bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Waterflood Design on the Recovery of Mobile DNAPLs
Authors: Gerhard Jason I. , Kueper Bernard H. , Hecox Gary R.
Published: August 2005

This 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

A 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.
Behavior of Nitrate‐Nitrogen Movement Around a Pumping High‐Capacity Well: A Field Example
Authors: Ayers Jerry F. , Chen Xunhong , Gosselin David C.
Published: August 2005

This study examines the near‐field flow regime influencing the chemical composition of water samples collected from an irrigation well during short pumping periods. Data on the radial and vertical distribution of nitrate‐nitrogen (NO3‐N) and on drawdown were collected from a closely spaced multi‐level monitoring well network installed around an irrigation well. Aquifer properties were determined from grain‐size analyses performed on samples collected from test holes drilled around the irrigation well and from drawdown data using the method of Neuman (1974). Grain‐size characteristics were determined from cumulative distribution curves and used to construct vertical hydraulic conductivity (K) profiles based on frequently used empirical formulas applied to grain‐size data for the determination of aquifer properties. Resultant vertical profiles show a general increase in K with depth. Results from the analysis of drawdown curves support the general trend of K determined from the grain‐size data, drawdown‐based K values, however, were 1.5 to 2 times greater than those determined from the empirical methods.

Results from four pump‐and‐sample experiments at different times during the irrigation season indicate: (1) the distribution of NO3‐N around the irrigation well is complex and variable over time and space; (2) shapes of concentration‐time curves for individual sample points are governed by the initial contaminant distribution, and shapes of concentration‐time curves for the pumping well are governed by variables such as well screen position and hydrogeologic properties; (3) irrigation well samples underestimate the highest, as well as the average NO3‐N concentrations within the aquifer; and (4) a sampling strategy based on the behavioral characteristics of the well as reflected in concentration‐time curves can improve the interpretation of water quality data collected from high‐capacity wells.
The Relationship Between Hydrogeologic Properties and Sedimentary Fades: An Example from Pennsylvanian Bedrock Aquifers, Southwestern Indiana
Authors: Fisher Andrew T. , Barnhill Mark , Revenaugh Justin
Published: August 2005

The relationship between the hydrogeologic properties and sedimentary fades of shallow Pennsylvanian bedrock aquifers was examined using detailed sedimentologic descriptions, aquifer (slug) tests, and gamma ray logs. The main goal of the study was to determine if it was possible to reliably estimate near‐well hydraulic conductivities using core descriptions and logging data at a complex field site, based on assignment of consistent conductivity indicators to individual facies. Lithologic information was gathered from three sources: core descriptions, simplified lithologic columns derived from the core descriptions, and drillers’ logs. Gamma ray data were collected with a conventional logging instrument. Slug tests were conducted in all wells containing screened zones entirely within the Pennsylvanian facies of interest.

Simplified subsets of sedimentologic facies were assembled for classification of subsurface geology, and all rocks within the screened intervals of test wells were assigned to individual facies based on visual descriptions. Slug tests were conducted to determine the bulk hydraulic conductivity (a spatial average within the screened interval) in the immediate vicinity of the wells, with measured values varying from 10−4 m/s to 10−8 m/s. Gamma ray logs from these wells revealed variations in raw counts above about 1.5 orders of magnitude.

Data were combined using simple linear and nonlinear inverse techniques to derive relations between sedimentologic facies, gamma ray signals, and bulk hydraulic conductivities. The analyses suggest that facies data alone, even those derived from detailed core descriptions, are insufficient for estimating hydraulic conductivity in this setting to better than an order of magnitude. The addition of gamma ray data improved the estimates, as did selective filtering of several extreme values from the full data set. Better estimates might be obtained through more careful field measurements and reduction of associated errors, collection and incorporation of some form of continuous porosity log, or use of spatial statistics or more sophisticated inversion techniques. The utility of the approach remains to be tested through modeling and additional direct measurements.
Lateral Chloride Migration from a Landfill in a Fractured Clay‐Rich Glacial Deposit
Authors: McKay L. D. , Balfour D. J. , Cherry J.A.
Published: August 2005

A plume of chloride (100 to > 1000 mg/L) was found to extend up to 40 m laterally from the edge of a landfill located on a thick sequence of clay‐rich glacial deposits. The plume is mainly confined to the seasonally saturated highly weathered and fractured zone (upper 3 to 4 m) of the deposits. In the high concentration region of the plume there was good agreement between chloride concentrations determined from piezometer water samples, which were expected to sample fracture pore water, and pore water extractions from continuous core samples, which were expected to be dominated by pore water from the fine‐grained matrix. The pore water extractions provided much better lateral and vertical resolution of the plume than was obtained from the piezometer water samples. The length of the plume based on the data from the piezometer water samples was 12 m less than the length determined from the core samples, apparently because the piezometers were located above or below the relatively thin plume, or were above the water table at the time of sampling. Chloride concentrations in many of the deeper piezometers were higher than measured in core samples. This was likely due to inflow from the shallow highly contaminated zone during drilling, as indicated by declining concentration values measured in many of these piezometers over a 10‐month period. The core samples were protected by a liner and were not significantly influenced by drilling‐induced contamination. Downhole electrical conductivity profiles measured with a Geonics EM‐39 correlated well with chloride concentration profiles determined from the core samples. Surface measurements of electrical conductivity with a Geonics EM‐31 were effective at detecting the edge of the waste (which was buried under 2 m of clay), but were less effective at detecting the lateral extent of the chloride plume. Based on this and previous investigations, it is expected that an equivalent porous medium (EPM) approach will be appropriate for simulating lateral contaminant transport in the highly weathered and fractured zone. However, predictive modeling of the behavior of the chloride plume will be complicated by the presence of multiple possible sources of chloride and uncertainty concerning the hydraulic conductivity distribution, as well as by difficulty in predicting the influence of large seasonal variations in the elevation and slope of the water table.
Windowed Spatial Zooming in Finite‐Difference Ground Water Flow Models
Authors: Székely Ferenc
Published: August 2005

A numerical technique for spatial (lateral and vertical) zooming in finite‐difference multiaquifer ground water flow models with a point‐centered finite‐difference scheme is presented. A composite, rectangular finite‐difference mesh is used, allowing for different mesh resolutions and/or layering in hierarchically associated windows of the flow domain. An iterative procedure, called mesh interface simulator (MIS), is developed to link the parent and child meshes along their boundaries, referred to as interfaces. MIS equates the piezometric head along and the lateral flux across the interface. A numerical example of four interbedded meshes in a two‐aquifer system with spatial zooming is evaluated. The results of numerical simulation are compared to an analytical solution to assess the overall approximation error of the numerical finite‐difference and MIS procedures.
Capture Zone Delineations on Island Aquifer Systems
Authors: Taylor James Z. , Person Mark
Published: August 2005

The objective of this study is to assess the effects of variable density ground water flow on capture zones for pumping wells on islands and the ability of numerical and analytical methods to account for these effects. Mathematical modeling is used to simulate variable density ground water flow for an island aquifer system. Coupled fresh water‐salt water transport equations derived using sharp interface theory are solved using the finite‐element method. Reverse particle tracking is used to compute the capture zone for a well. Sensitivity studies are completed using a quasi‐three‐dimensional model to identify the influence of variable density flow on the computed zone of contribution to a pumping well. Quantitative results indicate that the size and shape of the capture zone are sensitive to the natural geometry of the fresh water lens and the effects of fresh water‐salt water upconing. This is especially true for pumping wells located close to the coastline. For the conditions considered in this study, accounting for variable density ground water flow resulted in capture zones approximately 21% larger than those predicted assuming a uniform fresh water aquifer thickness and constant hydraulic gradient. This effect of variable density flow on the predicted capture zones diminished away from the coastline. The study results serve to caution model users of the limitations inherent in using analytical methods to compute capture zone delineations for island aquifers.
Sharp Interface Models of Salt Water Intrusion and Wellhead Delineation on Nantucket Island, Massachusetts
Authors: Person Mark , Taylor James Z. , Dingman S. Lawrence
Published: August 2005

Inferred increases in 1981 to 1997 pumping records suggest that by the year 2020, the majority of Nantucket Island municipal wellfields will be pumping near or at capacity. A sharp‐interface model is used in this study to assess the impact of projected increases in pumping from the Wyers Valley and proposed State Forest municipal wellfields on Nantucket Island, Massachusetts. The model was first calibrated as part of a sensitivity study using a nine‐year record of monthly water level data from a monitoring well network and salinity data from a deep borehole completed near the island's center. Best‐fit values of hydraulic conductivity and specific storage obtained in the sensitivity analysis are in good agreement with those measured by single and multiple well aquifer tests across the island.

The calibrated model was used to assess hydrologic conditions across the island between 1997 and 2020 due to projected increases in municipal wellfield pumping. Transient simulation results suggest that salt water will invade the well screen of the deep (32 m) Wyers Valley production well by the year 2014. Further, the width of the fresh water/salt water mixing zone under the municipal wellfields will triple by 2020 due to increasing seasonal fluctuations in pumping required to accommodate summer tourism. Using published estimates of 2020 municipal wellfield pumping, wellhead delineation zones were also calculated using a variety of assumptions regarding the island's fresh water lens geometry (uniform, variable thickness with no upconing; variable thickness with upconing). Results indicate that the calculated delineation zones are most sensitive to island geometry and, to a lesser extent, to the fresh water lens thickness.
Encapsulated Cell Bioremediation: Evaluation on the Basis of Particle Tracer Tests
Authors: Petrich C.R. , Stormo K.E. , Ralston D.R. , Crawford R.L.
Published: August 2005

Microencapsulation of degradative organisms enhances microorganism survivability (Stormo and Crawford 1994). The use of encapsulated cell microbeads for in situ biodegradation depends not only on microorganism survival but also on microbead transport characteristics. Two forced‐gradient, recirculating‐loop tracer experiments were conducted to evaluate the feasibility of encapsulated cell transport and bioremediation on the basis of polystyrene microsphere transport results. The tracer tests were conducted in a shallow, confined, unconsolidated, heterogeneous, sedimentary aquifer using bromide ion and 2 μm, 5 μn, and 15 μm microsphere tracers.

Significant differences were observed in the transport of bromide solute and polystyrene microspheres. Microspheres reached peak concentrations in monitoring wells before bromide, which was thought to reflect the influence of aquifer heterogeneity. Greater decreases in microsphere C/Co ratios were observed with distance from the injection wells than in bromide C/Co ratios, which was attributed to particle filtration and/or settling.

Several methods might be considered for introducing encapsulated cell microbeads into a subsurface environment, including direct injection into a contaminated aquifer zone, injection through a recirculating ground water flow system, or emplacement in a subsurface microbial curtain in advance of a plume. However, the in situ use of encapsulated cells in an aquifer is probably limited to aquifers containing sufficiently large pore spaces, allowing passage of at least some encapsulated cells. The use of encapsulated cells may also be limited by differences in solute and microbead transport patterns and flowpath clogging by larger encapsulated cell microbeads.
Aquifer Properties Determined from Two Analytical Solutions
Authors: Chen Xunhong , Ayers Jerry F.
Published: August 2005

In the analysis of pumping test data, the quality of the determined aquifer parameters can be greatly improved by using a proper model of the aquifer system. Moench (1995) provided an analytical solution for flow to a well partially penetrating an unconfined aquifer. His solution, in contrast to the Neuman solution (1974), accounts for the noninstantaneous decline of the water table (delayed yield). Consequently, the calculated drawdown in these two solutions is different under certain circumstances, and this difference may therefore affect the computation of aquifer properties from pumping test data. This paper uses an inverse computational method to calculate four aquifer parameters as well as a delayed yield parameter, α1 from pumping test data using both the Neuman (1974) and Moench (1995) solutions. Time‐drawdown data sets from a pumping test in an unconfined alluvial aquifer near Grand Island, Nebraska, were analyzed. In single‐well analyses, horizontal hydraulic conductivity values derived from the Moench solution are lower, but vertical hydraulic conductivity values are higher than those calculated from the Neuman solution. However, the hydraulic conductivity values in composite‐well analyses from both solutions become very close. Furthermore, the Neuman solution produces similar hydraulic conductivity values in the single‐well and composite‐well analyses, but the Moench solution does not. While variable α1, seems to play a role in affecting the computation of aquifer parameters in the single‐well analysis, a much smaller effect was observed in the composite‐well analysis. In general, specific yield determined using the Moench solution could be slightly higher than the values from the Neuman solution; however, they are still lower than the realistic values for sand and gravel aquifers.
Displacement of Nonwetting Liquids from Unsaturated Sands by Water Infiltration
Authors: Boley Troy M. , Overcamp Thomas J.
Published: August 2005

Xylene was spilled onto moist glass beads or various moist sands and water was trickled onto the columns every eight hours for periods up to 10 days. The xylene residual in the columns with water infiltration decreased compared to those of control columns, indicating a downward displacement of xylene. The extent of displacement increased with increasing size of the porous media and with increasing amounts of water infiltration.
Lanthanide‐Labeled Clay: A New Method for Tracing Sediment Transport in Karst
Authors: Mahler Barbara J. , Bennett Philip C. , Zimmerman Mitch
Published: August 2005

Mobile sediment is a fundamental yet poorly characterized aspect of mass transport through karst aquifers. Here the development and field testing of an extremely sensitive particle tracer that may be used to characterize sediment transport in karst aquifers is described. The tracer consists of micron‐size montmorillonite particles homoionized to the lanthanide form; after injection and retrieval from a ground water system, the lanthanide ions are chemically stripped from the clay and quantified by high performance liquid chromatography. The tracer meets the following desired criteria: low detection limit; a number of differentiable signatures; inexpensive production and quantification using standard methods; no environmental risks; and hydrodynamic properties similar to the in situ sediment it is designed to trace. The tracer was tested in laboratory batch experiments and field tested in both surface water and ground water systems. In surface water, arrival times of the tracer were similar to those of a conservative water tracer, although a significant amount of material was lost due to settling. Two tracer tests were undertaken in a karst aquifer under different flow conditions. Under normal flow conditions, the time of arrival and peak concentration of the tracer were similar to or preceded that of a conservative water tracer. Under low flow conditions, the particle tracer was not detected, suggesting that in low flow the sediment settles out of suspension and goes into storage.
LPM‐N: A Lumped Parameter Model for Nitrogen Leaching in Agricultural Lands
Authors: El‐Kadi Aly I. , Ling Ge
Published: August 2005

This paper documents a lumped parameter model for the assessment of nitrogen leaching under agricultural lands. The model considers nitrogen transformation processes, climate data, and multiple irrigation and fertilizer applications. The model is efficient due to its analytical nature and the limited data requirements. The documentation introduces a PC‐Windows interface module that simplifies the preparation of input data and the presentation of results. It also presents an example application of the model that compares simulated to measured nitrate values. The model is suitable for managing fertilizer applications, and for estimating leachate concentrations reaching ground water aquifers.
New Casing and Backfill Design for Neutron Logging Access Boreholes
Authors: Zawislanski Peter T. , Faybishenko Boris
Published: August 2005

In an effort to enhance the usefulness of neutron logging for environmental applications, a new combination of backfill and casing materials for access boreholes has been developed. The combination of acrylic casing and polyurethane foam backfill has been tested under laboratory and field conditions. Acrylic casing does not significantly attenuate fluxes of either high energy or thermal neutrons, in contrast with polyvinyl chloride casing which reduces the thermal neutron flux by more than 40% due to neutron absorption by chlorine. Polyurethane foam, which is inert, hydrophobic, and insoluble in water, adheres well to both dry and wetted soils, sediments, and rocks. It can be formed in situ at a low, but controllable, bulk density. At a bulk density of 0.08 g cm−3, and in combination with acrylic casing, polyurethane foam increases the thermal neutron count by less than 5% in a saturated sand, relative to background. In addition to its small effect on the neutron flux, polyurethane foam, unlike bentonite or cement, does not affect the moisture content of the surrounding formation during installation. Furthermore, because it is a closed‐cell foam, its moisture content does not change under varying formation moisture conditions. As was shown in related field tests, polyurethane foam is especially well suited for backfilling boreholes in fractured rocks because of its fast set time which minimizes penetration into fractures. The design proved to be convenient and durable under rugged field conditions.
Core‐Based Investigation of NMR Logging as a Tool for Characterization of Shallow Unconsolidated Aquifers
Authors: James Robert A. , Ehrlich Robert
Published: August 2005

Uncompacted vadose zone sand aquifers, with their highly interconnected pores and tendency to contain iron‐rich cements and clay skins, are not necessarily susceptible to characterization by nuclear magnetic resonance (NMR) wireline logging. A necessary condition for valid application of this technology to such aquifers is that the NMR signal may be quantitatively related to pore size. To test the hypothesis that this is the case, pore image and NMR data were acquired from cores collected from three sand units beneath the Savannah River Site in South Carolina. Statistical unmixing of pore image and transverse relaxation time (T2) data allowed the pore space to be subdivided into image‐based pore types and NMR endmembers, respectively. The image‐based pore classification bears a systematic relationship to hydraulic conductivity, and is thus shown to be petrophysically relevant. However, the image‐based and NMR components cannot be correlated with one another in terms of either volumetric abundance or size characteristics. The hypothesis was therefore rejected. The lack of correlation is attributed to either, or both, of two effects: coupling of NMR response from spatially associated pores of different pore types, and variation in pore wall relaxivity resulting from the heterogeneous distribution of pore lining iron‐stained clay skins. These results do not condemn the use of NMR logging in consolidated aquifers in which neither of these effects occurs, but further research is needed to establish whether there are any conditions under which unconsolidated aquifers may be validly characterized using this technique.
Factors Influencing Well Productivity in Glaciated Metamorphic Rocks
Authors: Mabee Stephen B.
Published: August 2005

Eight factors were examined to determine their influence on the transmissivities of 35 domestic wells drilled in glaciated, metamorphic bedrock. Wells were grouped into categories on the basis of bedrock type, topographic position, structural setting, proximity to fracture‐correlated lineaments, overburden type, overburden thickness, proximity to surface water bodies, and water table depth. Results indicate that bedrock type, topographic setting proximity to fracture‐correlated lineaments, and structural position explain 34,31,15 and 12% of the observed variation in transmissivity, respectively, and are the only variables that have a statistically significant (90% confidence level) relationship with transmissivity. In this study, wells situated in amphibolite bedrock in upland valleys and flats located 25 m from fracture‐correlated lineaments and positioned on the axes of major folds are the most productive. Review of the literature and comparison of results from this study with those from three other investigations, each representing geologic environments (carbonate, clastic sedimentary, and unglaciated metamorphic/igneous terrains), indicates that well productivity varies with geologic setting; a set of factors in one geologic environment does not necessarily have the same significance when applied to wells in a different geologic setting.
Two‐Dimensional Sensitivity Analysis of Contaminant Transport in the Unsaturated Zone
Authors: Boateng Samuel , Cawlfield Jeffrey D.
Published: August 2005

A two‐dimensional probabilistic transport model is developed‐by coupling a reliability algorithm to a two‐dimensional unsaturated flow and transport model. The goal is to determine the significance of the uncertainty of each variable to the probability outcome. Model input includes the mean, standard deviation, and probability distribution of each uncertain variable. The uncertain variables are assumed to be uncorrelated to each other. The uncertain variables are saturated water content, residual water content, van Genuchten model parameters alpha (α) and n, saturated hydraulic conductivity, bulk density, coefficient of distribution, molecular diffusion coefficient, and dispersivity. Coefficient of variation is used as the measure of uncertainty for each uncertain variable. Three soil samples are considered for model simulations. One half of the flow surface area is the source of a generic contaminant spill. The reliability analysis determines the probability of exceeding a specific target concentration value and also provides a sensitivity value that measures the relative significance of each uncertain transport variable to the probability outcome. Generally, saturated water content tends to be the most significant uncertain variable for transport in the unsaturated zone. Bulk density and coefficient of distribution also are significant for reactive transport. Molecular diffusion and van Genuchten model parameter n are significant in fine‐grained soils and also at locations far from the contaminant source area. The uncertainty of saturated hydraulic conductivity and dispersivity have no significant influence on the probability outcome and can be considered as deterministic input variables.
Framework for Ground Water Protection ‐ the Managua Ground Water System as an Example
Authors: Johansson P.‐O. , Scharp C. , Alveteg T. , Choza A.
Published: August 2005

A framework for ground water protection was developed and tested in the Eastern subarea of the Managua, Nicaragua, ground water system. The framework is a planning tool aimed at identifying areas with a high need for protection to aid future land‐use decisions. The basic components of the framework are vulnerability assessment, contaminant source characterization, and assignment of a protection value. The framework is developed for a geographic information system environment. The vulnerability assessment was carried out using a modified version of the DRASTIC method. The most vulnerable parts of the study area proved to be an area with a shallow ground water table coupled with shrinking/swelling clay soils, and an area where recent porous lava flows mean high recharge and low attenuation capacity. In the contaminant sources characterization, the type of contaminant, its relative concentration, mode of deposition, duration of contaminant load, and possibility for remediation were considered. The sources characterized as emitting a high potential contamination load were concentrated in a tax‐free industrial zone and three villages. The main contaminant sources were a tannery, chemical industries, and sewage water outlets. Both the ground water vulnerability and the potential contamination load were classified as high, moderate, or low. By superimposing the potential contamination load on the vulnerability map, the ground water contamination liability was evaluated by a skewed 3x3 matrix. A relative protection value of the ground water was calculated, based on classifications of available quantities, quality, sensitivity to changes in ground water level, and present or planned use. Together, these maps form an atlas to be used for ground water protection and land‐use planning.
Relationship Between Lineaments and Ground Water Occurrence in Western Botswana
Authors: Magowe Magowe , Carr James R.
Published: August 2005

Asemiarid region of western Botswana, the Ghanzi‐Makunda area, is the focus of a study to determine the relationship between lineaments and well yield. This relationship is inferred from geologic maps, aerial photographs, and Landsat TM (thematic mapper) images in conjunction with a well yield map produced using indicator kriging and based on 226 globally positioned wells. A composite image of Landsat TM, digital well yield, lineament trace, and well location data, formed using a raster‐based geographic information systems (GIS) technique, visually identifies a correlation between well yield, lineament density, and darker tones on Landsat TM images. Higher fracture densities correlate positively with higher well yields. Regression analysis identifies a statistically significant correlation between distance to lineament intersections and median well yield.
In‐Well Hydraulics of the Electromagnetic Borehole Flowmeter
Authors: Dinwiddie Cynthia L. , Foley Nicole A. , Molz Fred J.
Published: August 2005

Previous studies have suggested that head losses associated with the application of the electromagnetic borehole flowmeter (EBF) can have important and detrimental effects on the use of the instrument for measurement of hydraulic conductivity (K) profiles. Head losses associated with flow through the meter may cause bypass flow around the packer if the well is gravel packed. In any type of well, changing head losses with meter position can cause changes in flow into the well that are not related directly to the K distribution. Such flow changes, or redistribution, can cause errors in the calculation of the K profile.

Numerical simulations, based on measured head losses, indicate that bypass flow in gravel packed systems increases with increasing flow rate through the meter, increasing gravel pack conductivity, and increasing gravel pack thickness. Ideally, the EBF should not be used in gravel packed wells, due to the occurrence of bypass flow.

Investigations into the flow redistribution phenomenon indicate that the top portion of the aquifer is where the greatest over‐estimation of K occurs. The portion of the well below the flowmeter is isolated from the observed drawdown as measured from the surface. In this region, the well experiences a reduced drawdown, which differs from the observed drawdown by an amount equal to the head loss at that meter position. Flow redistribution causes a more pronounced effect in more highly conductive mediums and may be almost negligible in mediums of low conductivity.
Recharge Estimation by Stage‐Discharge Interpolation of Springflows from Cross‐Correlated Well Measurements
Authors: Avery William H. , Donovan Joseph J. , Ketchum J. Neil
Published: August 2005

For shallow phreatic aquifers, from which springflow is the predominant source of discharge, recharge volumes may be approximated as the time integral of springflow time series. However, field measurement of flows from numerous springs, with sufficient frequency to accurately estimate this time integral, is frequently impractical. A technique for interpolation of continuous springflow time series is presented, using cross‐correlation between flows and continuous head measurements in associated wells. Suitable wells must lie within the recharge catchment of the spring in question and display negligible phase lag between well and spring response to recharge. Brief (<1 year) periods of calibration may be sufficient to establish calibration upon which discharge interpolation from well data may be based. A 7 m thick highly heterogeneous mine‐waste aquifer, with springflows highly sensitive to recharge events, is examined as a test case. Over a 40 day recharge period, three well/spring pairs yielded acceptable cross‐correlation across four recharge events. Head from one of these wells was compared to a second nearby spring and found to show poor correlation, attributed to its location outside of that spring's catchment. Calibration statistics were found to be robust when the calibration dataset for one pair was reduced in size. Measured flows from one of the correlated springs also displayed correlation with summed discharge from the aquifer at all measured springs, based on concurrent flow measurements over time. Results suggest that continuous measurements of head from a small number of critically selected wells may allow accurate estimates of transient spring discharge rates following a relatively brief period of flow‐stage calibration. The success of the method may depend on specific characteristics of aquifers to which it is applied, such as size of spring catchments, aquifer conductance, aquifer heterogeneity, and spatial distribution of recharge.
The Channel Network Model—A Tool for Transport Simulations in Fractured Media
Authors: Gylling Björn , Moreno Luis , Neretnieks Ivars
Published: August 2005

The Channel Network model and its computer implementation, the code CHAN3D, are presented for simulations of fluid flow and transport of solutes. The tool may be used to simulate and interpret field experiments of flow and transport on a large or small scale. It also may also be used for performance and safety assessments of repositories for nuclear and other hazardous wastes, e.g., chemical wastes. From observations in the field it is deduced that the flow and transport take place in a three‐dimensional network of connected channels. The channels have different properties and are generated in the model from observed stochastic distributions. This allows us to represent the large heterogeneity of the flow distribution commonly observed in the field. Solute transport is modeled considering advection and rock interactions such as matrix diffusion and sorption within the interior of the rock. For repository conditions the main contributions to the dispersion of solutes come from the large variation in the flow field (channeling) and the rock interactions. Objects such as fracture zones, tunnels, and release sources can be incorporated in the model. In addition, a methodology of how data may be obtained for the model is described. Data may be obtained from borehole and laboratory measurements.
Optimal Configuration of a Wellfield
Authors: Swamee Prabhata K. , Tyagi Aditya , Shandilya Vishnu K.
Published: August 2005

Often in urban and rural water supply, the major source of water is an aquifer. An aquifer can be fully exploited by development of a wellfield. Considering well interference, individual wells have to be located in such a manner so that adjacent wells are at a distance of radius of minimum influence. Presently, as no optimal configuration is available, the wells are located by judgment. In this paper the optimal configurations of wellfields have been obtained by considering the minimum cost and the maximum reliability aspects for transporting the water to the center of the wellfield for its onward transmission to the treatment works.
Caffeine and Pharmaceuticals as Indicators of Waste Water Contamination in Wells
Authors: Seiler Ralph L. , Zaugg Steven D. , Thomas James M. , Howcroft Darcy L.
Published: August 2005

The presence of caffeine or human Pharmaceuticals in ground water with elevated nitrate concentrations can provide a clear, unambiguous indication that domestic waste water is a source of some of the nitrate. Water from domestic, public supply, and monitoring wells in three communities near Reno, Nevada, was sampled to test if caffeine or Pharmaceuticals are common, persistent, and mobile enough in the environment that they can be detected in nitrate‐contaminated ground water and, thus, can be useful indicators of recharge from domestic waste water. Results of this study indicate that these compounds can be used as indicators of recharge from domestic waste water, although their usefulness is limited because caffeine is apparently nonconservative and the presence of prescription Pharmaceuticals is unpredictable. The absence of caffeine or Pharmaceuticals in ground water with elevated nitrate concentrations does not demonstrate that the aquifer is free of waste water contamination. Caffeine was detected in ground water samples at concentrations up to 0.23 μg/L. The human Pharmaceuticals chlorpropamide, phensuximide, and carbamazepine also were detected in some samples.
Cross‐Well Slug Testing in Unconfined Aquifers: A Case Study from the Sleepers River Watershed, Vermont
Authors: Belitz Kenneth , Dripps Weston
Published: August 2005

Normally, slug test measurements are limited to the well in which the water level is perturbed. Consequently, it is often difficult to obtain reliable estimates of hydraulic properties, particularly if the aquifer is anisotropic or if there is a wellbore skin. In this investigation, we use partially penetrating stress and observation wells to evaluate specific storage, radial hydraulic conductivity and anisotropy of the aquifer, and the hydraulic conductivity of the borehole skin. The study site is located in the W9 subbasin of the Sleepers River Research Watershed, Vermont. At the site, ∼3 m of saturated till are partially penetrated by a stress well located in the center of the unconfined aquifer and six observation wells located above, below, and at the depth of the stress well at radial distances of 1.2 and 2.4 m. The observation wells were shut in with inflatable packers.

The semianalytical solution of Butler (1995) was used to conduct a sensitivity analysis and to interpret slug test results. The sensitivity analysis indicates that the response of the stress well is primarily sensitive to radial hydraulic conductivity, less sensitiive to anisotropy and the conductivity of the borehole skin, and nearly insensitive to specific storage. In contrast, the responses of the observation wells are sensitive to all four parameters. Interpretation of the field data was facilitated by generating type curves in a manner analogous to the method of Cooper et al. (1967). Because the value of radial hydraulic conductivty is obtained from a match point, the number of unknowns is reduced to three. The estimated values of radial hydraulic conductivity and specific storage are comparable to those derived from the methods of Bouwer and Rice (1976) and Cooper et al. (1967). The values and skin conductivity, however, could not have been obtained without the use of observation wells.
Numerical Simulation of Pumping Tests in Multilayer Wells with Non‐Darcian Flow in the Wellbore
Authors: Chen Chongxi , Jiao Jiu Jimmy
Published: August 2005

An important feature of pumping in a multilayer system is the dynamic interaction between the aquifers via non‐Darcian vertical flow within the wellbore. An equivalent hydraulic conductivity (EHC) approach is used to include this transient interaction as a special leakage through the confining layer in the flow system. Different flow regimes (laminar and turbulent flows, and the i transition range) are involved in a multilayer pumping test where the relation between the hydraulic gradient and flow velocity is complicated. The change of flow regimes is accommodated by varying the content of EHC as a function of the friction factor. For a particular well, the relation between friction factor and Reynolds number is unique and is obtained by interpolating Nikuradse's experimental results. A quasi‐three‐dimensional Galerkin finite‐element method is used to integrate the vertical one‐dimensional flow in the wellbore and confining layers and the two‐dimensional flow in the aquifers. This approach makes it possible to couple the aquifer and wellbore flows of different flow regimes and to solve them in a single numerical framework based on the same linear relation between gradient and velocity. A carefully designed pumping test in a multilayer aquifer system near Beihai City, Guangxi Autonomous Region, China, is used to demonstrate the performance of the approach.
Localized Sulfate‐Reducing Zones in a Coastal Plain Aquifer
Authors: Brown Craig J. , Coates John D. , Schoonen Martin A.A.
Published: August 2005

High concentrations of dissolved iron in ground water of coastal plain or alluvial aquifers contribute to the biofouling of public supply wells for which treatment and remediation is costly. Many of these aquifers, however, contain zones in which microbial sulfate reduction and the associated precipitation of iron‐sulfide minerals decreases iron mobility. The principal water‐ bearing aquifer (Magothy Aquifer of Cretaceous age) hi Suffolk County, New York, contains localized sulfate‐redudng zones hi and near lignite deposits, which generally are associated with clay lenses. Microbial analyses of core samples amended with [14C]‐acetate indicate that microbial sulfate reduction is the predominant terminal‐electron‐accepting process (TEAP) in poorly permeable, lignite‐rich sediments at shallow depths and near the ground water divide. The sulfate‐reducing zones are characterized by abundant lignite and iron‐sulfide minerals, low concentrations of Fe(III) oxyhydroxides, and by proximity to clay lenses that contain pore water with relatively high concentrations of sulfate and dissolved organic carbon. The low permeability of these zones and, hence, the long residence time of ground water within them, permit the preservation and (or) allow the formation of iron‐sulfide minerals, including pyrite and marcasite. Both sulfate‐reducing bacteria (SRB) and iron‐reducing bacteria (IRB) are present beneath and beyond the shallow sulfate‐reducing zones. A unique Fe(HI)‐reducing organism, MD‐612, was found in core sediments from a depth of 187 m near the southern shore of Long Island. The distribution of poorly permeable, lignite‐rich, sulfate‐reducing zones with decreased iron concentration is varied within the principal aquifer and accounts for the observed distribution of dissolved sulfate, iron, and iron suit Ides in the aquifer. Locating such zones for the placement of production wells would be difficult, however, because these zones are of limited aerial extent.
A Mathematical Model for the Hydraulic Properties of Deforming Porous Media
Authors: Kim Jun‐Mo , Parizek Richard R.
Published: August 2005

A new and relatively simple mathematical model is presented to predict the changes in porosity and saturated hydraulic conductivity that result from the skeletal deformation of porous media. A mathematical expression for the deformation‐dependent porosity is derived from the relationship between porosity and volumetric strain, assuming that the individual solid grains are relatively incompressible or less deformable compared to the solid skeleton of a porous medium. A mathematical expression for the deformation‐dependent saturated hydraulic conductivity is then obtained by substituting the deformation‐dependent porosity into the Kozeny‐Carman equation, assuming that the shape factor of the saturated hydraulic conductivity is independent of the skeletal deformation of the porous medium. To evaluate the effects of the deformation‐dependencies of the hydraulic properties on poro‐elastic consolidation, the mathematical model is applied to two different numerical experiments on fully saturated porous media. The simulation results show that the deformation‐dependencies of the hydraulic properties intrinsically induce hydraulic heterogeneity and nonlinear consolidation, and hence produce different trends than those obtained from analytical or numerical solutions with an assumption of constant hydraulic properties. Although the mathematical model presented in this paper is not applicable to all hydrogeomechanicai phenomena, the methodology should have useful application in many consolidation problems.
Uranium Removal from Ground Water Using Zero Valent Iron Media
Authors: Farrell James , Bostick William D. , Jarabek Robert J. , Fiedor Joseph N.
Published: August 2005

Removal of uranium from contaminated ground water using zero valent iron is currently under evaluation at several U.S. Department of Energy (DOE) facilities. Uranium removal by zero valent iron may occur via adsorption onto iron corrosion products, and by reduction to less soluble valence states by reactions with elemental iron. This research investigated the effects of water chemistry and surface precipitate buildup on the removal of soluble uranium by zero valent iron. Batch testing was performed to assess solution chemistry effects on uranium adsorption to the potential iron corrosion products, magnetite and a mixed valent amorphous iron oxide. Uranium adsorption to the simulated iron corrosion products was highly dependent on pH, and the concentration and speciation of the background electrolyte solution. Uranium removal via reduction by elemental iron closely approximated pseudo‐first‐order removal kinetics, despite the buildup of up to 40,000 monolayers of precipitated uranium on the iron surfaces. This indicates that the rate of uranium removal is not strongly dependent on the thickness of the adsorbed uranium layer. Short‐term rates of uranium reduction were similar for all solutions tested, but long‐term rates were highly dependent on water chemistry. Compared to deionized water, uranium removal rates were increased in sodium chloride containing solutions and reduced in sodium nitrate solutions. The strong influence of water chemistry on long‐term reduction rates indicates that system design will require extnded testing with the ground water of interest.