bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ Estimation of Transport Parameters: A Field Demonstration
Authors: Wise William R. , Charbeneau Randall J.
Published: August 2005

Linear sorption coefficients and first‐order biotransformation rates for para‐dichlorobenzene (pDCB) and naphthalene are fit to data from a three‐well forced‐gradient (injection‐production) field test performed at the site of an abandoned creosoting facility in Conroe, Texas. The breakthrough curve of an injected inert tracer, chloride, is used to describe the hydraulics of the field test. Along each streamline, the movement of a reactive solute is described by a one‐dimensional transport equation. The hydraulic and streamline transport models are coupled through a combination integral, the evaluation of which yields the effluent concentration (at the production well) of that reactive solute as a function of time. Transport parameters for the field site, sorption coefficients and biotransformation rates for pDCB and naphthalene, are obtained through inverse analysis of effluent data obtained at one of the production wells. The method is formulated such that no formal treatment of dispersion is required.
Two Methods for the Laboratory Identification of Transversal Dispersivity
Authors: Pisani Stefano , Tosi Nicola
Published: August 2005

The experimental identification of transversal dispersivity in the laboratory is not a very developed subject; the authors herein propose two methods for identifying transversal dispersivity in laboratory experiments, based on the analytical solution of a continuous, point‐like, injection of a nonreactive solute in a flow tank packed with a homogeneous porous medium. The solute transport is supposedly two‐dimensional, whereas the hydraulic flow is monodimensional with a uniform velocity.

Each identification method is based on the measurement of concentration in pairs of points. In the first method the points are taken along lines normal to the direction of the fluid flow, with one of the two points set on the central axis of the flow tank. In the second method the two measurement points are placed on lines passing through the solute injection point.

The stability of the two methods, with respect to concentration measurement errors, is analyzed to assess the reliability of the transversal dispersivity estimate. Furthermore, the two methods are found to be sensitive to variations of the concentrations.
Use of a Geographic Information System in Site‐Specific Ground‐Water Modelinga
Authors: El‐Kadi A. I. , Oloufa A. A. , Eltahan A. A. , Malik H. U.
Published: August 2005

Ground‐water modeling is hindered, in general, by the lack of adequate information about the ground‐water system and hence the need for an interactive and efficient system for data preparation and results analysis. Such a lack of information usually necessitates the use of a tedious iterative methodology within a sensitivity analysis scheme. This study facilitates modeling efforts by using the data‐handling and graphical capabilities of a geographic information system in site‐specific, numerical modeling of ground‐water resources. Data for the island of Oahu, Hawaii, are given to illustrate the approach. The modeling procedure is integrated within the GIS as an item in the main menu. A USGS model, known as MOC, is linked into the system and applied to a case study to illustrate the procedure. The linkage is generic in nature and can be extended to other models as well. The availability of a programming language in the GIS package facilitates pre‐ and post‐processing efforts within custom‐made dialogue boxes and pull‐down menus. On‐line help screens for modeling as well as data handling can also be designed.
Nonaqueous Phase Hydrocarbon in a Fine‐Grained Sandstone: 1. Comparison Between Measured and Predicted Saturations and Mobility
Authors: Huntley David , Hawk Robert N. , Corley Helen P.
Published: August 2005

The distribution and mobility of light, nonaqueous phase hydrocarbons in the subsurface is poorly understood, particularly in relation to observations of hydrocarbons in monitoring wells. Recent work by Lenhard and Parker (1990) and Farr et al. (1990) resulted in an equilibrium model in which the degree of hydrocarbon saturation was shown to be a function of the apparent thickness of hydrocarbon in a monitoring well, the height above the oil/water interface, and the capillary pressure/saturation characteristics of the soil. The current investigation compared measured hydrocarbon saturations, hydrocarbon volumes, and hydrocarbon mobility to those predicted by the capillary characteristic model of Farr et al. (1990) and Lenhard and Parker (1990). Five monitoring wells were completed in boreholes drilled in a hydrocarbon‐contaminated area of downtown San Diego, where apparent hydrocarbon thickness varied from zero to over 1.5 meters. Up to 2.5 meters of continuous core was obtained from each of the boreholes and split into 3 cm intervals. Alternating 3 cm samples were analyzed for total petroleum hydrocarbon, and the remaining samples were used for grain‐size analysis and measurement of capillary characteristic curves. Slug‐withdrawal tests were conducted on the hydrocarbon intervals, and constant‐rate discharge tests were conducted on the water‐saturated intervals of the monitoring wells.

The results show typical hydrocarbon saturations of 5% to 20%, with one borehole showing a limited zone of up to 50% saturation. Hydrocarbon mobility (relative permeability) is greatly reduced due to the low saturations, as predicted by capillary theory. These observations are consistent with both the capillary model of hydrocarbon distribution and with the very low recoveries achieved using hydrocarbon skimming systems.
Modeling Chemical Transformation Products Using Asymptotic Solutions
Authors: Mills William B. , Liu Sally
Published: August 2005

A method is developed to predict time‐variable concentrations of a degrading chemical and its first‐ and second‐generation transformation products for randomly located receptors in ground water. An asymptotically approximate solution for chemical concentrations is derived. To evaluate uncertainties in predicted concentrations, a Monte Carlo approach is implemented. Substantial computational savings are realized when asymptotically approximate solutions are used rather than the exact solutions; yet, the accuracy of the solutions is comparable.
Temporal Changes in Manganèse Concentrations in Water from the Fredericton Aquifer, New Brunswick
Authors: Thomas N. E. , Kan K. T. , Bray D. I. , MacQuarrie K.T.B.
Published: August 2005

A geochemical field study was conducted on the municipal aquifer in Fredericton, New Brunswick, Canada to determine the cause of increased manganese levels, from 0.02 mg/1 to about 1.0 mg/1 over a 34‐year period, in three of five production wells. The source of water for each of the five production wells has been determined to be infiltrated river water or precipitation, or a mixture of these sources. Wells that are predominately withdrawing infiltrated river water have corresponding high manganese concentrations, and redox potential data indicate that manganese tends to be in the aqueous form Mn2+. Geochemical modeling further suggests that the ground water is undersaturated with several common manganese minerals, while remaining supersaturated with iron oxide‐hydroxide minerals. The primary cause of the temporal increase in manganese concentrations is attributed to increased dissolved organic carbon introduced to the aquifer as a result of the escalating contribution of river water to the aquifer with time. Oxidation of organic matter proceeds in a ground‐water environment, as dissolved oxygen is depleted, by utilizing manganese oxides as electron acceptors.
Hydrology and Chemistry of Thermal Waters Near Wells, Nevada
Authors: Jewell Paul W. , Rahn Thomas A. , Bowman John R.
Published: August 2005

Anomalously warm water in shallow wells and surface springs is found in and around the town of Wells, Nevada. The geology of the Wells area is dominated by Paleozoic and Miocene sedimentary rocks which are cut by high angle normal faults. Thermal springs are associated with the normal faults, whereas thermal water from wells is the result of upward vertical fluid infiltration through the porous, Miocene lacustrine sedimentary rocks and Quaternary alluvium. Temperature logs from a nearby oil exploration well show locally high geothermal gradients (> 50° C/km). Analysis of static water heads indicates that vertical flow is greater than or equal to horizontal flow in low‐lying areas near the town of Wells. Solution of the advection‐diffusion equation using temperature data from the upper portion of the oil well suggests upward flow velocities of approximately 2–10 m/yr. Cold waters have a mixed cation‐bicarbonate chemistry whereas thermal waters are dominantly (Na + K)‐bicarbonate. Chemical geothermometers indicate fluid circulation to depths between 1–2 km. Deuterium and oxygen‐18 analyses have considerable variability, with modest deviations from the global meteoric water line. The occurrence of deuterium as light as – 145% suggests significant recharge to the hydrothermal system from very high elevations or water which has had a long subsurface residence time and is recording the signal of a cooler climate.
In Situ Surfactant Washing of Polychlorinated Biphenyls and Oils from a Contaminated Field Site: Phase II Pilot Study
Authors: Abdul Abdul S. , Ang Carolina C.
Published: August 2005

An in situ surfactant washing process was previously developed and successfully pilot‐tested at a field site contaminated with polychlorinated biphenyls (PCBs) and oils (Abdul et al., 1992). A second phase of the pilot study, conducted the following year at the same site, confirmed the technical viability of this process. The results of the phase II study surpassed the predictions of the long‐term performance of this technology based on the phase I results. Soil cores taken from the plot before the phase I and phase II studies and after the phase II study showed mass reduction and redistribution of the contaminants.

A continuous column washing study using the same contaminated soil showed consistency with field results. The amounts of PCBs removed in the laboratory and field studies, respectively, are 7% and 10% after 5.7 pore volume (PV) washings (phase I) and 19% and 24% after 8 PV washings (phase II). More than 85% of the PCBs were removed from the laboratory soil column after 105 PV washings. This study supports the phase I study which indicates that the in situ surfactant washing process is a viable remediation technology for hydrophobic contaminants.
A Geochemical and Isotopic Approach to Delineate Landfill Leachates in an RCRA Study
Authors: Fritz Steven J. , Bryan Jeffrey D. , Harvey F. Edwin , Leap Darrell I.
Published: August 2005

Under many circumstances during an RCRA investigation, the EPA will not allow intrusive sampling of an SWMU (Solid Waste Management Unit, or “waste dump”). This presented difficulties in characterizing the waste within a closed landfill identified as an SWMU located on land owned by Purdue University, 3 kilometers northwest of the West Lafayette (Indiana) campus because there were few records of what was discarded into this public dump during its operation from 1958–87. Chemical and isotopic data of shallow ground water and surface runoff provided a realistic means to infer movement of contaminants away from the landfill.

Leachate is characterized by high concentrations of Na+ and Cl− (∼ 4mN), sulfate (∼ 8 mN), total hardness (Ca+2+ Mg+2∼ 19 mN), and alkalinity (∼ 12mN). Disposal of road salt is responsible for the NaCl concentrations, while dissolution of concrete explains the high Ca+2, Mg+2, and alkalinity values for waters having a pC02 only slightly above the regional level for ground waters (10−1.82atm).

Deep and shallow uncontaminated ground waters in the vicinity of the SWMU have an average δ34S value of 0.5 per mil (CDT). Since the δ34S of leachate lies between + 10 and + 17 per mil (CDT), the high sulfate concentrations are most likely due to dissolution of interred plasterboard consisting primarily of gypsum.

Tritium activities for the leachate in two shallow wells emplaced 15 meters from the toe of the SWMU ranged from 55 to 85 TU. Correcting for half‐lives and correlating these activities to historical records of tritium in rainfall as measured at Chicago, these 3H activities suggest that the travel time between the SWMU interior and these wells is between 15 and 20 years.
Modeling the Effects of Salt‐Water Intrusion Dynamics for a Coastal Karstified Block Connected to a Detrital Aquifer
Authors: Calvache M. Luisa , Pulido‐Bosch Antonio
Published: August 2005

The contamination by salt‐water intrusion affecting the coastal aquifer at Castell de Ferro (Granada, Spain) is especially influenced by the coexistence of two coastline lithological formations with highly differing transmissivity (highly karstified limestones and detrital sediments). Despite not having a very high intrusion volume (0.1–0.2 hm3/year), the aquifer does have a high saline content. In order to explain this phenomenon, we first of all modeled the ground‐water flow (MODFLOW) in the aquifer. Two models were then used for the fresh‐water/salt‐water contact: one assuming a sharp interface (BADON2) and the other taking into account density‐dependent mass transport (MOCDENSE). Our conclusion is that the high saline content of the aquifer is due to the existence of a preferential route for ground‐water flow through the karstified materials in contact with the detrital materials and the sea. The detrital materials located beside the karstified massif therefore constitute the route for only 10%‐20% of the system's total outlet to the sea, which is not enough water to wash the salts resulting from salt‐water intrusion. We also find that in this type of aquifer two‐dimensional transport models do not provide the most realistic results, since the effect in a direction transverse to the ground‐water flow of very transmissive material cannot be simulated in this type of profile. In this case, and despite its limitations, better results are obtained using the sharp interface model.
Diffusive Disappearance of Immiscible‐Phase Organic Liquids in Fractured Geologic Media
Authors: Parker Beth L. , Gillham Robert W. , Cherry John A.
Published: August 2005

In a new conceptual model for immiscible‐phase organic liquids in fractured porous media that specifically includes the effect of molecular diffusion on the persistence of organic liquid in fractures, dissolved contaminant mass from the liquid in fractures is lost by diffusion from the fractures into the porous matrix between the fractures. Theoretical calculations for one‐dimensional diffusive fluxes from single, parallel‐plate fractures using parameter values typical of fractured porous geologic media establishes the concept of immiscible‐phase disappearance time, which is the time required for a given volume of immiscible liquid in a specified aperture to disappear following its arrival in the fracture. Nonlithified surficial clayey deposits with matrix porosities ranging from 25 to 70% are extensive across many regions of North America and Europe, and at shallow depth, typically have fractures with apertures in the range of 1 to 100 microns. The common chlorinated solvents such as dichloromethane (DCM), trichloroethene (TCE), and tetrachloroethene (PCE) are expected to completely disappear in these deposits within a few days to weeks. For fractured sedimentary rocks with much lower matrix porosities (5–15%), disappearance times for these solvents are generally less than several years for fracture apertures ranging from 10 to 200 microns typical for shales, siltstones, sandstones, and carbonate rocks. This is sufficient time for the immiscible phase of chlorinated solvent contamination to have disappeared at many industrial sites. This conceptual model has important implications with respect to ground‐water monitoring, diagnosis of the nature and degree of contamination, and expectations for ground‐water remediation at many contaminated sites. Proposed methods for enhancing immiscible‐phase mass removal using hydraulic manipulation, surfactants, or alcohols will be futile where the immiscible phase has disappeared into the clay or rock matrix, and reverse diffusion and desorption will control clean‐up time frames. Therefore, prospects for permanent restoration of many DNAPL and LNAPL sites in fractured porous media are more limited than previously thought.
A Refraction Statics Method for Mapping Bedrock
Authors: Taucher Paul , Fuller Brian N.
Published: August 2005

The bedrock surface beneath unconsolidated eolian sand and garbage at the active Casper, Wyoming landfill was successfully imaged using a refraction statics method. The method employed the summation of common‐detector refraction seismic traces in a manner analogous to common midpoint (CMP) reflection seismic methods. The method produces a seismic time section that is interpreted in much the same way as reflection seismic time sections. The method was very robust in imaging the bedrock surface, even when the refractions were poorly defined on both unprocessed and filtered shot records. Processing of a refraction statics data set is less expensive than CMP high‐resultion reflection processing and does not rely on the detailed graphical constructs of the more commonly used refraction seismic analysis methods. This alternative to more commonly used refraction and reflection seismic methods should be applicable in noisy and otherwise difficult data acquisition areas where the resolution of first breaks and/or reflections is difficult. The summation of data traces enhances the signal to noise ratio allowing direct observation of the bedrock image on the time section. A depth section can be calculated from the final time section. In poor data quality settings, the enhancement of the refraction signal by summation of multiple, common‐detector data traces is the significant advantage of the refraction statics method over other refraction seismic interpretation methods which are dependent on accurately picking refracted arrivals on individual data traces.

An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.
Numerical Modeling of Ground‐Water Resource Management Options in Kuwait
Authors: Mukhopadhyay Amitabha , Al‐Sulaimi Jawad , Barrat Jean Marie
Published: August 2005

Kuwait is an arid country with no surface water and very limited resources of useable ground water. These ground‐water reserves have been heavily exploited since the 1960s, which has led to substantial decline in the potentiometric surface of the aquifers. A regional numerical model, calibrated under both steady and unsteady‐state conditions, has been used to investigate the hydrodynamic impacts of different ground‐water management options on the potentiometry of the aquifers. The results indicate that there is a real danger of either dewatering the aquifers, or deteriorating water quality by upconing and sea‐water intrusion, if the present trend of increasing withdrawal rates continues unchecked. In fact, the study suggests that even if the withdrawals are completely stopped in the near future, the aquifers will not be restored to their pre‐1960 conditions by the year 2010. Artificial recharge of the aquifers will have, however, beneficial effects on the potentiometric surfaces and should be considered.
Monte Carlo Simulation and Effective Medium Approximation in Subsurface Flow Modeling
Authors: Shrestha S. P. , Loganathan G. V.
Published: August 2005

A refined Monte Carlo (MC) simulation procedure and an Effective Medium Approximation (EMA) are presented for solving the stochastic subsurface flow problem. The refined MC simulation procedure uses analytical means to estimate the sample size by controlling the error incurred in using the sample average in place of its population mean at a chosen confidence level for the pressure head. Also, an unbiased estimator of the pressure head that takes advantage of its correlation with the saturated conductivity to reduce its variance is proposed. This reduced variance results in a smaller width of uncertainty about the predicted pressure head thereby improving the precision. The EMA permits one to solve the stochastic subsurface flow problem in a single run to generate the expected pressure head field with the aid of a field‐scale effective hydraulic conductivity that has a form similar to the Gardner equation. Both the MC and the EMA approaches perform well when applied to example problems taken from the literature.
An Evaluation of the Reproducibility of Forced‐Gradient Solute Transport Tests
Authors: Bianchi‐Mosquera Gino C. , Mackay Douglas M.
Published: August 2005

Two forced‐gradient ground‐water transport tests were conducted in the Summers of 1989 and 1990 at Borden, Ontario. The tests were nearly identical in several respects and allow an assessment of the reproducibility of such efforts. In both experiments, carbon tetrachloride, tetrachloroethene, and a conservative tracer were injected as a pulse into the aquifer and monitored as they migrated towards an extraction well. Data were analyzed using moment techniques and fitted with a 1‐D transport model accounting for physical nonequilibrium conditions for the sorbing solutes. Visual inspection and simulations of the results indicate that the tests are reproducible. However, results from the moment analyses are less conclusive, perhaps due to data truncation. The differences in the modeling results or the parameter estimates derived from them are likely to have resulted from differences in the experimental conditions or duration. Simulations conducted using either year's fitted parameters are essentially indistinguishable from a practical point of view.
Chemical Leaching Near the Waiawa Shaft, Oahu, Hawaii: 1. Field Experiments and Laboratory Analysis
Authors: Loague Keith , Miyahira Robert N. , Oki Delwyn S. , Green Richard E. , Schneider Randi C. , Giambelluca Thomas W.
Published: August 2005

This paper is the first paper of a two‐part series concerned with assessing the potential for organic chemical leaching to a ground‐water skimming tunnel in the Pearl Harbor Basin, Oahu, Hawaii as a direct result of a proposed urban development. The objective of our simulation‐based assessment was to provide insight into the potential for chemicals, that may be introduced to the recharge areas of the Waiawa Shaft as a result of the proposed developments, to subsequently leach through the unsaturated zone to ground water. In this paper field and laboratory results are presented for experiments designed to support the modeling effort reported in the second paper of this series. The chemical leaching experiments were conducted at two field locations. The chemicals which were applied and then monitored for their downward movement in the near‐surface unsaturated zone are bromide, chlorpyrifos and fenamiphos. We found (1) good mass balance for bromide at both sites, (2) limited mobility of chlorpyrifos and fenamiphos at the field plots, and (3) good agreement between field and laboratory measured degradation rates.
Facilitated Transport of Contaminant Metals Through an Acidified Aquifer
Authors: Kaplan Daniel I. , Bertsch Paul M. , Adriano Domy C.
Published: August 2005

A highly acidic aqueous waste containing metals was released into unlined seepage basins between 1955 and 1988 resulting in the contamination of the underlying aquifer. To provide insight about the mechanism (s) responsible for the facilitated movement of several of these contaminant metals, ground‐water samples were recovered from the aquifer along a 1.02‐km transect at approximately the rate of ground‐water flow. Facilitated contaminant transport was attributed primarily to the poor cation‐sorbing capacity of the aquifer matrix and the soluble nature of the metals in the acidic plume. Based on chemical equilibrium calculations of ground‐water ultrafiltrates which agreed with results from cationic and anionic resin‐exchange experiments, over 90% of each contaminant metal (Cr, Ni, Cu, Cd, Pb, and U) existed in cationic forms in the aquifer: either as soluble metals or as sorbates associated with positively charged ground‐water colloids. These cationic species were not retained by the aquifer because the pH of the aquifer matrix was slightly below the measured point‐of‐zero charge, indicating the variable charge sites on the mineral surfaces within the aquifer likely had a net positive charge. Contaminants were associated with recovered ground‐water colloids and this association increased with the pH of the system. However, mobile colloids would likely play only a small role in the transport of contaminants through this aquifer because of their relatively low concentration.
The Effect of Zones of High Porosity and Permeability on the Configuration of the Saline‐Freshwater Mixing Zone
Authors: Wicks Carol M. , Herman Janet S.
Published: August 2005

Coastal karst aquifers have highly variable distributions of porosity and permeability. The ability to assess the volume of aquifer occupied by freshwater in coastal karst aquifers is limited by both the lack of understanding of the effect that regions of cavernous porosity and permeability have on the configuration of the saline‐freshwater mixing zone and by the limited knowledge of the location of the cavernous regions. A dual‐density ground‐water flow and solute transport model was used to explore the effect that the depth, lateral extent, and proximity to the coast of zones of high porosity and permeability has on the configuration of the saline‐freshwater mixing zone. These aquifer heterogeneities tend to shift the mixing zone upward relative to the position it would have in aquifers with homogeneous porosity and permeability. Zones of high porosity and permeability located at positions shallow in the aquifer or nearer to the coast had the greatest effect. In fact, for the conditions modeled, position was more important in modifying the configuration of the mixing zone than was changing the ratio of the intrinsic permeability of the cavernous zone to the aquifer matrix from 100 to 1000. Modeling results show that ground‐water flow is concentrated into the zones of high porosity and permeability and that flow configuration results in steep salinity gradients with depth. Field observations of the location of the halocline and of step changes in ground‐water composition coincident with regions of cavernous porosity in coastal karst aquifers corroborate the model results. In a coastal setting with saline water intruding into an aquifer, the effect of cavernous porosity and associated high permeability is to decrease the volume of aquifer in which freshwater occurs by a greater degree than would occur in an aquifer with homogeneous porosity and permeability.
Topographic Influence of Longwall Mining on Ground‐Water Supplies
Authors: Elsworth D. , Liu J.
Published: August 2005

The extent of potential aquifer dewatering resulting from underground longwall mining is determined through application of a nonlinear finite‐element model. The model represents the form of the body strain field that accompanies mining‐induced subsidence, and uses strain magnitudes to define the modified hydraulic conductivity field. The model is applied to test the sensitivity of the induced strain field to ground surface topography. The location and extent of three characteristic zones of conductivity enhancement are defined, representing gravitational detachment above the panel, shear failure above the abutment, and extensile deformation at the ground surface. Correspondingly, well completion locations are ranked with their potential for dewatering representing relatively high potential in upland areas and relatively low potential in valley base locations. These results amplify and offer a phenomenological explanation of observational data. Modeling results are compared with several documented studies in the Appalachian coal fields and favorable agreement achieved.
Distribution of Transmissivity in the Dammam Limestone Formation, Kuwait
Authors: Mukhopadhyay Amitabha
Published: August 2005

The transmissivity (T) distribution in the Dammam Formation aquifer within the State of Kuwait was investigated. It was found that up to 29% of the spatial variation in the log10 T values could be explained by a multiple linear relation with the coordinates of the observation site, whereby the log10 T showed a decreasing trend towards north and east. The deviations of the log10 T from the first degree trend were kriged using the semivariogram constructed on the basis of the available T data. The resulting values were added to the logio T values estimated from the linear relation with the coordinates, to derive the most likely values of log10 T at prespecified points. The technique provides estimates of transmissivity in areas away from the existing water fields. The T distribution with respect to the structure of the Dammam Formation was also investigated. The hypothesis that the transmissivity of the Dammam Formation was higher on the structural highs could not be substantiated, mostly because not enough data were available from such areas.
Localized Anisotropic Transmissivity in a Karst Aquifer
Authors: Greene Earl A. , Rahn Perry H.
Published: August 2005

Maps of cave passageways in the outcrop area of the uplifted Madison Limestone in the Black Hills, South Dakota, show that principal cavern development is oriented in the major direction of ground‐water flow, roughly radial to the Black Hills. Fracture‐trace analysis and measuremnt of joints in the Wind Cave area show that these orientations coincide with cave passageways. Aquifer testing at Rapid City indicates that a local principal transmissivity tensor is oriented in the direction of cave development and along the strikes of bedding‐plane fractures. This indicates that much of the permeability of the Madison aquifer is modern karst (post‐Laramide‐Orogeny).

From the above, we conclude that a localized anisotropic permeability (principal direction of transmissivity) is developed by ground water flowing through fractures, dissolving the rock, and producing dissolution‐enhanced conduits along the direction of ground‐water flow. This localized principal direction of transmissivity can be deduced from analysis of the potentiometric surface, stream‐aquifer hydrographs, mapped cave passageways, aquifer tests, fracture traces, and measurements of joints in the field.
MacWateqf: The Classic Speciation and Saturation Program Adapted to Macintosh Computers
Authors: Román F. Javier Sánchez San
Published: August 2005

This article presents MacWateqf, a version for Macintosh computers of the classic WATEQF program. This version of WATEQF can be used easily, as entry data do not need a rigid format, permitting the use of integer or real numbers, whether real or in scientific notation, with any quantity of decimals. Furthermore, a new program is also presented here: Mac Wat‐Intro, which makes it possible to create a datafile for WATEQF input with absolute ease.
Reducing Uncertainty Associated with Ground‐Water Flow and Transport Predictions
Authors: Poeter Eileen P. , McKenna Sean A.
Published: August 2005

Effective evaluation of ground‐water flow and transport problems requires consideration of the range of possible interpretations of the subsurface given the available, disparate types of data. Geostatistical simulation (using a modified version of ISIM3D) of hydrofacies units produces many realizations that honor the available geologic data and represent the range of subsurface interpretations of unit geometry. Hydraulic observations are utilized to accept or reject the geometric configurations of hydrofacies units and to estimate ground‐water flow parameters for the units (using MODFLOWP). These realizations are employed to evaluate the uncertainty of the resulting value of the response function (ground‐water flow velocity and contaminant concentration) using MT3D. The process is illustrated with a synthetic data set for which the “truth” is known, and produces a striking reduction in the distribution of predicted contaminant concentrations. The same system is evaluated three times: first with only hard data, then with both hard and soft data, and finally with only the realizations that honor the hydraulic data (i.e., those accepted after parameter estimation via inverse flow modeling). Using only hard data, the mean concentration predicted for all realizations at the point of interest is nearly two orders of magnitude lower than the true value and the standard deviation of the log of concentration is two. The addition of soft data brings the mean concentration within one order of magnitude of the true value and reduces the standard deviation of the log of concentration to one. After eliminating realizations using inverse flow modeling, the mean concentration is one‐third of the true value and the standard deviation of the log of concentration less than 0.5.
Correction for Temperature Effect in the Recovery of a Pumped Well
Authors: Kawecki M. W.
Published: August 2005

Water levels measured in tests on pumped or flowing wells tapping confined aquifers are generally affected by temperature changes in the water column. This temperature effect becomes significant in deep wells, making direct hydraulic analysis of test data meaningless. The problem can be avoided by using an observation well or by monitoring bottom‐hole pressure in the test well, but both these options are costly and consequently not always available. Therefore, a temperature correction method is proposed based on a simple model assumed to describe the cooling in the test well during recovery. The method is designed to determine the aquifer transmissivity from recovery data and to calculate the true drawdown during pumping. The only additional test data requirements are measurements of the initial and stabilized discharge temperatures. Despite several approximating assumptions in the cooling model, the method has given apparently successful results in a number of case studies. Although further testing of its effectiveness is still required, the method may prove to be a useful secondary alternative in many cases if observation wells and bottom‐hole pressure monitoring facilities are not available.
Ground‐Water Contaminant Plume Differentiation and Source Determination Using BTEX Concentration Ratios
Authors: Yang Y. Jeffrey , Spencer Rick D. , Mersmann Mark A. , Gates Todd M.
Published: August 2005

Concentration ratios of benzene, toluene, ethylbenzene, and xylenes (BTEX) in ground water can be used for ground‐water contaminant plume differentiation and source determination. Computer modeling utilizing BTEX soil‐water partitioning coefficients and biodegradation rates shows that hydraulic dispersion, retardation, and biodegradation do not significantly modify the BTEX concentration ratios in ground water, particularly those of ethylbenzene and xylenes. Therefore, the BTEX concentration ratios are similar in the contaminant plumes that are derived from a common source or sources of similar BTEX compositions. In the vadose zone, the BTEX concentration ratios in downward‐migrating contaminant free‐product remain essentially unchanged because of the dynamic nature of soil adsorption and restricted natural soil ventilation. The only significant change in the BTEX concentration ratios occurs in the partitioning between ground water and contaminant free‐product as the result of differential BTEX solubilities in water. In the partitioning, benzene/toluene and toluene/ethylbenzene concentration ratios of ground water are 3.6 and 3.3 times greater respectively than the ratios at the source, while the ratios of ethylbenzene and xylenes remain unchanged.

The geochemical methods were successfully applied and tested at two sites where multiple ground‐water contaminant plumes from different sources were superimposed. The conclusions of geochemical analysis are consistent with the site‐specific hydraulic characteristics and facility operation histories.
Analysis of Hydraulic Conductivity Averaging Schemes for One‐Dimensional, Steady‐State Unsaturated Flow
Authors: Srivastava Rajesh , Guzman‐Guzman Amado
Published: August 2005

The evaluation of average properties over a block or element is required for most numerical methods used for the solution of unsaturated flow equations. In this study, it is shown that the accuracy of a particular averaging scheme depends on the type of model used for unsaturated material properties. A systematic and thorough error analysis of the averaging techniques for some commonly used soil characteristic curves is performed. It is shown that the two‐point Gaussian quadrature is consistently more accurate than the arithmetic, geometric, and harmonic means for all types of constitutive models.
Delineation of a Saline Ground‐Water Boundary from Borehole Geophysical Data
Authors: Schnoebelen Douglas J. , Bugliosi Edward F. , Krothe Noel C.
Published: August 2005

This study uses borehole geophysical data to calculate the total dissolved solids (TDS) concentration of ground water in Devonian and Silurian carbonate aquifers in northern and southwestern Indiana and specifically, to delineate the 10,000 mg/l (milligrams per liter) TDS boundary. The 10,000 mg/l TDS boundary as used here refers to the transitional zone in the Devonian rocks where the TDS concentration of saline ground water changes from less than 10,000 mg/l to 10,000 mg/l or greater. The 10,000 mg/l boundary not only defines the maximum allowable TDS concentration recommended by the U.S. Environmental Protection Agency for potentially potable water, but also establishes an internal “limit” for the Silurian and Devonian carbonate aquifers in Indiana where density differences may be important for ground‐water flow modeling. The study demonstrated that geophysical log data can provide a useful means of estimating TDS concentration in areas where water‐quality data are lacking, found an excellent correlation between the resistivity‐porosity method and measured TDS concentrations, and found several anomalous areas in Indiana where TDS concentration in Devonian and Silurian aquifers were higher or lower than expected.

The TDS content of ground water in Devonian and some Silurian units was estimated by using three independent geophysical methods: static spontaneous‐potential, mud‐filtrate‐resistivity, and resistivity‐porosity. Each method yields values for formation‐water resistivity (Rw), from which TDS concentrations can be estimated. Calculated concentrations from each method were compared to available water‐quality analyses. Use of the resistivity‐porosity method produced the most accurate results. To help quantify the values used in the resistivity‐porosity method, 19 samples cut from cores were evaluated by laboratory analyses. The static spontaneous‐potential method was used only where data were not available for the resistivity‐porosity method. The mud‐filtrate‐resistivity method yielded poor results and was not used. Chemical analyses of ground water and TDS concentrations estimated from borehole geophysical log data (resistivity‐porosity and static spontaneous potential methods) were used to establish areas where TDS concentrations in ground water are less than or greater than 10,000 mg/l.

The concentrations of TDS of water from the Silurian and Devonian carbonates were generally found to increase in a consistent trend downdip with depth into the Illinois and Michigan Basins; however, this trend was not observed in several anomalous areas where the 10,000 mg/l TDS boundary becomes more irregular in shape. There are also areas where the underlying Silurian carbonates have TDS concentrations that are less saline than the overlying Devonian carbonates. These anomalous areas may be the result of nonuniform recharge during Pleistocene time or more recent times, or from differences in permeability that control flow paths and rates.
Site Characterization Using 3H/3 He Ground‐Water Ages, Cape Cod, MA
Authors: Solomon D. K. , Poreda R. J. , Cook P. G. , Hunt A.
Published: August 2005

Exploratory drilling to locate new water‐supply wells on Cape Cod, Massachusetts encountered fuel‐related organic contaminants in a shallow unconfined aquifer. However, the plume could not be traced back to the water table and estimates of ground‐water velocities were not consistent with plausible contaminant releases, and thus the source of contamination was not located. In conjunction with an expanded hydrogeologic investigation, tritium and helium isotope analyses were performed to delineate ground‐water ages and flow rates. Vertical profiles of ground‐water age were used to determine recharge rates that range from 70 to 115 cm/yr. The age of water near the leading edge of the contaminant plume along with estimates of dispersion were used to estimate when the contaminant release occurred (1975 ± 3 years). Recharge estimates, the geometry of the aquifer, and contaminant data were used in a simple mass balance model to determine both the location of the contaminant source and the horizontal ground‐water velocity (ranging from 20 ± 12 m/y to 90 ± 20 m/y across the site). Concurrent site investigations revealed fuel floating on the water table within the area (± 250 m) determined by the model. The configuration of the water table and recharge estimates were used to estimate a horizontal hydraulic conductivity of 130 ± 30 m/d. The mean hydraulic conductivity from a subsequent 72 hr, 12 well pumping test was 100 m/d.
Preparation of Specific‐Yield Logs for Clastic Bedrock Aquifers
Authors: Robson S. G.
Published: August 2005

Specific yield is the principal aquifer characteristic needed to estimate the volume of recoverable ground water in storage in an aquifer. Determination of specific yield can be difficult and costly, particularly in deep, confined aquifers where core drilling and core analyses may be needed to define specific yield. A method has been developed for preparation of specific‐yield geophysical logs that could greatly ease the determination of specific yields in such aquifers.

Three geophysical logs that were investigated as potential indicators of specific yield were the free fluid index log, the effective‐porosity log, and the apparent grain‐density log. The free fluid index log did not accurately represent conditions at the test site in central Colorado and may not be suitable for application in other shallow and permeable aquifers. The effective‐porosity and apparent grain‐density logs were each used in least‐squares linear regressions to correlate log response to specific yield measured in core samples. The resulting regression equations have coefficients of correlation (R) of 0.84 and 0.90, and were used to successfully prepare specific‐yield logs from the effective‐porosity and apparent grain‐density logs.
Theis Solution Under Aquifer Parameter Uncertainty
Authors: Cheng A. H‐D. , Ouazar D.
Published: August 2005

The Theis solution is one of the most widely used ground‐water flow solutions for the prediction of drawdown caused by a pumping well in a confined compressible aquifer. This paper extends the classical solution with the consideration of information uncertainty of aquifer parameters. The goal is to present a simple and practical theory that can be easily utilized by practicing hydrogeologists.
Soil‐Gas Signatures from Volatile Chlorinated Solvents: Borden Field Experiments
Authors: Rivett Michael O.
Published: August 2005

Field experiments have been conducted at the Borden research site to evaluate the widely applied soil‐gas survey method. In particular, the ability of surveys to delineate DNAPL chlorinated solvent sources and associated ground‐water plumes has been investigated. Field experiments indicated that dissolved‐phase plumes from DNAPL pools or residual located about a meter or more below the water table are unlikely to be directly detected by soil‐gas surveys. Soil‐gas plumes observed at real sites are attributed to volatilization of source material in the vadose zone and consequent formation of very shallow interface zone ground‐water contamination that is able to partition to the soil gas as it transports downgradient. The distribution of DNAPL sources and dissolved‐phase plumes deeper in the ground‐water zone may often bear little resemblance to the shallow interface zone ground‐water plume above, and hence the location of this deeper contamination will remain highly difficult to identify by soil‐gas surveys. Field observations are confirmed with simple analytical 1‐D diffusion modeling and the implications of the results to the practice of soil‐gas surveys at contaminated sites indicated.
Chemical Leaching Near the Waiawa Shaft, Oahu, Hawaii: 2. Modeling Results
Authors: Loague Keith , Miyahira Robert N. , Green Richard E. , Oki Delwyn S. , Giambelluca Thomas W. , Schneider Randi C.
Published: August 2005

This paper is the second part of a two‐part series concerned with assessing the potential for organic chemical leaching to a ground‐water skimming tunnel in the Pearl Harbor Basin, Oahu, Hawaii, as a direct result of proposed urban development. The Pesticide Root Zone Model (PRZM) was used, after testing with field and laboratory data described in the companion paper, to make long‐term predictions of the movement of chlorpyrifos, diazinon, metribuzin, and nitrate under various recharge scenarios. The PRZM simulations revealed that, with the exception of chlorpyrifos, detectable levels of all the chemicals considered in this study may leach through the unsaturated zone to the water table from where they may eventually migrate to the skimming tunnel. The simulated concentrations in leachate reaching the water table were sufficiently low, considering subsequent mixing in the ground water, to suggest no adverse health effects. The reliability of the simulated results are laced with enough uncertainty, however, to suggest the need for monitoring for diazinon, metribuzin, and nitrate, if development does proceed. The methodology presented in this series is a first attempt at establishing a protocol for using numerical modeling, supported by field and laboratory measurements to aid in land‐use change consideration in Hawaii when nonpoint ground‐water contamination from organic chemicals is of concern.
A Program to Calculate Ground‐Water Mound Heights
Authors: Finnemore E. John
Published: August 2005

Mounding of the ground‐water table beneath recharge sources may be of concern where the raised water table approaches too closely to near‐surface facilities or features. Because of its high accuracy and wide range of applicability, the method of Hantush is probably the most widely used to calculate the time‐varying heights of ground‐water mounds on extensive and near‐horizontal saturated zones. Use of that method entails a number of inconveniences, however, including function evaluations and two‐dimensional interpolations between tabulated values, which must be performed iteratively. A FORTRAN computer program was developed to rapidly perform the necessary iterations and to evaluate some rather long and complex equations. These equations avoid the need for interpolation or other approximation procedures, and they provide accurate calculations for all conditions. Comparison of results from the computer program with results from approximation procedures indicates the areas and extents of the unreliability of the approximation procedures.