bluuebunny/crossref_metadata_2025 huggingface dataset:
Using Thermal‐Infrared Imagery to Delineate Ground‐Water Discharged
Authors: Banks William S. L. , Paylor Randall L. , Hughes W. Brian
Published: August 2005

On March 8 and 9, 1992, a thermal‐infrared‐multispectral scanner (TIMS) was flown over two military ordnance disposal facilities at the Edgewood Area of Aberdeen Proving Ground, Maryland. The data, collected by the National Aeronautics and Space Administration, in cooperation with the U.S. Army and the U.S. Geological Survey, were used to locate ground‐water discharge zones in surface water. The images from the flight show areas where ground‐water discharge is concentrated, as well as areas of diffuse discharge. Concentrated discharge is predominant in isolated or nearly isolated ponds and creeks in the study area. Diffuse discharge is found near parts of the shoreline where the study area meets the surrounding estuaries of the Chesapeake Bay and the Gunpowder River. The average temperature for surface water, measured directly in the field, and the average temperature, calculated from atmospherically corrected TIMS images, was 10.6° C (Celsius) at the first of two sites.

Potentiometric surface maps of both field sites show discharge toward the nontidal marshes, the estuaries which surround the field sites, and creeks which drain into the estuaries. The average measured temperature of ground water at both sites was 10.7° C. The calculated temperature from the TIMS imagery at both sites where ground‐water discharge is concentrated within a surface‐water body is 10.4° C. In the estuaries which surround the field sites, field measurements of temperature were made resulting in an average temperature of 9.0° C. The average calculated TIMS temperature from the estuaries was 9.3° C. Along the shoreline at the first site and within 40 to 80 meters of the western and southern shores of the second site, water was 1° to 2° C warmer than water more than 80 meters away. This pattern of warmer water grading to cooler water in an offshore direction could result from diffuse ground‐water discharge. Tonal differences in the TIMS imagery could indicate changes in surface‐water temperatures. These tonal differences can be interpreted to delineate the location and extent of ground‐water discharge to bodies of surface water.
A Semianalytical Solution of One‐Dimensional Advective‐Dispersive Solute Transport Under an Arbitrary Concentration Boundary Condition
Authors: Ge Shemin , Lu Ning
Published: August 2005

By employing the principle of superposition, we offer a semianalytical solution for a one‐dimensional advective‐dispersive solute transport equation under an arbitrary concentration boundary condition. The technique is applicable to many other existing analytical solutions of solute transport problems.
Monitoring Networks in Fractured Rocks: A Decision Analysis Approach
Authors: Jardine Karen , Smith Leslie , Clemo Tom
Published: August 2005

Hydrogeological decision analysis is applied to the design of a performance monitoring network at a waste management facility overlying fractured bedrock. The objective of the monitoring system is to detect contaminants before they reach a regulatory compliance boundary in order to enable early and less costly on‐site remediation, and avoid the potentially more costly consequences of failure. Features in the design of the monitoring network include the number of monitoring wells to be installed and their locations, where in each borehole to position discrete monitoring zones, and how often to take water samples. The decision model identifies the preferred monitoring strategy as the design alternative, among all those considered, that minimizes the sum of the monitoring costs and the expected costs of failure and on‐site remediation. At a given distance from the facility, the highest probabilities of plume detection are obtained when the fractures intersecting the borehole wall that carry the largest flows are monitored. Monitoring intervals centered on fractures with highest aperture, or regions of highest fracture density, yield intermediate values, while intervals located at predetermined depths yield the lowest probabilities of detection. The monitoring scheme with the highest probability of detection is not necessarily the preferred monitoring strategy. For monitoring options that have a higher probability of detection than the preferred monitoring strategy, the higher expected cost of on‐site remediation, when combined with the increased cost of monitoring required to provide the higher probability of detection, can outweigh the reduction in the expected cost of failure brought about by a higher probability of detection. When the probability of contaminants migrating to the compliance boundary is small during the compliance period, changes in the probability of detection brought about by a more intense monitoring effort do not affect the expected cost of failure much; in these instances, the decision model may point to a reduced effort in performance monitoring.
Type‐Curve Matching Using a Computer Spreadsheet
Authors: Cleveland Theodore G.
Published: August 2005

This note shows how to construct and perform a graphical type‐curve analysis using a computer spreadsheet. Formulas are provided to generate the axis shifting behavior that is required for the graphical fit. Arbitrary match points are obtained by trial‐and‐error (or by closed form solution) for use in the calculation of aquifer hydraulic parameters. The analysis is illustrated using a leaky aquifer type curve and a confined aquifer type curve. Macro programming is not required, only data entry and the ability to use plotting features of a computer spreadsheet. The approach can be adapted for parameter estimation using any tabulated type curve.
Analysis of the Deformation of Homogeneous Electrical Fields Over Some Two‐Dimensional Structures
Authors: Srinivas M. , Sundararajan N.
Published: August 2005

An analysis of the deformation of a homogeneous electrical field caused by a long, thin inclined bed, which is of considerable importance in the exploration of ground water and minerals, is presented using the Hilbert transform. The thickness of the bed and the inclination are expressed as a function of the abscissae of the points of intersection of the horizontal and vertical derivatives of the field. The procedure is illustrated with a theoretical example and substantiated with field examples from the fractured Crystalline Basement Complex in Burkina Faso, Africa, and Pre‐Cambrian limestones of the Cuddappah Basin in Andhra Pradesh, India. The results derived from the analytical method are shown to agree well with the ground truth.
Interpretation of Sorption Studies for Compound Isomers or Mixtures
Authors: Soerens Thomas S. , Sabatini David A.
Published: August 2005

For compound mixtures or compounds with two or more differently sorbing isomers which are not analytically distinguished, combined sorption parameters determined in the laboratory are dependent upon the ratio of different compounds or isomers and upon experimental methods and conditions. The purpose of this paper is to mathematically examine the effects of these factors on sorption parameters calculated from batch (shake‐flask) and continuous flow column sorption studies of compound or isomer mixtures. The analysis in this paper helps explain the apparent anomalies between batch and column sorption results in previously published studies of Rhodamine WT (RWT). In batch reactors, the solid: liquid ratio, Rs, has a major effect on batch sorption results. As Rs decreases, partitioning coefficients determined from batch results approach those determined from column results, which is contrary to the trend that may be anticipated for single component analytes. A single column sorption coefficient or retardation factor for multiple constituents does not accurately describe the transport of the individual compounds. The implications of the effects of experimental methods suggest that sorption parameters determined from batch studies for compound or isomer mixtures (e.g., BTEX, combined xylenes, and others) should be interpreted with care. Significant errors in prediction and description of contaminant transport can result if the presence of multiple compounds or isomers is not recognized or if batch or column data for compound or isomer mixtures are misinterpreted.
Interactive Modeling of Ground‐Water Vulnerability Within a Geographic Information System Environmenta
Authors: Tim U. Sunday , Jain Dharmesh , Liao Hsiu‐Huka
Published: August 2005

During 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

A 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

Flow‐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

A 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

A 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

A 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

The 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

A 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

For 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

Ground‐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

Four 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

Site 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

A 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

The 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

The 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.
Numerical Ground‐Water Flow Modeling of the Snake River Plain Aquifer Using the Superposition Technique
Authors: Hubbel J. M. , Bishop C. W. , Johnson G. S. , Lucas J. G.
Published: August 2005

Predictive ground‐water flow modeling may be simplified by application of superposition when the governing equations are linear. The simplification allows evaluation of impacts of individual aquifer stresses and minimized model input, output, and interpretation. Modeling is performed by using (1) boundary conditions and aquifer properties provided by previous calibrations or analytical techniques, (2) setting the initial potentiometric surface and prescribed‐head boundaries to an arbitrary horizontal datum, and (3) simulating a specific recharge or discharge stress.

Superposition was applied to an existing, calibrated model of the Snake River Plain aquifer to simplify prediction of changes in interaction with the Snake River. Simulations predict the temporal relationships between ground‐water use at multiple locations within the Snake River Plain and surface‐water depletion in four hydraulically connected reaches of the Snake River. Simulated aquifer water use at a location approximately five miles from a hydraulically connected river reach results in river depletions greater than 80% of the pumping rate after 10 years. Water use further than 50 miles from hydraulically connected river reaches results in depletions from 10 to 30% of the annual average pumping rate after 100 years. Results present spatial and temporal impacts of water uses on the Plain that are conceptually and quantitatively beneficial to water resources planners and water users.
A Direct Substitution Method for Multicomponent Solute Transport in Ground Water
Authors: Shen Huiying , Nikolaidis Nikolaos P.
Published: August 2005

A numerical method was developed using a direct substitution approach for simulating one‐dimensional multicomponent solute transport in ground water. The method has the ability to treat equilibrium reactions of aqueous and surface complexation, and precipitation‐dissolution. The concentrations of aqueous component species, adsorbed component species, and precipitated species are chosen as the principal dependent variables. The substitution takes place after the transport equation is discretized. The resulting system of equations is solved using the Newton‐Raphson method and the Jacobian matrix is computed analytically. This method is computationally more efficient than sequential iteration methods due to its faster convergence rate. It is also computationally more efficient than other direct substitution methods which compute the Jacobian matrix numerically.
Incorporating Auxiliary Geophysical Data into Ground‐Water Flow Parameter Estimation
Authors: Cassiani Giorgio , Medina Miguel A.
Published: August 2005

The incorporation of auxiliary data into ground‐water flow parameter estimation is a challenging task which can ultimately result in a better site characterization. In this study a maximum likelihood estimation procedure has been applied to the joint identification of the parameters of the aquifer transmissivity random field, and the parameters of the linear regression between the logarithm of transmissivity and the logarithm of the electrical transverse formation factor (TF), determined from surface geoelectrical methods (Vertical Electrical Sounding or V.E.S.). This approach is basically a co‐kriging technique applied to the transmissivity and transverse formation factor random fields, but it avoids the independent estimation of the cross‐covariances and the secondary variable covariance. The procedure needs some direct well data for transmissivity and a (usually larger) number of V.E.S. measurements which have to be in part at a distance from the well locations in order to provide useful information. The algorithm determines the characteristics of the local (site dependent) transmissivity‐transverse formation factor relationship and utilizes this auxiliary information for a geostatistical transmissivity field estimation. The methodology is tested on a real field scenario: a fractured aquifer impacted by landfill leachate contamination. The use of the formation factor in place of the raw resistivity of the subsoil layers accounts for possible effects of clay and contaminant concentration on pore‐water resistivity. The information provided by the V.E.S. can add, to some extent, to the understanding of the aquifer characteristics and vulnerability. However, the specificity of each site has to be fully understood for an effective application of the present procedure. It seems unlikely that geoelectric data can differentiate between transmissivity values differing by less than two or three orders of magnitude.
Capture Zones for Passive Wells in Heterogeneous Unconfined Aquifers
Authors: Cole Bryce E. , Silliman Stephen E.
Published: August 2005

Many piezometers/wells produce at such low rates and frequency that their impact on local hydraulics is negligible, e.g. monitoring piezometers or homeowner wells installed in highly permeable soils. Defining a deterministic capture zone for such wells is often of limited utility as the capture zone is effectively a single flow line directed upgradient. In order to provide more insight into the capture zone of such wells, a statistically based capture zone, termed a “percentile capture contour” (PCC), is introduced and analyzed. The capture zone is defined by quantifying, for a given travel time, the variation of the length and orientation of the flow line emanating upgradient from the well. Capture zone variation herein depends on second‐order stationary random hydraulic conductivity fields and is calculated using Monte Carlo analysis.

Monte Carlo analysis yielded increases in mean travel distances as the variance and/or integral scale in log K increased, but decreases as the angle between the principal direction of the correlation structure and the regional flow increased. The average travel distance exceeded the travel distance estimated by a homogeneous solution using the geometric mean hydraulic conductivity. Transverse variation depended both on the variance and integral scale of log K, but was insensitive to the orientation of the principal correlation direction. The mean orientation of the flow path varied with the principal direction of the correlation structure, deviating up to 20° from the orientation of the hydraulic gradient. These observations are consistent with flow following preferential pathways and indicate that significant uncertainty exists for source prediction of water feeding passive wells.
Numerical Simulation of Air Sparging for Remediation of NAPL Contamination
Authors: McCray John E. , Falta Ronald W.
Published: August 2005

A numerical simulation study of air sparging for the removal of nonaqueous phase liquids (NAPLs) from the subsurface is presented. These simulations were performed using the T2VOC integrated finite‐difference, multiphase‐flow, contaminant transport code. The code is used to model two‐dimensional air sparging experiments from Ji et al. (1993) which include both homogeneous and heterogeneous permeability distributions. The model predicts the experimental gas plume shape and behavior very well. Field‐scale simulations using a radially symmetric, cylindrical mesh are then used to model hypothetical DNAPL and LNAPL spills and air sparging remediation performance in various hydrogeologic settings. Both homogeneous and heterogeneous systems are considered. The results of the study indicate that the sparging‐induced gas pressure increase, or “positive pressure,” measured at steady state below the water table, closely corresponds to both the subsurface gas distribution and the effective zone of contaminant reduction. Because this positive pressure is easily measured in the field with a simple monitoring device, it can be used to realistically define the sparging radius of influence.
A Framework for Assessing Risk Reduction Due to DNAPL Mass Removal from Low‐Permeability Soils
Authors: Freeze R. Allan , McWhorter David B.
Published: August 2005

Many emerging remediation technologies are designed to remove contaminant mass from source zones at DNAPL sites in response to regulatory requirements. There is often concern in the regulated community as to whether mass removal actually reduces risk, or whether the small risk reductions achieved warrant the large costs incurred. This paper sets out a proposed framework for quantifying the degree to which risk is reduced as mass is removed from DNAPL source areas in shallow, saturated, low‐permeability media. Risk is defined in terms of meeting an alternate concentration limit (ACL) at a compliance well in an aquifer underlying the source zone. The ACL is back‐calculated from a carcinogenic health‐risk characterization at a down gradient water‐supply well. Source‐zone mass‐removal efficiencies are heavily dependent on the distribution of mass between media (fractures, matrix) and phase (aqueous, sorbed, NAPL). Due to the uncertainties in currently available technology performance data, the scope of the paper is limited to developing a framework for generic technologies rather than making specific risk‐reduction calculations for individual technologies. Despite the qualitative nature of the exercise, results imply that very high total mass‐removal efficiencies are required to achieve significant long‐term risk reduction with technology applications of finite duration. This paper is not an argument for no action at contaminated sites. Rather, it provides support for the conclusions of Cherry et al. (1992) that the primary goal of current remediation should be short‐term risk reduction through containment, with the aim to pass on to future generations site conditions that are well‐suited to the future applications of emerging technologies with improved mass‐removal capabilities.
A Method for Evaluation of Artificial Recharge Through Percolation Tanks Using Environmental Chloride
Authors: Sukhija B. S. , Reddy D. V. , Nandakumar M. V. , Rama
Published: August 2005

For meeting the growing demand on ground water in hard rock areas of India, man‐made percolation tanks have become important structures for augmenting ground‐water recharge. Keeping in view their increasing number and cost involved in their construction and their temporal variation in percolation due to silting or desilting operations if undertaken, it is vital to develop proper methodology to evaluate the performance of these structures. A method employing the mass balance of environmental chloride in the tank has been developed for this purpose. The results obtained using this method at one experimental site indicate that an average of 30–35% of impounded water is recharged through this structure situated in granitic gneissic terrain of a semiarid region of India. The remainder is lost through evaporation. The method developed is simple, inexpensive, and sensitive enough to observe the temporal variation in the recharge rate through such tanks.
Transient Ground‐Water Flow Simulation Using a Fuzzy Set Approacha
Authors: Dou Chunhua , Woldt Wayne , Dahab Mohamed , Bogardi Istvan
Published: August 2005

The expense of characterizing aquifer spatial variability often results in a lack of available or realistically obtainable direct measurement data for ground‐water system simulation. As a consequence ground‐water models that are able to utilize imprecise or “soft” information need to be developed. In this paper, a methodology based on fuzzy set theory is developed to incorporate imprecise data into transient ground‐water flow simulation. The imprecise model parameters may come from indirect measurements, expert judgment, and subjective interpretation of available information. Fuzzy numbers are used to represent imprecise parameters. They are also used as a measure of the uncertainty associated with the hydraulic head due to the imprecision of input data. A fuzzy ground‐water flow model is developed by linking the finite‐difference method with fuzzy number representations. Fuzzy number operations (α‐level cuts) are used to solve the resulting fuzzy ground‐water flow model and are extended to consider the dependencies among hydraulic head coefficients. With the fuzzy number inputs, the transient fuzzy ground‐water flow model provides a direct measure of hydraulic head uncertainties in the time domain. The model outputs can be used as the inputs for subsequent risk analysis and decision‐making processes. The fuzzy modeling technique can handle imprecise information directly without generating a large number of realizations. It is also flexible as it can handle different types of membership functions describing fuzzy input parameters. The methodology can be used to combine data with different levels of quality into ground‐water flow models and provides a realistic method to handle parameter imprecision, especially expert judgment and subjective information. A numerical model based on the methodology was tested against the Theis analytical solution for a homogeneous aquifer with pumping. The tested model was also applied to two different heterogeneous flow fields to demonstrate the methodology.
Geoelectrical and Hydrogeochemical Studies for Delineating Ground‐Water Contamination Due to Salt‐Water Intrusion in the Northern Part of the Nile Delta, Egypt
Authors: Ebraheem Abdel‐Azim M. , Senosy Mahmoud M. , Dahab Kamal A.
Published: August 2005

A resistivity survey was conducted in the Nile Delta area to delineate ground‐water contamination caused by an improper sewage and irrigation drainage system, leaching from old lagoonal deposits, and salt‐water intrusion. Existing monitoring wells were used to measure the horizontal and vertical variations in water salinity. Vertical electrical sounding (VES) data for sounding points located near monitoring wells, together with the water salinity data of these wells, were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used together with the constructed apparent resistivity depth and geoelectric longitudinal sections to identify three zones of water‐bearing formation (fresh‐, brackish‐, and salt‐water zones). Along the studied profile, depth to the fresh‐brackish interface exceeds 150 m at Tanta City and decreases northward to 40 m or less between Qutor and Kafr El‐Sheikh. Depth to the brackish‐saline interface exceeds 180 m south of Kafr‐El‐Sheikh and decreases northward to 70 m near Hadadi village.
Potential Inaccuracies in MODFLOW Simulations Involving the SIP and SSOR Methods for Matrix Solution
Authors: Osiensky James L. , Williams Roy E.
Published: August 2005

The ground‐water flow model MODFLOW is the most widely used and accepted model of its type in the world today. Several modeling runs were completed with MODFLOW for relatively simple hydrogeologic conditions to evaluate the accuracy of the strongly implicit procedure (SIP), slice successive overrelaxation (SSOR) and preconditioned conjugate‐gradient 2 (PCG2) methods for matrix solution. A series of simulations was performed with the SIP, SSOR, and PCG2 methods while adjusting the matrix solution parameters sequentially one at a time. A wide range of converged solutions was generated for identical input data. The simulation results show that MODFLOW will produce accurate results for the specific conditions simulated with PCG2, or with SIP if the proper combination of SIP matrix solution parameters is chosen by the user. Accurate results could not be obtained with SSOR for any of the combinations of matrix solution parameters used in this investigation. The simulation results confirm that model convergence for a small head change convergence criterion is not a good indicator of accurate results unless water balance error also is small.
Analytical Mass Leaching Model for Contaminated Soil and Soil Stabilized Waste
Authors: Shackelford Charles D. , Glade Michael J.
Published: August 2005

An analytical model for evaluating mass leaching from contaminated soil or soil stabilized waste is presented. The model is based on mass transport due to advection, dispersion, and retardation and can be used to evaluate the suitability and/or efficiency of soil washing solutions based on the results of column leaching studies. The model differs from more traditional models for column leaching studies in that the analysis is based on the cumulative mass of leachate instead of leachate concentration. A cumulative mass basis for leaching eliminates the requirement for determination of “instantaneous” effluent concentrations in the more traditional column leaching approach thereby allowing for the collection of relatively large effluent volumes. The cumulative masses of three heavy metals—Cd, Pb, and Zn—leached from two specimens of soil mixed with fly ash are analyzed with the mass leaching model to illustrate application and limitation of the model.