bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vadose Zone Flow Model Uncertainty as Conditioned on Geophysical Data
Authors: Binley Andrew , Beven Keith 
Published: December 2005

AbstractAn 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

AbstractModel 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

SummaryOverall, 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

AbstractA 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

AbstractHydraulic 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

AbstractThe 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

AbstractWe 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

AbstractIn 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

AbstractPrevention 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

AbstractA 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

AbstractAtrazine, 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

AbstractAn 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

AbstractFour 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

AbstractThe 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.
A Methodology for Validating Numerical Ground Water Models
Authors: Hassan Ahmed E. 
Published: December 2005

AbstractGround water validation is one of the most challenging issues facing modelers and hydrogeologists. Increased complexity in ground water models has created a gap between model predictions and the ability to validate or build confidence in predictions. Specific procedures and tests that can be easily adapted and applied to determine the validity of site‐specific ground water models do not exist. This is true for both deterministic and stochastic models, with stochastic models posing the more difficult validation problem. The objective of this paper is to propose a general validation approach that addresses important issues recognized in previous validation studies, conferences, and symposia. The proposed method links the processes for building, calibrating, evaluating, and validating models in an iterative loop.The approach focuses on using collected validation data to reduce uncertainty in the model and narrow the range of possible outcomes. This method is designed for stochastic numerical models utilizing Monte Carlo simulation approaches, but it can be easily adapted for deterministic models. The proposed methodology relies on the premise that absolute validity is not theoretically possible, nor is it a regulatory requirement. Rather, the proposed methodology highlights the importance of testing various aspects of the model and using diverse statistical tools for rigorous checking and confidence building in the model and its predictions. It is this confidence that will encourage regulators and the public to accept decisions based on the model predictions. This validation approach will be applied to a model, described in this paper, dealing with an underground nuclear test site in rural Nevada.