bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surfactant Remediation Field Demonstration Using a Vertical Circulation Well
Authors: Knox R. C. , Sabatini D. A. , Harwell J. H. , Brown R. E. , West C. C. , Blaha F. , Griffin C. 
Published: August 2005

AbstractA field demonstration of surfactant‐enhanced solubilization was completed in a shallow unconfined aquifer located at a Coast Guard Station in Traverse City, Michigan. The primary objectives of the study were: (1) to assess the ability of the vertical circulation well (VCW) system for controlling chemical extractants added to the subsurface; and (2) to assess the behavior of the surfactant solution in the subsurface, with a goal of maximum surfactant recovery. A secondary objective was to demonstrate enhanced removal of PCE and recalcitrant components of a jet fuel. The analytical results showed that the surfactant increased the contaminant mass extracted by 40–fold and 90–fold for the PCE and jet fuel constituents, respectively. The surfactant solution demonstrated minimal sorption (retardation) and did not precipitate in the subsurface formation. In addition, the VCW system was able to capture in excess of 95% of the injected surfactant solution. Additional field testing and full‐scale implementation of surfactant‐enhanced subsurface remediation should be performed.
Design of a Surfactant Remediation Field Demonstration Based on Laboratory and Modeling Studies
Authors: Sabatini D. A. , Knox R. C. , Harwell J. H. , Soerens T. , Chen L. , Brown R. E. , West C. C. 
Published: August 2005

Abstract Surfactant‐enhanced subsurface remediation is being evaluated as an innovative technology for expediting ground‐water remediation. This paper reports on laboratory and modeling studies conducted in preparation for a pilot‐scale field test of surfactant‐enhanced subsurface remediation. Laboratory batch and column studies evaluated the surfactant‐contaminant ground‐water interactions in an effort to properly design the field‐scale demonstration. A series of laboratory tracer tests and numerical simulations were completed to demonstrate the effectiveness of the hydraulic system (a vertical circulation well—VCW) for capturing injected solutions in a shallow, highly conductive, unconfined ground‐water formation. The results of these studies were then used to optimize the performance of the VCW system during the subsequent field‐scale demonstration study which utilized the VCW for injecting and extracting a surfactant solution. Information from the simulation studies, combined with the results of the batch and column tests, was crucial for procuring regulatory approval for the field demonstration, and successful design of the field‐scale demonstration.
EPM Modeling of a Field‐Scale Tritium Tracer Experiment in Fractured, Weathered Shale
Authors: McKay L. D. , Stafford P. L. , Toran L. E. 
Published: August 2005

AbstractA 2D equivalent porous media (EPM) model was used to simulate transport of tritium for a field‐scale tracer experiment in a fractured and highly weathered shale saprolite. The tritium plume was characterized by rapid migration of the leading edge of the plume (up to 0.4 m/day), slower movement of the center of mass of the tritium pulse (0.009 m/day) and very slow decline of concentrations in the “tail” of the breakthrough curve (which has persisted at the site for at least 16 years). The EPM model successfully described the shape of the plume and the breakthrough curves for a monitoring well 3.7 m downgradient of the injection well using a flow velocity of 0.01 m/day and longitudinal and transverse dispersivity values of 0.8 m. An unusually low ratio of longitudinal and transverse dispersivity (αL/αT= 1) was needed to fit the nearly circular shape of the plume, which is believed to be caused by the water‐table slope being perpendicular to the orientation of the prominent bedding plane fractures (which are expected to correspond to Kmax). Simulated values for concentrations in the long “tail” of the breakthrough curve observed in a downgradient well were especially sensitive to the value of longitudinal dispersivity used. The best‐fit simulation, based on data over a 5 year period, was extrapolated to the most recent data point (16 years after the start of the injection) and the simulated concentration was very close to the measured value. Model predictions made with a slightly different value of longitudinal dispersivity resulted in very large errors at late time, indicating that duration of monitoring data (which strongly influences the fitting of longitudinal dispersivity) is a critical factor in accurate prediction. The experiment and simulations show that contaminant plumes can persist for long periods of time in fractured porous materials, presumably due to diffusive exchange between the rapidly moving water in the fractures and the relatively immobile pore water in the fine‐grained matrix.
Use of Chemical and Isotopic Tracers to Characterize the Interactions Between Ground Water and Surface Water in Mantled Karst
Authors: Katz Brian G. , Coplen Tyler B. , Bullen Thomas D. , Davis J. Hal 
Published: August 2005

AbstractIn the mantled karst terrane of northern Florida, the water quality of the Upper Floridan aquifer is influenced by the degree of connectivity between the aquifer and the surface. Chemical and isotopic analyses [18O/16O (δ18O), 2H/1H (δD), 13C/12C (δ13C), tritium (3H), and strontium‐87/strontium‐86 (87Sr/86Sr)] along with geochemical mass‐balance modeling were used to identify the dominant hydrochemical processes that control the composition of ground water as it evolves downgradient in two systems. In one system, surface water enters the Upper Floridan aquifer through a sinkhole located in the Northern Highlands physiographic unit. In the other system, surface water enters the aquifer through a sinkhole lake (Lake Bradford) in the Woodville Karst Plain. Differences in the composition of water isotopes (δ18O and <δD) in rainfall, ground water, and surface water were used to develop mixing models of surface water (leakage of water to the Upper Floridan aquifer from a sinkhole lake and a sinkhole) and ground water. Using mass‐balance calculations, based on differences in δ18O and δD, the proportion of lake water that mixed with meteoric water ranged from 7 to 86% in water from wells located in close proximity to Lake Bradford. In deeper parts of the Upper Floridan aquifer, water enriched in 18O and D from five of 12 sampled municipal wells indicated that recharge from a sinkhole (1 to 24%) and surface water with an evaporated isotopic signature (2 to 32%) was mixing with ground water.The solute isotopes, δ13C and 87Sr/86Sr, were used to test the sensitivity of binary and ternary mixing models, and to estimate the amount of mass transfer of carbon and other dissolved species in geochemical reactions. In ground water downgradient from Lake Bradford, the dominant processes controlling carbon cycling in ground water were dissolution of carbonate minerals, aerobic degradation of organic matter, and hydrolysis of silicate minerals. In the deeper parts of the Upper Floridan aquifer, the major processes controlling the concentrations of major dissolved species included dissolution of calcite and dolomite, and degradation of organic matter under oxic conditions. The Upper Floridan aquifer is highly susceptible to contamination from activities at the land surface in the Tallahassee area. The presence of post‐ 1950s concentrations of 3H in ground water from depths greater than 100 m below land surface indicates that water throughout much of the Upper Floridan aquifer has been recharged during the last 40 years. Even though mixing is likely between ground water and surface water in many parts of the study area, the Upper Floridan aquifer produces good quality water, which due to dilution effects shows little if any impact from trace elements or nutrients that are present in surface waters.
Estimation of αL, Velocity, Kd and Confidence Limits from Tracer Injection Test Data
Authors: Broermann James , Bassett R.L. , Weeks Edwin P. , Borgstrom Mark 
Published: August 2005

AbstractBromide and boron were used as tracers during an injection experiment conducted at an artificial recharge facility near Stanton, Texas. The Ogallala aquifer at the Stanton site represents a heterogeneous alluvial environment and provides the opportunity to report scale dependent dispersivities at observation distances of 2 to 15 m in this setting. Values of longitudinal dispersivities are compared with other published values. Water samples were collected at selected depths both from piezometers and from fully screened observation wells at radii of 2, 5, 10 and 15 m. An exact analytical solution is used to simulate the concentration breakthrough curves and estimate longitudinal dispersivities and velocity parameters. Greater confidence can be placed on these data because the estimated parameters are error bounded using the bootstrap method. The non‐conservative behavior of boron transport in clay rich sections of the aquifer were quantified with distribution coefficients by using bromide as a conservative reference tracer.
Modifications of Combined Mathematical Model of Flow in an Aquifer‐Vertical Well System
Authors: Tarshish Michael 
Published: August 2005

AbstractA combined mathematical model and calculation method was developed for steady‐state flow in a confined aquifer‐well system for a general case of partial penetration. The model can be used for analysis of systems where the ends of well screens may not be located in the boundary plains of a confined aquifer.The hydraulics of the system are studied without the assumption that inflow to the screen is uniform. A partially penetrating well is represented as a linear sink located along the well axis between the boundary planes for description of the flow in an aquifer. Description of the system includes equations of flow in the aquifer and in the radial and central orifices of the screen, taking into account energy losses and the momentum flux change along the well screen's axial (vertical) orifice.The use of the proposed combined model enables one (as in the specific case studied earlier where the upper end of the screen is located in the plane of the upper confining bed) to avoid substantial errors in calculations of the drawdown‐well discharge function and maximum specific discharge to the screen which influences sand pumping, incrustation and corrosion processes.
Modeling the Fate and Transport of Household Chemicals in Septic Systems
Authors: Lee Sijin , McAvoy Drew C. , Szydlik James , Schnoor Jerald L. 
Published: August 2005

AbstractA mathematical model was developed for the purpose of predicting the fate and transport of down‐the‐drain household chemicals in septic systems. The model was tested with field data collected from a typical septic system located near Cambridge, Ontario, Canada. Model simulations were in good agreement with field data for the laundry detergent builders tartrate monosuccinate (TMS) and tartrate dissuccinate (TDS). The model was also independently verified with phosphate data collected from the study site. A sensitivity analysis showed little change in model predictions when the distribution coefficient and biodegradation rate constants were varied by 10%. Results from this study support that this model is satisfactory as a screening level tool for predicting the fate and transport of household chemicals in septic systems.
Dissolved Gas Transport in the Presence of a Trapped Gas Phase: Experimental Evaluation of a Two‐Dimensional Kinetic Model
Authors: Donaldson J.H. , Istok J.D. , O'Reilly K.T. 
Published: August 2005

AbstractQuantitative information on dissolved gas transport in ground water aquifers is needed for a variety of site characterization and remedial design applications. The objective of this study was to gain further understanding of dissolved gas transport in the presence of trapped gas in the pore space of an otherwise water saturated porous medium, using a combination of laboratory experiments and numerical modeling. Transport experiments were conducted in a large‐scale (4 × 2 × 0.2 m) laboratory physical aquifer model containing a homogeneous sandpack. Tracer (Br−) and dissolved gas (O2 or H2) plumes were created using a two‐well injection/extraction scheme and then were allowed to drift in a uniform flow field. Plume locations and shapes were monitored by measuring tracer and dissolved gas concentrations as a function of position within the sandpack and tune. In all experiments, partitioning of the dissolved gases between the mobile ground water and stationary trapped gas phases resulted in substantial retardation and tailing of the dissolved O2 and H2 plumes relative to the Br− plumes. Most observed plume features could be reproduced in simulations performed with a numerical model that combined the advection‐dispersion equation with diffusion controlled mass transfer of dissolved gas between the mobile aqueous and stationary trapped gas phases. Fitted values of the volumetric trapped gas content and mass transfer coefficient ranged from 0.04 to 0.08 and from 10−6to 10−5 sec−1, respectively. Sensitivity analyses were used to examine how systematic variations in these parameters would be expected to affect dissolved gas transport under a range of potential field conditions. The experimental and modeling results indicate that diffusion controlled mass transfer should be considered when predicting dissolved gas transport in ground water aquifers in the presence of trapped gas.
Ground Water Contaminant Source and Transport Parameter Identification by Correlation Coefficient Optimization
Authors: Sidauruk P. , Cheng A.H‐D. , Ouazar D. 
Published: August 2005

AbstractInverse procedures based on correlation coefficient optimization are developed to locate ground water contaminant sources and to identify transport parameters. For cases involving two‐dimensional instantaneous and continuous sources, the inverse formulas are explicit. These procedures allow not only for the delineation of the sampled contaminant plume, but also the tracing and the projection of the plume history.
Model Identification Criteria for Inverse Estimation of Hydraulic Parameters
Authors: Hyun Yunjung , Lee Kang‐Kun 
Published: August 2005

AbstractThis study deals with the problem of model structure identification when the zonation method is adopted for parameterization. Our method applies four identification criteria, recommended by Carrera and Neuman (1986a), to a synthetic model and to a set of field data from the Taegu area, Korea. Study of the synthetic model demonstrates that the quality of head data, the depth of data acquisition, and the anisotropy ratio of parameters are important factors for the parameter structure when it is identified using the four criteria. It also shows that a specific criterion is not preferable for every case, but that all four criteria should be considered in order to choose the best among a set of alternative aquifer zonation models. The field example shows that the anisotropy of aquifer parameters should be considered for the parameterization of crystalline rock aquifers, which are the most common systems in Korea.
Obtaining Representative Ground Water Samples in a Fractured and Karstic Formation
Authors: McCarthy John , Shevenell Lisa 
Published: August 2005

AbstractGround water was sampled from a number of wells along recharge pathways between fractured shale and karstic carbonate formations to determine the effect of sampling methods on the colloid abundance and the chemical and hydrologic mechanisms controlling the abundance of ground water colloids. Low‐flow minimal drawdown purging and sampling produced samples with much lower and more consistent turbidity than had been obtained during compliance monitoring of the same wells using much higher flow rates and purging of three well volumes. Although some low‐yielding wells required very low pumping rates (10 ml/min) to prevent drawdown, water quality parameters (temperature, pH, electrode potential, dissolved oxygen, specific conductance, and turbidity) stabilized fairly quickly. The total volume of water removed during purging was small (usually only a few liters), and did not appear to be related to either the casing volume or the screen volume of the well. This lack of correlation may indicate that a limited volume of the formation is sampled at the low flow rates. Since only a portion of long screened intervals appear to be sampled, care must be given to placement of the sample tubing to access zones where contaminant migration is expected.
A Comparison of Zero‐Order, First‐Order, and Monod Biotransformation Models
Authors: Bekins Barbara A. , Warren Ean , Godsy E. Michael 
Published: August 2005

AbstractUnder some conditions, a first‐order kinetic model is a poor representation of biodegradation in contaminated aquifers. Although it is well known that the assumption of first‐order kinetics is valid only when substrate concentration, S, is much less than the half‐saturation constant, K s, this assumption is often made without verification of this condition. We present a formal error analysis showing that the relative error in the first‐order approximation is S/Ks and in the zero‐order approximation the error is Ks/S. We then examine the problems that arise when the first‐order approximation is used outside the range for which it is valid. A series of numerical simulations comparing results of first‐ and zero‐order rate approximations to Monod kinetics for a real data set illustrates that if concentrations observed in the field are higher than Ks, it may be better to model degradation using a zero‐order rate expression. Compared with Monod kinetics, extrapolation of a first‐order rate to lower concentrations under‐predicts the biotransformation potential, while extrapolation to higher concentrations may grossly over‐predict the transformation rate. A summary of solubilities and Monod parameters for aerobic benzene, toluene, and xylene (BTX) degradation shows that the a priori assumption of first‐order degradation kinetics at sites contaminated with these compounds is not valid. In particular, out of six published values of Ks for toluene, only one is greater than 2 mg/L, indicating that when toluene is present in concentrations greater than about a part per million, the assumption of first‐order kinetics may be invalid. Finally, we apply an existing analytical solution for steady‐state one‐dimensional advective transport with Monod degradation kinetics to a field data set.
The Influence of Waterflood Design on the Recovery of Mobile DNAPLs
Authors: Gerhard Jason I. , Kueper Bernard H. , Hecox Gary R. 
Published: August 2005

AbstractThis study examines the effectiveness of various waterflooding strategies to recover pooled dense nonaqueous phase liquid (DNAPL) from the subsurface at an industrial facility. The relative influence of horizontal injection/recovery well configuration, established hydraulic gradient, and fluid properties is investigated for a site characterized by a homogeneous silty sand underlain by an impermeable clay layer. The top of the clay layer is located 5 m below the water table and supports a laterally extensive 2 m deep DNAPL pool. The sensitivity study employs a two‐phase flow numerical model that simulates both DNAPL infiltration and redistribution, including the formation of immobilized DNAPL residual. This is accomplished with constitutive relations featuring hysteretic capillary pressure‐saturation pathways in which the local amount of residual formed is a function of the maximum non‐wetting saturation attained during infiltration. Sixteen simulations, performed in two‐dimensional vertical cross‐section, demonstrate that strategies effecting increased wetting phase gradients, namely increasing drawdown at the recovery drain, adding injection wells, and reducing their distance to the recovery drain, result in an increased DNAPL volume recovered with time at the expense of increased volumes of ground water removed per unit volume of DNAPL recovered. Strategies which do not increase wetting phase gradients result in DNAPL recovery with a minimum volume of produced contaminated ground water. Three pulsed pumping simulations indicate that increasing the length of pump shut‐down time decreases the recovery of DNAPL with time but increases efficiency with respect to ground water pumped. Decreased nonwetting density and increased interfacial tension result in poorer DNAPL recovery with respect to both time and volume of ground water removed, while reduced nonwetting viscosity corresponds to dramatically increased efficiency in both respects.
Determining Vertical Anisotropy Ratio Using a Graphical, Iterative Procedure Based on the Hantush Equation
Authors: Schafer David C. 
Published: August 2005

AbstractA method is presented for determining the transmissivity, storage coefficient, and vertical anisotropy ratio of a confined aquifer using constant rate pumping test data obtained from a system of partially penetrating wells. The vertical anisotropy ratio is defined as the ratio of vertical to horizontal hydraulic conductivity. Knowing the anisotropy ratio is essential for computing drawdown and capture zones around partially penetrating pumping structures such as vertical wells, horizontal wells, or trenches.In the method, drawdown data obtained from the observation wells are corrected for partial penetration using the Hantush equation and analyzed using conventional distance‐drawdown methods. Because the correction is dependent on knowing the aquifer coefficients, an iterative procedure is used in which each successive iteration improves on the estimates of transmissivity, storage coefficient and, ultimately, the vertical anisotropy ratio. Computer calculations are used to determine the drawdown correction factors but graphical methods are used to determine the aquifer coefficients so that the analyst can judge the quality of the data fit and become aware of any anomalies that may exist. Although no mathematical proof is offered herein, the iterative procedure in practice has always converged to produce a unique solution for the vertical anisotropy ratio. Based on the author's experience, accurate determination of the aquifer coefficients can be obtained when both deep and shallow observation wells are available.