bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transformation of the Herbicides MCPP and Atrazine under Natural Aquifer Conditions
Authors: Agertved Jeanette , Rugge Kirsten , Barker James F. 
Published: August 2005

AbstractThe potential for aerobic biotransformation of the herbicides MCPP [(+/ ‐)‐2‐(4‐chloro‐2‐methylphenoxy)propionic acid] and Atrazine [2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine] under natural aquifer conditions was investigated. A natural gradient experiment was carried out in an aerobic ground‐water zone at the Canadian Forces Base Borden, Borden, Ontario, Canada. Over 90 days, a continuous plume was created by weekly injections of the herbicides (average concentrations of 400 jug/1 each), together with a conservative tracer, chloride. The fate of the herbicides was monitored at multilevel piezometers located downgradient from the injection well. In parallel, experiments with in situ testers (Gillham et al., 1990) were set up in the aquifer and microcosms were set up in the laboratory.For MCPP, the natural gradient experiment showed an adaptation period of 42‐56 days followed by transformation from 400 to 30 μg/1. As predicted, MCPP was not retarded compared to the conservative tracer. No transformation was observed in the in situ testers over 47 days. In the laboratory experiments no transformation was observed over 74 days.Atrazine was recalcitrant within the experimental period of 96 days in the natural gradient experiment. A retardation factor R = 1.2, within the predicted range, was found for Atrazine in the Borden aquifer. No transformation was observed either in the in situ testers or in the laboratory experiments after a period of 96 and 74 days, respectively.These results suggest that both MCPP and Atrazine are mobile in sand aquifers. Atrazine appears persistent, at least for 96 days, while MCPP undergoes considerable transformation.
Effects of Urban Storm‐Runoff Control on Ground‐Water Recharge in Nassau County, New York
Authors: Ku Henry F. H. , Hagelin Nathan W. , Buxton Herbert T. 
Published: August 2005

AbstractBefore urban development, most ground‐water recharge on Long Island, New York, occurred during the dormant season, when evapotranspiration is low. The use of recharge basins for collection and disposal of urban storm runoff in Nassau County has enabled ground‐water recharge to occur also during the growing season. In contrast, the use of storm sewers to route storm runoff to streams and coastal waters has resulted in a decrease in ground‐water recharge during the dormant season. The net result of these two forms of urban storm‐runoff control has been an increase in annual recharge of about 12 percent in areas served by recharge basins and a decrease of about 10 percent in areas where storm runoff is routed to streams and tidewater. On a countywide basis, annual ground‐water recharge has remained nearly the same as under predevelopment conditions, but its distribution pattern has changed. Redistribution resulted in increased recharge in the eastern and central parts of the county, and decreased recharge in the western and nearshore areas. Model simulation of recharge indicates that the water‐table altitude has increased by as much as 5 ft above predevelopment levels in areas served by recharge basins and declined by as much as 3 feet in areas where stormwater is discharged to streams and tidewater.
Analysis of Observation‐Well Response During Constant‐Head Testing
Authors: Mishra S. , Guyonnet D. 
Published: August 2005

AbstractA simple method for computing transmissivity and storativity from the analysis of observation‐well response during constant‐head aquifer tests is presented. The proposed methodology is based on approximate solutions developed using the Boltzmann transformation technique, and is demonstrated to be valid for many practical situations. It is shown that familiar constant‐rate solutions (e.g., the Theis equation) can be generalized for the constant‐head case if the head change at the observation well is normalized by the flow rate at the test well and then used as the time‐dependent variable. A generalized form of the Jacob‐Lehman approximation which is valid at every point in the aquifer is presented. Analysis of several hypothetical constant‐head test data using the suggested approach indicate that estimates of transmissivity are much more reliable than those of storativity. However, both hydraulic parameters appear to be reasonably estimated if the interwell distance is at least two orders of magnitude larger than the wellbore radius.
Numerical Simulation of the Effects of Variable Density in a Contaminant Plume
Authors: Koch Manfred , Zhang Gangpeng 
Published: August 2005

AbstractNumerical simulations are performed to investigate quantitatively density effects of a contaminant plume on its movement in time and space. The numerical model used is a characteristics/finite difference method. The density of the solute is described by an equation of state similar to sea water or lead nitrate. The results of a large number of simulations do not allow us to establish a general empirical law for predicting the fate of a density‐dependent plume. Whether density effects are important or not depends on a variety of hydraulic parameters of the aquifer model, such as the permeability (isotropic or anisotropic), flow gradient, the hydrodynamic dispersivity, and the time‐scale considered. Following some theoretical ideas of previously derived analytical scaling laws for buoyant plumes, the concept of a near‐source and a far‐source region of the plume has been found very useful. The modeled plume centerlines compare favorably with the predictions of these scaling laws in the intermediate‐source region, but deviate significantly in the far‐source region where diffusion processes become important or necking instabilities at the plume edges occur. It is found that the combined influence of the various model parameters above can be very different, depending on whether the plume is still within the near‐source or has already extended into the far‐source region. In spite of the large dependency of the density effects on these model parameters, in some cases variable density might have an effect on the plume migration for already moderate density contrasts of~0.3% (which corresponds to a concentration of~4000 ppm for a leachate of salt or lead nitrate). Hydrodynamic dispersion tends to reduce the density effects. For sufficiently small values of the dispersivity, convective instabilities and fingering phenomena occur at the horizontal plume boundaries. For a lighter‐than‐water contaminant, such as acetone or methylethylketone, significant buoyant movements occur only for (unrealistically) high concentration of ~ 20,000 ppm. In conclusion the results of the simulations do not provide a generally applicable guideline for the evaluation of density‐dependence transport. Therefore, the individual numerical modeling of a particular site will often be indispensable.
Delivery of Chloride and Nitrate by Ground Water to the Great Lakes: Case Study for the Door Peninsula, Wisconsin
Authors: Cherkauer Douglas S. , McKereghan Peter F. , Schalch Linda H. 
Published: August 2005

AbstractA calibrated, two‐dimensional, finite‐element transport model of the dolomite aquifer of the Door Peninsula of Wisconsin is used to ascertain the mass loadings of chloride and nitrate delivered to Lake Michigan and Green Bay by ground water. Inclusion of unsteady transport effects and verification of the model have not been possible due to data limitations. With that caveat, the model shows that only 43, 33, and 38% of the water, chloride, and nitrate, respectively, entering the aquifer's upper surface as recharge actually discharges directly to the lake as ground water. The remainder is discharged to wells and other sinks beforehand. A concentration of agricultural and urban land use sources along the Green Bay coast results in 58 and 50% of the total chloride and nitrate, respectively, delivered by ground water going to the west shore, despite that side's receiving only 38% of the water volume. On the Lake Michigan side, agricultural land use is the largest source of both chemicals, with the second largest source from background contributions. Point sources are relatively minor contributors of both chemicals.In an earlier paper, Cherkauer and McKereghan (1991) showed that ground‐water discharge was focussed into embayments along the shore. That phenomenon repeats itself in solute loads as the greatest mass discharges occur in the bays. The simulated results show that discharge to both bays and nonbays on a given coast have similar solute concentrations, so the load differences are strictly the result of discharge focussing.Ground water's delivery of the solutes to these bays generally greatly exceeds that from precipitation. Comparison of loading to other sources or to mass budgets for the entire lake is not possible at this time.
Comparison of Methods Used to Delineate Capture Zones of Wells: 2. Stratified‐Drift Buried‐Valley Aquifer
Authors: Springer Abraham E. , Bair E. Scott 
Published: August 2005

AbstractAnalytical, semianalytical, and numerical models of the flow system in a stratified‐drift buried‐vailey aquifer were used with particle‐tracking/stream‐function programs to delineate traveltime‐related capture zones of a municipal wellfield and to assess conceptual errors imposed by requisite assumptions associated with each flow model. The analytical flow model uses the Theis equation describing two‐dimensional transient drawdown surrounding a well in a fully confined aquifer and superposition of a nonuniform regional flow field. The semianalytical flow model implicitly uses the Thiem equation describing two‐dimensional steady‐state drawdown surrounding a well in a fully confined aquifer and superposition of a uniform regional flow field. The numerical flow model uses a three‐dimensional steady‐state finite‐difference solution and incorporates four model layers, specified‐flux and head‐dependent flux boundary conditions, spatially variable recharge, and head‐dependent leakage to and from streams.The predictive ability of the flow models is based on comparison of mean absolute errors and root mean squared errors between measured and simulated heads as well as comparison of pathline distributions defining the one‐year capture zones. The comparisons show that the uniform flow field and uniform transmissivity required of the semianalytical flow model cause it to be less accurate than the analytical and numerical flow models. The inability of the analytical flow model to incorporate spatial variations in transmissivity causes it to be less accurate than the numerical flow model. These conceptual errors associated with use of the analytical and semianalytical flow models in this hydrogeologic setting cause their one‐year capture zones to be less reasonable than those from the numerical flow model.
A Forced Gradient Tracer Experiment in a Coastal Sandy Aquifer, Georgetown Site, South Carolina
Authors: Mas‐Pla Josep , Jim Yeh T.‐C. , McCarthy John F. , Williams T. M. 
Published: August 2005

AbstractA two‐well tracer experiment was conducted in a coastal, sandy aquifer in South Carolina to investigate tracer migration in ground‐water systems. Chloride tracer was injected into the aquifer under a steady flow condition created by continuous injection and withdrawal of ground water at an injection and a withdrawal well dipole separated by a distance of 5 meters. Breakthrough data were collected at several depths from two multilevel sampling wells, 1.5 meters apart, between the injection well and the withdrawal well.A one‐dimensional advection‐dispersion model that considers the nonuniform velocity field of the two‐well experiment was employed to estimate the hydrologic properties of the aquifer. The values of the porosity and dispersivity were estimated by fitting the model to the observed breakthrough data collected at three depths at one sampling well (Well A). These values were then used to predict the breakthroughs at the same depths in the other sampling well (Well B). A two‐dimensional flow and transport model was also employed to simulate the tracer migration. Results of both one‐ and two‐dimensional simulations show that these models fail to predict the tracer breakthrough at Well B using parameter values obtained from Well A.The failure of the model to predict breakthroughs at Well B suggests that a three‐dimensional characterization of aquifer heterogeneities and a three‐dimensional modeling effort may be needed in order to capture the complex flow pattern in the aquifer.
Hydrogeologie Characteristics and Deforestation of the Stone Forest Karst Aquifers of South China
Authors: Huntoon Peter W. 
Published: August 2005

AbstractStone forest aquifers comprise an important class of shallow, unconfined karstic aquifers in the south China karst belt. They occur under flat areas such as floors of karst depressions, stream valleys, and karst plains. The frameworks for the aquifers are the undissolved carbonate spires and ribs in epikarst zones developed on carbonate strata. The ground water occurs within clastic sediments which infill the dissolution voids.The aquifers are thin, generally less than 100 meters thick, and are characterized by large lateral permeabilities and small storage. The result is that the aquifers are difficult to manage because recharge during the rainy season moves rapidly out of the aquifers. Water levels fall sharply as the dry season progresses and the ground‐water supply falls off accordingly.The magnitude and duration of the seasonal recharge pulse that replenishes the stone forest aquifers have been severely impacted by massive post‐1958 deforestation in the south China karst region. Water that was formerly retained beyond the wet season in the forested uplands, later to be released to the stone forest aquifers under the lowland plains, now passes quickly through the system during the wet season. The loss of this seasonal upland storage has resulted in both a reduction in the volume of recharge to the lowland stone forest aquifers and a shortening of the seasonal recharge event. The result is accelerated water‐level declines in the stone forest aquifers as the dry season progresses which, in turn, causes premature dewatering of wells and decreased spring discharges. This response is compounded by increased ground‐water withdrawals as the people attempt to offset the declining supply. Management of the total water‐supply system requires not only tinkering with the aquifer, but massive reforestation efforts to restore dry season water retention in the upland parts of the watersheds.
Dissolution of Dense Chlorinated Solvents into Ground Water: 1. Dissolution from a Well‐Defined Residual Source
Authors: Anderson Michael R. , Johnson Richard L. , Pankow James F. 
Published: August 2005

AbstractWhen found dissolved in ground water, chlorinated hydrocarbon (CHC) solvents such as tetrachloroethylene (PCE) are nearly always encountered at concentrations far below their solubilities. This is true even in cases when it is known or at least strongly suspected that actual liquid solvent is present in the aquifer. In contrast, laboratory studies using columns packed with porous media containing various organic fluids have indicated that when water is forced to flow through a zone containing an immobile organic fluid, saturation concentrations can be achieved rapidly. This study investigated the concentrations and mass removal rates obtainable when simulated ground water is free to flow at least partially around a zone of porous medium that contains solvent in a state of stable, residual saturation. Reductions in the mass removal rate due to reduced permeability in the solvent zone were found to be minimal under the conditions of the experiment. Thus, near the source the plume was essentially the same width as the source zone, and PCE concentrations in the center of the plume were at or near saturation, even at water velocities of 100 cm/day. The fact that CHC aqueous concentrations in ground‐water samples are typically far below saturation is, therefore, likely not due to limited dissolution from the fingers of residual solvent. Probable explanations include the preferential formation of thin pools rather than fingers of CHC, dispersion during transport, and dilution by uncontaminated water in monitoring or pumping wells.
Using Cooper‐Jacob Approximation to Take Account of Pumping Well Pipe Storage Effects in Early Drawdown Data of a Confined Aquifer
Authors: Chapuis Robert P. 
Published: August 2005

AbstractMost hydrogeology textbooks warn the reader that in order to avoid large errors the Cooper‐Jacob solution should only be applied when the u‐parameter of the Theis solution is less than 0.01 or 0.02. This paper proposes a graphical representation for visualizing and quantifying the difference between the two solutions. The graph of drawdown vs log (time) may be divided into three zones, the early one being influenced by storativity, pumping well pipe capacity and skin effects (among others), the latest by boundary effects, and the intermediate one by the transmissivity and storativity of the aquifer. The differences between the theoretical solutions are maximal in the early data zone. Because both solutions consider a pumping well of infinitesimal diameter, the early time data graph may be distorted by the influence of real well pipe storage capacity and, consequently, may yield a poor estimate of the parameters of the aquifer. The method of Papadopulos and Cooper is already available to take pumping well pipe storage into account in interpreting the pumping well drawdown data, but may result in unreliable S values due to the difficulty in curve matching. A more practical solution, which is also applicable to observation wells, is proposed and demonstrated with a worked example. This solution can be used when the Cooper‐Jacob approximation is valid and it does not require curve matching. Early drawdown data in the pumping well cannot provide a reliable estimate of storativity for many reasons. These early data can be used, however, to obtain a better estimate of storativity and transmissivity from the drawdown data of observation wells. The effect of pumping well pipe storage in the early drawdown data may be significant in cases of low transmissivity aquifers and low pumping rates, which are quite common in ground‐water remediation.
Parameter Estimation for Step‐Drawdown Tests
Authors: Avci Cem B. 
Published: August 2005

AbstractStep‐drawdown tests may be used to evaluate the well loss component of the well drawdown and to obtain estimates of the aquifer properties. A procedure that analyzes step‐drawdown tests with pumping stages of unequal time durations was formulated and developed into a computer program; the method is applicable to confined aquifers where the water‐level drawdowns are governed by the Theis well function. A least‐squares‐fit error analysis is used in the determination of the aquifer properties and the well loss component of the drawdown.
The Use of Specific Capacity to Assess Transmissivity in Fractured‐Rock Aquifers
Authors: Huntley David , Nommensen Roger , Steffey Duane 
Published: August 2005

AbstractTransmissivity is often estimated from specific capacity data because of the expense of conducting standard aquifer tests to obtain transmissivity and the relative availability of specific capacity data. Most often, analytic expressions relating specific capacity to transmissivity derived by Thomasson and others (1960), Theis (1963), or Brown (1963) are used in this analysis. Razack and Huntley (1991) demonstrate that turbulent well loss produces poor correlation between measured transmissivities and those estimated from specific capacity from the above relations. This study focuses on a comparison between transmissivity and specific capacity of wells completed as open boreholes in fractured‐rock aquifers, where turbulent well loss may be less important.The analytic solutions typically used to predict transmissivity from specific capacity in alluvial aquifers do not agree well with the measured transmissivities in fractured‐rock aquifers. Measured transmissivities are less than those estimated from the theoretical solutions based on specific capacity. Some of the variation may be due to shorter testing periods for this data set, the difference between storage coefficients in fractured‐rock and alluvial aquifers, or aquifer anisotropy. Correction for these factors alone, however, does not markedly improve the correlation between theoretical and observed specific capacity/trans‐missivity relations. Transmissivities derived using the vertical fracture model of Gringarten and Witherspoon (1972), however, correlate very well with the observed specific capacities. Empirical relations between the log of transmissivity and the log of specific capacity for the fractured‐rock data set suggest they are linearly related (correlation coefficient of 0.89), but the width of 90% prediction interval is about 1.1 log cycles, indicating that the range of probable transmissivities corresponding to a single specific capacity was more than one order of magnitude.
Determination of Hydraulic Conductivity from Complete Grain‐Size Distribution Curves
Authors: Alyamani Mahmoud S. , Şen Zekâi 
Published: August 2005

AbstractCurrent methods of relating hydraulic conductivity to grain‐size distribution rely on a single so‐called representative grain‐size distribution parameter such as the effective diameter, geometric mean, median, standard deviation, etc. An alternative procedure is proposed which relates the hydraulic conductivity to the initial slope and intercept of the grain‐size distribution curve. The proposed methodology is documented with data from Australia and Saudi Arabia.
Unsaturated Zone and Ground‐Water Contamination by Organic Pollutants in a Sewage‐Effluent‐Irrigated Site
Authors: Muszkat Lea , Raucher Daniel , Magaritz Mordeckai , Ronen Daniel , Amiel Abraham J. 
Published: August 2005

AbstractThis study describes the distribution of organic pollutants from the ground surface, through the unsaturated zone, to the water table at a citrus grove irrigated by sewage effluent for about 20 years. The citrus grove, located in Israel, overlies an unconfmed Coastal Plain aquifer about 2 km inland from the Mediterranean Sea. The distribution of organic compounds at the citrus grove is compared with two control sites receiving moisture from nonpolluted water sources (one in another citrus grove irrigated by ground water and the other in an uncultivated area receiving only precipitation). Overall, 10 analyses were performed. At the effluent‐irrigated site, organic pollutants from the sewage had migrated through the 20 meter thick unsaturated zone to the water table; included in these were several pollutants, such as toluene and phthalates, that are considered to be biodegradable. Pollutant concentrations generally increased with depth. On the other hand, pollutant concentrations at the two control sites decreased significantly with depth through the unsaturated zone. The downward mobility of organic pollutants may be enhanced by the sewage itself. Because sewage effluent is considered to be a readily available source of irrigation water in many parts of the world, the results of this study suggest that what may seem to be a relatively simple solution to water scarcity problems may have potentially long‐term and dangerous effects on ground‐water quality.