bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ground‐Water Pollution of the Madras Urban Aquifer, India
Authors: Somasundaram M. V. , Ravindran G. , Tellam J. H. 
Published: August 2005

AbstractMost of the water requirement for Madras is met from surface‐ and ground‐water supplies piped in from outside the city limits. However, as is the case for many cities, a certain proportion of the population, usually the poorest, is forced to rely on wells within the urban area. A study was therefore carried out to gain an idea of the inorganic quality of the water in the wells penetrating the shallow (< 20 m thick) alluvial aquifer below the city. Two general surveys of selected wells across the city indicated that relative to Indian domestic water standards, of the 93 ground‐water samples obtained, 25% exceeded the Ca limit, 11% the Mg limit, 43% the total dissolved solids limit, 14% the SO4 limit, and 70% the NO3 limit. As an indicator of biological contamination, the high concentrations of NO3 (up to 1040 mg/l) are particularly worrying. A detailed survey of sites close to a city river was also undertaken. High heavy metal concentrations were detected, with As up to 0.42 mg/1, Hg to 0.02 mg/1, Pb to 1.82 mg/1, and Cd and 1.31 mg/1. Microbes have been found in several of the wells. It is clear that, as expected, the shallow ground water is grossly polluted.
The Use of Sulphur Hexafluoride as a Conservative Tracer in Saturated Sandy Media
Authors: Wilson Ryan D. , Mackay Douglas M. 
Published: August 2005

AbstractSulphur hexafluoride (SF6), a volatile, nontoxic, inorganic compound, behaved identically to bromide in a laboratory column tracer experiment with saturated sandy media. A simple system was used to achieve an SF6 injection concentration of approximately 7 mg/1, roughly 25% of its solubility. While this system requires more equipment and time than that involved in preparing ionic tracer solutions, certain benefits are realized. The detection limit for SF6 was approximately 5 μg/l using a simple headspace extraction technique and a gas Chromatograph with an electron capture detector. Thus, the tracer could be followed for a three order of magnitude decrease in concentration. For similar resolution, bromide had to be injected at a concentration over 1000 mg/1 (typical detection limit approximately 0.5 mg/1). When the required higher concentrations of the ionic tracers may lead to significant geochemical changes or density effects, SF6 may be the preferable tracer. Furthermore, unlike ionic tracers, the highly volatile SF6 may be readily removed from water. High volatility does, however, require that some care be taken to limit the potential loss of mass during injection, sampling, and analysis. Since others are developing procedures for analyzing SF6 in ground water with extremely low detection limits (on the order of 1 ng/1), it appears likely that measurable concentrations could range over six to seven orders of magnitude. This range is considerably wider than typically possible with ionic tracers, and may offer an important advantage in some applications.
The Significance of the Extent of Recovery in Interpreting Aquifer Pumping Test Data from Large Diameter Wells
Authors: Singh V. S. , Gupta C. P. 
Published: August 2005

AbstractTo estimate aquifer parameters from pumping test data obtained from large diameter wells, one must consider the recovery data. This is particularly important for low permeability formations. Observations on the recovery should be continued to the maximum possible extent for an accurate estimation of these parameters. Analysis of data from a few representative case studies for granitic and basaltic rocks are presented here to establish a criterion to decide how long observations should be taken during recovery in the well.
A Field Experiment to Study the Behavior of Tetrachloroethylene Below the Water Table: Spatial Distribution of Residual and Pooled DNAPL
Authors: Kueper Bernard H. , Redman David , Starr Robert C. , Reitsma Stanley , Mah May 
Published: August 2005

AbstractThis paper describes a field experiment involving the release of 230.9 liters of tetrachloroethylene (PCE) below the water table in a naturally occurring, unconfined sand aquifer. The release was executed in a 3 m X 3 m X 3.4 m deep, scalable‐joint steel sheet‐pile cell anchored into an underlying clay aquitard. After allowing 28 days for redistribution, excavation of the upper approximately 0.9 m of the cell revealed PCE pools and residual to be present in relatively coarser grained horizons, with substantial degrees of lateral flow having taken place. This lateral flow was observed in laminations and lenses ranging in thickness from a few mm to a few cm, with only subtle variations in texture separating individual migration pathways. Detailed sampling during the excavation procedure and subsampling of three cores extended down to the clay aquitard revealed a spatially variable distribution of PCE with saturations ranging from 1% to 38% of pore space. Laboratory measurement of a fully hysteretic capillary pressure curve demonstrated that the degree of nonwetting phase residual is a function of the maximum saturation attained along main drainage during the initial infiltration process. Various models for consolidated petroleum reservoir materials did not fit the experimental data well. The theory governing pool formation in heterogeneous porous media is also presented, and it is demonstrated that pools can form in homogeneous media exhibiting a distinct entry pressure.
Pentobarbital Found in Ground Water
Authors: Eckel William P. , Ross Benjamin , Isensee Robert K. 
Published: August 2005

AbstractA landfill in Florida which received wastes in 1968 and 1969 has contaminated nearby shallow ground water. Analysis of a sample of contaminated ground water collected in 1984 from a well approximately 300 m from the landfill tentatively indicated the presence of the addictive sedative pentobarbital, among many other compounds. A well at the same location was resampled in 1991, and pentobarbital was positively identified using gas chromatography/tandem mass spectrometry. The persistence over 21 years of a supposedly unstable drug in anoxic ground water raises the possibility that other pharmacologically active compounds may be found in plumes coming from landfills that have accepted medical wastes.
A Second‐Order Diagonally Implicit Runge‐Kutta Time‐Stepping Method
Authors: Baker Donald L. 
Published: August 2005

AbstractThis paper presents a subset of the family of diagonally implicit Runge‐Kutta (DIRK) time‐stepping methods for finite‐difference models of parabolic (diffusion‐like) equations. It includes the first‐order‐accurate Euler implicit (backward in time, DIRK1) and the second‐order Crank‐Nicolson (DIRK2) methods as special cases. It combines a series of DIRK1 partial time steps so as to eliminate additional power terms of the time step δt, in the local error, by the number of partial steps used. This offers a large increase in computational efficiency, going from a DIRK1 to a DIRK2 method, and improves on the Crank‐Nicolson method with a better choice of Runge‐Kutta parameters. For a linear diffusion example, an optimal‐parameter DIRK2 method offers the same accuracy as the Euler implicit method at two orders of magnitude larger time step, with an order of magnitude better accuracy than the Crank‐Nicholson method. In a highly nonlinear horizontal unsaturated water flow example, using eight simulated medium to coarse soils, a DIRK2 method produces either an average maximum accuracy improvement of 4.7 times over the Euler implicit method, without Newton or Picard iteration, or from 3.8 to 48 times faster computer run times for the same accuracy.
Cokriging of Geoelectric and Well Data to Define Aquifer Protective Layers
Authors: Pesti Geza , Bogardi Istvan , Kelly William E. , Kalinski Robert J. 
Published: August 2005

AbstractCokriging and ordinary kriging of geoelectric and well data are used to determine the thickness, lateral extent, and spatial variability of a naturally occurring clay layer near Ashland, Nebraska. The clay layer that protects the underlying ground water from contaminant sources is defined by mapping the estimated clay thickness; variance maps provide an assessment of the uncertainty of the thickness estimates. Two types of information are combined in the cokriging procedure: clay thickness data estimated from drillers'logs of 128 irrigation and municipal supply wells, and thicknesses estimated from interpretation of 44 vertical electrical soundings (VES); for the ordinary kriging, well data are used alone. Both types of maps demonstrate the existence of a continuous near‐surface clay layer extending over much of the Ashland wellfield; however, the cokriged map shows much more detail in the central part of the study area, where the well data are undersampled. The relatively dense VES network in the central area provides an important information bridge between the northern and southern areas making the cokriged map more continuous and accurate than the map prepared using the well data alone and ordinary kriging.
Microbiological Analysis of Iron‐Related Biofouling in Water Wells and a Flow‐Cell Apparatus for Field and Laboratory Investigations
Authors: Tuhela Laura , Smith Stuart A. , Tuovinen Olli H. 
Published: August 2005

AbstractA flow‐cell assembly was constructed to collect biofilm samples on glass slides in an effort to monitor Fe‐precipitating microorganisms in water wells. The flow‐cell was used with a once‐flow‐through connection to municipal‐water wells which had previous histories of Fe‐related precipitation and biofouling problems. Microscopic observations of biofilms attached to glass slides confirmed the presence of stalked and sheathed bacteria believed to be involved in Fe (III)‐precipitation. Scanning electron microscopy confirmed that biofilm samples contained Gallionella‐type morphological features composed of helical, intertwisted stalks. Attempts to recover these organisms with cultural methods were unsuccessful. For monitoring Fe‐precipitating microorganisms, a differential solid medium was developed from the general‐purpose heterotrophic platecount medium (R2A) by incorporating ferric ammonium citrate in the formulation. Organisms capable of using citrate in the modified medium yielded rust‐colored colonies due to the formation of Fe (III)‐precipitates. These Fe‐precipitating bacteria did not possess stalks, sheaths, or other appendages, and their presence could not be predicted from microscopic examination of the sample materials. Optical measurement of biofilm thickness was deemed unreliable because of large variation in the thickness of Fe(III)‐precipitation and associated bacterial attachment. Fe(III)‐precipitates were identified as ferrihydrite, a poorly crystalline Fe(III)‐oxide. Laboratory studies with amended well‐water samples recirculating through a flow‐cell were used to enrich for organisms involved in biofouling communities. These experiments yielded methylotrophic organisms capable of growing with methanol and methylamine, and they were classified as Hyphomicrobium spp.
Regional Flow in the Baltic Shield During Holocene Coastal Regression
Authors: Voss Clifford I. , Andersson Johan 
Published: August 2005

AbstractThe occurrence of saline waters in the Baltic Shield in Sweden is consistent with ongoing but incomplete Holocene flushing and depends on the geometry and connectivity of conductive structures at both regional and local scales, and on the surface topography. Numerical simulation of regional variable‐density fluid flow during Holocene land‐rise and coastal regression shows that the existence of any old saline water, whether derived from submarine recharge in regions below Sweden's highest postglacial coastline or geochemical processes in the crystalline rock, is an indication either of slow fluid movements through the bedrock over long times, or of long travel distances through fracture systems before arriving at measurement points. During the land‐rise period, regional flow is not affected by the variable density of fluids in the upper few kilometers of the shield, and the topography of the water table is the only driving force. The spatial distribution of meteoric flushing water and pre‐Holocene waters may be complex, with the possibility of relatively fresh water in fracture zones below salty units even at depths of a few kilometers. The domination of the topographic driving force implies that deep saline water is not necessarily stagnant, and significant flow may be expected to occur in well‐connected horizons even at depth. Local topography variation and fracture zone location combine to create a complex flow field in which local topographic driving forces extend to considerable depth in some areas, whereas regional topographic forces predominate in others. Thus, a pattern may be difficult to discern in measurements of the regional salinity distribution, although it is clear that the coastal region is the major zone of discharge for deeper pre‐Holocene fluids. During the land‐rise period, the regional flow field equilibrates with changing climatic conditions and coastal positions, while the distribution of flushing water and older water lags and will perpetually change between successive glaciations. These characteristics have direct implications for the safety of nuclear water repositories located at depth in Baltic Shield rocks.
SHYDG.FOR—Hydrograph Package for MODFLOW
Authors: Plato Paul R. 
Published: August 2005

AbstractSHYDG.FOR—Hydrograph Package for MODFLOW, was written for use with the USGS finite‐difference ground‐water flow model (MODFLOW). This program allows the user to specify a list of nodes where model generated heads are saved separately. The program was designed to assist in the calibration of ground‐water flow models by simplifying the process of creating hydrographs of simulated heads to compare with hydrographs of measured water levels. The program consists of two subroutines written in Fortran 77 to be added to MODFLOW and requires minor modification of the MODFLOW main program code.
Stable Isotopes of Oxygen and Nitrogen in Source Identification of Nitrate from Septic Systems
Authors: Aravena R. , Evans M. L. , Cherry J. A. 
Published: August 2005

AbstractStable isotopes, 15N and 18O, have been used as tracers to differentiate a contaminant nitrate plume emanating from a single domestic septic system, in a ground‐water system characterized by high and similar nitrate content outside and inside of the contaminant plume. A good delineation of the nitrate plume of septic origin was obtained using 15 N analysis in nitrate. The 15N content ofthe nonplunie nitrate is in agreement with the sources of nitrate: solid cattle manure, synthetic fertilizer (NH4‐NO3), and soil organic nitrogen, at the study site. 18O analysis in nitrate did not provide enough isotopic contrast to permit separation of nitrate derived from the septic system and that in the surrounding ground water, derived from agricultural fertilizer sources. 18O data indicated that nitrification of ammonium is the main process responsible for formation of nitrate at the study site. 18O in ground water clearly delineated the ground‐water plume associated with the septic system and suggest that this tracer should be considered in studies related with contaminant plumes of different origin.
Transient and Steady‐State Solute Transport Through a Large Unsaturated Soil Column
Authors: Porro I. , Wierenga P. J. 
Published: August 2005

AbstractThe use of steady‐state models can sometimes reduce the computational resources and input data required for solution of transient transport problems. A large column experiment was performed to test whether solute transport parameters determined from a steady flow experiment may be used in transient, unsaturated flow and transport model predictions. Tritiated water and bromide were applied at a steady rate to the top of a 0.95 m diameter by 6 m deep soil column containing unsaturated soil. After 10 days, tracers were eliminated from the irrigation water. When the soil moisture content within the column ceased to change, another 10‐day pulse of tritiated water and bromide was applied, followed by water without tracers. Transport model parameters were determined through optimization, using breakthrough curves observed at various depths. The tritiated water and bromide pulses lagged behind the wetting front during infiltration into the relatively dry soil. The bromide pulse moved 17–20% faster than the tritiated water pulse, because of anion exclusion. Breakthrough curves for the transient and steady‐state experiments were similar. Because the solute fronts lagged significantly behind the moisture fronts, steady‐state transport parameters, when used in a fully transient numerical model, fairly described the transport under transient conditions.
Classification of Transmissivity Magnitude and Variation
Authors: Krásný Jiri 
Published: August 2005

AbstractUntil now no objective classification of transmissivity has been introduced, in spite of the quantitative nature of transmissivity values and their obvious importance for quantitative appraisals of aquifers or major ground‐water systems. The usual subjective expression of transmissivity, for example as “high” or “low”, prevents the objective comparison of transmissivity values characterizing different areas and hydrogeological environments. A combined classification of magnitude and variation of transmissivity is proposed, with the intention to standardize the expression, comparison, and representation of transmissivity. This classification also enables its compact and unambiguous depiction in tables and maps.
Assessment of Long‐Term Withdrawal Rate for a Coastal Aquifer
Authors: Gupta A. Das , Amaraweera H.B.M.P. 
Published: August 2005

AbstractThe long‐term safe withdrawal rate for a coastal aquifer in Mannar Island of Sri Lanka was assessed through the simulation of interface movement. A range of estimates of natural recharge sequence was first obtained from a water balance study considering the variations of factors affecting the soil moisture balance. The representative recharge sequence was then determined through the simulation of a field observed interface profile along a selected section. Following this, the sustainability of continuous water withdrawal in the future was assessed by limiting the extent of salt‐water upconing. An increase in the withdrawal rate in the future would be possible through proper monitoring of the system response.
Chlorine‐36 in the Snake River Plain Aquifer at the Idaho National Engineering Laboratory: Origin and Implications
Authors: Beasley T. M. , Cecil L. D. , Sharma P. , Kubik P. W. , Fehn U. , Mann L. J. , Gove H. E. 
Published: August 2005

AbstractBetween 1952 and 1984, low‐level radioactive waste was introduced directly into the Snake River Plain aquifer at the Idaho National Engineering Laboratory (INEL), Idaho Falls, Idaho. These wastes were generated, principally, at the nuclear fuel reprocessing facility on the site. Our measurements of 36C1 in monitoring and production well waters, downgradient from disposal wells and seepage ponds, found easily detectable, nonhazardous concentrations of this radionuclide from the point of injection to the INEL southern site boundary. Comparisons are made between 3H and 36Cl concentrations in aquifer water and the advantages of 36C1 as a tracer of subsurface‐water dynamics at the site are discussed.
Vadose Zone Fertilizer‐Derived Nitrate and δ15N Extracts
Authors: Herbei Mitchell J. , Spalding Roy F. 
Published: August 2005

AbstractNitrate derived from commercial NH4NO3fertilizer, δ15N =+1.5 %0, applied to fertility plots was extracted from two cores to depths of 46 and 52 ft. In both cores the δ15N of the extracted nitrate‐nitrogen (NO3‐N) showed that it became heavier with depth. Although this isotope fractionation did not cause δ15N values to overlap with those characteristic of animal waste sources (> + 10%0), δ15N values were as high as +8%0at the bottom of one profile. The gradual increase in δ15N with depth in the bottom 20 to 30 ft of the cores is consistent with denitrification at these depths. Clay content was much more variable with depth and was significantly associated with NO3‐N concentrations (r =+0.9) in the core with 30% clay. Correlation of NO3‐N concentrations to clay content was not significant in the other core with 50% clay. In both cores smectite and illite were the dominant clays; chlorite, and aluminum and iron oxyhydroxides were not detected by XRD. Anion exchange capacity measurements confirmed that it was not responsible for the observed variability in NO3‐N concentrations or δ15N values.Potassium chloride (KC1) extracts yielded significantly higher NO3‐N concentrations (p < 0.005) and lighter δ15N values (p < 0.0001) than distilled deionized water (DDW) extracts. It is postulated that NO3−not extracted by DDW is trapped within the microstructure of the swelling clays. The strongly depleted δ15N of–16.3 %0may be attributed to pH‐mediated aqueous ammonia or nitrate diffusion and/or ammonia volatilization into the smectite microstructure. Results indicated that DDW rather than KC1 extractions of sediments high in smectite (> 40%) provide more realistic estimates of ground‐water loading from nonpoint sources.
Estimation of Dispersion Parameters for Two‐Dimensional Plumes
Authors: Zou S. , Parr A. 
Published: August 2005

AbstractAn analytical method is developed whereby longitudinal and transversal dispersivities can be determined for a two‐dimensional plume generated by slug tracer injection in a uniform ground‐water flow field. One solution procedure requires concentration versus time data from two sampling wells through which the plume passes. A second solution procedure uses a least‐squares method to obtain optimal parameter estimations when only one sampling well is available. Both methods are particularly useful since they do not require a priori knowledge of either the direction or magnitude of the pore velocity. Detailed example calculations illustrate the solution procedures and show that these methods are successful.
Fate of Organochlorine Compounds During Aquifer Storage and Recovery: The Las Vegas Experience
Authors: Mille C. J. , Wilson L. G. , Amy Gary L. , Brothers Kay 
Published: August 2005

AbstractTwo water quality concerns with aquifer storage and recovery (ASR) operations are (1) the fate of organochlorine compounds, such as trihalomethanes (THMs), in the treated recharge source, and (2) the formation of organochlorine compounds from precursor materials following the chlorination of recovered water. The fate of chloroorganic compounds in chlorinated Colorado River water was studied during a 1989 recharge/recovery operation conducted by the Las Vegas Valley Water District (LVVWD). Water samples were obtained from two dual‐purpose wells during the pumping cycle for THMs and other indicators of organochlorine precursors. The percentage recovery of THMs was approximately the same as the percentage recovery of Colorado River water. This suggests that the removal of organochlorine compounds (e.g., by sorption) did not appreciably occur in the aquifer materials at the two well sites. Recovery of source water was incomplete. Accordingly, dissolved organic carbon (DOC), representing precursor material, remained in the aquifer at the end of the pumping cycle. The Las Vegas experience suggests that prolonged recharge and storage of Colorado River water in similar hydrogeologic basins (e.g., the Tucson basin) could result in problems with THM compliance at the well head. This will be a problem if THM standards are reduced during the interval that water is stored.