bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Hydraulic Conductivities Calculated from Multiport‐Permeameter Measurements
Authors: Wolf Steven H. , Celia Michael A. , Hess Kathryn M.
Published: August 2005

A multiport permeameter was developed for use in estimating hydraulic conductivity over intact sections of aquifer core using the core liner as the permeameter body. Six cores obtained from one borehole through the upper 9 m of a stratified glacial‐outwash aquifer were used to evaluate the reliability of the permeameter. Radiographs of the cores were used to assess core integrity and to locate 5‐ to 10‐cm sections of similar grain size for estimation of hydraulic conductivity. After extensive testing of the permeameter, hydraulic conductivities were determined for 83 sections of the six cores. Other measurement techniques included permeameter measurements on repacked sections of core, estimates based on grain‐size analyses, and estimates based on borehole flowmeter measurements. Permeameter measurements of 33 sections of core that had been extruded, homogenized, and repacked did not differ significantly from the original measurements. Hydraulic conductivities estimated from grain‐size distributions were slightly higher than those calculated from permeameter measurements; the significance of the difference depended on the estimating equation used. Hydraulic conductivities calculated from field measurements, using a borehole flowmeter in the borehole from which the cores were extracted, were significantly higher than those calculated from laboratory measurements and more closely agreed with independent estimates of hydraulic conductivity based on tracer movement near the borehole. This indicates that hydraulic conductivities based on laboratory measurements of core samples may underestimate actual field hydraulic conductivities in this type of stratified glacial‐outwash aquifer.
Hydrogeological Decision Analysis: 2. Applications to Ground‐Water Contamination
Authors: Massmann Joel , Freeze R. Allan , Smith Leslie , Sperling Tony , James Bruce
Published: August 2005

Two case studies are presented as examples of a decision‐analysis approach to engineering design for projects in which the hydrogeological environment plays an important role. This approach to design involves quantifying benefits, costs, and risks for each design alternative under consideration. Risk, which is defined as the expected costs of failure, reflects both performance uncertainties and failure costs. Probabilities of failure are estimated by coupling stochastic ground‐water flow and solute transport models with uncertainty models that represent input parameters as random variables. The case studies that are used to describe the approach involve (1) selecting a pumping rate for an extraction well to capture an existing contaminant plume, and (2) designing a leachate collection system for a soil remediation facility. The examples illustrate that the decision‐analysis approach can be accomplished using relatively simple analytical models to simulate the behaviors of hydrogeological environments and engineering components. The results identify how the preferred design alternative depends upon the regulatory, hydrogeological, and economic environments in which the decision is made. For the extraction well example, the preferred alternative is relatively insensitive to the costs of failure but is dependent upon the expected dimensions of the contaminant plume. For the soil remediation example, the preferred design alternative depends upon the anticipated costs of failure and the regulatory standard for ground‐water contamination. Reducing the variance or uncertainty in dispersivity values by a factor of 3 had a relatively small effect on the overall design of the leachate collection system.
Geochemical Transformations and Modeling of Two Deep‐Well Injected Hazardous Wastes
Authors: Roy W. R. , Seyler B. , Steele J. D. , Mravik S. C. , Moore D. M. , Krapac I. G. , Peden J. M. , Griffin R. A.
Published: August 2005

Two liquid hazardous wastes (an alkaline brine‐like solution and a dilute acidic waste) were mixed with finely ground rock samples of three injection‐related lithologies (sandstone, dolomite, and siltstone) for 155 to 230 days at 325°K‐10.8 MPa. The pH and inorganic chemical composition of the alkaline waste were not significantly altered by any of the rock samples after 230 days of mixing. The acidic waste was neutralized as a consequence of carbonate dissolution, ion exchange, or clay‐mineral dissolution, and hence was transformed into a nonhazardous waste.

Mixing the alkaline waste with the solid phases yielded several reaction products: brucite, Mg(OH)2; calcite, CaCO3; and possibly a type of sodium metasilicate. Clay‐like minerals formed in the sandstone, and hydrotalcite, Mg6Al2‐CO3 (OH)16· 4H2O, may have formed in the siltstone at trace levels. Mixing the alkaline waste with a synthetic brine yielded brucite, calcite, and whewellite (CaC2O4· H2O). The thermodynamic model PHRQPITZ predicted that brucite and calcite would precipitate from solution in the dolomite and siltstone mixtures and in the alkaline waste‐brine system.

The dilute acidic waste did not significantly alter the mineralogical composition of the three rock types after 155 days of contact. The model PHREEQE indicated that the calcite was thermodynamically stable in the dolomite and siltstone mixtures, and was detected in small quantities in aged‐solid samples. The sandstone‐waste system appeared to equilibrate with amorphous silica, whereas silica equilibria may not have been attained in the dolomite and siltstone systems.

Computer models like PHRQPITZ and PHREEQE may be useful tools for estimating mineral equilibria in deep‐well scenarios, but there is a need to expand the database used in these kinds of calculations. Caution must be applied in interpreting the predicted equilibria. Fate modeling based on thermodynamic principles can predict simple geochemical interactions, but empirical, laboratory‐based investigations may be needed in addition to modeling for a reliable assessment of the fate of injected wastes.
Evaluation of Sorption Models in the Simulation of Naphthalene Transport Through Saturated Soils
Authors: Liu Ko‐Hui , Enfield Carl G. , Mravik Susan C.
Published: August 2005

To show the effect of sorption model selection, the one‐dimensional transport of naphthalene in two saturated porous media was simulated using numerical models, which included the processes of dispersion, advection, and sorption. Three vdifferent models describing the sorption process: (1) a local equilibrium model, (2) a first‐order kinetic sorption model, and (3) a two‐site model (a combination of equilibrium and kinetic sorption model), were examined. In addition, this study considered two types of boundary conditions: constant concentration and constant flux boundary conditions. Simulations were made for data of naphthalene transport through a laboratory soil column packed with Lincoln or Eustis soil series. Numerical simulation results show that the selection of the sorption model had significant effects on the numerical solutions. The numerical solution obtained using either the local equilibrium model or the first‐order kinetic sorption model described the experimental data very well from the Lincoln soil column. In contrast, the numerical solution obtained using the two‐site model described the experimental data for the Eustis soil better than either the equilibrium or kinetic models. Different boundary conditions had little influence on the numerical solutions. Different amounts of organic carbon in the Eustis (0.66%) and Lincoln (0.036%) soils are thought to cause the differences in breakthrough curves and the response to the sorption processes.
Calibration of a Texture‐Based Model of a Ground‐Water Flow System, Western San Joaquin Valley, Californiaa
Authors: Phillips Steven P. , Belitz Kenneth
Published: August 2005

The occurrence of selenium in agricultural drain water from the western San Joaquin Valley, California, has focused concern on the semiconfined ground‐water flow system, which is underlain by the Corcoran Clay Member of the Tulare Formation. A two‐step procedure is used to calibrate a preliminary model of the system for the purpose of determining the steady‐state hydraulic properties. Horizontal and vertical hydraulic conductivities are modeled as functions of the percentage of coarse sediment, hydraulic conductivities of coarse‐textured (Kcoarse) and fine‐textured (Kfine) end members, and averaging methods used to calculate equivalent hydraulic conductivities. The vertical conductivity of the Corcoran (Kcorc) is an additional parameter to be evaluated.

In the first step of the calibration procedure, the model is run by systematically varying the following variables: (1) Kcoarse/Kfine, (2) Kcoarse/Kcorc, and (3) choice of averaging methods in the horizontal and vertical directions. Root mean square error and bias values calculated from the model results are functions of these variables. These measures of error provide a means for evaluating model sensitivity and for selecting values of Kcoarse, Kfine, and Kcorc for use in the second step of the calibration procedure. In the second step, recharge rates are evaluated as functions of Kcoarse, Kcorc, and a combination of averaging methods. The associated Kfine values are selected so that the root mean square error is minimized on the basis of the results from the first step.

The results of the two‐step procedure indicate that the spatial distribution of hydraulic conductivity that best produces the measured hydraulic head distribution is created through the use of arithmetic averaging in the horizontal direction and either geometric or harmonic averaging in the vertical direction. The equivalent hydraulic conductivities resulting from either combination of averaging methods compare favorably to field‐ and laboratory‐based values.
Assessing Pesticide Contamination to Ground Water: A Rapid Approach
Authors: Ehteshami Majid , Peralta Richard C. , Eisele Hubert , Deer Howard , Tindall Terry
Published: August 2005

A methodology has been developed for identifying hazardous pesticides/site combinations threatening ground‐water contamination. Screening methodologies are required to determine which locations and pesticides now in use should receive the greatest attention to safeguard the public health. The presented method uses a hazard to ground‐water hydrogeological screening model (DRASTIC) and employs a one‐dimensional pesticide transport model (CMLS). The method is an efficient and practical technique to identify where particular combinations of pesticides, water management practices, soils, and geology result in the greatest potential hazard to ground‐water contamination. Use of the presented approach can reduce sampling needs and expense.
History Matching to Determine the Retardation of PCE in Ground Water
Authors: Rogers L.
Published: August 2005

Failure to incorporate retardation factors in solute transport predictions can lead to serious miscalculations of the degree of contamination and the time required for remediation. This study employs history matching, a vital component in the effort to calibrate models to specific field sites, to demonstrate the difficulties in matching historical well concentrations to a single retardation factor or source function. A 2‐D hybrid finite‐element/finite‐difference, advection‐dispersion code with retardation was used to match simulated perchloroethylene (PCE, also known as tetrachloroethylene) concentrations against observed concentrations in monitor wells at a well‐characterized Superfund site. The transport model yielded reasonable matches for retardation factors between 1 and 3. This was in comparison to the 6 to 22 range of retardation factors based on laboratory batch sorption experiments and the 1 to 5 range based on field measurements of soil and associated well‐water pore fluid. Simulation results demonstrated that for this site, retardation factors greater than or equal to 6 would imply releases of PCE prior to dates compatible with historical records. History matching can constrain the reasonable range of parameters necessary to model contaminants in ground water.
Fingerprinting Petroleum Contamination Using Synchronous Scanning Fluorescence Spectroscopy
Authors: Pharr Daniel Y. , McKenzie J. Keith , Hickman Aaron B.
Published: August 2005

Synchronous scanning fluorescence spectroscopy is a simple, cost‐effective method for fingerprinting many petroleum contaminants in ground‐water and soil samples. The extraction of contaminated ground‐water and soil samples with water and cyclohexane followed by the synchronous scanning fluorescence spectrophotometry of the organic extract is described for over 20 petroleum product standards and actual samples. This method allows for the classification and identification of aromatic‐containing products such as: gasoline, kerosene, diesel oil, various grades of fuel oil, and asphalt. This analytical method is more efficient than chromatographic methods typically used for quantitative analysis of petroleum contaminants and its spectra are easier to interpret for fingerprinting purposes. Several case studies of its use in determining among alternate sources of contamination are presented.
Transformation of the Herbicides MCPP and Atrazine under Natural Aquifer Conditions
Authors: Agertved Jeanette , Rugge Kirsten , Barker James F.
Published: August 2005

The 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

Before 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

A 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

Numerical 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

A 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

Analytical, 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

A 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

Stone 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

When 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

Most 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

Step‐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

Transmissivity 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

Current 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

This 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.
Ground‐Water Pollution of the Madras Urban Aquifer, India
Authors: Somasundaram M. V. , Ravindran G. , Tellam J. H.
Published: August 2005

Most of the water requirement for Madras is met from surface‐ and ground‐water supplies piped in from outside the city limits. However, as is the case for many cities, a certain proportion of the population, usually the poorest, is forced to rely on wells within the urban area. A study was therefore carried out to gain an idea of the inorganic quality of the water in the wells penetrating the shallow (< 20 m thick) alluvial aquifer below the city. Two general surveys of selected wells across the city indicated that relative to Indian domestic water standards, of the 93 ground‐water samples obtained, 25% exceeded the Ca limit, 11% the Mg limit, 43% the total dissolved solids limit, 14% the SO4 limit, and 70% the NO3 limit. As an indicator of biological contamination, the high concentrations of NO3 (up to 1040 mg/l) are particularly worrying. A detailed survey of sites close to a city river was also undertaken. High heavy metal concentrations were detected, with As up to 0.42 mg/1, Hg to 0.02 mg/1, Pb to 1.82 mg/1, and Cd and 1.31 mg/1. Microbes have been found in several of the wells. It is clear that, as expected, the shallow ground water is grossly polluted.
The Use of Sulphur Hexafluoride as a Conservative Tracer in Saturated Sandy Media
Authors: Wilson Ryan D. , Mackay Douglas M.
Published: August 2005

Sulphur hexafluoride (SF6), a volatile, nontoxic, inorganic compound, behaved identically to bromide in a laboratory column tracer experiment with saturated sandy media. A simple system was used to achieve an SF6 injection concentration of approximately 7 mg/1, roughly 25% of its solubility. While this system requires more equipment and time than that involved in preparing ionic tracer solutions, certain benefits are realized. The detection limit for SF6 was approximately 5 μg/l using a simple headspace extraction technique and a gas Chromatograph with an electron capture detector. Thus, the tracer could be followed for a three order of magnitude decrease in concentration. For similar resolution, bromide had to be injected at a concentration over 1000 mg/1 (typical detection limit approximately 0.5 mg/1). When the required higher concentrations of the ionic tracers may lead to significant geochemical changes or density effects, SF6 may be the preferable tracer. Furthermore, unlike ionic tracers, the highly volatile SF6 may be readily removed from water. High volatility does, however, require that some care be taken to limit the potential loss of mass during injection, sampling, and analysis. Since others are developing procedures for analyzing SF6 in ground water with extremely low detection limits (on the order of 1 ng/1), it appears likely that measurable concentrations could range over six to seven orders of magnitude. This range is considerably wider than typically possible with ionic tracers, and may offer an important advantage in some applications.
The Significance of the Extent of Recovery in Interpreting Aquifer Pumping Test Data from Large Diameter Wells
Authors: Singh V. S. , Gupta C. P.
Published: August 2005

To estimate aquifer parameters from pumping test data obtained from large diameter wells, one must consider the recovery data. This is particularly important for low permeability formations. Observations on the recovery should be continued to the maximum possible extent for an accurate estimation of these parameters. Analysis of data from a few representative case studies for granitic and basaltic rocks are presented here to establish a criterion to decide how long observations should be taken during recovery in the well.
A Field Experiment to Study the Behavior of Tetrachloroethylene Below the Water Table: Spatial Distribution of Residual and Pooled DNAPL
Authors: Kueper Bernard H. , Redman David , Starr Robert C. , Reitsma Stanley , Mah May
Published: August 2005

This paper describes a field experiment involving the release of 230.9 liters of tetrachloroethylene (PCE) below the water table in a naturally occurring, unconfined sand aquifer. The release was executed in a 3 m X 3 m X 3.4 m deep, scalable‐joint steel sheet‐pile cell anchored into an underlying clay aquitard. After allowing 28 days for redistribution, excavation of the upper approximately 0.9 m of the cell revealed PCE pools and residual to be present in relatively coarser grained horizons, with substantial degrees of lateral flow having taken place. This lateral flow was observed in laminations and lenses ranging in thickness from a few mm to a few cm, with only subtle variations in texture separating individual migration pathways. Detailed sampling during the excavation procedure and subsampling of three cores extended down to the clay aquitard revealed a spatially variable distribution of PCE with saturations ranging from 1% to 38% of pore space. Laboratory measurement of a fully hysteretic capillary pressure curve demonstrated that the degree of nonwetting phase residual is a function of the maximum saturation attained along main drainage during the initial infiltration process. Various models for consolidated petroleum reservoir materials did not fit the experimental data well. The theory governing pool formation in heterogeneous porous media is also presented, and it is demonstrated that pools can form in homogeneous media exhibiting a distinct entry pressure.
Pentobarbital Found in Ground Water
Authors: Eckel William P. , Ross Benjamin , Isensee Robert K.
Published: August 2005

A landfill in Florida which received wastes in 1968 and 1969 has contaminated nearby shallow ground water. Analysis of a sample of contaminated ground water collected in 1984 from a well approximately 300 m from the landfill tentatively indicated the presence of the addictive sedative pentobarbital, among many other compounds. A well at the same location was resampled in 1991, and pentobarbital was positively identified using gas chromatography/tandem mass spectrometry. The persistence over 21 years of a supposedly unstable drug in anoxic ground water raises the possibility that other pharmacologically active compounds may be found in plumes coming from landfills that have accepted medical wastes.
A Second‐Order Diagonally Implicit Runge‐Kutta Time‐Stepping Method
Authors: Baker Donald L.
Published: August 2005

This paper presents a subset of the family of diagonally implicit Runge‐Kutta (DIRK) time‐stepping methods for finite‐difference models of parabolic (diffusion‐like) equations. It includes the first‐order‐accurate Euler implicit (backward in time, DIRK1) and the second‐order Crank‐Nicolson (DIRK2) methods as special cases. It combines a series of DIRK1 partial time steps so as to eliminate additional power terms of the time step δt, in the local error, by the number of partial steps used. This offers a large increase in computational efficiency, going from a DIRK1 to a DIRK2 method, and improves on the Crank‐Nicolson method with a better choice of Runge‐Kutta parameters. For a linear diffusion example, an optimal‐parameter DIRK2 method offers the same accuracy as the Euler implicit method at two orders of magnitude larger time step, with an order of magnitude better accuracy than the Crank‐Nicholson method. In a highly nonlinear horizontal unsaturated water flow example, using eight simulated medium to coarse soils, a DIRK2 method produces either an average maximum accuracy improvement of 4.7 times over the Euler implicit method, without Newton or Picard iteration, or from 3.8 to 48 times faster computer run times for the same accuracy.
Cokriging of Geoelectric and Well Data to Define Aquifer Protective Layers
Authors: Pesti Geza , Bogardi Istvan , Kelly William E. , Kalinski Robert J.
Published: August 2005

Cokriging and ordinary kriging of geoelectric and well data are used to determine the thickness, lateral extent, and spatial variability of a naturally occurring clay layer near Ashland, Nebraska. The clay layer that protects the underlying ground water from contaminant sources is defined by mapping the estimated clay thickness; variance maps provide an assessment of the uncertainty of the thickness estimates. Two types of information are combined in the cokriging procedure: clay thickness data estimated from drillers'logs of 128 irrigation and municipal supply wells, and thicknesses estimated from interpretation of 44 vertical electrical soundings (VES); for the ordinary kriging, well data are used alone. Both types of maps demonstrate the existence of a continuous near‐surface clay layer extending over much of the Ashland wellfield; however, the cokriged map shows much more detail in the central part of the study area, where the well data are undersampled. The relatively dense VES network in the central area provides an important information bridge between the northern and southern areas making the cokriged map more continuous and accurate than the map prepared using the well data alone and ordinary kriging.
Microbiological Analysis of Iron‐Related Biofouling in Water Wells and a Flow‐Cell Apparatus for Field and Laboratory Investigations
Authors: Tuhela Laura , Smith Stuart A. , Tuovinen Olli H.
Published: August 2005

A flow‐cell assembly was constructed to collect biofilm samples on glass slides in an effort to monitor Fe‐precipitating microorganisms in water wells. The flow‐cell was used with a once‐flow‐through connection to municipal‐water wells which had previous histories of Fe‐related precipitation and biofouling problems. Microscopic observations of biofilms attached to glass slides confirmed the presence of stalked and sheathed bacteria believed to be involved in Fe (III)‐precipitation. Scanning electron microscopy confirmed that biofilm samples contained Gallionella‐type morphological features composed of helical, intertwisted stalks. Attempts to recover these organisms with cultural methods were unsuccessful. For monitoring Fe‐precipitating microorganisms, a differential solid medium was developed from the general‐purpose heterotrophic platecount medium (R2A) by incorporating ferric ammonium citrate in the formulation. Organisms capable of using citrate in the modified medium yielded rust‐colored colonies due to the formation of Fe (III)‐precipitates. These Fe‐precipitating bacteria did not possess stalks, sheaths, or other appendages, and their presence could not be predicted from microscopic examination of the sample materials. Optical measurement of biofilm thickness was deemed unreliable because of large variation in the thickness of Fe(III)‐precipitation and associated bacterial attachment. Fe(III)‐precipitates were identified as ferrihydrite, a poorly crystalline Fe(III)‐oxide. Laboratory studies with amended well‐water samples recirculating through a flow‐cell were used to enrich for organisms involved in biofouling communities. These experiments yielded methylotrophic organisms capable of growing with methanol and methylamine, and they were classified as Hyphomicrobium spp.