bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluid Density and Gravitational Variations in Deep Boreholes and Their Effect on Fluid Potential
Authors: Oberlander P. L.
Published: August 2005

As depth below the water table increases, there can be significant spatial variations in fluid density. Fluid density is a function of fluid temperature, total dissolved solids and gases content, fluid compressibility, and the force of gravity. Variations in fluid density can affect the applicability of measured water levels to represent fluid pressure at depth and the existence of a scalar fluid potential. Where ground water is sufficiently heterogeneous, fluid pressure and fluid density must be known spatially to properly determine the three‐dimensional impelling force per unit mass E =— [gk + (1/p) ▽P]. Assuming that the water‐level elevation in deep boreholes represents a fluid potential may result in significant errors in determining flow directions and quantities under conditions of a variable density fluid and low hydraulic gradients. Boreholes constructed to investigate the feasibility of deep geologic disposal of nuclear waste have penetrated to depths greater than 1,500 m below the Earth's surface. In these deep boreholes, fluid density variations may need to be considered as a part of the hydrologic analysis. Fluid density variations with depth, predicted as general cases based on simple models, indicate the relative importance of temperature, compressibility, and gravity variations at three potential high‐level nuclear waste repository locations. Fluid density generally decreases with depth for sites where geothermal gradients are greater than 20°C/km, and thermal expansion can offset the effects of fluid compressibility.
Brine Discharge and Salinization, Concho River Watershed, West Texas
Authors: Dutton Alan R. , Richter Bernd C. , Kreitler Charles W.
Published: August 2005

Discharge of naturally occurring brine from the Southern Great Plains regional ground‐water flow system significantly affects water quality in local aquifers in the Concho River watershed in West Texas. Aquifers in outcropping Permian rocks locally contain brine and hydrocarbons at depths as shallow as 135 ft (41 m). Maps of hydraulic head, salinity, and hydrochemical facies and graphs of ionic ratios and stable isotopic composition locate where brackish to saline ground water occurs naturally as a result of mixing between locally recharged meteoric water and subsurface brine in the regional flow system. Br/Cl, CI/SO4, Ca/Na, and δD/δ18O ratios distinguish between brine sources in the mixing zone. For example, chemical composition of brackish‐to‐saline shallow ground waters beneath the Concho River watershed more closely resembles the composition of Permian than of Pennsylvanian formation brines. Other possible salinity sources include (1) seepage of salt water from rocks beneath oil‐field brine‐disposal p ts, which ceased operation in the late 1960 s, and (2) upward flow of artesian salt water across confining beds through decades‐old abandoned oil‐exploration holes. These sources are superposed on the naturally occurring mixing zone between brine and fresh water.
Conjunctive Use of Geophysical and Geological Data in the Study of an Alluvial Aquifer
Authors: Ayers Jerry F.
Published: August 2005

A geoelectric survey, composed of vertical electrical soundings, was conducted over part of the lower Platte Valley alluvial aquifer of east‐central Nebraska. Survey results, in conjunction with seismic‐survey data and test‐ hole‐log information, provided the basis to map the areal extent and thickness of a near‐surface, low‐permeability clay unit. Because of the low hydraulic conductivity of the clay, the unit forms a confining layer over a significant part of the aquifer.

Generally, the approach to evaluating the lower Platte Valley alluvial aquifer for sustained yield has been to assume that the entire flow system is under water‐table conditions. However, numerical‐model simulations with and without the clay unit indicate that this confining layer has a significant effect on the hydraulic behavior of the groundwater flow system under pumping stresses.

An estimate of the bulk porosity of the aquifer was made by using geoelectric data and applying the Archie equation. Values of porosity ranged from 0·27 to 0·43; although reasonable for fluvial sand and gravel, the range is higher than previous estimates.
Geochemical Comparison of Ground Water in Areas of New England, New York, and Pennsylvania
Authors: Rogers Robert J.
Published: August 2005

The ground‐water geochemistry of glacial drift and bedrock of selected areas of New England, New York, and Pennsylvania differs considerably among the areas as a result of differences in bedrock geology. The New England study area is underlain primarily by feldspathic rock, large areas of New York are underlain primarily by carbonate and terrigenous sedimentary rock and some evaporite deposits, and glaciated areas of Pennsylvania are underlain primarily by clastic sedimentary rock with minor carbonate rocks. Mean concentrations of most solutes are greatest in the New York area and least in the New England area.

In New England, the ground‐water geochemistry results mainly from the reaction of CO2‐charged water with feldspar and other primary silicates. Water in the New England bedrock is more highly evolved geochemically than water in the drift, presumably as a result of its longer residence time.

In the New York area, the geochemistry of water in both types of aquifers results mainly from carbonate‐ mineral dissolution. Water in most glacial drift and bedrock is saturated with respect to calcite. In some parts of New York, the dissolution of evaporite minerals has a marked effect on the water chemistry of the bedrock.

In most of the Pennsylvania area, the geochemistry of water in both types of aquifers indicates that, although carbonate minerals are the principal reactants, their influence on water chemistry is less than in New York. In parts of Pennsylvania, chemical differences between ground water from drift and ground water from bedrock are attributed to a higher proportion of reactive minerals in the drift than in the local bedrock as a result of glacial transport.
Aerobic Biodegradation of Benzene, Toluene, and Xylene in a Sandy Aquifer—Data Analysis and Computer Modeling
Authors: Chiang C. Y. , Salanitro J. P. , Chai E. Y. , Colthart J. D. , Klein C. L.
Published: August 2005

Soluble hydrocarbon and dissolved oxygen (DO) in a shallow aquifer beneath a field site were characterized by sampling ground water at 42 monitoring wells. Results from 10 sampling periods over three years showed a significant reduction in total benzene mass with time in ground water. These reduction and leakage rates from sources were determined from material balance and nonlinear least‐squares analyses. The natural attenuation rate was calculated to be 0.95%/day. Spatial relationships between DO and total benzene, toluene, and xylene (BTX) were shown to be strongly correlated by statistical analyses and solute transport modeling. In addition, laboratory microcosm biodegradation experiments were performed to determine possible threshold limits for aromatic hydrocarbon oxidation under varying levels of dissolved oxygen. The results were remarkably consistent with field data on the presence of high or low levels of BTX and DO in several monitoring well‐water samples.
Origin of the Saline Ground Water in Wadi Ar‐Rumah, Saudi Arabia
Authors: Sowayan A. M. , Allayla Rashid
Published: August 2005

Among the geologic formations traversed by Wadi Ar‐Rumah in north central Saudi Arabia, is the Saq Sandstone, an extensive and vitally important aquifer. However, the aquifer contains highly saline water in the area where Wadi Ar‐Rumah intersects the outcrop of the aquifer. The area is agriculturally important, but the saline water has caused, and is likely to continue to cause problems due to its intrusion into other parts of the aquifer as a result of heavy pumping.

The geology, hydrogeology, and hydrochemistry of the area were examined in this study. Pertinent field data were used to explain the likely way in which the saline water was formed. At the end of the last pluvial period, the ephemeral runoff in the wadi decreased and a clay layer was deposited on its floor. Ground water was near the surface and its evaporation by capillary draw led to a concentration of solutes. A shallow clay layer prevented wadi flows from flushing out the saline ground water.
A Three‐Dimensional Mixing Cell Solute Transport Model and Its Application
Authors: Rao Bhasker K. , Hathaway Deborah L.
Published: August 2005

A three‐dimensional mixing cell solute transport model has been developed based on the principles of conservation of mass for water and solute. As a first approximation to solute transport phenomenon, dispersion is ignored, but it is recognized that the numerical dispersion introduced as an artifact of the solution procedure represents physical dispersion in the results obtained from the model. The numerical dispersion can be controlled to some extent. The simplicity of principles on which the model is based makes it easy to understand and use. The formulation is used in conjunction with the McDonald and Harbaugh ground‐water flow model.

The model has been applied to an aquifer located in southern New Mexico and Texas to predict chloride concentration changes resulting from proposed future pumping to supply municipal water for the city of El Paso, Texas.
Waste Stabilization in Multilayer Aquifers by Optimal Hydraulic Control
Authors: Aral M. M.
Published: August 2005

Migration of contaminant plumes in aquifer systems can be controlled by producing desired changes in local flow rates and hydraulic gradients through the use of pumping and recharge wells. Such management scenarios have been used in the past for controlled operations in main aquifers. It is also possible to describe similar control procedures for multilayer aquifer systems. In these applications the migration of contaminant plumes in one layer may be controlled through the use of pumping and recharge wells in other layers which control the hydraulic gradients in the contaminated aquifer. In such applications the contaminated aquifer will not be interfered with and hydraulic gradient control operations will be performed on adjacent aquifer layers avoiding direct contact with the contamination source. Such operations may prove useful in case of hazardous waste management. In the study discussed here, mathematical preliminaries of the models utilized in this type of an operation are reviewed, and the effects of management scenarios are discussed for a typical aquifer considering only the hydraulic control aspects of the management process. Management procedures which incorporate the contaminant transport process and operational cost optimization processes into the analysis are not the subject matter of this study.
The Electrical Resistivity of the Vadose Zone — Field Survey
Authors: Frohlich Reinhard K. , Parke Craig D.
Published: August 2005

An expansion of Archie's law relates the electrical resistivity of the unsaturated zone to pore‐water resistivity, porosity, saturation, electrical matrix conductivity, and lithological constants. With decreasing saturation the effect of the matrix conductivity increases relative to the electrical conduction of the pore fluid.

The bulk electrical resistivity depends on water quality and quantity due to its dependence on pore‐water resistivity and porosity. It is also influenced by the hydraulic conductivity due to the surface conductivity of the grain matrix, which is proportional to grain size. Pore‐water conductivity and grain‐surface conductivity can be distinguished from each other if resistivity measurements at various degrees of saturation are available.

Observations in test wells through glacial stream deposits with a neutron moisture probe show, as expected, a decrease in the saturation of the vadose zone during the transition from late spring to the dry summer season. This decrease was correlated with the transverse resistance of the unsaturated zone derived from an interpretation of geo‐electrical depth soundings near the test wells. In the fine to medium sand of the glacial outwash material, the surface conduction of the grains was found to be negligibly small.
Natural Bioremediation of Organic Contaminants in Ground Water Cliffs‐Dow Superfund Site
Authors: Klečka Gary M. , Davis John W. , Gray Doug R. , Madsen Steve S.
Published: August 2005

Ground water in the immediate vicinity of an area previously used for the disposal of charcoal manufacturing wastes has been shown to contain low levels of phenolic and polycyclic compounds. Based on the analysis of samples obtained from monitoring wells, the levels of the organic contaminants are reduced to near or below the detection limit within a distance of 100 meters downgradient of the fill. Examination of the ground‐water chemistry indicated that the aquifer is essentially aerobic across the site, except in the immediate vicinity of the fill. At this point, dissolved oxygen is apparently depleted due to the biodegradation of organic contaminants introduced into the ground water, with a concomitant increase in the inorganic carbon concentration. Laboratory microcosm experiments demonstrated that the naturally occurring microorganisms can readily degrade a mixture of the predominant organic contaminants. Half‐lives for biodegradation were in the range of 3 to 8 days for phenolic substrates, and 11 to 18 days for naphthalene. Computer model simulations indicated that the attenuation observed in the aquifer cannot be explained in terms of physical processes such as adsorption or dispersion, but is consistent with biological degradation.
Causes of Soil Salinization: 2. A Basin in East‐Central Alberta, Canada
Authors: Hendry M. J. , Chan G. W. , Harker D. B.
Published: August 2005

The cause of soil salinization in a 21‐ha area of gently rolling topography in Alberta was investigated. The geology of the basin consists of lenticular Cretaceous sediments overlain by tills and lacustrine deposits. Interpretation of vertical hydraulic‐head data showed that regional discharge of ground water from bedrock is not a cause of salinization in the study area. Results of stream‐function modeling suggested that most of the water causing salinization is not derived from local topographic highs. Modeling results also suggested that the direction of ground‐water flow throughout the area is vertically downward through unconsolidated Quaternary deposits and into bedrock. Tritium analyses of pore water distilled from core samples confirmed that the ground water causing salinization was not derived from the local topographic highs, nor from deeper geologic deposits. Hydrograph analysis indicated that the salinization was derived from evaporation from seasonally high water tables caused by ponded surface water and spring snowmelt in localized depressional areas.
Elucidating Ground‐Water Flow Paths in a Desert Terrane by Geochemical Methods
Authors: Fritz Steven J. , Lopez Hector J. , Wilson Michael P.
Published: August 2005

Delineating ground‐water flow paths is difficult to accomplish in desert terranes because paucity of wells and boreholes yields little data to construct hydrologic interpretations based upon physical parameters. This is especially true in the Big Bend National Park where, in a study area encompassing over 500 km2, there are only four wells and six perennial springs. These wells and springs were sampled and analyzed for major‐element chemistry as well as for stable and naturally occurring radioactive isotopes to identify sources of recharge for the springs which discharge along banks of arroyos incised in alluvial pediment lying about 900 meters below the uplands of the Chisos Mountains.

The springs recharge could be from three sources: (1) infiltration of precipitation falling on the desert floor to discharge at nearby arroyos; (2) infiltration of water at the onlap of the alluvial fan with the crystalline rock of the Chisos uplands and subsequent flow within the fan toward lowland springs; and (3) upward migration of deep‐seated water. Of these, the third scenario is least compatible with respect to temperature, dissolved oxygen, and isotopic data.

The waters total dissolved solids and calcite saturation indices increase with decreasing altitude, suggesting recharge from the Chisos uplands. However, temperature, dissolved oxygen, δ18O, tritium, and Carbon‐14 data indicate a significant recharge component to springs occurs by infiltration of infrequent precipitation falling on the arid alluvial lowlands. This water percolates through the soil zone to aquitards (essentially calcitic hardpans) which function as horizons which channel the water laterally toward discharge in springs. The springs recharge‐to‐discharge paths are short with flow being slow enough to reflect seasonal temperature differences of greater than 12°, yet recent enough to contain post‐bomb spikes of tritium and Carbon‐14.
A Field Evaluation of In‐Situ Biodegradation of Chlorinated Ethenes: Part I, Methodology and Field Site Characterization
Authors: Roberts Paul V. , Hopkins Gary D. , Mackay Douglas M. , Semprini Lewis
Published: August 2005

Careful site characterization and implementation of quantitative monitoring methods are prerequisites for a convincing evaluation of enhanced biostimulation for aquifer restoration. This paper describes the characterization of a site at Moffett Naval Air Station, Mountain View, California, and the implementation of a data acquisition system suitable for real‐time monitoring of subsequent aquifer restoration experiments. A shallow, confined aquifer was chosen for the enhanced biodegradation demonstration, and was shown to have suitable hydraulic and geochemical characteristics. Injection and extraction wells were installed at a distance of 6 m, with intermediate monitoring wells at distances of 1, 2.2, and 4 meters from the injection well. Bromide tracer tests revealed travel times of S to 27 hours from the injection well to the various monitoring wells, and 20 to 42 hours from the injection well to the extraction well. Complete breakthrough of the tracer at the monitoring wells was facilitated by choosing a line of wells aligned with the regional flow, and selecting injection and extraction flow rates of approximately 1.5 and 10 liters/min. Transport studies were conducted with selected halogenated organic compounds. The retardation factors were found to range from approximately 2 to 12. The breakthrough responses for the more strongly sorbing compounds, e.g. TCE, exhibited pronounced tailing, such that a minimum period of several weeks was required to achieve complete saturation of the aquifer. The microcomputer‐driven sampling, analysis and data management system provided automated data acquisition at sample intervals of 40 minutes, with coefficients of variation smaller than 20%, and allowed for real‐time surveillance of the dynamic responses. Overall, the conditions were favorable for a quantitative evaluation of in‐situ aquifer restoration by enhanced biodegradation.
A Device for In Situ Determination of Geochemical Transport Parameters 2. Biochemical Reactions
Authors: Gillham R. W. , Starr R. C. , Miller D. J.
Published: August 2005

Chemical and biological reaction rates are required in estimating migration rates of many reactive contaminants in ground water, and as input data for mathematical models. Reaction rates must be measured, and depend on environmental conditions that are often difficult to duplicate in the laboratory. In situ rate measurement minimizes the difficulties of controlling environmental variables such as temperature, pH, Eh, DO, solution and solid phase composition, and bacterial population.

The instrument described in this paper isolates a 1.9 liter portion of an aquifer for in situ biochemical rate measurement. The device has been used successfully to measure the rate of reactions involving inorganic and organic contaminants in sandy aquifers. Two applications of the device, measurement of denitrification rates and rates of biodegradation of benzene, are presented.
Column Studies on Methanotrophic Degradation of Trichloroethene and 1,2‐Dichloroethane
Authors: Lanzarone Nancy A. , McCarty Perry L.
Published: August 2005

The potential for and variables affecting enhanced aerobic biodegradation of 14C‐labeled trichloroethene (TCE) and 1,2‐dichloroethane (1,2‐DC A) were evaluated using laboratory columns packed with fully saturated sandy aquifer material. The column fluids were exchanged weekly to simulate the growth of native microorganisms capable of biotransforming halogenated aliphatics. The exchange solutions for seven columns, one of which served as a control, contained dissolved oxygen as the electron acceptor. The electron donor, or primary substrate, for another column was dissolved propane, and the remaining five columns were fed varying concentrations of dissolved methane.

Propane was not consumed, and TCE degradation did not occur in this column. However, methane was utilized in other columns, and the resulting stimulated populations mineralized both TCE and 1,2‐DCA to CO2. Little or no TCE degradation occurred when the methane concentration was 4.5 mg/1, but when the methane was reduced to 1.5 mg/1, degradation occurred. TCE degradation was greatest when either a low methane concentration (1.5 mg/1) or an alternating pulse of methane (4.5 mg/1 or 1.5 mg/1) with oxygen one week followed by oxygen only the next was used. Nutrient supplements (NH4+ and PO42‐) did not conclusively enhance TCE degradation.

When TCE addition was stopped and methanotrophic bacteria stimulation was continued, half of the 14C from previously sorbed TCE that was subsequently eluted by exchange was present as nonvolatile compounds and CO2, and the other half as TCE. With a caution that the results obtained are site‐specific, they do suggest that the addition of methane and oxygen to water circulated through a ground‐water system to remove TCE by aboveground treatment can, in some cases at least, result in a doubling of the rate of removal and affect mineralization of about one‐half of the TCE removed.
Effect of Sensor Error on Interpretation of Long‐Term Water‐Level Data
Authors: Rosenberry Donald O.
Published: August 2005

Submersible strain‐gage pressure transducers and potentiometer‐float systems were used to monitor water‐level fluctuations in wells. Use of uncorrected data from six pressure transducers at a site in New Hampshire would have caused an incorrect interpretation of the vertical hydraulic‐head distribution. Seven potentiometer‐float systems at a site in Nebraska provided data that indicated a slight attenuation of water‐level fluctuations, which likely caused some small fluctuations to go unobserved.

Digital data loggers were used at both sites to scan the sensors and calculate hourly and daily average values of water levels in the wells. Check measurements using a chalked steel tape were made weekly at the New Hampshire site and monthly at the Nebraska site. Comparisons of recorded data with check measurements indicated values measured by pressure transducers over periods of weeks to months were irregularly larger or smaller than the check measurement. This error was attributed to a drift of the zero reference point of the sensor, and was unpredictable. Values obtained by potentiometer‐float systems lagged the water‐level change indicated by the check measurements. The lag was attributed to the sum of the mechanical friction of the moving parts of the monitoring system. This error was somewhat constant and predictable. The average absolute error of six submersible pressure transducers that were in operation for 15 months was 0.098 foot. The average absolute error of seven potentiometer‐float systems that were operated for 17 months was 0.027 foot.
The Lognormal Distribution of Radon Concentration in Ground Water
Authors: Zikovsky L. , Chah B.
Published: August 2005

Data on the concentration of radon in ground water were compiled from the literature. From this compilation and data collected for this study, the means, medians, modes, standard deviations, coefficients of skewness and histograms have been calculated. The histograms were compared with the normal and lognormal distribution functions using chi‐square test values for goodness of fit. Based on this, the concentrations were found to be lognormally distributed in all cases studied but one. The measured medians and modes were compared with their theoretical counterparts assuming either normality or lognormality, and lognormality was found once more.
Use of Tree‐Ring Chemistry to Document Historical Ground‐Water Contamination Events
Authors: Vroblesky Don A. , Yanosky Thomas M.
Published: August 2005

The annual growth rings of tulip trees (Liriodendron tulipifera L.) appear to preserve a chemical record of ground‐water contamination at a landfill in Maryland. Zones of elevated iron and chlorine concentrations in growth rings from trees immediately downgradient from the landfill are closely correlated temporally with activities in the landfill expected to generate iron and chloride contamination in the ground water. Successively later iron peaks in trees increasingly distant from the landfill along the general direction of ground‐water flow imply movement of iron‐contaminated ground water away from the landfill. The historical velocity of iron movement (2 to 9 m/yr) and chloride movement (at least 40 m/yr) in ground water at the site was estimated from element‐concentration trends of trees at successive distances from the landfill. The tree‐ring‐derived chloride‐transport velocity approximates the known ground‐water velocity (30 to 80 m/yr). A minimum horizontal hydraulic conductivity (0.01 to .02 cm/s) calculated from chloride velocity agrees well with values derived from aquifer tests (about 0.07 cm/s) and from ground‐water modeling results (0.009 to 0.04 cm/s).
A Field Evaluation of In‐Situ Biodegradation of Chlorinated Ethenes: Part 2, Results of Biostimulation and Biotransformation Experiments
Authors: Semprini Lewis , Roberts Paul V. , Hopkins Gary D. , McCarty Perry L.
Published: August 2005

Results are presented from a field study that document the in‐situ biotransformation of trichloroethylene (TCE), cis‐dichLoroethylene (cis‐DCE), trans‐dichloroethylene (trans‐DCE), and vinyl chloride (VC) in a saturated, semiconfined aquifer. The enhanced biotransformation was accomplished by stimulating the growth of indigenous methane‐oxidizing bacteria (methanotrophs), which transform chlorinated aliphatic compounds by a cometabolic process to stable, nontoxic end products. Experiments were performed in the presence and absence of biostimulation by means of controlled chemical addition, frequent sampling, and quantitative analysis. The degree of biotransformation was assessed using mass balances and comparisons with bromide as a conservative tracer. Biostimulation of the test zone was successfully achieved by injecting methane‐ and oxygen‐containing ground water in alternating pulses under induced gradient conditions. After a few weeks of stimulation, methane concentrations gradually decreased below the detection limit within two meters of travel. Under active biostimulation conditions, 20 to 30% of the TCE was biotransformed during the first season of testing. Direct evidence for biotransformation of VC, trans‐DCE, cis‐DCE, and TCE was obtained in the second and third seasons of field testing. In the absence of biostimulation, the organic compounds concentrations at observation wells reached 95% of the injection concentration, demonstrating negligible losses due to abiotic processes. Biostimulation of the test zone resulted in a concurrent decrease in concentration of methane and the halogenated aliphatic compounds. The organic compounds were transformed within two meters of travel as follows: TCE, 20–30%; cis‐DCE, 45–55%; trans‐DCE, 80–90%; and VC, 90–95%. These results are in qualitative agreement with methane‐utilizing, mixed‐culture laboratory studies which indicate that the rate of biotransformation is more rapid when the molecules are less halogenated.

A biotransformation intermediate was observed which was identified by GC‐MS analysis as trans‐dichloroethylene oxide (trans‐DCE epoxide), an expected intermediate based on laboratory studies. When methane addition was stopped, the concentration of the intermediate rapidly decreased, while halogenated compound concentrations slowly increased, indicating that active methane utilization was required for biotransformation to occur.
pH and Redox Buffering Mechanisms in a Glacial Drift Aquifer Contaminated by Landfill Leachate
Authors: Kehew Alan E. , Passero Richard N.
Published: August 2005

The KL Landfill in Kalamazoo County, Michigan was closed in June 1979 because of ground‐water contamination. Study of water analyses from a monitoring‐well network has provided insight into a variety of pH and pe buffering reactions within the contaminant plume. The reactions occur when contaminated ground water containing dissolved organic acids from the landfill reacts with carbonate minerals and other solid phases in a glacial drift aquifer. Concentrations of Total Inorganic Carbon (TIC) in the plume, measured as the difference between Total Carbon (TC) and Total Organic Carbon (TOC), are lower than those obtained by alkalinity titrations. The difference results from the dissociation of organic acids in solution, producing organic anions that are included in the erroneously high titration alkalinity values.

Organic acids cause dissolution of carbonate minerals in the drift and increased concentrations of calcium, magnesium, and bicarbonate in the plume. Geochemical modeling using WATEQF indicates that the plume is supersaturated with respect to calcite, dolomite, and siderite. The dissolution reactions buffer pH in the plume at near background levels.

Redox potentials are below the level of sulfate reduction in the contaminant plume. Therefore, redox buffering mechanisms, reactions that inhibit changes in redox potential in the presence of a strong reducing agent, are much less effective than pH buffering in this system. Possible redox reactions occurring along the flow path include oxidation of organic compounds coupled with reduction of nitrate to ammonium and reduction of ferric iron in oxyhydroxide phases to ferrous iron.

WATEQF simulations indicate that dissolved iron concentrations in the plume are well above saturation levels with respect to sulfide phases, moderately above saturation with respect to siderite, and below saturation with respect to iron hydroxide. It is likely that iron precipitates as sulfide phases until the dissolved sulfide is consumed. The concentration of dissolved iron is subsequently controlled by precipitation of siderite, which occurs when moderate levels of supersaturation are reached.

These redox buffering reactions are insufficient to maintain high pe levels, and pe values drop to the level of sulfate reduction in the contaminant plume. Together, pH and redox buffering reactions control the concentrations of most major chemical species in the KL Landfill contaminant plume.
Hydrogeological Decision Analysis: 1. A Framework
Authors: Freeze R. Allan , Massmann Joel , Smith Leslie , Sperling Tony , James Bruce
Published: August 2005

This paper is the first in a four‐part series that describes the application of decision analysis to engineering design for projects in which the hydrogeological environment plays an important role. The methodology is well‐suited to the design of containment facilities at new waste‐management facilities, purge‐well networks in contaminant remediation applications, or drainage systems in geotechnical projects. It is based on a risk‐based philosophy of engineering design. It involves the coupling of three separate models: a decision model based on a risk‐cost‐benefit objective function, a simulation model for ground‐water flow and transport, and an uncertainty model that encompasses both geological uncertainty and parameter uncertainty. The approach can be used for the comparison of alternative engineered components of a system, for the design of monitoring systems, and for the assessment of data worth in the design of site investigation programs. This first paper lays the framework; the subsequent papers escribe how the methods can be applied in geotechnical and waste‐management applications.
Particle Tracking Analysis of Recharge Areas on Long Island, New York
Authors: Buxton Herbert T. , Reilly Thomas E. , Pollock David W. , Smolensky Douglas A.
Published: August 2005

Protection of ground‐water resources from the effects of anthropogenic contamination requires definition of the source of water flowing in developed aquifers. Aquifer recharge areas for the confined Magothy and Lloyd aquifers of Long Island, New York, are estimated by using a three‐dimensional model of the Long Island ground‐water flow system and a particle‐tracking algorithm.

Aquifer recharge areas under predevelopment conditions are consistent with an understanding of the ground‐water flow system operation. A budget comparison indicated that the recharge occurring in each area as calculated by particle tracking was within one percent of the flow entering that aquifer, according to the water budget computed from the flow model.

Aquifer recharge areas for two stressed conditions, one at the present time and the other an estimate for the year 2020, are more difficult to define because of numerous pumped wells. Maximum and minimuitn recharge areas for each aquifer are presented for both present conditions and the year 2020 to bracket the actual aquifer recharge areas. These results also are consistent with the water budgets computed from the flow model.

Results indicate that development causes large‐scale changes in flow patterns and the size and shape of aquifer recharge areas. The accuracy of defining recharge areas is limited by the model's representation of local‐scale characteristics of the flow system and the wells.
Ground‐Water Contamination from Two Small Septic Systems on Sand Aquifers
Authors: Robertson W. D. , Cherry J. A. , Sudicky E. A.
Published: August 2005

Distinct plumes of septic system‐impacted ground water at two single‐family homes located on shallow unconfined sand aquifers in Ontario showed elevated levels of Cl−, NO3−, Na+, Ca2+, K+, alkalinity, and dissolved organic carbon and depressed levels of pH and dissolved oxygen. At the Cambridge site, in use 12 years, the plume had sharp lateral and vertical boundaries and was more than 130 m in length with a uniform width of about 10 m. As a result of low transverse dispersion in the aquifer, mobile plume solutes such as NO3− and Na+ occurred at more than 50 percent of the source concentrations 130 m downgradient from the septic system. At the Muskoka site, in use three years, the plume also had discrete boundaries reflecting low transverse dispersion. After 1.5 years of system operation, the Muskoka plume began discharging to a river located 20 m from the tile field. Almost complete NOs attenuation was observed within the last 2 m of the plume flowpath before discharge to the river. This was attributed to denitrification occurring within organic matter‐enriched riverbed sediments.

The very weakly dispersive nature of the two aquifers was consistent with the results of recently reported natural‐gradient tracer tests in sands. Therefore, for many unconfined sand aquifers, the minimum distance‐to‐well regulations for permitting septic systems in most parts of North America should not be expected to be adequately protective of well‐water quality in situations where mobile contaminants such as NOs are not attenuated by chemical or microbiological processes.
Numerical Simulation of Subsurface‐Water Rise in Kuwait Citya
Authors: Hamdan L. , Mukhopadhyay A.
Published: August 2005

The residential areas of Kuwait City have been affected by a rise in the subsurface‐water level in recent years, causing waterlogging and flooding of the basements of buildings. To study this phenomenon, and to ascertain its causes, a numerical aquifer simulation model was developed. The aquifer model showed that, over the period 1961‐1985, the net yearly addition to the aquifer storage due to the contribution from man‐made sources like sewage systems, irrigation, and water distribution networks, ranged from 8,300 to 10,100 m3 d−1, causing a subsurface‐water‐level rise of about 5 m locally, resulting in high water‐table conditions. A maximum local rise in the water table of 2.5 m was predicted between the end of 1985 and 1990, if no remedial actions are undertaken. Preventive methods to reduce or eliminate recharge from man‐made activities would help control the water‐level rise and even lower the water table in affected areas. Remedial measures to lower and maintain the subsurface‐water level at acceptable depths would entail the withdrawal of significant quantities of ground water.
Estimation of Hydraulic Conductivity Values In a Coastal Aquifer
Authors: Pandit Ashok , EI‐Khazen Clovis C. , Sivaramapillai Sanjiv P.
Published: August 2005

A method is presented to compute the ratio of the vertical to horizontal component of the hydraulic conductivity of a homogeneous aquifer using a finite‐element model. The method requires knowledge of: (1) the boundary conditions along a vertical cross section of the aquifer, and (2) the hydraulic head measurements of two vertically separated well screens (preferably at the top and bottom of the aquifer). The method was used to estimate the anisotropy ratio for the aquifer at Port St. Lucie, Florida. The value of the horizontal component of the hydraulic conductivity was also estimated for this region by comparing measured tidally influenced ground‐water elevations to calculated elevations.
Aquifer Parameters from Constant Discharge Nonsteady‐Leaky Type Curves
Authors: Motz Louis H.
Published: August 2005

A drain function and set of type curves were defined for a simplified mathematical solution that represents one‐dimensional flow under nonsteady conditions in a leaky aquifer for the constant discharge boundary condition. The mathematical solution is in the form of exponential and complementary error functions, and it can be calculated using a polynomial approximation for the complementary error function. The mathematical solution and drain function are computationally easier to use than an equivalent integral‐form solution and drain function, which must be integrated numerically. A match‐point procedure was developed for determining aquifer diffuisivity (T/S), transmissivity (T), storage coefficient (S), and leakance (K′/b′) based on using the drain function and type curves. Use of the procedure is illustrated by an example that utilizes simulated aquifer drawdown and flowrate data. The match‐point procedure can be used to analyze drawdown data in leaky and nonleaky aquifers in cases where the flow is one‐dimensional and the discharge from the aquifer is constant. Applications of this procedure would include flow to a canal or river, flow to a highly permeable fracture that acts as a line sink, drainage of agricultural lands, and dewatering associated with strip mining operations.
Complex Aquifer‐Aquitard Relationships at an Appalachian Plateau Site
Authors: Peffer Jeffrey R.
Published: August 2005

Initial test data from a fractured, shale‐dominated sequence at a proposed landfill site in the Appalachian Plateau exhibited an apparent inconsistency: the unit performed in some ways as an aquitard; yet it was capable of high well yields which suggested it was an aquifer. High head drops (tens of feet) and dramatic ground‐water quality differences (hundreds of ppm for sulfate) occurred across the shale indicating that it is an aquitard. However, the shale sequence supported yields up to 60 gpm in test wells and one production well. This inconsistency suggested high anisotropy in vertical versus horizontal hydraulic conductivity.

A second detailed stage of testing confirmed the coincidence of some yielding zones to more brittle interbeds and bedding fractures within the shale sequence. An approach involving several different techniques, including analysis of hydrographs, vertical gradients, ground‐water quality differences, borehole geophysical logs, and pumping tests, was found to be effective in aquifer‐aquitard delineation at this site. The study showed that in waste disposal investigations in the Appalachian Plateau, it is inappropriate to use well yield alone to identify aquitards as these may be complex with numerous interlayered aquifers.
A Field Evaluation of In‐Situ Biodegradation of Chlorinated Ethenes: Part 3, Studies of Competitive Inhibition
Authors: Semprini Lewis , Hopkins Gary D. , Roberts Paul V. , Grbic‐Galic Dunja , McCarty Perry L
Published: August 2005

Results are presented that demonstrate the in‐situ biotransformation of vinyl chloride (VC), trans‐l,2‐dichloroethylene (t‐DCE), cis‐l,2‐dichloroethylene (c‐DCE), and trichloroethylene (TCE) by an enhanced population of methane‐utilizing (methanotrophic) bacteria. Biostimulation was accomplished by introducing dissolved methane and oxygen into a shallow, confined aquifer, to encourage the growth of the native methanotrophic bacteria. Biotransformation of the target compounds ensued immediately after the commencement of methane utilization, and reached steady‐state values within three weeks. The approximate extents of transformation achieved in the two meter biostimulated zone were as follows: VC, 95%; t‐DCE, 90%; c‐DCE, 50%; and TCE, 20%. The biotransformation of VC and t‐DCE was observed to be competitively inhibited by methane. Cyclic variations in methane concentration caused by the alternate pulse injection of dissolved methane into the test zone caused oscillations of the aqueous concentrations of VC and t‐DCE. When formate and methanol were substituted for methane as alternative electron donors, inhibition ceased (no oscillations), and concentrations were reduced to levels achieved during periods when no methane was present, confirming the inhibition by methane. Higher transformation rates were achieved temporarily, i.e., for several days, through the addition of formate or methanol. When electron donor addition was terminated, the concentration of target compounds rapidly increased, indicating that the transformation promptly ceased. Although these experiments indicated that methane competitively inhibits transformation rates, this competition is a second‐order effect: methane as substrate for growth was also required for transformation of VC, t‐DCE, c‐DCE, and TCE by methanotrophs.
Characteristics of Rhodamine WT and Fluorescein as Adsorbing Ground‐Water Tracers
Authors: Sabatini David A. , Austin T. AI
Published: August 2005

Fluorescent dyes are being used as adsorbing ground‐water tracers for conducting solute transport studies for adsorbing organic chemicals (e.g., pesticides). In this research, the ability of two fluorescent dyes (rhodamine WT and fluorescein) to mimic the adsorptive behavior of two herbicides (atrazine and alachlor) with alluvial aquifer sands was evaluated. Laboratory studies (batch and column) indicated the following order of increasing adsorption: fluorescein, atrazine, alachlor, and rhodamine WT. Thus, the use of fluorescein and rhodamine WT as adsorbing ground‐water tracers was observed to delimit the appearance of the atrazine and alachlor (fluorescein appeared before and rhodamine WT after the herbicides). Several adsorption characteristics of the fluorescent dyes differed from those commonly observed for pesticides. The levels of adsorption for the dyes were several orders of magnitude greater than predicted from empirical relationships based on Kowand foc. The presence of divalent cations was observed to increase the level of rhodamine WT adsorption. The rhodamine WT breakthrough curves were not of the conventional sigmoidal shape but instead leveled off at a C/CO value of 0.5 for a number of pore volumes prior to increasing again towards a C/CO value of 1.0. These characteristics indicate that the adsorptive mechanisms for the fluorescent dyes differed from the adsorptive mechanisms for most pesticides. These variations in fundamental adsorptive mechanisms raise concerns as to the transferability of the results of this research (fluorescein and rhodamine WT delimiting the appearance of atrazine and alachlor) to other subsurface media.
Embedding and Response Matrix Techniques for Maximizing Steady‐State Ground‐Water Extraction: Computational Comparison
Authors: Peralta Richard C. , Azarmnia Hossein , Takahashi Shu
Published: August 2005

Both response matrix and embedding techniques are used to compute optimal sustained‐yield ground‐water extraction strategies for confined aquifers. Historically, the response matrix method has been considered the most practical, because of numerical instability reported to occur when using the embedding approach for large aquifer systems. More recent studies have proven the embedding approach to be stable for large‐scale regional planning. Also, there is increasing emphasis on using microcomputers for ground‐water studies. Thus, it is appropriate to compare response matrix and embedding approaches to steady‐state problems in terms of computational efficiency and memory requirements.

For the hypothetical study area, a steady‐state embedding model requires less processing time than a comparable response matrix model. In addition, the embedding model sometimes requires less memory than a response matrix model. Required computer memory is frequently a function of the number of nonzero values in constraint equations. For embedding models, the number of nonzeroes is fixed for a particular study area. For response matrix models, the number of nonzeroes can increase dramatically in proportion to the number of pumping cells and cells at which heads must be constrained. For the sample system, if more than 25 percent of the cells can pump, the response matrix approach requires more memory than does the embedding approach. Before selecting an optimization model for a particular study, one should, as illustrated, evaluate potential memory requirements of both embedding and response matrix approaches. If there is a high percentage of pumping cells, or if many heads must be constrained or computed within the optimization model, the embedding approach seems preferable.
A Method to Determine the Formation Constants of Leaky Aquifers, and Its Application to Pumping Test Data
Authors: Kohlbeck F. , Alvarez A.
Published: August 2005

Abstract. A method to calculate aquifer transmissivity, storage coefficient, and the leakage coefficient from pumping test data for a leaky aquifer is presented. The method is carried out by a computer program and is based on a minimization of the sum of squares of differences between drawdown in the observation well and the theoretical values from the Hantush and Jacob formula. No user defined starting points are necessary. Random error estimates for the parameters are given. Applications of the method are illustrated using data from pumping tests performed in leaky aquifers at the Cauca River Valley, Colombia.
Interpretation of Pumping from Two‐Zone Layered Aquifers Using a Numerical Model
Authors: Rathod K. S. , Rushton K. R.
Published: August 2005

A numerical model is presented which represents both the radial and vertical flow components which usually result from pumping from boreholes in layered aquifers. This model, which is based on finite‐difference approximations, runs on a microprocessor system and can be used for the analysis of pumping test results. A discussion on the interaction between the radial and vertical flow components is followed by a description of the model. A computer program in BASIC and a typical computer output are provided. The application of the model for the analysis of a pumping test in a weathered‐fractured aquifer is described. Three case studies are reviewed where the numerical model is used to gain a greater understanding of the aquifer flow processes.