bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Electronic Minipermeameter for Use in the Field and Laboratory
Authors: Sharp J. M. , Fu L. , Cortez P. , Wheeler E. 
Published: August 2005

AbstractThe quantification of permeability and geostatistical scaling from laboratory to well field to regional systems requires large spatial data sets for which field and laboratory minipermeameters have proven to be effective tools. We developed an electronic gas minipermeameter for use in either the field or the laboratory. This design alleviates several problems common to minipermeameters. In particular, errors in measurement of gas flow rate, calibration of flow rate meters, and countering pressure and temperature effects were reduced by using electronic mass‐flow transducers. Problems of sealing the injector (probe) tips and of measuring the permeability of weathering rinds and fracture “skins” were remedied with a sample chamber capable of handling thin wafers or rock cores of arbitrary dimensions. Calibrations with samples of known permeability were excellent. It is now possible to measure permeability very accurately on weathering rinds, fracture surfaces, utcrops, and large hand samples.
Relation Between Hydraulic Conductivity and Texture in a Carbonate Aquifer: Observations
Authors: Rovey Charles W. , Cherkauer Douglas S. 
Published: August 2005

AbstractBased on analysis of over 300 injection‐pressure tests and their assignment to logged stratigraphic intervals, it is argued that the Silurian dolomite aquifer in Milwaukee County, Wisconsin, behaves as both a fractured and porous medium. This paradox is resolved by examining the aquifer's individual stratigraphic units and their respective sedimentologic characteristics. Like many carbonates, the aquifer contains shoaling upward sequences and cycling through a variety of depositional environments and textures. Most of the stratigraphic units are fine‐grained mudstones, but interbeds with porous coarsegrained packstones and grainstones are also present.The packstone and grainstone units have unimodal distributions of hydraulic conductivity with geometric means between 10 4 and 10 3 cm/sec. The high matrix porosity masks any effects of jointing in these deposits, and they behave as porous high conductivity media. In contrast, hydraulic conductivities within the mudstones are bimodal, with one mode of very low matrix conductivities and a second higher mode controlled by jointing. Mudstone conductivities increase logarithmically with joint frequency, but never attain the magnitude of the values for the coarse‐grained units. Because the geometric mean hydraulic conductivities of the porous units are up to 1000 times greater than the thicker mudstones, the aquifer's bulk hydraulic conductivity is controlled by the thinner porous zones. Therefore, as a whole, the aquifer behaves as a porous medium even though most of the section is fracture‐dominated.Only the large number of hydraulic conductivity measurements isolated within specific stratigraphic units has allowed recognition of the importance of porous medium conditions in this aquifer. Because upward shoaling sequences are common within carbonates, a similar combination of porous and fractured medium conditions may be present, but unnoticed, in other carbonate aquifers. Investigators working in dolomites with minimal tectonic deformation should be particularly alert for porous medium effects.
Ground‐Water Contribution to Stream Salinity in a Shale Catchment, R.S.A.
Authors: Greeff G. J. 
Published: August 2005

AbstractThe salinity in the Breede River in the Robertson area (S. W. Cape, South Africa) has increased at an alarming rate over the past two decades. Water analyses have shown that a few tributary streams which drain Bokkeveld Shale catchments are responsible for the high salinity in this agriculturally important river. Research carried out to investigate the sources of salinity in one such catchment, the Poesjesnels River Valley, found that heavy salt loads were contributed by return flow seepages after irrigation of deeply ripped, thin soils which overlie decomposed shale. A smaller contribution was coming from ground water which had leached out some salt from these shales while moving through bedrock fractures under pressure from the head in the encircling mountains, and eventually seeped into the river; evidence for this was provided by comparison of the oxygen isotope ratios of the various water bodies in the valley with that of the river water. A salt balance model drawn up to differentiate between the sources of salinity gave an indication of the systems which need management in future hydrological and agricultural development in this and similar valleys.
Unsaturated Hydrogeologic Properties of Reclaimed Coal Strip Mines
Authors: Diodato D. M. , Parizek R. R. 
Published: August 2005

AbstractTwo nuclear methods were used to quantify hydrogeologic parameters in the unsaturated zone of a reclaimed and revegetated coal strip mine in Clarion, Pennsylvania. Am‐Be (neutron) and Cs‐137 (gamma‐gamma) geophysical logging tools were used to quantify volumetric moisture content, bulk density, total porosity, and unsaturated hydraulic conductivity. An additional study at the same site used postsampling neutron activation analysis to determine concentrations of a bromide tracer in unsaturated zone water samples. Those additional data were used to independently calculate unsaturated hydraulic conductivity.Geophysical logging of six boreholes at the site was conducted on seven different dates. Temporal variations in volumetric moisture content versus depth were observed to be short‐lived, with the general shape of the volumetric moisture content profiles remaining spatially stable over the eight month period of investigation. Bulk density values ranged from less than 1.14 to 1.86 g/cm3, corresponding to total porosities of greater than 57% to 30.1%. Large void spaces were encountered during past and present drilling and observed at a measurement point. Unsaturated hydraulic conductivities were calculated using draining profile volumetric moisture content data as input to an explicit numerical solution of the unsaturated flow equation. Calculated values ranged from 2.4 × 10−7 to 1.5 × 10 −3 cm/s. Examination of all of the geophysical log data together showed sharp increases in volumetric moisture content spatially coincident with zones where bulk density increases (and porosity decreases). The bulk density contrast appears to be of more influence than the magnitude of the material property. Increased unsaturated hydraulic conductivity associated with increased volumetric moisture content was seen in several boreholes.Bromide tracer‐labeled waters were collected from pressure‐suction lysimeters installed at depths of up to 18.1 m for a period of 16 months. Unsaturated hydraulic conductivities, calculated by interpreting concentration peaks as average arrival times of steadily infiltrating water through a uniformly porous media, ranged from 2.8 × 10−6 to 7.2 × 10−5 cm/s. However, a dual‐permeability mechanism is suggested by the observed behavior of the tracer. Analysis of the data suggests that fluid flow in this hydrogeologic setting is dominantly transient. Ground‐water recharge occurs in short‐lived pulses. The periodicity of acid mine drainage formation and flushing to the water table is expected to correspond to infiltration and recharge events.
Modeling Free Product Migration and Recovery at Hydrocarbon Spill Sites
Authors: Parker J. C. , Zhu J. L. , Johnson T. G. , Kremesec V. J. , Hockman E. L. 
Published: August 2005

AbstractThe numerical model ARMOS, which simulates areal flow of water and light hydrocarbon in an unconiined aquifer, isdescribed. Based on the assumption of local vertical equilibrium, area! flow equations for water and hydrocarbon are derived which exhibit reduced dimensionality and nonlinearity. A finite‐element method is used to solve the water and oil equations using an efficient semidecoupled approach. Input required by the model includes area! boundaries, elevations of the aquifer lower boundary, and initial water and hydrocarbon levels in monitoring wells. Soil and fluid properties include hydrocarbon density, viscosity and surface tension, saturated hydraulic conductivity, van Genuchten air‐water capillary pressure curve parameters, and the maximum residual hydrocarbon saturations in the saturated and unsaturated zones. Fluid heads or fluxes may be specified on the domain perimeter and pumping rates are prescribed at recovery wells. The water pumping rate is automatically limited when drawdown reaches a pump‐off set point (or the screen bottom), and hydrocarbon recovery is limited when well hydrocarbon thickness becomes zero. Model output includes water and hydrocarbon levels in monitoring wells, cumulative product recovery, and free and residual hydrocarbon volumes in the soil. A hypothetical problem involving optimization of free product recovery and a field application of the model to a large pipeline leak are described.
Implementation and Use of Direct‐Flow Connections in a Coupled Ground‐Water and Surface‐Water Model
Authors: Swain Eric D. 
Published: August 2005

AbstractThe U.S. Geological Survey's MODFLOW finite‐difference ground‐water flow model has been coupled with three surface‐water packages–the MODBRANCH, River, and Stream packages–to simulate surface water and its interaction with ground water. Prior to the development of the coupling packages, the only interaction between these modeling packages was that leakage values could be passed between MODFLOW and the three surface‐water packages. To facilitate wider and more flexible uses of the models, a computer program was developed and added to MODFLOW to allow direct flows or stages to be passed between any of the packages and MODFLOW. The flows or stages calculated in one package can be set as boundary discharges or stages to be used in another package. Several modeling packages can be used in the same simulation depending upon the level of sophistication needed in the various reaches being modeled. This computer program is especially useful when any of the River, Stream, or MODBRANCH packages are used to model a river flowing directly into or out of wetlands in direct connection with the aquifer and represented in the model as an aquifer block. A field case study is shown to illustrate an application.
Natural Biological Attenuation of Benzene in Ground Water Beneath a Manufacturing Facility
Authors: Davis John W. , Klier Nancy J. , Carpenter Constance L. 
Published: August 2005

AbstractSubsurface unsaturated soils and ground water directly beneath a manufacturing site have been shown to contain benzene. The vadose zone appears to be the current source for benzene to the aquifer. Although the ground water contains several mg/1 of contamination in the area immediately beneath the source, benzene was not detected in monitoring wells approximately 400 feet downgradient. Based upon the length of time benzene has been present in the ground water, as well as the permeability of the aquifer, physical processes alone such as adsorption and advection/dispersion are unlikely to account for the observed attenuation. Results from this investigation indicated the attenuation was primarily due to the natural biological processes occurring within the aquifer.Evidence for the natural bioremediation of benzene from the ground water included: (1) analysis of ground‐water chemistry, (2) laboratory studies demonstrating benzene biodegradation in aquifer samples, and (3) computer simulations examining contaminant transport. Laboratory studies indicated that under conditions similar to those encountered in the ground water, benzene was degraded to carbon dioxide by the naturally occurring microorganisms. The aerobic degradation of benzene in aquifer samples was quite rapid, with the time for 50% disappearance of the parent compound ranging from 4 to 14 days. In situ analyses of the ground water indicated significant levels of dissolved oxygen throughout the aquifer. Thus, the availability of oxygen should not limit the aerobic biodegradation of benzene. However, benzene was also shown to degrade under anaerobic conditions in microcosms prepared with aquifer material. Computer model simulations were also conducted to examine the processes influencing the transport of benzene in the aquifer. Results from the model simulations indicated biodegradation was the dominant process influencing attenuation of the contaminant.
A Portable Air‐Minipermeameter for Rapid In Situ Field Measurements
Authors: Davis J. Matthew , Wilson John L. , Phillips Fred M. 
Published: August 2005

AbstractMeasurements of air‐permeability in outcrops provide a means of obtaining numerous spatially distributed measurements for statistical analysis and subsequent parameterization of ground‐water flow and transport modeling. The air‐minipermeameters previously used for such studies generally consist of a compressed air source, rotameters, and diaphragm gauges. We present a lightweight syringe‐based air‐minipermeameter (LSAMP) design that is significantly more portable than previous instruments. The prototype model is contained in a 12.7 × 15.2 × 23 centimeter (5 × 6 × 9 inch) electrical box and weighs approximately 2 kilograms. The prototype LSAMP has a sampling range of 0.5 to 200 darcys. Individual measurements in this range require less than one minute. Permeability measured with the LSAMP closely correspond to permeability measured with a traditional minipermeameter and those measured on cores. Measurement error caused by soil moisture is less than 5 percent for volumetric water contents less than 5 percent. An analysis of variance on 38 triplicate measurements indicates that the variability associated with measurement error is much less than the range of measured values. Repeated permeability measurements under field conditions on two standard cores indicate that while the measurement error is greater under field conditions, the prototype device field performance is consistent with laboratory calibration results.
Relative Importance of Baseflow and Quickflow from Hydrographs of Karst Spring
Authors: Padilla A. , Pulido‐Bosch A. , Mangin A. 
Published: August 2005

AbstractEvaluation of recession hydrographs, from four karst springs in Europe, provides important information concerning the flow process operating in karst aquifer systems. Three analytic equations are used to evaluate the hydrographs: Mangin's equation, that assumes the recession is composed of both quickflow and baseflow; Coutagne's equation which considers the recession to be the response of a single reservoir; and a new function, Ht (which is derived from Coutagne's equation), that refers to the whole recession curve. Using Mangin's equation it is apparent that the saturated zone and thus baseflow exerts nearly complete control over the discharge of La Villa spring and is fairly important at Fuente Mayor and Baget springs, but is much less significant at Aliou spring. The saturated zone accounts for 100%, 90%, 91%, and 40% respectively for these springs. Using Coutagne's equation and Ht it is concluded that for Aliou and Baget springs, water flows freely in the high transmissive zones, but in the poorly transmissive zones, there is little continuity of connection in the system. At Fuente Mayor spring the differences in these zones are not so apparent and a gradual transition occurs. However, at La Villa spring, the karst aquifer is evidently much more homogeneous and the discharge is similar to that of a porous intergranular aquifer.
Dissolution of a Toluene Pool Under Constant and Variable Hydraulic Gradients with Implications for Aquifer Remediation
Authors: Voudrias Evangelos A. , Yeh Moon‐Full 
Published: August 2005

AbstractFactors affecting the dissolution of a toluene pool floating at the water table were investigated using an experimental aquifer 85 cm long, 30 cm high, and 20 cm wide. Under conditions of steady, uniform flow, the dissolved toluene concentration decreased with increasing vertical distance from the free phase pool, resulting in steep concentration gradients. The concentration gradient steepened with increasing ground‐water velocity. The thickness of the dissolved plume increased with increasing distance along the pool and decreasing ground‐water velocity. In all cases, measured concentrations were a small fraction of toluene solubility.In pulsed pumping experiments, dissolved toluene concentrations in all sampling ports increased significantly during zero flow conditions and, when the flow was resumed, they gradually decreased to the same levels as before the flow was stopped. Under the experimental conditions used, comparison between the pulsed and continuous pumping showed that the total mass removal would be higher for continuous pumping and would result in shorter toluene removal times. However, the total volume of water pumped and needed to be treated would be lower by 50% for pulsed pumping. The latter would result in a higher by ∼ 20% mass removed per volume of water pumped, suggesting that pulsed pumping would be a more efficient operation compared to continuous pumping, when considering removal of dissolved toluene from the aquifer.
A Semipassive Nutrient Injection Scheme for Enhanced In Situ Bioremediation
Authors: Devlin J. F. , Barker J. F. 
Published: August 2005

AbstractA permeable wall injection system is capable of introducing dissolved substances into an aquifer in a manner which minimizes the displacement of naturally present ground water, and maximizes the potential for dispersive mixing. The system operates predominantly in a passive mode, and should require relatively little power and small amounts of chemicals. The injection wall is a permeable cutoff wall installed across the path of a contaminant plume. The ground water can be amended with the desired nutrient solution using pumping and injecting wells within the wall. The high permeability of the wall ensures that the injection‐withdrawal operation causes flow which is primarily confined to the wall itself. Thus, only a minimal disruption of the ambient flow need result from a nutrient injection. After the nutrients have been introduced to the wall, the pulse is permitted to drift into the aquifer under natural gradient conditions, spreading longitudinally as it goes. Theoretical calculations and preliminary results of a field trial indicate that if this pulsing cycle is repeated at intervals of weeks to months (site‐specific), a stable microbial population can be supported at some distance downgradient from the wall.The advantages of this system include the predominantly passive nature of its operation, the effective use of longitudinal dispersion to maximize the mixing of added substances with contaminated ground water, and the flexibility of the system with regard to the types of biodegradation reactions which it can promote.
Leachate Geochemistry at a Municipal Landfill, Memphis, Tennessee
Authors: Mirecki June E. , Parks William S. 
Published: August 2005

AbstractA leachate plume emanating from the Shelby County Landfill located at Memphis, Tennessee is defined using selected major and trace inorganic constituents. High specific conductance values and elevated concentrations of ammonia, barium, boron, calcium, chloride, dissolved solids, potassium, sodium, and strontium were measured in water samples from wells screened in the alluvial and Memphis aquifers downgradient from or proximal to the landfill. Of these constituents, barium, boron, chloride, and strontium were used in the geochemical model code PHREEQE to estimate the percent leachate component in selected Memphis aquifer samples. Estimates of the leachate component in samples from affected Memphis aquifer wells range from 5 to 37 percent for barium and strontium, the most reliable tracers found during this study.
Two‐ and Three‐Dimensional Pathline Analysis of Contributing Areas To Public‐Supply Wells of Cape Cod, Massachusetts
Authors: Barlow Paul M. 
Published: August 2005

AbstractSteady‐state two‐ and three‐dimensional ground‐water‐flow models coupled with particle tracking (fluid‐particle pathline analysis) have been evaluated to determine their relative effectiveness in delineating contributing areas and particle traveltimes to public‐supply wells in two contrasting stratified‐drift aquifers of Cape Cod, Massachusetts. Several contributing areas delineated by the three‐dimensional pathline analysis do not conform to simple ellipsoidal shapes that are typically delineated by use of two‐dimensional analytical and numerical modeling techniques. They also include discontinuous areas of the water table and do not surround the supply wells. Because two‐dimensional area! models do not account for vertical flow, they cannot adequately represent many of the hydrogeologic and well‐design variables that complicate the delineation of contributing areas in three‐dimensional flow systems on Cape Cod, including the presence and continuity of discrete zones of low hydraulic conductivity, large anisotropic ratios of horizontal to vertical hydraulic conductivity, partially penetrating supply wells, shallow streams and lakes, and low (less than about 0.1 million gallons per day) pumping rates.Particle traveltimes calculated by the two‐dimensional models are longer than those calculated by the three‐dimensional models, and time‐related capture zones determined by the two‐dimensional models underpredict the size of the land area contributing water to simulated wells. It appears that the two‐dimensional models do not accurately represent shallow, partially penetrating wells, or heterogeneous and anisotropic sediments for the purposes of simulating contributing areas and traveltimes in complex ground‐water systems.
Maximum Water‐Table Drawdown at a Fully Penetrating Pumping Well
Authors: Gefell Michael J. , Thomas George M. , Rossello Stephen J. 
Published: August 2005

AbstractThe magnitude of water‐table drawdown achievable by a fully penetrating pumping well in an unconfined aquifer commonly is limited to a small fraction of the initial aquifer thickness. The maximum potential water‐table drawdown can be estimated based on the aquifer thickness, the pumping well effective radius, and the estimated radius of influence in the aquifer during maximum steady‐state pumping (Kozeny, 1953). The maximum steady‐state flow rate into a well can be predicted if the aquifer hydraulic conductivity is known based on observed water‐table drawdown during a pumping period.To achieve the maximum potential pumping rate from a fully penetrating well in an unconfined aquifer, the water level inside the well must be maintained at the bottom (Kozeny, 1953; this paper). This condition creates a seepage face along the inside of the well screen. The hydraulics of the seepage face control the removal of water from the aquifer and the size of the resulting cone of depression. The area of the seepage face, which is a direct function of the effective radius of the pumping well, strongly influences the maximum potential water‐table drawdown and the maximum steady‐state pumping rate.The vertical component of the hydraulic gradient in the formation is downward and increases toward the pumping well. The hydraulic potential, therefore, decreases with increasing depth below the water table. Only shallow observation wells that are screened across the uppermost fraction of the saturated zone are adequate for delineating the actual water‐table position during pumping. Observation wells screened across deeper portions of the aquifer, including fully penetrating, fully screened observation wells, exhibit potentiometric drawdown in excess of true water‐table drawdown.