bluuebunny/crossref_metadata_2025 huggingface dataset:
Determining Extreme Parameter Correlation in Ground Water Models
Authors: Hill Mary C. , Østerby Ole
Published: December 2005

In ground water flow system models with hydraulic‐head observations but without significant imposed or observed flows, extreme parameter correlation generally exists. As a result, hydraulic conductivity and recharge parameters cannot be uniquely estimated. In complicated problems, such correlation can go undetected even by experienced modelers. Extreme parameter correlation can be detected using parameter correlation coefficients, but their utility depends on the presence of sufficient, but not excessive, numerical imprecision of the sensitivities, such as round‐off error. This work investigates the information that can be obtained from parameter correlation coefficients in the presence of different levels of numerical imprecision, and compares it to the information provided by an alternative method called the singular value decomposition (SVD). Results suggest that (1) calculated correlation coefficients with absolute values that round to 1.00 were good indicators of extreme parameter correlation, but smaller values were not necessarily good indicators of lack of correlation and resulting unique parameter estimates; (2) the SVD may be more difficult to interpret than parameter correlation coefficients, but it required sensitivities that were one to two significant digits less accurate than those that required using parameter correlation coefficients; and (3) both the SVD and parameter correlation coefficients identified extremely correlated parameters better when the parameters were more equally sensitive. When the statistical measures fail, parameter correlation can be identified only by the tedious process of executing regression using different sets of starting values, or, in some circumstances, through graphs of the objective function.
Interbasin Underflow Between Closed Altiplano Basins in Chile
Authors: Montgomery Errol L , Rosko Michael J. , Castro Santiago O. , Keller Barry R. , Bevacqua Paolo S.
Published: December 2005

Interbasin ground water movement of 200 to 240 L/sec occurs as underflow beneath a mountainous surface water divide separating the topographically higher Salar de Michincha from the topographically lower Salar de Coposa internally drained basins in the Altiplano of northern Chile. Salt‐encrusted flats (salars) and saline lakes occur on the lowest parts of the basin floors and comprise the principal evaporative discharge areas for the basins. Because a surface water divide separates the basins, surface water drainage boundaries do not coincide with ground water drainage boundaries. In the region, interbasin ground water movement is usually not recognized, but occurs for selected basins, and at places is an important component of ground water budgets. With increasing development of water for mining industry and potential exportation of ground water from the Altiplano for use at coastal cities, demonstration and quantification of interbasin movement is important for assessment of sustainable ground water development in a region of extreme aridity. Recognition and quantification of interbasin ground water underflow will assist in management of ground water resources in the arid Chilean Altiplano environment.
Animating Ground Water Levels with Excel
Authors: Shikaze Steven G. , Crowe Allan S.
Published: December 2005

This note describes the use of Microsoft Excel macros (programs written in Excel's internal language, Visual Basic for Applications) to create simple onscreen animations of transient ground water data within Excel. Compared to many specialized visualization software packages, the use of Excel macros is much cheaper, much simpler, and can rapidly be learned. The Excel macro can also be used to create individual GIF files for each animation frame. This series of frames can then be used to create an AVI video file using any of a number of graphics packages, such as Corel PhotoPaint. The technique is demonstrated through a macro that animates changes in the elevation of a water table along a transect over several years.
Stochastic Ground Water Flow Simulation with a Fracture Zone Continuum Model
Authors: Langevin Christian D.
Published: December 2005

A method is presented for incorporating the hydraulic effects of vertical fracture zones into two‐dimensional cell‐based continuum models of ground water flow and particle tracking. High hydraulic conductivity features are used in the model to represent fracture zones. For fracture zones that are not coincident with model rows or columns, an adjustment is required for the hydraulic conductivity value entered into the model cells to compensate for the longer flowpath through the model grid. A similar adjustment is also required for simulated travel times through model cells. A travel time error of less than 8% can occur for particles moving through fractures with certain orientations. The fracture zone continuum model uses stochastically generated fracture zone networks and Monte Carlo analysis to quantify uncertainties with simulated advective travel times. An approach is also presented for converting an equivalent continuum model into a fracture zone continuum model by establishing the contribution of matrix block trans‐missivity to the bulk transmissivity of the aquifer. The methods are used for a case study in west‐central Florida to quantify advective travel times from a potential wetland rehydration site to a municipal supply wellfield. Uncertainties in advective travel times are assumed to result from the presence of vertical fracture zones, commonly observed on aerial photographs as photolineaments.
Analysis of Slug Tests in Formations of High Hydraulic Conductivity
Authors: Butler James J. , Garnett Elizabeth J. , Healey John M.
Published: December 2005

A new procedure is presented for the analysis of slug tests performed in partially penetrating wells in formations of high hydraulic conductivity. This approach is a simple, spreadsheet‐based implementation of existing models that can be used for analysis of tests from confined or unconfined aquifers. Field examples of tests exhibiting oscillatory and nonoscillatory behavior are used to illustrate the procedure and to compare results with estimates obtained using alternative approaches. The procedure is considerably simpler than recently proposed methods for this hydrogeologic setting. Although the simplifications required by the approach can introduce error into hydraulic‐conductivity estimates, this additional error becomes negligible when appropriate measures are taken in the field. These measures are summarized in a set of practical field guidelines for slug tests in highly permeable aquifers.
Bacterial Transport Experiments in Fractured Crystalline Bedrock
Authors: Becker Matthew W. , Metge David W. , Collins Samantha A. , Shapiro Allen M. , Harvey Ronald W.
Published: December 2005

The efficiency of contaminant biodegradation in ground water depends, in part, on the transport properties of the degrading bacteria. Few data exist concerning the transport of bacteria in saturated bedrock, particularly at the field scale. Bacteria and microsphere tracer experiments were conducted in a fractured crystalline bedrock under forced‐gradient conditions over a distance of 36 m. Bacteria isolated from the local ground water were chosen on the basis of physicochemical and physiological differences (shape, cell‐wall type, motility), and were differentially stained so that their transport behavior could be compared. No two bacterial strains transported in an identical manner, and microspheres produced distinctly different breakthrough curves than bacteria. Although there was insufficient control in this field experiment to completely separate the effects of bacteria shape, reaction to Gram staining, cell size, and motility on transport efficiency, it was observed that (1) the nonmotile, mutant strain exhibited better fractional recovery than the motile parent strain; (2) Gram‐negative rod‐shaped bacteria exhibited higher fractional recovery relative to the Gram‐positive rod‐shaped strain of similar size; and (3) coccoidal (spherical‐shaped) bacteria transported better than all but one strain of the rod‐shaped bacteria. The field experiment must be interpreted in the context of the specific bacterial strains and ground water environment in which they were conducted, but experimental results suggest that minor differences in the physical properties of bacteria can lead to major differences in transport behavior at the field scale.
Air and Water Entrapment in the Vicinity of the Water Table
Authors: Dunn Andrea M. , Silliman Stephen E.
Published: December 2005

A laboratory tank was used to study entrapment of water in coarse sand lenses above the water table and of air in coarse sand lenses below the water table. Monitoring of these experiments involved a combination of visual inspection, measurement of moisture content, and measurement of air/water pressure. The medium consisted of coarse sand lenses with various degrees of vertical connectivity embedded within a fine sand matrix. Experiments were performed under conditions of both drainage (from a fully saturated medium) and imbibition. Observations during drainage included: (1) water was trapped in the coarse sand zones above the water table at heights significantly greater than anticipated from consideration of capillary rise in the coarse sand; (2) rapid drainage of these same coarse zones occurred when air penetrated into these zones through the surrounding fine sands; and (3) prior to the time of penetration of the coarse sand by air, water pressure in the coarse zone dropped significantly below atmospheric pressure. Observations during imbibition included: (1) entrapment of air within coarse sands below the water table, (2) the pore fluids in these zones varied spatially from predominantly air to predominantly water, and (3) pressure in the trapped air phase was significantly greater than pressure in the water phase in the surrounding fine sand. Overall, these results demonstrated significant sensitivity to the geometry of the coarse sand inclusions, particularly the vertical connectivity of the coarse sand lens.
Correlation Between Nitrate Contamination and Ground Water Pollution Potential
Authors: Chowdhury Shafiul H. , Kehew Alan E. , Passero Richard N.
Published: December 2005

AQUIPRO, a PC‐based method, was used to assess aquifer vulnerability using digital water well logs. The AQUIPRO model is a parameter/factor weighting system for rating the pollution potential of an aquifer. This method uses the well depth, as well as the clay and partial clay thickness in a well, to generate pollution potential scores. In this model, aquifer protection increases as the AQUIPRO vulnerability scores increase and ground water pollution potential decreases.

Computerized water well records of 2435 domestic wells with partial chemistry data were used to determine the ground water pollution potential of Kalamazoo County, Michigan. Theoretically, low AQUIPRO pollution potential scores should have more frequent occurrences of ground water contamination events than areas with high AQUIPRO scores with similar land‐use, well construction, and well densities. The relative AQUIPRO scores were compared with the frequency of occurrences of nitrate‐N in ground water wells. The average nitrate‐N concentrations within each relative AQUIPRO vulnerability scores category were also compared. The results indicate that domestic wells containing 5 mg/L or more nitrate‐N showed a positive correlation between the frequency of occurrences of nitrate‐N and relative decrease of AQUIPRO (r2= 0.99) vulnerability scores. In other words, as the ground water pollution potential increases, the occurrence frequency of nitrate‐N also increases. Furthermore, the results show that as the relative AQUIPRO (r2= 0.96) vulnerability scores decrease, the mean nitrate‐N concentrations also increase.
Behavior of Gasoline Pools Following a Denatured Ethanol Spill
Authors: McDowell Cory J. , Buscheck Timothy , Powers Susan E.
Published: December 2005

In 1999, ∼72 m3 of denatured fuel‐grade ethanol spilled at a bulk fuel terminal that had existing contamination within the subsurface. An unanticipated increase in the measured depth of the light nonaqueous phase liquid (LNAPL) was observed in nearby monitoring wells following the spill. This paper presents results of a laboratory analysis designed to understand the apparent increase in LNAPL mobility at this site. The two‐dimensional stainless steel and glass tank allowed visual assessment of the potential effects that the addition of denatured ethanol may have on a site with pre‐existing gasoline contamination. Digital images of gasoline and ethanol spill experiments were analyzed for changes in the characteristics of the existing gasoline pool and residual gasoline saturation in the unsatu‐rated zone. Reductions in the surface and interfacial tensions resulted in significant changes in the size, shape, and saturation of the gasoline pool after the addition of ethanol to the system. The final gasoline pool occupied a smaller area and had a higher saturation. In addition, some smearing of the gasoline into the saturated zone occurred as the capillary fringe was depressed.
Simulation of Submarine Ground Water Discharge to a Marine Estuary: Biscayne Bay, Florida
Authors: Langevin Christian D.
Published: December 2005

Variable density ground water flow models are rarely used to estimate submarine ground water discharge because of limitations in computer speed, data availability, and availability of a simulation tool that can minimize numerical dispersion. This paper presents an application of the SEAWAT code, which is a combined version of MODFLOW and MT3D, to estimate rates of submarine ground water discharge to a coastal marine estuary. Discharge rates were estimated for Biscayne Bay, Florida, for the period from January 1989 to September 1998 using a three‐dimensional, variable density ground water flow and transport model. Hydrologic stresses in the 10‐layer model include recharge, evapotranspiration, ground water withdrawals from municipal wellfields, interactions with surface water (canals in urban areas and wetlands in the Everglades), boundary fluxes, and submarine ground water discharge to Biscayne Bay. The model was calibrated by matching ground water levels in monitoring wells, baseflow to canals, and the position of the 1995 salt water intrusion line. Results suggest that fresh submarine ground water discharge to Biscayne Bay may have exceeded surface water discharge during the 1989, 1990, and 1991 dry seasons, but the average discharge for the entire simulation period was only ∼10% of the surface water discharge to the bay. Results from the model also suggest that tidal canals intercept fresh ground water that might otherwise have discharged directly to Biscayne Bay. This application demonstrates that regional scale variable density models are potentially useful tools for estimating rates of submarine ground water discharge.
Contaminant Transport in Fractured Chalk: Laboratory and Field Experiments
Authors: Witthüser K. , Reichert B. , Hotzl H.
Published: December 2005

Laboratory experiments were performed on chalk samples from Denmark and Israel to determine diffusion and distribution coefficients. Batch tests were used to define sorption isotherms for naphthalene and o‐xylene. Linear sorption isotherms were observed and described with Henry‐isotherms. Because of the high purity and low contents of clay minerals and organic carbon, Danish and white Israeli chalk generally have low retardation capacities. Con‐trarily, gray Israeli chalk, with organic carbon fractions as high as 1.092%, remarkably retards organic contaminants. TheKocconcept is not applicable to predicting distribution coefficients based on the organic carbon content in the chalk samples. Effective diffusivities ofo‐xylene, naphthalene, and several artificial tracers were determined using through‐diffusion experiments. Based on measured diffusion coefficients and available literature values, a chalk specific exponent of 2.36 for Archie's law was derived, allowing a satisfactory estimate of relative diffusivities in chalk. A field‐scale tracer test with uranine and lithium was performed in the Negev desert (Israel) to examine the transfer‐ability of diffusivities determined on small rock samples in the laboratory. Due to low recovery rates of the tracer, a modified single fissure dispersion model was used for inverse modeling of the breakthrough curves. Resulting diffusivities deviate insignificantly from the laboratory values, which are considered to be representative for the investigated part of the aquifer and applicable in transport models.
Ground Water Quality Assessment Using Multi‐Rectangular Diagrams
Authors: Ahmad Niaz , Sen Zekai , Ahmad Manzoor
Published: December 2005

A new graphical technique is proposed here for classifying chemical analyses of ground water. In this technique, a diagram is constructed using rectangular coordinates. The new diagram, called a multi‐rectangular diagram (MRD), uses adjacent multi‐rectangles in which each rectangle represents a specific ground water type. This new diagram has the capability to accommodate a large number of data sets. MRDs have been used to classify chemical analyses of ground water in the Chaj Doab area of Pakistan to illustrate this new approach. Using this graphical method, the differentiated ground water types are calcium bicarbonate, magnesium bicarbonate, sodium bicarbonate, and sodium sulfate. Sodium bicarbonate emerges as the most abundant ground water type. MRDs also offer a visual display of the Chebotarev sequence of ground water quality evolution.
Dip and Anisotropy Effects on Flow Using a Vertically Skewed Model Grid
Authors: Hoaglund John R. , PoIllard David
Published: December 2005

Darcy flow equations relating vertical and bedding‐parallel flow to vertical and bedding‐parallel gradient components are derived for a skewed Cartesian grid in a vertical plane, correcting for structural dip given the principal hydraulic conductivities in bedding‐parallel and bedding‐orthogonal directions. Incorrect‐minus‐correct flow error results are presented for ranges of structural dip (0 ≤θ≤ 90) and gradient directions (0 ≤φ≤ 360). The equations can be coded into ground water models (e.g., MODFLOW) that can use a skewed Cartesian coordinate system to simulate flow in structural terrain with deformed bedding planes. Models modified with these equations will require input arrays of strike and dip, and a solver that can handle off‐diagonal hydraulic conductivity terms.
Lithium Isotope Geochemistry and Origin of Canadian Shield Brines
Authors: Bottomley D.J. , Chan L.H. , Katz A. , Starinsky A. , Clark I.D.
Published: December 2005

Hypersaline calcium/chloride shield brines are ubiquitous in Canada and areas of northern Europe. The major questions relating to these fluids are the origin of the solutes and the concentration mechanism that led to their extreme salinity. Many chemical and isotopic tracers are used to solve these questions. For example, lithium isotope systematics have been used recently to support a marine origin for the Yellowknife shield brine (Northwest Territories). While having important chemical similarities to the Yellowknife brine, shield brines from the Sudbury/Elliot Lake (Ontario) and Thompson/Snow Lake (Manitoba) regions, which are the focus of this study, exhibit contrasting lithium behavior.

Brine from the Sudbury Victor mine has lithium concentrations that closely follow the sea water lithium‐bromine concentration trajectory, as well as δ6Li values of approximately—28 %o. This indicates that the lithium in this brine is predominantly marine in origin with a relatively minor component of crustal lithium leached from the host rocks. In contrast, the Thompson/Snow Lake brine has anomalously low lithium concentrations, indicating that it has largely been removed from solution by alteration minerals. Furthermore, brine and nonbrine mine waters at the Thompson mine have large δ6Li variations of ∼30 %o, which primarily reflects mixing between deep brine with δ6Li of—35 ± 2‰ and near surface mine water that has derived higher δ6Li values through interactions with their host rocks. The contrary behavior of lithium in these two brines shows that, in systems where it has behaved conservatively, lithium isotopes can distinguish brines derived from marine sources.
Geophysical Expression of Natural Recharge in Different Geological Terrains
Authors: Hodlur G.K. , Singh U.K. , Das R.K. , Rangarajan R. , Chand Ramesh , Singh S.B.
Published: December 2005

Behavior of the Dar‐Zarrouk parameters—longitudinal unit conductance, transverse unit resistance, longitudinal resistivity, and transverse resistivity—has been compared with the behavior of the natural recharge in two geological terrains. Contour patterns of the geophysical parameters and those of natural recharge have been analyzed and a qualitative relation in their behavior was recognized. Graphical comparison of the geophysical and hydrogeological parameters clearly illustrates a qualitative relationship between the two parameters. Use of such qualitative relation in the field of ground water exploration and management studies is explained. A modest beginning is attempted to arrive at a quantitative relation between natural recharge and Dar‐Zarrouk parameters.
Radar Determination of the Spatial Structure of Hydraulic Conductivity
Authors: Oldenborger Greg A. , Schincariol Robert A. , Mansinha Lalu
Published: December 2005

Spatial variability of hydraulic conductivity exerts a predominant control on the flow of fluid through porous media. Heterogeneities influence advective pathways, hydrodynamic dispersion, and density‐dependent dispersion; they are, therefore, a key concern for studies of ground water resource development, contaminant transport, and reservoir engineering. Ground‐penetrating radar contributes to the remote, geophysical characterization of the macroscale variability of natural porous media. On a controlled excavation of a glacial‐fluvial sand and gravel deposit in the Fan‐shawe Delta area (Ontario, Canada), the hydraulic conductivity field of a 45 × 3 m vertical exposure was characterized using constant‐head permeameter measurements performed on undisturbed horizontal sediment cores. Ground‐penetrating radar data were collected along the excavation face in the form of both reflection and common midpoint surveys. Comparison of geostatistical analyses of the permeameter measurements and the radar data suggests that the horizontal correlation structure of radar stack velocity can be used to directly infer the horizontal correlation structure of hydraulic conductivity. The averaging nature of the common midpoint survey is manifest in the vertical correlation structure of stack velocity, making it less useful. Radar reflection data do not exhibit a spatial structure similar to that of hydraulic conductivity possibly because reflections are a result of material property contrasts rather than the material properties themselves.
Deriving TDS Values in Coarse Sediments from Long Normal and Electromagnetic Logs
Authors: Van Meir Nathalie , Lebbe Luc
Published: December 2005

This paper presents an empirical relationship of quantitatively linked electromagnetic (EM) borehole recordings of the total dissolved solids (TDS) in pore water in the Quaternary deposits of the Belgian coastal plain. First, the long normal (LN) logs are linked to EM logs, then the already developed relationships between LN resistivity measurements and the TDS values are rewritten for EM recordings. The main parameter in these equations is the formation factor, which is derived from ground water analyses and LN logs through Archie's law. The EM recording has several advantages compared to the LN logs. The EM analysis allows measuring in PVC‐cased wells and is not hindered by the invasion zone around the well. Furthermore, it has a high vertical resolution. LN logs can be measured only once, after drilling a well; EM recordings can be repeated several times in monitoring wells, which allows the gathering of time‐dependent data over a complete vertical cross section. Such data could be obtained with LN logs only in wells with screens over the full‐depth interval, which causes a hydraulic short circuit. This short circuit can result in a large artificial flow through the well between different levels, resulting in a salinity profile, which is no longer representative for the studied site. Remediation against short circuiting is a reduction of the screened interval, which strongly reduces the gathered information. The application of the derived equations is one of setting up a monitoring network along the Belgian coast to monitor the trend in salinity levels and comparing present salinity levels with older LN recordings to investigate the salinity changes in the last 30 years. Deep wells already present in the Belgian coastal plain can then be used to monitor both the fresh water head changes and the salt water evolution. The technique has also been used for parameter identification for which real concentration measurements were needed.
Salinization of a Fresh Palaeo‐Ground Water Resource by Enhanced Recharge
Authors: Leaney F.W. , Herczeg A.L , Walker G.R.
Published: December 2005

Deterioration of fresh ground water resources caused by salinization is a growing issue in many arid and semi‐arid parts of the world. We discuss here the incipient salinization of a 104 km2 area of fresh ground water (<3000 mg/L) in the semiarid Murray Basin of Australia caused by widespread changes in land use. Ground water 14C concentrations and unsaturated zone Cl soil water inventories indicate that the low salinity ground water originated mainly from palaeo‐recharge during wet climatic periods more than 20,000 years ago. However, much of the soil water in the 20 to 60 m thick unsaturated zone throughout the area is generally saline (> 15,000 mg/L) because of relatively high evapotranspiration during the predominantly semiarid climate of the last 20,000 years.

Widespread clearing of native vegetation over the last 100 years and replacement with crops and pastures leads to enhancement of recharge rates that progressively displace the saline soil‐water from the unsaturated zone into the ground water. To quantify the impact of this new hydrologic regime, a one‐dimensional model that simulates projected ground water salinities as a function of depth to ground water, recharge rates, and soil water salt inventory was developed. Results from the model suggest that, in some areas, the ground water salinity within the top 10 m of the water table is likely to increase by a factor of 2 to 6 during the next 100 years. Ground water quality will therefore potentially degrade beyond the point of usefulness well before extraction of the ground water exhausts the resource.
Vadose Zone Flow Model Uncertainty as Conditioned on Geophysical Data
Authors: Binley Andrew , Beven Keith
Published: December 2005

An approach to estimating the uncertainty in model descriptions based on a landscape space to model space mapping concept is described. The approach is illustrated by an application making use of plot scale geophysical estimates of changes in water content profiles to condition a model of recharge to the Sherwood Sandstone Aquifer in the United Kingdom. It is demonstrated that the mapping is highly uncertain and that many different parameter sets give acceptable simulations of the observations. Multiple profile measurements over time offer only limited additional constraints on the mapping. The resulting mapping weights may be used to evaluate uncertainty in the predictions of vadose zone flow dynamics for the site.
A Post Audit of a Model‐Designed Ground Water Extraction System
Authors: Andersen Peter F. , Lu Silong
Published: December 2005

Model post audits test the predictive capabilities of ground water models and shed light on their practical limitations. In the work presented here, ground water model predictions were used to design an extraction/treatment/injection system at a military ammunition facility and then were re‐evaluated using site‐specific water‐level data collected approximately one year after system startup. The water‐level data indicated that performance specifications for the design, i.e., containment, had been achieved over the required area, but that predicted water‐level changes were greater than observed, particularly in the deeper zones of the aquifer. Probable model error was investigated by determining the changes that were required to obtain an improved match to observed water‐level changes. This analysis suggests that the originally estimated hydraulic properties were in error by a factor of two to five. These errors may have resulted from attributing less importance to data from deeper zones of the aquifer and from applying pumping test results to a volume of material that was larger than the volume affected by the pumping test. To determine the importance of these errors to the predictions of interest, the models were used to simulate the capture zones resulting from the originally estimated and updated parameter values. The study suggests that, despite the model error, the ground water model contributed positively to the design of the remediation system.
NAPLANAL: A Tool for Analyzing NAPL Saturation and Composition
Authors: McCray John E. , Cohen Robert M.
Published: December 2005

Overall, NAPLANAL is excellent freeware. The software is useful for engineers and scientists to understand the spatial heterogeneities in NAPL distribution and composition at a site. This information can be useful for designing NAPL remediation schemes, and potentially for modeling contaminant transport from NAPL‐mixture source zones if enough soil chemical and physical data were available. The program is also useful for university teaching because students can rapidly assess multiphase concentrations of NAPL mixtures while integrating physical and chemical information obtained from typical analyses performed on soil samples collected while drilling monitoring wells.
A Digital Procedure for Ground Water Recharge and Discharge Pattern Recognition and Rate Estimation
Authors: Lin Yu‐Feng , Anderson Mary P.
Published: December 2005

A digital procedure to estimate recharge/discharge rates that requires relatively short preparation time and uses readily available data was applied to a setting in central Wisconsin. The method requires only measurements of the water table, fluxes such as stream baseflows, bottom of the system, and hydraulic conductivity to delineate approximate recharge/discharge zones and to estimate rates. The method uses interpolation of the water table surface, recharge/discharge mapping, pattern recognition, and a parameter estimation model. The surface interpolator used is based on the theory of radial basis functions with thin‐plate splines. The recharge/discharge mapping is based on a mass‐balance calculation performed using MODFLOW. The results of the recharge/discharge mapping are critically dependent on the accuracy of the water table interpolation and the accuracy and number of water table measurements. The recharge pattern recognition is performed with the help of a graphical user interface (GUI) program based on several algorithms used in image processing. Pattern recognition is needed to identify the recharge/discharge zonations and zone the results of the mapping method. The parameter estimation program UCODE calculates the parameter values that provide a best fit between simulated heads and flows and calibration head‐and‐flow targets. A model of the Buena Vista Ground Water Basin in the Central Sand Plains of Wisconsin is used to demonstrate the procedure.
A Spreadsheet Method of Estimating Best‐Fit Hydraulic Gradients Using Head Data from Multiple Wells
Authors: Devlin J.F.
Published: December 2005

Hydraulic gradients from planar water tables, or piezometric surfaces, and horizontal flow regimes can be quickly and conveniently calculated from data sets involving numerous wells. The matrix‐solving functions of a modern spreadsheet program (Excel®) were used to determine the equation of a water‐table plane, Ax + By + Cz ‐ D = 0, and the equation coefficients were then used to determine the magnitude of the hydraulic gradient, according to gradient = and its direction, according to α= arctan B/A, where a is the angle measured from the x‐axis. A pre‐prepared Excel file constructed to handle data from up to 20 wells at once is available for free downloading at http://www.geo.ku.edu/hydro/KUHydro.html.
The Permeability of the Elkhorn Fault Zone, South Park, Colorado
Authors: Marler John , Ge Shemin
Published: December 2005

The purposes of this study are to use both field and modeling approaches to characterize the permeability of a fault and to assess the role of the fault on regional ground water flow. The study subject is the Elkhorn fault, a low‐angle reverse fault that brings Precambrian crystalline rocks over the sediments of Colorado's South Park Basin. The fault is hypothesized to act as a low‐permeability barrier to flow, restricting interaction between the crystalline aquifer and the basin sediments. To test this hypothesis and to better predict the permeability structure of the fault, we synthesized geologic data to create a geologic model of the fault, conducted aquifer tests to estimate the hydrogeologic properties of the fault zone, and used ground water modeling to test the influence of a range of hydraulic properties for the fault zone on ground water flow in the region.

Our study suggests that the fault is a low‐permeability feature. Estimated heads are best matched to observations by modeling the fault as a 10‐foot‐thick interval of low‐permeability fault gouge. Steady‐state flow models show that much of the flow in the study area is topographically driven near land surface. Flow rates decrease with depth in the aquifers. In the footwall, ground water moves updip in the Michigan‐San Isabel syncline to discharge in the South Park Basin. In the hanging wall, ground water moves east to a regional ground water divide. Sensitivity analyses indicate that hydraulic heads are most sensitive to changes in hydraulic conductivity and recharge.
Flow Dimension as an Indicator of Hydraulic Behavior in Site Characterization of Fractured Rock
Authors: Kuusela‐Lahtinen A. , Niemi A. , Luukkonen A.
Published: December 2005

We examine the possibility of using the flow dimension identified from constant pressure injection tests as a tool for characterizing the hydraulic conditions of fractured media. The data comes from a low‐conductivity crystalline rock site, from depths of up to 450 m, and is obtained with 2 m and 10 m measurement scales. In the analysis, the general solution for n‐dimensional flow by Barker (1988) is applied. The results show that the most prominent characteristics of the medium can be identified; that is, linear and sublinear flow dimensions as distinguished from dimensions higher than two. In many cases, however, there is significant difficulty in distinguishing the dimensions n = 2, 2.5, and 3 from each other. This is usually because of the experimental difficulties in achieving the ideal conditions required by the theory during the early part of the experiment. In such cases, a full flow curve is not available for the type‐curve fitting. In the nonunique cases the higher dimensions typically correspond to higher, sometimes unrealis‐tically high, values of specific storage and to the less reliable and less representative early part of the experiment. Therefore, most of the dimensions in categories n= 3 can be excluded, thus leaving the majority observations in the categories of n= 2 and n = 2–2.5. The dominance of dimension n = 2 is more pronounced for data related to fracture zones in comparison to that related to “average” rock, in particular in the 2 m scale data. The proportion of low (n < 1.5) flow dimensions is small, but for the 10 m scale data it is relatively higher at greater depths and corresponds to lower conductivities. For the smaller 2 m scale data, the low dimensions are not linked to greater depths or systematically smaller conductivities, giving preliminary indication of different flow dimension behavior for the two different scales.
Semianalytical Solutions for Stream Depletion in Partially Penetrating Streams
Authors: Chen Xunhong , Yin Yanfeng
Published: December 2005

In the analysis of streamflow depletion, the Hunt (1999) solution has an important advantage because it considers a partially penetrating stream. By extending the Hunt drawdown solution, this paper presents semianalytical solutions for gaining streams that evaluate the induced stream infiltration and base flow reduction separately. Simulation results show that for a given δh (the initial hydraulic head difference between stream and aquifer beneath the channel), the base flow reduction is in direct proportion to the product of streambed leakage (λ) and the distance between pumping well and stream (L), and the induced stream infiltration is in inverse proportion to λL. Δh has a significant effect on the ratio of stream infiltration to base flow reduction. The results from the semianalytical solutions agree well with those from MODFLOW simulations. The semianalytical solutions are useful in the verification of numerical simulations and in the analysis of stream‐aquifer interactions where water quantity or quality is concerned.
Predictability of Surface Mine Spoil Hydrologic Properties in the Appalachian Plateau
Authors: Hawkins Jay W.
Published: December 2005

Prevention of acid mine drainage at surface coal mines in the Appalachian region relies to an extent on minimizing ground water contact with acid‐forming materials, and maximizing ground water contact with alkalinity‐yielding materials. Acid‐forming materials are often selectively handled to minimize or prevent contact with ground water. Controlling ground water contact with acidic or alkaline materials depends on forecasting the level and range of fluctuation of the postmining water table within the mine backfill. Physical measurements and aquifer testing of more than 120 wells from 18 reclaimed mines in Kentucky, Ohio, Pennsylvania, and West Virginia have led to improved forecasting of the postmining ground water system. Factors that influence the ground water regime include spoil lithology and particle size, age of reclamation, spoil thickness, distance from the final highwall, and pit floor dip angle and direction. Spoil hydraulic conductivity (K) exhibits a 95% confidence interval range of six orders of magnitude about a mean K of 1.7 × 10−5 m/sec. Spoil aquifer saturated thickness is related to the overall thickness of the spoil, the lithology of the spoil, dip of the pit floor, and distance to the highwall. Saturated spoil thickness has a 95% confidence interval of 2.2 to 3.6 m about the mean of 2.9 m. The predicted saturated zone averages 19% of the total spoil thickness.
Transient Analysis of the Source of Water to Wells: Cape Cod, Massachusetts
Authors: Masterson John P. , Walter Donald A. , LeBlanc Denis R.
Published: December 2005

A transient flow modeling analysis for potential public‐supply wells on western Cape Cod, Massachusetts, demonstrates the difference between transient and steady‐state recharge areas can have important implications for wellhead protection. An example of a single pumping well illustrates that commonly used steady‐state time‐related capture areas do not represent the recharge area and travel times of water being pumped from the well until sufficient time has elapsed for steady‐state flow conditions to be established. Until that time, transient recharge areas are needed to account for the portion of water discharging from the well that entered the aquifer before pumping started.

An example of two pumping wells demonstrates the same area at the water table cannot supply water to more than one well under steady‐state flow conditions. Transient recharge areas to multiple wells can overlap, however, until steady‐state flow conditions are established. The same area can, therefore, be a source of water to more than one well during early pumping times, and the water pumped from a given well may derive from source areas, including contaminated areas, that do not lie within the well's steady‐state recharge area.
Simulating Nonequilibrium Transport of Atrazine Through Saturated Soil
Authors: Mao Meng , Ren Li
Published: December 2005

Atrazine, an herbicide widely used for selective control of grassy weeds in the fields where maize is grown, is a potential ground water contaminant in China and, consequently, there is interest in predicting its mobility in agricultural soils. In this study, we determined the nonequilibrium transport characteristics of atrazine in Shahe soil (Beijing sandy loam) using the advection‐dispersion equation, and using a sensitivity analysis, we evaluated the contribution of the uncertainty in a given input parameter to the overall uncertainty in model results. The asymmetrical shape and tailing of the atrazine breakthrough curve (BTC) showed that atrazine was subject to nonequilibrium transport. The observed atrazine BTC was best fitted by the chemical nonequilibrium model with a nonlinear least‐squares optimization approach. Results from the sensitivity analysis indicated that the retardation factor was the most sensitive parameter. Considering the reliability of the estimated parameters, the best fit to the atrazine BTC was obtained by fixing the retardation factor based on the linear distribution coefficient, and by calculating the dispersion coefficient from the bromide BTC and the average pore water velocity from the measured data; nonequilibrium parameters were the only unknown parameters that were optimized. Model verification procedures were based on best‐fit parameters optimized from one soil column experiment and applied to simulate the transport of atrazine in the duplicate experiment. The results showed there was good agreement between measured and simulated concentrations for atrazine leaching in the soil column.
Anaerobic Biodegradation of TCE in Laboratory Columns of Fractured Saprolite
Authors: Lenczewski Melissa E. , McKay Larry D. , Layton Alice
Published: December 2005

An experiment was conducted to determine if biodegradation of trichloroethylene (TCE) can occur in previously uncontaminated ground water in saturated fractured saprolite (highly weathered material derived from sedimentary rocks). Two undisturbed columns (0.23 m diameter by 0.25 m long) of fractured saprolite were collected from ∼2 m depth at an uncontaminated site on the Oak Ridge Reservation, Oak Ridge, Tennessee. Natural, uncontaminated ground water from the site, which was degassed and spiked with dissolved phase TCE, was continuously pumped through one column containing the natural microbial communities (the biotic column). In a second column, the microorganisms were inhibited and the dissolved phase TCE was added under aerobic conditions (dissolved oxygen conditions > 2 ppm). In effluent from the biotic column, reducing conditions rapidly developed and evidence of anaerobic biodegradation of TCE, by the production of cDCE, first appeared ∼31 days after addition of TCE. Reductive dechlorination of TCE occurred after iron‐reducing conditions were established and about the same time that sulfate reduction began. There was no evidence of methanogenesis. Analyses using polymerase chain reaction with specific primers sets detected the bacteria Geothrix, Geobacter, and Desulfococcus‐Desulfonema‐Desulfosarcina in the effluent of the biotic column, but no methanogens. The presence of these bacteria is consistent with iron‐ and sulfate‐reducing conditions. In the inhibited column, there were no indicators of TCE degradation. Natural organic matter that occurs in the saprolite and ground water at the site is the most likely primary electron donor for supporting reductive dechlorination of TCE. The relatively rapid appearance of indicators of TCE dechlorination suggests that these processes may occur even in settings where low oxygen conditions occur seasonally due to changes in the water table.
Effect of Iron Type on Kinetics and Carbon Isotopic Enrichment of Chlorinated Ethylenes During Abiotic Reduction on Fe(0)
Authors: VanStone Nancy A. , Focht Robert M. , Mabury Scott A. , Lollar Barbara Sherwood
Published: December 2005

Four samples of two commercially available iron brands used as substrate for iron permeable reactive barriers (PRBs) were tested for suitability for remediation of perchloroethylene (PCE), trichloroethylene (TCE), cis‐dichloroethylene (cDCE) and vinyl chloride (VC). Kinetic studies indicate that rates of reaction are enhanced for cDCE and VC on Connelly iron (2.8 × 10−4 to 6.9 × 10−4 L/m2/hr and 2.0 × 10−4 to 9.0 × 10−4 L/m2/hr, for cDCE and VC, respectively) vs. Peerless iron (3.1 × 10−5 to 4.6 × 10−5 L/m2/hr and 2.4 × 10−5 to 4.1 × 10−5 L/m2/hr, for cDCE and VC, respectively). Carbon isotopic analyses of the residual chlorinated ethylene (CE) during degradation indicate significant fractionation occurs during reductive dechlorination, with, for example, up to 70 %o enrichment in carbon isotopic values observed when VC is more than 99% degraded. Comparison of fractionation factors (×) indicates significant differences in carbon isotopic fractionation for different iron types and for different CEs. For the lower CEs (cDCE and VC) in particular, both slower reaction rates and larger fractionation are observed for degradation on Peerless vs. Connelly iron. This is the first study to establish a correlation between the rate of abiotic degradation on Fe(0) and the extent of isotopic fractionation, and the first to confirm consistent differences in these two parameters as a function of iron type. The possibility that these differences in kinetics and carbon isotopic fractionation for cDCE and VC are related to differences in branching ratios between competing hydrogenolysis and β‐elimination reactions during reductive dechlorination on the iron surfaces is discussed.
Magnetic Resonance Sounding: New Method for Ground Water Assessment
Authors: Lubczynski M. , Roy J.
Published: December 2005

The advantage of magnetic resonance sounding (MRS) as compared to other classical geophysical methods is in its water selective approach and reduced ambiguity in determination of subsurface free water content and hydraulic properties of the media due to the nuclear magnetic resonance (NMR) principle applied. Two case examples are used to explain how hydrogeological parameters are obtained from an MRS survey. The first case example in Delft (the Netherlands) is a multiaquifer system characterized by large signal to noise ratio (S/N = 73), with a 24 m thick, shallow sand aquifer, confined by a 15 m thick clay layer. For the shallow aquifer, a very good match between MRS and borehole data was obtained with regard to effective porosity nc∼28% and specific drainage Sd∼20%. The MRS interpretation at the level deeper than 39 m was disturbed by signal attenuation in the low resistivity (∼10 Ωm) media. The second case of Serowe (Botswana) shows a fractured sandstone aquifer where hydrogeological parameters are well defined at depth >74 m below ground surface despite quite a low S/N = 0.9 ratio, thanks to the negligible signal attenuation in the resistive environment. Finally, capabilities and limitations of the MRS technology are reviewed and discussed. MRS can contribute to subsurface hydrostratigraphy description, hydrogeological system parameterization, and improvement of well siting. The main limitations are survey dependence upon the value of the S/N ratio, signal attenuation in electrically conductive environments, nonuniformity of magnetic field, and some instrumental limitations. At locations sufficiently resistive to disregard the signal attenuation problems, the MRS S/N ratio determines how successfully MRS data can be acquired. Both signal and noise vary spatially; therefore, world scale maps providing guidelines on spatial variability of signal and noise are presented and their importance with respect to the MRS survey results is discussed. The noise varies also temporally; therefore, its diurnal and seasonal variability impact upon the MRS survey is covered as well.