bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial and Temporal Characteristics of Saline Springs: Sea of Galilee, Israel
Authors: Rimmer Alon , Hurwitz Shaul , Gvirtzman Haim 
Published: August 2005

AbstractSpatial and temporal characteristics of the saline springs that emerge along the western shore of the Sea of Galilee (Lake Kinneret) are analyzed. Three groups of onshore springs (Tiberias, Fuliya, and Tabgha) and two groups of offshore springs (Barbutim and Maagan), contribute saline water to the lake with concentrations in the range of 300 to 18,000 mgCl/L, depending on location and season. It is well accepted that water emerging from these springs is a mixture of two endmembers: deep‐seated saline ground water and shallow, fresh circulating ground water. Temporal trends of discharge rates and of chloride (representing the deep saline aquifer) and nitrate (representing the shallow fresh water aquifer) concentrations within each group of springs are presented. Results show the proportions of the two water bodies while mixing are time dependent. Discharge and concentration peaks in Tabgha springs precede those in Fuliya and Tiberias springs by approximately two months. An analytical solution shows that in Tabgha, variations of these parameters are mainly controlled by recharge variations in the Galilee, and follow an exponential function. In Fuliya and Tiberias, variations of these parameters are mainly dependent on lake level, and follow a sine‐cosine function. The different patterns are attributed to different hydraulic properties of the discharge area.
Characterizing a Faulted Aquifer by Field Testing and Numerical Simulation
Authors: Allenaan Diana M. , Michel Frederick A. 
Published: August 2005

AbstractFaulted aquifers constitute one of the most complex geological environments for analysis and interpretation of hydraulic test data because of the inherent ability of faults to act not only as highly transmissive zones but also as hydraulic barriers. Previous studies of the fractured carbonate aquifer at Carleton University, Ottawa, Canada, characterized the flow regime as predominantly linear, but with limited radial nature, and undertook to analyze constant discharge test data using both radial and linear flow models. When used as direct input to a numerical model, the hydraulic parameters, calculated directly from hydraulic test data, were inappropriate and resulted in a poorly calibrated model. While our interpretation of the faulted aquifer remains linear‐radial in nature, parameter estimation by numerical simulation highlighted the presence of hydraulic barriers associated with the faults. These barriers are not readily apparent in the constant discharge test data and act to modify the hydraulic test curves at early to mid time, leading to incorrect estimates of the hydraulic parameters. This paper describes the conceptual model and the numerical approach, and demonstrates the importance of using transient simulations for model calibration.
Monitoring the Hydraulic Performance of a Containment System with Significant Barometric Pressure Effects
Authors: Hare Paul W. , Morse Ralph E. 
Published: August 2005

AbstractUnder certain circumstances, wells in unconfined aquifers can display significant water level fluctuations in response to changes in barometric pressure. This is illustrated by Hare and Morse (1997) at a site where a portion of the unconfined aquifer is isolated by a soil‐bentonite cutoff wall and clay cap. A relief well located within the containment system displays water level fluctuations that mirror barometric pressure changes. Water levels fluctuated 0.37 m in response to barometric pressure changes of 2.87 centimeters mercury (cm‐Hg), representing a barometric efficiency of 93.6%. As described in this paper, the short‐term variability in water level elevations inside the containment system had to be considered to develop a reliable post‐enhancement performance monitoring program. The approach that was ultimately selected involves correcting the water level elevations obtained in the relief well within the containment system for the effects of barometric pressure changes prior to comparison with the water level elevations in an observation well in the aquifer outside the system. The reliability of the post‐enhancement performance monitoring program is improved further by simply requiring that any decision to enhance the containment system be based on the water level measurements obtained during two consecutive months. Using this approach, the probability that the containment system's performance will erroneously be deemed unacceptable is low. The post‐enhancement performance monitoring program also requires no extra field work and does not involve any specialized equipment, which helps to keep operation and maintenance costs to a minimum.
Modeling Ground Water Flow and Radioactive Transport in a Fractured Aquifer
Authors: Pohll Greg , Hassan Ahmed E. , Chapman Jenny B. , Papelis Charalambos , Andricevic Roko 
Published: August 2005

AbstractThree‐dimensional numerical modeling is used to characterize ground water flow and contaminant transport at the Shoal nuclear test site in north‐central Nevada. The fractured rock aquifer at the site is modeled using an equivalent porous medium approach. Field data are used to characterize the fracture system into classes: large, medium, and no/small fracture zones. Hydraulic conductivities are assigned based on discrete interval measurements. Contaminants from the Shoal test are assumed to all be located within the cavity. Several challenging issues are addressed in this study. Radionuclides are apportioned between surface deposits and volume deposits in nuclear melt glass, based on their volatility and previous observations. Surface‐deposited radionuclides are released hydraulically after equilibration of the cavity with the surrounding ground water system, and as a function of ground water flow through the higher‐porosity cavity into the low‐porosity surrounding aquifer. Processes that are modeled include the release functions, retardation, radioactive decay, prompt injection, and ingrowth of daughter products. Prompt injection of radionuclides away from the cavity is found to increase the arrival of mass at the control plane but is not found to significantly impact calculated concentrations due to increased spreading. Behavior of the other radionuclides is affected by the slow chemical release and retardation behavior. The transport calculations are sensitive to many flow and transport parameters. Most important are the heterogeneity of the flow field and effective porosity. The effect of porosity in radioactive decay is crucial and has not been adequately addressed in the literature. For reactive solutes, retardation and the glass dissolution rate are also critical.
A Field Study of Nonequilibrium and Facilitated Transport of Cd in an Alluvial Gravel Aquifer
Authors: Pang Liping , Close Murray 
Published: August 2005

AbstractA natural‐gradient tracer experiment was conducted to study Cd transport in an alluvial gravel aquifer. Both a conservative tracer and Cd exhibited tailing in their breakthrough curves (BTCs), indicating the presence of nonequilibrium transport. Solute transport was evaluated using a three‐dimensional nonequilibrium analytical model, and the results were compared with those obtained from a previous laboratory study. At similar flow velocities, the field Cd data gave significantly lower retardation factors (R=7 to 30, median 22), higher fractions of instantaneous sorption sites (β), and greater mass transfer coefficients (ω) than the laboratory data because of a high degree of aquifer heterogeneity, the presence of preferential flow, and the larger transport scale in the field conditions. Multiple peaks in the Cd BTCs were observed due to bacteria‐facilitated and perhaps also colloid‐facilitated transport. The early peaks showed narrower, more symmetric shapes with higher concentrations than the later peaks, and compared well to those of the bacterial BTCs. The multiple peaks of the Cd BTCs imply that a significant fraction of Cd could travel with little, if any, retardation over a 20 to 40 m travel distance when Cd and bacteria coexist in a contamination event.
Modeling In Situ Iron Removal from Ground Water
Authors: Appelo C.A.J. , Drijver B. , Hekkenberg R. , de Jonge M. 
Published: August 2005

AbstractIn situ iron removal is conducted routinely in a number of European countries. A volume of oxygenated water is injected, and subsequently a larger volume of ground water can be pumped with a lower iron concentration than is found in native ground water. The underlying reaction mechanism has not been well described so far, and the process has not been modeled quantitatively. The essential problem is how the electron transfer takes place between the dissolved oxygen in injection water and the dissolved iron in ground water. An intermediate reaction step, involving cation exchange of ferrous iron and subsequent oxidation by oxygen of injection water, explains the efficiency increase during the initial cycles and the absence of clogging by precipitated iron‐oxyhydroxide. A hydrogeochemical transport model has been used to model column experiments with good results. The quantification of the reaction mechanism allows the assessment of operational conditions. For example, it can be shown that increasing the oxidant concentration in the injected water has an insignificant effect when exchangeable ferrous iron is low.
Risk‐Based Decision Analysis of Atmospheric Emission Alternatives to Reduce Ground Water Degradation on the European Scale
Authors: Wladis David , Rosen Lars , Kros Hans 
Published: August 2005

AbstractEnvironmental degradation due to emissions of sulfur dioxide, nitrate oxides, and ammonia from diffuse sources amounts to substantial costs to society and so do the alternatives to protect and restore the environment. Damage to ground water includes acidification, aluminum leaching, elevated concentrations of nitrate, and eutrophication. Monetary risk‐based decision analysis (on a national scale) is applied to compare alternative actions designed to protect ground water from further degradation. This decision analysis uses simulations of nitrate and aluminum concentrations over a 15 year period with two reduction scenarios for sulfur dioxide, nitrate oxides, and ammonia, and results in estimates of economic uncertainty. For each alternative, an objective function is estimated including the implementation costs, the economic risk associated with failure according to the selected decision criteria, and the economic benefits related to the implementation. The decision criteria are based on the European Community drinking water quality standards for nitrate and aluminum. The study aims at incorporating the hydrogeologic uncertainty resulting from the propagation of errors from data input to model output. A range of economic values has been applied to the ground water resource to study the sensitivity of the decision analysis to valuing ground water. The results indicate that higher reduction rates of the studied pollutants reduce the economic uncertainty but also lead to larger total costs. The study also indicates that the economic uncertainty may be equal to the total cost provided by the objective function. The contamination level of nitrate is much more responsive to the reduction scenarios than the aluminum concentration. For high, but not unrealistic, ground water valuing, the economic uncertainty makes the decision between the studied alternatives unclear.
Determining Karst Transmissivities with Inverse Modeling and an Equivalent Porous Media
Authors: Larocque M. , Banton O. , Ackerer P. , Razack M. 
Published: August 2005

AbstractFlow simulation is difficult to implement in heterogeneous media such as karst aquifers, primarily because the structure of the rock is extremely complex and usually unknown. The aim of this study was to verify the possibility of using inverse modeling and an equivalent porous media to identify transmissivities in a slightly karstified aquifer, the La Rochefoucauld karst (Charente, France). Different simulation scenarios were tested: using two spatial discretizations with different finite‐element cell sizes and using measured or interpolated heads. The inverse modeling was performed with the downscaling parameterization procedure, using a finite‐element representation of bidimensional ground water flow. The inverse modeling converged satisfactorily with all scenarios: head residuals were small and spring flow rates and the river/aquifer exchanges were adequately simulated. The scenario using small cells and measured heads generated a highly heterogeneous transmissivity field, indicating an overpa‐rameterization of the problem. The calibrated transmissivities and simulated heads of this scenario proved less reliable overall than those of the other scenarios. The use of interpolated heads generated more uniform transmissivities as a result of the head smoothing. A rotation of the initial parameter mesh showed that the scenarios using interpolated heads generate the most stable and reliable results. The scenarios with interpolated heads could therefore be used when head measurements are limited or are unevenly distributed over the aquifer. Overall, the calibrated transmissivities reproduced the entire range of transmissivities measured in the field using different methods. The results indicate that inverse modeling and an equivalent porous media can be used to determine transmissivities in a moderately karstified aquifer.
Hydrologic Setting of Two Interdunal Valleys in the Central Sand Hills of Nebraska
Authors: Gosselin David C. , Drda Steve , Harvey F. Edwin , Goeke Jim 
Published: August 2005

AbstractThe Sand Hills of Nebraska, one of the largest grass‐stabilized dune regions in the world, has nearly 5000 km2 of wetland environments and is one of the most productive waterfowl regions of the United States. Yet, the hydrology of the region is not well defined. This paper presents the results of a two‐and‐a‐half‐year study to characterize the hydrology of two distinctly different interdunal valleys within the Sand Hills. The valleys, located at the Gudmundsen Sand Hills Laboratory in the central Sand Hills, reflect the two major types of interdunal environments: dry, short grass valleys (the east valley) and subirrigated wet meadows (the west valley). In the west valley, ground water flows from west to east and there are significant, upward vertical gradients (0.005 to 0.045). In contrast, ground water in the east valley predominantly flows from west‐southwest to east‐northeast. Where vertical gradients exist, they are downward (0.0025 to 0.07). Therefore, the east valley is a “recharge” or flow‐through valley. Seasonal ground water table fluctuations indicate that net recharge is greatest between growing seasons. The relatively high topographic relief of the water table on the flanks of the west valley, resulting from higher topographic relief of the adjacent dunes, drives ground water discharge into the valley wetland, developing a local flow system. In contrast, the topography of the water table in the east valley, which is flanked by dunes with lower relief, is insufficient to generate a distinct local ground water flow system.
Sample Concentration Response to Laminar Wellbore Flow: Implications to Ground Water Data Variability
Authors: Martin‐Hayden James M. 
Published: August 2005

AbstractGround water data variability and sample repsentativeness ness are controlled by internal monitoring‐well flow and mixing, processes that require further investigation. By defining a representative sample using flow weighted average concentrations and modeling laminar wellbore flow, this study uses deviations from those representative concentrations as a measure of data variability. The laminar wellbore flow model relates ground water concentration and permeability distributions to the concentration response at a pump during purging or sampling. Given laminar wellbore flow, even if the concentrations within the well are not chemically altered, transient responses of concentrations to pumping lead to various amounts of variability depending on the screen length and position relative to hydraulic and chemical heterogeneities. In the simplest case, uniform inflow and inflowing concentrations, the concentration response to pumping is the same as the concentration response with thorough mixing. In more complex situations involving ground water concentration and permeability heterogeneities, pumped concentrations are controlled by those heterogeneities and wellbore flow. A model that describes concentration responses in the presence of linear heterogeneities allows a first‐order approximation of variability during pumping. Using field screening of concentration and permeability heterogeneities, this first‐order approximation can be used to design screen lengths that will limit the variability to study‐specific tolerances. In the case of existing wells, measurement of inflows and concentration variability will allow the assessment of variability during pumping. This investigation demonstrates that, in order to decipher sources of data variability, investigations must examine internal wellbore processes in detail as well as the relationships to external conditions characterized in the field.
Quantitative Estimates of the Uncertainty in the Evaluation of Ground Water Remediation Schemes
Authors: Copty Nadim K. , Findikakis Angelos N. 
Published: August 2005

AbstractDue to the natural heterogeneity of subsurface formations and to the often limited number of data, the definition of the physical and chemical parameters that govern flow and contaminant transport processes is normally characterized by a high level of uncertainty. Uncertainty in the relevant input parameters leads to uncertainty in modeling predictions, which may influence the selection of the optimal remedial alternative. This paper describes a statistical procedure for quantifying the uncertainty in modeling predictions made in support of the evaluation of ground water remediation designs. The hydraulic conductivity field is defined as a random spatial variable whose statistical structure is inferred from the available hydraulic conductivity data. Monte Carlo simulations are used to generate equiprobable multiple realizations of the hydraulic conductivity conditioned on the available hydraulic conductivity measurements. Using Bayes’theorem, probability‐based weights for each of the hydraulic conductivity realizations are estimated from “soft” data consisting of historical concentration data and contamination source information. The probability weights are expressed in terms of the simulated concentration distributions and the observed concentration data. Ground water flow and contaminant transport simulation models are then used to probabilistically evaluate and optimize ground water remediation schemes based on the statistical analysis of key model predictions, such as the probability of a particular part of the aquifer being within the capture zone of an extraction well, or the recovered mass of contaminants as a function of time.
Single‐Well Dipole Flow Tests: Parameter Estimation and Field Testing
Authors: Hvilshøj S. , Jensen K.H. , Madsen B. 
Published: August 2005

AbstractThe single‐well dipole method proposed by Kabala (1993) has been tested at a field site in Denmark representing an alluvial sandy unconfined aquifer. A critical review of the method has been carried out, and both the originally proposed analytical solutions to the problem and a numerical model have been tested. The analysis showed that the hydraulic parameters determined from the test data were correlated. Particularly it was shown that the vertical hydraulic conductivity and the specific storage could not be determined to an acceptable degree of reliability when based on the originally proposed analytical solution and on measurements from only the dipole well. Instead, an inverse numerical multilayer model was proposed for parameter identification using the pressure response data measured not only in the dipole well but also in adjacent piezometers. The vertical profiles of horizontal and vertical hydraulic conductivities obtained at the site using the single‐well dipole method were in accordance with the results from previous investigations that used other methods.
Field‐Scale Migration of Colloidal Tracers in a Fractured Shale Saprolite
Authors: McKay L.D. , Sanford W.E. , Strong J.M. 
Published: August 2005

AbstractA field‐scale tracer experiment carried out under natural gradient ground water flow conditions showed that colloids can be highly mobile in a fractured and highly weathered shale saprolite. Four colloidal tracers (0.100 μm fluorescent latex microspheres, bacteriophage strains PRD‐1 and MS‐2, and INA, a dead strain of Pseudemonas syringae), were introduced to a 6.4 m deep well, and concentrations of the tracers were monitored in the source well and in downgradient monitoring wells at distances of 2 to 35 m. All of the colloidal tracers were detected to distances of at least 13.5 m and two of the tracers (microspheres and INA) were detected in all of the downgradient wells. In most wells the colloidal tracers appeared as a “pulse”, with rapid first arrival (corresponding to 5 to 200 m/d transport velocity), one to six days of high concentrations, and then a rapid decline to below the detection limit. The colloids were transported at velocities of up to 500 times faster than solute tracers (He, Ne, and rhodamine‐WT) from previous tests at the site. This is believed to be largely due to greater diffusion of the solutes into the relatively immobile pore water of the fine‐grained matrix between fractures. Peak colloid tracer concentrations in the monitoring wells varied substantially, with the microspheres exhibiting the highest relative concentrations and hence the least retention. Rates of concentration decline with distance also varied, indicating that retention is not a uniform process in this heterogeneous material. Two of the tracers, INA and PRD‐1, reappeared in several monitoring wells one to five months after the initial pulse had passed, and the reappearance generally corresponds with increased seasonal precipitation. This is consistent with subsequent laboratory experiments that showed that colloid retention in these materials is sensitive to factors such as flow rate and ionic strength, both of which are expected to vary with the amount of precipitation.