bluuebunny/crossref_metadata_2025_split huggingface dataset:
Noble Gas and Major Element Constraints on the Water Dynamics in an Alpine Floodplain
Authors: Holocher Johannes , Matta Vijay , Aeschbach‐Hertig Werner , Beyerle Urs , Hofer Markus , Peeters Frank , Kipfer Rolf 
Published: December 2005

AbstractThe hydrogeological system of an ecologically sensitive alpine floodplain in the Valle di Blenio, Switzerland, was investigated using hydrochemical and 3H‐3He dating methods. Water samples from six wells and from different surface locations were analyzed. The analysis of the concentrations of major ions in conjunction with age determination by the 3H‐3He‐method allowed the main hydrological properties of the system to be consistently characterized. Two geochemically distinct water zones can be distinguished: Ca‐SO4‐dominated water from the main river and Ca‐HCO3‐dominated floodplain water. The floodplain water component characterizes the whole floodplain including the surficial hillslope drainage system. Within the ground water samples, two spatially and temporally different types of water can be determined. A younger (age < 1.5 years), less mineralized water is found in the upper part of the aquifer during the summer season. The underlying aquifer zone contains older and more highly mineralized water. However, the general hydrochemical characterization of both types of ground water is similar. In winter, the water ages increase with decreasing ground water levels. Because precipitation is stored temporarily in the snow cover, the contribution of the younger near‐surface ground water decreases, resulting in higher apparent water ages and higher mineralization in the upper zone of the aquifer. Water exchange between the main river and the ground water system is limited to ground water exfiltration from the shallow aquifer zone, whereas the hydrochemical separation of the deeper aquifer zone indicates the isolation of the deeper ground water from the main river.
Improved Calculations for Dewatered Cells in MODFLOW
Authors: Doherty John 
Published: December 2005

AbstractUse of the United States Geological Survey ground water flow model MODFLOW is often hampered by the occurrence of “dry cells.” While MODFLOW allows such cells to “rewet” in the course of a simulation, stability of the heads solution process is often problematical with rewetting functionality operative. In many cases of practical interest (particularly in mining applications), MOD‐FLOW simply fails to converge. However by making a number of adjustments to the MODFLOW Block‐Centered Flow package, it is possible to overcome this problem in many instances of MODFLOW deployment. These adjustments are such as to allow a layer to transmit water, albeit with a vastly reduced transmissivity, even if the water level in that layer is below its base. With these alterations MODFLOW cells can remain active even if they lie within the unsaturated zone.Testing of the code has demonstrated its ability to perform well in situations where performance of the unmodified MODFLOW is degraded by the necessity to dry and rewet cells. Comparison of heads calculated using the modified MODFLOW with those calculated using MODFLOW‐SURFACT (a MODFLOW‐based code developed by HydroGeoLogic Inc. that prevents the occurrence of dry cells through use of pseudo soil functions) reveals near‐identical results between the two codes. Comparison with analytical solutions of water table location also reveals near coincidence. An example of one such application is presented herein.
Analytical Studies on the Impact of Land Reclamation on Ground Water Flow
Authors: Jiao Jiu J. , Nandy Subhas , Li Hailong 
Published: December 2005

AbstractLand reclamation has been a common practice to produce valuable land in coastal areas. The impact of land reclamation on coastal environment and marine ecology is well recognized and widely studied. It has not been recognized yet that reclamation may change the regional ground water regime, which may in turn modify the coastal environment, flooding pattern, and stability of slopes and foundations. This paper represents the first attempt to examine quantitatively the effect of reclamation on ground water levels. Analytical solutions are developed to study the ground water change in response to reclamation based on two hypothetical models. In the first model, the ground water flow regime changes only in the hillside around the reclamation areas. In the second model, the ground water regime changes in the entire hill. Both models assume that the ground water flow is in a steady state and satisfies the Dupuit assumptions. Hypothetical examples are used to demonstrate how the ground water level, ground water divide and ground water submarine discharge will change with the scale and hydraulic conductivity of the reclamation materials. The results show that the change of ground water regime depends mainly on the length of the reclaimed area and the values of hydraulic conductivity of the reclaimed materials. It is also seen that the reclamation may impact not only the ground water regime near the coast areas around the reclamation site, but also that in the coast areas opposite the reclamation area. A reclamation site near Tseung Kwan O in the New Territories in Hong Kong, China, is used as a case study to discuss the possible modification of the ground water system caused by reclamation.
Characterization of Iron and Manganese Precipitates from an In Situ Ground Water Treatment Plant
Authors: Mettler S. , Abdelmoula M. , Hoehn E. , Schoenenberger R. , Weidler P. , von Gunten U. 
Published: December 2005

AbstractAquifer samples from the precipitation zone of an in situ iron and manganese removal plant that was operated for 10 years were analyzed for iron and manganese minerals. Measurements were performed by various chemical extraction techniques (5 M HC1,0.008 M Ti(III)‐EDTA, 0.114 M ascorbic acid), X‐ray diffraction and Mössbauer spectroscopy. Chemical extractions showed that iron was precipitated as ferric oxides, whereas manganese was not oxidized but deposited as Mn(II) probably within carbonates. The ferric oxides in particular accumulate preferentially in the smaller grain‐ size fractions. This tendency was observed to a lesser extent for manganese. X‐ray diffraction and Mössbauer spectroscopy showed that the ferric oxides were mainly crystalline (goethite, 50% to 100% of the iron). Ferrihydrite was found as well, but only as a minor fraction (≤ 12%). Pure manganese minerals were not found by X‐ray diffraction. The precipitated amounts of iron (5 to 27 μmol/g Fe as ferric oxide) and manganese (1 to 4 μmol/g Mn) during 10 years operation of the treatment plant agree with values that were estimated from operational parameters (9 to 31 μmol/g Fe and 3 to 6 μmol/g Mn). Considering the small amounts of precipitated iron and manganese, no long‐term risks of clogging of the aquifer are expected.
Dispersion in VLEACH and Similar Models
Authors: Sukop Michael C. 
Published: December 2005

AbstractVLEACH is a simple one‐dimensional vadose zone leaching model capable of simulating volatile chemical transport. There is no explicit dispersion coefficient in VLEACH. Solutions computed with it show dispersion due to diffusion in the gaseous phase and its interaction with the liquid phase and also due to the discretization of the problem domain. By turning off gaseous diffusion and comparing VLEACH results to the standard convection dispersion equation, this Computer Note illustrates that the effective dispersivity due to the discretization is equal to half of the model cell size.
Natural Attenuation Reactions at a Uranium Mill Tailings Site, Western U.S.A.
Authors: Zhu Chen , Anderson Greg M. , Burden David S. 
Published: December 2005

AbstractThis paper presents a modeling analysis of the geochemical evolution of a contaminated sandy aquifer at a uranium mill tailings site in the western United States. The tailings pond contains fluids having a pH of 1.5 to 3.5 and high levels of As, Be, Cd, Cr, Pb, Mo, Ni, Se, 226Ra, 228Ra, 230Th, 238U, and 234U. Seepage of tailings fluids into the aquifer has formed a low‐pH ground water plume. The reclamation plan is to install a low‐permeability cover on the tailings pond to stop the seepage and allow the plume to be attenuated by reactions with the aquifer matrix and flushed by uncontaminated upgradient ground water. To evaluate this reclamation scenario, ground water and sediment core samples were analyzed along one flowpath. Speciation‐solubility and mass‐transfer modeling revealed two sets of chemical reactions for acid seepage and flushing, respectively. The current concentrations and distribution of ground water constituents can be interpreted as being controlled by stepwise pH‐buffer reactions with calcite, amorphous aluminum hydroxide, and amorphous iron hydroxides. These buffer reactions divide the aquifer into zones of near‐constant pH, separated by interface zones. For the flushing stage, it is predicted that reactions with surface‐bound species will dominate the reaction paths, and more pore volumes are required to neutralize the plume than predicted by models that do not consider surface reactions. Direct mineralogical and surface analysis is needed to substantiate this assertion.
A Reassessment of Ground Water Flow Conditions and Specific Yield at Borden and Cape Cod
Authors: Grimestad Garry 
Published: December 2005

AbstractRecent widely accepted findings respecting the origin and nature of specific yield in unconfined aquifers rely heavily on water level changes observed during two pumping tests, one conducted at Borden, Ontario, Canada, and the other at Cape Cod, Massachusetts. The drawdown patterns observed during those tests have been taken as proof that unconfined specific yield estimates obtained from long‐duration pumping tests should approach the laboratory‐estimated effective porosity of representative aquifer formation samples. However, both of the original test reports included direct or referential descriptions of potential supplemental sources of pumped water that would have introduced intractable complications and errors into straightforward interpretations of the drawdown observations if actually present. Searches for evidence of previously neglected sources were performed by screening the original drawdown observations from both locations for signs of diagnostic skewing that should be present only if some of the extracted water was derived from sources other than main aquifer storage. The data screening was performed using error‐guided computer assisted fitting techniques, capable of accurately sensing and simulating the effects of a wide range of non‐traditional and external sources. The drawdown curves from both tests proved to be inconsistent with traditional single‐source pumped aquifer models but consistent with site‐specific alternatives that included significant contributions of water from external sources. The corrected pumping responses shared several important features. Unsaturated drainage appears to have ceased effectively at both locations within the first day of pumping, and estimates of specific yield stabilized at levels considerably smaller than the corresponding laboratory‐measured or probable effective porosity. Separate sequential analyses of progressively later field observations gave stable and nearly constant specific yield estimates for each location, with no evidence from either test that more prolonged pumping would have induced substantially greater levels of unconfined specific yield.
Correlation of Lineaments to Ground Water Inflows in a Bedrock Tunnel
Authors: Mabee Stephen B. , Curry Patrick J. , Hardcastle Kenneth C. 
Published: December 2005

AbstractLineaments derived from three image types (1:80,000 black and white, 1:58,000 color infrared, and 1:250,000 side‐looking airborne radar) were compared to water‐bearing features within a 9.6 km section of tunnel being constructed through foliated crystalline metamorphic bedrock in a glaciated region of eastern Massachusetts. Lineaments drawn by three observers during two independent trials (N = 9137) were reduced to three sets (one per image type) of coincident lineaments (N = 794). Thirty‐five coincident lineaments crossed the tunnel. Nineteen discrete flow zones, each producing ≥ 19 L/min, were identified in the tunnel and used to quantify the reliability of lineament analysis as a method of predicting water‐bearing features in glaciated metamorphic rocks.Thirteen (68%) of the flow zones correlate with coincident lineaments, six zones correlate with more than one image type, and one zone correlates with all three image types. Overall, without additional corroborating evidence, it is difficult to interpret in advance which lineaments will result in a successful correlation with water‐producing zones in the subsurface and which ones will not. Most of the observed flow (80%) correlates with northwest‐trending coincident lineaments; however, the majority of the flow (67%) associated with these lineaments is produced from structures that strike to the north or northeast. In addition, only 15 of the 35 coincident lineaments correlate with the flow zones, indicating that 20 lineaments are not associated with any appreciable flow. Six flow zones are undetected by the lineament analysis.
Redox Patterns and Trace‐Element Behavior in the East Midlands Triassic Sandstone Aquifer, U.K.
Authors: Smedley Pauline L. , Edmunds W. Mike 
Published: December 2005

AbstractRedox conditions exercise important controls on water chemistry in the red‐bed Sherwood Sandstone Aquifer of the English East Midlands. A distinct redox boundary exists some 3 to 5 km downgradient of the onset of confined conditions, defined by a 300 mV drop in Eh and complete reaction of dissolved oxygen. The aerobic aquifer contains polluted water with high nitrate concentrations and organic carbon significantly above background concentrations (> 0.2 mg/L). Concentrations of Fe, Mn, and Mo are highest in reducing ground water. As, Sb, Se, and U show a residence‐time‐dependent increase in aerobic ground water, but are much lower under reducing conditions. Iron oxides are believed to play a key role in determining the spatial patterns in many of these trace elements as a result of Eh‐ and pH‐controlled sorption/desorption reactions, as well as some reductive dissolution in the confined aquifer. Fresh ground water persists in the confined aquifer to approximately 30 km downgradient of the redox boundary. However, SO4 concentrations increase progressively along the flowline as a result of the dissolution of gypsum or anhydrite. Concentrations of available organic carbon are low in ground water (1 mg/L or less) and are also likely to be limited in the sediments; conditions are insufficiently reducing for significant sulphate reduction to have taken place. Only in the extreme down‐gradient (eastern) part of the aquifer do conditions become sufficiently reducing with some evidence of sulphate reduction. In this part of the aquifer, ground water is more saline (TDS values up to 10 g/L) and is believed to be composed substantially of older formation water. This has distinctive concentrations of several redox‐influenced trace elements, with relatively high Fe, Mn, As, and Sb, occasional high Cr, and low Mo relative to the confined fresh ground water upgradient.
A Permeable Reactive Barrier for Treatment of Heavy Metals
Authors: Ludwig Ralph D. , McGregor Rick G. , Blowes David W. , Benner Shawn G. , Mountjoy Keith 
Published: December 2005

AbstractHistorical storage of ore concentrate containing sulfide minerals at an industrial site in British Columbia, Canada, has resulted in widespread contamination of the underlying soil and ground water. The oxidation of sulfide minerals has released significant quantities of heavy metals, including Cu, Cd, Co, Ni, and Zn, into the ground water. A pilot‐scale, compost‐based, sulfate‐reducing permeable reactive barrier was installed in the path of the dissolved heavy‐metal plume. The permeable reactive barrier uses sulfate‐reducing bacteria to promote precipitation of heavy metals as insoluble metal sulfides. Monitoring over a 21‐month period indicated significant removal of heavy metals within the barrier. Copper concentrations declined from a mean concentration of 3630 μg/L in the influent to a mean concentration within the barrier of 10.5 μg/L, Cd from 15.3 μg/L to 0.2 μg/L, Co from 5.3 μg/L to 1.1 μg/L, Ni from 131 μg/L to 33.0 μg/L, and Zn from 2410 μg/L to 136 μg/L. Within the lower half of the barrier where tidal influences were more limited and sulfate‐reducing conditions were better maintained, mean treatment levels of 2.9 μg/L (Cu), 0.1 μg/L (Cd), 0.4 μg/L (Co), 2.7 μg/L (Ni), and 6.3 μg/L (Zn) were observed.
Fluid Flow and Solute Migration Within the Capillary Fringe
Authors: Silliman Stephen E. , Berkowitz Brian , Simunek Jirka , van Genuchten M. Th. 
Published: December 2005

AbstractLaboratory experiments involving both homogeneous and heterogeneous porous media are used to demonstrate that fluid flow and solute transport will occur regularly in the capillary fringe (CF), including both vertical (upward as well as downward) and horizontal flow velocities. Horizontal flow above the water table appears to be limited primarily to the region of high water saturation (i.e., the CF), an observation supported by numerical modeling and consistent with the literature. Beyond observations presented in prior literature, it was observed that exchange of water within the CF with water below the water table is active, with flux both from the CF downward across the water table and from the region below the water table, upward into the CF. This flux is enhanced by the presence of physical heterogeneity. These findings strongly contrast the common conceptualization of predominantly downward vertical fluid flow through the unsaturated zone, with transition to fully three‐dimensional flow only below the water table. Based on these observations, it is suggested that the CF may affect, far more significantly than is usually assumed, the natural geochemical and microbial conditions present in the region of transition from unsaturated to saturated ground water flow.
Generating MODFLOW Grids from Boundary Representation Solid Models
Authors: Jones Norman L. , Budge Trevor J. , Lemon Alan M. , Zundel Alan K. 
Published: December 2005

AbstractComplex stratigraphy can be difficult to simulate in MODFLOW models. MODFLOW uses a structured grid that requires that each grid layer be continuous throughout the model domain. This makes it difficult to explicitly represent common features such as pinchouts and embedded seams in a MODFLOW model. In this paper, we describe a method for automatically generating MODFLOW‐compatible grids from boundary‐representation solid models. Solid models are data structures developed originally for computer‐aided design applications that define the geometry of three‐dimensional objects. Solid models can be used to represent arbitrarily complex stratigraphy. The elevations defined by the solids are then extracted from the solids in a manner that preserves the continuous‐layer requirement imposed by MODFLOW. Two basic approaches are described: The first method adjusts the MODFLOW grid dimensions (layer elevations) to fit the solid model boundaries, and the second method creates a regular MODFLOW grid and adjusts the material properties to match the changes in stratigraphy. One of the main benefits of using solid models to define stratigraphy for MODFLOW models is that it provides a grid‐independent definition of the layer elevations that can be used to immediately re‐create the MODFLOW grid geometry after any change to the grid resolution.
Nonparametric Method for Transmissivity Distributions Along Boreholes
Authors: Fransson Åsa 
Published: December 2005

AbstractThe transmissivities of individual fractures along a borehole are difficult to obtain unless each fracture is tested. To estimate a fracture‐transmissivity distribution from section transmissivities, a method was developed based on fixed‐interval‐length transmissivities and the corresponding number of fractures for each interval. The method is nonparametric and iterative, and the fractures are viewed as two‐dimensional features, in which the total transmissivity of a borehole is equal to the sum of individual fracture transmissivities. Initially, a linear a priori assumption of the transmissivity distribution is made, and from this a so‐called mean transmissivity function is derived. Subsequently, the mean transmissivity of the Nj fractures within a section, j, of the borehole is estimated, and the same value of the mean transmissivity function represents Nj‐ possible fracture transmissivities from the initial distribution. This is repeated for each borehole section, and, eventually, all fracture transmissivities are sorted to give the next iteration's transmissivity distribution and the corresponding mean transmissivity function. Finally, the distributions converge, yielding a possible fracture‐transmissivity distribution. The method was verified for a synthetic data sample and then tested on a sample from a borehole at the Aspo Hard Rock Laboratory, Sweden. For the synthetic data, the method gave a distribution that was fairly close to the original one; for the Aspo data, 15% of the fractures had a transmissivity larger than the measurement limit (1×10−9 m2/sec), and these transmissivities follow a log‐normal distribution.
Prediction of Diffusion Coefficients in Porous Media Using Tortuosity Factors Based on Interfacial Areas
Authors: Saripalli K. Prasad , Serne R. Jeffery , Meyer Philip D. , McGrail B. Peter 
Published: December 2005

AbstractDetermination of aqueous phase diffusion coefficients of solutes through porous media is essential for understanding and modeling contaminant transport. Prediction of diffusion coefficients in both saturated and unsaturated zones requires knowledge of tortuosity and constrictivity factors. No methods are available for the direct measurement of these factors, which are empirical in their definition. In this paper, a new definition for the tortuosity factor is proposed, as the real to ideal interfacial area ratio. We define the tortuosity factor for saturated porous media (τs) as the ratio S/So (specific surface of real porous medium to that of an idealized capillary bundle). For unsaturated media, tortuosity factor (τa) is defined as 2awla (ratio of the specific air‐water interfacial area of real and the corresponding idealized porous medium). This tortuosity factor is suitably measured using sorptive tracers (e.g., nitrogen adsorption method) for saturated media and interfacial tracers for unsaturated media. A model based on this new definition of tortuosity factors, termed the interfacial area ratio (IAR) model, is presented for the prediction of diffusion coefficients as a function of the degree of water saturation. Diffusion coefficients and diffusive resistances measured in a number of saturated and unsaturated granular porous media, for solutes in dilute aqueous solutions, agree well with the predictions of the IAR model. A comparison of permeability of saturated sands estimated based on τs and the same based on the Kozeny‐Carman equation confirm the usefulness of the τs parameter as a measure of tortuosity.