bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interactive Modeling of Ground‐Water Vulnerability Within a Geographic Information System Environmenta
Authors: Tim U. Sunday , Jain Dharmesh , Liao Hsiu‐Huka 
Published: August 2005

AbstractDuring the last several years, the geographic information system (GIS) technology has emerged as an extremely effective tool for analyzing and prioritizing natural resource management alternatives. Because natural resource management problems are spatial in nature, the GIS technology provides a tool for defining the extent of the problem, and facilitates the design and implementation of alternative management strategies. The flexible design of a GIS coupled with the ability to integrate models with spatial data gives resource managers and planners the tools to effectively manage natural resources and to assess the implementation of regulatory policies before they are implemented.This paper describes an interactive modeling system developed within a GIS environment to facilitate rapid appraisal of the susceptibility of ground water to contamination by pesticides. The interactive system combines three widely used screening models with the ARC/INFO GIS software and a graphical user interface. Implemented on a color‐graphic engineering workstation, the interactive modeling system can be used to visualize the spatial distribution of model inputs and outputs. The advantage of this system is that instead of ad‐hoc linkage between GIS software and a simulation model, a fully integrated and interactive system in which the model equations are programmed within the GIS was developed. The impetus for developing the interactive ground‐water modeling system was the relative lack of tools that fully integrate models with GIS and the potential benefits to the resource manager in developing such integrated environmental modeling systems. There is an increasing demand, from the GIS perspective, for tools that perform functions other than organization and display of spatial data. From the ground‐water modeling perspective, several advantages can be derived from fully integrating process‐based models with the data management, analysis, and display capabilities of the GIS.
Determining 3D Capture Zones in Homogeneous, Anisotropic Aquifers
Authors: Schafer David C. 
Published: August 2005

AbstractA method is presented for determining steady‐state capture zones in three dimensions around horizontal drains and vertical wells in homogeneous, anisotropic aquifers in a uniform flow field. Equations are presented for determining drawdown and velocity vector components in three dimensions around drains and wells. Using these equations, a second‐order Runge‐Kutta particle tracking algorithm is applied to trace streamlines in three dimensions. By tracking a large number of particles, it is possible to determine areas where capture occurs and areas where particles escape capture. The resulting 3D capture zones are diagrammed as both 2D (section view) plots and 3D plots.
Microcosms for Aquifer Research: Application to Colonization of Various Sized Particles by Ground‐Water Microorganisms
Authors: Dodds Walter K. , Randel Clay A. , Edler Christopher C. 
Published: August 2005

AbstractFlow‐through microcosms were constructed to conduct ecological experiments on aquifer organisms. The two 5‐channel microcosms were simple to construct, were fed by an artesian spring, and maintained close to in situ temperature and O2 concentrations. They were used to test relative microbial colonization of three substrate sizes: silt (0.063 mm), sand (0.9 mm), and gravel (3 mm). After 96 days of incubation, O2 microelectrode measurements revealed the lowest O2 tension in the silt, the highest in the gravel, and intermediate values in the sand. Microbial activity (3[H]‐thymidine incorporation) was greatest in the gravel, followed by sand and then silt. Denitrification was greatest in the silt, followed by sand and then gravel. Microbial activity may be greatest with the largest particle size because of increased water exchange through pores, and denitrification may be greatest with the smallest particle sizes because of the occurrence of anaerobic microzones.
The Geometry of Nonwetting Liquids in the Unsaturated Zone
Authors: Hartz Michael J. , Overcamp Thomas J. 
Published: August 2005

AbstractA theory is developed to describe the geometry of nonwetting or nonaqueous phase liquids in moist unsaturated media. This theory predicts that liquids with positive values of the classical two‐dimensional spreading coefficient form pendular rings. Liquids with negative values form pendular rings in regions of high‐water tension or in regions of relatively high concentration of the nonwetting fluid, but they form insular lenses in regions of low‐water tension or regions of low concentration of the nonwetting fluid. A three‐dimensional spreading coefficient was developed to predict this behavior. Infiltrating water can cause transitions by breaking the pendular rings of nonwetting liquids in the unsaturated zone, and forming larger insular blobs as these rings coalesce. These blobs may drain downward due to gravity. These conditions may contribute to the mobility of nonwetting liquids due to percolation of water through the unsaturated zone.
A Bayesian Markov Geostatistical Model for Estimation of Hydrogeological Properties
Authors: Rosen Lars , Gustafson Gunnar 
Published: August 2005

AbstractA geostatistical methodology based on Markov‐chain analysis and Bayesian statistics was developed for probability estimations of hydrogeological and geological properties in the siting process of a nuclear waste repository. The probability estimates have practical use in decision‐making on issues such as siting, investigation programs, and construction design. The methodology is nonparametric which makes it possible to handle information that does not exhibit standard statistical distributions, as is often the case for classified information. Data do not need to meet the requirements on additivity and normality as with the geostatistical methods based on regionalized variable theory, e.g. kriging. The methodology also has a formal way for incorporating professional judgments through the use of Bayesian statistics, which allows for updating of prior estimates to posterior probabilities each time new information becomes available. A Bayesian Markov Geostatistical Model (BayMar) software was developed for implementation of the methodology in two and three dimensions. This paper gives (1) a theoretical description of the Bayesian Markov Geostatistical Model; (2) a short description of the BayMar software; and (3) an example of application of the model for estimating the suitability for repository establishment with respect to the three parameters of lithology, hydraulic conductivity, and rock quality designation index (RQD) at 400–500 meters below ground surface in an area around the Äspö Hard Rock Laboratory in southeastern Sweden.
Transport of Bromide and Other Inorganic Ions by Infiltrating Storm Water Beneath a Farmland Plot
Authors: Iqbal Mohammad Z. , Krothe Noel C. 
Published: August 2005

AbstractA hydrogeochemical study in the clay‐soil mantled portion of a karst terrane in southern Indiana demonstrated preferential flow of soil water through macropore structures that are of higher permeability than the soil matrix. Variable transport of several inorganic ions, such as Cl–, SO4=, Na+, Ca++, and Mg++, through the unsaturated zone was observed immediately after a major storm event in April, 1992. A KBr salt spray experiment during the storm led to recovery of bromide, a nonreactive, conservative ion, at a depth of 10 ft within 24 hours after the storm. The observed Br− transport rate (5 in/hr) is approximately six times greater than the expected rate of transport in the absence of preferential flow. Temporal changes in cation to anion ratios demonstrated that anions are more mobile due to the process of anionic exclusion which drives more anions out of the clay matrix whereas cations are attenuated by adsorption on the clay particles due to their charge differences. In the absence of storm‐water infiltration, the ion transport proceeds largely by matrix flow of soil water.The storm event also initiated considerable mixing of ground water through lateral flow within the aquifer. The ions, such as Cl–, NO3, Ca++, and Mg++, showed immediate dilution by storm water. Subsequently, ion concentrations in the aquifer increased to the initial level because of reequilibration with soil matrix water released from the lower part of the unsaturated zone.
Probabilistic Assessment of Ground‐Water Contamination: 2. Results of Case Study
Authors: Istok Jonathan D. , Rautman Christopher A. 
Published: August 2005

AbstractThe first paper in this series (Rautman and Istok, 1996) presented a geostatistical framework for obtaining a probabilistic assessment of ground‐water contamination. This paper presents the results of a case study that applies this framework to define the spatial extent and severity of nitrate and Dacthal (dimethyl tetrachloroterephthalate or DCPA, a herbicide) contamination in the unsaturated and saturated zones for a 150 km2 site near Ontario, Oregon. Sediment samples collected from 35 boreholes were used to compute vertical accumulations of nitrate and DCPA in the unsaturated zone. Measured nitrate and DCPA concentrations in ground‐water samples collected from 42 wells were used to compute vertical accumulations of nitrate and DCPA in the saturated zone. Sample variograms were fit with nugget and spherical models to describe the pattern of spatial continuity of nitrate and DCPA concentrations and accumulations. Conditional, sequential Gaussian simulation was used to generate 100 simulations for each variable on a 0.5 × 0.5 km grid. Probabilistic summaries of these simulations were used to develop (a) maps showing the probability of contamination exceeding specified theshold values, (b) probability distributions for contaminant accumulation and concentration at unsampled locations, (c) probabilistic descriptions for the location of contaminant‐plume boundaries, and (d) probability distributions for the total contaminated area and total contaminant mass. The results demonstrate that interpretations of site characterization data to determine the extent and magnitude of contamination at a site will vary depending upon the level of uncertainty that will be tolerated by the decision maker. This case study also illustrates the potential applicability and utility of the probabilistic approach for the interpretation of site characterization data and the design of future data collection activities.
Fracture Aperture Measurements and Migration of Solutes, Viruses, and Immiscible Creosote in a Column of Clay‐Rich Till
Authors: Hinsby K. , McKay L.D. , JØrgensen P. , Lenczewski M. , Gerba C.P. 
Published: August 2005

AbstractA series of ground‐water flow and tracer experiments were performed on an undisturbed column of fractured clay‐rich till, 0.5 m diameter by 0.5 m long, in a pressure‐controlled cell. The measured hydraulic conductivity of the sample was 1.0 to 1.2 × 10–6 m/sec and the average hydraulic gradient during the tracer experiments ranged from 0.45 to 0.49. The experiments clearly show that ground‐water flow and contaminant migration through the sample is primarily controlled by fractures and root holes. Tracer experiments using a solute (chloride), colloid‐sized bacteriophage (PRD‐1 and MS‐2) and uncharged latex microspheres, indicated very fast transport rates of 4 to 360 m/day. These rates are similar to fracture flow velocities calculated on the basis of the measured bulk hydraulic conductivity of the column, and measured fracture spacing, using the cubic law for flow through parallel‐walled fractures. Fracture aperture values calculated from the ground‐water flow data (35 to 56 μxm) are of the same magnitude as values calculated from the breakthrough of tracers (13 to 120 μm). Aperture values calculated for fractures (1 to 94 μm) and root holes (2 to 188 μm), on the basis of measured immiscible creosote entry pressures, are also comparable with these values. The injected creosote, a DNAPL, penetrated most of the visible and a few invisible fractures and root holes, indicating that, for this till, fractures and root holes are important conduits for the transport of DNAPL's.
Analysis of a Marine Intrusion by Parameters Derived from Salt‐Water Conductivity
Authors: Rozycki Alexander 
Published: August 2005

AbstractFor a one year period, conductivity and temperature were measured in extraction wells situated in two coastal aquifers in the South of Spain. Sensors were placed 3 m below water level. Spatial distributions of water conductivity fit well to an exponential function. The cross plots of the exponential function parameters emphasized the cyclical character of the marine intrusion. They also permitted analysis of the salt‐water movement during the entry and recession of the marine intrusion. The integration of the condutivity distribution improved the aquifer analysis.In the studied area, the marine intrusion corresponded to a thermal effect.Temporal distributions of the parameter, derivated from the temperature, advanced the development of the salt‐water intrusion by two weeks.An effective short‐term prediction can be accomplished through analysis of the relationship between the temporal sequence of the conductivity and the parameters obtained from the spatial distributions of conductivity.
Deformation‐Induced Changes in Hydraulic Head During Ground‐Water Withdrawal
Authors: Hsieh Paul A. 
Published: August 2005

AbstractGround‐water withdrawal from a confined or semiconfined aquifer causes three‐dimensional deformation in the pumped aquifer and in adjacent layers (overlying and underlying aquifers and aquitards). In response to the deformation, hydraulic head in the adjacent layers could rise or fall almost immediately after the start of pumping. This deformation‐induced effect is analyzed by a linear poroelasticity model using properties typical of unconsolidated sedimentary materials. Model simulations suggest that an adjacent layer undergoes horizontal compression and vertical extension when pumping begins. Hydraulic head initially drops in a region near the well and close to the pumped aquifer, but rises outside this region. Magnitude of head change varies from a few centimeters to more than 10 centimeters. Factors that influence the development of deformation‐induced effects includes matrix rigidity (shear modulus), the arrangement of aquifer and aquitards, their thicknesses, and proximity to land surface. Induced rise in hydraulic head is prominent in an aquitard that extends from land surface to a shallow pumped aquifer. Induced drop in hydraulic head is likely observed close to the well in an aquifer that is separated from the pumped aquifer by a relatively thin aquitard. Induced effects might last for hours in an aquifer, but could persist for many days in an aquitard. Induced effects are eventually dissipated by fluid flow from regions of higher head to regions of lower head, and by propagation of drawdown from the pumped aquifer into adjacent layers.
Impacts on a Sand Aquifer from an Old Septic System: Nitrate and Phosphate
Authors: Harman J. , Robertson W. D. , Cherry J. A. , Zanini L. 
Published: August 2005

AbstractFour hundred ground‐water sampling points were used to delineate a plume in an unconfined sand aquifer at a 44 year old septic system servicing a school in Ontario, Canada. A bromide tracer test indicated a residence time of one to two weeks for sewage effluent in the 1.6 meter unsaturated zone beneath the tile bed. This is sufficient time for the oxidation of all nitrogen to nitrate to be complete and for the content of dissolved organic carbon to decrease from about 19 mg/l in the septic tank to about 1 mg/l at the water table. The 15m wide plume core emanates more than 110 meters downgradient of the tile bed, has detectable dissolved oxygen, high nitrate (20–120 mg/l as N), chloride (42–209 mg/l), sodium (34–101 mg/l), calcium (120–249 mg/l), and above background sulphate, and potassium. Ground‐water flow velocity at this site is rapid (100 m/yr); thus the mapped extent of the plume (110 m) represents about one year effluent loading. Phosphate (PO43‐) concentrations at the water table (∼ 1–2 mg/l as P) appear to have reached steady state at values significantly lower than that of the effluent (9 mg/l as P). Steady‐state concentrations suggest that mineral precipitation reactions control attenuation in the unsaturated zone. A comparison of phosphate sorbed (74 mg/kg) and total P in the soil (1000 mg/kg) suggests that precipitation is a more important process in the unsaturated zone than is sorption. PO43‐ levels in the plume, however, remain elevated (0.3–1.8 mg/l as P) relative to background levels in ground water (<0.01 mg/l as P) up to 75 meters away from the tile bed. This migration distance of PO43‐ in ground water is greater than that observed at other younger septic system sites. The extent of the plume at this site suggests that long‐term PO43‐ migration in the ground‐water zone may be controlled by adsorption processes that allow slow but progressive advancement of PO43‐.
The Successful Use of Microgravity Profiling to Delineate Faults in Buried Bedrock Valleys
Authors: Allen D. M. , Michel F. A. 
Published: August 2005

AbstractSite selection for ground‐water production wells was made easier using a microgravity survey technique. The ground‐water regime beneath the Carleton University campus is dominated by fracture flow associated with major faults. These faults are located within buried bedrock valleys where preferential erosion of the bedrock has occurred. A series of faults is inferred from bedrock topography and hydrogeological testing; however, the precise orientation of the faults is to a large extent uncertain. The bedrock surface is masked by fluvial, glacial, and glaciomarine overburden of variable thickness.High precision, small‐scale microgravity profiling was carried out to identify the bedrock valleys. Gravity anomalies of up to 0.05 mgal correspond to valley depths ranging from 5 to 15 meters. The density contrast between overburden and limestone bedrock is estimated as 0.3 g/cm3. Forward modeling using a polygon technique suggests that the observed, corrected gravity profile is a smoothed reflection of the bedrock surface at depth.Based on the locations of the bedrock valleys, several faults were identified and four test wells were drilled as part of the development of Phase 2 of the Carleton Groundwater Energy Project. Three of these wells produced high yields, exceeding 60 I/sec, when converted to 12 inch diameter production wells. The fourth well also encountered a bedrock valley but with a slightly lower yield of water.The favorable drilling results have shown that small‐scale microgravity profiling, in an area that is largely unsuitable for the detection of subsurface features using other geophysical techniques, is an effective method for imaging the bedrock surface. The positions of the faults, which are known to exist on the basis of stratigraphy, geophysical well log correlations, bedrock topography, and calcite‐filled fractures exposed in outcrop or core, have been more accurately defined.
Modeling the Response of a Karstic Spring at Arteta Aquifer in Spain
Authors: Estrela T. , Sahuquillo A. 
Published: August 2005

AbstractA linear response model based on daily spring discharges has been applied in simulating the response of the karstic aquifer feeding the Arteta spring in Navarra (Spain), which is used for the water supply of the city of Pamplona. The model is derived from the eigenvalue solution of the ground‐water flow partial differential equation, a method that provides a continuously in time solution of this equation for finite‐difference or finite‐element space discretization. The modeling approach explains the recession curves composed by several decreasing exponentials observed in many karstic aquifers and differs from the classic assumption where the recession coefficients of these exponentials are identified with different flow regimes in conduit zones. Recharge‐discharge transfer has been simulated using a limited number of parameters without having to resort to methods where the impulse‐response function of the system is obtained by deconvolution.
The Different Characteristics of Aquifer Parameters and Their Implications on Pumping‐Test Analysis
Authors: Jiao J. J. , Zheng C. 
Published: August 2005

AbstractThe concepts of two‐way coordinates and one‐way coordinates are used to describe the different characteristics of two key aquifer parameters, transmissivity and storativity, under constant‐rate pumping conditions. A two‐way coordinate is such that the conditions at a given location are influenced by changes in conditions on either side of that location; a one‐way coordinate is such that the conditions at a given location are influenced by changes in conditions on only one side of that location. Results from sensitivity analysis indicate that storativity has the characteristics of two‐way coordinates, but transmissivity has the characteristics of one‐way coordinates, i.e., its information can be transferred mainly from upstream to downstream. An upstream observation well can produce information on storativity both upstream and downstream, but it can produce little information on transmissivity downstream.These characteristics of the aquifer parameters have important implications on pumping‐test designs and interpretation. For example, to estimate the parameters of an anomalous zone in an aquifer, an observation well should be located downstream but near the zone. It should not be placed upstream if the parameters downstream are to be estimated. An observation well which can provide adequate information for estimating storativity may not provide adequate information for estimating transmissivity, and vice versa. The aquifer area represented by estimated storativity may be different from that represented by estimated transmissivity.
The Point Eidothermometric Method in the Study of Coastal Aquifers
Authors: Calò Giuseppe C. , Tinelli Roccaldo 
Published: August 2005

AbstractThe eidothermometric method consists of the visualization (from the Greek word “eidos”= image) of the time evolution of thermometry in a water column, by reconstruction of the various isotherms. The image thus obtained, where basal thermometry is subject to influences of different kinds, will show such disturbances through thermometric anomalies.The main advantage offered by this method is to obtain, even at those wells with no previous information, reliable and useful data on the aquifer permeability, the occurrence of preferential discharge levels or impervious levels, and water circulation dynamics.The use of said method, moreover, proved to be fully satisfactory both when used in relation to short‐term thermal influences caused by tides and when used in relation to long‐term influences caused by sea conditions. Similar to eidothermometry, eidosalinometry also provided useful information not usually obtained by normal saline logs.