bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Recharge Mechanisms in an Alluvial Aquifer Zone in Northeast Brazil
Authors: Santiago Marlucia F. , Frischkorn Horst , Neto Porfírio Sales , Filho Josué Mendes 
Published: December 2005

AbstractThe state government of Ceará has initiated a program of releasing water from dams in order to sustain a continual flow of water in the state's naturally intermittent rivers. However, river/ ground water connections in alluvial areas impose heavy losses on regulated discharges. Our study area, the “Ilha de Limoeiro” (Isle of Limoeiro), is located in the Lower Jaguaribe Basin and comprises an area of approximately 120 km2. We used environmental oxygen‐18 and deuterium, together with hydrochemistry, in order to identify the origin of ground water which is heavily exploited for intensive small‐scale irrigation in that part of the flood‐plain of the Jaguaribe River. This paper discusses the mechanisms of recharge for the different hydrogeologic systems: crystalline basement, thick alluvium, and alluvium/Agu.
Identifying Potential Land Use‐Derived Solute Sources to Stream Baseflow Using Ground Water Models and GIS
Authors: Boutt David F. , Hyndman David W. , Pijanowski Bryan C. , Long David T. 
Published: December 2005

AbstractThis paper presents an approach to examine potential relationships between land use‐derived solutes and baseflow surface water quality using regional ground water and solute transport models linked to geographic information systems (GIS). We demonstrate this approach by estimating chloride concentrations in surface water due to road salt transport through ground water in a large coastal watershed in Michigan. The geologically parameterized model for this study provides a good fit to measured hydraulic heads in the watershed and offers a method to estimate spatially and temporally variable solute fluxes via ground water to streams and lakes. The results demonstrate that there is a considerable legacy of land use influencing surface water quality at the study site. The simulated chloride concentrations produced with salted roads as the only chloride source are similar to measured surface water chloride concentrations throughout most of the watershed, except in regions where other sources for chloride (e.g., high‐density septic systems, locations of oil brine fields) likely exist. Impacts of other land use related solutes on baseflow surface water quality could also be explored using this approach. As a result, watershed managers could be provided with quantitative information about the potential impacts of developments and associated surface‐applied solutes on future surface water quality.
Mapping Coastal Aquifers by Joint Inversion of DC and TEM Soundings‐Three Case Histories
Authors: Albouy Yves , Andrieux Pierre , Rakotondrasoa Gérard , Ritz Michel , Descloitres Marc , Join Jean‐Lambert , Rasolomanana Eddy 
Published: December 2005

AbstractElectrical and electromagnetic methods are well suited for coastal aquifer studies because of the large contrast in resistivity between fresh water‐bearing and salt water‐bearing formations. Interpretation models for these aquifers typically contain four layers: a highly resistive unsaturated zone; a surficial fresh water aquifer of intermediate resistivity; an underlying conductive, salt water saturated aquifer; and resistive substratum. Additional layers may be added to allow for variations in lithology within the fresh water and salt water layers. Two methods are evaluated: direct current resistivity and time domain electromagnetic soundings. Use of each method alone produces nonunique solutions for resistivities and/or thicknesses of the different layers. We show that joint inversion of vertical electric and time domain electromagnetic soundings produces a more tightly constrained interpretation model at three test sites than is produced by inversion methods applied to each data set independently.
Forecasting of Turbid Floods in a Coastal, Chalk Karstic Drain Using an Artificial Neural Network
Authors: Beaudeau P. , Leboulanger T. , Lacroix M. , Hanneton S. , Wang H.Q. 
Published: December 2005

AbstractWater collected at the Yport (eastern Normandy, France) Drinking Water Supply well, situated on a karst cavity, is affected by surface runoff‐related turbidity spikes that occur mainly in winter. In order to forecast turbidity, precipitation was measured at the center of the catchment basin over two years, while water level and turbidity were monitored at the well site.Application of the approach of Box and Jenkins (1976) leads to a linear model that can accurately predict major floods about eight hours in advance, providing an estimate of turbidity variation on the basis of precipitation and water level variation over the previous 24 hours. However, this model is intrinsically unable to deal with (1) nonstationary changes in the time process caused by seasonal variations of in ground surface characteristics or tidal influence within the downstream part of the aquifer, and (2) nonlinear phenomena such as the threshold for the onset of runoff. This results in many false‐positive signals of turbidity in summer.Here we present an alternative composite model combining a conceptual runoff submodel with a feedforward artificial neural network (ANN). This composite model allows us to deal with meaningful variables, the actioneffect of which on turbidity is complex, nonlinear, temporally variable and often poorly described. Predictions are markedly improved, i.e., the variance of the target variable explained by 12‐hour forward predictions increases from 28% to 74% and summer inaccuracies are considerably lowered. The ANN can adjust itself to new hydrological conditions, provided that on‐line learning is maintained.
A Conceptual Model for DNAPL Transport in Karst Ground Water Basins
Authors: Loop Caroline M. , White William B. 
Published: December 2005

AbstractDense nonaqueous phase liquids (DNAPLs) such as perchloroethylene, polychlorinated biphenyls, creosote mixtures, and many solvents and degreasers can be released into karst aquifers through sinkholes and sinking streams in quantities up to tanker car volumes. Although DNAPLs are easily injected into karst aquifers, discharge of the contaminants through springs may be significantly delayed depending on transport mechanism, storm water recharge, and storage sites within the karst aquifer. Storage sites include (1) the epikarst; (2) pools and depressions within underground streams; (3) incorporation of DNAPL within clastic sediments that are present in most conduits; (4) adsorption onto organic materials and onto manganese oxides, iron oxides, and other substrates; and (5) migration to depth within the fracture system. Effective transport of DNAPL contaminants during storm flow pulses requires the exceedance of thresholds best defined in terms of the conduit stream power. Movement of pooled DNAPL requires a boundary shear between the liquid and water flowing over it. DNAPL stored in clastic sediment bleeds out slowly or dissolves into surrounding pore water until storm pulses create a stream flow sufficient to flush the pore water, or possibly move the sediment pile itself. Under extreme flow conditions the entire sediment pile, including the DNAPL, can be entrained and ejected from the conduit system.
Three‐Dimensional Modeling of Density‐Dependent Salt Water Intrusion in Multilayered Coastal Aquifers in Jahe River Baisn, Shandong Province, China
Authors: Cheng Jian M. , Chen Chong X. 
Published: December 2005

AbstractA three‐dimensional variable density flow and transport model has been developed to study salt water intrusion in the Jahe River Basin, Shandong Province, China, A coupled Eulerian‐Lagrangian method is applied to solve the transport equation, in which the advection part is calculated by a hybrid method of characteristics. In using the density‐dependent tidal effect model, the seaward boundary in the confined apuifer is determined according to tidal‐effect information. The aquifer parameters in the Jahe River Basin are estimated by converging long‐term observational data of the hydraulic head and chloride concentration. Through numerical analysis and prediction, it can be concluded that the main reasons for salt water intrusion are excessive ground water exploitation and an improper arrangement of pumping wells in the lower reaches of the Jahe River Basin as well as the tidal‐affected river. After predicting the effect of several remedial schemes, two measures are suggested to prevent salt water intrusion.
Atrazine Retention and Degradation in the Vadose Zone at a Till Plain Site in Central Indiana
Authors: Bayless E. Randall 
Published: December 2005

AbstractThe vadose zone was examined as an environmental compartment where significant quantities of atrazine and its degradation compounds may be stored and transformed. The vadose zone was targeted because regional studies in the White River Basin indicated a large discrepancy between the mass of atrazine applied to fields and the amount of the pesticide and its degradation compounds that are measured in ground and surface water. A study site was established in a rotationally cropped field in the till plain of central Indiana. Data were gathered during the 1994 growing season to characterize the site hydrogeology and the distribution of atrazine, desethylatrazine, deisopropylatrazine, didealkylatrazine and hydroxyatrazine in runoff, pore water, and ground water. The data indicated that atrazine and its degradation compounds were transported from land surface to a depth of 1.5 m within 60 days of application, but were undetected in the saturated zone at nearby monitoring wells. A numerical model was developed, based on the field data, to provide information about processes that could retain and degrade atrazine in the vadose zone. Simulations indicated that evapotranspiration is responsible for surface directed soil‐moisture flow during much of the growing season. This process causes retention and degradation of atrazine in the vadose zone. Increased residence time in the vadose zone leads to nearly complete transformation of atrazine and its degradation products to unquantified degradation compounds. As a result of macropore flow, small quantities of atrazine and its degradation compounds may reach the saturated zone.
Evaluation of Ground Water Monitoring Network by Principal Component Analysis
Authors: Gangopadhyay Subhrendu , Das Gupta Ashim , Nachabe M.H. 
Published: December 2005

AbstractPrincipal component analysis is a data reduction technique used to identify the important components or factors that explain most of the variance of a system. This technique was extended to evaluating a ground water monitoring network where the variables are monitoring wells. The objective was to identify monitoring wells that are important in predicting the dynamic variation in potentiometric head at a location. The technique is demonstrated through an application to the monitoring network of the Bangkok area. Principal component analysis was carried out for all the monitoring wells of the aquifer, and a ranking scheme based on the frequency of occurrence of a particular well as principal well was developed. The decision maker with budget constraints can now opt to monitor principal wells which can adequately capture the potentiometric head variation in the aquifer. This was evaluated by comparing the observed potentiometric head distribution using data from all available wells and wells selected using the ranking scheme as a guideline.
Natural Attenuation of Volatile Organic Compounds (VOCs) in the Leachate Plume of a Municipal Landfill: Using Alkylbenzenes as Process Probes
Authors: Eganhouse Robert P. , Cozzarelli Isabelle M. , Scholl Martha A. , Matthews Lara L. 
Published: December 2005

AbstractMore than 70 individual VOCs were identified in the leachate plume of a closed municipal landfill. Concentrations were low when compared with data published for other landfills, and total VOCs accounted for less than 0.1 % of the total dissolved organic carbon. The VOC concentrations in the core of the anoxic leachate plume are variable, but in all cases they were found to be near or below detection limits within 200 m of the landfill. In contrast to the VOCs, the distributions of chloride ion, a conservative tracer, and nonvolatile dissolved organic carbon, indicate little dilution over the same distance. Thus, natural attentuation processes are effectively limiting migration of the VOC plume. The distribution of C2–3‐benzenes, paired on the basis of their octanol‐water partition coefficients and Henry's law constants, were systematically evaluated to assess the relative importance of volatilization, sorption, and biodegradation as attenuation mechanisms. Based on our data, biodegradation appears to be the process primarily responsible for the observed attenuation of VOCs at this site. We believe that the alkylbenzenes are powerful process probes that can and should be exploited in studies of natural attenuation in contaminated ground water systems.
Distribution Functions of Spring Discharges According to Their Lithologies and the Influence of Lower Limit to Flow: An Example from Spain
Authors: Pérez Eugenic Sanz 
Published: December 2005

AbstractSpecific functions of distribution of the number of springs and of their contributions according to flow for each of nine lithological groups are established. These functions confirm the suitability of a general type of distribution (Sanz 1996), which is a borderline case of the lognormal distribution. The statistical methods proposed for the lithological types presented can be applied to any region if data on flow and Ethology of the aquifers drained by springs are available. These methods have been applied to Spain, a representative region with varied geology, climate and topography; 71.2% of spring flow is supplied by limestones, 19.17% by alluvial sediments and marls, 6.7% by conglomerates and sandstones, and 3% by slates, plutonic rocks, quartzites, and other groups. Springs with discharge rates exceeding 2000 L/s exist only in limestones. The majority of springs with low flow occur in marls. If we consider springs with flow greater than 0.5 L/s, alluvial sediments, sandstones, marls, and limestones have the greatest density of springs per surface area, although the average flow varies greatly from one lithology to the next. The cumulative estimated discharge and the estimated number of springs depend upon the definition of the lower limit of flow. For example, total discharge is reduced by 30% if we eliminate all springs with flow lower than 0.5 L/min.
Chemical Erosion of the Lilburn Cave System, Kings Canyon National Park, California
Authors: Abu‐Jaber Nizar , Hess John W. , Howcroft William 
Published: December 2005

AbstractMulti‐year Instrumental records for input, throughflow and output waters of the Lilburn Cave system provide control on denudation rates as they respond to seasonal and spatial variability. Data suggest that maximum denudation is in the late fall and early winter. This is when non‐snowmelt discharge is at Its maximum. At lower discharge rates the volume of water moving through the cave system Is the limiting control on the volume of denudation. During periods of snowmelt the limiting control is the rate at which the calcite dissolves. This is probably the result of water flowing through wider channels during these times. Based on instrumental measurements, there is considerable variation in terms of where denudation occurs inside the cave. The loci of dissolution change from year to year. This is to be expected in the dynamic environment of the cave where materials shift routinely. This variability should be studied over longer periods of time in order to more fully understand its extent. The relatively small area of carbonate exposure relative to the area of the drainage basin gives rise to relatively high denudation rates. The carbonate Is being removed at a rate of about 5000 metric tons per year, or at about 830 mm/y. This is about five times the rate reported in the humid karst regions of Malaysia. This information indicates that the relative proportion of carbonate in the drainage basin needs to be considered when trying to estimate denudation in other areas.
A Rapid Screening‐Level Method to Optimize Location of Infiltration Ponds
Authors: Fennemore G.G. , Davis Andy , Goss L. , Warrick A.W. 
Published: December 2005

AbstractA rapid‐screening technique was developed to identify Ethologies that best disperse artificial recharge via surface infiltration and minimize effects on ground water chemistry. The technique prospectively evaluates basin infiltration rates and water chemistry influences by integrating geotechnical, hydraulic, and water quality data with column test data and numerical modeling. The technique was validated using field data collected from surface infiltration basins designed to recharge ground water pumped from the Pipeline pit gold mine in Nevada. Observed recharge rates at these infiltration sites correlated most significantly with depth to groundwater, with basins in coarse‐grained lithologies performing better (0.45 to 0.85 m/day) than those with fine‐grained layers (<0.30 m/day). Observed water quality resulting from leaching of the previously unsaturated vadose zone showed a transitory (< six months) increase in solute concentrations followed by a decrease to baseline conditions, a phenomenon also observed in column tests that leached native soils with local ground water. Leaching of fine‐grained soils with evaporites resulted in greater solute concentrations (TDS > 2000 mg/L) than coarse‐grained soils (<1200 mg/L). The results of HYDRUS_2D simulations using the accumulated data as input were in agreement with observed ground water chemistry downgradient of the infiltration basins for a variety of lithologies. Sites for infiltration basins can be rapidly screened to include areas with greatest depth to groundwater and in coarsest alluvial sediments, and impact to ground water chemistry can be reliably predicted using computer modeling and column test results.
Sources of Salinity in Ground Water from Jericho Area, Jordan Valley
Authors: Marie Amer , Vengosh Avner 
Published: December 2005

AbstractOne of the major problems in the lower Jordan Valley is the increasing salinization (i.e., chloride content) of local ground water. The high levels of salinity limit the utilization of ground water for both domestic and agriculture applications. This joint collaborative study evaluates the sources and mechanisms for salinization in the Jericho area. We employ diagnostic geochemical fingerprinting methods to trace the potential sources of the salinity in (1) the deep confined subaquifer system (K2) of Lower Cenomanian age; (2) the upper subaquifer system (K1) of Upper Cenomanian and Turanian ages; and (3) the shallow aquifer system (Q) of Plio‐Pleistocene ages.The chemical composition of the saline ground water from the two Cenomanian subaquifers (K1 and K2) point to a single saline source with Na/CI ∼0.5 and Br/CI∼7 × 10−3. This composition is similar to that of thermal hypersaline springs that are found along the western shore of the Dead Sea (e.g., En Gedi thermal spring). We suggest that the increasing salinity in both K1 and K2 subaquifers is derived from mixing with deep‐seated brines that flow through the Rift fault system. The salinization rate depends on the discharge volume of the fresh meteoric water in the Cenomanian Aquifer. In contrast, the chemical composition of ground water from the Plio‐Pleistocene Aquifer shows a wide range of CI (100–2000 mg/L), Na/CI (0.4–1.0), Br/Cl (2–6 ×10−3), and SO4/CI (0.01–0.4) ratios. These variations, together with the high SO42‐, K+, and NO3− concentrations, suggest that the salinity in the shallow aquifer is derived from the combination of (1) upconing of deep brines as reflected by low Na/Cl and high Br/Cl ratios; (2) leaching of salts from the Lisan Formation within the Plio‐Pleistocene Aquifer, as suggested by the high SO42 concentrations; and (3) anthropogenic contamination of agriculture return flow and sewage effluents with distinctive high K+ (80 mg/L) and NO3−(80 mg/1) contents and low Br/Cl ratios (2 ×10−3). Our data demonstrates that the chemical composition of salinized ground water can be used to delineate the sources of salinity and hence to establish the conceptual model for explaining salinization processes.
Extension of Vedernikov's Graph for Seepage from Canals
Authors: Chahar Bhagu R. 
Published: December 2005

AbstractIn this investigation, using previously derived equations by Vedernikov and Morel‐Seytoux, closed‐form solutions have been obtained to compute the seepage from a slit and a strip. Also, a graphical solution as an extension of Vedernikov's graph has been presented for computing quantity of seepage from triangular, rectangular, and trapezoidal canals. The solution replaces approximately the cumbersome evaluation of improper integrals with unknown implicit transformation variables.
Influence of Transient Flow on Contaminant Biodegradation
Authors: Schirmer Mario , Durrant Graham C. , Molson John W. , Frind Emil O. 
Published: December 2005

AbstractThe rate of biodegradation in contaminated aquifers depends to a large extent on dispersive mixing processes that are now generally accepted to result from spatial variations in the velocity field. It has been shown, however, that transient flow fields can also contribute to dispersive mixing. The influence of transient flow on biodegrading contaminants is particularly important since it can enhance mixing with electron acceptors, further promoting the reactive process. Using numerical simulations, the effect of transient flow on the behavior of a biodegradable contaminant is evaluated here both with respect to the development of apparently large horizontal transverse dispersion and also with respect to enhanced mixing between the substrate (electron donor) and electron acceptor. The numerical model BIO3D, which solves for advective‐dispersive transport coupled with Monod‐type biodegradation of substrates in the presence of an electron acceptor, was used for the simulations. The model was applied in a two‐dimensional plan view mode considering a single substrate. Transient flow fields were found to yield larger apparent transverse dispersion because the longitudinal dispersivity also acts transverse to the mean flow direction. In the reactive case, the transient flow field increases substrate‐oxygen mixing, which in turn enhances the overall rate of biodegradation. The results suggest that in the case of moderate changes of flow directions, a steady‐state flow field can be justified, thereby avoiding the higher computational costs of a fully transient simulation. The use of a higher transverse horizontal dispersivity in a steady flow field can, under these conditions, adequately forecast plume development.