bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deep Ground‐Water Investigation by Combined VES/MTS Methods Near Ho Chi Minh City, Viet Nam
Authors: Van Pham Ngoc , Boyer Daniele , Thoa Nguyen Thi Kim , Van Nguyen Giang 
Published: August 2005

AbstractIn the agglomeration of Ho Chi Minh City (HCMC), South Viet Nam, located near the eastern edge of the Mekong Delta, both superficial Quaternary and deep Tertiary Alluvium may contain brackish or saline water from ground surface to great depths. The combination of two complementary geophysical methods, the Vertical Electrical Sounding (VES) for shallow investigation, and the Magnetotelluric Sounding (MTS) for deep investigation, gives a more complete electrical image of the sedimentary series from the surface to the deep crystalline basement. It turned out to be very efficient in delineating the ground‐water contamination in both superficial and deep aquifers. The combined results reveal a close correlation of the extent of the contamination with the paleo‐geomorphology of laterites, and subsequently with the paleorelief during the Tertiary and Quaternary periods. A simple guide for hydrogeological investigation is proposed in connection with the present topography and the Tertiary tectonics.
Spatial Variability in Hydrologic Properties of a Volcanic Tuff
Authors: Istok J. D. , Rautman C. A. , Flint L. E. , Flint A. L. 
Published: August 2005

AbstractSpatial variability of hydrologic properties was quantified for a nonwelded‐to‐welded ash flow tuff at Yucca Mountain, Nevada, the potential site of a high‐level, nuclear waste repository. Bulk density, porosity, saturated hydraulic conductivity, and sorptivity were measured on core specimens collected from outcrops on a grid that extended vertically through the entire unit thickness and horizontally 1.3 km in the direction of ash transport from the volcanic vent. A strong, geologically determined (deterministic) vertical trend in properties was apparent that correlated with visual trends in degree of welding observed in the outcrop. The trend was accurately described by simple regression models based on stratigraphic elevation (vertical distance from the base of the unit divided by unit thickness). No significant horizontal trends in properties were detected along the length of the transect. The validity of the developed model was tested by comparing model predictions with measured porosity values from additional outcrop sections and boreholes that extended 3000 m north, 1500 m northeast, and 6000 m south of the study area. The model accurately described vertical porosity variations except for locations very close to the source caldera, where the model underpredicted porosity in the upper half of the section. The presence of deterministic geologic trends, such as those demonstrated for an ash flow unit in this study, can simplify the collection of site characterization data and the development of site‐scale models.
Interpretation of Slug and Packer Tests in Anisotropic Aquifers
Authors: Zlotnik Vitaly 
Published: August 2005

AbstractSlug and packer tests provide data for determining the local value of hydraulic conductivity in aquifers. However, most techniques commonly used for test interpretation disregard any anisotropy of the tested formation. Using dimensional analysis, an extension of available methods for interpretation of slug and packer tests to anisotropic conditions is developed. The technique is a transformation of the radial dimension via the well radius, and involves dividing the true well radius by the square root of the anisotropy ratio which must be specified a priori. This technique can be applied to formulae, computer programs, graphs, or tabulated data available for confined or unconfined isotropic conditions. It also reduces the number of computer computations. As an example, the technique is used to extend the Bouwer and Rice (1976) method, which was developed for isotropic conditions, to anisotropic conditions. A comparison of the Bouwer and Rice (1976) method corrected for anisotropy, with the Widdowson et al. (1990) method, yields horizontal hydraulic conductivities differing by 8% (in one typical case). Ignoring anisotropy for the same case results in a 44% underestimation of horizontal conductivity.
Applicability of Sharp‐Interface Models for NAPL Transport: 2. Spreading of a LNAPL
Authors: El‐Kadi Aly I. 
Published: August 2005

AbstractThis paper, the second in a two‐part series, examines the applicability of the sharp‐interface approach to modeling initial accumulation and spreading of a light nonaqueous phase liquid (LNAPL) in the ground‐water aquifer. The sharp‐interface approach models NAPL transport by developing a time‐distance profile from Darcy's law by assuming a piston or plug flow. The approach is tested here against 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, in obtaining an order‐of‐magnitude estimate of travel times, and in describing the approximate extent of the free and dissolved NAPL contamination. In the absence of data for calibration, the paper introduces guidelines for estimating the parameters of the model. By integrating the formulation in Part 1 and this part, a practical approach for analysis of NAPL contamination is defined; the underlying assumptions and simplifications have to be recognized, however.
Analysis of Particle Tracking Errors Associated with Spatial Discretization
Authors: Zheng C. 
Published: August 2005

AbstractThis paper addresses two particular problems which arise in particle tracking calculations because of the spatial discretization used in the block‐centered finite‐difference flow model. These two problems are: (1) the presence of a “weak” sink or source (i.e., a sink or source that does not result in complete inward or outward gradients on all interfaces of the cell containing the sink or source); and (2) the use of a model grid with varying vertical cell dimensions within an individual layer. While these problems can be mitigated by using a sufficiently fine spatial discretization, there are always computational and practical limitations on the number of model nodes. Two procedures are presented in this paper which minimize particle tracking errors associated with weak sinks/sources or vertically distorted grids. The first procedure uses an approximate analytical solution to define the velocity distribution inside a model cell containing a weak sink/source so that the capture of the particles entering the cell can be determined accurately. The second procedure establishes an automatic adjustment of the particle vertical coordinate according to the degree of vertical grid distortion. These procedures are shown to be effective, and improve the accuracy of particle tracking results under nonideal spatial discretizations.
Inverse Analysis Implementation of the SUTRA Ground‐Water Model
Authors: Piggott Andrew R. , Bobba A. Ghosh , Xiang Jiannan 
Published: August 2005

AbstractNumerical simulation of ground‐water flow and transport is often impeded by a lack of information regarding the conceptual model and properties that best represent the water‐bearing formation. Inverse analysis assists in the estimation of the properties of the formation once a defensible form of the conceptual model is defined. In essence, inverse analysis reverses the direction of model application to determine the properties that best match data collected from the formation under investigation. This paper describes the development of an inverse analysis implementation of the well‐known and versatile SUTRA model of ground‐water flow and transport. The inverse analysis algorithm retains the extensive functionality of SUTRA in forward simulation and allows various forms of parameter constraints to be stipulated. Addition of inverse analysis functionality to an existing ground‐water model circumvents the development of redundant models, reduces development time, and ensures the consistent and concurrent development of predictive and interpretive capabilities. Two example analyses are presented to demonstrate a portion of the functionality of the novel inverse analysis algorithm.
A Method of Collecting and Analyzing Lineaments for Regional‐Scale Fractured‐Bedrock Aquifer Studies
Authors: Mabee Stephen B. , Hardcastle Kenneth C. , Wise Donald U. 
Published: August 2005

AbstractA new method is proposed for collecting and reducing large collections of lineament data. The method consists of three steps: (1) collection of lineament data using multiple observers, multiple observation trials, and several types of imagery; (2) reproducibility tests; and (3) domain overlap analysis. Collection of lineament data and reproducibility tests are performed by overlaying lineament maps drawn by several observers or by superimposing multiple maps prepared by a single observer and identifying lineaments which are coincident (coincident lineaments = lineaments that have azimuths within 5 ± and separation distances are within 1–2 mm at the scale of drawing). Domain overlap analysis is accomplished by measuring the trends of near‐vertical fractures at outcrops distributed over the study region and comparing the spatial distribution of these trends with similar‐trending coincident lineaments. Lineaments that are not reproducible and are not geographically correlative with fractures are considered unimportant and removed from the data base. The method was applied to a 44 km2 study area in Maine and resulted in a reduction in the lineament data base from 6500 to 217. Transmissivities determined for bedrock wells located within 30 meters of lineaments that are both reproducible and geographically correlative with outcrop‐scale fractures are generally higher than the transmissivities of wells located near lineaments that are not separated on the basis of these criteria. Application of the method serves as an important filter by providing a more manageable lineament data base from which to begin detailed field checking and/or geophysical surveys directed toward specific lineaments.
Specific Yield as Determined by Type‐Curve Analysis of Aquifer‐Test Data
Authors: Moench Allen F. 
Published: August 2005

AbstractType‐curve analysis of water‐table aquifer pumping‐test data has often resulted in values of specific yield that are unrealistically low when compared with values obtained by volume‐balance calculations. It has been suggested that such values are the result of inadequate representation of drainage processes in the unsaturated zone. The commonly used analytical solution developed by Neuman for a homogeneous, water‐table aquifer assumes that the drainage of pores in the zone above the water table due to lowering of the water table occurs instantaneously. Published pumping‐test data from three relatively homogeneous, unconsolidated, granular aquifers with significantly different hydraulic conductivities are used to show that type‐curve analysis based on the Neuman model will result in estimates of specific yield that agree with volume‐balance calculations, provided that established procedures are followed. These involve the use of composite plots of drawdown observed at more than one location and inclusion of effects of partial penetration. Noninstantaneous drainage of pores in the unsaturated zone accounts for the finding that both type‐curve analysis and volume‐balance calculations yield values of specific yield that are slightly less than those obtained from laboratory column‐drainage experiments. It may also account for a slight underestimation of vertical hydraulic conductivity as obtained by type‐curve analysis.
Field Study of a Long and Very Narrow Contaminant Plume
Authors: van der Kamp G. , Luba L. D. , Cherry J. A. , Maathuis H. 
Published: August 2005

AbstractA contaminant plume more than 7,700 meters long and a few hundred meters wide has been delineated using a network of bundle piezometers. The location, concentration, and starting time of the source are well‐defined. The plume occurs in a stratified, highly permeable, sand and gravel aquifer in which the ground‐water flow is unusually steady in direction and magnitude. A ground‐water velocity of 380 meters per annum and a longitudinal dispersivity of 60 to 120 meters are obtained by simulating chloride breakthrough data at 7,700 meters from the source. Simulation of the cross‐sectional distribution of chloride concentrations at 5,500 meters shows the horizontal transverse dispersivity to be at most 0.10 meters. This very small maximum value for horizontal transverse dispersivity is two to four orders of magnitude smaller than values reported in the literature for plumes of similar lengths. It is postulated that the very weak lateral dispersion is due primarily to the steadiness of the ground‐water flow.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.
Quantification of Uncertainty in Exposure Assessments at Hazardous Waste Sites
Authors: Goodrich Michael T. , McCord James T. 
Published: August 2005

AbstractMany of the risk assessment approaches being applied at hazardous waste sites fail to adequately account for the ground‐water flow and solute transport processes (and their uncertainties) that move the contaminant from the source to the receptor. For example, one recommended model assumes the contaminant concentration at the source is equal to the contaminant concentration at the receptor. A more realistic way to estimate receptor concentrations for risk assessment would be to use technically accepted ground‐water flow equations coupled with the advection‐dispersion equation and use Monte Carlo techniques to address parameter uncertainty. A complex numerical model and a simple analytical model were used to simulate ground‐water flow and solute transport from a hypothetical waste site to a subsurface drain using both small and larger scale hydraulic properties. Results indicate that the predicted receptor concentration is considerably lower than the source concentration when knowledge of the local hydrogeology is considered in the transport simulations.
Ground‐Water Flow Simulation for Management of a Regulated Aquifer System: A Case Study in the North Carolina Coastal Plain
Authors: Reynolds Jeffrey W. , Spruill Richard K. 
Published: August 2005

AbstractThe State of North Carolina designated a portion of the North Carolina Coastal Plain as its first and only Capacity Use Area in 1969 in response to large‐scale withdrawals from the Castle Hayne aquifer system for phosphate mining operations. Withdrawals from this regulated aquifer require water‐use permits. Applications for water‐use permits require information on the use of the water, including an assessment of the impacts on the source aquifer(s). The U.S. Geological Survey finite‐difference model MODFLOW was used to simulate ground‐water flow in a 1,300 square mile area in the Capacity Use Area to estimate the effects of a proposed mine advance anticipated to require more extensive pumping from the aquifer. In addition, the model was used to evaluate the effects of a proposed municipal wellfield also to be located in the Capacity Use Area. The model provided estimates of required pumping rates for the mining activities. Simulated potentiometric surfaces and hydrographs for the Castle Hayne aquifer resulting from both the mining and the wellfield operations indicated that the Castle Hayne aquifer achieves steady state relatively rapidly and is impacted over a large area as a result of the depressurization pumping. Wellfield pumping has a relatively minor effect. Impacts on ground‐water levels in the Castle Hayne aquifer at nearby communities are mainly dependent on the location of the active mining center. Regional‐scale ground‐water flow models can provide information on the potential effects on the flow system of significant hydrologic stresses and could therefore be useful in assessing the impacts of the stresses as required in the permitting process.
The Geochemistry of Chromium Migration and Remediation in the Subsurface
Authors: Davis Andy , Olsen Roger L. 
Published: August 2005

AbstractFrom a human health perspective, knowledge of Cr speciation in soils is important in assessing risk related to ingestion of Cr‐contaminated soils, and in selecting appropriate remedial alternatives that are protective of ground‐water quality. In this study, good agreement was found between Cr (VI) soil concentrations and the mass of Cr (VI) leached from columns over a range of Cr (III):Cr (VI) soil ratios (0.2‐28) and ΣCr concentrations (27–290 mg/kg). In batch tests, adsorption of Cr(VI) to sandy soils was rapid and linear, with a KdCr(VI) of 0.2 liters/kg, suggesting Cr(Vl)‐contaminated vadose‐ and saturated‐zone materials may be remediated by soil flushing or pump‐and‐treat methods. In column tests, soil flushing removed 85% of the soil‐Cr(VI), while pump‐and‐treat leached only 17% of Cr attributable to aquifer contamination. Use of oxidizing agents increased Cr released from Cr(III)‐contaminated soils, but only from 1.3% to 2.3% of ΣCr mass. Based on Cr speciation in soils, Cr(VI) was mobile, while Cr(III)was retained in the soil column, indicating that reduction of Cr(VI) to Cr(III), and the proportion of Cr(III) in the soil, will constrain remedial efficiency. Reduction of Cr(VI) to Cr(III), and subsequent precipitation of CrxFe1−x (OH)3, occurred in a Cr(VI)‐contaminated soil augmented with Fe+2, resulting in < 0.01 mg/1 Cr in the supernatant, suggesting that in situ Cr fixation may mitigate Cr‐contaminated ground water.
Use of Weighted Least‐Squares Method in Evaluation of the Relationship Between Dispersivity and Field Scale
Authors: Xu Moujin , Eckstein Yoram 
Published: August 2005

AbstractRegression formulas relating dispersivity and field scale have been suggested in the literature by few researchers, among others: Arya (1986) and Neuman (1990). These studies employ conventional statistical techniques that cannot take into account the relative reliability level of a data point. Neuman (1990), using conventional statistics, discarded the low reliability data obtained by calibrating numerical grid models against solute concentrations of large‐scale plumes. Although the numerical modeling data are of low reliability, they are important to consider because of the very limited overall availability of the data. Another problem is with the slope reduction of log10αL versus log10L for large values of L, where L is the field scale, and αL is the longitudinal dispersivity. Neuman (1990) used a different line of best fit with a reduced slope for L ≤ 100 m. Fitting two straight lines on a logarithmic scale, one for L ≤ 100 m and another one for L ≤ 100 m, takes care of the slope change to some extent, but results in loss of data points for both statistical groups. In order to provide a better statistical model using the available data with varying reliabilities, a weighted least‐squares data fitting method was used to define a relationship between dispersivity and field scale. By using this technique, less reliable data points were not simply ignored, but rather assigned a lower weight. The linear model is further improved by fitting a curve through the data drawn on a log10αL versus log10 L diagram. The analysis shows a significant difference between the weighted and the unweighted curves. Further analysis indicated that the increase in longitudinal dispersivity is practically negligible when the scale of flow exceeds 1 km.
Simulations of Flow in Crystalline Rock and Recharge from Overlying Glacial Deposits in a Hypothetical New England Setting
Authors: Harte Philip T. , Winter Thomas C. 
Published: August 2005

AbstractCross‐sectional, finite‐difference, steady‐state ground‐water‐flow models of a generalized New England landscape were constructed to examine the effects of hydraulic conductivity and topography on bulk‐fluid flow processes in fractured crystalline rock. The generalized landscape consists of a flat hilltop, a hillside that has a slope of 0.17 ft/ft, and a flat river valley. It includes three hydrogeologic units, stratified drift in the river valley, glacial till, and underlying crystalline rock.Distribution of recharge to and discharge from bedrock is affected by the presence of small topographic features, such as terraces on the hillside. Most of these terraces consist partly or entirely of sand, and they create localized areas of recharge to and discharge from bedrock. Maximum recharge to bedrock commonly occurs at downward inflections of the water table, and discharge occurs at upward inflections of the water table. These inflections of the water table are associated with inflections in topography because the shallow depth of water on hilltops and hillsides resemble the configuration of the land surface.Regional ground‐water flow in crystalline rock and distribution of bedrock recharge and discharge are also affected by heterogeneities in hydraulic conductivity of the bedrock. Vertical heterogeneity creates short, shallow flow paths in high‐relief terrain. Horizontal heterogeneity causes large variations in the size of bedrock recharge areas; in some cases the difference from homogeneous conditions is more than 50 percent.
A Method for Estimating Field‐Scale Mass Transfer Rate Parameters and Assessing Aquifer Cleanup Times
Authors: Brogan Scott D. , Gailey Robert M. 
Published: August 2005

AbstractA general method for estimating ground‐water solute mass transfer rate parameters from field test data is presented. The method entails matching solute concentration and hydraulic head data collected during the recovery phase of a pumping test through application of a simulation‐regression technique. Estimation of hydraulic conductivity and mass transfer rate parameter values is performed by fitting model simulations to the data. Parameter estimates are utilized to assess cleanup times for pump‐and‐treat aquifer remediation scenarios. Uncertainty in the cleanup time estimate is evaluated using statistical information obtained with the parameter estimation technique.Application of the method is demonstrated using a hypothetical ground‐water flow and solute transport system. Simulations of field testing, parameter estimation, and remedial time frames are performed to evaluate the usefulness of the method. Sets of random noise that signify potential field and laboratory measurement errors are combined with the hypothetical data to provide rigorous testing of the method. Field tests are simulated using ranges of values for data noise, the mass transfer rate parameters, the test pumping rates, and the duration of recovery monitoring to evaluate their respective influence on parameter and cleanup time estimates. The demonstration indicates the method is capable of yielding accurate estimates of the solute mass transfer rate parameters. When the parameter values for the hypothetical system are well estimated, cleanup time predictions are shown to be more accurate than when calculated using the local equilibrium assumption.