bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Annual Regime of Shallow Ground‐Water Levels in Poland
Authors: Chelmicki Wojciech 
Published: August 2005

AbstractThe annual regime of shallow ground‐water levels across Poland is analyzed according to the dominance of continental and oceanic air masses. Mean monthly ground‐water levels are transformed into relative values and, in order to show the spatial patterns of the annual regime throughout Poland, the contours of such values are derived for each month of the year.The shallow ground‐water regime in Poland can be correlated with the degree of the climatic continentality. The main difference between the mildly oceanic northwestern part of Poland and the continental eastern part is the pattern of the winter regime which responds differentially to snowmelt. In the northwestern part of Poland, ground‐water levels during late fall and winter are higher than those in the continental eastern part of the country. From April to September, there is no distinct difference between the ground‐water levels in those two parts of Poland.
Urban Ground‐Water Pollution: A Case Study from Coventry, United Kingdom
Authors: Nazari M. M. , Burston M. W. , Bishop P. K. , Lerner D. N. 
Published: August 2005

AbstractA regional ground‐water quality survey from 28 wells in the Coventry area of the United Kingdom identified widespread ground‐water pollution. Chlorinated hydrocarbon solvents (CHSs) were detected at concentrations exceeding l microgram per liter (μg/I) in all industrial and public water supply wells within the urban area. Of the CHSs analyzed, trichloroethene was most ubiquitous and was also detected at the highest concentrations, reaching a maximum of 547 μg/I at the industrial “Site A” during this study. By comparison with CHS pollution, inorganic and trace element concentrations were elevated relative to assumed baseline levels only in some industrial wells. The limited extent of inorganic contamination may be due to (1) retention of pollutants within the unsaturated zone, (2) ground‐water mixing in wells, (3) ferric hydroxide precipitation resulting in heavy metal coprecipitation, and (4) sorption on sand grains coated with ferric hydroxide. For inorganic determinants, a pollution index was devised which ranked zinc and boron as primary indicators of inorganic contamination. Regionally, concentrations of CHS and inorganic determinants did not reveal any significant correlation with depth.
In Situ Soil Remediation Using Vapor Extraction Wells, Development and Testing of a Three‐Dimensional Finite‐Difference Model
Authors: Sepehr Mansour , Samani Zohrab A. 
Published: August 2005

AbstractSoil vapor extraction technology is becoming increasingly popular in soil remediation in removing volatile and semivolatile organic compounds from the vadose zone. The rate and extent of removal of volatile organic compounds from the vadose zone by active or passive vapor extraction systems are known to be affected by a number of factors, including soil permeability, soil moisture content, applied suction, air flow rate, temperature, vapor pressure, and external boundary conditions. Some techniques used to describe the dynamics of gas flow are based on simplifying assumptions which limit their application in “real world” situations. This paper describes the development and testing of a three‐dimensional gas flow model “GAS3D” for the design of soil venting systems. The model takes into account the effect of partial penetration and partial screening of vapor extraction wells as well as the nonhomogeneity and anisotropy of the soil. The simulated pressure around a vapor extraction well by the developed GAS3D model was verified and validated by comparing the results of the finite‐difference solution to the actual field measurements and the results of an analytical solution under homogeneous and isotropic conditions. The model was used in a case study to demonstrate the utility of the developed model under heterogeneous and anisotropic conditions for designing a vapor extraction system.
Design and Evaluation of a Mesoscale Model Vadose Zone and Ground‐Water System
Authors: Lawrence J. R. , Zanyk B. N. , Hendry M. J. , Wolfaardt G. M. , Robarts R. D. , Caldwell D. E. 
Published: August 2005

AbstractA mesoscale model soil and ground‐water system was constructed and instrumented to study physical, chemical, and microbial processes, including transport and degradation of contaminants. The model system was 4.6 m in height by 2.4 m in diameter and contained up to 65 tonnes of soil and geologic materials. The model was filled with Ap (11 cm), B (20 cm), C1 and C2 (369 cm) horizons; the water table was 3.3 m from the soil surface. A rain simulation system applied uniform coverage of rain and/or chloride tracer to the model. Sampling of soil, sediment, pore waters, and gas phase was carried out using a series of in situ collectors and sampling ports. Major anions, metals, pH, alkalinity, CO2, N2, O2, CH4, microbial numbers, microbial biomass and heterotrophic potential (14 C‐amino‐acid uptake) were monitored over time (120 days) and depth. The system approached steady state with respect to solution chemistry and gases after approximately 60–70 days. During this interval, carbon dioxide rose from atmospheric to 3–5% of total gas volume measured at each sampling depth above the water table. Physical, chemical, and biological conditions in the model system after the initial 120 days were comparable to those reported for vadose and saturated zones during field studies on shallow phreatic aquifers. These results indicated that the mesoscale model preserved many of the features of natural systems while providing controlled conditions for studies such as evaluating the fate, and ground‐water contamination potential, of agricultural and industrial chemicals.
A Geographic Information System (GIS) User Interface for Delineating Wellhead Protection Areas
Authors: Rifai H. S. , Hendricks L. A. , Kilborn K. , Bedient P. B. 
Published: August 2005

AbstractDigital tools such as Geographic Information Systems (GIS) store, analyze, map, and illustrate large amounts of diverse electronic data. This paper develops a GIS modeling user interface for delineating Wellhead Protection Areas (WHPAs) around public water‐supply wells. With this modeling interface, the user can extract the necessary information from the GIS database automatically. The GIS database can then store the delineated WHPAs for further analysis and display. The modeling interface allows local agencies to delineate and manage WHPAs for hundreds of wells more efficiently and effectively than with the traditional paper maps and overlay system.In order to demonstrate the efficiency of the user interface, this paper presents a wellhead delineation pilot study for the City of Houston. WHPAs for the 202 active public water‐supply wells in the city were delineated using GIS and the modeling interface. Detailed sensitivity analyses were completed to evaluate the effect of uncertainty in model parameters on the delineated WHPAs. Potential sources of contamination within the delineated WHPAs were then identified using the GIS database.While GIS are perceived as an important tool that can enhance a user's ability for spatial data analyses, they have many problems. The system hardware and software require a substantial investment in financial and human resources. Database development is a tricky process requiring planning and commitment; in most cases, the anticipated outcome from GIS software development is not immediately realized.
Airborne Geophysics: Application to a Ground‐Water Study in Botswana
Authors: Bromley J. , Mannström B. , Nisca D. , Jamtlid A. 
Published: August 2005

SummaryA ground‐water study carried out in the Serowe area of eastern Botswana between 1985–1988 has provided the opportunity to evaluate the role of a multiparameter low‐level airborne geophysical survey in a hydrogeological investigation. The survey included magnetic, VLF (very low frequency), and coaxial EM (electromagnetic) measurements. In total, 7,500 line kilometers were flown over an area of 3,300 km2 with a nominal ground clearance of 20 m and a line spacing of 400 m.The main aquifer, the Ntane Sandstone Formation (Karoo age), is confined between mudstones below and basalt above, and is broken into a series of graben and horst structures by numerous E‐W striking faults. All bedrock, however, is completely masked by a 20–60 m thick overburden of sands, calcretes, silcretes, and sandstones known collectively as the Kalahari beds.Airborne magnetic and VLF geophysical surveys have been used to penetrate this masking cover. Images and stacked profiles obtained from the survey revealed structural and geological features of major hydrogeological significance. This provided the information necessary for the formulation of a conceptual model.The results helped guide the subsequent exploration drilling program in an efficient and effective manner, cutting down the need for extensive ground surveys. The investigation confirmed the availability of a 35,000 m3/day resource, sustainable for a 25‐year period. Highest yields were obtained from fracture zones associated with VLF anomalies. Potential wellfields were identified in confined sections of the aquifer, with production boreholes to be sited, where possible, on fractures associated with VLF anomalies.
Assessment of Ground‐Water Flow and Chemical Transport in a Tidally Influenced Aquifer Using Geostatistical Filtering and Hydrocarbon Fingerprinting
Authors: Marquis Samuel A. , Smith Eric A. 
Published: August 2005

AbstractTraditional environmental investigations at tidally influenced hazardous waste sites such as marine fuel storage terminals have generally failed to characterize ground‐water flow and chemical transport because they have been based on only a cursory knowledge of plume geometry, chemicals encountered, and hydrogeologic setting and synoptic ground‐water‐ level measurements. Single‐time observations cannot be used to accurately determine flow direction and gradient in tidally fluctuating aquifers since these measurements delineate hydraulic head at only one point in time during a tidal cycle, not the net effect of the fluctuations. In this study, a more rigorous approach was used to characterize flow and chemical transport in a tidally influenced aquifer at a marine fuel storage terminal using: (1) ground‐water‐level monitoring over three tidal cycles (72 hours), (2) geostatistical filtering of ground‐water‐level data using 25‐hour and 71‐hour filtering methods, and (3) hydrocarbon fingerprinting analysis.The results from the study indicate that naphtha released from one of the on‐site naphtha tanks has been the predominant contributor to the hydrocarbon plume both on‐site and downgradient off‐site and that net ground‐water and hydrocarbon movement has been to the southeast away from the tank since 1989. These conclusions are supported by: (1) the elongate configuration of the hydrocarbon plume parallel to the mean ground‐water flow directions determined using the 25‐hour and 71‐hour filtering methods; and (2) the occurrence of free‐naphtha‐product and elevated levels of BTXE and TPH in the naphtha range (C7 to C14) downgradient, but not upgradient, of the naphtha tank. The results also indicate that ground water containing 2.1 to 3.6 ppm TPH in the motor oil range (C22 to C32) is migrating onto the site from an upgradient source area to the north and/or northwest. Therefore, the background concentration or cleanup level of TPH for the facility is 2.1 ppm or greater. This study provides a more quantitative approach than traditional approaches for characterizing flow, assessing chemical transport and upgradient impacts, determining site‐specific ground‐water cleanup levels, and optimally locating ground‐water monitor wells and extraction wells or trenches at tidally influenced hazardous waste sites.
A Rewetting Approximation for a Simulator of Flow in a Surficial Aquifer Overlain by Seasonally Inundated Wetlands
Authors: Merritt Michael L. 
Published: August 2005

AbstractAn approximation is presented to rectify situations occurring as part of the three‐dimensional simulation of surficial aquifer flows in which surface grid cells become dry (zero saturated thickness) and then cannot readily receive flows that would again partially saturate them. The approximation permits the cells to be rewetted by adjusting dry cell pressures by the same amount as the pressure change computed for the uppermost nondry cells in the vertical column. This is continued in successive timesteps until the dry cells once again become partially or fully saturated.The rewetting procedure was tested in a recent transient simulation of flows in the surficial Biscayne aquifer of Dade County, Florida, which is partly covered by seasonally inundated wetlands. The uppermost layer of the model (layer 1) was used to represent overland sheetflow and grid cells of high equivalent hydraulic conductivity in this layer became dry and were rewetted seasonally, requiring a relatively robust representation of rewetting. The rewetting procedure made possible a simulation of overland sheetflow stages and aquifer water‐table altitudes between 1945 and 1989 that was generally correct to within about 1 foot in inundated and noninundated regions.In a 6‐year time period (1962–67) in which the behavior of the rewetting procedure was studied in detail, there were 4,723 simulated cell rewettings, of which 3,172 were in the overland sheetflow layer and 1,551 were in the uppermost aquifer layer (layer 2). The average head adjustment in a cell rewetting was 0.10 foot in layer 1 and 0.15 foot in layer 2. This study demonstrates an empirical approach to the problem of cell rewetting that might prove useful in other models of flow in surficial aquifers.
A General Solution to the Step‐Drawdown Test
Authors: Helweg Otto J. 
Published: August 2005

AbstractA more general solution to the step‐drawdown test, called the General Well Function, GWF, is proposed to replace the classic Jacob's step‐drawdown equation for situations when the time that wells are continuously pumped varies greatly. Jacob's equation requires a preselected discharge duration and does not incorporate time as an independent variable. Jacob's equation has been criticized for that shortcoming since drawdown is obviously dependent on time as well as discharge. The General Well Function, GWF, not only corrects for this weakness but appears to better predict drawdowns that extend beyond the test data than, for example, the FASTEP code based on Jacob's equation. The GWF assumes that both formation and well losses increase over time.
Assessment of Critical Flow Path for Improved Remediation Management
Authors: Poeter Eileen , Townsend Peter 
Published: August 2005

AbstractA multiple indicator conditional simulation technique is used to generate realizations of hydrofacies units in a two‐dimensional section of the fluvial, unconfined aquifer on the Hanford Site, Richland, WA. Two conceptual geologic models are considered and evaluated for spatial connectivity. The two conceptual models yielded different probabilities of occurrence for three “families” of simulations with distinct styles of connectivity. Critical ground‐water flow paths of each simulated section are evaluated as the paths with the highest percent of high hydraulic conductivity hydrofacies. The effective hydraulic conductivity of these critical paths is evaluated analytically by computing harmonic averages. Estimated ground‐water travel times are consistent with the observed rate of plume migration in the field. This procedure can be used to evaluate the probability of occurrence of alternative paths for contaminant transport as input to risk assessments, and design of characterization programs and remediation systems.
Numerical Modeling of Axisymmetric Flow
Authors: Pandit Ashok , Abi Aoun Jean M. 
Published: August 2005

AbstractA Galerkin finite‐element model is developed to solve axisymmetric flow problems in confined aquifers subjected to pumping by a single well. The model can be used to analyze axisymmetric problems involving pumping from multiaquifer systems by wells which are partially screened, fully screened, or have multiple screens. A simplified boundary condition at the well bore produces results that match analytical solutions. The location of the zero‐drawdown boundary is determined by using the concept of effective radius of influence. This concept is also used to generate a mesh that automatically expands radially in time. The expanding mesh feature may lead to savings in computational time since it uses relatively few elements and nodes for simulations at small times and progressively adds elements and nodes to the mesh for simulations at higher times.
Recommendations for Usage of SURFER to Gridding Model Results
Authors: Shan Chao , Stephens Daniel B. 
Published: August 2005

AbstractContouring is an important aspect of virtually all hydrogeological and contamination investigations. The popular computer contouring package SURFER saves enormous effort in preparing contour plots, but for some cases its misuse can lead to significant errors. We have demonstrated that where regularly spaced data with uniform grid size are to be input to SURFER for contouring, certain procedures are recommended to obtain improved accuracy. For optimal results, the grid size in SURFER should be exactly the same as that in the input file, and the number of nearest points for searching should be set to 1. If these procedures are not followed, contour lines are often not smooth. Consequently, the plots can introduce bias that appears as though there is numerical dispersion. For cases where calculated data have a nonuniform grid size, we recommend using Quadrant as the search method and setting the number of nearest search points to 1.
A Survey of Charge‐Balance Errors on Published Analyses of Potable Ground and Surface Waters
Authors: Fritz Steven J. 
Published: August 2005

AbstractAlthough the charge balance for a single chemical analysis of a water's electrolytes is not a reliable gauge for the accuracy of that analysis, the percent charge‐balance error (%CBE) becomes more credible as a means for evaluating analytical technique when applied to groups of analyses.Just how good are charge balances for chemical analyses of potable ground and stream waters in mainline geological journals? Starting with each journal's first volume, a search found 68 articles in six journals (Appl. Geochem., Chem. Geol, Geochim. Cos. Acta., Ground Water, J. Hydrol, and Water Resources Res.) that had what was deemed to be “complete” analyses of individual samples' major ions. Analyses of brines and hydrothermal solutions were excluded as were “composite” averages. A total of 1,062 %CBEs were computed and tabulated, and the average was 3.99%$ 6.56 (1σ).The average %CBE (by journals) ranges from 1.55% to 9.34%. Quality of %CBE is slightly better for articles published after 1970. Not surprisingly, low ionic strength samples are prone to charge‐balance errors > 10%. Of the 1,062 charge balances calculated, 612 were positive and 450 were negative. Eight of the 68 articles had analyses that were evenly balanced between positive and negative CB errors. There are 21 articles in which the majority of analyses had negative charge‐balance errors. Thus a clear majority (39) of articles had analyses in which there were more positive than negative charge‐balance errors.Systematic error is likely for situations where the analyses in an article are predominantly positive or predominantly negative. The likely reason for the former occurrence is lab determination of alkalinity from the nonacidified field aliquot. Failure to filter samples may cause the latter situation—especially in carbonate terranes. Systematic laboratory errors involving salt standards and dilutions can also yield charge‐balance errors for a suite of analyses that are skewed to either positive or negative errors. The care with which the analyst did his/her job may also impact charge‐balance errors.
Assessment of Methods and Conditions to Locate Boundaries: II. One Straight Recharge Boundary
Authors: Chapuis Robert P. 
Published: August 2005

AbstractA straight recharge boundary in an ideal aquifer is easily detected in the drawdown graph of an observation well. Two known and one proposed methods can be used to find the location and orientation of the recharge boundary. This paper assesses their performance. Both the law of times and the method of inflection point overestimate the distance ri to the imaginary well when the ratio β= ri/ rr is smaller than 20. In this case, known methods also give incorrect estimates of aquifer parameters. The proposed method gives directly the β‐value when it is higher than 20. For lower β‐values, a correction factor transforms the apparent β‐value into the correct β‐value. Two examples illustrate the quality of predictions by the known and proposed methods. Two known and one proposed methods relative to impervious boundaries are assessed in a companion paper.
Geostatistical Modeling of Heterogeneity in Glaciofluvial, Buried‐Valley Aquifers
Authors: Ritzi Robert W. , Jayne Dale F. , Zahradnik Arthur J. , Field Adrian A. , Fogg Graham E. 
Published: August 2005

AbstractIn the buried‐valley aquifers of the western and central glaciated plains of North America, assemblages of permeable outwash facies may form large and productive regional aquifer systems. In glacially derived aquifers it is common to have low‐permeability facies (e.g., till or lacustrine clay) juxtaposed with high‐permeability facies (e.g., sand and gravel outwash). The heterogeneity in the Miami buried‐valley aquifer system in southwestern Ohio was examined as an example. Practical approaches for evaluating the lithological uncertainty were explored in the areas lacking data. The facies types were represented by an indicator random function, which exhibited an isotropic, exponential covariance structure. A comparative, quantitative analysis of the facies boundaries was accomplished using three different indicator geostatistical methodologies: (1) hydrostratigraphic analysis with indicator point kriging and probability cutoff, (2) hydrostratigraphic analysis with conditional indicator simulation, and (3) leakance zonation with indicator block kriging and grid‐cell averaging. With the first method, it was shown in a theoretical analysis that the 0.5 probability level computed by indicator point kriging may or may not correspond to the boundary between high‐ and low‐permeability facies, depending upon the level of data support. With the data support for the Miami aquifer system, the 0.65 probability contour gave an areal distribution of low‐permeability facies that honored both the original data and the declustered global mean of the original indicator data. The first and third methods gave rise to a single model, in which the facies distribution was best in some local accuracy sense. The second method gave rise to many alternative models, in which the global texture of the facies distribution took precedence over local estimation of the expected value. The first two methods involved evaluating the geometry of the boundaries between the facies types in advance of creating the grid of the numerical ground‐water model, so that grid cell boundaries could be made to correspond to facies boundaries. The third method was useful when updating an existing ground‐water model that has grid cell boundaries not necessarily corresponding to facies boundaries.