bluuebunny/crossref_metadata_2025 huggingface dataset:
Biology of estrogens in skin: implications for skin aging
Authors: Verdier‐Sévrain Sylvie , Bonté Frédéric , Gilchrest Barbara
Published: December 2005

Abstract:  Estrogens have a profound influence on skin. The relative hypoestrogenism that accompanies menopause exacerbates the deleterious effects of both intrinsic and environmental aging. Estrogens clearly have a key role in skin aging homeostasis as evidenced by the accelerated decline in skin appearance seen in the perimenopausal years. Estrogens improve skin in many ways. Among these, they increase collagen content and skin thickness and improve skin moisture. However, despite the knowledge that estrogens have such important effects on skin, the cellular and subcellular sites and mechanisms of estrogen action are still poorly understood. Estrogen receptors (ERs) have been detected in skin, and recent studies suggest that estrogens exert their effect in skin through the same molecular pathways used in other non‐reproductive tissues. Although systemic hormone replacement therapy (HRT) has been used for many years, recent trials have reported a significant increased risk of breast cancer and other pathologies with this treatment. This has led to reconsider the risks and benefits of HRT. For this reason, systemic HRT cannot be recommended today to treat skin aging. Currently, intensive research is conducted to develop new drugs called selective ER modulators (SERMs). These drugs exert mixed estrogenic and antiestrogenic effects depending on the tissue and cell type. One might expect in the future such a drug targeting specifically the skin without systemic side effects.
Structural variation of the monoamine oxidase A gene promoter repeat polymorphism in nonhuman primates
Authors: Wendland J. R. , Hampe M. , Newman T. K. , Syagailo Y. , Meyer J. , Schempp W. , Timme A. , Suomi S. J. , Lesch K. P.
Published: December 2005

By conferring allele‐specific transcriptional activity on the monoamine oxidase A (MAOA) gene in humans, length variation of a repetitive sequence [(variable number of tandem repeat (VNTR)] in the MAOA promoter influences a constellation of personality traits related to aggressive and antisocial behavior and increases the risk of neurodevelopmental and psychiatric disorders. Here, we have analyzed the presence and variability of this MAOA promoter repeat in several species of nonhuman primates. Sequence analysis of MAOA's transcriptional control region revealed the presence of the VNTR in chimpanzee (Pan troglodytes), bonobo (Pan paniscus), gorilla (Gorilla gorilla), orangutan (Pongo pygmaeus), rhesus macaque (Macaca mulatta) and Gelada baboon (Theropithecus gelada). The majority of P. troglodytes and P. paniscus showed a single repeat with a sequence identical to the VNTR sequence in humans. In contrast, analyses of the remaining species revealed shorter sequences similar to the first 18 bp of human VNTR. Compared with other nonhuman primates, the VNTR sequence of M. mulatta showed the highest length variability with allele frequencies of 35, 25 and 40% for the five, six and seven repeat variants, respectively. The extent of variability of the MAOA promoter repeat in both rhesus monkeys and humans supports the notion that there may be a relationship between functional MAOA expression and aggression‐related traits in humans and rhesus macaque populations.
Environmental bias? Effects of housing conditions, laboratory environment and experimenter on behavioral tests
Authors: Lewejohann L. , Reinhard C. , Schrewe A. , Brandewiede J. , Haemisch A. , Görtz N. , Schachner M. , Sachser N.
Published: December 2005

Behavioral testing does not always yield similar results when replicated in different laboratories, and it usually remains unclear whether the variability in results is caused by different laboratory environments or different experimenters conducting the tests. In our study, we applied a systematic variation of housing conditions, laboratories and experimenters in order to test the influence of these variables on the outcome of behavioral tests. We wanted to know whether known effects of different housing conditions on behavior can be demonstrated regardless of the respective laboratory and experimenters. In this study, we compared the behavior of mice kept under enriched housing conditions with mice kept in unstructured cages regarding their exploratory, locomotor and anxiety‐related behavior in the barrier test, in the open‐field test and in the elevated plus‐maze test. Experiments were conducted by six different persons in two different laboratories. In spite of an extensive protocol standardizing laboratory environment, animal maintenance and testing procedures, significant differences in absolute values between different laboratories as well as between different experimenters were noticed in the barrier test and in the elevated plus‐maze test but not in the open‐field test. However, with regard to the differences between enriched and unstructured housing conditions, overall consistent results were achieved by different experimenters in both laboratories. We conclude that the reliability of behavioral phenotyping is not challenged seriously by experimenter and laboratory environment as long as appropriate standardizations are met and suitable controls are involved.
Distinct genetic influences on grammar and phonological short‐term memory deficits: evidence from 6‐year‐old twins
Authors: Bishop D. V. M. , Adams C. V. , Norbury C. F.
Published: December 2005

Children with language impairments have limitations of phonological short‐term memory (STM) and have distinctive problems with certain aspects of grammar. Both deficits have been proposed as phenotypic markers of heritable language impairment. We studied 173 twin pairs, selected to be over‐representative of children with risk of developmental language impairment, using a battery of standardized language and intelligence tests, a test of nonword repetition to index phonological STM and two elicitation tasks to assess use of verb tense marking. As predicted, the phonological STM and the verb tense measures both discriminated children with risk of language impairment from low risk children, and DeFries–Fulker analysis showed that impairments on both tasks were significantly heritable. However, there was minimal phenotypic and etiological overlap between the two deficits, suggesting that different genes are implicated in causing these two kinds of language difficulty. From an evolutionary perspective, these data are consistent with the view that language is a complex function that depends on multiple underlying skills with distinct genetic origins.
Microcebus murinus: a useful primate model for human cerebral aging and Alzheimer's disease?
Authors: Bons N. , Rieger F. , Prudhomme D. , Fisher A. , Krause K.‐H.
Published: December 2005

Age‐associated dementia, in particular Alzheimer's disease (AD), will be a major concern of the 21st century. Research into normal brain aging and AD will therefore become increasingly important. As for other areas of medicine, the availability of good animal models will be a limiting factor for progress. Given the complexity of the human brain, the identification of appropriate primate models will be essential to further knowledge of the disease. In this review, we describe the features of brain aging and age‐associated neurodegeneration in a small lemurian primate, the Microcebus murinus, also referred to as the mouse lemur. The mouse lemur has a relatively short life expectancy, and animals over 5 years of age are considered to be elderly. Among elderly mouse lemurs, the majority show normal brain aging, whereas approximately 20% develop neurodegeneration. This Microcebus age‐associated neurodegeneration is characterized by a massive brain atrophy, abundant amyloid plaques, a cytoskeletal Tau pathology and a loss of cholinergic neurons. While elderly mouse lemurs with normal brain aging maintain memory function and social interaction, animals with age‐associated neurodegeneration lose their cognitive and social capacities and demonstrate certain similarities with age‐associated human AD. We conclude that M. murinus is an interesting primate model for the study of normal brain aging and the biochemical dysfunctions occurring in age‐associated neurodegeneration. Mouse lemurs might also become an increasingly important model for the development of novel treatments in this domain.
Progressive cognitive decline in a transgenic mouse model of Alzheimer's disease overexpressing mutant hAPPswe
Authors: Middei S. , Daniele S. , Caprioli A. , Ghirardi O. , Ammassari‐Teule M.
Published: December 2005

The possibility of detecting progressive changes in cognitive function reflecting the spatio‐temporal pattern of β‐amyloid peptide (Aβ) deposition was investigated in Tg2576 mice overexpressing the human mutant amyloid precursor protein (hAPP). Here, we show that at 7 months of age, Tg2576 mice exhibited a selective deficit in hippocampus‐based operations including a defective habituation of object exploration, a lack of reactivity to spatial novelty and a disruption of allothetic orientation in a cross‐shaped maze. At 14 months of age, Tg2576 mice displayed a more extended pattern of behavioral abnormalities, because they failed to react to object novelty and exclusively relied on motor‐based orientation in the cross‐shaped maze. However, an impaired reactivity to spatial and object novelty possibly reflecting age‐related attention deficits also emerged in aged wild‐type mice. These findings further underline that early cognitive markers of AD can be detected in Tg2576 mice before Aβ deposition occurs and suggest that as in humans, cognitive deterioration progressively evolves from an initial hippocampal syndrome to global dementia because of the combined effect of the neuropathology and aging.
Comparison of the Living Conditions of Adults with Intellectual Disabilities in a Swedish County and in the General Population
Authors: Umb‐Carlsson Õie , Sonnander Karin
Published: December 2005

Abstract  This study describes the living conditions of adults with intellectual disabilities (ID) as compared to the general population. People with ID born in Uppsala County between 1959 and 1974 constituted the study population (n = 213). Proxy questionnaire reports and national welfare statistics were used to collect data. The results demonstrated differences in living conditions between the two groups, particularly regarding employment and social life. Whereas people in general had paid employment, most people with ID were provided supported daily activities and their main income source was a disability benefit from the social insurance system. Typically, people with ID lived in a more restricted social environment and had more limited social life than the general population. The social network of people with ID was mainly bulit on family ties (parents and siblings); caregiver‐care receiver relations and included few chosen friends (with or without disability). The authors suggest that the way in which help and support is provided by professionals using the special and generic help systems may actually prevent or restrain individuals with ID from influencing their own life course.
Occurrence of glucosylsucrose [α‐D‐glucopyranosyl‐ (1→2)‐α‐D‐glucopyranosyl‐(1→2)‐β‐D‐fructofuranoside] and glucosylated homologues in cyanobacteria
Authors: Fischer Daniela , Geyer Armin , Loos Eckhard
Published: December 2005

Little is known about the structure and function of oligosaccharides in cyanobacteria. In this study, a new class of saccharides from Nostoc was identified by MS and NMR techniques, consisting of α‐d‐glucopyranosyl‐(1→2)‐[α‐d‐glucopyranosyl‐(1→2)]n‐β‐d‐fructofuranosides ranging from the trisaccharide (n = 1) to decasaccharide (n = 8). In Nostoc ellipsosporum the cell content of saccharides increased 10–20‐fold after heat stress (1 day, 40 °C) or during prolonged cultivation. Under these conditions the abundance of homologues of higher molecular mass (> pentasaccharide) increased and finally exceeded that of homologues of lower molecular mass including sucrose. Total intracellular content of the saccharides after heat stress was 5–10 mg·(g dry weight)−1 corresponding to intracellular concentrations of 0.25–0.5% (w/v). A possible role of the oligosaccharides identified is in the protection of enzymes against heat inactivation. Whereas amylase from Nostoc was only weakly protected by the decasaccharide, α‐amylase from porcine pancreas was more efficiently stabilized by the octasaccharide and decasaccharide. Evidence is presented for the widespread occurrence of the newly identified saccharides in cyanobacteria. The results are discussed including previous reports on cyanobacterial oligosaccharides and with respect to possible functions of these compounds in the living cell.
The natural mutation by deletion of Lys9 in the thrombin A‐chain affects the pKa value of catalytic residues, the overall enzyme's stability and conformational transitions linked to Na+ binding
Authors: De Cristofaro Raimondo , Carotti Andrea , Akhavan Sepideh , Palla Roberta , Peyvandi Flora , Altomare Cosimo , Mannucci Pier Mannuccio
Published: December 2005

The catalytic competence of the natural thrombin mutant with deletion of the Lys9 residue in the A‐chain (ΔK9) was found to be severely impaired, most likely due to modification of the 60‐loop conformation and catalytic triad geometry, as supported by long molecular dynamics (MD) simulations in explicit water solvent. In this study, the pH dependence of the catalytic activity and binding of the low‐molecular mass inhibitor N‐α‐(2‐naphthylsulfonyl‐glycyl)‐4‐amidinophenylalanine‐piperidine (α‐NAPAP) to the wild‐type (WT) and ΔK9 thrombin forms were investigated, along with their overall structural stabilities and conformational properties. Two ionizable groups were found to similarly affect the activity of both thrombins. The pKa value of the first ionizable group, assigned to the catalytic His57 residue, was found to be 7.5 and 6.9 in ligand‐free ΔK9 and WT thrombin, respectively. Urea‐induced denaturation studies showed higher instability of the ΔK9 mutant compared with WT thrombin, and disulfide scrambling experiments proved weakening of the interchain interactions, causing faster release of the reduced A‐chain in the mutant enzyme. The sodium ion binding affinity was not significantly perturbed by Lys9 deletion, although the linked increase in intrinsic fluorescence was lower in the mutant. Essential dynamics (ED) analysis highlighted different conformational properties of the two thrombins in agreement with the experimental conformational stability data. Globally, these findings enhanced our understanding of the perturbations triggered by Lys9 deletion, which reduces the overall stability of the molecule, weakens the A–B interchain interactions, and allosterically perturbs the geometry and protonation state of catalytic residues of the enzyme.
Sorption and Intraparticle Diffusion of Fluorescent Dyes with Consolidated Aquifer Media
Authors: Sabatini David A.
Published: December 2005

Sorption of two fluorescent dyes (fluorescein and sulforhodamine B) was evaluated with two oppositely charged, consolidated aquifer materials (sandstone and limestone). Fluorescein, which has an anionic carboxylic group, experienced negligible sorption onto negatively charged sandstone and sorbed much less than sulforhodamine B, with its two sulfonic groups, onto positively charged limestone. The cationic charge on sulforhodamine B caused it to adsorb onto negatively charged sandstone. These results validate and extend previous research with pure mineral surfaces (alumina and silica). Sorption kinetic rates decreased with increasing particle size, which is consistent with diffusion‐limited intraparticle sorption. Tortuosity factors were determined by fitting a diffusion ‐limited intraparticle sorption model to kinetic data for one particle size (all other parameters being determined independently). This tortuosity factor, which was consistent with Archie's law‐based estimates and other independently determined parameters, was subsequently used to predict kinetic adsorption results for a second particle size. Close agreement between experimental data and model predictions corroborated intraparticle diffusion‐limited sorption as an important process. Diffusion‐limited sorption can impact dye transport in unconsolidated grains having internal porosity or consolidated or fractured media having dual porosity. These results thus demonstrate the importance of understanding both the equilibrium and kinetics of dye sorption when designing and interpreting tracer studies.
Effects of Heterogeneity in Aquifer Permeability and Biomass on Biodegradation Rate Calculations—Results from Numerical Simulations
Authors: Scholl Martha A.
Published: December 2005

Numerical simulations were used to examine the effects of heterogeneity in hydraulic conductivity (K) and intrinsic biodegradation rate on the accuracy of contaminant plume‐scale biodegradation rates obtained from field data. The simulations were based on a steady‐state BTEX contaminant plume undergoing biodegradation under sulfate‐reducing conditions, with the electron acceptor in excess. Biomass was either uniform or correlated with K to model spatially variable intrinsic biodegradation rates. A hydraulic conductivity data set from an alluvial aquifer was used to generate three sets of 10 realizations with different degrees of heterogeneity, and contaminant transport with biodegradation was simulated with BIOMOC. Biodegradation rates were calculated from the steady‐state contaminant plumes using decrease in concentration with distance downgradient and a single flow velocity estimate, as is commonly done in site characterization to support the interpretation of natural attenuation. The observed rates were found to underestimate the actual rate specified in the heterogeneous model in all cases. The discrepancy between the observed rate and the “true” rate depended on the ground water flow velocity estimate, and increased with increasing heterogeneity in the aquifer. For a lognormal K distribution with variance of 0.46, the estimate was no more than a factor of 1.4 slower than the true rate. For an aquifer with 20% silt/clay lenses, the rate estimate was as much as nine times slower than the true rate. Homogeneous‐permeability, uniform‐degradation rate simulations were used to generate predictions of remediation time with the rates estimated from the heterogeneous models. The homogeneous models generally overestimated the extent of remediation or underestimated remediation time, due to delayed degradation of contaminants in the low‐K areas. Results suggest that aquifer characterization for natural attenuation at contaminated sites should include assessment of the presence and extent of, and contaminant concentrations in, low‐permeability areas of an aquifer.
Recharge and Preservation of Laurentide Glacial Melt Water in the Canadian Shield
Authors: Clark Ian D. , Douglas Malcolm , Raven Kenneth , Bottomley Dennis
Published: December 2005

Ground water inflows to drifts ranging from 700 to 1615 m below ground surface at the Con Mine, Yellowknife, Northwest Territories, Canada, were used to study deep hydrogeological flow regimes in Shield terrain. Salinity trends are due to mixing between low‐TDS ground water and deep Ca(Na)‐C1 brines (>290 g/L) likely derived from Devonian sea water. C1‐−δ18O relationships demonstrate that all inflows are a mixture of three distinct components: modern meteoric ground water (δ18O ∼−18.9 ± 0.1%o), brine (δ18O ∼−10%o), and an isotopically depleted water (δ18O ∼−28%o). The origin of this third endmember is attributed to glacial melt water injected into the subsurface during ablation of the Laurentide Ice Sheet at ca. 10 ka. A mechanism is proposed where high hydrostatic pressure in the ablation zone imposes strong downward gradients beneath the ice sheet margin. Numerical simulation with the SWIFT II finite‐difference code recreates the observed salinity gradients within a modeled 50‐year interval, corresponding with the rate of retreat of the ice sheet across the landscape at this time. The persistence of this melt water in the subsurface for some 10,000 years following retreat of the ice and decay of the steep hydraulic gradients highlights the importance of gradient, in addition to permeability, as a major control on ground water flow and transport in deep crystalline settings.
Impacts of Unsaturated Zone Properties on Oxygen Transport and Aquifer Reaeration
Authors: Neale C. Nelson , Hughes Joseph B. , Ward C.H.
Published: December 2005

This study investigated the unsaturated zone properties that affect ground water reaeration (i.e., the diffusive flux of oxygen through the unsaturated zone and into an aquifer system). Laboratory column experiments were undertaken to quantify oxygen flux into anaerobic ground water as a function of soil type, soil water content, soil oxygen demand, and unsaturated zone thickness. Soils used in these studies included coarse sand, sand, loamy fine sand, fine sandy loam, silt, silty clay loam, bentonite, kaolin, and peat. The results showed that reaeration flux rates ranging from 11,000 to 12,000 mg/m2‐day were possible under conditions typical of the natural environment. Soil water content provided the greatest resistance to oxygen transport in the unsaturated zone while the remaining factors of soil type, soil oxygen demand, and unsaturated zone thickness did not significantly inhibit reaeration flux into ground water. An unsaturated zone transport model based on Fick's second law and gas‐liquid interfacial mass transport was developed and showed good agreement with the experimental results derived from the column studies. The results of this study suggest that unsaturated zone reaeration of anaerobic ground water may be a contributing factor in controlling the steady–state size and shape of hydrocarbon plumes and incorporating reaeration into ground water models—based on unsaturated zone properties—may allow for a more accurate representation of bioattenuation reactions taking place in subsurface environments.
Geostatistical Inversion of Cross‐Hole Pumping Tests for Identifying Preferential Flow Channels Within a Shear Zone
Authors: Meier Peter M. , Medina Agustin , Carrera Jesús
Published: December 2005

Cross‐hole pumping tests within a subvertical shear zone in granite were interpreted using a geostatistical inverse approach. The objective was to identify flow channels that influence tracer experiments. The spatial correlation structure of transmissivity (T) was unknown. Therefore, a wide variety of geostatistical hypotheses were made for estimating a total of 40 T fields, that honor equally well the pumping tests, the static head measurements, and the point T data. All estimated T fields reveal channels with similar topology and with a preferred horizontal orientation, possibly due to vertical displacements within the subvertical shear zone. This shows that inverse geostatistical modeling of abundant hydraulic measurements can be useful to reveal a coarse heterogeneity structure, even when data are insufficient to identify the geostatistical structure. However, numerical simulations of a field tracer test were highly sensitive to the geostatistical hypotheses. In summary, T fields leading to successful hydraulic data fitting do not necessarily lead to successful transport predictions, even when they appear to reproduce the coarse heterogeneity structure.
Risk‐Cost Analysis in Ground Water Contaminant Transport: The Role of Random Spatial Variability and Sorption Kinetics
Authors: Andersson Charlotta , Destouni Georgia
Published: December 2005

We outline a methodology for quantifying the risk (probability) to exceed environmental regulation standards for ground water quality and coupling this risk quantification with an analysis of abatement costs for attaining an acceptable risk level. The methodology accounts for the uncertainty that results from random spatial variability in the subsurface, and for sorption‐desorption kinetics. Random spatial variability implies that, with a deterministic regulating framework, the risk (probability) of exceeding given water quality targets may remain high even after abatement measures have been taken. We show how this risk can be set in focus by use of a probabilistic regulating framework, which enables better risk management. Both the environmental risk and the associated abatement costs will depend on the actual combination of subsurface variability, the ground water sampling method, and sorption kinetics, through the underlying quantification of pollutant concentration statistics. Our results emphasize the importance of a relevant account of the kinetics of the sorption‐desorption process, by illustrating that neglect, or equilibrium simplification of that process, may result in highly misleading risk and abatement cost estimates.
Geochemical Evolution of Ground Water in the Great Plains (Dakota) Aquifer of Nebraska: Implications for the Management of a Regional Aquifer System
Authors: Gosselin David C. , Harvey F. Edwin , Frost Carol D.
Published: December 2005

The Great Plains (Dakota) aquifer system is one of the most extensive in North America extending from the Arctic Circle to New Mexico, and underlies approximately 94% of Nebraska. In Nebraska, we do not have the physical ground water monitoring data at the scale that is necessary to manage ground water flow systems. However, first‐order management strategies for this regional aquifer can be developed by understanding the geochemical evolution of the ground water. Using major‐ion water chemistry data from 203 wells in 19 counties in eastern Nebraska, reconnaissance δ180, δD, and δ87Sr data, and two geochemical models, PHREEQC and SNORM, we determine that modern meteoric water, NaCl brines from underlying formations, and cold glacial melt water are the primary sources for the water in the Dakota Aquifer. Based on these three water sources and the geochemical evolution of the various water types, the following first‐order management strategies are suggested. In areas where CaSO4 and Ca‐Na SO4 type water occur, Pleistocene‐age glacial meltwater is the source. This water supply is not easily renewable. It is recommended that detailed water resource evaluation be conducted before extensive development occurs. The source of Ca (± Mg) HCO3 type water is from recharge by local precipitation and should be managed to maintain them as a renewable resource. In mixed ground water type areas, the ground water chemistry reflects the interaction of two distinct water types, one of which is meteoric water and the other is either CaSO4 and Ca‐Na SO4‐type water or NaCl‐type water. If the relatively fresh ground water is extracted at a rate that changes the location of the interface between the endmembers, then monitoring changes in water chemistry in a well over time could be used as an early warning system for the onset of potential problems related to overpumping.
Stress‐Strain Analyses for Aquifer‐System Characterization
Authors: Burbey Thomas J.
Published: December 2005

Subsidence data historically have been collected using costly extensometers. Recent advances in InSAR and GPS technology may provide noninvasive methods for collecting these data, which can be used in conjunction with hydrograph information to estimate the skeletal specific storage and hydraulic conductivity values of compressible units. Numerical analysis is used to evaluate the conditions affecting nonrecoverable (inelastic) and recoverable (elastic) skeletal specific storage and to investigate the affects of horizontal strain on the extensometer record. Stress‐strain diagrams represented as subsidence‐drawdown plots are one‐dimensional in scope, yet are typically used for estimating specific storage. Simulation results indicate that nonrecoverable specific can be estimated from these diagrams even when the storage contribution from horizontal strain is significant. Hysteresis effects are common during recovery and recompression of cyclically pumped confined aquifers. Several factors were found to affect the shape of the hysteresis loops; these include (a) the hydraulic diffusivity of the confining unit, (b) the distance from the pumped well, (c) length of the recovery cycle, (d) the ratio of confined aquifer to confining unit hydraulic conductivities, and (e) the thickness of the confining unit. Stress‐strain analyses can supplement classical time‐drawdown data to yield valuable parameter estimation of the confining unit that would be otherwise difficult to quantify.
A Stream Depletion Field Experiment
Authors: Hunt Bruce , Weir Julian , Clausen Bente
Published: December 2005

A field experiment was carried out to measure drawdowns in observation wells and stream depletion flows that occurred when water was abstracted from a well beside a stream. The field data is analyzed herein to determine the aquifer transmissivity, T, the aquifer storage coefficient, S, and a streambed leakage parameter, λ, by comparing measurements with a solution obtained by Hunt (1999). The analysis uses early time drawdowns with a match‐point method to determine T and S, and stream depletion measurements at later times are used to determine λ. The final results are reasonably consistent for measurements taken in four observation wells. The advantages and disadvantages of this approach are discussed, and two alternative ways of estimating λ are also discussed.
Effect of Heterogeneity on Radionuclide Retardation in the Alluvial Aquifer Near Yucca Mountain, Nevada
Authors: Painter S. , Cvetkovic V. , Turner D.R.
Published: December 2005

The U.S. Department of Energy is currently studying Yucca Mountain, Nevada, as a potential site for a geological high‐level waste repository. In the current conceptual models of radionuclide transport at Yucca Mountain, part of the transport path to pumping locations would be through an alluvial aquifer. Interactions with minerals in the alluvium are expected to retard the downstream migration of radionuclides, thereby delaying arrival times and reducing ground water concentrations. We evaluate the effectiveness of the alluvial aquifer as a transport barrier using the stochastic Lagrangian framework. A transport model is developed to account for physical and chemical heterogeneities and rate‐limited mass transfer between mobile and immobile zones. The latter process is caused by small‐scale heterogeneity and is thought to control the macroscopic‐scale retardation in some field experiments. A geostatistical model for the spatially varying sorption parameters is developed from a site‐specific database created from hydrochemical measurements and a calibrated modeling approach (Turner and Pabalan 1999). Transport of neptunium is considered as an example. The results are sensitive to the rate of transfer between mobile and immobile zones, and to spatial variability in the hydraulic conductivity. Chemical heterogeneity has only a small effect, as does correlation between hydraulic conductivity and the neptunium distribution coefficient. These results illustrate how general sensitivities can be explored with modest effort within the Lagrangian framework. Such studies complement and guide the application of more detailed numerical simulations.
Coefficient of Permeability Determined By Measurable Parameters
Authors: Barr Douglas W.
Published: December 2005

Selection of a coefficient of permeability or the hydraulic conductivity in practical situations has required a fair amount of judgment and the expectation of accuracy can range over an order of magnitude. A determination of the coefficient based on measurable characteristics would greatly reduce the judgment aspect. The coefficient of permeability of a porous media can be derived from the following measurable parameters: the density and viscosity of the permeating fluid, the porosity of the media, the average hydraulic radius of the pores, and the gravitation constant. The hydraulic radius is calculated from the grain size distribution analysis of the porous media assuming spherical particles and a factor to account for the shape of the particles. The shape factor ranges from 1.0 to 1.4 in the extreme but, for common porous media, ranges only from 1.0 to about 1.1. All of the variables, except the shape factor, are measurable by standard test procedures. An important advantage of using this procedure for determining permeability is that the factors can be visualized as part of the physical flow process. The procedure assumes laminar flow and applies equally to liquid or gas fluids.
Travel‐Time Based Model of Bioremediation Using Circulation Wells
Authors: Cirpka Olaf A. , Kitanidis Peter K.
Published: December 2005

Vertical circulation wells can efficiently provide microorganisms with substrates needed for enhanced bioremediation. We present a travel‐time based approach for modeling bioreactive transport in a flow field caused by a series of circulation wells. Mixing within the aquifer is due to the differences in sorption behavior of the reactants. Neglecting local dispersion, transport simplifies to a single one‐dimensional problem with constant coefficients for each well. Recirculation is characterized by the discharge densities over travel time. We apply the model to the stimulation of cometabolic dechlorination of trichloroethene (TCE) by alternate injection of oxygen and toluene into the circulation wells. Mixing within the wells can be minimized by interposing sufficiently long breaks between the oxygen and toluene pulses. In our simulation, the proposed injection scheme stimulates biomass growth without risking biofouling of the aquifer.
Numerical Simulation of a Natural Gradient Tracer Experiment for the Natural Attenuation Study: Flow and Physical Transport
Authors: Julian Hank E. , Boggs J. Mark , Zheng Chunmiao , Feehley C. Erin
Published: December 2005

Results are presented for numerical simulations of ground water flow and physical transport associated with a natural gradient tracer experiment conducted within a heterogeneous alluvial aquifer of the Natural Attenuation Study (NATS) site near Columbus, Mississippi. A principal goal of NATS is to evaluate biogeochemical models that predict the rate and extent of natural biodegradation under field conditions. This paper describes the initial phase in the model evaluation process, i.e., calibration of flow and physical transport models that simulate conservative bromide tracer plume evolution during NATS. An initial large‐scale flow model (LSM) is developed encompassing the experimental site and surrounding region. This model is subsequently scaled down in telescopic fashion to an intermediate‐scale ground water flow model (ISM) covering the tracer‐monitoring network, followed by a small‐scale transport model (SSM) focused on the small region of hydrocarbon plume migration observed during NATS. The LSM uses inferred depositional features of the site in conjunction with hydraulic conductivity (K) data from aquifer tests and borehole flowmeter tests to establish large‐scale K and flow field trends in and around the experimental site. The subsequent ISM incorporates specified flux boundary conditions and large‐scale K trends obtained from the calibrated LSM, while preserving small‐scale K structure based on some 4000 flowmeter data for solute transport modeling. The configuration of the ISM‐predicted potentiometric surface approximates that of the observed surface within a root mean squared error of 0.15 m. The SSM is based on the dual‐domain mass‐transfer approach. Despite the well‐recognized difficulties in modeling solute transport in extremely heterogeneous media as found at the NATS site, the dual‐domain model adequately reproduced the observed bromide concentration distributions. Differences in observed and predicted bromide concentration distributions are attributed to aquifer heterogeneity at the decimeter (dm) and smaller scales. The calibrated transport parameters for the SSM (i.e., 1:7 for the ratio of mobile‐to‐total porosity; 2.5 × 10−3 day−1 for the mass‐transfer coefficient; 1 m for longitudinal dispersivity; and 0.1 m for transverse dispersiv‐ity) are consistent with separate numerical simulations of two earlier tracer experiments at the site. The multiscale modeling approach adopted in this study permits the incorporation of both large‐scale geologic features important for flow simulation and small‐scale heterogeneities critical for transport simulation. In addition, the dual‐domain transport model provides a foundation for multispecies reactive transport modeling studies of natural attenuation of hydrocarbons during NATS.
A Joint TEM‐HLEM Geophysical Approach to Borehole Siting in Deeply Weathered Granitic Terrains
Authors: Meju M.A. , Fontes S. L. , Ulugergerli E.U. , La Terra E.F. , Germano C.R. , Carvalho R.M.
Published: December 2005

The accurate location of aquiferous fracture zones in granite beneath a > 50 m thick weathered mantle in semi‐arid regions is a major hydrogeological problem. It is expected that the zone of intensive fracturing will be more susceptible to weathering and thus be characterized by the thickest development of saprolite, a good electrically conductive target for deep‐probing electromagnetic systems. The single‐loop transient electromagnetic (TEM) technique is well known to have the capability for detecting concealed steep mineralized targets in mining environments and can be adapted to this hydrogeological problem. We propose that combining the conventional frequency‐domain horizontal‐loop electromagnetic (HLEM) and single‐loop TEM is an effective practical approach to locating concealed aquiferous fracture zones. In the supporting case studies presented here, we deployed multifre‐quency HLEM profiling (with 50 m transmitter‐receiver separation) and TEM soundings with contiguous 10 or 20 m sided loops along the survey lines in a granitic terrain affected by deep (> 50 m) weathering in northeast Brazil. A somewhat layered structure consisting of resistive hardpan/leached zone, conductive saprolite, and resistive basement is identifiable in the typical TEM depth sounding data. We obtained coincident HLEM and TEM anomalies at all the sites, enabling a relatively straightforward selection of potential drilling positions. Simple resistivity‐depth transformation of the TEM data was done for each site, yielding an approximate section from which drilling depths were estimated. All of the boreholes located were successful. Although our results appear to indicate that the single‐loop TEM method could be used independently for borehole siting in deeply weathered granitic terrains and that the weathering profile over granite can be mapped using TEM depth soundings of appropriate observational bandwidth, we recommend a joint electromagnetic approach for optimal well siting.
Calibration of the DRASTIC Ground Water Vulnerability Mapping Method
Authors: Rupert M.G.
Published: December 2005

Ground water vulnerability maps developed using the DRASTIC method have been produced in many parts of the world. Comparisons of those maps with actual ground water quality data have shown that the DRASTIC method is typically a poor predictor of ground water contamination. This study significantly improved the effectiveness of a modified DRASTIC ground water vulnerability map by calibrating the point rating schemes to actual ground water quality data by using nonparametric statistical techniques and a geographic information system. Calibration was performed by comparing data on nitrite plus nitrate as nitrogen (NO2+ NO3‐N) concentrations in ground water to land‐use, soils, and depth to first‐encountered ground water data. These comparisons showed clear statistical differences between NO2+ NO3‐N concentrations and the various categories. Ground water probability point ratings for NO2+ NO3‐N contamination were developed from the results of these comparisons, and a probability map was produced. This ground water probability map was then correlated with an independent set of NO2+ NO3‐N data to demonstrate its effectiveness in predicting elevated NO2+ NO3‐N concentrations in ground water. This correlation demonstrated that the probability map was effective, but a vulnerability map produced with the uncalibrated DRASTIC method in the same area and using the same data layers was not effective. Considerable time and expense have been outlaid to develop ground water vulnerability maps with the DRASTIC method. This study demonstrates a cost‐effective method to improve and verify the effectiveness of ground water vulnerability maps.
Potential Artifacts in Interpretation of Differential Breakthrough of Colloids and Dissolved Tracers in the Context of Transport in a Zero‐Valent Iron Permeable Reactive Barrier
Authors: Zhang Pengfei , Johnson William P. , Piana Michael J. , Fuller Christopher C. , Naftz David L.
Published: December 2005

Many published studies have used visual comparison of the timing of peak breakthrough of colloids versus conservative dissolved tracers (hereafter referred to as dissolved tracers or tracers) in subsurface media to determine whether they are advected differently, and to elucidate the mechanisms of differential advection. This purely visual approach of determining differential advec‐tion may have artifacts, however, due to the attachment of colloids to subsurface media. The attachment of colloids to subsurface media may shift the colloidal peak breakthrough to earlier times, causing an apparent “faster” peak breakthrough of colloids relative to dissolve tracers even though the transport velocities for the colloids and the dissolved tracers may actually be equivalent. In this paper, a peak shift analysis was presented to illustrate the artifacts associated with the purely visual approach in determining differential advection, and to quantify the peak shift due to colloid attachment. This peak shift analysis was described within the context of microsphere and bromide transport within a zero‐valent iron (ZVI) permeable reactive barrier (PRB) located in Fry Canyon, Utah. Application of the peak shift analysis to the field microsphere and bromide breakthrough data indicated that differential advection of the microspheres relative to the bromide occurred in the monitoring wells closest to the injection well in the PRB. It was hypothesized that the physical heterogeneity at the grain scale, presumably arising from differences in inter‐ versus intra‐particle porosity, contributed to the differential advection of the microspheres versus the bromide in the PRB. The relative breakthrough (RB) of microspheres at different wells was inversely related to the ionic strength of ground water at these wells, in agreement with numerous studies showing that colloid attachment is directly related to solution ionic strength.
Implications of Observed and Simulated Ambient Flow in Monitoring Wells
Authors: Elci Alper , Molz Fred J. , Waldrop William R.
Published: December 2005

A recent paper by Hutchins and Acree (2000) has called attention to ground water sampling bias due to ambient (natural gradient‐induced) flows in monitoring wells. Data collected with borehole flowmeters have shown that such ambient flows are ubiquitous in both confined and unconfined aquifers. Developed herein is a detailed three‐dimensional model of flow and transport in the vicinity of a fully penetrating monitoring well. The model was used to simulate a measured ambient flow distribution around a test well in a heterogeneous aquifer at the Savannah River Site (SRS) near Aiken, South Carolina. Simulated ambient flows agreed well with measurements. Natural flow was upward, so water entered the well mainly through high K layers in the lower portion of the aquifer and exited through similar layers in the upper portion. The maximum upward discharge in the well was about 0.28 L/min, which implied an induced exchange of 12 m3/month from the bottom half of the aquifer to the upper half. Tracer transport simulations then illustrated how a contaminant located initially in a lower portion of the aquifer was continuously transported into the upper portion and diluted throughout the entire well by in‐flowing water. Even after full purging or micropurging, samples from such a well will yield misleading and ambiguous data concerning solute concentrations, location of a contaminant source, and plume geometry. For all of these reasons, use of long‐screened monitoring wells should be phased out, unless an appropriate multilevel sampling device prevents vertical flow.
Viral Transport in a Sand and Gravel Aquifer Under Field Pumping Conditions
Authors: Woessner William W. , Ball Patrick N. , DeBorde Dan C. , Troy Thomas L.
Published: December 2005

Ground water supplies contaminated with microbes cause more than 50% of the water‐borne disease outbreaks in the United States. Proposed regulations suggest natural disinfection as a possible mechanism to treat microbe‐impacted ground water under favorable conditions. However, the usefulness of current models employed to predict viral transport and natural attenuation rates is limited by the absence of field scale calibration data. At a remote floodplain aquifer in western Montana, the bac‐teriophages MS2, φX174, and PRD1; attenuated poliovirus type‐1 (CHAT strain); and bromide were seeded as a slug 21.5 m from a well pumping at a steady rate of 408 L/min. Over the 47‐hour duration of the test, resulting in the exchange of 12 to 13 pore volumes, 77% of the bromide, 55% of the PRD1,17% of the MS2,7% of the φX174, and 0.12% of the poliovirus masses were recovered at the pumping well. Virus transport behavior was controlled by mechanical dispersion, preferential flow, time‐dependent nonreversible and reversible attachment, and apparent mass transfer to immobile domains within the sand and gravel dominated aquifer. The percentage of virus recovery appears correlated with reported viral isoelectric point (pI) values. Successful modeling of viral transport in coarse‐grained aquifers will require separation of viral specific properties from reported lumped viraltransport system parameters.
Development and Evaluation of an Ultrasonic Ground Water Seepage Meter
Authors: Paulsen Ronald J. , Smith Christopher F. , O'Rourke Daniel , Wong Teng‐Fong
Published: December 2005

Submarine ground water discharge can influence significantly the near‐shore transport and flux of chemicals into the oceans. Quantification of the sources and rates of such discharge requires a ground water seepage meter that provides continuous measurements at high resolution over an extended period of time. An ultrasonic flowmeter has been adapted for such measurements in the submarine environment. Connected to a steel collection funnel, the meter houses two piezoelectric transducers mounted at opposite ends of a cylindrical flow tube. By monitoring the perturbations of fluid flow on the propagation of sound waves inside the flow tube, the ultrasonic meter can measure both forward and reverse fluid flows in real time. Laboratory and field calibrations show that the ultrasonic meter can resolve ground water discharges on the order of 0.1 μm/sec, and it is sufficiently robust for deployment in the field for several days. Data from West Neck Bay, Shelter Island, New York, elucidate the temporal and spatial heterogeneity of submarine ground water discharge and its interplay with tidal loading. A negative correlation between the discharge and tidal elevation was generally observed. A methodology was also developed whereby data for the sound velocity as a function of temperature can be used to infer the salinity and source of the submarine discharge. Independent measurements of electrical conductance were performed to validate this methodology.