bluuebunny/crossref_metadata_2025_split huggingface dataset:
Water and Radioactive Tracer Flow in a Heterogeneous Field‐Scale System
Authors: Dunnivant Frank M. , Newman Meredith E. , Bishop Carolyn W. , Burgess Dave , Giles John R. , Higgs Brian D. , Hubbell Joel M. , Neher Erick , Norrell Greg T. , Pfiefer M. Cathy , Porro Indrek , Starr Robert C. , Wylie Allan H. 
Published: August 2005

AbstractA coupled field‐scale aquifer pumping and water infiltration test was conducted at the Idaho National Engineering and Environmental Laboratory in order to evaluate subsurface water and contaminant transport processes in a heterogeneous flow system. The test included an aquifer pumping test to determine the storage properties of the aquifer and the state of confinement of the aquifer (∼190 m below land surface), and a vadose zone infiltration test to determine vertical moisture and radioactive tracer migration rates. Pump test results indicated that the Snake River Plain Aquifer was locally unconfined with a transmissivity ranging from 5.57 × 105 to 9.29 × 104 m2day. Moisture monitoring with neutron probes indicated that infiltrating water was initially transported vertically through the upper basalt layer of the vadose zone, primarily through fractures and rubble zones, at an average rate of 5 m/day (based on vertical distance traveled and first arrival of water at the monitoring points). Analysis of breakthrough curves for a conservative tracer allowed estimation of the arrival of the peak concentration and yielded an average velocity of 1 m/day. The migration velocities from the neutron probe and tracer tests are in good agreement given the scale of the test and difference in analysis techniques. None of the data sets showed a correlation between migration velocity (arrival time) and distance from the point source, but they strongly indicate preferential flow through discrete fractures. Upon reaching the first continuous sedimentary interbed layer in the basalt formation, water flow was diverted laterally along the interbed surface where it spread outward in primarily three areas corresponding to topographic lows on the interbed surface, and slowly infiltrated into the interbed. The nonpredictable movement of water and tracer through specific fractures underlying the site suggests that a priori prediction of trans‐missive fractures in this media is not possible. Results do suggest that the continuous sedimentary interbed layers, in general, impede vertical water flow and contaminant migration.
A Critique of a Steady‐State Analytical Method for Estimating Contaminant Degradation Rates
Authors: McNab Walt W. , Dooher Brendan P. 
Published: August 2005

AbstractContaminant transformation rates are routinely estimated from monitoring well data using a regression method based on a steady‐state analytical model. This approach assumes one‐dimensional solute transport in the presence of a continuous boundary concentration and a uniform first‐order degradation coefficient. It must be recognized that this type of analysis is easily subject to misinterpretation, particularly when few monitoring points are used. This is because the dispersive nature of solute transport can produce concentration profiles which closely resemble those associated with a degrading contaminant even in the absence of any transformation processes. Monte Carlo analyses using simulated plumes suggest that this method may lead to significant overestimates of apparent transformation rates.
Improving a Complex Finite‐Difference Ground Water Flow Model Through the Use of an Analytic Element Screening Model
Authors: Hunt Randall J. , Anderson Mary P. , Kelson Victor A. 
Published: August 2005

AbstractThis paper demonstrates that analytic element models have potential as powerful screening tools that can facilitate or improve calibration of more complicated finite‐difference and finite‐element models. We demonstrate how a two‐dimensional analytic element model was used to identify errors in a complex three‐dimensional finite‐difference model caused by incorrect specification of boundary conditions. An improved finite‐difference model was developed using boundary conditions developed from a far‐field analytic element model. Calibration of a revised finite‐difference model was achieved using fewer zones of hydraulic conductivity and lake bed conductance than the original finite‐difference model. Calibration statistics were also improved in that simulated base‐flows were much closer to measured values. The improved calibration is due mainly to improved specification of the boundary conditions made possible by first solving the far‐field problem with an analytic element model.
Arsenic Hydrogeochemistry in an Irrigated River Valley—A Reevaluation
Authors: Nimick David A. 
Published: August 2005

AbstractArsenic concentrations in ground water of the lower Madison River valley, Montana, are high (16 to 176 μg/L). Previous studies hypothesized that arsenic‐rich river water, applied as irrigation, was evapoconcentrated during recharge and contaminated the thin alluvial aquifer. Based on additional data collection and a reevaluation of the hydrology and geochemistry of the valley, the high arsenic concentrations in ground water are caused by a unique combination of natural hydrologic and geochemical factors, and irrigation appears to play a secondary role. The high arsenic concentrations in ground water have several causes: direct aquifer recharge by Madison River water having arsenic concentrations as high as 100 μg/L, leaching of arsenic from Tertiary volcano‐clastic sediment, and release of sorbed arsenic where redox conditions in ground water are reduced. The findings are consistent with related studies that demonstrate that arsenic is sorbed by irrigated soils in the valley. Although evaporation of applied irrigation water does not significantly increase arsenic concentrations in ground water, irrigation with arsenic‐rich water raises other environmental concerns.
How Observations and Structure Affect the Geostatistical Solution to the Steady‐State Inverse Problem
Authors: Kitanidis Peter K. 
Published: August 2005

AbstractThe solution to the steady‐state inverse problem can be expanded into a series of spline functions with weights adjusted to reproduce the observations within the observation error. The splines depend on the model spatial structure, the ground water flow model, and the location of the observations. This representation of the solution, which is a rigorous and exact expansion, provides insight into the form of the best estimate and explicitly shows how observations and the conceptual model may affect the solution.
A Wetland Simulation Module for the MODFLOW Ground Water Model
Authors: Restrepo Jorge I. , Montoya Angela M. , Obeysekera Jayantha 
Published: August 2005

AbstractThe alteration of wetland habitats by natural and anthropogenic processes is an issue of worldwide concern. Understanding the changes that occur in wetlands often requires knowledge of how surface water levels relate to adjacent aquifer systems. The ability to simulate surface water movement and its interaction with ground water and wetland slough channels is a desirable step in the design of many projects constructed in or near wetlands. Currently, most ground water flow models incorporate wetland systems as general head boundary nodes. The purpose of this research was to develop a computer package for the widely used MOD‐FLOW code that would simulate three‐dimensional wetland flow hydroperiods and wetland interactions with aquifers and slough channels. The ground water flow model was used to reproduce the surface water flow process through wetlands, and then to estimate new flow rates and values using a Manning‐type equation. This package represents flow routing, export and import of water, and evapotranspiration from wetlands for different hydroperiods. A basic verification procedure for the numerical solution of the diffusion equation was applied, based on a test case that was solved using a two‐dimensional surface water model. This example is a transient solution to the diffusion equation, in which the initial conditions were depicted by a sinusoidal water surface profile and a flat bottom.
Isotopic Constraints on Off‐Site Migration of Landfill CH4
Authors: Desrocher S. , Lollar B. Sherwood 
Published: August 2005

AbstractOccurrences of CH4 in residential areas in the vicinity of the Beare Road landfill, Toronto, Canada, have raised public concern about potential off‐site migration of CH4 from the landfill site. Carbon isotopic analysis of dissolved and gas phase CH4 at the Beare Road site, however, indicates that CH4 in the ground water systems in the vicinity of the landfill is related to naturally occurring microbial methanogenesis within these geologic units, rather than to contamination by landfill CH4. CH4 gas in the landfill and landfill cover has δ13C values (−60.2 ± 0.9%e) typical of microbially produced gas. Concentrations of CH4 (508 to 693 uM) found in deep ground water in the Scarborough, Don, and Whitby Formations underlying the landfill are isotopically distinct from the landfill gases. They are isotopically and compositionally similar, however, to naturally occurring microbial CH4 identified in organic‐rich glacial deposits throughout Ontario. The lack of any significant CH4 concentrations or concentration gradients in the upper till zone between the landfill and the deep ground water aquifer is further evidence that no transport between the landfill and deep ground water is occurring.
Practical Approximations of the Well Function
Authors: Srivastava Rajesh , Guzman‐Guzman Amado 
Published: August 2005

AbstractComputation of the well function is required in the analysis of pumping test data for leaky or confined aquifers. Existing electronic dataloggers facilitate collection of hydraulic test data, which is commonly interpreted using computer programs. Approximate expressions have recently been proposed to compute the well function over the entire range of argument values. We propose approximations that, while providing reasonable accuracy, are less computationally intensive than previous approximations. A detailed comparative analysis of the execution times and the errors of these approximations is performed. The proposed expressions are generally accurate to within 1%, and result in a savings of computation time on the order of 15 to 87% for confined aquifers, and 29 to 76% for leaky aquifers.
Stochastic Determination of the Wierden (Netherlands) Capture Zones
Authors: van Leeuwen Matthijs , te Stroet Chris B. M. , Butler Adrian P. , Tompkins Jacob A. 
Published: August 2005

AbstractA spatial stochastic approach was adopted to estimate the capture zones of a welifield in eastern Netherlands near the town of Wierden. The main sources of uncertainty were found to be the hydraulic conductivity of the production aquifer and the spatial distribution and thickness of an impeding clay layer situated above the production aquifer. Both were modeled as random space functions and a Monte Carlo analysis was performed to assess the probability distributions of the capture zones for t = 25 years and t →∞. The distributions were compared with two deterministic capture zones to show how the stochastic approach preserves the discontinuous character of the impeding clay layer while the deterministic approach smooths out the discontinuities. Furthermore, it is shown how the stochastic approach reveals the uncertainty about the location of the capture zones while the deterministic approach obscures it.
An Analytical Solution for Steady Flow into a Ttonnel
Authors: Lei Shizhong 
Published: August 2005

AbstractAn analytical solution is derived for two‐dimensional, steady ground water flow into a horizontal tunnel in a fully saturated, homogeneous, isotropic, and semi‐infinite aquifer. The hydraulic head and streamline distributions in the flow field, as well as the inflow rate, are obtained for a constant hydraulic head boundary condition at the tunnel perimeter. The inflow rate formula derived in this paper is an extension to the Polubarinova‐Kochina (1962) formula, which can be considered a special case of the present solution.
Designing a Monitoring Network for Contaminated Ground Water in Fractured Chalk
Authors: Nativ R. , Adar E.M. , Becker A. 
Published: August 2005

AbstractOne of the challenges of monitoring network design in a fractured rock setting is the heterogeneity of the rocks. This paper summarizes the activities and problems associated with the monitoring of contaminated groundwater in porous, low‐permeability fractured chalk in the Negev Desert, Israel. Preferential flow documented in the study area required siting the monitoring boreholes in the predominant fracture systems. Lineaments traced from aerial photographs were examined in the field to sort out the large‐extension, through‐going, multilayer fracture systems crossing the study area. At each proposed drilling site, these fractures were exposed below the sediment cover using trenches. Slanted boreholes were drilled at a distance from the fracture systems so that each borehole would intersect the targeted fracture plane below the water table. Based on their short recovery period and contaminated ground water, these newly drilled, fracture‐oriented boreholes appeared to be better connected to preferential flowpaths crossing the industrial site than the old boreholes existing on site. Other considerations concerning the drilling and logging of monitoring boreholes in a fractured media were: (1) coring provides better documentation of the vertical fracture distribution, but dry augering is less costly and enables immediate ground water sampling and the sampling of vadose rock for contaminant analysis; (2) caliper and TV camera logs appear to provide only partial information regarding the vertical fracture distribution; and (3) the information gained by deepening the monitoring boreholes and testing fractures crossing their uncased walls has to be carefully weighed against the risk of potential cross‐contamination through the monitoring boreholes, which is enhanced in fractured media.
Multicell Model for Ground Water Recharge Analysis: The Ibi River Basin, Japan
Authors: Sato Takeshi , Kojima Junichi , Loaiciga Hugo A. 
Published: August 2005

AbstractA coupled water quantity/quality model was developed and applied to estimate ground water recharge and simulate tracer concentrations in the Ibi River Basin of Japan. The ground water basin was divided into five sub‐basins, each of which contains a surface reservoir and up to three subsurface reservoirs. The reservoirs exchange water and solute mass among themselves and contribute direct runoff and base flow to adjacent streams. The simulation model is parameterized in terms of 14 water quantity and three water quality parameters. A parameter calibration procedure was implemented wherein streamflow and tracer concentration data were used in parameter estimation. Prior information on the parameters can be used to initialize and constrain calibrated parameters.The calibrated model was validated successfully and used to simulate Na+ and Ca2+ and to estimate ground water recharge in the sub‐basins and the Ibi River Basin as a whole. Ground water recharge varied substantially among sub‐drainage basins, reflecting the predominant role of precipitation variability in determining deep percolation to the first confined aquifer. It was determined that about 10% of the gross precipitation becomes ground water recharge over the entire Ibi River Basin. Analysis of ground water recharge to a large pulse of precipitation demonstrated the important effect of impermeable clay layers in controlling the magnitude and timing of deep ground water recharge. The validation results indicate that the equilibrium concentrations of Na− and Ca2+ in the first confined aquifer have negligible sensitivity to their initial concentrations in the simulation model. Similar behavior was observed for the equilibrium concentrations of these two tracers in reservoir 3, and to a lesser extent in reservoir 2. The top reservoir exhibited large fluctuations in tracer concentrations due to the effect of direct rainfall input.
A Model of Ground Water Discharge from an Unconfined Coastal Aquifer
Authors: Robinson Michael A. , Gallagher Daniel L. 
Published: August 2005

AbstractA two‐dimensional, field scale, finite‐element ground water model was developed to simulate the ground water discharge process within an unconfined coastal aquifer. Model development was based on the density dependent fluid flow approach with water table and dynamic tidal boundary conditions. The performance of the model was compared against data collected from the Columbia Aquifer on the eastern shore of Virginia. The dynamic tidal boundary conditions were necessary to reproduce the surficial mixing zone observed within the ground water intertidal zone of the aquifer. The model was able to reproduce field data on the movement of the near‐shore water table, ground water salt concentrations, and ground water discharge rates and patterns. The model was not able to replicate the short‐term fluctuation in salt concentration observed within the surficial mixing zone. The inability to account for the wave action of the tides within the intertidal zone is believed to be responsible for this difficulty. The development of the model provided a new method to investigate ground water discharge to coastal systems.
Unsteady Stream Depletion from Ground Water Pumping
Authors: Hunt Bruce 
Published: August 2005

AbstractA solution is obtained for stream flow depletion created by pumping from a well beside a stream. This solution assumes that streambed penetration of the aquifer and dimensions of the streambed cross section are all relatively small. It also assumes that the streambed is clogged and that a linear relationship exists between the outflow seepage through the streambed and the change in piezometric head across the semipervious clogging layer. The solution is general enough to include the earlier solutions of Theis, Glover and Balmer, and Hantush. A solution is also obtained for the drawdown at any point within the aquifer, and it is suggested that this solution might be matched with experimental field data to obtain estimates for aquifer and streambed leakage parameters.
Tracing Ground Water Recharge in an Agricultural Watershed with Isotopes
Authors: Cane Greg , Clark Ian D. 
Published: August 2005

AbstractNitrate and pesticide use in the 800 km2 Raisin River agricultural watershed in eastern Ontario, Canada, threatens the quality of ground water in the highly exploited regional carbonate aquifer overlain by sandy till. To assess local recharge contributions through the cultivated fields, monthly monitoring of ground water levels, geochemistry, and environmental isotopes (δ2H H2O, (δ13CDIC) was carried out for 12 wells over a 14‐month period.Seasonal water level variations suggest that recharge is constrained to spring and late fall when transpiration is minimized and the ground is not frozen. However,2H monitoring shows that early summer precipitation also contributes to recharge. Variations in (δ2H values between monitoring sites suggest a local component to recharge.δ13CDIC was used to distinguish between dissolved inorganic carbon (DIC) originating from natural (C3) vegetation and DIC from the cultivated corridors where corn is grown (C 4 vegetation). Seasonal variations in δ13CDIC are remarkably coherent for all wells, with uniform trends to positive values during periods of low water table elevation. During periods of high water table (spring and late fall), δ13CDIC values are between ‐13 and ‐ 16%c VPDB (Vienna Peedee Belemnite), reflecting DIC originating from a dominantly natural (C3) vegetation. When ground water levels are low (summer and mid‐winter), δ13CDIC values shift to between ‐11 and ‐l%c. The seasonal enrichments in δ13CDIC are clear evidence for a local contribution to recharge by direct infiltration though the fields. This contribution is enhanced during periods of low water level, likely due to drainage from the phreatic aquifer. High DOC (dissolved organic carbon) concentrations (> 10 to 30 mg‐C/L) correlate with periods of high water levels indicating infiltration of labile organics to the carbonate aquifer.The work carried out for this paper shows that the conjunctive use of environmental isotope geochemistry and physical parameters are fundamental to assessing the risk of ground water contamination in agricultural watersheds.
Dynamics of DNAPL Penetration into Fractured Porous Media
Authors: Ross Benjamin , Lu Ning 
Published: August 2005

AbstractDense nonaqueous phase liquids (DNAPLs) that pool above stratigraphic contacts as a result of capillary forces can migrate downward through fractures in the underlying fine‐grained layer. Although the DNAPL in the fracture is excluded from the surrounding porous matrix by capillary forces, the DNAPL constituent will dissolve and migrate by diffusion into the matrix. As a front of moderately soluble DNAPL advances into a fracture, the flux of dissolved material into the matrix increases until it becomes comparable to the rate of flow into the fracture, reducing the pressure in the DNAPL phase and slowing its advance. If the DNAPL front encounters a constriction with sufficiently large entry pressure, its advance will halt temporarily. But as the concentration gradients driving diffusion into the matrix decrease, there will be less DNAPL lost by diffusion and the DNAPL pressure at the constriction will increase until it exceeds the entry pressure, causing the downward advance of the front to suddenly resume. Because the time scales of diffusion are much slower than those of density flow, this analysis suggests that under certain circumstances a DNAPL can suddenly resume its downward advance after a long period of apparent immobility. In one plausible example, a dichloromethane front passes through 5 m of fractured clay in 16 days, is immobile for more than four years, and then suddenly moves again. Where this phenomenon is possible, removal of DNAPL to protect underlying aquifers becomes more important as a remediation goal.
Flow to a Well in a Water Table Aquifer: Speeding Up the Computation of Type Curves for Low Beta Values
Authors: Gieske A. 
Published: August 2005

AbstractA study is made of the computer implementation of a recently developed Laplace transform solution (Moench 1996) for flow to a well in a water table aquifer. Some improvements are suggested to increase the speed of computation, especially for low beta values. The first is to calculate the type curves at points which are spaced a factor of two apart, thus allowing more efficient use of the Stehfest inversion algorithm. An improved numerical method to determine the roots of the equation xtanx =α is suggested. Finally, more efficient determination of the number of terms in the required series summation may lead to significant reduction in computing time.