bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monte Carlo Simulations of Multiphase Flow Incorporating Spatial Variability of Hydraulic Properties
Authors: Essaid Hedeff I. , Hess Kathryn M. 
Published: August 2005

AbstractTo study the effect of spatial variability of sediment hydraulic properties on multiphase flow, oil infiltration into a hypothetical glacial outwash aquifer, followed by oil extraction, was simulated using a cross‐sectional multiphase flow model. The analysis was simplified by neglecting capillary hysteresis. The first simulation used a uniform mean permeability and mean retention curve. This was followed by 50 Monte Carlo simulations conducted using 50 spatially variable permeability realizations and corresponding spatially variable retention curves. For the type of correlation structure considered in this study, which is similar to that of glacial outwash deposits, use of mean hydraulic properties reproduces the ensemble average oil saturation distribution obtained from the Monte Carlo simulations. However, spatial variability causes the oil saturation distribution in an individual oil lens to differ significantly from that of the mean lens. Oil saturations at a given location may be considerably higher than would be predicted using uniform mean properties. During cleanup by oil extraction from a well, considerably more oil may remain behind in the heterogeneous case than in the spatially uniform case.
Variation in Specific Capacity in Fractured Rocks, Pennsylvania
Authors: Knopman Debra S. , Hollyday E. F. 
Published: August 2005

AbstractStatistical analyses were used to determine the relation of hydrogeologic, well construction, and field measurement factors to the extremely variable yield of wells located in consolidated rocks in the Piedmont, Blue Ridge, and Valley and Ridge provinces of Pennsylvania. Specific capacity values (a total of 4,391) from the U.S. Geological Survey well record file were chosen as a measure of yield. Results underscore the importance in regional analysis of accounting for differences due to variables related to well construction and field measurement of specific capacity before attempting to account for differences due to hydrogeology. The approach taken was to organize a hierarchy of variables that relate to differences in specific capacity. Linear regression using log‐transformed specific capacity as the response variable provided estimates of the extent to which variables account for variation in the specific capacity values. Among the variables available for consideration, casing diameter, primary water use, and duration of discharge during the well production test are most important and can explain 24 percent of the variation observed in the specific capacity data. Lithology alone can account for only about 12 percent of the variation observed in the specific capacity data. However, a classification of rocks based on lithology and also accounting for differences in casing diameter, water use, duration of discharge, topographic setting, well depth, and casing depth can explain about half the variation in specific capacity values.
A Diffusive Sampler for Passive Monitoring of Volatile Organic Compounds in Ground Water
Authors: Karp Kenneth E. 
Published: August 2005

AbstractA diffusive sampler was developed to provide a passive in situ method for long‐term monitoring of volatile organic compounds (VOCs) in the ground water at hazardous waste sites and waste disposal facilities. The sampler was constructed of a sorbent tube that fits inside a specially designed sampling chamber equipped with a diffusional membrane that is not permeable to water but has a high permeability rate for organic vapors. VOCs in the ground water, having relatively high Henry's Law constants, enter the chamber by molecular diffusion and are collected by the sorbent. After a predetermined exposure period, the sorbent is easily retrieved for laboratory analyses by gas chromatography/mass spectrometry (GC/MS), or qualitative concentrations can be determined in the field directly using specific‐indicator detectors in place of the sorbent. The measurement approach was evaluated in the laboratory by exposing the device to a solution of 22.5 μg/1o‐xylene before testing at a field site where the ground water was contaminated by trichlorethylene (TCE). Results of the laboratory and field studies indicate the sampling approach is viable for monitoring relatively low concentrations of VOCs over a one‐day sampling period, as well as providing longer monitoring periods up to 51 days.
Sea‐Water Intrusion in the Coastal Area of Laizhou Bay, China: 2. Sea‐Water Intrusion Monitoring
Authors: Wu Jichun , Xue Yuqun , Liu Peimin , Wang Jianji , Jiang Qingbo , Shi Hongwen 
Published: August 2005

AbstractChina's first sea‐water intrusion observation network is in the Laizhou Bay region. The data obtained for four consecutive years are presented. There is usually a wide transition zone in the study area, but in some regions, a relatively distinct and sharp interface is formed. A detailed analysis has shown that there are at least two types of salt‐water/fresh‐water interface. The interface in the study area had moved about 140 m along the main observed section in a period of three years and three months due to the effect of pumping wells. Salt water may invade via the riverbed deposits but usually changes its invading direction due to the united effect of the pumping wells. Sea‐water intrusion was caused by the excessive pumping of ground water from the coastal aquifer. The interface was generally formed on the inland side not far away from the powerful discharge pumping center, and sea‐water intrusion stops there. The monitoring data suggested that if the powerful discharge pumping center moves landward, salt water will start advancing landward until a new equilibrium is reached, and even if a new pumping well, whose discharge is very small, is drilled, the equilibrium would be upset, thus causing the interface to advance inland slowly.
The Catchment Area of the Sv. Ivan Karst Spring in Istria (Croatia)
Authors: Bonacci Ognjen , Magdalenić Antun 
Published: August 2005

AbstractThis paper discusses the results of a geological, hydrogeological, and hydrological analysis of the catchment boundaries and area of the Sv. Ivan karst spring. The underground watershed has been determined by geological and hydrogeological methods. The control used was the hydrologie water budget analysis appropriate for karst basins with limited data (Turc, 1954). The Sv. Ivan spring includes one main spring and several intermittent springs. The water in the main spring penetrates the flysch layers which limit the spring's discharge; therefore, the discharge of the main spring is fairly uniform. The ratio between minimum and maximum yearly discharges ranges from 1:3.3 to 1:12.8. Only a part of the water flows through the main spring while the other springs in the zone are overflows. The catchment area of Sv. Ivan spring zone is defined as 65 km2.
Effects of Physical and Chemical Heterogeneity on Water‐Quality Samples Obtained from Wells
Authors: Reilly Thomas E. , Gibs Jacob 
Published: August 2005

AbstractFactors that affect the mass of chemical constituents entering a well include the distributions of flow rate and chemical concentrations along and near the screened or open section of the well. Assuming a layered porous medium (with each layer being characterized by a uniform hydraulic conductivity and chemical concentration), a knowledge of the flow from each layer along the screened zone and of the chemical concentrations in each layer enables the total mass entering the well to be determined. Analyses of hypothetical systems and a site at Galloway, NJ, provide insight into the temporal variation of water‐quality data observed when withdrawing water from screened wells in heterogeneous ground‐water systems.The analyses of hypothetical systems quantitatively indicate the cause‐and‐effect relations that cause temporal variability in water samples obtained from wells. Chemical constituents that have relatively uniform concentrations with depth may not show variations in concentrations in the water discharged from a well after the well is purged (evacuation of standing water in the well casing). However, chemical constituents that do not have uniform concentrations near the screened interval of the well may show variations in concentrations in the well discharge water after purging because of the physics of ground‐water flow in the vicinity of the screen.Water‐quality samples were obtained through time over a 30 minute period from a site at Galloway, NJ. The water samples were analyzed for aromatic hydrocarbons, and the data for benzene, toluene, and meta+para xylene were evaluated for temporal variations. Samples were taken from seven discrete zones, and the flow‐weighted concentrations of benzene, toluene, and meta+para xylene all indicate an increase in concentration over time during pumping. These observed trends in time were reproduced numerically based on the estimated concentration distribution in the aquifer and the flow rates from each zone.The results of the hypothetical numerical experiments and the analysis of the field data both corroborate the impact of physical and chemical heterogeneity in the aquifer on water‐quality samples obtained from wells. If temporal variations in concentrations of chemical constituents are observed, they may indicate variability in the ground‐water system being sampled, which may give insight into the chemical distributions within the aquifer and provide guidance in the positioning of new sampling devices or wells.
A Comparison of Pumping and Slug Tests for Estimating the Hydraulic Conductivity of Unweathered Wisconsian Age Till in Iowa
Authors: Jones LaDon 
Published: August 2005

AbstractThe low conductivity of glacial till is usually thought to preclude pumping tests, which has led to the predominate use of laboratory permeameter and single well response (slug) tests for estimating hydraulic conductivity. Slug tests only sample a small region around the well and may be more representative of the disturbance of well installation or development than in situ conductivity. To provide a larger scale comparison to slug test estimates of hydraulic conductivity for unweathered Wisconsin age till in Iowa, a pumping test was performed, with both the pumping and monitoring wells placed in unweathered till. Maintaining a constant drawdown of 439 cm in the pumping well for over five days yielded an average flowrate of only 26.3 ml/min, but produced a maximum drawdown of 104 cm at a radial distance of 178 cm. Assuming radial and vertical flow, least‐squares parameter estimation yielded a hydraulic conductivity estimate of 7.5 · 10‐7 cm/s and a specific storage estimate of 6.6 · 10‐6 cm‐1. Slug test results compared favorably, with geometric mean hydraulic conductivity estimates of 4.9 · 10‐7 cm/s from a Cooper et al. (1967) analysis and 7.1 · 10‐7 cm/s from a Hvorslev (1951) analysis. For this relatively low clay till (20% clay fraction), borehole smearing does not appear to have a significant impact on slug tests. The results indicate pumping tests can be performed, on an appropriate scale, in some unweathered tills.
Influence of Rhodamine WT Properties on Sorption and Transport in Subsurface Media
Authors: Shiau Bor‐Jier , Sabatini David A. , Harwell Jeffrey H. 
Published: August 2005

AbstractLaboratory batch and column studies with two subsurface media demonstrated that structural isomers of rhodamine WT (RWT) are responsible for the observed two‐step sigmoidal breakthrough curve. A linear isotherm was observed at RWT concentrations < 100 ·/1 and a Freundlich isotherm was observed at concentrations > 100 μ/1. In column studies, the breakthrough curve for RWT was observed to exhibit a plateau at values of C/ Coaround 0.43 to 0.49. Titration curves for RWT indicated a single pKavalue of 5.1. The pH effects on the breakthrough curve for RWT were evaluated and showed no evidences related to the observed two‐step breakthrough curve. Sorption of RWT was observed to be much more significant at low values of pH (e.g., 3.0), and to decrease at elevated values of pH (e.g., 11.3); both observations are consistent with the ionogenic nature of RWT and the surface charge of the media. Chromatographic separation of RWT resulted in two UV spectrophotoscopically distinct peaks indicating two structural isomers. Combination of the individual breakthrough curves for each of the two RWT isomers resulted in a two‐step breakthrough curve similar to that observed for the original RWT solution. The distinct sorptive characteristic of the different isomers is explained by the relative positions of two carboxyl groups (COO‐) attached to the phenyl ring of RWT.
Bayesian Decision Analysis for Plume Interception Wells
Authors: Wijedasa Hewa A. , Kemblowski Marian W. 
Published: August 2005

AbstractIn this paper we apply the Bayesian decision analysis to the engineering design of a ground‐water interception well whose purpose is to capture a contaminant plume. Two decision variables are considered: (1) pumping rate of an interception well when the desired width of interception zone is known, and (2) optimal number of slug tests needed to estimate the statistics of mean log‐conductivity. The optimal number of slug tests is calculated for the case when no prior information regarding the mean of log‐conductivity is available. The analysis is performed for steady‐state ground‐water flow in a linear‐type aquifer. Two utility functions are considered. The utility functions account for the risk associated with not capturing the contaminant plume, cost of pumping, and cost of aquifer testing.
Stochastic Simulation of Solute Transport in Heterogeneous Formations: A Comparison of Parametric and Nonparametric Geostatistical Approaches
Authors: Wen Xian‐Huan , Kung Chen‐Shan 
Published: August 2005

AbstractThe Monte Carlo simulation of solute transport in heterogeneous formations generates equally likely realizations of hydraulic conductivity using geostatistical approaches. The available field data on hydraulic conductivity can be classified as hard data (i.e., measurements with a low degree of uncertainty) and soft data (i.e., measurements with a greater degree of uncertainty). Information on hydraulic conductivity should be honored in the generated realizations in order to reduce uncertainty in the simulation. The traditional parametric approaches, such as the Turning Bands (TUBA) method, are multi‐Gaussian and make it difficult (if not impossible) to include the use of soft data. A recently developed nonparametric geostatistical approach, the Sequential Indicator Simulation (SIS) method, can incorporate soft data easily and generate any distribution functions not limited by multi‐Gaussian. The main goal of this paper is to investigate the effects of incorporating soft data on solute transport simulations by using SIS. Two synthetic 2‐D heterogeneous reference hydraulic conductivity fields, one with an isotropic multi‐Gaussian underlying model and the other with an anisotropic non‐Gaussian model, are sampled to obtain limited hard hydraulic conductivity data and a relatively large number of soft data. Based on the sampled data, realizations of simulated hydraulic conductivity fields are generated by using SIS for different cases depending on whether or not the soft data are used. TUBA is also used to generate realizations when only the hard data are used for the comparisons. Solute transport results are calculated by the Monte Carlo method. It is shown that when only limited hard data are available, SIS and TUBA provide similar simulation results which in these cases deviate from the results of the reference fields. The main conclusion of this study is that, by adding a relatively large number of soft data, the statistical features of the reference hydraulic conductivity fields are better characterized and transport simulation results are improved significantly. The uncertainties in predictions of both solute arrival time and arrival position are reduced when soft data are included. More investigations are needed to study the effects on solute transport of high continuity at extreme hydraulic conductivity values and the effects of incorporating large amounts of soft data with larger degrees of uncertainty, e.g., the soft data interpreted from seismic lines.
Computation of Type Curves for Flow to Partially Penetrating Wells in Water‐Table Aquifers
Authors: Moench Allen F. 
Published: August 2005

AbstractEvaluation of Neuman's analytical solution for flow to a well in a homogeneous, anisotropic, water‐table aquifer commonly requires large amounts of computation time and can produce inaccurate results for selected combinations of parameters. Large computation times occur because the integrand of a semi‐infinite integral involves the summation of an infinite series. Each term of the series requires evaluation of the roots of equations, and the series itself is sometimes slowly convergent. Inaccuracies can result from lack of computer precision or from the use of improper methods of numerical integration. In this paper it is proposed to use a method of numerical inversion of the Laplace transform solution, provided by Neuman, to overcome these difficulties. The solution in Laplace space is simpler in form than the real‐time solution; that is, the integrand of the semi‐infinite integral does not involve an infinite series or the need to evaluate roots of equations. Because the integrand is evaluated rapidly, advanced methods of numerical integration can be used to improve accuracy with an overall reduction in computation time. The proposed method of computing type curves, for which a partially documented computer program (WTAQ1) was written, was found to reduce computation time by factors of 2 to 20 over the time needed to evaluate the closed‐form, real‐time solution.
Modeling Transport of Subsurface Salinity from a Mancos Shale Hillslope
Authors: Azimi‐Zonooz Ali , Duffy Christopher J. 
Published: August 2005

AbstractIn the Upper Colorado River Basin, irrigated agriculture is associated with increasing stream salinity. In areas targeted for control of salinity transport to streams, as much as 90% of stream salinity has been estimated to originate from ground water flowing through salt‐bearing stratum. Primary salt sources are the marine shales and the shale residuum that underlie the soils throughout much of the basin. Shallow subsurface flow systems, created by seepage from canals and deep percolation of irrigation water, are believed to be the primary agents leaching the salts from underlying shale deposits and carrying them to streams. This study attempts to determine the relative importance of advective, dispersive, and diffusive salt transport processes from the alluvium covered, shale hillslopes of the region. The results of various irrigation management schemes for appraising the possibility of controlling salt loading to streams are presented.
A Caution on the Regulatory Use of Numerical Solute Transport Models
Authors: Dougherty David E. , Bagtzoglou Amvrossios C. 
Published: August 2005

AbstractNumerical models of solute transport in water‐saturated porous media are routinely used to make regulatory and design decisions. For many contaminants, decisions are based on concentrations of 5 parts per billion (ppb) or less. This “action level“ is usually a small fraction (<0.01) of the concentrations near a source of contamination. Two one‐dimensional example problems are used to demonstrate that modeling errors using classical numerical methods are largest where concentrations are lowest. This implies that in regions of low dimensionless concentration, that is near the action level, large relative errors can be expected. Hence, decisions based on numerical model solutions at low concentrations must be taken cautiously. Modern numerical methods for the solution of transport equations provide better behavior, in this sense, than classical methods.
Modeling Advective Contaminant Transport During Soil Vapor Extraction
Authors: Falta Ronald W. , Pruess Karsten , Chesnut Dwayne A. 
Published: August 2005

AbstractA general semianalytical method for modeling the advective transport of a volatile organic compound (VOC) to a soil vapor extraction well has been developed. Assuming that the VOC is not present in the form of a nonaqueous phase liquid (NAPL), this technique is applicable to cases in which the VOC is partitioned in the unsaturated zone between the gas, aqueous, and solid phases. The VOC may have a one‐, two‐, or three‐dimensional initial distribution. The method may be applied to problems having a one‐ or two‐dimensional steady‐state gas flow field in which the gas streamfunction and gas travel time distributions are known. Examples are included to show the application of the method to radial and two‐ dimensional cylindrical gas flow fields with different VOC distributions and characteristics.
Infiltration in Soils with Fractal Permeability Distribution
Authors: Kemblowski Marian W. , Chang Ching‐Min 
Published: August 2005

AbstractStochastic analysis of flow and transport in soils usually assumes that the soil permeability is a stationary, homogeneous stochastic process. Some field data suggest, however, that permeability distributions may have a fractal character with long‐range correlations. One such set of data is analyzed in this paper. We also investigate the relationship between the fractal character of hydraulic conductivity distribution and the statistics of unsaturated flow. This was studied by means of Monte Carlo simulations of steady‐state infiltration in soils with generated fractal permeability distribution. The results of these simulations were compared to theoretical results obtained from spectral analysis of unsaturated flow.
Effects of Small‐Scale Vertical Variations in Well‐Screen Inflow Rates and Concentrations of Organic Compounds on the Collection of Representative Ground‐Water‐Quality Samples
Authors: Gibs Jacob , Brown G. Allan , Turner Kenneth S. , MacLeod Cecilia L. , Jelinski James C. , Koehnlein Susan A. 
Published: August 2005

AbstractBecause a water sample collected from a well is an integration of water from different depths along the well screen, measured concentrations can be biased if analyte concentrations are not uniform along the length of the well screen. The resulting concentration in the sample, therefore, is a function of variations in well‐screen inflow rate and analyte concentration with depth. A multiport sampler with seven short screened intervals was designed and used to investigate small‐scale vertical variations in water chemistry and aquifer hydraulic conductivity in ground water contaminated by leaded gasoline at Galloway Township, Atlantic County, New Jersey. The multiport samplers were used to collect independent samples from seven intervals within the screened zone that were flow‐rate weighted and integrated to simulate a 5‐foot‐long, 2.375‐inch‐outside‐diameter conventional wire‐wound screen. The integrations of the results of analyses of samples collected from two multiport samplers showed that a conventional 5‐foot‐long well screen would integrate contaminant concentrations over its length and resulted in an apparent contaminant concentration that was as little as 28 percent of the maximum concentration observed in the multiport sampler.