bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cokriging Limited Transmissivity Data Using Widely Sampled Specific Capacity from Pump Tests in an Alluvial Aquifer
Authors: Hughson Lance , Huntley David , Razack M. 
Published: August 2005

AbstractUse of the specific capacity of a pumping well to predict aquifer transmissivity is desirable due to the cost of pumping tests and the availability of specific capacity measurements. The geostatistical technique of cokriging is a method of incorporating the spatial variability of a correlated variable (e.g., specific capacity) in estimating a related undersampled variable (e.g., transmissivity). This study examines the reliability of cokriging transmissivity estimates using a data set of 215 pairs of transmissivity and specific capacity. Subsets of pairs of transmissivity and specific capacity were selected and cokriged to estimate transmissivity at the remaining well locations. The estimates of transmissivity were then compared to actual measurements of transmissivity. The same subsets of pairs were used to estimate transmissivity with loglinear regression of transmissivity on specific capacity and ordinary kriging of transmissivity alone. Comparison of these three methods indicates the number of wells with both transmissivity and specific capacity data necessary to obtain improvement in transmissivity estimates with cokriging over the simpler regression and kriging methods. The results show that significant improvement in the transmissivity estimate is obtained by cokriging with 50 or more pairs of transmissivity and specific capacity, and that loglinear regression is superior when less than 30 pairs are available. With between 30 and 50 pairs of available data measurements, cokriging does not reliably improve the estimate over loglinear regression.
Evaluation of Simple Methods for Estimating Contaminant Removal by Flushing
Authors: Brusseau Mark L. 
Published: August 2005

AbstractThe purpose of this work was to briefly outline and evaluate simple methods used for estimating the volume of water and the time required to remove contaminants from the subsurface by flushing (e.g., “pump‐and‐treat,”“soil washing”). The methods are based on three general approaches to treating flow and transport: perfectly mixed flow, hydraulic, and advective‐dispersive. Data obtained from a small field experiment designed to evaluate aquifer flushing was used to illustrate the performance of the estimation methods. The methods based on the hydraulic and ideal advective‐dispersive transport approaches will generally provide estimates that underpredict the actual time. The magnitude of the underprediction will depend, in part, on the degree of nonideal behavior influencing contaminant removal (e.g., heterogeneity, rate‐limited mass transfer) and on the ratio of target to initial contaminant concentration. The perfectly mixed flow reactor approach, because of its asymptotic removal curve, may be useful in providing rough approximations of required pore volumes and times. However, it cannot be overemphasized that all estimation techniques are prone to failure as long as the conceptual models upon which they are based do not accurately represent field‐scale contaminant transport.
An Examination of Short‐Term Variations in Water Quality at a Karst Spring in Kentucky
Authors: Ryan Martin , Meiman Joe 
Published: August 2005

AbstractWater quality at many karst springs undergoes very high amplitude but relatively brief degradation following influxes of runoff. Accurately recording transient variations requires more rigorous sampling strategies than traditional methods. A pilot study to determine the usefulness of high‐frequency, flow‐dependent sampling strategies, combined with coincidental quantitative dye tracer tests, was implemented in the Big Spring Ground‐Water Basin in Mammoth Cave National Park, Kentucky.Data recorded following two separate runoff events showed that the concentrations of two nonpoint source pollutants, fecal coliform bacteria and suspended sediment, greatly exceeded prerunoff event values for very short periods of time. A phreatic conduit segment, calculated at 17 million liters in volume, instantaneously propagated head changes, caused by direct runoff entering the aquifer, from the ground‐water inputs to Big Spring. A significant delay between the initial increases in discharge and the arrival of direct runoff, as indicated by a steady decrease in specific conductance, represented the time required to displace this volume of phreatic water. The delay showed that sampling a karst spring only during peak discharge would be an unreliable sampling method.Runoff from two different subcatchments was tagged with tracer dye and the timing of the passage of the resultant dye clouds through Big Spring were compared to water quality variations. Distinct lag times between the arrival of direct runoff at Big Spring and the bacteria and suspended sediment waveforms were shown through the concurrent quantitative tracer tests to be related to the areal distribution of land‐cover type within the basin.
Biotransformation of Organics in Soil Columns and an Infiltration Area
Authors: Bosma Tom N. P. , Marlies E. , Ballemans W. , Hoekstra Nanne K. , te Welscher Ruud A. G. , Smeenk Johannes G.M.M. , Schraa Gosse , Zehnder Alexander J. B. 
Published: August 2005

AbstractLaboratory column experiments were performed to evaluate the fate of a series of chlorinated and nonchlorinated organic contaminants in Rhine sediment and in sediment from the infiltration area of the Municipal Water Works of Amsterdam, near Zandvoort, The Netherlands. Columns were operated under aerobic, denitrifying, and methanogenic conditions. All nonchlorinated and few chlorinated compounds were aerobically transformed. Of the compounds tested under denitrifying conditions, only 1,2‐dichloro‐4‐nitrobenzene was partially transformed. Methanogenic conditions favored the transformation of chlorinated substances by reductive dechlorination. Toluene was the only nonhalogenated compound that was transformed under methanogenic conditions. Steady‐state effluent concentrations after biotransformation were at least 10 times lower than the drinking water limit of 1 μg/l except in the case of 1,2,4‐trichlorobenzene which had a steady‐state effluent concentration of 2.6 μg/l. Steady‐state effluent concentrations did not depend on the influent concentration applied. Most transformations proceeded at the same steady‐state rates at a temperature of 4° C, although the process of reductive dechlorination was slower at 4° C than at 20° C. Hydrological calculations revealed that the combined action of hydrology and sorption to organic matter in the infiltration system can reduce the concentrations of 2 week pulses of polar and nonpolar contaminants by at least 80 and 95%, respectively. There was a good qualitative agreement between removals observed in column experiments and in the dune infiltration area.
Monitoring of Water Flow and Solute Transport Through the Unsaturated Zone Using a Large‐Diameter Borehole
Authors: Zilberbrand Michael , Gvirtzm Haim 
Published: August 2005

AbstractA method for monitoring water flow and solute transport through the unsaturated zone is of crucial necessity for early detection of threats to ground water. A method developed by Ukrainian hydrogeologists in the 1970s involves a borehole of a large enough diameter for a person to enter, that provides the possibility of installing monitoring equipment, and enables collecting undisturbed sediment blocks and samples of pore water and gas. Practically, tensiometers and vacuum lysimeters are installed at various levels in the borehole walls. They provide high quality sampling and measurements, and enable determining parameters of unsaturated water flow and solute transport and their temporal and spatial variability.The method was tested at several locations. Selected results from two sites, showing the temporal and spatial distributions of capillary pressure and solute concentrations, are presented. The results exhibit the difference between lateral variation in water flow and solute transport characteristics. The accuracy and representativeness of the measurements were tested against the mutual interaction between the various instruments installed in the borehole walls. Monitoring using the large‐diameter boreholes provides the possibility of early detection of threats to ground water under areal contamination inputs, and of quantitative prediction of its future trends.
Subsurface Injection of Dissolved Ferric Chloride to Form a Chemical Barrier: Laboratory Investigations
Authors: Morrison S. J. , Spangler R. R. , Morris S. A. 
Published: August 2005

AbstractA chemical barrier is a permeable zone of reactive materials emplaced in the subsurface to remove ground‐water contaminants while allowing clean ground water to pass through. Because dissolved ferric chloride hydrolyzes to amorphous ferric oxyhydroxide when it contacts calcite (CaCO3), it may be viable to emplace a zone of amorphous ferric oxyhydroxide (an absorbent for U, Mo, and other inorganic contaminants) into calcite‐bearing geologic units by injecting ferric chloride through wells. For a chemical barrier to be successful, it must remain permeable and must be immobile.This investigation monitored chemical compositions, hydraulic conductivity, and iron mobility in laboratory columns and in a two‐dimensional tank to determine the viability of injecting ferric chloride to form an amorphous ferric oxyhydroxide chemical barrier. We introduced a ferric chloride solution (1,345 mg/l [0.024 m] Fe) to calcite‐bearing alluvial gravel to form a chemical barrier of amorphous ferric oxyhydroxide, followed by solutions contaminated with U and Mo. The simulated chemical barriers decreased U and Mo concentrations to less than 0.05 mg/1 (2.1×10‐7 m) and 0.01 (1.0×10‐7 m), respectively; however, the breakthrough front is spread out with concentrations increasing to more than regulatory guideline values sooner than predicted. The hydraulic conductivity of calcite‐bearing alluvial gravel decreased substantially during ferric chloride introduction because of the formation of carbon dioxide but increased to within factors of 1 to 5 of the original value as synthetic ground water flowed through the system. Amorphous ferric oxyhydroxide that formed in these experiments remained immobile at flow rates exceeding those typical of ground water. These laboratory results, in conjunction with site‐specific characterization data, can be used to design chemical barriers emplaced by injection of ferric chloride.
Combined Use of Flowmeter and Time‐Drawdown Data to Estimate Hydraulic Conductivities in Layered Aquifer Systems
Authors: Hanson R. T. , Nishikawa Tracy 
Published: August 2005

AbstractThe vertical distribution of hydraulic conductivity in layered aquifer systems commonly is needed for model simulations of ground‐water flow and transport. In previous studies, time‐drawdown data or flowmeter data were used individually, but not in combination, to estimate hydraulic conductivity. In this study, flowmeter data and time‐drawdown data collected from a long‐screened production well and nearby monitoring wells are combined to estimate the vertical distribution of hydraulic conductivity in a complex multilayer coastal aquifer system. Flowmeter measurements recorded as a function of depth delineate nonuniform inflow to the wellbore, and this information is used to better discretize the vertical distribution of hydraulic conductivity using analytical and numerical methods. The time‐drawdown data complement the flowmeter data by giving insight into the hydraulic response of aquitards when flow rates within the wellbore are below the detection limit of the flowmeter. The combination of these field data allows for the testing of alternative conceptual models of radial flow to the wellbore.
Application of Factor Analysis to the Study of Contamination in the Aquifer System of Ayamonte‐Huelva (Spain)
Authors: Grande J. A. , González A. , Beltrán R. , Sánchez‐Rodas D. 
Published: August 2005

AbstractThe growth of cultivation (strawberries and citrus fruits) in the coastal region of the Huelva province of Spain in the last 10 years has meant an increase in the demand of water from the Ayamonte‐Huelva aquifer system. It has also meant the introduction of an excess of nitrogen via fertilizers from farming.The system now has two problems: salt‐water intrusion in the southern sector (González and Romero, 1991; González, 1992); and a general increase in the nitrate content in the saturated zone. This second problem has led to average concentrations of nitrates in the aquifer above potable limits (50 ppm), reaching local values near to 400 ppm of NO3‐(González and Romero, 1991; Grande et al., 1993).This paper delineates the sphere of influence of the two factors being considered (salt‐water intrusion and agricultural contamination) on the different variables studied. The proximity between both factors is justified for each of the contaminating processes.
Residual Diesel Measurement in Sand Columns After Surfactant/Alcohol Washing
Authors: Martel Richard , Gélinas Pierre J. 
Published: August 2005

AbstractA new simple gravimetric technique has been designed to determine residual oil saturation of complex hydrocarbon mixtures (e.g., diesel) in sand column experiments because reliable methods are lacking. The He/N2 technique is based on drying of sand columns by circulating helium gas to drag oil droplets in a cold trap (liquid nitrogen). With this technique, residual diesel measurement can be performed easily immediately after alcohol/surfactant washing and in the same lab. For high residual diesel content in Ottawa sand (25 to 30 g/kg), the technique is much more accurate (± 2% or 600 mg/kg) than the standard analytical methods for the determination of mineral oil and grease. The average relative error on partial diesel dissolution in sand column estimated after alcohol/surfactant flooding (residual saturation of 10 to 15 g/kg) is as low as 5%. The precision of the He/N2 technique is adequate to compare relative efficiency of washing solutions when partial extraction of residual oil in Ottawa sand columns is performed. However, this technique is not adapted for determination of traces of oil in sediment or for environmental control of contaminated soils. Each diesel determination by the He/N2 technique costs less than 8 $US in chemical products (helium and liquid nitrogen). A simple laboratory drying setup can be built for less than 400 $US which makes this technique valuable for diesel analyses when a large number of tests are required.
Transient Capture Zone for a Single Well
Authors: Musa Mohammad , Kemblowski Marian W. 
Published: August 2005

AbstractGround‐water wells are frequently used to intercept contaminant plumes. The conventional design procedure is to plot the steady‐state capture zone and check whether the contaminant plume lies inside it. This approach ignores the pollutant's movement during the transient development of the cone of depression. In this paper we present a new method to analyze the transient performance of a single well that combines the analytical solutions for the steady‐state capture zones and transient velocity field with particle tracking. Using the particle trajectories, an effective capture zone can be estimated. No contaminant which is outside of this zone at the start of pumping can be captured by the well. The use of this method is illustrated by a hypothetical example.
Effect of Trapped Gas on Dissolved Oxygen Transport — Implications for In Situ Bioremediation
Authors: Fry Virginia A. , Istok Jonathan D. , O'Reilly Kirk T. 
Published: August 2005

AbstractIn situ bioremediation of contaminated aquifers is often limited by the concentration of dissolved oxygen in the ground water. Various methods have been used to increase dissolved oxygen concentrations in ground water, but the effect of a trapped gas phase on the distribution and transport of dissolved oxygen needs to be understood. The two‐dimensional transport of dissolved oxygen is investigated in experiments conducted in a large‐scale physical aquifer model (2 m × 4 m × 0.2 m) where a gas phase is trapped in the pore spaces of an otherwise‐saturated porous medium. The transport of dissolved oxygen is shown to be retarded up to 11.2 times the transport of the bulk water due to the mass transfer of oxygen between the aqueous phase and the trapped gas phase. The theoretical model for dissolved gas transport in the presence of a trapped gas phase is evaluated in a two‐dimensional ground‐water flow field using the U.S.G.S. numerical model MOC. The results show that dissolved oxygen transport can be modeled with the advection‐dispersion equation with linear equilibrium mass transfer but only when the longitudinal dispersion is increased compared to the value determined using a bromide tracer of the water flow. Increased longitudinal dispersion of the dissolved oxygen plume may be due to a temporally or spatially varying retardation factor or rate‐limited mass transfer. The presence of even a small amount of a trapped gas phase in an aquifer will significantly affect the distribution and transport of dissolved oxygen (trapped gas filling only 5% of the pore space will cause a retardation factor for oxygen of 2.6 at T = 15°C) and thus should be considered when designing ways to increase the dissolved oxygen concentration in ground water for in situ bioremediation.
Locating VOC Contamination in a Fractured‐Rock Aquifer at the Ground‐Water/Surface‐Water Interface Using Passive Vapor Collectors
Authors: Vroblesky D. A. , Rhodes L. C. , Robertson J. F. , Harrigan J. A. 
Published: August 2005

AbstractChlorinated organic solvents introduced to unlined lagoons at an industrial waste‐water treatment plant in the Inner Piedmont of South Carolina resulted in ground‐water contamination of a fractured‐rock aquifer. Part of the ground‐water contamination discharges to Little Rocky Creek, downgradient from the waste‐water treatment plant. Passive vapor collectors were buried in the bottom sediment of the creek to locate areas where ground water contaminated with volatile organic compounds was discharging to the creek. High concentrations of volatile organic compounds (VOCs) were found in passive vapor collectors in an area where VOCs were known to be discharging from ground water to surface water. This area was also a site where very low frequency electromagnetic anomalies (interpreted as fracture zones) intersected the creek or converged near the creek. The data show that passive vapor collectors in bottom sediment of Little Rocky Creek provided information on the location of fractures that were discharging contaminated ground water to surface water.
SF6 as a Conservative Tracer in Saturated Media with High Intragranular Porosity or High Organic Carbon Content
Authors: Wilson Ryan D. , Mackay Douglas M. 
Published: August 2005

AbstractThe application of dissolved stable gases as injected ground‐water tracers is a relatively new area of study, and the transport behavior of dissolved gases in a comprehensive range of saturated porous media types is poorly understood. Gas tracers, and sulphur hexafluoride (SF6) in particular, possess many of the characteristics of an ideal conservative, nonreactive tracer. SF6 is a volatile, nontoxic, inorganic gas that, when dissolved in water, behaved similarly to bromide in an idealized highly uniform saturated medium, exhibiting little physical nonequilibrium. For sand possessing significant intragranular porosity, SF6 did not show persistent tailing as a result of physical nonequilibrium transport to the same degree as bromide. This is consistent with less mass transfer of SF6 to immobile porosity due to its lower diffusion coefficient. This nonequilibrium is enhanced by the high pore‐water velocities employed. SF6 is slightly hydrophobic, with a measured octanol‐water partitioning coefficient of 13.8. This raises the question of whether SF6 would be slightly retarded in media with significant organic carbon, but no evidence of retardation was seen in sand with foc as high as 2.5 wt%.
Pumping Strategies for Management of a Shallow Water Table: The Value of the Simulation‐Optimization Approach
Authors: Barlow Paul M. , Wagner Brian J. , Belitz Kenneth 
Published: August 2005

AbstractThe simulation‐optimization approach is used to identify ground‐water pumping strategies for control of the shallow water table in the western San Joaquin Valley, California, where shallow ground water threatens continued agricultural productivity. The approach combines the use of ground‐water flow simulation with optimization techniques to build on and refine pumping strategies identified in previous research that used flow simulation alone. Use of the combined simulation‐optimization model resulted in a 20 percent reduction in the area subject to a shallow water table over that identified by use of the simulation model alone. The simulation‐optimization model identifies increasingly more effective pumping strategies for control of the water table as the complexity of the problem increases; that is, as the number of subareas in which pumping is to be managed increases, the simulation‐optimization model is better able to discriminate areally among subareas to determine optimal pumping locations.The simulation‐optimization approach provides an improved understanding of controls on the ground‐water flow system and management alternatives that can be implemented in the valley. In particular, results of the simulation‐optimization model indicate that optimal pumping strategies are constrained by the existing distribution of wells between the semiconfined and confined zones of the aquifer, by the distribution of sediment types (and associated hydraulic conductivities) in the western valley, and by the historical distribution of pumping throughout the western valley.
Ground‐Water Potential Evaluation of West Godavari District, Andhra Pradesh State, India—A GIS Approach
Authors: Kamaraju M.V.V. , Bhattacharya A. , Reddy G. Sreenivasa , Rao G. Chandrasekhar , Murthy G. S. , Rao T. Ch. Malleswara 
Published: August 2005

AbstractVoluminous geoscientific data related to various ground‐water parameters provide enormous scope for using the Geographic Information System (GIS) to draw meaningful conclusions on the ground‐water propsects of an area. To demonstrate the efficacy of the GIS for ground‐water studies, information on the parameters controlling ground water such as lithology, geomorphology, structure, and recharge condition of West Godavari district were analyzed using ARC/INFO GIS. Existing maps and records were used as data. An evaluation of ground‐water potential and generation of a map showing three major hydrogeological conditions with distinct ground‐water prospects which would serve as a basic tool in the exploitation of ground‐water resources of the district has resulted. The study has also revealed that the GIS techniques are time/cost‐effective and can be employed successfully in the planning stages of a ground‐water exploration programme. In addition, the GIS data generated for the study of ground‐water prospects can be updated and used for the planning and management of ground‐water resources of the district.