bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Evaluation of a Drive‐Point Ground‐Water Sampler for Hydraulic Conductivity Measurement
Authors: Scaturo David M. , Widdowson Mark A. 
Published: August 2005

AbstractDrive‐point ground‐water samplers, designed to enable delineation of the vertical and areal extent of a contaminant plume, have been modified to obtain an in situ measurement of hydraulic conductivity in aquifers. The multlevel drive‐point sampler (MLDPS) consists of a 30‐cm long screen pushed to a desired depth within a retractable outer sleeve and a pressure transducer to monitor the rate of fill within a sample chamber. The accuracy and variability of a MLDPS to measure hydraulic conductivity was evaluated in a 50‐m3 laboratory aquifer comprised of a uniform medium sand. Twelve measurements were performed using the MLDPS followed by duplicate slug tests performed at identical locations and depths within the aquifer. MLDPS and slug test data were analyzed using the method of Widdowson et al. (1990). The MLDPS provided an estimation of hydraulic conductivity at least one order of magnitude below slug test‐derived hydraulic conductivity and the range of hydraulic conductivity associated with a medium sand. MLDPS‐derived hydraulic conductivity values also show greater variability and range relative to the slug test‐derived values. Hydraulic conductivity ranges from 0.072 to 2.3 m/d using the MLDPS (coefficient of variation = Cv= 1.3) compared to a range of 10 to 16 m/d (Cv= 0.14) for the slug test values. Variability and magnitude of the MLDPS‐derived hydraulic conductivity is attributed to disturbance of aquifer material and experimental factors inherent to the design of the instrument.
NCF: A Finite‐Element Computer Program to Simulate Ground‐Water Flow Within the U.S. Geological Survey Modular Ground‐Water Flow Model (MODFLOW)
Authors: Jones Michael A. 
Published: August 2005

AbstractA finite‐element package has been developed for the U.S. Geological Survey Modular Ground‐Water Flow Model, MODFLOW (McDonald and Harbaugh, 1988). The package, entitled the Node Centered Flow (NCF) Package, offers alternatives for constructing and solving ground‐water flow problems. As with MODFLOW's Block Centered Flow (BCF) package, NCF uses a finite‐difference solution for vertical flow, but unlike BCF it uses a 2d Galerkin finite‐element solution for flow within a layer. The algorithm used in NCF is described in Neuman et al. (1982). This technique permits simulation within a layer of off‐diagonal elements in the (2 × 2) transmissivity or hydraulic conductivity tensor. The most advantageous feature of the NCF Package is the capability for designing a nonrectangular grid. User specification of the horizontal (x, y) coordinates of individual nodes allows model features such as meandering stream channels, faults, and wells to be more precisely represented. NCF uses the same input style as BCF and will be immediately familiar to MODFLOW users; BCF input files are also easily converted to NCF input files. NCF parameters are input by layer, row, and column, allowing NCF and BCF to work with all of the same MODFLOW packages with the exception of matrix solving packages.
Using Water‐Supply Wells to Investigate Vertical Ground‐Water Quality
Authors: Collar Robert J. , Mock Peter A. 
Published: August 2005

AbstractGround‐water contamination in the arid southwestern United States often shows up in ground‐water samples from deep water‐supply wells. For water‐supply wells with large or multiple perforated intervals, collection of depth‐specific samples in conjunction with spinner flowmeter measurements within the well while pumping may be used to estimate the vertical distribution of contamination in aquifers from which the well draws ground water. This paper presents some of our experience with spinner logging and depth‐specific sampling in water‐supply wells, as well as methodology, general assumptions, and limitations of this technique for investigating vertical ground‐water quality.
Optimal Remediation Policy Selection under General Conditions
Authors: Wang M. , Zheng C. 
Published: August 2005

AbstractA new simulation‐optimization model has been developed for the optimal design of ground‐water remediation systems under a variety of field conditions. The model couples genetic algorithm (G A), a global search technique inspired by biological evolution, with MODFLOW and MT3D, and two commonly used ground‐water flow and solute transport codes. The model allows for multiple management periods in which optimal pumping/injection rates vary with time to reflect the changes in the flow and transport conditions during the remediation process. The objective function of the model incorporates multiple cost terms including the drilling cost, the installation cost, and the costs to extract and treat the contaminated ground water. The simulation‐optimization model is first applied to a typical two‐dimensional pump‐and‐treat example with one and three management periods to demonstrate the effectiveness and robustness of the new model. The model is then applied to a large‐scale three‐dimensional field problem to determine the minimum pumping needed to contain an existing contaminant plume. The optimal solution as determined in this study is compared with a previous solution based on trial‐and‐error selection.
A Stochastic‐Analytical Framework for Safety Assessment of Waste Repositories: 2. Application
Authors: Selroos Jan‐Olof 
Published: August 2005

AbstractAn analytical framework for probabilistic safety assessment of geological repositories is applied for a high‐level nuclear waste repository. The framework is based on stochastic‐analytical solution techniques and offers a versatile tool for the analysis of various scenarios. Features, events, and processes for a hypothetical repository, geosphere, and biosphere are considered. Explicit solutions in terms of the expected value and variance of the mass flux or cumulative mass flux are derived for each case considered. The uncertainty pertaining to features and events results in increased time spans of elevated hazard levels with possible exceedance of given regulatory criteria. Mass transfer processes, such as sorption and matrix diffusion, may result in significant reductions of radioactivity fluxes and subsequent doses in the biosphere.
Ground‐Water Sampling and Time‐Series Evaluation Techniques to Determine Vertical Concentration Distributions
Authors: Cosler Douglas J. 
Published: August 2005

AbstractData analysis methodologies are developed for using time‐series measurements of effluent concentrations during continuous sampling to determine the vertical shape and location of a horizontally uniform contaminant plume and to estimate physical/ chemical aquifer parameters such as vertical anisotropy, effective porosity, and retardation factor. Temporal water‐quality variations during constant‐flow sampling are calculated in the form of concentration type curves for a wide variety of plume shapes and positions and are shown to be directly related to the geometry and growth rate of the three‐dimensional capture volume of the well. An analytical type‐curve solution is derived for discrete‐interval sampling in homogeneous and isotropic/anisotropic aquifers containing plumes with complex vertical shapes that are described by the superposition of multiple Gaussian distributions. Results from two‐dimensional, axisymmetric simulations of ground‐water flow and particle transport demonstrate the sensitivity of concentration type curves to sandpack hydraulic conductivity, screen length, well diameter, flow through the well screen during discrete‐interval sampling, aquifer anisotropy and heterogeneities, pumping rate, effective porosity, and chemical retardation. Two applications of the concentration type‐curve method for determining plume and aquifer characteristics are presented. The first illustrates the use of discrete‐interval sampling to evaluate the vertical shape and location of a hypothetical plume in a homogeneous, isotropic aquifer. In the second, extraction‐well effluent data collected during a field experiment were used to evaluate the vertical concentration distribution in a sulfate plume and estimate the vertical anisotropy ratio of the aquifer. The results demonstrate the importance of developing consistency in purge and sample volumes to minimize artificial measurement variability in monitoring programs.
Ground‐Water Exploration Based on Lineament Analysis and Reproducibility Tests
Authors: Sander Per , Minor Timothy B. , Chesley Matthew M. 
Published: August 2005

AbstractLineaments derived from remote sensing data are analyzed with respect to ground‐water exploration in the Voltaian Basin of central Ghana. The lineament data were collected using both Landsat TM and SPOT imagery, multiple interpreters, and multiple trials. Three types of reproducibility tests are analyzed: (1) azimuth‐length comparisons, disregarding location; (2) lineament coincidence using a raster‐based comparison method; and (3) feature agreement using a rule‐based approach. The reproducibility tests show that there are clear differences in length and location of individual line segments between interpreters, but that a large proportion of the inferred structural features are detected by all interpreters. Fifty percent of the features on both imagery types are detected by any two interpreters and 40 percent by all interpreters. Lineaments classed as more hydrologically significant show a reproducibility of up to 90 percent between interpreters and justify the use of classifiers in lineament mapping. The application of the feature agreement approach, including classification by hydrological significance, shows the greatest promise for targeting successful well sites.
Biofouling of Contaminated Ground‐Water Recovery Wells: Characterization of Microorganisms
Authors: Taylor Stewart W. , Lange Clifford R. , Lesold Elizabeth A. 
Published: August 2005

AbstractThe taxonomy and physiology of microorganisms isolated from contaminated ground‐water recovery wells prone to biofouling are characterized for an industrial site in Rochester, New York. Principal aquifer contaminants include acetone, cyclohexane, dichloroethane, dichloromethane, 1,4–dioxane, isopropanol, methanol, and toluene. These contaminants represent a significant fraction (up to 95%) of the total organic carbon in the ground water. Ground‐water samples from 12 recovery wells were used to isolate, quantify, and identify aerobic and anaerobic bacterial populations. Samples from selected wells were also characterized geochemically to assess redox conditions and availability of essential and trace nutrients. Dominant bacteria, listed in order of descending numbers, including sulfate‐reducers (Desulfovibrio desulfuricans), anaerobic heterotrophs (Actinomyces, Bacteriodes, Bacillus, Agrobacterium), aerobic heterotrophs (Pseudomonas, Flavobacterium, Nocardia, Citrobacter), iron‐oxidizers (Gallionellaferruginea, Crenothrixpolyspora), iron‐reducers (Shewanella), and sulfur‐oxidizers (Thiobacillusferrooxi‐dans). Fungi were also recovered in low numbers. Both aerobic and anaerobic heterotrophs were able to utilize all principal contaminants as sole carbon and energy sources except 1,4–dioxane. The prevalence of heterotrophic bacteria and their ability to use the available anthropogenic carbon suggests that aerobic and anaerobic heterotrophs contribute to the biofouling of wells at this site, in addition to the often cited fouling due to iron‐oxidizing bacteria and sulfate‐reducing bacteria.
Estimation of Basin‐Wide Recharge Rates Using Spring Flow, Precipitation, and Temperature Data
Authors: Pérez Eugenio Sanz 
Published: August 2005

AbstractA method is proposed for the estimation of ground‐water recharge rates in karstic aquifers by the analysis of hydrograph recession and multiple regression. Several methods are mentioned of estimating recharge rates by recession analysis of discharge at springs and from which recharge records can be obtained. Recharge (R) can also be estimated from precipitation (P) and air temperature (T) by the formula R = aP – bT + c. The components a, b, and c were derived from time‐series data of four aquifers in the Mediterranean zone. For the first two of these aquifers, the recharge was calculated by integrating spring discharge between two points with the equal flow. For the third aquifer, a more elaborate calculation was based on multiple aquifers with semi logarithmic depletions. A numerical model, SIMERO, was used for the fourth. Given the appropriate correlation coefficients, the procedure is advantageous because of its simplicity. Limiting relationships between P and T are deduced.
Effect of Sewage Sludge on Formation of Acidic Ground Water at a Reclaimed Coal Mine
Authors: Cravotta Charles A. 
Published: August 2005

AbstractData on rock, ground water, vadose water, and vadose gas chemistry were collected for two years after sewage sludge was applied at a reclaimed surface coal mine in Pennsylvania to determine if surface‐applied sludge is an effective barrier to oxygen influx, contributes metals and nutrients to ground water, and promotes the acidification of ground water. Acidity, sulfate, and metals concentrations were elevated in the ground water (6‐ to 21‐m depth) from spoil relative to unmined rock because of active oxidation of pyrite and dissolution of aluminosilicate, carbonate, and Mn‐Fe‐oxide minerals in the spoil. Concentrations of acidity, sulfate, metals (Fe, Mn, Al, Cd, Cu, Cr, Ni, Zn), and nitrate, and abundances of iron‐oxidizing bacteria were elevated in the ground water from sludge‐treated spoil relative to untreated spoil having a similar mineral composition; however, gaseous and dissolved oxygen concentrations did not differ between the treatments. Abundances of iron‐oxidizing bacteria in the ground water samples were positively correlated with concentrations of ammonia, nitrate, acidity, metals, and sulfate. Concentrations of metals in vadose water samples (<5‐m depth) from sludge‐treated spoil (pH 5.9) were not elevated relative to untreated spoil (pH 4.4). In contrast, concentrations of nitrate were elevated in vadose water samples from sludge‐treated spoil, frequently exceeding 10 mg/L. Downgradient decreases in nitrate to less than 3 mg/L and increases in sulfate concentrations in underlying ground water could result from oxidation of pyrite by nitrate. Thus, sewage sludge added to pyritic spoil can increase the growth of iron‐oxidizing bacteria, the oxidation of pyrite, and the acidification of ground water. Nevertheless, the overall effects on ground water chemistry from the sludge were small and probably short‐lived relative to the effects from mining only.
Impacts of Positive Skin Effects on Borehole Flowmeter Tests in a Heterogeneous Granular Aquifer
Authors: Young Steven C. 
Published: August 2005

AbstractIn heterogeneous granular aquifers, an important issue affecting the analysis of pump test data is whether or not positive skin effects exist. Positive skin effects include head losses and changes in radial flow patterns caused by a local reduction of aquifer permeability near a well. In order to investigate the impact and formation of positive skins, field tests were performed at seven pairs of closely‐spaced wells located in the vicinity of a paleochannel at Columbus Air Force Base (CAFB), Mississippi. In the paleochannel a 1–2 m thick zone of high‐K channel lag deposits lies beneath a 2–3 m thick zone of fine‐grained channel fill deposits. Each well pair consisted of a well with and without a gravel pack. At the well pairs outside of the paleochannel boundaries, borehole flowmeter tests produce similar field results. At the well pairs inside of the paleochannel boundaries, however, borehole flowmeter tests produced very different results. Examination of the test results indicate that positive skins exist at wells without gravel packs that intersect the paleochannel. During well installations, positive skins appear to be produced by the downward mixing of the fine‐grained deposits into the channel lag deposits. Notable positive skin effects include increased specific capacities, increased total drawdowns, and changes in the distribution of horizontal flow to a pumped well. Among the key implications regarding borehole flowmeter tests in heterogeneous aquifers similar to that at CAFB are: (1) wells should be installed with gravel packs; and (2) transmissivity values should be calculated using the Cooper‐Jacob straight‐line method rather than the Cooper‐Jacob equation.
Productivity Comparison of Horizontal and Vertical Ground Water Remediation Well Scenarios
Authors: Sawyer Charles S. , Lieuallen‐Dulama Karen K. 
Published: August 2005

AbstractA productivity parameter was developed to compare vertical and horizontal ground water remediation scenarios. The parameter was determined by dividing the cumulative mass of contaminant removed from an aquifer in a specified time by the total volume of ground water extracted to remove the mass. This was compared to two other methods of assessing remediation effectiveness: (1) the mass of contaminant removed at specified times; and (2) the volume of aquifer containing contaminants above a specified concentration limit as a function of time.A finite‐difference flow and a contaminant mass transport model were used to simulate a hypothetical contaminated aquifer. Productivity indices were calculated for the remediation scenarios developed in this paper. It is shown that these indices can be used as an additional tool in choosing among possible remediation scenarios.It was demonstrated that a ranking can be obtained for the various remediation scenarios, using each of our three methods for assessing remediation effectiveness. The ranking of a scenario depended on which method was used, and the selection of one particular remediation scenario over the other can be made taking the three methods into account. The relative importance of the three methods depended on the goal of the remediation. In an actual design, these methods can be used as part of the overall feasibility study that includes cost considerations.
Long‐Term Performance of an In Situ “Iron Wall” for Remediation of VOCs
Authors: O'Hannesin Stephanie F. , Gillham Robert W. 
Published: August 2005

AbstractThe use of granular iron for in situ degradation of dissolved chlorinated organic compounds is rapidly gaining acceptance as a cost‐effective technology for ground water remediation. This paper describes the first field demonstration of the technology, and is of particular importance since it provides the longest available record of performance (five years). A mixture of 22% granular iron and 78% sand was installed as a permeable “wall” across the path of a contaminant plume at Canadian Forces Base, Borden, Ontario. The major contaminants were trichloroethene (TCE, 268 mg/L) and tetrachloroethene (PCE, 58 mg/L). Approximately 90% of the TCE and 86% of the PCE were removed by reductive dechlorination within the wall, with no measurable decrease in performance over the five year duration of the test. Though about 1% of the influent TCE and PCE appeared as dichloroethene isomers as a consequence of the dechlorination of TCE and PCE, these also degraded within the iron‐sand mixture. Performance of the field installation was reasonably consistent with the results of laboratory column studies conducted to simulate the field behavior. However, if a more reactive iron material, or a higher percentage of iron had been used, complete removal of the chlorinated compounds might have been achieved. Changes in water chemistry indicated that calcium carbonate was precipitating within the reactive material; however, the trace amount of precipitate detected in core samples collected four years after installation of the wall suggest that the observed performance should persist for at least another five years. The study provides strong evidence that in situ use of granular iron could provide a long‐term, low‐maintenance cost solution for many ground water contamination problems.
Relationship Between Pumping‐Test and Slug‐Test Parameters: Scale Effect or Artifact?
Authors: Butler James J. , Healey John M. 
Published: August 2005

AbstractIn most field investigations, information about hydraulic conductivity (K) is obtained through pumping or slug tests. A considerable body of data has been amassed that indicates that the K estimate from a pumping test is, on average, considerably larger than the estimate obtained from a series of slug tests in the same formation. Although these data could be interpreted as indicating a natural underlying scale dependence in K, an alternate explanation is that the slug‐test K is artificially low as a result of incomplete well development and, to a much lesser extent, failure to account for vertical anisotropy. Incomplete well development will often result in only the most permeable zones being cleared of drilling debris, with much of the screened interval remaining undeveloped. More cursory development can leave a low‐K skin along the entire screened interval. Failure to recognize such conditions can result in a K estimate from a slug test that is much lower than the average K of the formation in the vicinity of the well. By contrast, neither a skin nor vertical anisotropy will have a significant impact on K estimates from pumping tests when semi‐log analyses and/or observation wells are used. However, a reasonable estimate of aquifer thickness is required to convert the transmissivity calculated from a pumping test into an average K for the aquifer. Prior to invoking a natural scale dependence to explain the results of different types of hydraulic tests, head data should be closely examined and serious consideration given to alternate explanations.
AIRSLUG: A Fortran Program for the Computation of Type Curves to Estimate Transmissivity and Storativity from Prematurely Terminated Air‐Pressurized Slug Tests
Authors: Greene Earl A. , Shapiro Allen M. 
Published: August 2005

AbstractThe Fortran code AIRSLUG can be used to generate the type curves needed to analyze the recovery data from prematurely terminated air‐pressurized slug tests. These type curves, when used with a graphical software package, enable the engineer or scientist to analyze field tests to estimate transmissivity and storativity. Prematurely terminating the slug test can significantly reduce the overall time needed to conduct the test, especially at low‐permeability sites, thus saving time and money.
Probabilistic Analysis of Monitoring Systems for Detecting Subsurface Contaminant Plumes
Authors: Warrick A.W. , Younga M.H. , Wierenga P.J. 
Published: August 2005

AbstractWe study the probabilities that monitoring systems will be capable of detecting subsurface contaminant plumes. The analysis is an extension of previous research which focused on detection of ore bodies and contaminant releases to the subsurface using probabilistic models; the previous research assumed that releases to the subsurface are elliptical in shape, and that detections are absolute when a monitoring point intercepts a release. New features are introduced into the analytical framework that include irregular, rather than regular, sampling arrays, as well as nonuniform probabilities of a release occurring at a particular location of the site. These features allow the user to optimize the location of sampling devices based on site knowledge, by concentrating monitoring locations where a release is believed more likely. The stratified Monte Carlo approach used in this paper is tested on a number of cases with uniform and nonuniform sampler distribution and release probabilities. The results provide statistical probabilities that one is capable of finding releases of different sizes with a system of monitoring points.