bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tracer Test Evaluation of a Drainage Ditch Capture Zone
Authors: Chambers Lucy W. , Bahr Jean M. 
Published: August 2005

AbstractRecent analytical and numerical modeling studies (Zheng et al., 1988a, 1988b) suggest that drainage ditches within the central sand plain of Wisconsin may serve to limit the spread of agricultural chemicals. In this study a natural‐gradient tracer test was conducted to determine flow paths around a sand plain drainage ditch. The flow paths define a capture zone for the ditch. These results were used to evaluate the predictive capabilities of an analytical model (Zheng et al., 1988a).The natural‐gradient tracer test began with injections of iodide at two depths and bromide at an intermediate depth. Movement of these tracers reveals that average ground‐water velocity ranged from 0.4 ft/day at a depth of 20 ft to greater than 1 ft/day near the water table. The delineated capture zone was deeper than 12 ft below the water table. These results are encouraging because they indicate that the capture depth of the ditch should allow for the effective removal of shallow agricultural contaminants. The observed capture depth falls within the range predicted by the analytical model of Zheng et al. (1988a). However, a sensitivity analysis of the analytical method reveals that the predicted range of capture depths is large. This range results from the variability and uncertainty of the model parameters. The analytical solution appears best suited for estimating the minimum capture depth, which is a conservative estimate of contaminant capture.
Applicability of Sharp‐Interface Models for NAPL Transport: 1. Infiltration
Authors: El‐Kadi Aly I. 
Published: August 2005

AbstractA sharp‐interface, or piston flow model is developed for nonaqueous phase liquids (NAPL) flow through the unsaturated zone. This model, which assumes saturated plug flow downward from the surface, is verified through comparison with an immiscible‐phase model that includes capillarity effects in the formulation. Although significant assumptions are included in the sharp‐interface model, it may be useful for initial screening and in obtaining an order‐of‐magnitude estimate of the time of travel of NAPL in the unsaturated zone. In the absence of data for calibration, guidelines are introduced for estimating the model's parameters.
Unsaturated and Saturated Flow in Response to Pumping of an Unconfined Aquifer: Numerical Investigation of Delayed Drainage
Authors: Akindunni Festus F. , Gillham R. W. 
Published: August 2005

AbstractIn this study, numerical methods are used to examine the capillary fringe hypothesis proposed by Nwankwor et al. (1992) to explain variations in the storage property of an unconfined aquifer during pumping. Based on field observations, the hypothesis suggested that the response of an unconfmed aquifer to the stress imposed by pumping is largely controlled by the magnitude of vertical hydraulic gradients developed above the moving water table. After validation with a 1‐D hysteretic laboratory experiment and a 2‐D axisymmetric variably saturated semianalytical model, the numerical solution was used to simulate the pumping test of Nwankwor et al. (1992). Numerical parameters used for the simulation were chosen from experiments independent of the pumping test. There was good agreement between numerical results and field data at different depths and different radial distances from the pumping well. Numerically obtained variations in the magnitude of vertical gradients above the water table and the resulting variations in values of apparent specific yield also showed similar trends with the field data. The good agreement between the numerical and field results provides convincing evidence that the field observations and the resulting capillary fringe hypothesis concerning time variations of specific yield, are indeed consistent with the physical principles of variably saturated flow. The high storativity values frequently obtained by fitting early‐time data to type curves were shown to correspond to the period of increasing hydraulic gradients, and may not be related to intrinsic properties of the aquifer, such as compressibility. In agreement with the “volume‐balance method” of Nwankwor et al. (1984), it was also shown that the results confirm that the ultimate specific yield of an unconfmed aquifer is more related to the drainable porosity than the low values often obtained from type‐curve analysis.
Three‐Dimensional Modeling of a Two‐Well Tracer Test
Authors: Güven O. , Molz F. J. , Melville J. G. , Didy S. El , Boman G. K. 
Published: August 2005

AbstractA three‐dimensional (3‐D), advection‐based numerical model has been developed for simulating two‐well injection withdrawal tracer tests in heterogeneous granular aquifers, and the model has been applied to perform various simulations of an actual two‐well tracer test conducted previously in a confined aquifer at a field site near Mobile, Alabama. Information obtained from a series of independent field tests is used as input in the model to account for the 3‐D spatial distribution of the hydraulic conductivity (K) at the test site.The numerical model is based on a simplified, Lagrangian approach in which the transport of the tracer between the injection and withdrawal wells is modeled taking into account advection only. Processes such as dispersion, sorption, and chemical or biological reactions are neglected. Despite field data limitations and various simplifying assumptions, the model predictions of the withdrawal‐well concentration breakthrough and of the mean tracer arrival times at various levels of two multilevel observation wells are in good overall agreement with the corresponding field observations.The results of this study indicate that it will be possible to construct realistic, predictive models of contaminant transport in heterogeneous granular aquifers if the necessary effort is made to obtain field measurements of the 3‐D spatial distribution of hydraulic conductivity. The extent and feasibility of such an effort are expected to depend on the particular contamination problem at hand. Future research should be directed toward the problems of field measurement scale selection and the development of K distributions for models from sparse data sets.
Design of Ground‐Water Monitoring Networks Using the Monitoring Efficiency Model (MEMO)
Authors: Wilson Charles R. , Einberger Carl M. , Jackson Ronald L. , Mercer Richard B. 
Published: August 2005

AbstractAn analytical Monitoring Efficiency Model (MEMO) has been developed to assist in the design of monitoring well networks. The method simulates the migration of hypothetical contaminant plumes from a site and quantifies the efficiency of alternative well network designs in detecting the plumes. The computed detection efficiency provides a basis for optimizing the design. Maps of the site showing areas from which releases would or would not be detected by a given well network are produced, providing insight into the benefits of adding, deleting, or moving specific wells.
A Neural‐Network Approach to the Determination of Aquifer Parameters
Authors: Aziz Abd. Rashid Abd. , Wong Kau‐Fui Vincent 
Published: August 2005

AbstractA new approach to determine aquifer parameter values from aquifer‐test data has been developed that uses the pattern‐matching capability of a neural network. The network is trained to recognize patterns of normalized drawdown data as input and the corresponding aquifer parameters as output. The Theis and Hantush‐Jacob solutions for confined and leaky‐confined aquifer conditions are used to derive the input patterns based on the parameter values selected from predetermined ranges. The trained network produces output of aquifer parameter values when it receives the aquifer‐test data as the input patterns. The results obtained from this new approach are in good agreement with published results using other techniques. The advantages of the present approach are the automated process of obtaining aquifer parameter values and the ability of the network to associate drawdown to the corresponding Theis and Hantush‐Jacob solutions.
A Comparison of Three Functional Forms for Representing Soil Moisture Characteristics
Authors: Bumb Amar C. , Murphy Carolyn L. , Everett Lome G. 
Published: August 2005

AbstractThree functional forms relating capillary pressure to soil saturation (the Brooks and Corey equation, the Boltzmann distribution, and the Fermi distribution) were evaluated and compared by matching each form to soil moisture characteristic data for 12 different soil types.Out of 113 data sets, the Boltzmann distribution and the Brooks and Corey equation performed very well–and almost equally well–in matching the soil moisture data. Only 10 data sets were significantly better matched by the Boltzmann distribution, and only nine data sets were significantly better matched by the Brooks and Corey equation. The Fermi distribution did not achieve as high a rate of success, although unlike the other two functional forms, it was able to match data in all regions of the curve, including the capillary fringe.Considering that the Brooks and Corey equation and the Boltzmann distribution performed almost equally well, the Boltzmann distribution has an additional advantage: it is amenable to an analytic solution to the governing differential equation for flow in unsaturated media. Based on the results of this study, the authors recommend use of the Boltzmann distribution.
Geochemical and Kinetic Evolution of a Karst Flow System: Laurel Creek, West Virginia
Authors: Groves Christopher G. 
Published: August 2005

AbstractAn approach that couples flow rate measurement with mass balance calculations has been used to evaluate the geochemical evolution and kinetic behavior of Laurel Creek, West Virginia as it flows from a siliceous, noncarbonate caprock onto the Greenbrier Group Limestones, into and through the Laurel Creek‐Cross Road Cave System, and out of the spring at the lower end of the system. At a discharge of 1.0 m3 s−1, the stream was calculated to be removing calcite from the aquifer by dissolution at a rate of 4.1 mg 1−1 hr−1, for a total removal of 46 kg CaCO3/hr. Laurel Creek remained undersaturated with respect to calcite throughout the entire reach studied. Comparison of calculated saturation states with laboratory based kinetic mechanism information provided by the work of Plummer et al. (1978) suggests that the elementary reaction that describes attack by carbonic acid dominates calcite dissolution within the main conduit portion of the flow system.
Salt‐Water Upconing in an Aquifer Overlain by a Leaky Confining Bed
Authors: Motz Louis H. 
Published: August 2005

AbstractSalt‐water upconing that occurs in an aquifer overlain by a leaky confining bed is described in terms of an analytical model that assumes the existence of a sharp interface between the fresh water and salt water and the occurrence of a critical rise in the interface, above which only an unstable cone can exist. Drawdown is calculated along the salt‐water/fresh‐water interface due to pumping from a well that partially penetrates the fresh‐water zone, and then the Ghyben‐Herzberg relation is used to calculate the steady‐state rise in the interface, which is assumed to be small compared to the thickness of the aquifer. The interface rise and the critical pumping rate (Qc) are determined in terms of aquifer and confining bed properties and the degree of penetration of the pumping well into the fresh‐water zone. The critical rise is assumed to occur when the interface rise is equal to 0.3 times the distance from the original interface location to the bottom of the well. Based on the analytical model, the nondimensional critical pumping rate increases as the ratio of vertical to horizontal hydraulic conductivity (Kz/ Kr) is decreased, and it decreases as the degree of well penetration (t/b) is increased. As an example application, Qc was calculated using site‐specific data from a test well in Pasco County, Florida. A value of Qc= 4.28 × 105 cubic feet per day was determined by assuming that Kz/Kr= 1.0. If Kz/Kr were subsequently determined to be less than or greater than 1.0, then the estimated value of Qc would be increased or decreased, respectively.
Comparison of Flow Models Used to Delineate Capture Zones of Wells:
Authors: Bair E. Scott , Roadcap George S. 
Published: August 2005

AbstractAnalytical, semianalytical, and numerical flow models of a leaky‐confined fractured‐carbonate aquifer were used with particle‐tracking/stream‐function programs to delineate traveltime‐related capture zones of a municipal wellfield and to assess “model” errors imposed by requisite assumptions associated with each flow model. The analytical flow model uses the Hantush‐Jacob equation describing two‐dimensional transient drawdown surrounding a well in a leaky‐confined aquifer with superposition of a nonuniform regional flow field. The semianalytical flow model employs the Thiem equation describing two‐dimensional steady‐state drawdown surrounding a well in a fully confined aquifer with superposition of a uniform regional flow field. The numerical flow model uses a finite‐difference solution describing three‐dimensional steady‐state flow and incorporates five model layers, specified‐flux boundary conditions, spatially variable recharge, and recharge from a lake. Goodness‐of‐fit statistics show that the semianalytical flow model does not calibrate as well to measured heads as do the analytical and numerical flow models. Model errors caused by the inability of the semianalytical flow model to account for vertical leakage and by the required use of a uniform regional flow field cause the size of the five‐year capture zone to be overestimated and its shape to be too simplistic compared to those of the analytical and numerical flow models. Polar plots of reverse‐tracked pathline endpoints suggest that model error also produces significant differences in pathline trajectories. The results show that in this type of hydrogeologic setting, it is necessary to use a flow model that accounts for vertical leakage and for the nonuniform character of the regional flow field.
Methanogenic Biodégradation of Creosote Contaminants in Natural and Simulated Ground‐Water Ecosystems
Authors: Godsy E. Michael , Goerlitz Donald F. , Grbic‐Galic Dunja 
Published: August 2005

AbstractWastes from a wood preserving plant in Pensacola, Florida have contaminated the near‐surface sand‐and‐gravel aquifer with creosote‐derived compounds and pentachlorophenol. Contamination resulted from the discharge of plant waste waters to and subsequent seepage from unlined surface impoundments that were in direct hydraulic contact with the ground water. Two distinct phases resulted when the creosote and water mixed: a denser than water hydrocarbon phase that moved vertically downward, and an organic‐rich aqueous phase that moved laterally with the ground‐water flow. The aqueous phase is enriched in organic acids, phenolic compounds, single‐ and double‐ring nitrogen, sulfur, and oxygen containing compounds, and single‐ and double‐ring aromatic hydrocarbons. The ground water is devoid of dissolved O2, is 60–70% saturated with CH4 and contains H2S. Field analyses document a greater decrease in concentration of organic fatty acids, benzoic acid, phenol, 2‐, 3‐, 4‐methylphenol, quinoline, isoquinoline, l(2H)‐quinolinone, and 2(lH)‐isoquinolinone during downgradient movement in the aquifer than could be explained by dilution and/or dispersion. Laboratory microcosm studies have shown that within the study region, this effect can be attributed to rnicrobial degradation to CH4 and CO2. A small but active methanogenic population was found on sediment materials taken from highly contaminated parts of the aquifer.
The Use of Solute and Isotopic Chemistry to Identify Flow Patterns and Factors Which Limit Acid Mine Drainage in the Wasatch Range, Utah
Authors: Mayo Alan L. , Nielsen Peter J. , Loucks Mark , Brimhall Willis H. 
Published: August 2005

AbstractIn this case study, we have demonstrated how a minimal amount of relatively inexpensive isotopic data can be used to help solve a complex Hydrogeologie problem.Acidic (pH 3 to 4) and neutral (pH 6.0 to 7.7) mine drain waters have been identified and sampled in the mining districts in the central Wasatch Range of Utah. The chemical evolution of acid and neutral mine waters follow fundamentally different chemical and isotopic evolutionary pathways which reflect fundamentally different flow histories. Most neutral mine discharges are either low iron calcium‐bicarbonate waters or iron and sulfate rich waters. Stable isotopic values of δ2 H and δ18 O plot near and parallel to the meteoric water line (MWL), suggesting a meteoric origin for all mine waters. 3H concentrations (20.9 to 40.8 TU) and 14C activities (46.2 to 96.3 pmc) indicate mine waters have a major component of modern recharge water. Shallow circulation of most mine discharges is suggested by low TDS, nonthermal discharge temperatures and the proximity of most mine workings to the surface.The δ34 S values of mine discharge waters tend to cluster about two nodes. Neutral mine drainages with low SO42‐ contents cluster about δ34 S = 0/o, whereas neutral mine drainages with high Sü42 contents cluster about δ34S =+5.5%o. An acid mine drainage also has a 534 S value of about 0 %o. δ34 S values of ∼ 0 %o are attributed to the oxidation ofpyrite and other sulfide minerals, whereas more positive isotopic values are attributed to isotopic fractionation accompanying the dissolution of gypsum and anhydrite. Only mine discharges with a δ34S δ 0%o have the potential to produce acid drainage. Geologic and δ13C data suggest acid mine waters (mean δ13C =−15.0%o) discharge from ground‐water flow systems generally devoid of carbonate rocks. Neutral mine waters (mean δ13C =− 9.7%o) discharge from aquifers containing abundant carbonate rocks which neutralize excess H+ ions released by the oxidization of sulfide minerals.
Sealing Characteristics of Selected Grouts for Water Wells
Authors: Edil Tuncer B. , Chang Michael M. K. , Lan L. T. , Riewe Thomas V. 
Published: August 2005

AbstractSealing characteristics of commonly used water well annular space grouts were investigated using a large‐scale laboratory model. The investigation was carried out in two phases. In the first phase, a bentonite drilling mud, often used as a well sealant, was investigated both in the laboratory well model and in the field. For this purpose, Quik‐Gel® mud with different amounts of formation material (in this case sand) entrained in it was used as a sealant. In the second phase, an evaluation of four grouts: neat cement, bentonite‐cement, powder bentonite (Volclay®), and granular bentonite (Benseal® and bentonite slurry mixed according to the “Ohio” recipe) was undertaken with respect to their effectiveness in sealing the annular space. A well model consisting of a sand‐filled plexiglass container was constructed in this investigation. Four metal well casings were installed in boreholes formed in the sand. The annular space between the well casings and the boreholes formed in the sand were filled with various grouts. The effectiveness of these materials in sealing the annular space was evaluated by observation of their structural stability, infiltration of water placed on top of the sealants, and inspection of the sealants dissected during disassembling of the models. A finite‐element computer program modeling the seepage in these well experiments was used to assist in the interpretation of the experimental results. The results indicate that the final success of a sealant depends on its structural stability as much as its permeability. Benseal®‐bentonite slurry grout behaved best; neat cement and bentonite‐cement grouts also provided good seals. Volclay® and various Quik‐Gel® slurries formed poorer seals compared to these. Among the Quik‐Gel® slurries, best results were obtained in the laboratory when a Marsh Funnel Viscosity of about 70 sec/qt was achieved and a mud weight of about 10 to 11 Ib/gal resulted from mixing of formation soils. However, field observations of drilling mud slurries with entrained cuttings exhibited problems of excessive settling even when the slurries had heavy mud weight, greater than 11 Ib/gal. The extent of settling appears to be positively correlated with the relative permeability of the native formation. This limits the types of well construction where these slurries may be used as annular space seal.
A Code to Generate Random Identifiers and Select QA/QC Samples
Authors: Mehnert Edward 
Published: August 2005

AbstractSAMPLID is a PC‐based, FORTH AN‐77 code which generates unique numbers for identification of samples, selection of QA/QC samples, and generation of labels. These procedures are tedious, but using a computer code such as SAMPLID can increase efficiency and reduce or eliminate errors and bias. The algorithm, used in SAMPLID, for generation of pseudorandom numbers is free of statistical flaws present in commonly available algorithms.
Vapor Extraction of Volatile Organic Compounds from Clay Soil: A Long‐Term Field Pilot Study
Authors: Gibson Thomas L. , Abdul Abdul S. , Glasson William A. , Ang Carolina C. , Gatlin Dallas W. 
Published: August 2005

AbstractA vapor‐extraction method was evaluated for remediation of clay soil contaminated by a paint thinner, consisting of a mixture of volatile aromatic hydrocarbons. Natural clays have low permeability to liquid or gas flow, and remediation by in situ methods is usually considered inappropriate. However, successful vapor flow through the clay was predicted on the basis of laboratory studies showing increased clay porosity and fracturing in the presence of organic solvents. A vapor extraction pilot study was conducted in a test area containing an estimated 1780 kg of paint thinner. The site was instrumented with vapor extraction wells and numerous soil vapor and pressure monitoring wells to delineate the zone of reduced pressure and sample the soil gases within the test site. Monitoring for eight months indicated that the contaminated clay was permeable to air and vapor flow with an effective range of influence extending 20 ft from the vapor extraction well and that 19% of the initial paint thinner was removed.
A Numerical Model for Water Flow and Chemical Transport in Variably Saturated Porous Media
Authors: Yeh T.‐C. Jim , Srivastava Rajesh , Guzman Amado , Harter Thomas 
Published: August 2005

AbstractA two‐dimensional numerical model is developed for the simulation of water flow and chemical transport through variably saturated porous media. The nonlinear flow equation is solved using the Calerkin finite‐element technique with either the Picard or the Newton iteration scheme. A continuous velocity field is obtained by separate application of the Galerkin technique to the Darcy's equation. A two‐site adsorption‐desorption model with a first‐order loss term is used to describe the chemical behavior of the reactive solute. The advective part of the transport equation is solved with one‐step backward particle tracking while the dispersive part is solved by the regular Galerkin finite‐element technique. A precondi tioned conjugate gradient‐like method is used for the iterative solution of the systems of linear simultaneous equations to save on computer memory and execution time. The model is applied to a few flow and transport problems, and the numerical results are compared with observed and analytic values. The model is found to duplicate the analytic and observed values quite well, even near very sharp fronts.