bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative Measurement of Channel‐Block Hydraulic Interactions by Experimental Saturation of a Large, Natural, Fissured Rock Mass
Authors: Guglielmi Yves , Mudry Jacques 
Published: December 2005

AbstractThe hydrodynamic behavior of fissured media relies on the relationships between a few very conductive fractures (channels) and the remaining low‐conductivity fractures and matrix (blocks). We made a quantitative measurement of those relationships and their effect on water drainage and storage in a 19,000 m3 natural reservoir consisting of karstified limestones. This reservoir was artificially saturated with water by closing a water gate on the main outlet during a varying time (Δt) fixed by the operator. The water gate was completely or partly closed until the water pressure reached a particular specified value. If the water gate was left completely closed long enough, the water pressure was fixed by the elevation of temporary outlets at the site boundaries. The water elevation within the reservoir was monitored by means of pressure cells located on single fractures representative of the bedding plane and the two families of fractures of the massif network.The comparison of pressure variations with the network geometry allows us to identify a typical double permeability characterized by a few very conductive channels along 10 vertical faults. These channels limit blocks consisting of low‐conductivity bedding planes and a rather impervious matrix.Depending on the closure interval, Δt, of the water gate, the total volume of water stored in the reservoir can vary from 0.8 m3 (Δt = 5 minutes) to 18.6 m3 (Δt = 2 days). Such a variance of storage versus closure time is explained by the reservoir's double permeability that is characterized by blocks that saturate much more slowly than channels. If plotted versus time, this injected volume fits a power relationship, according to the saturation state of the blocks. In less than 34 minutes, storage is close to zero in the blocks and to 1.6 to 2 m3 in the channels. For closing times shorter than 1 hour, only 1% of the volume that flows in the channels is stored into the blocks. Depending on the water pressure and for a given Δt = 3000 minutes, the volume of water stored is controlled by the geometry of the joint network and of the aquifer boundaries.Such an experiment shows that the flow is concentrated in about 10% of the fractured network (channels). The water storage that takes place in the 90% remaining fractures (blocks) depends mainly on time during which pressure remains high into the 10% channels. The accurate modeling of such typical double‐permeability media needs a careful study of the geometry of the channels whose narrowings modify the flow and induce dam effects that maintain a high pressure gradient with surrounding blocks.
Fracture Wall Cements and Coatings from Two Clayey Till Aquitards
Authors: Corrigan Catherine A. , Jamieson Heather E. , Remenda Victoria H. 
Published: December 2005

AbstractSecondary minerals occurring at the faces of fractures, the only reliable visual evidence of the presence of hydraulically conductive fractures in clayey unlithified aquitards, have been characterized for two uncontaminated field sites, Dalmeny, Saskatchewan, and Laidlaw, Ontario. Preliminary identification of secondary minerals and their variations with depth was made using a MunsellTM Color Chart. Subsequent microscopic analyses (petrography, electron microprobe analysis, scanning electron microscopy, and X‐ray diffraction) were used to identify iron‐oxide mineralogy. Iron oxides were identified as goethite, ferrihydrite, and hematite at Dalmeny, where they occur to depths of 10 to 15 m, and goethite and ferrihydrite at Laidlaw, observed to depths of 7 m. In both cases, the identification of ferrihydrite was tentative due to the problems of small sample size and peak overlap in X‐ray diffraction. The iron oxides do not form coatings on the surfaces of the fractures as had been previously thought; rather they form cements linking the matrix grains. Thus there is potential for decreased permeability and increased surface reactivity parallel to and inward from the fracture faces. The pattern of iron‐oxide distribution suggests that the youngest deposits, and those with the greatest surface reactivity and potential for contaminant retardation, are found at greatest depths in the fractures. Manganese oxides form in isolated clusters in larger pores and indentations, although the exact manganese minerals could not be firmly identified.
Colloid Mobilization in the Field Using Citrate to Remediate Chromium
Authors: Johnson Carol R. , Hellerich Lucas A. , Nikolaidis Nikolaos P. , Gschwend Philip M. 
Published: December 2005

AbstractWe investigated the feasibility of cleaning aquifer sediments, long contaminated with chromium (Cr) from a metal plating facility, by detaching colloid‐sized sorbents from the immobile aquifer solids and then pumping those colloids to the surface for treatment. In laboratory experiments using aquifer solids from the site, several solutions (water at various pHs, phosphate, oxalate, ascorbate, citrate) were examined for their ability to disperse colloids and Cr. Based on these tests, a 5 mM citrate solution at pH 7 was selected. Subsequently, such a citrate solution was used in the field in two single‐well injection‐withdrawal experiments. Large quantities of colloids were released immediately after injection. The colloidal particles mobilized by citrate in the field had more than 20 times higher Cr concentrations than did the average aquifer sediments, implying success in mobilizing Cr‐associated phases. Further, laboratory and field tests showed that anion exchange of citrate for chromate caused some additional release of Cr from these aquifer solids.
Ground Water Flow Analysis of a Mid‐Atlantic Outer Coastal Plain Watershed, Virginia, U.S.A.
Authors: Robinson Michael A. , Reay William G. 
Published: December 2005

AbstractModels for ground water flow (MODFLOW) and particle tracking (MODPATH) were used to determine ground water flow patterns, principal ground water discharge and recharge zones, and estimates of ground water travel times in an unconfined ground water system of an outer coastal plain watershed on the Delmarva Peninsula, Virginia. By coupling recharge and discharge zones within the watershed, flowpath analysis can provide a method to locate and implement specific management strategies within a watershed to reduce ground water nitrogen loading to surface water. A monitoring well network was installed in Eyreville Creek watershed, a first‐order creek, to determine hydraulic conductivities and spatial and temporal variations in hydraulic heads for use in model calibration. Ground water flow patterns indicated the convergence of flow along the four surface water features of the watershed; primary discharge areas were in the noontide portions of the watershed. Ground water recharge zones corresponded to the surface water features with minimal development of a regional ground water system. Predicted ground water velocities varied between < 0.01 to 0.24 m/day, with elevated values associated with discharge areas and areas of convergence along surface water features. Some ground water residence times exceeded 100 years, although average residence times ranged between 16 and 21 years; approximately 95% of the ground water resource would reflect land use activities within the last 50 years.
Rapid Evolution of Redox Processes in a Petroleum Hydrocarbon‐Contaminated Aquifer
Authors: Chapelle Francis H. , Bradley Paul M. , Lovley Derek R. , O'Neill Kathleen , Landmeyer James E. 
Published: December 2005

AbstractGround water chemistry data collected over a six‐year period show that the distribution of contaminants and redox processes in a shallow petroleum hydrocarbon‐contaminated aquifer has changed rapidly over time. Shortly after a gasoline release occurred in 1990, high concentrations of benzene were present near the contaminant source area. In this contaminated zone, dissolved oxygen in ground water was depleted, and by 1994 Fe(lll) reduction and sulfate reduction were the predominant terminal electron accepting processes. Significantly, dissolved methane was below measurable levels in 1994, indicating the absence of significant methanogenesis. By 1996, however, depletion of solid‐phase Fe(lll)‐oxyhydroxides in aquifer sediments and depletion of dissolved sulfate in ground water resulted in the onset of methanogenesis. Between 1996 and 2000, water‐chemistry data indicated that methanogenic metabolism became increasingly prevalent. Molecular analysis of 16S‐rDNA extracted from sediments shows the presence of a more diverse methanogenic community inside as opposed to outside the plume core, and is consistent with water‐chemistry data indicating a shift toward methanogenesis over time. This rapid evolution of redox processes reflects several factors including the large amounts of contaminants, relatively rapid ground water flow (∼0.3 m/day [∼1 foot/day]), and low concentrations of microbially reducible Fe(lll) oxyhydroxides (∼ 1 umol/g) initially present in aquifer sediments. These results illustrate that, under certain hydrologic conditions, redox conditions in petroleum hydrocarbon‐contaminated aquifers can change rapidly in time and space, and that the availability of solid‐phase Fe(lll)‐oxyhydroxides affects this rate of change.
Measuring the Hydraulic Conductivity of Shallow Submerged Sediments
Authors: Kelly Susan E. , Murdoch Lawrence C. 
Published: December 2005

AbstractThe hydraulic conductivity of submerged sediments influences the interaction between ground water and surface water, but few techniques for measuring K have been described with the conditions of the submerged setting in mind. Two simple, physical methods for measuring the hydraulic conductivity of submerged sediments have been developed, and one of them uses a well and piezometers similar to well tests performed in terrestrial aquifers. This test is based on a theoretical analysis that uses a constant‐head boundary condition for the upper surface of the aquifer to represent the effects of the overlying water body. Existing analyses of tests used to measure the hydraulic conductivity of submerged sediments may contain errors from using the same upper boundary conditions applied to simulate terrestrial aquifers. Field implementation of the technique requires detecting minute drawdowns in the vicinity of the pumping well. Low‐density oil was used in an inverted U‐tube manometer to amplify the head differential so that it could be resolved in the field. Another technique was developed to measure the vertical hydraulic conductivity of sediments at the interface with overlying surface water. This technique uses the pan from a seepage meter with a piezometer fixed along its axis (a piezo‐seep meter). Water is pumped from the pan and the head gradient is measured using the axial piezometer. Results from a sandy streambed indicate that both methods provide consistent and reasonable estimates of K. The pumping test allows skin effects to be considered, and the field data show that omitting the skin effect (e.g., by using a single well test) can produce results that underestimate the hydraulic conductivity of streambeds.
Deep Water Circulation, Residence Time, and Chemistry in a Karst Complex
Authors: Aquilina L , Ladouche B. , Doerfliger N. , Bakalowicz M. 
Published: December 2005

AbstractWe investigated the hydrochemistry of a complex karst hydrosystem made of two carbonate units along a coastal lagoon. Ground water emerges on the lagoon floor from a submarine spring. In addition, thermal waters circulate through the limestone and mix with karst water near the lagoon shore.A distinction between the water from the two carbonate units is related to marine influences and human activities. In one of the massifs, the data show an incongruent dissolution of dolomite with time. In the other system, a slight contamination by saline fluids from the thermal reservoir has led to high calcium and magnesium concentrations. 36C1, I4C, and 3H data constrain the residence time of the water, and allow for the distinguishing of four circulation types: (1) shallow surface circulation (primarily above sea level) in the karstic units with short residence times (<20 years); (2) shallow subsurface circulation (approximately 0 to ‐50 m) below the karstic units with residence time in the order of 50 years; (3) deep circulation at depth of 700 to 1500 m in the Jurassic limestones below thick sedimentary cover, with residence time of several thousand years for a part of the water; and (4) deep circulation at a depth of ∼2500 m, which represents the thermal reservoir in the Jurassic units with residence time of ∼100,000 years.An interpretative hydrogeological framework is based on the constraints of the geochemical analyses of the deep thermal system, and by water flow from the surface to the deep parts of the carbonate formations.
A Finite World, Earth Sciences, and Public Trust
Authors: Narasimhan T.N. 
Published: December 2005

AbstractThe beginning of the 21st century has coincided with our recognition that life‐sustaining earth cycles are remarkably fine‐tuned, and that humans have developed technological abilities to perturb these cycles. Also, inspired by the gifts of freedom and democracy, humans have given themselves laws to exploit nature for profit. The upshot is that nature's balance, governed by immutable physical laws, is being confronted by social laws driven by human aspirations. This conflict and its implications to the human relevance of the earth sciences are explored in the context of an extraordinary tradition of European culture known as public trust.
A Statistical Estimator of the Spatial Distribution of the Water‐Table Altitude
Authors: Sepúlveda Nicasio 
Published: December 2005

AbstractAn algorithm was designed to statistically estimate the areal distribution of water‐table altitude. The altitude of the water table was bounded below by the minimum water‐table surface and above by the land surface. Using lake elevations and stream stages, and interpolating between lakes and streams, the minimum water‐table surface was generated. A multiple linear regression among the minimum water‐table altitude, the difference between land‐surface and minimum water‐table altitudes, and the water‐level measurements from surficial aquifer system wells resulted in a consistently high correlation for all groups of physiographic regions in Florida. A simple linear regression between land‐surface and water‐level measurements resulted in a root‐mean‐square residual of 4.23 m, with residuals ranging from — 8.78 to 41.54 m. A simple linear regression between the minimum water table and the water‐level measurements resulted in a root‐mean‐square residual of 1.45 m, with residuals ranging from –7.39 to 4.10 m. The application of the multiple linear regression presented herein resulted in a root‐mean‐square residual of 1.05 m, with residuals ranging from — 5.24 to 5.63 m. Results from complete and partial F tests rejected the hypothesis of eliminating any of the regressors in the multiple linear regression presented in this study.
A Fresh Water Odyssey: Some Observations on the Global Resource
Authors: Wood Warren W. 
Published: December 2005

AbstractAppreciable increases in the human population are expected to continue in the next 50 to 100 years. This population will require additional water for nonfungible (nonexchangeable) uses such as irrigated agriculture, livestock watering, domestic supply, and ecosystem support. Because most of the world's easily captured water is already identified and allocated, society must improve efficiency, change the present allocations, and/or develop new sources to meet the expected demands. As the global economy expands, apparently unrelated changes in policy or technology may have large, unexpected consequences for water resources. Foreshadowing these changes in stress on these resources will be the result of nonlinear thinking. Whereas policy cannot create new water, it can provide strategies to promote more efficient use of present water and foster an environment in which important technological improvements can be made. This manuscript provides a brief overview of some of the physical and policy considerations relating to fresh water resources.
MODFLOW 2000 Head Uncertainty, a First‐Order Second Moment Method
Authors: Glasgow Harry S. , Fortney Matthew D. , Lee Jejung , Graettinger Andrew J. , Reeves Howard W. 
Published: December 2005

AbstractA computationally efficient method to estimate the variance and covariance in piezometric head results computed through MODFLOW 2000 using a first‐order second moment (FOSM) approach is presented. This methodology employs a first‐order Taylor series expansion to combine model sensitivity with uncertainty in geologic data. MOD‐FLOW 2000 is used to calculate both the ground water head and the sensitivity of head to changes in input data. From a limited number of samples, geologic data are extrapolated and their associated uncertainties are computed through a conditional probability calculation. Combining the spatially related sensitivity and input uncertainty produces the variance‐covariance matrix, the diagonal of which is used to yield the standard deviation in MODFLOW 2000 head. The variance in piezometric head can be used for calibrating the model, estimating confidence intervals, directing exploration, and evaluating the reliability of a design. A case study illustrates the approach, where aquifer transmis‐sivity is the spatially related uncertain geologic input data. The FOSM methodology is shown to be applicable for calculating output uncertainty for (1) spatially related input and output data, and (2) multiple input parameters (trans‐missivity and recharge).
Sources of Ground Water Salinity on Islands Using 18O,2H, and 34S
Authors: Allen D.M. 
Published: December 2005

AbstractStable isotopes of 18O and 2H in water, and 34S and l8O in dissolved SO4 are used to verify the interpretation of the chemical evolution and proposed sources of salinity for two islands that have undergone postglacial rebound. Results for δ18O and δ34S in dissolved SO4 on the Gulf Islands, southwest British Columbia, Canada, suggest a three‐component mixing between (1) atmospheric SO4 derived largely from recharge of meteoric origin, (2) modern marine SO4 associated with either modern‐day salt water intrusion or Pleistocene age sea water, and (3) terrestrial SO4. The age of the marine SO4 is uncertain based on the geochemistry and SO4 isotopes alone. Two options for mixing of saline ground waters are proposed—either between current‐day marine SO4 and atmospheric SO4, or between older (Pleistocene age) marine SO4 and atmospheric SO4. δ18O and δ2H compositions are relatively consistent between both islands, with a few samples showing evidence of mixing with water that is a hybrid mixture of Fraser River water and ocean water. The isotopic composition of this hybrid water is ∼δ18O = 10 %c. δ18O and δ2H values for many saline ground waters plot close to the global meteoric water line, which is distinctly different from the local meteoric water line. This suggests a meteoric origin for ground waters that is different from the current isotopic composition of meteoric waters. It is proposed these waters may be late Pleistocene in age and were recharged when the island was submerged below sea level and prior to rebound at the end of the last glaciation.
Multiple‐Aquifer Characterization from Single Borehole Extensometer Records
Authors: Pope Jason P. , Burbey Thomas J. 
Published: December 2005

AbstractMeasurement and analysis of aquifer‐system compaction have been used to characterize aquifer and confining unit properties when other techniques such as flow modeling have been ineffective at adequately quantifying storage properties or matching historical water levels in environments experiencing land subsidence. In the southeastern coastal plain of Virginia, high‐sensitivity borehole pipe extensometers were used to measure 24.2 mm of total compaction at Franklin from 1979 through 1995 (1.5 mm/year) and 50.2 mm of total compaction at Suffolk from 1982 through 1995 (3.7 mm/year). Analysis of the extensometer data reveals that the small rates of aquifer‐system compaction appear to be correlated with withdrawals of water from confined aquifers. One‐dimensional vertical compaction modeling indicates measured compaction is the result of nonrecoverable hydrodynamic consolidation of the fine‐grained confining units and interbeds, as well as recoverable compaction and expansion of coarse‐grained aquifer units. The calibrated modeling results indicate that nonrecoverable specific storage values decrease with depth and range from 1.5 × 10−5/m for aquifer units to 1.5 × 10−4/m for confining units and interbeds. The aquifer and Potomac system recoverable specific storage values were all estimated to be 4.5 × 10−6/m, while the confining units and interbeds had values of 6.0 × 10−6/m. The calibrated vertical hydraulic conductivity values of the confining units and interbeds ranged from 6.6 × 10−4m/year to 2.0 × 10−3 m/year. These parameter values will be useful in future management and modeling of ground water in the Virginia Coastal Plain.
Geophysical Monitoring and Evaluation of Coastal Plain Aquifers
Authors: Land Lewis A. , Lautier Jeff C. , Wilson Nathaniel C. , Chianese Gabrielle , Webb Steven 
Published: December 2005

AbstractWe use time domain electromagnetic (TDEM) soundings to monitor ground water conditions beneath the coastal plain in eastern North Carolina. The TDEM method measures the earth's response to an induced electromagnetic field. The resulting signal is converted, through a complex inversion process, to apparent resistivity values, which can be directly correlated to borehole resistivity logs. TDEM soundings are used to map the interface between fresh and salt water within coastal aquifers, and estimate depth to basement when siting new monitoring wells. Focused TDEM surveys have identified areas of salt water encroachment caused by high volumes of discharge from local supply wells. Electromagnetic sounding, when used in tandem with the state's network of monitoring wells, is an accurate and inexpensive tool for evaluating fresh water/salt water relationships on both local and regional scales within coastal plain aquifers.