bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThis 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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractInferred 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

AbstractMicroencapsulation 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

AbstractIn 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

AbstractXylene 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

AbstractMobile 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

AbstractThis 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

AbstractIn 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

AbstractUncompacted 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

AbstractEight 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.