bluuebunny/crossref_metadata_2025 huggingface dataset:
The Use of Geophysical Logs for Determining Formation Water Quality
Authors: Kwader Thomas
Published: March 2006

In situ water‐quality measurements, with respect to various ion and dissolved solids concentrations, have been closely approximated using open‐hole borehole geophysical logs. Analyses have shown good correlation between water resistivity (Rw, as determined from the logs) and dominant ion concentrations sampled from a wide range of water quality in Tertiary carbonate and granular formations.

Rw can be accurately determined by cross‐plotting saturated formation resistivity (Ro), obtained from normal or lateral resistivity logs, against formation bulk porosity from neutron, density, or acoustic velocity logs. Plotting these data on Hingle Resistivity‐Porosity Cross Plot (RPCP) paper with the proper matrix cementation factor (m, commonly 1.4 for unconsolidated sands or 1.6 for noncompacted Tertiary carbonates), will yield a graphical solution for Rw based upon the relationship Rw=φm Ro. The graphical technique also provides information concerning water‐quality variations with depth, true matric resistivity, location of confining beds, and vertical changes in formation porosity.

Once Rw has been determined, other ion concentrations can be estimated based upon chemical analyses of water samples from adjacent wells tapping a similar type water mass (i.e., calcium‐bicarbonate, sodium‐chloride water, etc.). Total dissolved solids (TDS), chloride, sulfate, potassium, sodium, magnesium, and hardness (as CaCO3) concentrations have consistently shown a high correlation with Rw.
Application of Continuous Seismic Reflection Methods to Hydrologic Studies
Authors: Haeni F. P.
Published: March 2006

Oil and gas exploration and engineering studies in water‐covered areas routinely use continuous seismic profiling techniques to obtain subsurface geologic information. Such profiling also can be used effectively in hydrologic studies to define the geologic framework of aquifer systems, to locate hydrologic boundaries, and in some places, to interpret the lithologic character of aquifers and confining beds.

High‐resolution continuous seismic profiling, through the use of nonexplosive sound sources, can be used to produce continuous records that require little data processing before hydrogeologic interpretation. High‐resolution tuned transducer, minisparker, Uniboom, and small airgun systems operating from small boats in shallow water are capable of transmitting energy that can penetrate up to a hundred meters of earth materials. The resulting analog records of the reflected seismic signal closely resemble geologic sections.

Surveys on the Housatonic River in Connecticut and Massachusetts, and on the Connecticut River, in water from 1 to 10 meters deep, have defined the bedrock surface beneath 60 meters of stratified drift. Seismic‐reflection profiling also was used to determine the extent and thickness of recent lake‐bottom deposits in two Connecticut lakes.

Surveys along 90 kilometers of river channels in the Sarasota‐port Charlotte, Florida, area defined in detail the stratigrapahy and continuity of the shallow aquifers.
Inverse Problem in Ground Water: Model Development
Authors: Khan Irfan A.
Published: March 2006

A model to solve the inverse problem in ground water has been developed. The model consists of an unconstrained multivariable optimization algorithm and a ground‐water simulation model. The optimization algorithm is a modified version of Newton's second derivative method. It is a ground‐water‐specific algorithm and was found to be more efficient than other more general unconstrained optimization algorithms requiring first‐ and/or second‐order derivatives and those requiring no derivatives. The groundwater simulation model is based on a finite‐difference technique but it can be replaced easily by a finite‐element model. The results of an application of this model to a real aquifer are discussed in a companion paper titled “Inverse Problem in Ground Water: Model Application.”
Aquifer Test Analysis in Fractured Rocks with Linear Flow Pattern
Authors: Şen Zekâi
Published: March 2006

A major vertical fracture in a permeable rock mass may act as an extended well and can provide water through pumping cither directly from the fracture itself or if the fracture width is not enough to install pumps, from an abstraction well drilled in the fracture. In such a case the ground‐water flow is not radial but linear toward the fracture and the flow lines are perpendicular to the fracture axis.

A mathematical description of ground‐water flow toward vertical fractures is presented. The cases considered are: (1) an infinitesimally small fracture width corresponding to a planar source or sink, and (2) a finite width fracture in which the effects of ground‐water storage in the fracture are taken into account. The necessary type curves are presented for the main and observation wells. It is observed that the type curve in the linear flow pattern case is extremely different from the radial flow solution especially for long times. In addition, recovery type curves are also given. The application of the method is presented for some available data in the literature.
Depositional Environments of Buried‐Valley Aquifers in North Dakota
Authors: Kehew Alan E. , Boettger William M.
Published: March 2006

Many buried‐valley aquifers in North Dakota occupy narrow, trench‐like valleys incised through glacial sediment into bedrock. By analogy with nonburied valleys of similar size, shape, and geomorphic characteristics, the buried valleys are interpreted to be glacial‐lake spillways formed during glaciations prior to the last advance and retreat. Water‐bearing sediments that fill these buried valleys, although traditionally interpreted as glacial outwash, are commonly composed of nonglacial fluvial sediments deposited between glaciations. Interglacial fluvial systems that occupied the glacial‐lake spillways include major trunk streams draining the Rocky Mountains as well as sluggish, underfit streams with small drainage areas. Deposits associated with the latter type consist of fine‐grained fluvial and lacustrine sediments in the valley centers grading into coarser sediments of alluvial‐fan origin along the valley sides. Thus, in some buried valleys, the most productive aquifers may lie along the valley sides rather than in the valley centers.
Analysis of Geophysical Logs of Water Wells with a Microcomputer
Authors: Keys W. Scott
Published: March 2006

A microcomputer can be a significant aid in the analysis of geophysical logs of wells used in investigations of ground‐water systems. Geophysical logs, test data, and laboratory analyses present a large volume of data that can most efficiently be manipulated with a computer. Techniques for the analysis of logs using mainframe computers and minicomputers have been developed and used in the petroleum industry for a number of years. These techniques have not been used widely in ground‐water investigations because available programs were oil‐oriented, and both programs and computers were too expensive to be cost‐effective for most ground‐water investigations. These programs also tended to be too complex for the part‐time user to learn. The advent of the relatively inexpensive microcomputer and a number of inexpensive, easy‐to‐use generic programs made computer‐aided log analysis available to most hydrologists.

A microcomputer can be used to transfer well logs by telephone and to correct the data received. The logs then can be collated, compared, and analyzed statistically. Two logs can be cross‐plotted in order to identify lithology or to provide porosity corrected for matrix effects. Logs can be plotted against laboratory analyses of cores or samples for purposes of log calibration.

As an example of this technique, logs and core data from a test well completed in the Madison Limestone were analyzed using a microcomputer and generic programs. Computer‐aided log analysis facilitated the identification of the lithologic units penetrated and the intervals of secondary porosity that produced water. Plots of logs and other data included in the paper were reproduced directly from the graphics subprogram that is part of the spreadsheet program.
Problems Interpreting Samples Taken with Large‐Volume, Falling‐Suction Soil‐Water Samplers
Authors: Anderson Linda Davis
Published: March 2006

Chemical data resulting from sampling heterogeneous, variably saturated soils with large‐volume, falling‐suction samplers must be cautiously interpreted. Nitrate and chromium data from a tannery waste‐disposal project illustrate the difficulties in distinguishing chemical and physical effects of sampling procedures from natural variability. Dramatically different interpretations of soil‐water chemistry can result if precipitation in the porous cup or influence of the sampler on the soil‐fluid flow is ignored. Additional laboratory studies are needed to assess adsorption on and screening of trace metals by the porous cup of the sampler. In the field, redox conditions as well as pH should be carefully monitored, soil structure noted, and pore‐size distribution quantified. Use of numerical simulations could aid in planning monitoring strategies and interpreting results.
Design and Cost Analysis of Rapid Aquifer Restoration Systems Using Flow Simulation and Quadratic Programming
Authors: Lefkoff L. Jeff , Gorelick Steven M.
Published: March 2006

Detailed two‐dimensional flow simulation of a complex ground‐water system is combined with quadratic and linear programming to evaluate design alternatives for rapid aquifer restoration. The design model ensures that a contaminant plume is removed and treated within four years at the least possible cost. Rapid restoration is accomplished by maintaining specified velocities around the plume perimeter toward a group of pumping wells located near the plume center. Ground‐water velocities are adjusted to include the effects of solute retardation due to sorption. As a simplification, the model does not account for hydrodynamic dispersion. Results show how treatment and pumping costs depend dynamically on the type of treatment process, the capacity of pumping and injection wells, and the number of wells. The design for an inexpensive treatment process minimizes pumping costs, while an expensive process results in the minimization of treatment costs. Substantial reductions in pumping costs occur with increases in injection capacity or in the number of wells. Treatment costs are reduced by expansions in pumping capacity or injection capacity. The analysis identifies maximum pumping and injection capacities.

Maintenance of the high ground‐water velocities required by rapid restoration strategies is difficult and expensive. In order to meet the four‐year target date, about ten times the initial volume of contaminated water must be pumped and treated. Rapid restoration forces large pumping volumes and high costs.
INVERSE SOLUTIONS OF HANTUSH'S EQUATIONS FOR AXISYMMETRIC MOUNDING
Authors: Allen Dan H.
Published: March 2006

Abstract. Hantush (1967) provided time‐dependent equations for describing ground‐water mounds resulting from axisymmetric recharge. Because these equations contain the well function, they cannot be solved explicitly for the several variables employed in terms of the known mound height. Newton's method provides a means to achieve solutions for specific yield, hydraulic conductivity, time, or radius. An additional routine is provided which searches for the second solution in the case in which the inverse solution for hydraulic conductivity is doublevalued. The iterations can be performed on an HP‐41C handheld calculator with three memory modules. The code is provided and will run with or without the printer attached.
BIOINDICATORS OF GROUND WATER IN VARAHAMIHIRA'S BRIHAT SAMHITA*
Authors: Prasad E.A.V.
Published: March 2006

Every year enormous amounts of wasteful expenditure are incurred due to faulty location of well sites in the hardrock terrains by either the most commonly adopted mystic methods of “water‐divining” or the geophysical methods.

The strikingly visible and easily recognizable bio indicators of ground water, described in Varahamihira's Brihat Samhita, are ideally suited for rapid economic development of the drought‐prone areas.

The prevailing wrong notions, regarding the efficacy of these bioindicators, are due to lack of sound theoretical and practical knowledge of applied ecology involved in “tropical ground‐water hydrology.”
Modeling of TCE Contamination and Recovery in a Shallow Sand Aquifer
Authors: Freeberg K. M. , Bedient P. B. , Connor J. A.
Published: March 2006

The U.S. Geological Survey (USGS) Solute Transport Model is a widely used, well‐documented computer code which simulates contaminant transport in ground water using a finite‐difference grid and the method of characteristics. In this study, the model was applied to an industrial site where trichloroethylene (TCE) and other industrial solvents had contaminated a shallow sand aquifer. At the study site, the geology was well‐characterized and the migration of the contaminant plume was monitored by a network of 15 wells.

Although the rate of release of the industrial solvents to the aquifer was unknown, the model gave a good prediction of the movement of the plume when the release of contaminants was modeled as a point source injection. The model was also successful in simulating the behavior of the plume under the influence of a recovery system. During simulation of a four‐well withdrawal system, model predictions of TCE concentrations and hydraulic head in the aquifer matched actual data collected at two points in time after start‐up of the recovery system. The model predicted that the same configuration of withdrawal wells would reduce concentrations of TCE in the ground water from approximately 1000 μg/1 to 6 μg/1 after two years of pumping.
Distribution Coefficient of Trichloroethylene in Soil‐Water Systems
Authors: Mehran Mohsen , Olsen Roger L. , Rector Bryan M.
Published: March 2006

The distribution coefficient of trichloroethylene (TCE) was obtained from field and theoretical methods. The field method was based on measuring TCE concentrations in the soil samples and in the adjacent ground water. The theoretical method was based on using the organic carbon content of the soil and the octanol/water partition coefficient for TCE. The average distribution coefficient for 19 field samples and four methods of calculation was 0.18 ml/g which is in agreement with literature data and octanol/water partition coefficients results. For soils containing greater than 0.1 percent organic carbon, the theoretical methods of calculating the distribution coefficient appear to be valid. For soils low in organic carbon content, laboratory determinations of the distribution coefficient can provide reasonable estimates for predicting actual migration rates. Field determinations of distribution coefficients are, however, preferred because they integrate the effect of various factors on partitioning of TCE.
An Alternate Procedure for Analyzing Aquifer Tests Using the Theis Nonequilibrium Solution
Authors: Franke O. L.
Published: March 2006

A classical dimensional analysis of the Theis non‐equilibrium radial flow problem in a confined aquifer indicates that three dimensionless parameters are required for its representation. A new set of type curves based on three dimensionless parameters sT/Q, Qt/sr2, and S, is developed that can be employed to analyze aquifer test data by a curve‐matching procedure similar to the procedure used at present with two dimensionless variables.

The possible advantages of the proposed new type curves are as follows: (1) The concave shape of the type curves along the x‐axis and particularly their point of vertical tangency permits curve matching with a minimum of ambiguity. Furthermore, the possibility of gross errors in the curve‐matching procedure is reduced because both type curves and the plot of field data use the same dimensionless parameter on the horizontal axis (x‐axis) so that the process of curve matching permits movement of the field curve only parallel to the vertical axis (y‐axis). (2) The shape of the proposed type curves provides a focus for aquifer‐test design‐that is, given very approximate estimates for the field parameters (T and S), the investigator can target a specific range for the field‐measured parameters for which curve matching will give best possible results.
PREDICTIVE APPLICATION OF AN ORNL GEOHYDROLOGY MODEL
Authors: Wong Kau‐Fui Vincent , Yeh G. T. , Davis E.C.
Published: March 2006

The purpose of this work is to demonstrate the predictive capability of the Oak Ridge National Laboratory finite‐element computer model of water flow through aquifers, FEWA. The computer code for FEWA was written by G. T. Yeh and D. D. Huff. The area investigated was the Hialeah‐Preston wells in Miami, Florida over the Biscayne aquifer. The field data of May 3, 1977, for the area were used for calibration of the model. The model was then integrated over time until October 4, 1977, using the data on rainfall, infiltration, and pumpage of wells during that period. The predicted potentiometric head for the area compared well with the field data. It may be concluded that substantial confidence in the predictive capability of the model has been established for the site in Florida.
Statistical Prediction Intervals for the Evaluation of Ground‐Water Quality
Authors: Gibbons Robert D.
Published: March 2006

Factors for a normal distribution are given such that one may be 99% confident that the two‐sided prediction interval x̄+rsor the one‐sided prediction interval x̄+rswill contain all of thekfuture values, where x̄ andsare the sample mean and standard deviation obtained fromnprevious values. In the context of ground‐water monitoring, the future samples may represent new monitoring values at each ofkdowngradient wells, and thenprevious values might be the historical monitoring results for one or more upgradient wells. The Tables provided in this paper allow the computation of one‐sided and two‐sided99%prediction intervals for previous sample sizes ofn= 4 to 100 and future samples ofk= 1 to 100. Modification of these intervals for log‐normally distributed data is also presented.
Interface Upconing Due to a Horizontal Well in Unconfined Aquifer
Authors: Gupta A. Das , Gaikwad Vilas P.
Published: March 2006

A simplified mathematical model is developed to predict the equilibrium location of upconed interface due to a horizontal well in an unconfined coastal aquifer of finite thickness. The model is based on Dupuit assumption and Ghyben‐Herzberg approximation with modified boundary conditions along the shoreline deduced from available analytical solutions. For a specified natural flow condition, the amount of fresh‐water discharge to the sea as well as interface profile and length of intrusion can be determined. With the specification of the permissible extent of upconing from the natural interface location at any section, the model provides an estimate of the amount of water that can be withdrawn by a horizontal well, the upconed interface profile, and the additional length of intrusion. The computed interface profile for the natural flow condition is found to be in good agreement with the results of available analytical solutions. Comparison with the laboratory tests for the upconing case indicates that the simplified model provides a reasonable approximation of the interface profile for assessment of water withdrawal from a coastal aquifer at the initial stage of planning.
On Methods of Determining Specific Yield
Authors: Neuman Shlomo P.
Published: March 2006

A comparative discussion of several methods for the determination of specific yield is presented. The discussion relies on a pumping test conducted recently by Nwankwor and coworkers from the University of Waterloo in an unconfined aquifer at Borden, Ontario, Canada. We show that a water‐balance method promulgated by these workers and used earlier by others, including Wenzel in 1942 and 1946, is invalid because it overlooks a major component of the water budget. This method suggests erroneously that specific yield increases with time during a pumping test. The method can therefore lead to arbitrarily large specific yield values which may lack physical significance. By relying on this water‐balance method and on laboratory drainage experiments, Nwankwor and coworkers conclude incorrectly that type‐curve methods, such as those proposed by Prickett in 1965 and Neuman in 1975, give unreasonably low specific yield values. We show instead that these specific yield values are consistent with water‐balance considerations when all the components of the water budget are properly taken into account. We further point out that whereas the larger specific yields usually obtained from laboratory drainage experiments may be well suited for the evaluation of ground‐water reserves that can potentially be recovered from an unconfined aquifer over long periods of time, they are not directly relevant to the problem of relating ground‐water level variations to pumpage which is characterized by a shorter time scale. This is especially true when specific yield is taken to be the difference between water content at saturation and residual water content at high suctions as done by Nwankwor and coworkers. The rate at which ground‐water levels drop or fluctuate in response to pumpage is controlled by the smaller specific yield that one obtains from time‐drawdown analyses.
Theis' Solution by Nonlinear Least‐Squares and Finite‐Difference Newton's Method
Authors: Yeh Hund‐Der
Published: March 2006

A method using the nonlinear least‐squares and finite‐difference Newton's method to determine the aquifer parameters via a pumping test in a homogeneous and isotropic confined aquifer system is proposed. The nonlinear least‐squares is used to find the values of transmissivity and storage coefficient such that the sum of the squares of differences between the predicted drawdowns and observed drawdowns is minimized. The finite‐difference Newton's method is used to solve the system of nonlinear least‐squares equations for transmissivity and storage coefficient.

Comparisons of the results between the proposed method and graphical methods including the Theis, Cooper‐Jacob, and Chow methods are discussed in detail, showing data of a 6‐hour pumping test.

The proposed method has the advantages of high accuracy and quick convergence for most initial guesses.
Relation of Lake Bed Leakance to Geoelectrical Properties
Authors: Cherkauer Douglas S. , Taylor Robert W. , Bradbury Kenneth R.
Published: March 2006

An inverse relationship exists between the longitudinal electrical conductance (S) and the leakance (I.) of sediments between a bedrock aquifer and a surface‐water body. The empirical relationship for western Lake Michigan, first reported by Bradbury and Taylor (1984), has been refined after additional measurements. Leakance can now be predicted from longitudinal conductance with 95% confidence to within ±½ order of magnitude. Evidence is also presented that sediment samples collected by coring give erroneously low values for hydraulic conductivity and leakance.
Optimal Siting of Artificial Recharge: An Analysis of Objective Functions
Authors: Li Cijun , Bahr Jean M. , Reichard Eric G. , Butler James J. , Remson Irwin
Published: March 2006

A simulation model was used in conjunction with linear and nonlinear programming to examine the effects of various management choices on the optimal allocation of imported water for artificial ground‐water recharge in the San Juan Valley of Central California. The simple linear objective of minimizing the sum of absolute values of drawdowns was of little value due to its dependence on hydro‐geologic properties. The choice between more complex linear and nonlinear objectives is shown to depend on the economic impacts of drawdowns one wishes to emphasize. Suitability of different drawdown reference levels was found to be a function of the specific form of the objective. Sensitivity analysis showed that the imported water could be recharged anywhere in the central portions of the cone of depression with minimal effect on the value of the objective function. Parametric variation of the total recharge rate illustrated the dependence of the various objective functions on the distribution of drawdown, discharge rates, and hydrogeologic properties. A preliminary analysis allowed the importance of conveyance cost to be demonstrated.

This study has demonstrated that decisions regarding objective functions and their reference levels can be made only after careful consideration of basin characteristics and management goals.
Statistical Characteristics of Ground‐Water Quality Variables
Authors: Montgomery Robert H. , Loftis Jim C. , Harris Jane
Published: March 2006

The emerging problem of contamination of ground‐water resources has created a need for information which can be supplied by properly designed ground‐water quality monitoring programs. The effective design of monitoring programs and the subsequent utilization of data obtained depends upon an understanding of the general statistical characteristics of ground‐water quality variables. In order to provide some background information on these characteristics, a synthesis of current literature and a statistical analysis of existing ground‐water quality data were conducted. Specifically, the purpose of the study was to determine whether ground‐water quality variables: (1) are normally distributed, (2) exhibit seasonal patterns, and (3) are correlated in time. The results of the investigation suggest that many ground‐water quality variables: are not normally distributed, but have skewed right distributions; can exhibit seasonal fluctuations of various shapes and magnitudes, especially in shallow or highly permeable aquifers; and can exhibit significant serial correlation when samples are collected quarterly.
A Technique to Evaluate Aquifer Constants by Pumping Test Data of a Cavity Well
Authors: Sharma H. C. , Chauhan H. S. , Singh K. K.
Published: March 2006

Most of the solutions proposed by various workers to solve a nonequilibrium equation for the flow towards a nonpenetrating cavity well are based on the curve‐matching technique or an approximate straight‐line method. In this paper, another technique to solve an inverse problem has been proposed. This approach is simpler and more realistic since the element of human judgement is practically eliminated.
Parametric Modeling of the Upper Rio Cobre Basin
Authors: Walters Michael O.
Published: March 2006

Similarity of ground‐water hydrographs in karst aquifers with surface runoff hydrographs indicates that some models used in unit hydrograph analysis could adequately model the ground‐water system. Two such models are used to model ground‐water levels in a karst aquifer. The aquifer was treated as a linear time‐invariant system with a response function representing the rise in ground‐water levels in response to rainfall. Two discrete parametric models, the Nash and Muskingum, were tested as response functions. Parameters for both models were identified from one year of data by applying the theory of moments to sets of input and output data. The models were verified using rainfall and water‐level data for a second year. The Muskingum method did not adequately model the system. Results of the Nash model were good.
Statistical Models for the Analysis of Volatile Organic Compounds in Waste Disposal Sites
Authors: Gibbons Robert D.
Published: March 2006

The occurrence of low‐level hits of volatile organic priority pollutant compounds is statistically modeled as a Poisson process. Methods are developed to estimate the mean of the Poisson distribution for a random sample of volatile organic measurements as well as 99% prediction limits and 99% tolerance limits. The prediction limits provide an interval estimate that will include values obtained for the next k future measurements based on a sample of n previous measurements with 99% confidence. The tolerance limits provide an interval estimate for the n previous measurements that will contain 99% of the population of background measurements with 95% confidence. These methods are illustrated with measurements obtained from 61 field blanks, 56 trip blanks, and 162 samples obtained from 29 upgradient wells. Both prediction and tolerance limits yielded extremely similar results in all three examples.
Perched Water Identification with Nuclear Logs
Authors: Poetera Eileen P.
Published: March 2006

The presence, nature, and extent of perched zones are frequently important during investigation of potential waste disposal sites and contaminated sites. Often such zones are overlooked and cased off during drilling and completion of monitor wells. Typically large differences in water levels over short distances are the first indicator that perched conditions may exist at a site. Installation of piezometers can provide conclusive evidence of the presence, nature, and extent of perched zones, but such activity is costly and time‐consuming. Combined interpretation of the gamma‐gamma (GG) and neutron‐epithermal neutron (NN) geophysical well logs can assist in evaluating perched conditions and guide placement of additional piezometers in an effective and efficient manner. Subsequently, logs from the shallow portion of existing wells that are completed in deeper zones can be used to interpolate and extrapolate knowledge of perched conditions.

Perched zones are often indicated on logs by an inverse response of the GG and NN logs at a higher elevation than a direct response of the same logs. Because interpretation of geophysical logs is nonunique, it cannot provide conclusive evidence as to whether a particular zone is saturated or unsaturated. Limitations on conditions that will result in a false response can be determined. When logs are used in conjunction with hydrologic and geologic information, they are a valuable tool for investigating zones of perched ground water.
Mobility and Effects in Liner Clay of Fluorobenzene Tracer and Leachate
Authors: Llgenfritz E. M. , Blanchard Fred A. , Masselink R. L. , Panigrahi Bijay K.
Published: March 2006

To help demonstrate the ability to operate a hazardous waste landfill with no escape of leachate, permeameter tests of the effects on clay liner material of leachates containing ppm levels of organics such as chloroform, methylene chloride, toluene, and chlorobenzene were run. To get an unambiguous future determination of a detection of failure by leachate leakage into the landfill underliner monitoring system, a single compound or agent was sought which could be used as a tracer material. Fluorobenzene was chosen because of its physicochemical properties and its uniqueness in the normal industrial waste stream.

The leachate permeameter testing confirmed literature data indicating that dilute concentrations of organic solvents in landfill leachate do not impair the barrier properties of clay even after several pore volumes of throughput.

The appropriateness of the choice of fluorobenzene was confirmed by examining its comparative migration and by looking for its effects on the clay. Modeling of permeameter solute effluent concentration data with the transport equation of Ogata (1970) has shown a reasonable fit. Retardations of the major components of the particular landfill leachate evaluated were as expected, with chlorobenzene > toluene > fluorobenzene = chloroform > methylene chloride. Fluorobenzene is a good representative of the least retarded chemicals. There were no adverse effects on the clay's barrier properties from the ppm level of fluorobenzene added to the leachate.
Determination of Aquifer Parameters at a Ground‐Water Recharge Site
Authors: Urban J. B. , Gbureka W. J.
Published: March 2006

Porous asphalt pavement is a storm‐water management technique which reduces runoff and enhances ground‐water recharge. Planned applications of this, or other ground‐water recharge techniques, require that ground‐water response to induced recharge be quantified. Here, we emphasize determination of the aquifer parameters hydraulic conductivity (K) and specific yield (Sy) at a porous asphalt ground‐water recharge facility installed near Willow Grove, Pennsylvania.

We compare values of these aquifer properties derived from conventional laboratory and field techniques to those derived using recharge event data collected at the site. By the comparisons, we illustrate the techniques of aquifer property determination apropos to the design of ground‐water recharge installations. Because of the fractured nature of the aquifer, the K‐values determined from pumping test and slug test analyses are about an order of magnitude greater than those of rock core samples, while the field‐based specific yield values are about an order of magnitude less than effective porosities of the rock cores. Ratios of K/Sy derived from a chemical tracer test agree with the pumping test values. Finally, the K and Sy necessary to simulate facility response to recharge using a numerical model of ground‐water flow correspond to those derived from field‐oriented techniques rather than those of the rock cores.

The results show that the design parameters K and Sy should be obtained from field‐based techniques, such as the nonsteady pump test, which match the time and space scale in which the facility is expected to affect the aquifer.
Macromolecular Transport of Hydrophobic Contaminants in Aqueous Environments.
Authors: Enfield Carl G. , Bengtssona Göran
Published: March 2006

The mobility of a model macromolecule, blue dextran, was compared under laboratory conditions to the mobility of tritiated water through a sandy soil. The blue dextran eluted from the soil prior to the tritiated water. The phenomenon was compared to exclusion chromatography where molecules are separated by size with the largest eluting first and each molecule flowing through a different portion of the total porosity. The porosity occupied by the macromolecule was 0.87 times the porosity occupied by water. When the soil was amended with a mixture of kaolinite and bentonite clay in a 1:1 ratio to weight fractions of 2% and 6% total clay, the porosity occupied by the macromolecule was decreased to 0.81 and 0.66 times the porosity occupied by water, respectively. The implications to hydrophobic chemical transport based on the presence and mobility of a macromolecule were evaluated from a theoretical basis. Macromolecules should increase the relative mobility of slightly mobile compounds more than they increase the relative mobility of highly mobile compounds. Very hydrophobic compounds should show greater mobility under natural conditions than predicted, ignoring the presence of dissolved organic carbon.
Assessment of Ground‐Water Contamination Near Lantana Landfill, Southeast Floridaa
Authors: Russell Gary M. , Higer Aaron L.
Published: March 2006

The Lantana landfill located in Palm Beach County rises 40 to 50 feet above normal ground level and consists of about 250 acres of compacted garbage and trash, some below the water table. Surface‐resistivity measurements and water‐quality analyses indicate a contaminant plume along the eastern perimeter of the landfill that has migrated about 300 feet eastward toward an adjacent lake. Concentrations of chloride, ammonia, and nitrate were elevated within the plume. The surficial aquifer consists primarily of sand from 0 to about 68 feet, and sand interbedded with sandstone and limestone from 68 to 220 feet. A slight hydraulic gradient exists, indicating ground‐water movement from the landfill toward a lake to the east. Analyses of geoelectric, lithologic, and water‐quality data indicate that surface geophysical techniques were successful in determining the areal and vertical extent of leachate migration at this location.
Tracing Ground‐Water Movement in Abandoned Coal Mined Aquifers Using Fluorescent Dyes
Authors: Aldousa P. J. , Smartb P. L.
Published: March 2006

In shallow, essentially free‐draining abandoned coal mine workings, quantitative ground‐water tracing using the orange fluorescent dye Sulpho Rhodamine B (CI 45100) provides a powerful hydrogeological tool for determining ground‐water flow regimes. However, this is not the case in deep, confined, abandoned coal mine workings where various dyes exhibit a nonconservative behavior due to adsorption onto ferric hydroxide deposits. This is a more significant problem than that of the effects of pH or acidity on fluorescence. Laboratory tests indicate that dyes with sulphonic functional groups should be selected in such situations and that dye concentrations need to be maintained at the highest level commensurate with aesthetic and toxicological conditions.
Electromagnetic Mapping of Fresh‐Water Lenses on Small Oceanic Islands
Authors: Stewart Mark
Published: March 2006

Many small oceanic islands have fresh‐water lenses that can be used for domestic water supplies or dry season augmentation for rainfall catchment systems. However, these small lenses are often irregular in extent and thickness. Some islands have several small, isolated lenses. By making a few reasonable assumptions, the electromagnetic (EM) profiling method can be used to estimate lens thickness. If it can be assumed that the water table is close to sea level, and that the unsaturated and fresh‐water saturated geologic units have low bulk conductivities, the interface depth can be obtained from a three‐layer solution. The first layer is the unsaturated zone. Its thickness is assumed to be the land surface elevation above sea level. The third layer is the salt‐water saturated zone; it is assumed to be infinitely thick. The layer conductivities are either estimated or obtained from DC resistivity soundings. In resistive environments only the third‐layer conductivity has a significant effect on the calculated interface depth. The only remaining unknown is the second‐layer thickness, which represents the fresh‐water saturated zone. The second‐layer thickness is sensitive to the value used for the third‐layer conductivity. Calibration of the EM‐derived interface depth with other geophysical or water‐quality data is recommended, unless relative lens thicknesses are sufficient to meet the survey objectives. Application of this method to field studies of a sandy barrier island and a carbonate key, both in Florida, has provided useful data which correlate well with other geophysical and water‐quality data.
MRCON: COMPUTER PROGRAM FOR ESTIMATING SOIL MOISTURE RETENTION AND UNSATURATED HYDRAULIC CONDUCTIVITY
Authors: Block L. O. , Hendry M. J. , Chan G. W.
Published: March 2006

Abstract. MRCON is an interactive computer program designed to approximate soil moisture retention (Θ‐Ψ) and/or unsaturated hydraulic conductivity (K‐Θ) for soils. MRCON, which is written in BASIC, uses empirical methods obtained from the literature to calculate K‐Θ and a modified method to calculate Θ‐Ψ. Input data for the program consist of a saturated moisture content and a minimum of three values of Θ‐Ψ. A measured value of saturated hydraulic conductivity can be used as input to better approximate the K‐Θ curves to field conditions.
WATEQB – BASICA REVISION OF WATEQF FOR IBM PERSONAL COMPUTERS
Authors: Arikan Alparslan
Published: March 2006

Abstract. WATEQB is a BASICA revision for IBM PC of WATEQF, a geochemical model for chemical equilibrium and saturation of natural waters. This model computes the speciation of inorganic ions and complex species in solution for a given water analysis.

WATEQB is identical to the FORTRAN IV version from the standpoint of chemical process; however, the structure of the program differs from the original version. The structure of the program is not complex and allows the user to try some new modifications, if necessary.

Due to the limited memory of personal computers and in contrast to the large volume of the original version of the program, the author has created four data files, one of which is of random access type. Reading the thermochemical data is possible through these four data files.

This paper demonstrates how to set up the input data to execute WATEQB and describes the program rather than the model. The users of WATEQB will increase as personal computers become more common.
The Victoria Province Drought Relief Project, I. Geophysical Siting of Boreholes
Authors: White C. C. , Houston J.F.T. , Barker R. D.
Published: March 2006

As a result of the recent drought in central Africa, an accelerated well drilling program was commissioned in Victoria Province, Zimbabwe, to help alleviate the shortage of water.

An analysis of the data collected during the siting of these boreholes showed that geophysical techniques can be used reliably to determine regolith thickness and provide an indication of regolith lithology. Valleys and the zone of deep weathering around bornhardts were found to have the greatest potential for water‐supply boreholes. The relationship between regolith resistivity and specific capacity is masked by the clay mineralogy of the regolith which must be taken into account when siting boreholes. Despite this effect, optimum values of regolith resistivity for production boreholes in Victoria Province were established which may be of value in similar Basement terrain elsewhere.
Influence of Outlying Observations on Selected Estimates of Parameters of Distributions
Authors: Rajagopal R.
Published: March 2006

Most measures of ground‐water quality are positively skewed with a few observations occurring with significantly large values. Using a set of mathematical expressions and readily available software, the effect of deleting one or more large‐valued observation(s) on selected estimates of parameters of underlying distributions are evaluated. The effect of deleting a single large‐valued observation on the mean is linear, and on the standard deviation it is nonlinear (approximately quadratic). In the case of multiple deletions, the effect of sum of the large‐valued observations on the mean is linear and on the standard deviation it is nonlinear. The effect on the standard deviation is a function of the sum of squares of deleted observations. The standard deviation is much more sensitive to the magnitude of deleted observations than the mean. Analysis of a large data set consisting of 17 primary and secondary drinking‐water constituents showed that (with a few exceptions) the effect of deleting large‐valued observations on the standard deviation is considerably higher than that on the mean, the 95th and the 99th percentiles. Seldom are percentiles below the 75th affected by the deletion of large‐valued observations. Analyses of upper quantiles and the maximum can be of much value in the study of maximum contaminant level (MCL) violations and population exposures to toxic chemicals above and beyond certain threshold levels. Since large‐valued observations affect the estimates of different parameters differently, it is extremely important to choose the relevant parameter first and then study the change in its estimate based on the deletion of large‐valued observations.

Note: For the sake of brevity, the terms mean, standard deviation, and quantiles (or percentiles) are often used in this paper, instead of the more precise estimated mean, estimated standard deviation, and estimated quantiles (or percentiles).
AN EXERCISE IN GROUND‐WATER MODEL CALIBRATION AND PREDICTION
Authors: Freyberg David L.
Published: March 2006

Abstract. For a classroom exercise, nine groups of graduate students calibrated a numerical ground‐water flow model to a set of perfectly observed hydraulic head data for a hypothetical phreatic aquifer. All groups used exactly the same numerical model and identical sets of observed data. After calibration, the students predicted the hydraulic head distribution in the aquifer resulting from a modification in one boundary condition. A quantitative analysis of the results of this calibration‐prediction exercise vividly demonstrates some of the difficulties in parameter identification for ground‐water flow models. Group predictions differed significantly. Successful prediction was strongly correlated with successful estimation of conductivity values, and was essentially unrelated to successful estimation of aquifer bottom elevations or with the number of trial‐and‐error simulations required for calibration. Most importantly, success in prediction was unrelated to success in matching observed heads under premodification conditions. In this sense, good calibration did not lead to good prediction.
The Recharge‐Discharge Function of Wetlands Near Juneau, Alaska: Part I. Hydrogeological Investigations
Authors: Siegela D.I.
Published: March 2006

Water levels in piezometers and the hydraulic conductivity of organic and mineral soils were measured during spring and summer 1986 to evaluate the recharge‐discharge function of wetlands in the vicinity of the Mendenhall Valley near Juneau, Alaska. Computer modeling experiments were also done to evaluate the function of a large patterned fen.

The blanket bogs are probably recharge zones, whereas forested wetlands are discharge zones. Approximately the upper third of the patterned fen is a ground‐water recharge zone, whereas its northern margin receives ground‐water discharge from flow systems recharged on moraines.

The amounts of wetland recharge and discharge are very small. Recharge from wetlands to viable aquifers is probably less than 1% of the total annual recharge to the aquifer system. The amount of ground‐water discharge to streams from wetlands is too small to measure.
An Automated Numerical Evaluation of Slug Test Data
Authors: Kemblowski M. W. , Klein C. L.
Published: March 2006

Development of a numerical algorithm to analyze slug test data is described. This type of test is very popular for aquifer testing, primarily because of its simplicity. Many such tests are performed to estimate the hydraulic conductivity values of ground‐water‐bearing formations. Those values in turn are used to calculate pore‐water velocities. The algorithm was coded and successfully tested for a hypothetical data set. It has also been applied at a number of field locations. One such application is presented.
Analysis of Sustained Ground‐Water Withdrawals by the Combined
Authors: Chau T. S.
Published: March 2006

The long‐term ground‐water withdrawal potential of a regional confined aquifer in the Cold Lake area is analyzed with a combined simulation‐optimization model. The Galerkin finite‐element method is used in the simulation model to obtain numerical approximations to the hydraulics of ground‐water flow. This method produces a set of linear algebraic equations containing ground‐water variables which are embedded as equality constraints within the constraint set of a linear programming optimization model. Other constraints in this set include restrictions on drawdown, water demand, and hydraulic gradient. The objective of the optimization model is to maximize total withdrawal from potential ground‐water development sites. The objectives of this modeling study are to assist planners and water managers in formulating a long‐term water management plan on water allocation to industrial users and to establish a long‐term withdrawal limit for the aquifer. Analyses include the determination of users’ground‐water withdrawals to maximize total ground‐water use from the aquifer, the analysis of ground‐water supply tradeoff among water users, and the identification of pumping locations and their pumpages that best intercept ground‐water flow in the aquifer system. Modeling results show that there is an interdependency of optimal ground‐water withdrawals among water users. The maximum total withdrawal obtained from potential ground‐water development sites is 90 percent of total inflow into the aquifer. This withdrawal limit for the aquifer can be increased with a new set of sites chosen for ground‐water development.