bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of Optimal, Reliable Plume Capture Schemes: Application to the Gloucester Landfill Ground‐Water Contamination Problem
Authors: Gailey Robert M. , Gorelick Steven M.
Published: August 2005

A ground‐water quality management model is applied to the Gloucester Landfill site, located near Ottawa, Canada, to examine the effectiveness of various single‐well pumping schemes for the capture of dissolved contaminants. Deterministic and stochastic design analyses are conducted through ground‐water solute transport modeling of the site. The purpose of the modeling analysis is to develop contaminant capture designs that both require minimum pumping rates and possess high probabilities of success.

Optimization based upon deterministic simulation indicates that a well located at the front of the plume would effect plume capture and require the lowest pumping rate. However, a smaller total volume of water could be pumped and still effect plume capture if the well were located at the center of the plume and pumped at a higher rate for a shorter time. Stochastic optimization analyses are used to overdesign the pumping rates so that possible design error is overcome. The analyses indicate that design reliability may be increased from 50 to 90 percent by pumping an additional 18 percent at the front or 27 percent at the center of the plume. These pumping overdesign factors are the first such values calculated using the stochastic optimization approach applied to a field site.
Monte Carlo Simulations of Multiphase Flow Incorporating Spatial Variability of Hydraulic Properties
Authors: Essaid Hedeff I. , Hess Kathryn M.
Published: August 2005

To 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

Statistical 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

A 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

China'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

This 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

Factors 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

The 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

Laboratory 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

In 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

The 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

Evaluation 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

In 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

Numerical 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

A 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

Stochastic 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

Because 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.
Uncertainty Analyses of Unsaturated Zone Travel Time at Yucca Mountain
Authors: Nichols William E. , Freshley Mark D.
Published: August 2005

Uncertainty analysis methods can be applied to numerical models of ground‐water flow to estimate the relative importance of physical and hydrologie input variables with respect to ground‐water travel time. Monte Carlo numerical simulations of unsaturated flow in the Calico Hills nonwelded zeolitic (CHnz) layer at Yucca Mountain, Nevada, indicate that variability in recharge, and to a lesser extent in matrix porosity, explains most of the variability in predictions of water travel time through the unsaturated zone. Variations in saturated hydraulic conductivity and unsaturated curve‐fitting parameters were not statistically significant in explaining variability in water travel time through the unsaturated CHnz unit. The results of this study suggest that the large uncertainty associated with recharge rate estimates for the Yucca Mountain site is of concern because the performance of the potential repository would be more sensitive to uncertainty in recharge than to any other parameter evaluated. These results are not exhaustive because of the limited site characterization data available and because of the preliminary nature of this study, which is limited to a single stratigraphie unit, one dimension, and does not account for fracture flow or other potential fast pathways at Yucca Mountain.
A Program to Analyze Aquifer Test Data and Check for Validity with the Jacob Method
Authors: Field Malcolm S.
Published: August 2005

The Jacob straight‐line method of aquifer analysis deals with the late‐time data and small radius of the Theis type curve which plot as a straight line if the drawdown data are plotted on an arithmetic scale and the time data on a logarithmic (base 10) scale. Correct analysis with the Jacob method normally assumes that (1) the data lie on a straight line, (2) the value of the dimensionless time factor is less than 0.01, and (3) the site's hydrogeology conforms to the method's assumptions and limiting conditions. Items 1 and 2 are usually considered for the Jacob method, but item 3 is often ignored, which can lead to incorrect calculations of aquifer parameters. A BASIC computer program was developed to analyze aquifer test data with the Jacob method to test the validity of its use. Aquifer test data are entered into the program and manipulated so that a slope and time intercept of the straight line drawn through the data (excluding early‐time and late‐time data) can be used to calculate transmissivity and storage coefficient. Late‐time data are excluded to eliminate the effects of positive and negative boundaries. The time‐drawdown data then are converted into dimensionless units to determine if the Jacob method's assumptions are valid for the hydrogeologic conditions under which the test was conducted.
Estimating Movement of Ground Water from a Pond or Large‐Radius Conduit
Authors: Brikowski T.
Published: August 2005

Evaluation of ground‐water exchange between ponds or large‐radius conduits and surrounding aquifers is a common problem in contaminant migration studies. Analytic solutions are useful tools for this evaluation, particularly when the system is incompletely characterized. Solutions are derived below for application to ponds, lakes, and natural or artificial conduits with a known discharge/recharge flux. General features of migration in this setting are determined by the ratio of pond flux (source/sink) to regional flux crossing the pond boundary. When this ratio is large (pond dominates) the effect of the pond is indistinguishable from a well. At intermediate values, movement from the pond against the regional flow is inhibited, and discharge plumes are shifted downgradient relative to those for a well. At small ratios only a narrow plume will emerge from the downgradient side of a discharging pond, considerably narrower but longer than predicted for a well of the same strength.
Coupled Simulation‐Optimization Modeling for Municipal Ground‐Water Supply Protection
Authors: Varljen Mark D. , Shafer John M.
Published: August 2005

A technique based on numerical ground‐water flow modeling and unconstrained nonlinear optimization has been developed to provide guidance for protecting municipal ground‐water supplies from contamination through capture zone management. The technique involves conventional finite‐difference ground‐water flow modeling and numerical flowpath/travel time calculation coupled with nonlinear mathematical programming. The objective of the technique is to specify pumping rates for wells in a wellfield such that the configuration of capture zones in relation to existing potential sources of contamination minimizes the risk of contamination while maintaining the required total water output from the wellfield. An important feature of the technique is its ability to incorporate realistic boundary conditions, complicated aquifer configurations, and spatially varying aquifer properties to whatever degree site‐specific data are available. Also, the technique is implemented on a personal computer. This approach to ground‐water supply protection enhances conventional wellhead protection area delineation because a greater level of protection can be achieved if potential contaminant sources are not even included in capture zones, rather than attempting to reduce the threat of those sources. The effectiveness of the technique was verified through application to a hypothetical ground‐water system. Practical aspects were demonstrated with an application in Pékin, Illinois. These efforts demonstrate the utility of an innovative modeling technique in ground‐water quality protection.
Extension of the Method of Characteristics for Simulation of Solute Transport in Three Dimensions
Authors: Zheng C.
Published: August 2005

The method of characteristics (e.g., Garder et al., 1964; Konikow and Bredehoeft, 1978) has been widely used in the simulation of solute transport in ground‐water systems because of its effectiveness for handling advection‐dominated problems. However, the method requires a large amount of computer memory and execution time when it is necessary to track a large number of moving particles, especially in three dimensions. The method can also lead to large mass balance discrepancies under certain circumstances. This paper describes a number of changes which may be made in the traditional method of characteristics approach to mitigate these difficulties. These changes include a dynamic particle allocation procedure, which often reduces dramatically the total number of moving particles needed in a simulation; and a consistent velocity interpolation scheme and higher‐order particle tracking techniques, which, coupled with effective handling of particle insertion and deletion at sources and sinks, can provide improved mass balance results. The accuracy of a method‐of‐characteristics model incorporating these changes is evaluated by comparison with analytical solutions for (1) three‐dimensional advection and dispersion in a spherical flow field, and (2) concentration change in a well during an injection/pumping cycle.
Simulation of Cylindrical Flow to a Well Using the U.S. Geological Survey Modular Finite‐Difference Ground‐Water Flow Model
Authors: Reilly Thomas E. , Harbaugh Arien W.
Published: August 2005

Cylindrical (axasymmetric) flow to a well is an important specialized topic of ground‐water hydraulics and has been applied by many investigators to determine aquifer properties and determine heads and flows in the vicinity of the well. A recent modification to the U.S. Geological Survey Modular Three‐Dimensional Finite‐Difference Ground‐Water Flow Model provides the opportunity to simulate axisymmetric flow to a well. The theory involves the conceptualization of a system of concentric shells that are capable of reproducing the large variations in gradient in the vicinity of the well by decreasing their area in the direction of the well. The computer program presented serves as a preprocessor to the U.S. Geological Survey model by creating the input data file needed to implement the axisymmetric conceptualization. Data input requirements to this preprocessor are described, and a comparison with a known analytical solution indicates that the model functions appropriately.
Henry Darcy and the Fountains of Dijon
Authors: Freeze R. Allan
Published: August 2005

The life and career of Henry Darcy are intimately connected with the city of Dijon. He was born there; he died there; and it was there that he carried out the experiments that have brought him lasting fame. Darcy was not an obscure scientist; he was a well‐known and respected public figure. His efforts as an engineer and advocate put Dijon on the main line of the Paris‐Lyon railway, and brought a modern water‐distribution system to Dijon some 25 years before such a system was put in place in Paris. During his life he received great honors, suffered political persecution, and carried out his most productive research in his later years despite ill health. He died at the relatively young age of 55. The main square in the city of Dijon is named Place Darcy in his honor.
Correlation Between DRASTIC Vulnerabilities and Incidents of VOC Contamination of Municipal Wells in Nebraska
Authors: Kalinski Robert J. , Kelly William E. , Bogardi Istvan , Ehrman Richard L. , Yaniamoto Paul D.
Published: August 2005

Because it considers basic hydrogeologic variables believed to influence contaminant transport from surface sources to ground water, the DRASTIC method can be a valuable tool for identifying ground‐water supplies that are vulnerable to contamination. Theoretically, areas with high DRASTIC scores should have more frequent occurrences of ground‐water contamination events than areas with low scores given similar land use, well construction, and well densities. Relationships between DRASTIC scores and incidents of contamination, however, have not been extensively documented. In Nebraska, significant positive correlation appears to exist between incidents of VOC contamination of ground‐water supplied community water systems and the relative hydrogeologic vulnerability of surficial aquifers as quantified with the DRASTIC method. These results provide a means of verifying the usefulness of planning tools such as DRASTIC for identifying areas where water supplies are most vulnerable to contamination from surface sources.
Comparison of Modeled Disposal Well Plumes Using Average and Variable Injectate Densities
Authors: Larkin Randall G. , Clark James E. , Papadeas Philip W.
Published: August 2005

“No Migration” Petitions must be submitted by operators of Class I hazardous disposal wells to apply for an exemption from the federal land ban restrictions on the disposal of hazardous waste. In many Class I disposal well operations, the injectate density can vary daily and usually has a different density than the native formation brine. The influence of the density contrast on the fluid potential must be included in a “No Migration” Petition modeling demonstration. After the model wells (s) is shut‐in, the density contrast results in a net updip (lower density injectate) or downdip (higher density injectate) component of flow near the center of mass of the calculated plume (neglecting regional flow). In many cases, two model runs are required: one using the lowest anticipated injectate density and one using the highest anticipated injectate density for the entire modeled operational period. This was intended to provide adequate plume delineation over the injectate density range and implies that buoyancy effects on the plume position are not related to the average density. Three separate cases of a two‐dimensional generic numerical model were used to examine buoyancy effects using constant and variable injectate density input values. Case 1 used a random selection of the daily variation about the mean density, and case 2 used correlated daily injectate densities over a five day period. The model calculated concentrations from cases 1 and 2 were compared to the results from a third case that used the mean density input value for the entire operational period. The calculated plume extent for all three cases is virtually identical for simulation times up to 10,000 years. The modeling results demonstrate that using a long‐term average injectate density in “No Migration” Petition modeling rather than the range of extreme values may be justifiable by operators of Class I injection well facilities.
Estimation of Residual Dense NAPL Mass by Inverse Modeling
Authors: Butcher Jonathan B. , Gauthier Thomas D.
Published: August 2005

Ground water at many sites is contaminated by chlorinated solvents which are of relatively low solubility and denser than water, as well as other contaminants of similar properties. The presence of a dense nonaqueous phase liquid (DNAPL) in an aquifer can provide continued flux to the dissolved phase long after the initial discharge. The flux may be significant even when the nonaqueous phase has dispersed to a state of residual saturation, in which little or no free product can be detected or recovered. At an industrial site we required an estimate of the magnitude of a DNAPL source without undertaking invasive exploration. In theory, the presence and magnitude of a residual DNAPL source can be inferred from observations of downgradient concentrations by (1) developing an inverse modeling solution to estimate flux, and (2) matching estimated flux to a conceptual model of NAPL dissolution, which yields an estimate of residual mass. Such a method can provide a qualitative indication of the presence of a residual DNAPL source. However, the sensitivity of the solution to assumptions regarding physical characteristics of the source medium are such that a useful quantitative estimate cannot be made without observations over long periods of time.
Ground‐Water Tracing with Injected Helium
Authors: Gupta S. K. , Lau L. Stephen , Moravcik Philip S.
Published: August 2005

Helium has several characteristics that make it attractive for use as a tracer in hydrological studies. Two types of experiments were conducted to investigate applicability of helium as a tracer of ground‐water movement. The experiments included studies using laboratory sand and soil columns and field ground‐water tracing in a basaltic aquifer. A water helium analyzer comprised of a thin quartz glass membrane and diode ion pump (making use of the preferential permeation of helium through the quartz glass into an evacuated space) was developed and used for the experiments.

Results of our studies demonstrated that breakthrough curves of specific conductance and helium were similar under saturated conditions. In the unsaturated sand/soil columns, breakthrough curves of helium were retarded relative to specific conductance reducing the usefulness of helium as a tracer.
Recovery Performance for Vertical and Horizontal Wells Using Semianalytical Simulation
Authors: Cleveland Theodore G.
Published: August 2005

A semianalytical transient expression was used to evaluate the performance of a finite‐length horizontal well as compared to a vertical well in a hypothetical recovery scenario. Recovery was simulated in two hypothetical confined aquifers to study the effect of aquifer thickness and well orientation on recovery performance. The results show that horizontal wells can initially mobilize larger volumes of ground water (and contaminants) but that vertical wells have the same ultimate recovery ability in a homogeneous, isotropic medium.
Modeling Ground‐Water Remediation in the High Plains Aquifer
Authors: Mergia Girma , Kelly William E.
Published: August 2005

The Princeton Transport Code (PTC), a three‐dimensional finite‐element flow and transport model, was used to evaluate contaminant movement and recovery in the vicinity of a manufacturing facility in western Nebraska. The modeling was complicated by seasonal recharge from a nearby irrigation canal, a drainage ditch flowing across the site, municipal wells pumping at variable rates and screened at different levels in the underlying semiconfined aquifer, and the pumping of the three high‐capacity wells being used to recover contaminated ground water. The flow model was calibrated in several steps: steady‐state calibration using the unstressed (no pumping) conditions; steady‐state calibration using the prerecovery pumping conditions; and finally, transient calibration using results obtained for the early recovery pumping period–first for the nonirrigation season and then for the irrigation season. The calibrated flow model was further tested by simulating transport during the early stages of the recovery pumping.
Relation Between Hydraulic Conductivity and Texture in a Carbonate Aquifer: Regional Continuity
Authors: Rovey Charles W. , Cherkauer Douglas S.
Published: August 2005

In the dolomite aquifer of Milwaukee County, Wisconsin, stratigraphic units deposited as mudstones have little or no visible macroporosity and, based on injection‐pressure tests, have average horizontal hydraulic conductivities of approximately 10−6 cm/sec, controlled by jointing. Coarse‐grained units (packstones and grainstones), however, have horizontal hydraulic conductivities of 10−4 cm/sec and greater, argued to be controlled by granularity, not jointing. Using this relationship between texture and hydraulic conductivity in Milwaukee County and a sedimentary facies analysis, trends in hydraulic conductivity values are predicted for five stratigraphic units over an area of approximately 3500 km2. The predictions are tested qualitatively with sets of specific capacity values within the various stratigraphic units, and quantitatively with injection‐pressure test values from five additional locations. Seven of eight qualitative and four of six quantitative predictions are judged to be successful. Therefore, trends in hydraulic conductivity, and to some extent local values, in this carbonate aquifer are predictable over areas of thousands of square kilometers without any site‐specific data on jointing.

The success rate could not have been this high if hydraulic conductivity were not controlled by the granularity of the lithologic units. It is argued, therefore, that the local bulk hydraulic conductivity of this carbonate aquifer is controlled by the granular porosity, and the aquifer will generally behave as a porous medium, even at the small scale of a typical pumping test.
Nonlinear Adsorption of Uranyi: Analytical Modeling of Liner Migration
Authors: Johnson Robert O.
Published: August 2005

This paper is concerned with establishing the breakthrough time for leachate to migrate out of waste facilities containing large quantities of low‐level, radioactive uranium. The impoundments have clay liners which adsorb uranyl cations dissolved in the leachate. A nonlinear isotherm, derived from a consideration of the phenomenological basis and chemical kinetics of the adsorption process, is used in conjunction with a time‐dependent, one‐dimensional species transport equation to develop a mathematical expression for the retarded migration time interval. The nonlinear transport equation is identical to one occurring in theoretical gas dynamics for the description of shock waves, and whose solution is well‐known. Results indicate that large breakthrough time‐interval errors can arise if a linear isotherm is used to model the adsorption process, particularly if leachate concentrations along the floor of the pit are near saturation. Conversely, at dilute concentrations, computations based on the linear isotherm underpredict the time interval required for the onset of leakage. The underprediction is acceptable from an engineering viewpoint because environmental protection afforded by the liner is not overstated.
Analysis of In Situ Permeability Tests in Nonpenetrating Wells
Authors: Avci Cem B.
Published: August 2005

Recent interest in ground‐water contamination problems has led to a renewed interest in the development of accurate procedures for the analysis of in situ permeability tests. The present study involves the derivation of analytical procedures for slug tests and constant head tests performed in wells with casings open at the bottom and installed flush with the upper confining boundary of a finite‐depth, anisotropic, homogeneous aquifer; the analysis takes into account the effects of a finite‐thickness skin located at the casing bottom. The Laplace transform is used on the governing ground‐water flow equations to derive the transform of time‐dependent water levels measured in the casing. The expression is numerically inverted back into the real time domain to obtain (1) a set of dimensionless type curves for analyzing slug test data, and (2) a relation between the inflow rate, the head maintained in the well, the hydraulic conductivity, and a shape factor expression for the analysis of constant head data. Existing methods of analysis are reviewed and compared with the presently derived analytical procedures.
Two‐Dimensional Dispersivity Estimation Using Tracer Experiment Data
Authors: Zou S. , Parr A.
Published: August 2005

This paper presents two analytical methods for estimating longitudinal and transversal dispersivities for a two‐dimensional plume generated by a slug tracer injection in a uniform ground‐water flow field. The first method requires the mapped plume area measurements at a given time after the tracer sources are injected. The second method requires concentration versus time data from one sampling well through which the plume passes. Detailed example calculations and comparisons with other procedures show that the methods presented herein represent improvements in both accuracy and ease of use over previous methods.
A Laboratory Analysis of the Effect of Macropores on Solute Transport
Authors: Wildenschild D. , Jensen K. H. , Villholth K. , Illangasekare T. H.
Published: August 2005

Macropores play an important role in many soils in relation to ground‐water contamination by providing preferential pathways from the root zone to the water table. Surface‐applied agrochemicals may hereby be carried quickly to the shallow ground water. The reduced retention combined with a small contact area between the flowing water and the soil implies that little removal from physical, chemical, and microbiological processes may take place, thus increasing the risk of ground‐water contamination.

A laboratory procedure for evaluating the effect of macropores in a given soil is proposed and tested. The procedure involves the following sequence of experiments on two undisturbed soil monoliths: (1) measurements of the distribution of outflow, (2) measurements of breakthrough curves, (3) dye application for visual observation of macropores; and (4) horizontal slicing of the monoliths to measure macropore distribution and continuity of macropores. The experimental procedure is based on well‐documented techniques that combined will provide evidence on the significance of macropores in relation to ground‐water contamination and guidance for selecting the appropriate model for simulating flow and transport at the field in question.

The laboratory procedure was tested on two large, undisturbed soil monoliths (30 cm in diameter) removed from the unsaturated zone at a clayey moraine agricultural field in Denmark. This soil was known to have many macropores. The investigations documented the strong influence of these structures on flow and transport suggesting that a traditional flow and transport model would be inadequate for simulating the processes occurring in the field.