bluuebunny/crossref_metadata_2025_split huggingface dataset:
Site Characterization by Neuronets: An Application to the Landfill Siting Problem
Authors: Basheer Imad A. , Reddi Lakshmi N. , Najjar Yacoub M. 
Published: August 2005

AbstractFor a large number of geotechical/ground‐water applications, determining the spatial distribution of the subsoil properties constitutes a major challenge in both design and construction phases. Models that are frequently used for characterization of site properties emphasize the use of probabilistic models that incorporate a number of model parameters to be evaluated. In this paper, neural networks (or neuronets) are used to map the variation of permeability for purposes of identifying boundaries of landfill to be constructed on a real site. The neural network, as a simple technique, was found to be able to logically predict the variation. The sensitivity of the produced permeability maps to both the quality and number of observations was also studied to investigate the accuracy of the proposed mapping methodology. The use of neuronets as a mapping tool can help identify the regions within a site where additional subsoil exploration is warranted.
Extension of the “Pore Tree” Model to Describe Transport in Soil
Authors: Simons Girard A. 
Published: August 2005

AbstractThe “pore tree” model of pore structure was originally developed for catalyst and sorbent grains to allow coupled reactions and diffusion into and out of nonpermeable porous media in the absence of convection through the media. The pore tree model is extended herein to describe the permeable pore structure which characterizes the subsurface transport of gas and water in soil, the dispersion of contaminants, and in situ remediation. The interconnectivity of the pore structure is obtained via a statistical determination of the “branches” that are common to several trees to allow convection and diffusion through the large scale (permeable) structure in addition to diffusion and reactions in the smaller scale (nonpermeable) structure. The extended pore tree model has successfully explained measurement errors in the permeability of soil due to the measurement scale size and has successfully predicted the bulk gaseous diffusivity in partially saturated soil as a function of a saturation scale size. The extended pore tree model provides an analytic description of the pore structure of soil upon which bulk transport, small scale diffusion, and coupled chemical reactions may be added to accurately describe contaminant transport and in situ remediation.
A Two‐Dimensional MODFLOW Numerical Approximation of Mise‐A‐La‐Masse Electrical Flow Through Porous Media
Authors: Osiensky James L. , Williams Roy E. 
Published: August 2005

AbstractTwo‐dimensional, finite‐difference, saturated, ground‐water flow models such as MODFLOW can be useful in simulating “mise‐a‐la‐masse” electrical flow through conductive porous media. A new technique for using an existing numerical code to develop an approximate solution for point source electrical flow is presented. Incorporating a change in variables from ground‐water flow to electrical flow within the MODFLOW input file allows the ground‐water flow code to model the effects of resistivity contrasts directly. By adjusting the input data as presented herein, spherical electrical flow through contaminated porous media can be approximated in two dimensions.
A New Method to Determine Storage Coefficient from Pumping Test Recovery Data
Authors: Banton Olivier , Bangoy Lumony Mulongo 
Published: August 2005

AbstractA new method is presented to determine the transmissivity and the storage coefficient from recovery data measured after a pumping period of an aquifer test. Previously available methods can determine the storage coefficient during the pumping period only or under restrictive conditions. This method requires observations from a minimum of two points (e.g., the pumping well and an observation well). For each time during recovery, the drawdowns observed in the two wells are first plotted with regard to the distance from the pumping well centrum, giving an intercept A and a slope B for each pair of data. The plot of A values with regard to time allows to calculate the transmissivity value, while the plot of B values versus time gives the storage coefficient value. The method is applied to two sets of field data, and the results obtained are close to those obtained using the classical methods (Theis or Jacob) applied to the drawdown data obtained during the pumping period. This method well determines transmissivity and storativity from recovery data obtained at short times after the completion of pumping, i.e., for times shorter than those which can be used by the Cooper‐Jacob approximation.
Subsurface Stormflow Modeling with Sensitivity Analysis Using a Latin‐Hypercube Sampling Technique
Authors: Gwo J. P. , Toran L. E. , Morris M. D. , Wilson G. V. 
Published: August 2005

AbstractDuring storm events, the shallow disposal facilities at Oak Ridge National Laboratory become inundated, and subsurface stormflow may intermittently extract radionuclides from the surrounding soils and the wastes themselves. It is estimated that 90% of the rain water infiltrating the soil horizons becomes subsurface stormflow, yet stormflow is a poorly understood process. The objectives of this research are to model stormflow: (1) to identify important parameters for waste site monitoring and data collections; (2) to evaluate remediation designs; and (3) to investigate the effect of local heterogeneities on stormflow paths. Numerical models of a proposed waste disposal site were developed, and a Latin‐hypercube simulation technique was used to study the uncertainty of model parameters. Sensitivity analyses of model parameters suggested that hydraulic conductivity was the most influential parameter. However, local heterogeneities may alter flow patterns and result in complex recharge and discharge processes. Hydraulic conductivity, therefore, may not be used as the only reference for subsurface flow monitoring and engineering designs. Neither of two engineering designs, capping and French drains, was found to be effective in hydrologically isolating downslope waste trenches. However, combinations of both designs may prove more effective than either one alone.
Seepage Relationships Between Lake Chad and the Chad Aquifers
Authors: Isiorho S. A. , Matisoff G. , Wehn K. S. 
Published: August 2005

AbstractLake Chad, a closed basin lake, is the only large surface‐water body in the African Sahel. Future water resource development in the Chad Basin requires an understanding of the hydrogeology of the basin. In this paper we examine the hydraulic relationship between the lake and the phreatic aquifer of the Chad Formation. Electrical resistivity data from 30 surveys were combined with over 60 open well measurements to construct a water‐table map of the southwestern quadrant of the lake. The map indicates that the Lake Chad water level is at a higher hydraulic level than the phreatic aquifer and that the ground‐water flow is southwest, away from the lake. The average measured seepage rate into the phreatic aquifer in the southwestern and southern parts of the lake was 7.1 × 10−3 m/d (median = 1.3 × 10−3 m/d) which is about 21% of the annual water input to the lake. This measured seepage flux (9.96 × 109 m3/yr) can account for about 107% of the annual solute input to the lake. Solute transport model simulations indicate about 32% (15.3 × 109 m3/yr) of the input water and 152% (2.87 × 1012 g/yr) of the total solute input can be removed by ground‐water recharge (seepage) from the lake. These results provide an explanation to account for the freshness of Lake Chad's water despite its surficial closed basin geologic setting: solutes delivered to the lake via surface‐water inflow leave the lake via ground‐water recharge. These results also indicate recharge from the lake (∼ 1010 m3/yr) represents an enormous amount of water available as a ground‐water resource in the African Sahel.
Variations in Capture‐Zone Geometry of a Partially Penetrating Pumping Well in an Unconfined Aquifer
Authors: Bair E. Scott , Lahm Terry D. 
Published: August 2005

AbstractDesign of effective and efficient pump‐and‐treat systems requires capture zones of recovery wells to closely circumscribe the contaminant plume. Overestimation of capture zones incurs the undesired expense of treating clean water. Underestimation of capture zones enables contaminants to escape downgradient. Recovery wells in unconfined aquifers commonly penetrate only part of the aquifer either because of its large saturated thickness or the shallow vertical extent of contamination. The capture‐zone geometry of a partially penetrating pumping well can differ greatly from that of a fully penetrating one because of vertical flow components near the well. The differences in geometry are far greater if the medium is anisotropic (Kh≠ Kv).To estimate the capture‐zone geometry of a partially penetrating pumping well, a steady‐state, finite‐difference model was constructed to simulate flow to a well in a regional flow system. The model was used to simulate differences in the velocity field created by changes in (1) the depth of well penetration, (2) the magnitude of the regional hydraulic gradient, and (3) the degree of anisotropy. Following each simulation particle tracking was performed to determine the maximum width, depth, and distance to the stagnation point of the capture zone. Graphs were developed between capture‐zone width, relative capture‐zone depth, distance to the stagnation point, versus the ratio of Q/q (pumping rate/specific discharge). The graphs enable estimates to be made of these geometric parameters for a variety of pumping rates, regional hydraulic gradients, hydraulic conductivities, anisotropy ratios, and degrees of partial penetration. The results show that for isotropic conditions, particularly for small ratios of Q/q and wells that penetrate less than 40 percent of the aquifer, the shape of a capture zone can deviate significantly from that of a fully penetrating well. For anisotropic conditions, these differences are more pronounced and apply to a wider range of Q/q ratios and well penetration depths.In sequences of sediment, anisotropy is produced by textural, architectural, and stratigraphic elements that occur at different scales. Capture zones should be estimated using Kh:Kv ratios determined from pumping tests. This assures that the measured degree of anisotropy is commensurate with the scale of elements encountered by the stress created by a pumping well. Tabulated Kh:Kv ratios from analysis of pumping tests in unconfined aquifers suggest there are few isotropic sand and gravel aquifers. Recognition of this characteristic and consideration of the effects of partial penetration and regional hydraulic gradient on the geometry of capture zones may lead to the design of more efficient and effective pump‐and‐treat systems.
A Controlled Field Test of Surfactant‐Enhanced Aquifer Remediation
Authors: Fountain John C. , Starr Robert C. , Middleton Thomas , Beikirch Michael , Taylor Craig , Hodge Dennis 
Published: August 2005

AbstractThe presence of dense nonaqueous phase liquids is one of the principal problems associated with current ground‐water remediation efforts. Standard pump‐and‐treat methods are ineffective largely because of the low aqueous solubilities of DNAPL components. Surfactants can increase DNAPL solubility and hence have the potential for increasing the rate of DNAPL dissolution in pump‐and‐treat systems. To test the effectiveness of surfactants under field conditions, a controlled field test at Canadian Forces Base Borden was undertaken. Results indicate surfactant‐enhanced aquifer remediation can rapidly remove the majority of DNAPL using simple modifications of a pump‐and‐treat system. As in all pump‐and‐treat systems, the efficiency is a function of the hydraulic conductivity. The persistence of high DNAPL concentrations at specific elevations within the aquifer throughout the test indicates that little vertical movement of DNAPL occurred as a result of the introduction of the surfactant. Since the test was stopped when small amounts of DNAPL still remained, the limit of removal was not investigated.
Aquifer Response to Record Low Barometric Pressures in the Southeastern United States
Authors: Landmeyer James E. 
Published: August 2005

AbstractA late‐winter cyclone classified as one of the most intense of the 20th century moved across the Southeastern states of Georgia and South Carolina and onto the Northeast during March 12–14, 1993. Record low barometric pressures were recorded in Augusta, Georgia (28.93 inches of mercury) and Columbia, South Carolina (28.63 inches of mercury) on March 13, 1993, and pressures returned to normal values (near 30 inches of mercury) within one day following these record lows. This relatively unusual event provided an opportunity to examine the attendant water‐level response in continuously monitored ground‐water wells in regional Atlantic Coastal Plain, Piedmont, and Blue Ridge aquifers in the Southeast. Water levels in all wells examined responded inversely to the short duration, extreme drop in barometric pressure. Barometric efficiencies (Δground‐water level/Δbarometric‐pressure level) calculated were dependent on depth to screened‐ or open‐interval midpoint (highest correlation coefficient, r2= 0.89) and, to a lesser extent, total thickness of confining material above the aquifer tapped (highest r2= 0.65). Wells in crystalline‐rock aquifers had a correlation with depth to open‐interval midpoint (r2= 0.89) similar to the sedimentary aquifers examined. The magnitude of barometric efficiency was also strongly related to a well's increased distance from aquifer outcrop areas in the Cretaceous aquifers in South Carolina (r2= 0.95) and the upper Brunswick aquifer in Georgia (r2= 0.90), because these aquifers are more deeply buried toward the coast. This relation between barometric efficiency, well depth, and extent of confinement suggests that barometric efficiency determinations can provide useful information to hydrologists concerned with examining an aquifer's degree of confinement and corresponding isolation from land surface, particularly when the aquifer is used as a source for public supply.
Numerical Simulation of Deep‐Well Injection in Geismar, Louisiana
Authors: Jin Peikang , Barber Michael E. , Flowers George C. 
Published: August 2005

AbstractIndustrial waste water has been injected into a permeable part of the Upper Miocene injection reservoirs near Geismar, Louisiana since 1971. The injection zone is a series of alternating extremely permeable sands and impermeable clays, hydraulically isolated from the surficial aquifer system by a thick layer of clay, which acts as a confining layer. The study area encompasses four industrial facilities and 12 active injection wells. Numerical simulations were performed to evaluate injection‐well design and potential for movement of injected waste water within the hydrogeologic system. Numerical modeling was conducted in both cylindrical coordinates and Cartesian coordinates. A convection cell developed around a single prototype injection well in cylindrical‐coordinate system with a buoyant injection rising to form a lens within the injection zone. Around an ideal, fully penetrating well cased into the injection sand and open from a depth of 5,056 feet to 5,456 feet, simulations show the injectant moves upward to a depth of 4,866 feet, forms a lens about 400 feet thick, and spreads radially outward to a distance of 1,670 feet after 10 years. Comparison simulations of injection through wells having open depth intervals of 5,056 to 5,256 feet and 5,256 to 5,456 feet demonstrate that such changes in well design have little effect on the areal spread of the injectant lens or the rate of upward movement. Multiple injection well simulations in Cartesian coordinates indicate that about 5,10, and 80 percent of the study area would be underlain by injected waste water after 10,20, and 100 years of injection, respectively. Outward movement of waste water proceeds even after injection stops. The rate of outward movement under the post‐operational period (after injection ceases) is much smaller than under the operational period (injection period).
Two‐Dimensional Advective Transport in Ground‐Water Flow Parameter Estimation
Authors: Anderman Evan R. , Hill Mary C. , Poeter Eileen P. 
Published: August 2005

AbstractNonlinear regression is useful in ground‐water flow parameter estimation, but problems of parameter insensitivity and correlation often exist given commonly available hydraulic‐head and head‐dependent flow (for example, stream and lake gain or loss) observations. To address this problem, advective‐transport observations are added to the ground‐water flow, parameter‐estimation model MODFLOWP using particle‐tracking methods. The resulting model is used to investigate the importance of advective‐transport observations relative to head‐dependent flow observations when either or both are used in conjunction with hydraulic‐head observations in a simulation of the sewage‐discharge plume at Otis Air Force Base, Cape Cod, Massachusetts, USA. The analysis procedure for evaluating the probable effect of new observations on the regression results consists of two steps: (1) parameter sensitivities and correlations calculated at initial parameter values are used to assess the model parameterization and expected relative contributions of different types of observations to the regression; and (2) optimal parameter values are estimated by nonlinear regression and evaluated. In the Cape Cod parameter‐estimation model, advective‐transport observations did not significantly increase the overall parameter sensitivity; however: (1) inclusion of advective‐transport observations decreased parameter correlation enough for more unique parameter values to be estimated by the regression; (2) realistic uncertainties in advective‐transport observations had a small effect on parameter estimates relative to the precision with which the parameters were estimated; and (3) the regression results and sensitivity analysis provided insight into the dynamics of the ground‐water flow system, especially the importance of accurate boundary conditions. In this work, advective‐transport observations improved the calibration of the model and the estimation of ground‐water flow parameters, and use of regression and related techniques produced significant insight into the physical system.
Advection‐Dispersion Analysis of Solute Transport in Undisturbed Soil Monoliths
Authors: Jensen Karsten Høgh , Destouni Georgia , Sassner Mona 
Published: August 2005

AbstractThe results of an extended analysis of the chloride breakthrough curves (BTCs) obtained from transport experiments on undisturbed soil monoliths previously reported by Sassner et al. (1994) are discussed. Parameter values for different forms of the advection‐dispersion equation (ADE) were obtained by curve‐fitting using the nonlinear least‐squares optimization code CXTFIT developed by Parker and van Genuchten (1984). Good fits to the experimental BTCs from the individual soil monoliths were obtained for three different forms of the ADE, allowing for anion exclusion, immobile water, and both of these processes, respectively. Although the more complex forms of the ADE possess more flexibility to provide a slightly more refined fit to the individual breakthrough curves, larger uncertainty is associated with the fitted parameter values. Due to the limited amount of information manifested in the BTCs it is not possible on the basis of this information to distinguish which of the models is physically more meaningful. Furthermore, when more parameters are included in the optimization procedure, the resulting values are more uncertain. The same ADE models were also fitted with equally good results to a hypothetical large‐scale BTC derived by flux‐averaging the responses from the individual monoliths. However, regardless of the form of the ADE used, the resulting parameter values for the large‐scale transport (i.e., not only the dispersivity value that is expected to increase) were inconsistent with the corresponding parameter values obtained for the individual BTCs. This supports previous indications that ADE models may not be accurate for predicting large‐scale transport in heterogeneous soil systems corresponding to e.g. the scale of an agricultural field or a grid element in a numerical catchment model because model parameters are not determinable from independent measurements on a scale corresponding to a practical manageable core size or to standard intrumentation.
Determination of Nonvolatile Organic Carbon in Aquifer Solids After Carbonate Removal by Sulfurous Acid
Authors: Heron G. , Barcelona M. J. , Andersen M. L. , Christensen T. H. 
Published: August 2005

AbstractThe precise determination of total organic carbon (TOC) in aquifer materials is important in the estimation of retardation coefficients for organic compound transport. Commonly used methods for TOC determination after carbonate removal by acidification include: weight loss on ignition of solids at 550° C, acid‐dichromate oxidation, and combustion at 800–950° C. Since carbonate carbon frequently is more abundant than organic carbon all TOC methods depend on efficient and complete carbonate removal prior to the TOC quantification step. A method for the determination of TOC in aquifer solids involving carbonate removal by 0.73 M sulfurous acid and subsequent combustion at 800° C was tested on solids from three aquifers and on mineral standards. The carbon quantification by combustion and infrared detection of CO2 was accurate at solid organic carbon contents between 30 and 10,000 μgC/g. The acid treatment added small amounts of carbon to the sample, and siderite removal was incomplete. For samples without siderite or dolomite, the accuracy of TOC determinations was enhanced by grinding the solids. Measurement of very low TOC contents (50–100 /μgC/g) requires supplementary testing of grinding and acid treatment effects.
PMFCT‐2D: A Transport Simulator for Various Grid Peclet Numbers
Authors: Aimo N. J. , Oostrom M. 
Published: August 2005

AbstractSolute transport simulation using numerical models is an important and widespread tool for evaluation of clean‐up strategies as well as for prediction of future transport. Classical simulation algorithms for advective‐dispersive transport usually introduce large numerical errors where concentrations are lowest. In general, numerical errors tend to spread (disperse) the solute more than physical processes alone. For simulations where the Peclet number (Pe) is greater than about 2, numerical dispersion can be very significant and could lead to erroneous conclusions. Recent numerical techniques for simulating advective transport minimize numerical errors and provide much better solutions. One such technique, Flux‐Corrected Transport (FCT), can preserve sharp concentration fronts by virtually eliminating numerical dispersion. In general, it has been observed that as more detailed knowledge of subsurface flow fields is obtained, smaller dispersivity values are needed to match observed and simulated data. However, for many numerical codes the use of small dispersivities is not practical, because it requires fine grids to keep the grid Peclet number limited. A general purpose transport code, PMFCT‐2D, has been developed, including a fast and efficient FCT algorithm, to simulate advective‐dispersive transport in variably saturated, heterogeneous porous media, with nonuniform aquifer thickness in the third dimension. PMFCT‐2D can be used to accurately simulate high Peclet number transport, including purely advective transport (Pe =∞), resulting from transient or steady‐state flow conditions. The code is easily coupled to any flow simulator via generated velocity, saturation, and cell thickness fields.