bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aquifer Parameters from Constant Discharge Nonsteady‐Leaky Type Curves
Authors: Motz Louis H. 
Published: August 2005

AbstractA drain function and set of type curves were defined for a simplified mathematical solution that represents one‐dimensional flow under nonsteady conditions in a leaky aquifer for the constant discharge boundary condition. The mathematical solution is in the form of exponential and complementary error functions, and it can be calculated using a polynomial approximation for the complementary error function. The mathematical solution and drain function are computationally easier to use than an equivalent integral‐form solution and drain function, which must be integrated numerically. A match‐point procedure was developed for determining aquifer diffuisivity (T/S), transmissivity (T), storage coefficient (S), and leakance (K′/b′) based on using the drain function and type curves. Use of the procedure is illustrated by an example that utilizes simulated aquifer drawdown and flowrate data. The match‐point procedure can be used to analyze drawdown data in leaky and nonleaky aquifers in cases where the flow is one‐dimensional and the discharge from the aquifer is constant. Applications of this procedure would include flow to a canal or river, flow to a highly permeable fracture that acts as a line sink, drainage of agricultural lands, and dewatering associated with strip mining operations.
Complex Aquifer‐Aquitard Relationships at an Appalachian Plateau Site
Authors: Peffer Jeffrey R. 
Published: August 2005

AbstractInitial test data from a fractured, shale‐dominated sequence at a proposed landfill site in the Appalachian Plateau exhibited an apparent inconsistency: the unit performed in some ways as an aquitard; yet it was capable of high well yields which suggested it was an aquifer. High head drops (tens of feet) and dramatic ground‐water quality differences (hundreds of ppm for sulfate) occurred across the shale indicating that it is an aquitard. However, the shale sequence supported yields up to 60 gpm in test wells and one production well. This inconsistency suggested high anisotropy in vertical versus horizontal hydraulic conductivity.A second detailed stage of testing confirmed the coincidence of some yielding zones to more brittle interbeds and bedding fractures within the shale sequence. An approach involving several different techniques, including analysis of hydrographs, vertical gradients, ground‐water quality differences, borehole geophysical logs, and pumping tests, was found to be effective in aquifer‐aquitard delineation at this site. The study showed that in waste disposal investigations in the Appalachian Plateau, it is inappropriate to use well yield alone to identify aquitards as these may be complex with numerous interlayered aquifers.
A Field Evaluation of In‐Situ Biodegradation of Chlorinated Ethenes: Part 3, Studies of Competitive Inhibition
Authors: Semprini Lewis , Hopkins Gary D. , Roberts Paul V. , Grbic‐Galic Dunja , McCarty Perry L 
Published: August 2005

AbstractResults are presented that demonstrate the in‐situ biotransformation of vinyl chloride (VC), trans‐l,2‐dichloroethylene (t‐DCE), cis‐l,2‐dichloroethylene (c‐DCE), and trichloroethylene (TCE) by an enhanced population of methane‐utilizing (methanotrophic) bacteria. Biostimulation was accomplished by introducing dissolved methane and oxygen into a shallow, confined aquifer, to encourage the growth of the native methanotrophic bacteria. Biotransformation of the target compounds ensued immediately after the commencement of methane utilization, and reached steady‐state values within three weeks. The approximate extents of transformation achieved in the two meter biostimulated zone were as follows: VC, 95%; t‐DCE, 90%; c‐DCE, 50%; and TCE, 20%. The biotransformation of VC and t‐DCE was observed to be competitively inhibited by methane. Cyclic variations in methane concentration caused by the alternate pulse injection of dissolved methane into the test zone caused oscillations of the aqueous concentrations of VC and t‐DCE. When formate and methanol were substituted for methane as alternative electron donors, inhibition ceased (no oscillations), and concentrations were reduced to levels achieved during periods when no methane was present, confirming the inhibition by methane. Higher transformation rates were achieved temporarily, i.e., for several days, through the addition of formate or methanol. When electron donor addition was terminated, the concentration of target compounds rapidly increased, indicating that the transformation promptly ceased. Although these experiments indicated that methane competitively inhibits transformation rates, this competition is a second‐order effect: methane as substrate for growth was also required for transformation of VC, t‐DCE, c‐DCE, and TCE by methanotrophs.
Characteristics of Rhodamine WT and Fluorescein as Adsorbing Ground‐Water Tracers
Authors: Sabatini David A. , Austin T. AI 
Published: August 2005

AbstractFluorescent dyes are being used as adsorbing ground‐water tracers for conducting solute transport studies for adsorbing organic chemicals (e.g., pesticides). In this research, the ability of two fluorescent dyes (rhodamine WT and fluorescein) to mimic the adsorptive behavior of two herbicides (atrazine and alachlor) with alluvial aquifer sands was evaluated. Laboratory studies (batch and column) indicated the following order of increasing adsorption: fluorescein, atrazine, alachlor, and rhodamine WT. Thus, the use of fluorescein and rhodamine WT as adsorbing ground‐water tracers was observed to delimit the appearance of the atrazine and alachlor (fluorescein appeared before and rhodamine WT after the herbicides). Several adsorption characteristics of the fluorescent dyes differed from those commonly observed for pesticides. The levels of adsorption for the dyes were several orders of magnitude greater than predicted from empirical relationships based on Kowand foc. The presence of divalent cations was observed to increase the level of rhodamine WT adsorption. The rhodamine WT breakthrough curves were not of the conventional sigmoidal shape but instead leveled off at a C/CO value of 0.5 for a number of pore volumes prior to increasing again towards a C/CO value of 1.0. These characteristics indicate that the adsorptive mechanisms for the fluorescent dyes differed from the adsorptive mechanisms for most pesticides. These variations in fundamental adsorptive mechanisms raise concerns as to the transferability of the results of this research (fluorescein and rhodamine WT delimiting the appearance of atrazine and alachlor) to other subsurface media.
Embedding and Response Matrix Techniques for Maximizing Steady‐State Ground‐Water Extraction: Computational Comparison
Authors: Peralta Richard C. , Azarmnia Hossein , Takahashi Shu 
Published: August 2005

AbstractBoth response matrix and embedding techniques are used to compute optimal sustained‐yield ground‐water extraction strategies for confined aquifers. Historically, the response matrix method has been considered the most practical, because of numerical instability reported to occur when using the embedding approach for large aquifer systems. More recent studies have proven the embedding approach to be stable for large‐scale regional planning. Also, there is increasing emphasis on using microcomputers for ground‐water studies. Thus, it is appropriate to compare response matrix and embedding approaches to steady‐state problems in terms of computational efficiency and memory requirements.For the hypothetical study area, a steady‐state embedding model requires less processing time than a comparable response matrix model. In addition, the embedding model sometimes requires less memory than a response matrix model. Required computer memory is frequently a function of the number of nonzero values in constraint equations. For embedding models, the number of nonzeroes is fixed for a particular study area. For response matrix models, the number of nonzeroes can increase dramatically in proportion to the number of pumping cells and cells at which heads must be constrained. For the sample system, if more than 25 percent of the cells can pump, the response matrix approach requires more memory than does the embedding approach. Before selecting an optimization model for a particular study, one should, as illustrated, evaluate potential memory requirements of both embedding and response matrix approaches. If there is a high percentage of pumping cells, or if many heads must be constrained or computed within the optimization model, the embedding approach seems preferable.
Interpretation of Pumping from Two‐Zone Layered Aquifers Using a Numerical Model
Authors: Rathod K. S. , Rushton K. R. 
Published: August 2005

AbstractA numerical model is presented which represents both the radial and vertical flow components which usually result from pumping from boreholes in layered aquifers. This model, which is based on finite‐difference approximations, runs on a microprocessor system and can be used for the analysis of pumping test results. A discussion on the interaction between the radial and vertical flow components is followed by a description of the model. A computer program in BASIC and a typical computer output are provided. The application of the model for the analysis of a pumping test in a weathered‐fractured aquifer is described. Three case studies are reviewed where the numerical model is used to gain a greater understanding of the aquifer flow processes.
Evaluation of Hydraulic Conductivities Calculated from Multiport‐Permeameter Measurements
Authors: Wolf Steven H. , Celia Michael A. , Hess Kathryn M. 
Published: August 2005

AbstractA multiport permeameter was developed for use in estimating hydraulic conductivity over intact sections of aquifer core using the core liner as the permeameter body. Six cores obtained from one borehole through the upper 9 m of a stratified glacial‐outwash aquifer were used to evaluate the reliability of the permeameter. Radiographs of the cores were used to assess core integrity and to locate 5‐ to 10‐cm sections of similar grain size for estimation of hydraulic conductivity. After extensive testing of the permeameter, hydraulic conductivities were determined for 83 sections of the six cores. Other measurement techniques included permeameter measurements on repacked sections of core, estimates based on grain‐size analyses, and estimates based on borehole flowmeter measurements. Permeameter measurements of 33 sections of core that had been extruded, homogenized, and repacked did not differ significantly from the original measurements. Hydraulic conductivities estimated from grain‐size distributions were slightly higher than those calculated from permeameter measurements; the significance of the difference depended on the estimating equation used. Hydraulic conductivities calculated from field measurements, using a borehole flowmeter in the borehole from which the cores were extracted, were significantly higher than those calculated from laboratory measurements and more closely agreed with independent estimates of hydraulic conductivity based on tracer movement near the borehole. This indicates that hydraulic conductivities based on laboratory measurements of core samples may underestimate actual field hydraulic conductivities in this type of stratified glacial‐outwash aquifer.
Hydrogeological Decision Analysis: 2. Applications to Ground‐Water Contamination
Authors: Massmann Joel , Freeze R. Allan , Smith Leslie , Sperling Tony , James Bruce 
Published: August 2005

AbstractTwo case studies are presented as examples of a decision‐analysis approach to engineering design for projects in which the hydrogeological environment plays an important role. This approach to design involves quantifying benefits, costs, and risks for each design alternative under consideration. Risk, which is defined as the expected costs of failure, reflects both performance uncertainties and failure costs. Probabilities of failure are estimated by coupling stochastic ground‐water flow and solute transport models with uncertainty models that represent input parameters as random variables. The case studies that are used to describe the approach involve (1) selecting a pumping rate for an extraction well to capture an existing contaminant plume, and (2) designing a leachate collection system for a soil remediation facility. The examples illustrate that the decision‐analysis approach can be accomplished using relatively simple analytical models to simulate the behaviors of hydrogeological environments and engineering components. The results identify how the preferred design alternative depends upon the regulatory, hydrogeological, and economic environments in which the decision is made. For the extraction well example, the preferred alternative is relatively insensitive to the costs of failure but is dependent upon the expected dimensions of the contaminant plume. For the soil remediation example, the preferred design alternative depends upon the anticipated costs of failure and the regulatory standard for ground‐water contamination. Reducing the variance or uncertainty in dispersivity values by a factor of 3 had a relatively small effect on the overall design of the leachate collection system.
Geochemical Transformations and Modeling of Two Deep‐Well Injected Hazardous Wastes
Authors: Roy W. R. , Seyler B. , Steele J. D. , Mravik S. C. , Moore D. M. , Krapac I. G. , Peden J. M. , Griffin R. A. 
Published: August 2005

AbstractTwo liquid hazardous wastes (an alkaline brine‐like solution and a dilute acidic waste) were mixed with finely ground rock samples of three injection‐related lithologies (sandstone, dolomite, and siltstone) for 155 to 230 days at 325°K‐10.8 MPa. The pH and inorganic chemical composition of the alkaline waste were not significantly altered by any of the rock samples after 230 days of mixing. The acidic waste was neutralized as a consequence of carbonate dissolution, ion exchange, or clay‐mineral dissolution, and hence was transformed into a nonhazardous waste.Mixing the alkaline waste with the solid phases yielded several reaction products: brucite, Mg(OH)2; calcite, CaCO3; and possibly a type of sodium metasilicate. Clay‐like minerals formed in the sandstone, and hydrotalcite, Mg6Al2‐CO3 (OH)16· 4H2O, may have formed in the siltstone at trace levels. Mixing the alkaline waste with a synthetic brine yielded brucite, calcite, and whewellite (CaC2O4· H2O). The thermodynamic model PHRQPITZ predicted that brucite and calcite would precipitate from solution in the dolomite and siltstone mixtures and in the alkaline waste‐brine system.The dilute acidic waste did not significantly alter the mineralogical composition of the three rock types after 155 days of contact. The model PHREEQE indicated that the calcite was thermodynamically stable in the dolomite and siltstone mixtures, and was detected in small quantities in aged‐solid samples. The sandstone‐waste system appeared to equilibrate with amorphous silica, whereas silica equilibria may not have been attained in the dolomite and siltstone systems.Computer models like PHRQPITZ and PHREEQE may be useful tools for estimating mineral equilibria in deep‐well scenarios, but there is a need to expand the database used in these kinds of calculations. Caution must be applied in interpreting the predicted equilibria. Fate modeling based on thermodynamic principles can predict simple geochemical interactions, but empirical, laboratory‐based investigations may be needed in addition to modeling for a reliable assessment of the fate of injected wastes.
Evaluation of Sorption Models in the Simulation of Naphthalene Transport Through Saturated Soils
Authors: Liu Ko‐Hui , Enfield Carl G. , Mravik Susan C. 
Published: August 2005

AbstractTo show the effect of sorption model selection, the one‐dimensional transport of naphthalene in two saturated porous media was simulated using numerical models, which included the processes of dispersion, advection, and sorption. Three vdifferent models describing the sorption process: (1) a local equilibrium model, (2) a first‐order kinetic sorption model, and (3) a two‐site model (a combination of equilibrium and kinetic sorption model), were examined. In addition, this study considered two types of boundary conditions: constant concentration and constant flux boundary conditions. Simulations were made for data of naphthalene transport through a laboratory soil column packed with Lincoln or Eustis soil series. Numerical simulation results show that the selection of the sorption model had significant effects on the numerical solutions. The numerical solution obtained using either the local equilibrium model or the first‐order kinetic sorption model described the experimental data very well from the Lincoln soil column. In contrast, the numerical solution obtained using the two‐site model described the experimental data for the Eustis soil better than either the equilibrium or kinetic models. Different boundary conditions had little influence on the numerical solutions. Different amounts of organic carbon in the Eustis (0.66%) and Lincoln (0.036%) soils are thought to cause the differences in breakthrough curves and the response to the sorption processes.
Calibration of a Texture‐Based Model of a Ground‐Water Flow System, Western San Joaquin Valley, Californiaa
Authors: Phillips Steven P. , Belitz Kenneth 
Published: August 2005

AbstractThe occurrence of selenium in agricultural drain water from the western San Joaquin Valley, California, has focused concern on the semiconfined ground‐water flow system, which is underlain by the Corcoran Clay Member of the Tulare Formation. A two‐step procedure is used to calibrate a preliminary model of the system for the purpose of determining the steady‐state hydraulic properties. Horizontal and vertical hydraulic conductivities are modeled as functions of the percentage of coarse sediment, hydraulic conductivities of coarse‐textured (Kcoarse) and fine‐textured (Kfine) end members, and averaging methods used to calculate equivalent hydraulic conductivities. The vertical conductivity of the Corcoran (Kcorc) is an additional parameter to be evaluated.In the first step of the calibration procedure, the model is run by systematically varying the following variables: (1) Kcoarse/Kfine, (2) Kcoarse/Kcorc, and (3) choice of averaging methods in the horizontal and vertical directions. Root mean square error and bias values calculated from the model results are functions of these variables. These measures of error provide a means for evaluating model sensitivity and for selecting values of Kcoarse, Kfine, and Kcorc for use in the second step of the calibration procedure. In the second step, recharge rates are evaluated as functions of Kcoarse, Kcorc, and a combination of averaging methods. The associated Kfine values are selected so that the root mean square error is minimized on the basis of the results from the first step.The results of the two‐step procedure indicate that the spatial distribution of hydraulic conductivity that best produces the measured hydraulic head distribution is created through the use of arithmetic averaging in the horizontal direction and either geometric or harmonic averaging in the vertical direction. The equivalent hydraulic conductivities resulting from either combination of averaging methods compare favorably to field‐ and laboratory‐based values.
Assessing Pesticide Contamination to Ground Water: A Rapid Approach
Authors: Ehteshami Majid , Peralta Richard C. , Eisele Hubert , Deer Howard , Tindall Terry 
Published: August 2005

AbstractA methodology has been developed for identifying hazardous pesticides/site combinations threatening ground‐water contamination. Screening methodologies are required to determine which locations and pesticides now in use should receive the greatest attention to safeguard the public health. The presented method uses a hazard to ground‐water hydrogeological screening model (DRASTIC) and employs a one‐dimensional pesticide transport model (CMLS). The method is an efficient and practical technique to identify where particular combinations of pesticides, water management practices, soils, and geology result in the greatest potential hazard to ground‐water contamination. Use of the presented approach can reduce sampling needs and expense.
History Matching to Determine the Retardation of PCE in Ground Water
Authors: Rogers L. 
Published: August 2005

AbstractFailure to incorporate retardation factors in solute transport predictions can lead to serious miscalculations of the degree of contamination and the time required for remediation. This study employs history matching, a vital component in the effort to calibrate models to specific field sites, to demonstrate the difficulties in matching historical well concentrations to a single retardation factor or source function. A 2‐D hybrid finite‐element/finite‐difference, advection‐dispersion code with retardation was used to match simulated perchloroethylene (PCE, also known as tetrachloroethylene) concentrations against observed concentrations in monitor wells at a well‐characterized Superfund site. The transport model yielded reasonable matches for retardation factors between 1 and 3. This was in comparison to the 6 to 22 range of retardation factors based on laboratory batch sorption experiments and the 1 to 5 range based on field measurements of soil and associated well‐water pore fluid. Simulation results demonstrated that for this site, retardation factors greater than or equal to 6 would imply releases of PCE prior to dates compatible with historical records. History matching can constrain the reasonable range of parameters necessary to model contaminants in ground water.
Fingerprinting Petroleum Contamination Using Synchronous Scanning Fluorescence Spectroscopy
Authors: Pharr Daniel Y. , McKenzie J. Keith , Hickman Aaron B. 
Published: August 2005

AbstractSynchronous scanning fluorescence spectroscopy is a simple, cost‐effective method for fingerprinting many petroleum contaminants in ground‐water and soil samples. The extraction of contaminated ground‐water and soil samples with water and cyclohexane followed by the synchronous scanning fluorescence spectrophotometry of the organic extract is described for over 20 petroleum product standards and actual samples. This method allows for the classification and identification of aromatic‐containing products such as: gasoline, kerosene, diesel oil, various grades of fuel oil, and asphalt. This analytical method is more efficient than chromatographic methods typically used for quantitative analysis of petroleum contaminants and its spectra are easier to interpret for fingerprinting purposes. Several case studies of its use in determining among alternate sources of contamination are presented.