bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sampling Colloids and Colloid‐Associated Contaminants in Ground Water
Authors: Backhus Debera A. , Ryan Joseph N. , Groher Daniel M. , MacFarlane John K. , Gschwend Philip M. 
Published: August 2005

AbstractIt has recently been recognized that mobile colloids may affect the transport of contaminants in ground water. To determine the significance of this process, knowledge of both the total mobile load (dissolved + colloid‐associated) and the dissolved concentration of a ground‐water contaminant must be obtained. Additional information regarding mobile colloid characteristics and concentrations are required to predict accurately the fate and effects of contaminants at sites where significant quantities of colloids are found. To obtain this information, a sampling scheme has been designed and refined to collect mobile colloids while avoiding the inclusion of normally immobile subsurface and well‐derived solids. The effectiveness of this sampling protocol was evaluated at a number of contaminated and pristine sites.The sampling results indicated that slow, prolonged pumping of ground water is much more effective at obtaining ground‐water samples that represent in situ colloid populations than bailing. Bailed samples from a coal tar‐contaminated site contained 10–100 times greater colloid concentrations and up to 750 times greater polycyclic aromatic hydrocarbon concentrations as were detected in slowly pumped samples. The sampling results also indicated that ground‐water colloid concentrations should be monitored in the field to determine the adequacy of purging if colloid and colloid‐associated contaminants are of interest. To avoid changes in the natural ground‐water colloid population through precipitation or coagulation, in situ ground‐water chemistry conditions must be preserved during sampling and storage. Samples collected for determination of the total mobile load of colloids and low‐solubility contaminants must not be filtered because some mobile colloids are removed by this process. Finally, suggestions that mobile colloids are present in ground water at any particular site should be corroborated with auxiliary data, such as colloid levels in “background” wells, colloid‐size distributions, ground‐water geochemistry, and colloid surface characteristics.
Numerical Simulation of the Wicking Effect in Liner Systems
Authors: Yeh T.‐C. Jim , Guzman Amado , Srivastava Rajesh , Gagnard Philip E. 
Published: August 2005

AbstractNumerical simulations were carried out to investigate the capillary barrier effect and the wicking ability of multilayer earth liner systems. Two specific cases were studied: a two‐layer liner composed of a fine‐ over a coarse‐textured material, and a three‐layer liner composed of a medium‐textured material in between a fine‐ and a coarse‐textured material. Results of the simulations show that a quadratic relationship exists between the thickness of the fine‐textured material and the arrival time of the wetting front to the interface. At the time the wetting front reaches the interface, the width of the lateral spreading within the fine material is smaller than the thickness of this material. The lateral spreading and thickness are linearly related. The wicking ability of the different materials is more significant under relatively smaller infiltration rates and is controlled by the magnitude of the hydraulic diffusivity. For the two‐layer liner the criteria of minimizing the vertical movement and maximizing the wicking effect within the fine‐textured material conflict. A three‐layer liner satisfies both of these criteria. The results for the three‐layer system show that the medium‐textured material has more superior wicking properties than the fine material does.
Estimation of Aquifer Diffusivity from Analysis of Constant‐Head Pumping Test Data
Authors: Hiller Christian K. , Levy Benjamin S. 
Published: August 2005

AbstractAn approximation of the drawdown function developed by Hantush (1964) for late times was used to estimate the aquifer diffusivity directly from measured data from a constant‐head pumping test. This method of evaluation is especially useful in cases where early time data are absent or are obscured by other phenomena The use of the constant‐head time type curves allows ambiguity in the choice of the time match point because of the shallow slopes of the type curves for later times.Using the described approximation, constant‐head time type curves specific to the dimensionless distance from the pumping well may be compared with the measured data to find anomalies and bias in the measured data. A case study is presented to compare the results of the analyses with the constant‐head time type curves and with the approximation of the drawdown function. The results show that the approximation is valid after the first 100 minutes of measurement.
Testing an Automated Method to Estimate Ground‐Water Recharge from Streamflow Records
Authors: Rutledge A. T. , Daniel C. C. 
Published: August 2005

AbstractThe computer program, RORA, allows automated analysis of streamflow hydrographs to estimate ground‐water recharge. Output from the program, which is based on the recession‐curve‐displacement method (often referred to as the Rorabaugh method, for whom the program is named), was compared to estimates of recharge obtained from a manual analysis of 156 years of streamflow record from 15 streamflow‐gaging stations in the eastern United States. Statistical tests showed that there was no significant difference between paired estimates of annual recharge by the two methods. Tests of the slopes of best‐fit lines through paired estimates showed that the slopes were not significantly different from unity. Tests of results produced by the four workers who performed the manual method showed that results can differ significantly between workers. Twenty‐two percent of the variation between manual and automated estimates could be attributed to having different workers perform the manual method. The program RORA will produce estimates of recharge equivalent to estimates produced manually, greatly increase the speed of analysis, and reduce the subjectivity inherent in manual analysis.
Comparison of Drilling Reports and Detailed Geophysical Analysis of Ground‐Water Production in Bedrock Wells
Authors: Paillet Frederick , Duncanson Russell 
Published: August 2005

AbstractThe most extensive data base for fractured bedrock aquifers consists of drilling reports maintained by various state agencies. We investigated the accuracy and reliability of such reports by comparing a representative set of reports for nine wells drilled by conventional air percussion methods in granite with a suite of geophysical logs for the same wells designed to identify the depths of fractures intersecting the well bore which may have produced water during aquifer tests. Production estimates reported by the driller ranged from less than 1 to almost 10 gallons per minute. The moderate drawdowns maintained during subsequent production tests were associated with approximately the same flows as those measured when boreholes were dewatered during air percussion drilling. We believe the estimates of production during drilling and drawdown tests were similar because partial fracture zone dewatering during drilling prevented larger inflows otherwise expected from the steeper drawdowns during drilling. The fractures and fracture zones indicated on the drilling report and the amounts of water produced by these fractures during drilling generally agree with those identified from the geophysical log analysis. Most water production occurred from two fractured and weathered zones which are separated by an interval of unweathered granite. The fractures identified in the drilling reports show various depth discrepancies in comparison to the geophysical logs, which are subject to much better depth control. However, the depths of the fractures associated with water production on the drilling report are comparable to the depths of the fractures shown to be the source of water inflow in the geophysical log analysis. Other differences in the relative contribution of flow from fracture zones may by attributed to the differences between the hydraulic conditions during drilling, which represent large, prolonged drawdowns, and pumping tests, which consisted of smaller drawdowns maintained over shorter periods. We conclude that drilling reports filed by experienced well drillers contain useful information about the depth, thickness, degree of weathering, and production capacity of fracture zones supplying typical domestic water wells. The accuracy of this information could be improved if relatively simple and inexpensive geophysical well logs such as gamma, caliper, and normal resistivity logs were routinely run in conjunction with bedrock drilling projects.
Evidence for Dedolomitization and Mixing in Paleozoic Carbonates Near Oak Ridge, Tennessee
Authors: Saunders James A. , Toran Laura E. 
Published: August 2005

AbstractMultiport ground‐water sampling systems in five deep core holes near DOE's Y‐12 facility at Oak Ridge, Tennessee provide data on the three‐dimensional distribution of ground‐water types and chemical evolution processes. Interpretation of ground‐water chemistry, coupled with data on the primary and authigenic mineralogy from drill core, indicates the ground water evolves chemically by three main processes: (1) open system dissolution of calcite and dolomite at shallow depths to produce Ca‐Mg‐HCO3 waters; (2) irreversible dissolution of gypsum, which causes dedolomitization and leads to the formation of Ca‐Mg‐SO4 waters at deeper levels; and (3) mixing with deep brines to form saline Na‐Ca‐Cl waters. Evidence for dedolomitization included the precipitation of authigenic calcite in gypsum dissolution cavities, decrease in ground‐water pH, and increases in dissolved Ca, Mg, and SO4. In this study, we document the dedolomitization process along a relatively short (< 2000 ft) flow path in low permeability Paleozoic carbonates. Mixing of the shallower ground water with an Na‐Ca‐Cl brine thought to be present at depth can account for the progressive increase in salinity of ground water with depth and the precipitation of authigenic barite and celestite. The mixing process could be a combination of diffusion from below, diffusion from older matrix water into fractures, or advective mixing.
Characterization of Flow Parameters Controlling Soil Vapor Extraction
Authors: Beckett G. D. , Huntley David 
Published: August 2005

AbstractSoil parameters controlling vapor flow in the subsurface are necessary to design soil vapor extraction (SVE) cleanup systems. Previous work assumes a confined flow model, with concrete and asphalt surface covers providing the confining layer and preventing air leakage into the zone of vapor transmission. SVE field tests conducted as part of this investigation, however, exhibited responses that are inconsistent with a confined flow model; it appears that the real world leaks. This paper develops a transient soil vapor extraction (SVE) testing method that considers the effects of vertical leakage. Analytic methodologies are developed that allow use of commonly available ground‐water flow type curves to evaluate SVE test data. The key implications of leaky compared to confined flow are (1) smaller values of derived vapor permeability, and (2) decreased radial cleanup efficacy, both with time and distance.
Attenuation and Biodegradation of Chlorophenols in Ground Water at a Former Wood Treating Facility
Authors: Davis Andy , Campbell Jim , Gilbert Craig , Ruby Michael V. , Bennett Meridan , Tobin Susan 
Published: August 2005

AbstractThis communication describes novel methods to measure site‐specific sorption data, and to determine if biodegradation of pentachlorophenol (PCP) in complex technical‐grade formulations occurs at industrial facilities. Ground‐water slurry samples containing between 0.012 and 230 mg/l PCP were collected from a former wood treating site, the liquid and solid fractions separated, and both fractions analyzed for PCP using selective ion monitoring to determine sorption coefficients (Kd(PCP)). Although field sorption coefficients could not be represented by simple Freundlich and Langmuir isotherms, an empirical hyperbolic function (Kd(PCP)) = 0.054 + 0.086/Caq) fit the isotherm (r > 0.99), demonstrating that for PCP > 10 mg/l, no measurable retardation occurred in the aquifer. Biodegradation of PCP in ground water was apparent when PCP concentrations were < 20 mg/1, while at higher concentrations, PCP in the technical‐grade formulation appeared to break down less readily. The results imply that, at the plume periphery, PCP in the subsurface will be attenuated and degrade, while at higher concentrations (i.e., at the source), PCP is mobile, and more recalcitrant to degradation.
A Study of the DRASTIC Methodology with Emphasis on Swedish Conditions
Authors: Rosen Lars 
Published: August 2005

AbstractA study of the DRASTIC classification methodology, with special emphasis on Swedish conditions, indicated both favorable and unfavorable properties of the system. The study showed that the fairly large number of parameters (seven) and the correlations between these parameters give DRASTIC some advantageous statistical properties. A comparison of the DRASTIC parameters with parameters found to determine the effects on ground‐water quality in surficial aquifers in southwestern Sweden from acid deposition showed a good agreement between these two parameter sets; the study thus indicated that the selection of parameters is relevant for general ground‐water vulnerability assessments in Sweden. The concept of hydrogeologic settings and the possibility to trace results backwards in the system is excellent, but the qualitative weight functions in DRASTIC result in a simplistic index of unclear meaning that is less useful and less distinctive than desired. The system tends to overestimate the vulnerability of porous media aquifers compared to aquifers in fractured media; the rating tables need to be revised so that more weight is given to specific surface and effective porosity, and less to hydraulic conductivity. The applicability of the results would be enhanced and the risk of misuse reduced if the results were more clearly directed toward scientifically defined factors, e.g. sorption capacity, travel time, and dilution.
A Simple and Powerful Method of Parameter Estimation Using Simplex Optimization
Authors: Devlin J. F. 
Published: August 2005

AbstractThe need for objective parameter estimates is common in hydrogeology. The simplex optimization algorithm provides a fast, simple, and versatile method for making such estimates when used to minimize the residuals sum of squares between calculated and observed data points. Examples of the method applied to Pick's Second Law, the advection dispersion equation, and the integrated Monod kinetics equation illustrate its utility. Compiled programs have been developed, and are available on request, for the estimation of diffusion coefficients, contaminant transport parameters (average linear ground‐water velocities, dispersivities, porosities), and biodegradation kinetic constants.
Monitoring Drainage Solution Concentrations and Solute Flux in Unsaturated Soil with a Porous Cup Sampler and Soil Moisture Sensors
Authors: McGuire Patrick E. , Lowery Birl 
Published: August 2005

AbstractSoil solution samples are often collected and analyzed without consideration for either the drainage period or changes in solution or solute flux. A sampling method to assess the vertical flux of solution and solute in the unsaturated zone was evaluated. Potassium bromide (KBr) solution and distilled water were applied to the surface of a soil. Estimated and measured solution and solute discharge through the soil column were compared. The column consisted of Plainfield sand (mixed, mesic, Typic Udipsamments) packed in a 208‐liter cylinder. Following solution application, discrete samples were collected at one‐ to two‐hour intervals with a ceramic soil solution sampler centrally located in the column. In each test, the Br concentrations of discrete samples were measured, and the Br concentration of a time‐integrated composite sample was calculated. Solution flux was estimated by monitoring vertical soil‐water tension and content gradients with tensiometers and time domain reflectometry probes, respectively, and applying the unsaturated form of Darcy's equation. In three of four tests, differences between measured and estimated solution discharge were 20%. Differences in measured and estimated Br mass discharge ranged from 1 to 37%. Correlation coefficients between estimated and measured Br mass discharge based on discrete and composite sample concentrations were 0.905 (p = 0.095) and 0.70 (p = 0.30), respectively.
An Expert Systems Approach for Assessing the Potential for Pesticide Contamination of Ground Water
Authors: Crowe A. S. , Mutch J. P. 
Published: August 2005

AbstractThe EXPRES expert system (EX pert system for Pesticide/Regulatory Evaluations and Simulations) has been developed to assist those who are knowledgeable, but not proficient, in the theory of pesticide transport in the subsurface or in the use of pesticide assessment models with a means of assessing the potential for pesticides to contaminate ground water. EXPRES is not intended to replace expert opinion but rather EXPRES is intended to be used as a screening tool by nonexperts who need to evaluate the potential for pesticides to contaminate ground water. EXPRES combines a knowledge‐based system, a graphically based user‐system interface, extensive geographical and pesticide data bases, and three existing pesticide assessment models (LP/LI, PRZM, and LEACHM). Based on the user's available data, objectives of the assessment and time constraints, EXPRES selects the most appropriate model, assists the user in the construction of an input data set, initiates an assessment, and aids in the interpretation of the results of an assessment model. Specific assistance in the construction of the input data set includes providing pertinent data for characterizing a site or a pesticide from its data bases, assisting the user to respond to a prompt from EXPRES, aiding the user in estimating missing values for pesticide or site parameters, and ensuring the zintegrity of the input data set. The inclusion of three models allows EXPRES to select the model which is most applicable for the objectives on the investigation, including: (1) a review of pesticide properties and site characteristics that influence the fate of pesticides in the subsurface, (2) a relative assessment, with respect to other pesticides, of the potential for a pesticide to leach to the water table, (3) a quantitative prediction of the distribution and migration rates of the pesticide with both time and depth, and (4) an evaluation of the processes and factors controlling the fate of the pesticides in the subsurface.
Adsorbed Concentration vs. Lab‐Reported Concentration in Soil
Authors: Mohsen Mohammad F. N. 
Published: August 2005

AbstractThe current practice of how concentration of contaminants in soil is measured allows room for the reported value to be confused with adsorbed concentration. This note clarifies the distinction between lab‐reported concentration and adsorbed concentration in soils. The paper shows that for highly adsorbed substances, the distinction virtually vanishes. However, for poorly adsorbed substances, this distinction can be significant.
Well Discharge Optimization Using Analytic Elements
Authors: Fitts Charles R. 
Published: August 2005

AbstractUsing superpositioned analytic functions (elements), it is possible to directly solve the following well discharge optimization problems in general flow models:1. Determine the discharge of well A which will produce a certain head or drawdown at location B.2. Determine the discharge of well A which will produce a specified component of aquifer discharge at location B. These problems often arise while designing contamination remediation systems, designing dewatering systems, ormaking ground‐water resource allocation decisions. Such problems are solved by trial and error with nonoptimized models, or solved iteratively with standard optimizing methods. With this analytic formulation, they can be solved directly. This approach can be used to optimize the performance of a single well or to simultaneously optimize the performance of numerous wells. For example, it is possible to solve directly for the combination of discharges at wells A, B, C, D, and E that will produce specified heads at locations F and G while producing specified aquifer discharges at locations H, I, and J. Applications of the method are demonstrated using TWODAN, a program for analytic two‐dimensional flow modeling.
Physical and Mathematical Modeling of Diesel Fuel Liquid and Vapor Movement in Porous Media
Authors: Johnson T. E. , Kreamer D. K. 
Published: August 2005

AbstractTwo‐dimensional physical modeling of diesel fuel leaks was conducted in sand tanks to determine liquid and vapor migration characteristics. Mathematical modeling provided estimation of vapor concentrations at discrete times and distances from the vapor source and was compared to the physical experiment. The mathematical gaseous diffusion model was analogous to the Theis equation for ground‐water flow, accounted for sorptive effects of the media, and was calibrated using measured concentrations from the sand tank. Mathematically different positions of the vapor source were tested to better relate observed liquid flow rates and media configuration to gaseous concentrations. The calculated diffusion parameters were then used to estimate theoretical, three‐dimensional vapor transport from a hypothetical liquid leak of 2.0 1/hr for 30 days. The associated three‐dimensional vapor plume, which would be reasonably detectable by commercially available vadose zone monitors, was estimated to have a diameter of 8 m with a vapor concentration of 50 ppm at the outside edge of the vapor plume. A careful application of the method and values can be used to give a first approximation to the number of vapor monitors required at a field site as well as the optimal locations for the monitors.
Analysis of Slope‐Matching Methods for Aquifer Parameter Determination
Authors: Srivastava Rajesh , Guzman‐Guzman Amado 
Published: August 2005

AbstractVarious methods for numerical determination of aquifer transmissivity and storage coefficients from a single observation well data have recently been proposed. Most of these methods involve reading the slope values from a table or providing an initial estimate for iterative solution. A different formulation of the slope‐matching technique has been suggested in the field of petroleum engineering which obtains the parameter values without using any tables or iterative procedures. In this study we adopt a similar approach and compare the prediction of various techniques. The modification of the approach to include cases with time‐varying parameters is examined. Numerical experiments are performed first on synthetic data to ascertain the relative accuracy of different slope evaluation techniques. It is shown that the slope of the drawdown with respect to the logarithm of time results in the most accurate prediction of aquifer parameters. The inaccuracy involved in application of the slope‐matching methods to cases involving time‐varying parameters is analyzed. The methods are then applied to some field data and the results are compared with published data. AH the methods are found to work reasonably well for the field application.