ground water flow model, lakes are represented by specified head nodes requiring that lake levels be known a priori. To remove this limitation, previous researchers assigned high hydraulic conductivity (K) values to nodes that represent a lake, under the assumption that the simulated head at the nodes in the high‐K zone accurately reflects lake level. The solution should also produce a constant water level across the lake. We developed a model of a simple hypothetical ground water/lake system to test whether solutions using high‐K lake nodes are sensitive to the value of K selected to represent the lake. Results show that the larger the contrast between the K of the aquifer and the K of the lake nodes, the smaller the error tolerance required for the solution to converge. For our test problem, a contrast of three orders of magnitude produced a head difference across the lake of 0.005 m under a regional gradient of the order of 10−3 m/m, while a contrast of four orders of magnitude produced a head difference of 0.001 m. The high‐K method was then used to simulate lake levels in Pretty Lake, Wisconsin. Results for both the hypothetical system and the application to Pretty Lake compared favorably with results using a lake package developed for MODFLOW (Merritt and Konikow 2000). While our results demonstrate that the high‐K method accurately simulates lake levels, this method has more cumbersome postprocessing and longer run times than the same problem simulated using the lake package.
Improving a Regional Model Using Reduced Complexity and Parameter Estimation
Authors: Kelson Victor A. , Hunt Randall J. , Haitjema Henk M.
Published: December 2005

The availability of powerful desktop computers and graphical user interfaces for ground water flow models makes possible the construction of ever more complex models. A proposed copper‐zinc sulfide mine in northern Wisconsin offers a unique case in which the same hydrologic system has been modeled using a variety of techniques covering a wide range of sophistication and complexity. Early in the permitting process, simple numerical models were used to evaluate the necessary amount of water to be pumped from the mine, reductions in streamflow, and the drawdowns in the regional aquifer. More complex models have subsequently been used in an attempt to refine the predictions. Even after so much modeling effort, questions regarding the accuracy and reliability of the predictions remain.

We have performed a new analysis of the proposed mine using the two‐dimensional analytic element code GFLOW coupled with the nonlinear parameter estimation code UCODE. The new model is parsimonious, containing fewer than 10 parameters, and covers a region several times larger in areal extent than any of the previous models. The model demonstrates the suitability of analytic element codes for use with parameter estimation codes. The simplified model results are similar to the more complex models; predicted mine inflows and UCODE‐derived 95% confidence intervals are consistent with the previous predictions. More important, the large areal extent of the model allowed us to examine hydrological features not included in the previous models, resulting in new insights about the effects that far‐field boundary conditions can have on near‐field model calibration and parameterization. In this case, the addition of surface water runoff into a lake in the headwaters of a stream while holding recharge constant moved a regional ground watershed divide and resulted in some of the added water being captured by the adjoining basin. Finally, a simple analytical solution was used to clarify the GFLOW model's prediction that, for a model that is properly calibrated for heads, regional drawdowns are relatively unaffected by the choice of aquifer properties, but that mine inflows are strongly affected. Paradoxically, by reducing model complexity, we have increased the understanding gained from the modeling effort.
More Realistic Soil Cleanup Standards with Dual‐Equilibrium Desorption
Authors: Chen W. , Kan A.T. , Newell C.J. , Moore E. , Tomson M.B.
Published: December 2005

The desorption of contaminants from soils/sediments is one of the most important processes controlling contaminant transport and environmental risks. None of the currently adopted desorption models can accurately quantify desorption at relatively low concentrations; these models often overestimate the desorption and thus the risks of hydrophobic organic chemicals, such as benzene and chlorinated solvents. In reality, desorption is generally found to be biphasic, with two soil‐phase compartments. A new dual‐equilibrium desorption (DED) model has been developed to account for the biphasic desorption. This model has been tested using a wide range of laboratory and field data and has been used to explain key observations related to underground storage tank plumes. The DED model relates the amount of a chemical sorbed to the aqueous concentration, with simple parameters including octanol‐water partition coefficient, solubility, and fractional organic carbon; thus, it is the only biphasic model, to date, that is based on readily available parameters. The DED model can be easily incorporated into standard risk and transport models. According to this model, many regulatory standards of soils and sediments could be increased without increasing the risks.
Using Direct Current Resistivity Sounding and Geostatistics to Aid in Hydrogeological Studies in the Choshuichi Alluvial Fan, Taiwan
Authors: Yang Chieh‐Hou , Lee Wei‐Feng
Published: December 2005

Ground water reservoirs in the Choshuichi alluvial fan, central western Taiwan, were investigated using direct‐current (DC) resistivity soundings at 190 locations, combined with hydrogeological measurements from 37 wells. In addition, attempts were made to calculate aquifer transmissivity from both surface DC resistivity measurements and geostatistically derived predictions of aquifer properties.

DC resistivity sounding data are highly correlated to the hydraulic parameters in the Choshuichi alluvial fan. By estimating the spatial distribution of hydraulic conductivity from the kriged well data and the cokriged thickness of the correlative aquifer from both resistivity sounding data and well information, the transmissivity of the aquifer at each location can be obtained from the product of kriged hydraulic conductivity and computed thickness of the geoelectric layer. Thus, the spatial variation of the transmissivities in the study area is obtained.

Our work is more comparable to Ahmed et al. (1988) than to the work of Niwas and Singhal (1981). The first “constraint” from Niwas and Singhal's work is a result of their use of linear regression. The geostatistical approach taken here (and by Ahmed et al. [1988]) is a natural improvement on the linear regression approach.
Determination of Confined Phreatic Aquifer Anisotropy
Authors: Fallico Carmine , Mazzuca Rosa , Troisi Salvatore
Published: December 2005

The determination of anisotropy in a phreatic aquifer by means of a pumping test can be carried out, under given conditions, with common analysis methods. This paper develops and applies an amended method based on a technique proposed by Boulton (1970). This new method enables a quick, simple determination of vertical hydraulic conductivity, given drawdown data from a pumping well and at least one observation well, that is applicable to confined phreatic aquifers.
Influence of the Amount of Available K Data on Uncertainty About Contaminant Transport Prediction
Authors: Bright John , Wang Fuli , Close Murray
Published: December 2005

The effect of increasing the amount of hydraulic conductivity (K) data on the level of uncertainty about contaminant concentration predictions was examined. Contaminant concentrations were predicted using Monte Carlo numerical simulations with progressively more K information, and were compared to reference data obtained from a physical experiment. Increasing the amount of K data used in generating the aquifer's K field improved the measure of confidence in the predicted contaminant concentration. The normalized concentration interval with 95% confidence decreased from 1.29 to 0.75 when the amount of K data increased from 20 to 71. However, the trade‐off is the increase in the costs of aquifer investigation. Conducting Monte Carlo numerical simulations may help design an optimal aquifer investigation scheme, so that it can provide enough input data to predict concentrations with the desired level of confidence and at the same time avoid the excessive costs of aquifer investigation.
Delineation of Three‐Dimensional Well Capture Zones for Complex Multi‐Aquifer Systems
Authors: Frind E.O. , Muhammad D.S. , Molson J.W.
Published: December 2005

The delineation of well capture zones is a basic component of ground water protection. The conventional methodology for capture zone delineation is backward advective particle tracking, often applied under the assumption of a two‐dimensional aquifer. The suitability of the conventional approach for complex heterogeneous multi‐aquifer systems was investigated, using the Waterloo Moraine aquifer system as an example. It was found that the conventional approach produces irregular particle tracks that require judgment to interpret in a meaningful way, and it can raise questions that may affect the credibility of the capture zone delineation. As an alternative, the potentially powerful but little‐used backward‐in‐time advective‐dispersive transport approach was investigated. A key advantage of this approach is its capability to represent local heterogeneities through the dispersion term. The dispersion process has a natural smoothing effect that results in unambiguous capture zones without the need for interpretation, thus enhancing credibility. The question of capture zone validation is also addressed. The meaning of a three‐dimensional capture zone is considered, and it is shown that a fully three‐dimensional representation of the system is crucial for valid results. The distinction between the maximum extent capture zone and the surface capture zone is also explained. In the case of complex heterogeneous systems, advective particle tracking can be used as an initial screening tool, whereas the more realistic backward‐transport modeling approach can be used for final capture‐zone delineation.
Optimized System to Improve Pumping Rate Stability During Aquifer Tests
Authors: Young Michael H. , Rasmussen Todd C. , Lyons F. Comer , Pennell Kurt D.
Published: December 2005

Aquifer hydraulic properties are commonly estimated using aquifer tests, which are based on an assumption of a uniform and constant pumping rate. Substantial uncertainties in the flow rate across the borehole‐formation interface can be induced by dynamic head losses, caused by rapid changes in borehole water levels early in an aquifer test. A system is presented that substantially reduces these sources of uncertainty by explicitly accounting for dynamic head losses. The system which employs commonly available components (including a datalogger, pressure transducers, a variable‐speed pump motor, a flow controller, and flowmeters), is inexpensive, highly mobile, and easily set up. It optimizes the flow rate at the borehole‐formation interface, making it suitable for any type of aquifer test, including constant, step, or ramped withdrawal and injection, as well as sinusoidal. The system was demonstrated for both withdrawal and injection tests in three aquifers at the Savannah River Site. No modifications to the control system were required, although a small number of characteristics of the pumping and monitoring system were added to the operating program. The pumping system provided a statistically significant, constant flow rate with time. The range in pumping variability (95% confidence interval) was from ±2.58 × l0−4 L/sec to ±9.07 × 10−4L/sec, across a wide range in field and aquifer conditions.
The Lisse Effect Revisited
Authors: Weeks Edwin P.
Published: December 2005

The Lisse effect is a rarely noted phenomenon occurring when infiltration caused by intense rain seals the surface soil layer to airflow, trapping air in the unsaturated zone. Compression of air by the advancing front results in a pressure increase that produces a water‐level rise in an observation well screened below the water table that is several times as large as the distance penetrated by the wetting front. The effect is triggered by intense rains and results in a very rapid water‐level rise, followed by a recession lasting a few days. The Lisse effect was first noted and explained by Thal Larsen in 1932 from water‐level observations obtained in a shallow well in the village of Lisse, Holland. The original explanation does not account for the increased air pressure pushing up on the bottom of the wetting front. Analysis of the effect of this upward pressure indicates that a negative pressure head at the base of the wetting front, Ψf, analogous to that postulated by Green and Ampt (1911) to explain initially rapid infiltration rates into unsaturated soils, is involved in producing the Lisse effect. Analysis of recorded observations of the Lisse effect by Larsen and others indicates that the water‐level rise, which typically ranges from 0.10 to 0.55 m, should be only slightly larger than |Ψf| and that the depth of penetration of the wetting front is no more than several millimeters.
Hydrogeological Research: Just Getting Started
Authors: Miller Cass T. , Gray William G.
Published: December 2005

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.
New Combined Log and Tracer Test Interpretation Method for Identifying Transfers in Fissured Aquifers
Authors: Pistre Séverin , Marliac Séphane , Jourde Hervé , Bidaux Pascal
Published: December 2005

Tracer tests represent the most appropriate approach for assessing hydrodispersive parameters such as transversal and longitudinal dispersivities or kinematic porosity on an aquifer scale. They are generally carried out by injecting a tracer in a borehole and measuring its concentration over time in neighboring boreholes by extracted volume sampling or downhole measurements. Logging is one of the most suitable methods for evaluating fissured reservoirs. But short circuits between fractures with different hydraulic potential through boreholes induce mixing phenomena that cannot be avoided without packers. This mixing can shift the breakthrough curves deduced from the logs for each producing fracture and distort determination of their location.

The method proposed in this paper aims at measuring the flow rate and the solute breakthrough for hydraulically active fractures, in open boreholes. It involves estimating a velocity profile along the borehole column by the analysis of two successive logs: a shift function according to depth is thus determined by comparison between log portions on each successive one. The velocity gradients reflect the inward or outward flow rates produced by each fracture. On the basis of these flow rates, it is possible to determine the mixing effects inside the borehole and then to plot unbiased breakthrough curves for each producing fracture.

This method was applied at a granitic site in the eastern Pyrenees. In spite of some questionable limitations, the results showed that the method seems adapted to situations with many fractures. The precise hydraulic pattern which is obtained at the borehole scale is discussed in terms of a dual porosity model. Furthermore, interpretation of the breakthrough curves for fractures corrected for mixing effects revealed that Peclet numbers are strongly underestimated if this phenomenon is not considered.