bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessment of Methods and Conditions to Locate Boundaries: I. One or Two Straight Impervious Boundaries
Authors: Chapuis Robert P. 
Published: August 2005

AbstractA straight impervious boundary within an ideal confined aquifer may be detected in the semilog drawdown graph of an observation well. This paper gives and assesses two known and one proposed equations that may help to determine the location and orientation of an impervious boundary. Then the two conditions for an adequate detection are established. First, if the distance of the pumping well to the boundary is called “a,” only those observation wells at a distance smaller than a/5 from the pumping well can detect the boundary. Second, data must be collected for approximately two time log cycles after the slope has changed in the drawdown graph. Similar equations, and time or distance conditions, are given for the case of two intersecting straight impervious boundaries. Frequently, the two conditions are not met. In this case, the drawdown graphs give incorrect estimates of aquifer parameters. In most field conditions, a combination of drawdown data, geophysical surveys, and exploratory boreholes is mandatory to locate one or two impervious boundaries. Available methods and a proposed one for recharge boundaries are assessed in a companion paper.
Hydrochemistry of the Mahomet Bedrock Valley Aquifer, East‐Central Illinois: Indicators of Recharge and Ground‐Water Flow
Authors: Panno S. V. , Hackley K. C. , Cartwright K. , Liu C. L. 
Published: August 2005

AbstractA conceptual model of the ground‐water flow and recharge to the Mahomet Bedrock Valley Aquifer (MVA), east‐central Illinois, was developed using major ion chemistry and isotope geochemistry. The MVA is a “basal” fill in the east‐west trending buried bedrock valley composed of clean, permeable sand and gravel to thicknesses of up to 61 m. It is covered by a thick sequence of glacial till containing thinner bodies of interbedded sand and gravel. Ground water from the MVA was found to be characterized by clearly defined geochemical regions with three distinct ground‐water types. A fourth ground‐water type was found at the confluence of the MVA and the Mackinaw Bedrock Valley Aquifer (MAK) to the west.Ground water in the Onarga Valley, a northeastern tributary of the MVA, is of two types, a mixed cation‐SO42‐ type and a mixed cation‐HCO3 type. The ground water is enriched in Na+ Ca2+, Mg2+, and SO42‐ which appears to be the result of an upward hydraulic gradient and interaction of deeper ground water with oxidized pyritic coals and shale. We suggest that recharge to the Onarga Valley and overlying aquifers is 100% from bedrock (leakage) and lateral flow from the MVA to the south.The central MVA (south of the Onarga Valley) is composed of relatively dilute ground water of a mixed cation‐HC03 type, with low total dissolved solids, and very low concentrations of Cl‐ and SO42‐. Stratigraphie relationships of overlying aquifers and ground‐water chemistry of these and the MVA suggest recharge to this region of the MVA (predominantly in Champaign County) is relatively rapid and primarily from the surface.Midway along the westerly flow path of the MVA (western MVA), ground water is a mixed cation‐HCO3‐ type with relatively high Cl‐, where Cl‐ increases abruptly by one to two orders of magnitude. Data suggest that the increase in Cl‐ is the result of leakage of saline ground water from bedrock into the MVA. Mass‐balance calculations indicate that approximately 9.5% of recharge in this area is from bedrock. Concentrations of Na+, HCO3‐, As, and TDS also increase in the western MVA.Ground water in the MAK is of a Ca2+‐HCO32‐ type. Mass‐balance calculations, using Cl‐ as a natural, conservative tracer, indicate that approximately 17% of the ground water flowing from the confluence area is derived from the MVA.
One‐Dimensional Moving Finite‐Element Model of Solute Transport
Authors: Gottardi G. , Venutelli M. 
Published: August 2005

AbstractSolute transport problems with sharp transitions or high advection are difficult to solve with traditional finite‐difference (FD) and finite‐element (FE) techniques. When advection dominates, the solutions obtained by these traditional methods typically suffer numerical smearing or oscillations. In these cases, acceptable numerical solutions of the classical advection‐dispersion equation by FE and FD techniques can be obtained only by using a fine discretization on space and time that allows the stability requirements expressed by the Courant and Peclet numbers to be satisfied. This leads to large computer times. A way for overcoming this problem is to use a moving‐grid method. The dynamically self‐adaptive moving finite‐element (MFE) grid method, used in this work, obtains accurate and efficient solutions of the advection‐dispersion equation in a very wide range of Courant and Peclet numbers. The MFE method accurately simulates, with no oscillations, very steep fronts using space and time step sizes well beyond conventional constraints of the Peclet and Courant numbers. To demonstrate the accuracy and efficiency of the MFE method, some test cases are presented where the MFE, FD, and analytical solutions are compared.
An Investigation of the Relationship Between Actual and Apparent Gasoline Thickness in a Uniform Sand Aquifer
Authors: Ballestero Thomas P. , Fiedler Fritz R. , Kinner Nancy E. 
Published: August 2005

AbstractA common effort involved in the remediation of contamination by petroleum hydrocarbons in porous media is the monitoring and volume estimation of the immiscible hydrocarbon fluid. The apparent free product thickness indicated by a standard monitoring well is typically much greater than the actual free product thickness in the surrounding soil. This results in significant errors in estimates of drainable fluid (product) volume, which in turn leads to inaccuracies (i.e., over design, improper pump sizing, etc.) with remediation system design.An equation to predict actual thickness was developed using heterogeneous fluid flow mechanics and hydrostatics. This equation is: tg= t(l – Sg) ‐ ha, where tg= actual formation free product thickness, t = apparent (well bore product) thickness, Sg= specific gravity of petroleum hydrocarbon (gasoline in this research), and ha= distance between the ground‐water table and the free product in the formation.The developed theory was compared to data collected from a physical model which simulated field conditions. The theory was used to estimate product thickness in the model, and then these estimates were statistically tested for accuracy. The theoretical slope, (1 – Sg), was not statistically different from the regression slope at test levels of α= 0.05 and α= 0.01, while the theoretical intercept (ha) was statistically different at α– 0.05 and α– 0.01. The discrepancy between the theoretical intercept and the regression intercept was probably due to either an incorrect assumption that ha= hc (hc= average wetting capillary rise), or an incorrect laboratory measurement of hc.The effects of water‐table fluctuations were also studied. A rising water table caused a decrease in apparent thickness and an increase in actual thickness, and vice versa. No theoretical equation was developed for the effects of water‐table fluctuations, but it was reasoned that hysteresis of the saturation curve and adsorption were the primary factors in the observed trends.Finally, the developed theoretical equation was compared to the results of previously published predictive methods and experiments. The comparison was made by calculating percent error and using a chi‐square statistic. The developed theory was found to be the best predictor of actual product thickness for both laboratory data sets used.
Estimation of Solute Concentrations Using the Pathline Counting Method
Authors: Johnson Jeffrey A. , Ravi Varadhan , Rumery J. Kevin 
Published: August 2005

AbstractThe paper discusses the use of the “pathline counting” approach to estimate solute concentrations at an extraction well using particle‐tracking flow models. The pathline counting approach is a unique method for predicting solute concentrations due to mixing. The pathline counting method using the semianalytical module RESSQC, contained within the WHPA model, was compared to MT3D, a numerical mass transport code, for a simple hypothetical problem. Results from the comparison indicate that results from the pathline counting approach were in reasonable agreement with the MT3D results. This approach was then applied to a field study, the Park City Bioremediation Project. The migration of a conservative tracer injected into three upgradient cells was simulated to estimate the concentration of solute at two pumping wells. The calculated concentrations compared favorably with measured field concentrations.
Hydrothermal Estimation of Vertical Ground‐Water Flow, Cañutillo, Texas
Authors: Wade Shirley C. , Reiter Marshall 
Published: August 2005

AbstractThe vertical component of specific discharge was estimated across several depth zones in the aquifer system at Cañutillo, Texas. The specific discharge was estimated using temperature and thermal conductivity data from four observation wells bottoming near the base of the aquifer system.Specific discharge was first calculated (using a steady‐state model) from the slopes of conductive heat flow versus temperature plots. The heat flow plots for all four wells suggested a zone of downward ground‐water flow from ∼ 70 to ∼ 220 feet depth and one or two zones of upward flow from ∼ 800 to ∼ 220 feet depth. Head data from observation wells did support the conclusion of an upper zone of downflow as indicated by the temperature data; however, the head data suggested that ground water should presently be moving downward from ∼ 220 to ∼ 800 feet.A computer model was developed to determine if the temperatures may be remanent and therefore reflect prepumping ground‐water flow, particularly in the deep flow zone. Computer model estimates were made of during‐pumping downflow in the upper flow zone. For the deep flow zone computer model estimates were made of prepumping upflow. The computer model estimates and steady‐state vertical specific discharge estimates were similar for the upper zone having downward flow. In the deep zone prepumping upflow estimates modeled on the computer were the same order of magnitude as steady‐state heat flow specific discharge estimates. Hence, present temperature data may demonstrate a significant remanent groundwater flow component and therefore might be used to estimate past vertical ground‐water flow.
Nonaqueous Phase Hydrocarbon in a Fine‐Grained Sandstone: 2. Effect of Local Sediment Variability on the Estimation of Hydrocarbon Volumes
Authors: Huntley David , Wallace James W. , Hawk Robert N. 
Published: August 2005

AbstractThe exaggeration of light nonaqueous phase liquids (LNAPL), typically hydrocarbon, by monitoring wells is a well‐known problem that introduces significant errors in the estimation of recoverable hydrocarbon. Farr et al. (1990) and Lenhard and Parker (1990) show that significantly different volumes of hydrocarbon may produce the same thickness of hydrocarbon in a monitoring well, due to differences in the capillary characteristics between soil types. The purpose of our investigation was to evaluate the influence of local sediment variability on estimation of hydrocarbon volumes. Sediment samples from two sites underlain by a relatively homogeneous sandy deposit were collected within a small area. Capillary characteristic curves were determined for 10 samples from one site and 41 samples from the second site using a pressure plate. Grain‐size analysis was performed on all samples for which pressure plate data were available.The results show significant variability, even for small sites. For example, a hydrocarbon volume of three cm3/cm2 could produce anywhere between 45 and 200 cm of hydrocarbon within an observation well. This suggests that use of an “average” soil sample to characterize hydrocarbon exaggeration, within even a very small site, can lead to substantial errors. It also suggests that maps of apparent hydrocarbon thickness can be extremely misleading, leading hydrologists to place remediation wells in areas of greatly exaggerated thicknesses produced by fine‐grained materials.Comparison between characteristic curves calculated from grain‐size analysis using the approach of Mishra et al. (1989) to those measured using the pressure plate shows poor correlation that introduces large errors into the estimated hydrocarbon volumes.
An Image‐Well Method for Predicting Drawdown Distribution in Aquifers with Irregularly Shaped Boundaries
Authors: Kuo M.C.T. , Wang W. L. , Lin D. S. , Lin C. C. , Chiang C. J. 
Published: August 2005

AbstractMany analytical methods use radial and rectangular systems to interpret unsteady‐state reservoir flow problems. However, there is no information currently available for irregularly shaped aquifers. For many practical cases the aquifer drainage shape is too complicated to be approximated by a circular or rectangular shape. This paper develops an image‐well method for predicting drawdown transient in an aquifer with irregularly shaped boundaries. Previously, the use of the image‐well method to predict drawdown transient was only possible for aquifer boundaries of regular shape.In this paper, the well function is obtained by superposing the Theis solution of image wells in time. The image‐well method is first applied to regularly shaped aquifers. The validity of the approach is then proved by comparison of the calculated well functions with literature values for various regular drainage shapes. The proven method was applied to interpret a field pumping test and to characterize the reservoir boundaries with irregular shape.
Testing the Limits of ICP‐MS: Determination of Trace Elements in Ground Water at the Part‐Per‐Trillion Level
Authors: Stetzenbach Klaus J. , Amano Megumi , Kreamer David K. , Hodge Vernon F. 
Published: August 2005

AbstractAn ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.
Hydraulic Connections Among Subaquifers of the Coastal Plain Aquifer, Israel
Authors: Nativ Ronit , Weisbrod Noam 
Published: August 2005

AbstractThe intensive use of the Coastal Plain aquifer, Israel, as well as its ongoing contamination by domestic and industrial waste and agrichemicals has resulted in the deterioration of its water quality. The Coastal Plain aquifer is divided into a number of calcareous sandstone units, separated by silt and shale lenses. Whereas the shallow, uppermost units are unconfined, the lowermost aquifers are partly confined. Although the presence of hydrological subunits is geologically well‐documented, the aquifer has been traditionally managed by the Israel Water Authority as a single water system. This study focused on the deeper units of the Coastal Plain aquifer where contamination may be less significant. The hydraulic connections between the overlying shallow units and the deep units were examined along two regions parallel to the main ground‐water flow direction, from east‐southeast to west‐northwest. The working hypothesis was that if hydraulic separation by the silt and shale lenses is effective, chemical and isotopic variations can be traced, and ground‐water‐level variations in each unit are likely to be different. The observed difference in hydraulic heads, distinct patterns of temporal water‐level variations, different C‐14 and tritium activities, and diverse chemical compositions suggest that the silt and shale lenses form an effective hydraulic partition between the shallow and deep sand units, both in the western and eastern parts of the aquifer. Our limited observations indicate that although the nature of the hydraulic separation and its effects are spatially variable, the prevailing conceptualization of the aquifer as one water body lacking vertical separation is incorrect.
Use of Tension Infiltrometer Data with Unsaturated Hydraulic Conductivity Models
Authors: Nachabe Mahmood H. , Illangasekare Tissa 
Published: August 2005

AbstractA new method is presented to estimate the relationship between unsaturated hydraulic conductivity and soil‐water pressure using tension infiltrometer data. In this method, both the early transient and the subsequent quasi‐steady stages of the infiltration process underneath a tension infiltrometer disc are analyzed. Our investigation indicates that the infiltration rate at early times closely follows the aquare‐root‐of‐time relationship (Philip, 1969). This behavior permits the evaluation of the sorptivity, which is an integrated measure of soil diffusivity. At later times, three‐dimensional quasi‐steady flow beneath the infiltrometer disc develops, and the Wooding equation for flow from a circular pond is used to evaluate the sorptive number and the saturated hydraulic conductivity. Simple algebraic expressions are introduced to relate the sorptivity and sorptive number to the parameters of the Brooks and Corey model of unsaturated hydraulic conductivity. The method described here extends the utility of tension infiltrometer data to a large class of hydraulic conductivity models and provides an in situ technique to determine suitable parameters values for these models.An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.
Location Analysis in Ground‐Water Remediation Using Neural Networks
Authors: Johnson Virginia M. , Rogers Leah L. 
Published: August 2005

AbstractFormal optimization techniques, of the kind developed in operations research to aid business decision‐making, show promise as tools for controlling the high costs of ground‐water remediation. A major barrier to the adoption of these tools in the industry, however, is the burden they place on the computational resources of an organization. Whenever a new pumping strategy is considered, a flow and transport model must be called to evaluate its effectiveness. Since it is common for optimization techniques to examine hundreds of strategies, at the very least, the bottleneck caused by the modeling step quickly becomes prohibitive. A method has been developed which uses artificial neural networks to substitute for the full model, permitting millions of strategies to be evaluated within reasonable time‐frames on conventional computer equipment. This method was applied to a 28‐location pump‐and‐treat problem at a western Superfund site. Networks were first trained to predict mass‐extraction and containment information normally generated by the 2‐D model SUTRA. They were then used in an optimization procedure to identify 250 (out of over 4 million) pumping patterns which met restoration goals at minimum cost. Analyses of the winning patterns classified individual locations as popular vs. unpopular. Sensitivity analyses on each location further distinguished: (1) locations which were strong performers under most circumstances from those which depended on other locations, and (2) locations which didnt aid the cleanup from those which were actually detrimental to it. All these analyses were made possible by the rapid evaluation of patterns provided by the neural networks.
Scale Dependency of Hydraulic Conductivity Measurements
Authors: Rovey Charles W. , Cherkauer Douglas S. 
Published: August 2005

AbstractThe hydraulic conductivity of five stratigraphic units in a carbonate aquifer has been measured with slug, pressure, and pumping tests, and with two calibrated digital models. The effective test radii range from less than one to greater than 10,000 meters. On log‐log plots hydraulic conductivity increases approximately linearly with test radius to a range between 20 and 220 meters, but thereafter, it is constant with scale.The increase in magnitude of hydraulic conductivity is similar to scaling effects reported at seven additional sites in a variety of geologic media. Moreover, the increase in magnitude correlates with an increase in variance of log‐hydraulic conductivity measured at successively greater separation distances.The rate of increase in both parameters, and particularly the range, have characteristic values for different pore systems. The larger ranges are consistently present in units with greater secondary porosity. Therefore, scaling effects provide a qualitative measure of the relative importance of secondary and primary permeability, and they can potentially be used to distinguish the dominant type of pore system.
A Model for Estimating the Hydraulic Conductivity of Granular Material Based on Grain Shape, Grain Size, and Porosity
Authors: Sperry James M. , Peirce J. Jeffrey 
Published: August 2005

AbstractA model for delineating the relative importance of particle size, particle shape, and porosity, (and their interactions), in explaining the variability of hydraulic conductivity of a granular porous medium is developed and tested. Three types of porous media are considered in this work: spherical glass beads; granular sand; and irregularly shaped, shredded glass particles. A reliable method for quantifying the three‐dimensional shape and packing of large samples of irregular particles based on their angle of repose is presented. The results of column experiments indicate that in the size range examined (i.e., 149 μm to 2380 μm), the single most important predictor of hydraulic conductivity is seen to be particle size, explaining 69% of the variability. Porous media comprising irregular particles exhibit lower hydraulic conductivity only for the larger (707 to 841 μm) particles. For the smaller (149 to 177 μm) particles, particle shape has no observable influence on hydraulic conductivity. The results of the regression analysis reveal the importance of the interaction between particle size and porosity, indicating that similar pore configurations for a given type of particle are not achieved at different sizes. This empirical model seems to provide better estimates of the hydraulic conductivity of granular porous media comprising irregular particles than selected models based solely on grain size, including Hazen, Kozeny‐Carman, and more recently Alyamani and Sen.