bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of TCE Contamination and Recovery in a Shallow Sand Aquifer
Authors: Freeberg K. M. , Bedient P. B. , Connor J. A. 
Published: March 2006

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTThe 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

ABSTRACTFactors 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

ABSTRACTA 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

ABSTRACTA 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

ABSTRACTA 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

ABSTRACTAn 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

ABSTRACTA 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

ABSTRACTThe 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

ABSTRACTMost 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

ABSTRACTSimilarity 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTTo 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

ABSTRACTPorous 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

ABSTRACTThe 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

ABSTRACTThe 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.