bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Viscous, Gravitational, and Capillary Forces on DNAPL Saturation
Authors: Dawson Helen E. , Roberts Paul V.
Published: August 2005

Four dense nonaqueous phase liquids (DNAPLs)—bromoform, chlorobenzene, tetrachloroethylene, and trichloro‐ethylene—were used to investigate the influence of viscous, gravitational, and capillary forces on DNAPL saturation in a natural aquifer sand. The relative magnitudes of these forces are expressed in terms of two dimensionless groups, the Capillary Number (NCa), defined as the ratio of the viscous force to capillary force, and the Bond Number (NBo), defined as the ratio of the gravitational force to capillary force.

Nondimensionalization of the equations governing two‐phase flow suggests that DNAPL saturation should be a function of a linear combination of the Capillary and Bond Numbers (NCa/krw— NBo), provided the permeability to water (krw) in the presence of discontinuous DNAPL is considered. Experimental studies in which DNAPL saturations were measured over a range of Capillary and Bond Numbers for upward, horizontal, and downward displacement of DNAPL by water corroborate the results of the nondimensionlization. DNAPL saturations generally decreased with increasing Capillary Number and with decreasing Bond Number until NCa/krw— NBo was greater than approximately 1 × 10‐5 at which point residual saturation was attained. For the DNAPLs used in this study, with adhesion tensions on the order of 26 dynes/cm and Bond Numbers ranging from 1.3 × 10‐7 to 2.4 × 10‐6, residual saturation was attained at Capillary Numbers greater than approximately 5 × 10‐5. These results provide a means of estimating the system conditions under which the DNAPLs studied achieve residual saturation in aquifer material.
Estimating Ground‐Water Recharge from Streamflow Hydrographs for a Small Mountain Watershed in a Temperate Humid Climate, New Hampshire, USA
Authors: Mau David P. , Winter Thomas C.
Published: August 2005

Hydrographs of stream discharge were analyzed to determine ground‐water recharge for two small basins draining into Mirror Lake, New Hampshire. Two methods of hydrograph analysis developed for determining ground‐water recharge were evaluated, the instantaneous recharge method and the constant recharge method. For the instantaneous recharge method, recharge is assumed to be instantaneous and uniform over the basin. For the constant recharge method, recharge is assumed to be constant and uniform over the basin for a period of weeks to months. Both methods require that a ground‐water recession slope be determined. The recession slope is used directly in the calculation for the instantaneous recharge method, and it is used as a base of reference for fitting a type curve in the constant recharge method. Results of the study indicated that the estimates of ground‐water recharge for both methods agree to within about 10 percent. Two approaches to the instantaneous recharge method, manual and automated, were also evaluated, and the results were statistically similar.

The baseflow component of streamflow commonly is assumed to be equivalent to ground‐water recharge; therefore, two methods developed for determining the baseflow component of streamflow, graphical partitioning and digital filtering, were evaluated also. Baseflow values determined by graphical partitioning of hydrographs were about 25 percent less than the ground‐water recharge values. Baseflow values determined by two different approaches to the mathematical digital filtering method were generally less than baseflow determined by graphical partitioning. However, one of the approaches to digital filtering agreed reasonably well with graphical partitioning if an appropriate filter constant was used. The other approach to digital filtering resulted in baseflow values that were much less than the other baseflow values and was therefore deemed inappropriate for use on these small mountain watersheds.
Analytic Modeling of Impermeable and Resistant Barriers
Authors: Fitts Charles R.
Published: August 2005

Superpositioned analytic functions are used to efficiently and accurately model ground‐water flow fields containing thin barriers such as slurry walls and sheet‐pile walls. Barriers are modeled as a series of straight‐line segments strung together to create irregularly shaped open or closed boundaries with zero thickness. The complex analytic functions employed provide perfect continuity of flow across the boundary while approximating normal flux boundary conditions along the boundary. Along an impermeable boundary the normal flux is specified as zero, and along a resistant (leaky) barrier the normal flux is proportional to a specified resistance parameter and the potential difference across the boundary. Solution of a given flow problem requires solving a system of equations with one equation per boundary corner. These equations are linear for impermeable boundaries and for resistant boundaries in confined aquifers or single‐strata unconfined aquifers. In other cases, the boundary condition equations associated with resistant barriers can be nonlinear and a new technique for iterative solution is employed. Implementation of these techniques in a computer program is tested and it is demonstrated by modeling various configurations of flow funneled into a gap between two barriers.
Durov Plot: A Computer Program for Processing and Plotting Hydrochemical Data
Authors: Al‐Bassam Abdulaziz M. , Awad Hussein S. , Al‐Alawi Jomaah A.
Published: August 2005

The expanded Durov diagram has been widely used to represent the dissolved constituents of natural water and to show plausible hydrochemical processes occurring within the hydrological systems. Because of the time required to calculate Durov diagram coordinates and to plot the points, especially when dealing with large numbers of chemical analyses, the treatment of such data is often quite a tedious process. To alleviate this problem, DurovPlot program is designed to help users in calculating and plotting the diagram in a very short time. The program is written in BASIC as a special menu‐driven hydrochemical data analyses code. It was compiled using Microsoft QuickBASIC version 4.5 compiler. The utilization of this program requires the acquisition of an IBM‐PC or compatible with at least 512K bytes of memory, one disk drive (at least 360K bytes), a graphic card (EGA or VGA), and at least DOS version 5.0. DurovPlot possesses several advantages such as the ease with which the data can be entered, edited, and retrieved. The results of computation and plotting are obtained in seconds, depending on the amount of data analyzed and the speed of the computer processor.
Implementing Spatially Variable Anisotropy in MODFLOW
Authors: Kladias Michael P. , Ruskauff Gregory J.
Published: August 2005

The U.S. Geological Survey modular ground‐water flow model (MODFLOW) allows column to row anisotropy to vary only in different layers. Modifications to the code were made to allow each grid block in the model to have its own anisotropy, and still retain backward compatibility with the original formulation. Memory usage increases because of the need to allocate storage for every grid block in the model versus a single entry for each layer. The example shown requires about 30 percent more memory for the spatially variable versus original anisotropy formulations. Storing anisotropy for each grid block is the same as specifying both column and row components of hydraulic conductivity or transmissivity.
Comparison of Neutron Moisture Gauges and a Neutron Tool for Use in Monitoring Wells
Authors: Bishop C. W. , Porro I.
Published: August 2005

Research at the Idaho National Engineering Laboratory investigated the movement of water through a thick fractured basalt vadose zone. Measurements taken in 20‐cm diameter boreholes completed with 10.2‐cm diameter PVC casing and in specially constructed test containers filled with basalt showed that 50‐m Ci neutron moisture gauges could distinguish differences in moisture levels in the basalt formation beyond the well's annular space. Measurements made at depths up to 55 m in similarly constructed monitoring wells in the field showed that moisture gauge readings lead to the same interpretation of moisture movement as readings made with a 3‐Ci neutron tool.
Statistical Evaluation of the Vulnerability of Ground‐Water Wells, A Case Study of Data from the Strasbourg Polygone Pumping Field
Authors: Jameta Ph. , Sampson P. D. , Vincent F.
Published: August 2005

The case study presented in this paper illustrates how statistical methods can help to understand the relationships between ground‐water wells and pollutant sources in alluvial systems. The observation of a time series of chloride concentrations in a specific well in Strasbourg, France, influenced by the infiltration of chlorinated water from the Rhine river, made it possible to derive a two‐predictor model of the water quality in the well. This model combines a linear dependence upon a time‐lagged chloride concentration in the river, reflecting the steady‐state water balance in the well, and a nonlinear dependence upon average lagged water output pumped from the well. This simple model explains 86% of the variance in well chloride concentration measured weekly over a two year period.
Electrical Imaging of Fractures Using Ground‐Water Salinity Change
Authors: Slater Lee D. , Binley Andrew , Brown David
Published: August 2005

Cross‐borehole Eletrical Resistivity Tomography (ERT) has been applied to map the spatial distribution of an electrically conductive zone within a hydrologically complex limestone environment. Advantage has been taken of a “natural” conductive tracer provided by salt‐water migration resulting from long‐term pumping at a “well” within the fieldsite. The resistivity distribution of 13 between‐borehole planes has been reconstructed from borehole resistance measurements, and comparisons between resistivity images obtained prior to, and during, saline migration have been made. The distribution of resistivity obtained from the a priori measurements revealed the location of electrically conductive pathways between boreholes which correlate with cavity features obtained from Borehole Television (BHTV) logging. The continuity of these pathways between boreholes suggests the presence of a laterally extensive electrically conductive zone. The reconstruction of differences in resistivity caused by the salt‐water migration confirmed the presence of this conductive zone and has shown that the saline water passed primarily through this zone. This preferential flow illustrates the hydrological importance of this zone and suggests that it is not only an electrically conductive, but also a highly hydraulically conductive feature.
Model Simulations in Support of Field Scale Design and Operation of Bioremediation Based on Cometabolic Degradation
Authors: Lang Margaret M. , Roberts Paul V. , Semprini Lewis
Published: August 2005

This paper addresses questions fundamental to the design and operation of aquifer bioremediation based on cometabolic degradation. A model of a full‐scale, in situ system for bioremediation of chlorinated ethenes relying on cometabolic degradation was developed and applied to a hypothetical aquifer being considered for a large‐scale field demonstration of in situ bioremediation with recirculation. The model was used to identify feasible substrate (electron donor and electron acceptor) delivery schedules. Trichloroethylene (TCE) was the target contaminant. Methane and phenol were considered as electron donors. The delivery of the electron donors and the electron acceptor, oxygen, was varied to evaluate the rate and extent of bioremediation under different substrate delivery schedules. Maximum removal of TCE was predicted when substrates are delivered at ratios near the stoichiometric requirement of electron donor and acceptor for net microbial growth.

Additionally, the decrease in TCE removal that results from using substrate delivery schedules other than those achieving the maximum removal of TCE was quantified. This decrease was greater for the methane‐oxygen system because the two gaseous substrates compete for transfer into the recirculated ground water. If one substrate is introduced in excess of the amount required for net microbial growth, it accumulates, thus limiting the ability to introduce the second substrate. This imbalance both limits the introduction of the second substrate and accelerates the accumulation of the substrate added in excess. The phenol‐oxygen system is less sensitive to deviation away from the best observed substrate delivery schedule because phenol is a relatively soluble liquid and its introduction does not compete with the mass transfer of oxygen.
Electromagnetic Investigations of Aquifers in the Grand Brulé Coastal Area of Piton de la Fournaise Volcano, Reunion Island
Authors: Robineau Bernard , Ritz Michel , Courteaud Michel , Descloitres Marc
Published: August 2005

A geophysical survey was carried out on the eastern flank of Piton de la Fournaise volcano in the Grand Brulé area using combined audiomagnetotelluric (AMT) and time domain electromagnetic (TDEM) techniques. The aims of the present study were firstly to define the shallow geoelectrical structure, and subsequently to locate large bodies of ground water with anomalous electrical properties. Most of the AMT sites are isotropic across the entire observational bandwidth (7500‐10 Hz), except for a few sites where static‐shift effects are present. Joint one‐dimensional interpretation of the TDEM and AMT data indicates basically three‐layered structures with the following resistivity zones, progressing from the surface downward: (1) a resistive unsaturated surface layer of subaerial basaltic flows with a 2000 to 10,000 ohin‐m resistivity, its base being approximately at mean sea level, (2) an intermediate‐resistivity layer (100‐250 ohm‐m) 50–300 m thick, interpreted as being fresh‐water‐saturated basaltic formations, and (3) a low‐resistivity layer of less than 15 ohm‐m probably due to more saline water at depth and/or higher clay content in crushed materials. In the center of the study area, the results have also shown the presence of a prominent boundary dividing the area into a southern zone where the aquifer sequence is thin (60‐100 m) and a northern zone corresponding to a relatively thick aquifer (>150 m). Geoelectrical models are compared with the available geological information given by two geothermiic exploration drillings. The coastal drill hole gives a crucial information, i.e. the thick intermediate‐resistivity layer in the northern part of Grand Brule can be related to water‐saturated alluvium deposits down to 200 m below sea level. AMT and TDEM soundings have revealed a major paleoalluvial drainage system buried under recent lava flows. A delimitation of sectors with different hydrogeological characteristics can be proposed.
The Problem of Modeling Limestone Springs: The Case of Bagnara (North Apennines, Italy)
Authors: Angelini Paola , Dragoni Walter
Published: August 2005

The Bagnara spring (Central Italy), fed by a fractured, carbonate, and, in some areas, karstic aquifer, was examined. The available information is derived from geological mapping and daily flows over a period of 20 consecutive years. There are no data on the hydrogeological parameters nor on the aquifer hydraulic head, which is known only at the elevation of the spring.

The objective of the work was to construct an appropriate mathematical model for the spring despite the scarcity of available information. The MODFLOW code was used to simulate the system following the equivalent porous media approach. The hydraulic conductivity and the specific yield equivalents were estimated by calibrating the model on the master depletion curve and taking into consideration the topographic elevation of the system's surface. The size of the protection area around the spring was investigated on the basis of the isochrons constructed from the results of the model.
Evidence for Ground‐Water Circulation in the Brine‐Filled Aquitard, Oak Ridge, Tennessee
Authors: Nativ Ronit , Halleran Amy , Hunley Arnold
Published: August 2005

Various geologic, hydrologic, and geochemical methods were used to assess active ground‐water circulation in a brine‐filled, deep (> 50 m below land surface) aquitard underlying the Oak Ridge Reservation, Tennessee. In places, the brine which was presumed to be stagnant in the past, contains various contaminants. If ground‐water circulation is viable in the brine‐containing formations, then remediation or containment of the deep‐seated contaminants should be considered a high priority. Data used to determine this included (1) spatial and temporal pressures and hydraulic heads measured in the aquitard, (2) hydraulic parameters of the formations in question, (3) vertical temperature gradients, and (4) spatial and temporal chemical and isotopic composition of the saline ground water. Conclusions suggest that the saline water contained at depth is not isolated (in terms of recharge and discharge) from the overlying active and fresh‐water‐ (< 500 mg/1) bearing units. Consequently, influx of young water (and contamination) from land surface does occur. Potential discharge into the shallow aquifers was assumed where the hydraulic head of the saline water was higher than that in the shallow aquifers, accounting for temperature and salinity anomalies observed close to land surface. The confined water (and dissolved solutes) move along open conduits at relatively high velocity into adjacent, more permeable units.
Modeling Sea‐Water Intrusion with Open Boundary Conditions
Authors: Padilla Francisco , Cruz‐Sanjulián Javier
Published: August 2005

The present study concerns the application of a new numerical approach to describe the fresh‐water /sea‐water relationships in coastal aquifers. Essentially, a solution to the partial differential equation governing the regional motion of a phreatic surface and the resulting interface between fresh water and salt water is analyzed by a Galerkin finite‐element formulation. A single‐phase steady numerical model was applied to approximate, with simple triangular elements, the regional behavior of a coastal aquifer under appropriate sinks, sources, Neumann, outflow face, and open boundary conditions. On the one hand, outflow open boundaries at the coastline were not treated with other classical boundary conditions (Dirichlet or the outflow face approach), but instead with a formal numerical approach for open boundaries inspired in this particular case by the Dupuit approximation of horizontal outflow at the boundary. The solution to this numerical model, together with the Ghyben‐Herzberg principle, allows the correct simulation of fresh‐water heads and the position of the salt‐water interface for a steeply sloping coast. Although the solutions were precise and do not present classical numerical oscillations, this approach requires a previous solution with Dirichlet boundary conditions at the coastline in order to find a good convergence of the solution algorithm. On the other hand, the same precise results were obtained with a more restrictive open boundary condition, similar in a way to the outflow face approach, which required less computer time, did not need a prior numerical solution and could be extended to different coastline conditions. The steady‐state problem was solved for different hypothetical coastal aquifers and fresh‐water usage through three types of numerical tests. Calculated fresh‐water heads, interface positions and discharges show very precise results throughout the domain and especially at the coastline when compared to analytical, experimental, and numerically correct solutions. Therefore, interface positions, fresh‐water heads, and discharges originating from the steady regional behavior of coastal aquifers can be precisely predicted by numerical modeling when open boundaries towards the sea are properly treated for the likely conditions of the coastline.
Determination of Transmissivity from Specific Capacity Tests in a Karst Aquifer
Authors: Mace Robert E.
Published: August 2005

Specific capacity tests are useful for estimating transmissivity in aquifers that have few good‐quality pump tests. In karst aquifers, this has been done by (1) correcting specific capacity for turbulent well loss and using analytical relationships between transmissivity and specific capacity, and (2) correcting specific capacity for well loss and deriving an empirical relationship between transmissivity and specific capacity. This study focuses on the uncertainties of estimating well loss and presents an empirical relationship between transmissivity and uncorrected specific capacity for a karst aquifer.

Well loss is difficult to estimate without good‐quality step‐drawdown tests. Pipe‐flow theory tends to underestimate well loss, and an empirical relationship between specific capacity and well‐loss constant has a large prediction interval that leads to well loss exceeding measured drawdown. To overcome uncertainties of estimating well loss, transmissivity and uncorrected specific capacity were related for aquifer tests from the Edwards aquifer in Texas. The resulting best‐fit line is T = 0.76(Sc)1.08 for T and Sc in m2 d–1 with a coefficient of determination, R2, of 0.89 and a 95‐percent prediction interval spanning approximately 1.4 log cycles. Though the prediction interval is large, approximate but useful estimates of transmissivity can be determined because the relationship extends over five orders of magnitude from 1 to 100,000 m2 d‐1. The relationship is applicable in at least one other karst aquifer and therefore may be useful for others.
Utilization of the Hantush Solution for the Simultaneous Determination of Aquifer Parameters
Authors: Chen Xunhong , Ayers Jerry F.
Published: August 2005

A method is presented to determine aquifer parameters simultaneously and uniquely based on time‐drawdown data collected from a single observation well in the vicinity of a pumping well partially penetrating a confined leaky aquifer. The Hantush solution is analyzed inversely for the identification of hydraulic properties using the Taylor series and a nonlinear least squares method. Aquifer parameters investigated include vertical and horizontal hydraulic conductivities, storage coefficient, and the leakage factor of the overlying aquitard. The developed method is verified using a hypothetical example and is applied to a field case. Error limits between the determined and true parameter values can be less than 0.1% depending on the quality of the field data.
Using the Deconvolution Approach for Slug Test Analysis: Theory and Application
Authors: Chakrabarty C. , Enachescu C.
Published: August 2005

This paper presents a new analysis methodology for determining hydrogeological parameters from a single well slug test. The procedure involves converting pressure versus time data from a slug test into a form equivalent to that from a constant rate test using an exact relationship. Deconvolution techniques are applied to remove wellbore storage effects. The converted data are then analyzed using existing head and head derivative type curves for constant (downhole) rate conditions. It is demonstrated that the analysis of the converted data yields reliable estimates of aquifer transmissivity from conventional slug tests and even from short duration (i.e., small recovery) tests in low transmissivity rocks. This method allows successful analysis of data from slug tests that would be considered unanalyzable using conventional interpretation techniques. Moreover, the proposed method is able to determine aquifer storativity independent of the influence of wellbore skin factor. This is impossible using existing techniques such as those based on Cooper et al. (1967) or Ramey et al. (1975). The applicability of the proposed methodology is demonstrated using several synthetic and field examples.
Effects of Anisotropy on the Capture Zone of a Partially Penetrating Well
Authors: Zlotnik Vitaly A.
Published: August 2005

Dimensional analysis is used to show the effects of aquifer anisotropy on capture zone geometry for a partially penetrating well that is screened from the top of a confined aquifer. Dimensionless similarity criteria are identified which allow an extension of results for advective transport modeling from isotropic conditions to anisotropic ones. Using published results of modeling capture zones in isotropic aquifers, it is shown that anisotropy is important in determining the size and shape of the capture zone under two conditions: (1) the pumping rate is small compared to the scaled regional flow velocity, and (2) the well has a low degree of penetration. Examples are used to show that disregard of even modest aquifer anisotropy can significantly affect estimates of capture zone.
Climatic Control of Hydraulic Conductivity of Bahamian Limestones
Authors: Whitaker Fiona F. , Smart Peter L.
Published: August 2005

Data from 244 single‐well pumping tests of the karstified Lucayan Limestone on 14 different islands distributed through the Bahamian Archipelago, demonstrate a strong log‐linear relationship between annual rainfall and the effective mean island effective hydraulic conductivity, which averages over two orders of magnitude higher in the wetter northern Bahamas (mean anual rainfall 1550 mm) than in the more arid southern islands (mean annual rainfall 810 mm). This relationship is independent of the saturated depth of the boreholes tested, although the hydraulic conductivity of the lower part of the formation is significantly greater (about 0.6–0.7 order of magnitude) than the upper unit, reflecting progressive secondary porosity generation with time.

The direct effect of increasing ground‐water flux on rates of dissolutional porosity generation in the wetter northern islands is supplemented by the greater geochemical potential for carbonate dissolution resulting from higher primary vegetative production. This both increases soil pCO2 via root respiration (a process augmented by higher soil moisture permitting more microbial activity), and the availability of organic matter for in situ oxidation within the aquifer. Effective hydraulic conductivity may also be directly related to island size. Islands in the north of the Archipelago are larger than those in the south, thus the fresh‐water lens and fresh‐/ salt‐water mixing zone are greater in size and expose more bedrock to dissolution.
Confidence Intervals for Ground‐Water Models Using Linearization, Likelihood, and Bootstrap Methods
Authors: Cooley Richard L.
Published: August 2005

Four methods were applied to obtain confidence intervals for selected dependent variables from a nonlinear regression formulation of a ground‐water flow model. The methods examined are (1) the linearization method, (2) the likelihood method, (3) a simple, percentile bootstrap method, and (4) a regression‐based percentile bootstrap method that is a generalization of the first one.

The methods were applied to a highly nonlinear regression model of a hypothetical ground‐water system involving an infiltrating stream crossing a heterogeneous aquifer. Confidence intervals were computed for a hydraulic head and a parameter that is proportional to the streamflow infiltration rate. All confidence intervals computed by the likelihood method are virtually exact. Confidence intervals for hydraulic head by the linearization, likelihood, and the second bootstrap methods are similar, but confidence intervals by the first bootstrap method are very different and highly inaccurate. Confidence intervals for the streamflow infiltration parameter by the linearization and first bootstrap methods are identical and inaccurate; confidence intervals by the second bootstrap method lie between those by the likelihood and the other two methods. These characteristics of the confidence intervals result because (1) the regression model is highly nonlinear, and (2) much of the nonlinearity can be removed by some transformation of model parameters.
Simulated Recovery of Light, Nonaqueous Phase Liquid from Unconfined Heterogeneous Aquifers
Authors: Waddill Dan W. , Parker Jack C.
Published: August 2005

A multiphase flow model (ARMOS) was used to evaluate the effects of subsurface heterogeneities on the recovery of light, nonaqueous phase liquids (LNAPLs or simply “oil”). Stochastic inputs for the model included the saturated hydraulic conductivity (Ksw), van Genuchten α and n, the water saturation at field capacity (Sm), and the maximum residual oil saturations in the saturated (Sor) and the unsaturated zones (Sog). The turning bands method was used to generate stochastic soil parameters representing three hypothetical sandy loam soils. Oil recovery in the three heterogeneous cases was compared to an “equivalent” homogeneous soil with effective parameters computed as the geometric means of the stochastic parameters. Distributions of the free oil plumes were described over time using statistical and spatial moment analyses. Due to the smoothing effect of the flow process, the predicted well oil thickness (Ho) and free oil specific volume (Vof) were less variable than the input stochastic parameter In(Ksw). However, Ho and Vof became more variable as free oil volume diminished and the oil distribution was controlled more by soil variability than gradients in the fluid levels. At the onset of oil recovery, the free oil area was greater in all three heterogeneous soils than the homogeneous soil. Nevertheless, soil heterogeneities did not greatly affect oil recovery or trapping in the saturated and unsaturated zones. Heterogeneities may have had a greater influence on oil recovery if a smaller spill had been studied or if the vertical dimension had been simulated explicitly. The results suggest that the geometric mean soil properties provide a useful estimate of the potential for oil recovery from oil spills that span a large number of correlation scales.
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

A 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

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

A 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

In 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

Bromide 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

A 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

A 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

Quantitative 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

Inverse 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

This 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

Ground 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

Under 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.