bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsaturated Hydrogeologic Properties of Reclaimed Coal Strip Mines
Authors: Diodato D. M. , Parizek R. R.
Published: August 2005

Two nuclear methods were used to quantify hydrogeologic parameters in the unsaturated zone of a reclaimed and revegetated coal strip mine in Clarion, Pennsylvania. Am‐Be (neutron) and Cs‐137 (gamma‐gamma) geophysical logging tools were used to quantify volumetric moisture content, bulk density, total porosity, and unsaturated hydraulic conductivity. An additional study at the same site used postsampling neutron activation analysis to determine concentrations of a bromide tracer in unsaturated zone water samples. Those additional data were used to independently calculate unsaturated hydraulic conductivity.

Geophysical logging of six boreholes at the site was conducted on seven different dates. Temporal variations in volumetric moisture content versus depth were observed to be short‐lived, with the general shape of the volumetric moisture content profiles remaining spatially stable over the eight month period of investigation. Bulk density values ranged from less than 1.14 to 1.86 g/cm3, corresponding to total porosities of greater than 57% to 30.1%. Large void spaces were encountered during past and present drilling and observed at a measurement point. Unsaturated hydraulic conductivities were calculated using draining profile volumetric moisture content data as input to an explicit numerical solution of the unsaturated flow equation. Calculated values ranged from 2.4 × 10−7 to 1.5 × 10 −3 cm/s. Examination of all of the geophysical log data together showed sharp increases in volumetric moisture content spatially coincident with zones where bulk density increases (and porosity decreases). The bulk density contrast appears to be of more influence than the magnitude of the material property. Increased unsaturated hydraulic conductivity associated with increased volumetric moisture content was seen in several boreholes.

Bromide tracer‐labeled waters were collected from pressure‐suction lysimeters installed at depths of up to 18.1 m for a period of 16 months. Unsaturated hydraulic conductivities, calculated by interpreting concentration peaks as average arrival times of steadily infiltrating water through a uniformly porous media, ranged from 2.8 × 10−6 to 7.2 × 10−5 cm/s. However, a dual‐permeability mechanism is suggested by the observed behavior of the tracer. Analysis of the data suggests that fluid flow in this hydrogeologic setting is dominantly transient. Ground‐water recharge occurs in short‐lived pulses. The periodicity of acid mine drainage formation and flushing to the water table is expected to correspond to infiltration and recharge events.
Modeling Free Product Migration and Recovery at Hydrocarbon Spill Sites
Authors: Parker J. C. , Zhu J. L. , Johnson T. G. , Kremesec V. J. , Hockman E. L.
Published: August 2005

The numerical model ARMOS, which simulates areal flow of water and light hydrocarbon in an unconiined aquifer, isdescribed. Based on the assumption of local vertical equilibrium, area! flow equations for water and hydrocarbon are derived which exhibit reduced dimensionality and nonlinearity. A finite‐element method is used to solve the water and oil equations using an efficient semidecoupled approach. Input required by the model includes area! boundaries, elevations of the aquifer lower boundary, and initial water and hydrocarbon levels in monitoring wells. Soil and fluid properties include hydrocarbon density, viscosity and surface tension, saturated hydraulic conductivity, van Genuchten air‐water capillary pressure curve parameters, and the maximum residual hydrocarbon saturations in the saturated and unsaturated zones. Fluid heads or fluxes may be specified on the domain perimeter and pumping rates are prescribed at recovery wells. The water pumping rate is automatically limited when drawdown reaches a pump‐off set point (or the screen bottom), and hydrocarbon recovery is limited when well hydrocarbon thickness becomes zero. Model output includes water and hydrocarbon levels in monitoring wells, cumulative product recovery, and free and residual hydrocarbon volumes in the soil. A hypothetical problem involving optimization of free product recovery and a field application of the model to a large pipeline leak are described.
Implementation and Use of Direct‐Flow Connections in a Coupled Ground‐Water and Surface‐Water Model
Authors: Swain Eric D.
Published: August 2005

The U.S. Geological Survey's MODFLOW finite‐difference ground‐water flow model has been coupled with three surface‐water packages–the MODBRANCH, River, and Stream packages–to simulate surface water and its interaction with ground water. Prior to the development of the coupling packages, the only interaction between these modeling packages was that leakage values could be passed between MODFLOW and the three surface‐water packages. To facilitate wider and more flexible uses of the models, a computer program was developed and added to MODFLOW to allow direct flows or stages to be passed between any of the packages and MODFLOW. The flows or stages calculated in one package can be set as boundary discharges or stages to be used in another package. Several modeling packages can be used in the same simulation depending upon the level of sophistication needed in the various reaches being modeled. This computer program is especially useful when any of the River, Stream, or MODBRANCH packages are used to model a river flowing directly into or out of wetlands in direct connection with the aquifer and represented in the model as an aquifer block. A field case study is shown to illustrate an application.
Natural Biological Attenuation of Benzene in Ground Water Beneath a Manufacturing Facility
Authors: Davis John W. , Klier Nancy J. , Carpenter Constance L.
Published: August 2005

Subsurface unsaturated soils and ground water directly beneath a manufacturing site have been shown to contain benzene. The vadose zone appears to be the current source for benzene to the aquifer. Although the ground water contains several mg/1 of contamination in the area immediately beneath the source, benzene was not detected in monitoring wells approximately 400 feet downgradient. Based upon the length of time benzene has been present in the ground water, as well as the permeability of the aquifer, physical processes alone such as adsorption and advection/dispersion are unlikely to account for the observed attenuation. Results from this investigation indicated the attenuation was primarily due to the natural biological processes occurring within the aquifer.

Evidence for the natural bioremediation of benzene from the ground water included: (1) analysis of ground‐water chemistry, (2) laboratory studies demonstrating benzene biodegradation in aquifer samples, and (3) computer simulations examining contaminant transport. Laboratory studies indicated that under conditions similar to those encountered in the ground water, benzene was degraded to carbon dioxide by the naturally occurring microorganisms. The aerobic degradation of benzene in aquifer samples was quite rapid, with the time for 50% disappearance of the parent compound ranging from 4 to 14 days. In situ analyses of the ground water indicated significant levels of dissolved oxygen throughout the aquifer. Thus, the availability of oxygen should not limit the aerobic biodegradation of benzene. However, benzene was also shown to degrade under anaerobic conditions in microcosms prepared with aquifer material. Computer model simulations were also conducted to examine the processes influencing the transport of benzene in the aquifer. Results from the model simulations indicated biodegradation was the dominant process influencing attenuation of the contaminant.
A Portable Air‐Minipermeameter for Rapid In Situ Field Measurements
Authors: Davis J. Matthew , Wilson John L. , Phillips Fred M.
Published: August 2005

Measurements of air‐permeability in outcrops provide a means of obtaining numerous spatially distributed measurements for statistical analysis and subsequent parameterization of ground‐water flow and transport modeling. The air‐minipermeameters previously used for such studies generally consist of a compressed air source, rotameters, and diaphragm gauges. We present a lightweight syringe‐based air‐minipermeameter (LSAMP) design that is significantly more portable than previous instruments. The prototype model is contained in a 12.7 × 15.2 × 23 centimeter (5 × 6 × 9 inch) electrical box and weighs approximately 2 kilograms. The prototype LSAMP has a sampling range of 0.5 to 200 darcys. Individual measurements in this range require less than one minute. Permeability measured with the LSAMP closely correspond to permeability measured with a traditional minipermeameter and those measured on cores. Measurement error caused by soil moisture is less than 5 percent for volumetric water contents less than 5 percent. An analysis of variance on 38 triplicate measurements indicates that the variability associated with measurement error is much less than the range of measured values. Repeated permeability measurements under field conditions on two standard cores indicate that while the measurement error is greater under field conditions, the prototype device field performance is consistent with laboratory calibration results.
Relative Importance of Baseflow and Quickflow from Hydrographs of Karst Spring
Authors: Padilla A. , Pulido‐Bosch A. , Mangin A.
Published: August 2005

Evaluation of recession hydrographs, from four karst springs in Europe, provides important information concerning the flow process operating in karst aquifer systems. Three analytic equations are used to evaluate the hydrographs: Mangin's equation, that assumes the recession is composed of both quickflow and baseflow; Coutagne's equation which considers the recession to be the response of a single reservoir; and a new function, Ht (which is derived from Coutagne's equation), that refers to the whole recession curve. Using Mangin's equation it is apparent that the saturated zone and thus baseflow exerts nearly complete control over the discharge of La Villa spring and is fairly important at Fuente Mayor and Baget springs, but is much less significant at Aliou spring. The saturated zone accounts for 100%, 90%, 91%, and 40% respectively for these springs. Using Coutagne's equation and Ht it is concluded that for Aliou and Baget springs, water flows freely in the high transmissive zones, but in the poorly transmissive zones, there is little continuity of connection in the system. At Fuente Mayor spring the differences in these zones are not so apparent and a gradual transition occurs. However, at La Villa spring, the karst aquifer is evidently much more homogeneous and the discharge is similar to that of a porous intergranular aquifer.
Dissolution of a Toluene Pool Under Constant and Variable Hydraulic Gradients with Implications for Aquifer Remediation
Authors: Voudrias Evangelos A. , Yeh Moon‐Full
Published: August 2005

Factors affecting the dissolution of a toluene pool floating at the water table were investigated using an experimental aquifer 85 cm long, 30 cm high, and 20 cm wide. Under conditions of steady, uniform flow, the dissolved toluene concentration decreased with increasing vertical distance from the free phase pool, resulting in steep concentration gradients. The concentration gradient steepened with increasing ground‐water velocity. The thickness of the dissolved plume increased with increasing distance along the pool and decreasing ground‐water velocity. In all cases, measured concentrations were a small fraction of toluene solubility.

In pulsed pumping experiments, dissolved toluene concentrations in all sampling ports increased significantly during zero flow conditions and, when the flow was resumed, they gradually decreased to the same levels as before the flow was stopped. Under the experimental conditions used, comparison between the pulsed and continuous pumping showed that the total mass removal would be higher for continuous pumping and would result in shorter toluene removal times. However, the total volume of water pumped and needed to be treated would be lower by 50% for pulsed pumping. The latter would result in a higher by ∼ 20% mass removed per volume of water pumped, suggesting that pulsed pumping would be a more efficient operation compared to continuous pumping, when considering removal of dissolved toluene from the aquifer.
A Semipassive Nutrient Injection Scheme for Enhanced In Situ Bioremediation
Authors: Devlin J. F. , Barker J. F.
Published: August 2005

A permeable wall injection system is capable of introducing dissolved substances into an aquifer in a manner which minimizes the displacement of naturally present ground water, and maximizes the potential for dispersive mixing. The system operates predominantly in a passive mode, and should require relatively little power and small amounts of chemicals. The injection wall is a permeable cutoff wall installed across the path of a contaminant plume. The ground water can be amended with the desired nutrient solution using pumping and injecting wells within the wall. The high permeability of the wall ensures that the injection‐withdrawal operation causes flow which is primarily confined to the wall itself. Thus, only a minimal disruption of the ambient flow need result from a nutrient injection. After the nutrients have been introduced to the wall, the pulse is permitted to drift into the aquifer under natural gradient conditions, spreading longitudinally as it goes. Theoretical calculations and preliminary results of a field trial indicate that if this pulsing cycle is repeated at intervals of weeks to months (site‐specific), a stable microbial population can be supported at some distance downgradient from the wall.

The advantages of this system include the predominantly passive nature of its operation, the effective use of longitudinal dispersion to maximize the mixing of added substances with contaminated ground water, and the flexibility of the system with regard to the types of biodegradation reactions which it can promote.
Leachate Geochemistry at a Municipal Landfill, Memphis, Tennessee
Authors: Mirecki June E. , Parks William S.
Published: August 2005

A leachate plume emanating from the Shelby County Landfill located at Memphis, Tennessee is defined using selected major and trace inorganic constituents. High specific conductance values and elevated concentrations of ammonia, barium, boron, calcium, chloride, dissolved solids, potassium, sodium, and strontium were measured in water samples from wells screened in the alluvial and Memphis aquifers downgradient from or proximal to the landfill. Of these constituents, barium, boron, chloride, and strontium were used in the geochemical model code PHREEQE to estimate the percent leachate component in selected Memphis aquifer samples. Estimates of the leachate component in samples from affected Memphis aquifer wells range from 5 to 37 percent for barium and strontium, the most reliable tracers found during this study.
Two‐ and Three‐Dimensional Pathline Analysis of Contributing Areas To Public‐Supply Wells of Cape Cod, Massachusetts
Authors: Barlow Paul M.
Published: August 2005

Steady‐state two‐ and three‐dimensional ground‐water‐flow models coupled with particle tracking (fluid‐particle pathline analysis) have been evaluated to determine their relative effectiveness in delineating contributing areas and particle traveltimes to public‐supply wells in two contrasting stratified‐drift aquifers of Cape Cod, Massachusetts. Several contributing areas delineated by the three‐dimensional pathline analysis do not conform to simple ellipsoidal shapes that are typically delineated by use of two‐dimensional analytical and numerical modeling techniques. They also include discontinuous areas of the water table and do not surround the supply wells. Because two‐dimensional area! models do not account for vertical flow, they cannot adequately represent many of the hydrogeologic and well‐design variables that complicate the delineation of contributing areas in three‐dimensional flow systems on Cape Cod, including the presence and continuity of discrete zones of low hydraulic conductivity, large anisotropic ratios of horizontal to vertical hydraulic conductivity, partially penetrating supply wells, shallow streams and lakes, and low (less than about 0.1 million gallons per day) pumping rates.

Particle traveltimes calculated by the two‐dimensional models are longer than those calculated by the three‐dimensional models, and time‐related capture zones determined by the two‐dimensional models underpredict the size of the land area contributing water to simulated wells. It appears that the two‐dimensional models do not accurately represent shallow, partially penetrating wells, or heterogeneous and anisotropic sediments for the purposes of simulating contributing areas and traveltimes in complex ground‐water systems.
Maximum Water‐Table Drawdown at a Fully Penetrating Pumping Well
Authors: Gefell Michael J. , Thomas George M. , Rossello Stephen J.
Published: August 2005

The magnitude of water‐table drawdown achievable by a fully penetrating pumping well in an unconfined aquifer commonly is limited to a small fraction of the initial aquifer thickness. The maximum potential water‐table drawdown can be estimated based on the aquifer thickness, the pumping well effective radius, and the estimated radius of influence in the aquifer during maximum steady‐state pumping (Kozeny, 1953). The maximum steady‐state flow rate into a well can be predicted if the aquifer hydraulic conductivity is known based on observed water‐table drawdown during a pumping period.

To achieve the maximum potential pumping rate from a fully penetrating well in an unconfined aquifer, the water level inside the well must be maintained at the bottom (Kozeny, 1953; this paper). This condition creates a seepage face along the inside of the well screen. The hydraulics of the seepage face control the removal of water from the aquifer and the size of the resulting cone of depression. The area of the seepage face, which is a direct function of the effective radius of the pumping well, strongly influences the maximum potential water‐table drawdown and the maximum steady‐state pumping rate.

The vertical component of the hydraulic gradient in the formation is downward and increases toward the pumping well. The hydraulic potential, therefore, decreases with increasing depth below the water table. Only shallow observation wells that are screened across the uppermost fraction of the saturated zone are adequate for delineating the actual water‐table position during pumping. Observation wells screened across deeper portions of the aquifer, including fully penetrating, fully screened observation wells, exhibit potentiometric drawdown in excess of true water‐table drawdown.
A Modified Mise‐A'‐La‐Masse Method for Contaminant Plume Delineation
Authors: Osiensky James L. , Donaldson Paul R.
Published: August 2005

Ground‐water monitoring to delineate contaminant plumes in complex hydrogeologic settings often is uncertain. This uncertainty is manifested by the fact that ground‐water contaminants often migrate along preferred pathways formed by lateral and vertical heterogeneity within definable stratigraphic units. A somewhat obscure surface, electrical geophysical method first suggested in 1920 holds great promise as a tool to help delineate conductive contaminant plumes in suitable hydrogeologic environments. This tool known as the mise‐a'‐la‐masse method has been used with success by other investigators to map conductive orebodies.

A modified mise‐a'‐la‐masse method was used with great success in this investigation during a controlled field experiment. The method was used to track the evolution of a conductive tracer plume migrating through fluvial sands and gravels under a forced hydraulic gradient. Voltage differences between 171 stationary, surface electrodes and a reference electrode were monitored over time to map an evolving tracer plume. For this particular experiment, the method proved to be sensitive to changes in the specific electrical conductance of the ground water of less than 10% above the baseline values. Data derived by the modified mise‐a'‐la‐masse method show close agreement to specific electrical conductance measurements of ground‐water samples collected from wells during the tracer experiment. However, uncertainty in the significance of the variable specific electrical conductance data, especially at early times during the experiment, is reduced greatly by comparison with the plume maps generated by the modified mise‐a'‐la‐masse method.
In Situ Remediation of Contaminated Ground Water: The Funnel‐and‐Gate System
Authors: Starr Robert C. , Cherry John A.
Published: August 2005

The funnel‐and‐gate system for in situ treatment of contaminant plumes consists of low hydraulic conductivity cutoff walls with gaps that contain in situ reactors, such as reactive porous media, that remove contaminants by abiotic or biological processes. Funnel‐and‐gate systems can be installed at the front of plumes to prevent further plume growth, or immediately downgradient of contaminant source zones to prevent contaminants from moving into plumes. Cutoff walls (the funnel) modify flow patterns so that ground water flows primarily through high conductivity gaps (the gates). This approach is largely passive in that after installation, in situ reactors are intended to function with little or no maintenance for long periods. This approach contrasts with the energy and maintenance‐intensive character of pump‐and‐treat systems. This paper describes the funnel‐and‐gate concept, and uses two‐dimensional computer simulations to illustrate the effects of cutoff wall and gate configuration on capture zone size and shape and on the residence time for reaction of contaminants in gates.
Geochemical Reduction of Hexavalent Chromium in the Trinity Sand Aquifer
Authors: Henderson Thomas
Published: August 2005

Ground water of the Trinity Sand aquifer at the Odessa I site has become contaminated with hexavalent chromium due to release of plating wastes during the 1970s. Measured hexavalent chromium partition coefficients for Trinity Sand aquifer sediments compare favorably with values derived from the literature, and with retardation factors calculated from observed plume migration rates between 1986 and 1991. Dissolved and adsorbed masses of hexavalent chromium were calculated from contoured plume maps using ground‐water data collected between 1986 and 1991 to estimate the total mass of hexavalent chromium in the aquifer. Comparison of the calculations from each year indicated that only 30 percent of the hexavalent chromium present in the aquifer in 1986 remained in 1991.

Decreasing hexavalent chromium mass in the Trinity Sand aquifer at the Odessa I site indicates that natural geochemical reactions are occurring to reduce mobile hexavalent chromium to the insoluble trivalent form. Thermodynamic calculations based on platinum electrode redox and pH measurements indicate that solid trivalent chromium hydroxide species are the stable phase in these ground waters. Reduction of hexavalent chromium to the trivalent state results in precipitation from solution of a solid chromium (III) hydroxide, probably in association with iron oxyhydroxides present in the aquifer. Two possible reducing agents in the Trinity Sand aquifer are naturally occurring organic carbon and ferrous iron.

Laboratory measurements of the rate of hexavalent chromium reduction indicate that the reaction proceeds slowly at near‐neutral pH values representative of the Odessa I site. Assuming first‐order reaction kinetics, these laboratory reduction rates are consistent with the rate of hexavalent chromium loss at the Odessa I site between 1986 and 1991, and indicate a hexavalent chromium half‐life of approximately 2.5 years. An analytical contaminant transport model was calibrated to simulate historical chromium concentrations for the aquifer, and then used to predict that hexavalent chromium will naturally decrease below the drinking water standard within approximately 10 years.
Modifications to the Computer Program TENSOR2D
Authors: Maslia Morris L.
Published: August 2005

The U.S. Geological Survey computer program TENSOR2D may be used to compute the directional components of the anisotropic transmissivity tensor of two‐dimensional ground‐water flow. In this note, modifications to the original computer code, developed in 1987, are described. Because of the modifications, TENSOR2D now conforms to the Fortran 77 Standard and can be run on most personal computers without user modification. Additionally, a new routine generates the polar coordinates of the computed theoretical transmissivity (or diffusivity) ellipse.
Evaluation of Fluorobenzoate Tracers in Surface Soils
Authors: Jaynes Dan B.
Published: August 2005

The availability of several conservative, noninteracting tracers is desirable for the study of water movement in porous media. Recent studies have identified a family of fluorinated benzoic acid derivatives as having transport properties similar to Br. The transport properties of 2,6‐difluorobenzoate (2,6‐DFBA), 2,5‐difluorobenzoate (2,5‐DFBA), 3,4‐difluorobenzoate (3,4‐DFBA), 3,5‐difluorobenzoate (3,5‐DFBA), o‐(trifluoromethyl)benzoate (o‐TFMBA), m‐(trifluoromethyl)benzoate (m‐TFMBA), and pentafluorobenzoate (PFBA) were compared to Br in two neutral pH, high organic soils from Iowa. Batch equilibrium studies and column transport studies showed that 2,6‐DFBA, PFBA, and o‐TFMBA have transport properties very similar to Br, although their behavior may deviate slightly as the organic carbon and clay fractions of the soil increase. 2,5‐DFBA is retarded less and dispersed slightly more than the above tracers in these soils, but may be a useful tracer since it is still conservative. The other fluorobenzoates showed greater degrees of interaction with the soil matrix and were not conservative precluding their use as acceptable tracers. Plant growth studies using corn (Zea mays L.) and soybean (Glycine max [L] Merr.) showed significantly (P = 0.05) decreased growth for treatments using 3,4‐DFBA and 3,5‐DFBA, precluding their use in agronomic settings. Given the variation shown here and in earlier studies, the transport behavior of any of the fluorobenzoates should be evaluated prior to use in new environments.
Solubilization and Microemulsification of Chlorinated Solvents Using Direct Food Additive (Edible) Surfactants
Authors: Shiau Bor‐Jier , Sabatini David A. , Harwell Jeffrey H.
Published: August 2005

Surfactant enhanced subsurface remediation is being evaluated as an innovative technology to expedite contaminant extraction from the subsurface. Regulatory approval of this technology will likely be enhanced by use of surfactants with FDA direct food additive status (“edible” surfactants). This research establishes edible surfactant systems capable of solubilizing (via micellar partitioning) and microemulsifying (via middle phase microemulsions) chlorinated solvents (PCE, TCE, and trans 1,2‐DCE). Micellar partition coefficients with edible surfactants are observed to be comparable to values previously reported for other surfactants, with solubilization increasing aqueous concentrations by one to two orders of magnitude for the chlorinated organics. Middle phase microemulsion formation is dependent on surfactant structure and cosurfactant concentration. Solubility enhancement in the middle phase systems (microemulsification) is at least one to two orders of magnitude higher than solubilization for the same surfactant concentration, but is much more sensitive to the surfactant system and the contaminant. In addition, successful microemulsion formation is seen to be a function of ground‐water temperature and hardness, indicating the need to consider these and additional factors for successful design and implementation of surfactant enhanced subsurface remediation. This research thus establishes a variety of edible surfactant systems that can significantly expedite subsurface remediation of chlorinated solvents, and illustrates the importance of proper selection and design of surfactant systems.
Regional Scale Ground‐Water Vulnerability Estimates: Impact of Reducing Data Uncertainties for Assessments in Hawaii
Authors: Loague Keith
Published: August 2005

Nonpoint source ground‐water contamination, resulting from regional scale applications of agrichemicals, is a major environmental issue. Several federal and state government funded modeling efforts were undertaken in the 1980s to assess ground‐water vulnerability from past and current chemical use and to potentially aid in the regulation of new chemicals. This paper is concerned with the impact of data uncertainties in regional scale pesticide leaching assessments for the chemical diuron in the Pearl Harbor Basin on the Hawaiian island of Oahu. In the first part of the paper uncertainties in soil, recharge, and chemical data are artificially reduced to study the impact of reduced data uncertainties on ground‐water vulnerability assessments made with simple mobility indices; the greatest improvements were realized for improvements in the chemical data. In the second part of the paper the impact of improvements to the Hawaii soil data, in the form of new soil organic carbon information, is characterized relative to changes in ground‐water vulnerability assessments made with a simple index. The additional soil organic carbon data does not yield improvements to the original vulnerability assessment that would be considered justifiable. The best use of regional scale chemical leaching assessments based upon modeling approaches as simple as index methods is for guiding data collection strategies.
Biogeochemical Evolution of Domestic Waste Water in Septic Systems: 1. Conceptual Model
Authors: Wilhelm Sheryl R. , Schiff Sherry L. , Cherry John A.
Published: August 2005

This paper presents a conceptual model, developed by synthesizing the results of many researchers, which describes the geochemical evolution of domestic waste water in conventional on‐site septic systems as the result of the interactions of a few major constituents. As described by the model, the evolution of waste water is driven by the microbially catalyzed redox reactions involving organic C and N in waste water and occurs in as many as three different redox zones. Anaerobic digestion of organic matter and production of CO2, CH4, and NH4+ predominate in the first zone, which consists mainly of the septic tank. In the second zone, gaseous diffusion through the unsaturated sediments of the drain field supplies O2 for aerobic oxidation of organic C and NH4+ and a consequent decrease in waste‐water alkalinity. The NO3− formed by NH4+ oxidation in this zone is the primary adverse impact of septic systems at most sites and is generally an unavoidable consequence of the proper functioning of conventional septic systems. If adequate O2 is not available in the drain field, aerobic digestion is incomplete, and the accumulation of organic matter may cause septic‐system failure. In the third redox zone, NO3 is reduced to N2 by the anaerobic process of denitrification. However, this setting is rarely found below septic systems due to a lack of labile organic C in the natural setting. Consideration of the changing redox and pH conditions in each zone aids our understanding of the fate of other constituents in septic systems.
Enhanced Degradation of Halogenated Aliphatics by Zero‐Valent Iron
Authors: Gillham Robert W. , O'Hannesin Stephanie F.
Published: August 2005

Laboratory tests were conducted to examine zero‐valent iron as an enhancing agent in the dehalogenation of 14 chlorinated methanes, ethanes, and ethenes. All compounds were tested by batch procedures in which 10 g of 100‐mesh electrolytic iron was added to 40 ml hypovials. Aqueous solutions of the respective compounds were added to the hypovials, and the decline in concentration was monitored over time. Substantial rates of degradation were observed for all compounds tested with the exception of dichloromethane. The degradation process appeared to be pseudo first‐order with respect to the organic compound, with the rate constant appearing to be directly proportional to the surface area to volume ratio and increasing with increasing degree of chlorination. Column tests showed the process to proceed under flow conditions with degradation rates indpendent of velocity and consistent with those measured in the batch tests. When normalized to 1 m2/ml, the t50 values ranged from 0.013 to 20 hr, and were about 5 to 15 orders of magnitude lower than values reported for natural rates of abiotic degradation. The results indicate abiotic reductive dechlorination, with iron serving as the source of electrons; the mechanism is, however, uncertain. Based on the rapid rates of degradation, both in situ and aboveground applications for remediation of contaminated ground water are proposed.
Some Calculations on Multicomponent Transport with Cation Exchange in Aquifers
Authors: Appelo C.A.J.
Published: August 2005

Multicomponent transport with cation exchange induces a separation of cations during displacement of waters in aquifers. The spatial separation is due to different retardations of the various cations which originate from differences in selectivity of the exchange complex. The composition patterns are complex, and calculated mostly with numerical models. However, a basic notion of features such as salinity fronts, chromatographic sequence, and front type is useful for general understanding of the processes. These aspects have not obtained the level of generality in hydrochemical studies that they deserve, and are introduced and applied in the paper. Demonstrated are: (1) the calculation of a multicomponent exchange complex from solution composition with the law of mass action; (2) the front type (broadening, indifferent, sharpening) that develops in relation to the slope of the sorption isotherm; (3) the calculation of a chromatographic pattern for the case of sharp fronts; (4) the effects of salinity changes on solution composition. All these features are illustrated with examples and then applied to calculate and compare water compositions in an observation well from two field studies, one of a salt‐water injection which displays the salinity effects very clearly in accordance with theory, and one of a fresh‐water injection for which the complete sequence of three ions Na+, Mg2+, and Ca2+ can be calculated simply with a quadratic equation.
Ground Water for WindowsTM— A New Ground‐Water Information System Software
Authors: Karanjac Jasminko
Published: August 2005

As suggested in the computer note printed in this journal in March‐April 1993 and titled “United Nations Ground‐Water Software,” to which this note is a sequel, the Windows version is completed and ready for distribution. The software, known as Ground Water for Windows (GWW), is the United Nations contribution to the ground‐water data information processing and management. GWW is flexible, user‐controlled, sophisticated, and versatile. It is an object oriented, relational data base and tailored for use as a ground‐water information system (GWIS). The software integrates classical ground‐water information (lithology, hydrographs, chemistry, pumping tests, etc.) with geographic displays. The software is programmed as a Windows application, and it uses all Windows resources: memory management, fonts, colors, screen, printer, and plotter drivers, etc. It is input and output device independent, and has no memory limitations except for the ones that are intrinsic to any Windows application. The data base can be filtered; that is, a large set of information can be reduced to subset having user‐selected attributes on any part of the data. The user designs the structure of the data base and creates entry and reporting forms. The software is primarily intended for the creation of large relational data bases on a site, region, province, county, or country wide basis.

In addition to ground‐water data processing, GWW has its own powerful mapping utility. Various location and thematic content maps become an integral part of the ground‐water base. The exchange of information with other software packages is enabled via import and export of AutoCad's DXF and ASCII files.

Following the philosophy that a picture is worth a thousand words, GWW emphasizes graphics on screen and printed in: maps, logs, cross sections, hydrographs, various chemical diagrams, etc. The current version of this software is in the public domain and is available through the United Nations for the developing world or through educational courses for the developed world.
A Computer Model for DNAPL Potential Migration Study
Authors: Yan Song‐kai , Landry Glen R. , Tate Tim
Published: August 2005

A computer model, named DNAPMIG (DNAPL Potential Migration), was developed to calculate the dense nonaqueous phase liquid (DNAPL) critical length required to initiate movement and direction of potential migration at locations within an area of interest. The model takes into consideration the potentiometric gradient, bottom structure elevation, DNAPL density, interfacial tension, contact angle, soil grain size, partitioning coefficient, effective solubility, and water saturation. The model is interfaced with SURFER graphics software to use vectors to indicate the DNAPL critical length and the potential migration direction. The potential for DNAPL existence and migration at a specific site can be estimated by relating chemical concentration in the ground water to its solubility limit and the DNAPL critical length. The possibility of vertical migration can also be determined.

This model can be used to determine and compare the effectiveness of existing or alternative recovery well systems to capture a DNAPL plume or arrest its movement; to help determine optimum locations and pumping rates of recovery wells; and to help determine the optimum location of environmental borings to locate DNAPL. This paper presents two hypothetical examples and two site applications in south Louisiana.
The Relationship Between Monitoring Well and Aquifer Solute Concentrations
Authors: Chiang Chen , Raven Gary , Dawson Clint
Published: August 2005

Disparities between organic solute concentration in the aquifer and that in monitoring wells have been observed; an order of magnitude disparity had been recorded in some cases. Therefore, it is important to be able to relate concentrations between the two media for design of remediation systems. More significantly, to assess the impact of leachate from a landfill on a downgradient drinking water well, it is important to correlate aquifer concentration with that in a drinking water well such that the true risk is properly estimated. A three‐dimensional finite‐difference flow and transport model has been applied to demonstrate that the disparity between aquifer and well concentrations results primarily from advective flow phenomena and can be quantified. The modeling shows that the concentration in the well is a function of the initial vertical concentration profile in the aquifer, the volumetric flow rate from below the partially penetrated well, the penetration fraction, and the amount of water purged before sampling. Under steady‐state conditions, the dilution of concentrations in monitoring wells may be expressed as a simple analytic function of the above parameters. The result from this analytic function agrees well with numerical solutions and field sampling data.
Simultaneous Determination of Argon and Nitrogen
Authors: Martin Glen E. , Snow Daniel D. , Kim Euisik , Spalding Roy F.
Published: August 2005

Denitrification can be confirmed by the presence of excess N2 as indicated by measurement of argon and nitrogen. Previously reported Ar/N2 ratios in ground water have been measured by static gas mass spectrometry, quadrupole mass spectrometry, and gas chromatography. The detector geometry and flared flight tube of the VG Optima isotope ratio mass spectrometer (IRMS) were determined to be fortuitously engineered for the simultaneous and highly precise measurement of Ar (mass 40) and N2+ (mass 28). Certified gas mixtures containing known Ar/N2 ratios were analyzed to assess instrument accuracy. A preparation system for the extraction and purification of Ar and N2 from water samples was developed and tested. δ(Ar/N2) values for prepared air‐saturated water (ASW) samples (24°C) averaged + 1149 ± 8‰ and did not significantly differ from the predicted value relative to atmospheric Ar/N2 of + 1144‰) (p < 0.001). The δ(Ar/N2) from in situ microcosms averaged +1280 ± 22‰ versus atmospheric Ar/N2 and approximated the expected level for ASW of + 1218 at 12°C. Much lower δ5(Ar/N2) values were measured in 18 ground‐water samples collected from a site where denitrification had previously been documented. Samples collected from a site where conditions indicate little or no denitrification have δ(Ar/N2) values close to those for ASW.
Sensitivity of Drawdown to Parameters and Its Influence on Parameter Estimation for Pumping Tests in Large‐Diameter Wells
Authors: Jiao Jiu J. , Rushton Ken R.
Published: August 2005

The sensitivity features of drawdown to aquifer parameters and their influence on parameter estimation and pumping‐test design are investigated in terms of pumping tests conducted in a large‐diameter well. It is concluded that the well storage reduces the sensitivities of drawdown to transmissivity and storativity, and increases the correlation between them. This leads to uncertainties in estimating the aquifer parameters, especially storativity. The most informative drawdowns in terms of parameter estimation change with time and space. This is instructive for pumping‐test design in a large‐diameter well. Both hypothetical and real examples are used to demonstrate key ideas.
Lab and Field Measurements of the Hydraulic Conductivity of Clayey Silts
Authors: Döll Petra , Schneider Wilfried
Published: August 2005

Various lab and field experiments were conducted to determine the vertical hydraulic conductivity of two highly compressible, organic‐rich clayey silts (Holocene marsh sediments Klei and gyttja). Constant‐head permeameter tests in the lab show an increase in measured hydraulic conductivity with sample size by a factor of 5 (Klei) and 20 (gyttja). On a field scale, six different methods were tested: (1) evaluation of the propagation of the tidal wave from the aquifer into the silts; (2) aquitard reaction test; (3) evaluation of aquifer drawdown; (4) slug test; (5) evaluation of vertical profiles of measured organic contaminant concentrations in the silts; (6) evaluation of benzene concentrations measured in aquifer wells. Porous cup pressure cells instead of piezometers must be used to measure relatively fast changes of hydraulic head in these low‐permeability media. Comparison of the results is hampered by spatial heterogeneity.
A Method for Passive Release of Solutes from an Unpumped Well
Authors: Wilson Ryan D. , Mackay Douglas M.
Published: August 2005

A new method was developed for releasing dissolved solutes into ground water which has application in both academic studies and practical efforts to stimulate in situ bioremediation, introduce chemical reactants, or understand flow and transport properties. The method involves the diffusion of solutes out of inexpensive, simple emitter devices which are installed in large diameter wells. Mass flux from an emitter depends on the geometry of the emitter, ground‐water flow rate, the imposed concentration gradient from the stock solution inside the emitter, and the diffusion coefficient of the solute through the emitter material. Diffusion coefficients are constants of a solute/tubing pair, and are established in simple experiments. If ground‐water flow rates and diffusion coefficients are known, emitter geometry and stock solution concentration can be tailored for a wide range of performance requirements.

In laboratory experiments, benzene was released at or near 1.3 mg/1 for a total of 31 days, TCE for 17 days at approximately 4.5 mg/1, and bromide for 23 days at 667 mg/1. The emitted concentration of a wide range of solutes can be stabilized for much longer periods of time once the mass flux in the flow‐through system reaches steady‐state, provided the concentration gradient is maintained.

A simple computer model was written to aid in the design of source emitters. The model was used to match diffusion coefficients to data for three solute‐tubing combinations. Once the diffusion coefficient of a given solute in a given type of tubing is determined from experimental data by curve‐matching, the model can be used in a predictive capacity. A second TCE release test showed that the diffusion coefficient calibrated from the model can be used to predict the steady‐state release concentration of TCE under different conditions.

Simple two‐dimensional transport modeling suggests that a relatively uniform plume of solutes may be generated by emitters placed in wells spaced close together. The uniform introduction of nutrients and oxygen by this passive method may encourage more efficient in situ remediation, and in some situations, save time and money.
Relation of Ground‐Water Quality to Land Use on Long Island, New York
Authors: Eckhardt David A. V. , Stackelberg Paul E.
Published: August 2005

Water‐quality data from 90 monitoring wells screened within 50 feet of the water table in the unconfined upper glacial aquifer beneath five areas of differing land use in Nassau and Suffolk Counties, Long Island, were compared to assess the effects of land use on ground‐water quality. The areas, which range from 22 to 44 square miles, represent suburban land sewered more than 22 years at the time of the study (long‐term sewered), suburban land sewered less than 8 years (recently sewered), suburban land without a regional sewer system, agricultural land, and undeveloped (forested) land. Comparison of water‐quality data from the 90 wells indicated that samples from the undeveloped area had the lowest and smallest range in concentrations of several human‐derived constituents, such as nitrate, alkalinity, boron, synthetic solvents, and pesticides. Concentrations of these constituents in samples from the three suburban areas and the agricultural area generally were intermediate to high and had the widest variation.

Maximum‐likelihood logistic regression analysis of explanatory variables that characterize the type of land use and population density within a 1/2‐mile radius of each of the 90 wells was used to develop predictive equations for contaminant occurrence in ground water within 50 feet of the water table. Two logistic regression equations for the 90 monitoring wells were compared with equations developed independently from ground‐water quality data at more than 240 other wells throughout Nassau and Suffolk Counties to evaluate the predictive value of the land‐use variables at the larger two‐county scale. The results demonstrate that the population density and amount of agricultural, commercial, and high‐ and medium‐density residential land within specified areas around wells can be reliable predictors of contaminant presence. The strength of the correlations supports the premise that land use affects the quality of water in water‐table aquifers overlain by highly permeable material because land use commonly determines the types and amounts of chemicals introduced at land surface. When coupled with GIS technology and accurate, detailed land‐use and water‐quality information, the methods and results of this study can be useful to local planning boards in evaluation of potential effects of development on ground‐water quality. The methods can also be useful to hydrologists in the analysis and design of ground‐water‐monitoring networks.