bluuebunny/crossref_metadata_2025 huggingface dataset:
Using Water‐Supply Wells to Investigate Vertical Ground‐Water Quality
Authors: Collar Robert J. , Mock Peter A.
Published: August 2005

Ground‐water contamination in the arid southwestern United States often shows up in ground‐water samples from deep water‐supply wells. For water‐supply wells with large or multiple perforated intervals, collection of depth‐specific samples in conjunction with spinner flowmeter measurements within the well while pumping may be used to estimate the vertical distribution of contamination in aquifers from which the well draws ground water. This paper presents some of our experience with spinner logging and depth‐specific sampling in water‐supply wells, as well as methodology, general assumptions, and limitations of this technique for investigating vertical ground‐water quality.
Optimal Remediation Policy Selection under General Conditions
Authors: Wang M. , Zheng C.
Published: August 2005

A new simulation‐optimization model has been developed for the optimal design of ground‐water remediation systems under a variety of field conditions. The model couples genetic algorithm (G A), a global search technique inspired by biological evolution, with MODFLOW and MT3D, and two commonly used ground‐water flow and solute transport codes. The model allows for multiple management periods in which optimal pumping/injection rates vary with time to reflect the changes in the flow and transport conditions during the remediation process. The objective function of the model incorporates multiple cost terms including the drilling cost, the installation cost, and the costs to extract and treat the contaminated ground water. The simulation‐optimization model is first applied to a typical two‐dimensional pump‐and‐treat example with one and three management periods to demonstrate the effectiveness and robustness of the new model. The model is then applied to a large‐scale three‐dimensional field problem to determine the minimum pumping needed to contain an existing contaminant plume. The optimal solution as determined in this study is compared with a previous solution based on trial‐and‐error selection.
A Stochastic‐Analytical Framework for Safety Assessment of Waste Repositories: 2. Application
Authors: Selroos Jan‐Olof
Published: August 2005

An analytical framework for probabilistic safety assessment of geological repositories is applied for a high‐level nuclear waste repository. The framework is based on stochastic‐analytical solution techniques and offers a versatile tool for the analysis of various scenarios. Features, events, and processes for a hypothetical repository, geosphere, and biosphere are considered. Explicit solutions in terms of the expected value and variance of the mass flux or cumulative mass flux are derived for each case considered. The uncertainty pertaining to features and events results in increased time spans of elevated hazard levels with possible exceedance of given regulatory criteria. Mass transfer processes, such as sorption and matrix diffusion, may result in significant reductions of radioactivity fluxes and subsequent doses in the biosphere.
Ground‐Water Sampling and Time‐Series Evaluation Techniques to Determine Vertical Concentration Distributions
Authors: Cosler Douglas J.
Published: August 2005

Data analysis methodologies are developed for using time‐series measurements of effluent concentrations during continuous sampling to determine the vertical shape and location of a horizontally uniform contaminant plume and to estimate physical/ chemical aquifer parameters such as vertical anisotropy, effective porosity, and retardation factor. Temporal water‐quality variations during constant‐flow sampling are calculated in the form of concentration type curves for a wide variety of plume shapes and positions and are shown to be directly related to the geometry and growth rate of the three‐dimensional capture volume of the well. An analytical type‐curve solution is derived for discrete‐interval sampling in homogeneous and isotropic/anisotropic aquifers containing plumes with complex vertical shapes that are described by the superposition of multiple Gaussian distributions. Results from two‐dimensional, axisymmetric simulations of ground‐water flow and particle transport demonstrate the sensitivity of concentration type curves to sandpack hydraulic conductivity, screen length, well diameter, flow through the well screen during discrete‐interval sampling, aquifer anisotropy and heterogeneities, pumping rate, effective porosity, and chemical retardation. Two applications of the concentration type‐curve method for determining plume and aquifer characteristics are presented. The first illustrates the use of discrete‐interval sampling to evaluate the vertical shape and location of a hypothetical plume in a homogeneous, isotropic aquifer. In the second, extraction‐well effluent data collected during a field experiment were used to evaluate the vertical concentration distribution in a sulfate plume and estimate the vertical anisotropy ratio of the aquifer. The results demonstrate the importance of developing consistency in purge and sample volumes to minimize artificial measurement variability in monitoring programs.
Ground‐Water Exploration Based on Lineament Analysis and Reproducibility Tests
Authors: Sander Per , Minor Timothy B. , Chesley Matthew M.
Published: August 2005

Lineaments derived from remote sensing data are analyzed with respect to ground‐water exploration in the Voltaian Basin of central Ghana. The lineament data were collected using both Landsat TM and SPOT imagery, multiple interpreters, and multiple trials. Three types of reproducibility tests are analyzed: (1) azimuth‐length comparisons, disregarding location; (2) lineament coincidence using a raster‐based comparison method; and (3) feature agreement using a rule‐based approach. The reproducibility tests show that there are clear differences in length and location of individual line segments between interpreters, but that a large proportion of the inferred structural features are detected by all interpreters. Fifty percent of the features on both imagery types are detected by any two interpreters and 40 percent by all interpreters. Lineaments classed as more hydrologically significant show a reproducibility of up to 90 percent between interpreters and justify the use of classifiers in lineament mapping. The application of the feature agreement approach, including classification by hydrological significance, shows the greatest promise for targeting successful well sites.
Biofouling of Contaminated Ground‐Water Recovery Wells: Characterization of Microorganisms
Authors: Taylor Stewart W. , Lange Clifford R. , Lesold Elizabeth A.
Published: August 2005

The taxonomy and physiology of microorganisms isolated from contaminated ground‐water recovery wells prone to biofouling are characterized for an industrial site in Rochester, New York. Principal aquifer contaminants include acetone, cyclohexane, dichloroethane, dichloromethane, 1,4–dioxane, isopropanol, methanol, and toluene. These contaminants represent a significant fraction (up to 95%) of the total organic carbon in the ground water. Ground‐water samples from 12 recovery wells were used to isolate, quantify, and identify aerobic and anaerobic bacterial populations. Samples from selected wells were also characterized geochemically to assess redox conditions and availability of essential and trace nutrients. Dominant bacteria, listed in order of descending numbers, including sulfate‐reducers (Desulfovibrio desulfuricans), anaerobic heterotrophs (Actinomyces, Bacteriodes, Bacillus, Agrobacterium), aerobic heterotrophs (Pseudomonas, Flavobacterium, Nocardia, Citrobacter), iron‐oxidizers (Gallionellaferruginea, Crenothrixpolyspora), iron‐reducers (Shewanella), and sulfur‐oxidizers (Thiobacillusferrooxi‐dans). Fungi were also recovered in low numbers. Both aerobic and anaerobic heterotrophs were able to utilize all principal contaminants as sole carbon and energy sources except 1,4–dioxane. The prevalence of heterotrophic bacteria and their ability to use the available anthropogenic carbon suggests that aerobic and anaerobic heterotrophs contribute to the biofouling of wells at this site, in addition to the often cited fouling due to iron‐oxidizing bacteria and sulfate‐reducing bacteria.
Estimation of Basin‐Wide Recharge Rates Using Spring Flow, Precipitation, and Temperature Data
Authors: Pérez Eugenio Sanz
Published: August 2005

A method is proposed for the estimation of ground‐water recharge rates in karstic aquifers by the analysis of hydrograph recession and multiple regression. Several methods are mentioned of estimating recharge rates by recession analysis of discharge at springs and from which recharge records can be obtained. Recharge (R) can also be estimated from precipitation (P) and air temperature (T) by the formula R = aP – bT + c. The components a, b, and c were derived from time‐series data of four aquifers in the Mediterranean zone. For the first two of these aquifers, the recharge was calculated by integrating spring discharge between two points with the equal flow. For the third aquifer, a more elaborate calculation was based on multiple aquifers with semi logarithmic depletions. A numerical model, SIMERO, was used for the fourth. Given the appropriate correlation coefficients, the procedure is advantageous because of its simplicity. Limiting relationships between P and T are deduced.
Effect of Sewage Sludge on Formation of Acidic Ground Water at a Reclaimed Coal Mine
Authors: Cravotta Charles A.
Published: August 2005

Data on rock, ground water, vadose water, and vadose gas chemistry were collected for two years after sewage sludge was applied at a reclaimed surface coal mine in Pennsylvania to determine if surface‐applied sludge is an effective barrier to oxygen influx, contributes metals and nutrients to ground water, and promotes the acidification of ground water. Acidity, sulfate, and metals concentrations were elevated in the ground water (6‐ to 21‐m depth) from spoil relative to unmined rock because of active oxidation of pyrite and dissolution of aluminosilicate, carbonate, and Mn‐Fe‐oxide minerals in the spoil. Concentrations of acidity, sulfate, metals (Fe, Mn, Al, Cd, Cu, Cr, Ni, Zn), and nitrate, and abundances of iron‐oxidizing bacteria were elevated in the ground water from sludge‐treated spoil relative to untreated spoil having a similar mineral composition; however, gaseous and dissolved oxygen concentrations did not differ between the treatments. Abundances of iron‐oxidizing bacteria in the ground water samples were positively correlated with concentrations of ammonia, nitrate, acidity, metals, and sulfate. Concentrations of metals in vadose water samples (<5‐m depth) from sludge‐treated spoil (pH 5.9) were not elevated relative to untreated spoil (pH 4.4). In contrast, concentrations of nitrate were elevated in vadose water samples from sludge‐treated spoil, frequently exceeding 10 mg/L. Downgradient decreases in nitrate to less than 3 mg/L and increases in sulfate concentrations in underlying ground water could result from oxidation of pyrite by nitrate. Thus, sewage sludge added to pyritic spoil can increase the growth of iron‐oxidizing bacteria, the oxidation of pyrite, and the acidification of ground water. Nevertheless, the overall effects on ground water chemistry from the sludge were small and probably short‐lived relative to the effects from mining only.
Impacts of Positive Skin Effects on Borehole Flowmeter Tests in a Heterogeneous Granular Aquifer
Authors: Young Steven C.
Published: August 2005

In heterogeneous granular aquifers, an important issue affecting the analysis of pump test data is whether or not positive skin effects exist. Positive skin effects include head losses and changes in radial flow patterns caused by a local reduction of aquifer permeability near a well. In order to investigate the impact and formation of positive skins, field tests were performed at seven pairs of closely‐spaced wells located in the vicinity of a paleochannel at Columbus Air Force Base (CAFB), Mississippi. In the paleochannel a 1–2 m thick zone of high‐K channel lag deposits lies beneath a 2–3 m thick zone of fine‐grained channel fill deposits. Each well pair consisted of a well with and without a gravel pack. At the well pairs outside of the paleochannel boundaries, borehole flowmeter tests produce similar field results. At the well pairs inside of the paleochannel boundaries, however, borehole flowmeter tests produced very different results. Examination of the test results indicate that positive skins exist at wells without gravel packs that intersect the paleochannel. During well installations, positive skins appear to be produced by the downward mixing of the fine‐grained deposits into the channel lag deposits. Notable positive skin effects include increased specific capacities, increased total drawdowns, and changes in the distribution of horizontal flow to a pumped well. Among the key implications regarding borehole flowmeter tests in heterogeneous aquifers similar to that at CAFB are: (1) wells should be installed with gravel packs; and (2) transmissivity values should be calculated using the Cooper‐Jacob straight‐line method rather than the Cooper‐Jacob equation.
Productivity Comparison of Horizontal and Vertical Ground Water Remediation Well Scenarios
Authors: Sawyer Charles S. , Lieuallen‐Dulama Karen K.
Published: August 2005

A productivity parameter was developed to compare vertical and horizontal ground water remediation scenarios. The parameter was determined by dividing the cumulative mass of contaminant removed from an aquifer in a specified time by the total volume of ground water extracted to remove the mass. This was compared to two other methods of assessing remediation effectiveness: (1) the mass of contaminant removed at specified times; and (2) the volume of aquifer containing contaminants above a specified concentration limit as a function of time.

A finite‐difference flow and a contaminant mass transport model were used to simulate a hypothetical contaminated aquifer. Productivity indices were calculated for the remediation scenarios developed in this paper. It is shown that these indices can be used as an additional tool in choosing among possible remediation scenarios.

It was demonstrated that a ranking can be obtained for the various remediation scenarios, using each of our three methods for assessing remediation effectiveness. The ranking of a scenario depended on which method was used, and the selection of one particular remediation scenario over the other can be made taking the three methods into account. The relative importance of the three methods depended on the goal of the remediation. In an actual design, these methods can be used as part of the overall feasibility study that includes cost considerations.
Long‐Term Performance of an In Situ “Iron Wall” for Remediation of VOCs
Authors: O'Hannesin Stephanie F. , Gillham Robert W.
Published: August 2005

The use of granular iron for in situ degradation of dissolved chlorinated organic compounds is rapidly gaining acceptance as a cost‐effective technology for ground water remediation. This paper describes the first field demonstration of the technology, and is of particular importance since it provides the longest available record of performance (five years). A mixture of 22% granular iron and 78% sand was installed as a permeable “wall” across the path of a contaminant plume at Canadian Forces Base, Borden, Ontario. The major contaminants were trichloroethene (TCE, 268 mg/L) and tetrachloroethene (PCE, 58 mg/L). Approximately 90% of the TCE and 86% of the PCE were removed by reductive dechlorination within the wall, with no measurable decrease in performance over the five year duration of the test. Though about 1% of the influent TCE and PCE appeared as dichloroethene isomers as a consequence of the dechlorination of TCE and PCE, these also degraded within the iron‐sand mixture. Performance of the field installation was reasonably consistent with the results of laboratory column studies conducted to simulate the field behavior. However, if a more reactive iron material, or a higher percentage of iron had been used, complete removal of the chlorinated compounds might have been achieved. Changes in water chemistry indicated that calcium carbonate was precipitating within the reactive material; however, the trace amount of precipitate detected in core samples collected four years after installation of the wall suggest that the observed performance should persist for at least another five years. The study provides strong evidence that in situ use of granular iron could provide a long‐term, low‐maintenance cost solution for many ground water contamination problems.
Relationship Between Pumping‐Test and Slug‐Test Parameters: Scale Effect or Artifact?
Authors: Butler James J. , Healey John M.
Published: August 2005

In most field investigations, information about hydraulic conductivity (K) is obtained through pumping or slug tests. A considerable body of data has been amassed that indicates that the K estimate from a pumping test is, on average, considerably larger than the estimate obtained from a series of slug tests in the same formation. Although these data could be interpreted as indicating a natural underlying scale dependence in K, an alternate explanation is that the slug‐test K is artificially low as a result of incomplete well development and, to a much lesser extent, failure to account for vertical anisotropy. Incomplete well development will often result in only the most permeable zones being cleared of drilling debris, with much of the screened interval remaining undeveloped. More cursory development can leave a low‐K skin along the entire screened interval. Failure to recognize such conditions can result in a K estimate from a slug test that is much lower than the average K of the formation in the vicinity of the well. By contrast, neither a skin nor vertical anisotropy will have a significant impact on K estimates from pumping tests when semi‐log analyses and/or observation wells are used. However, a reasonable estimate of aquifer thickness is required to convert the transmissivity calculated from a pumping test into an average K for the aquifer. Prior to invoking a natural scale dependence to explain the results of different types of hydraulic tests, head data should be closely examined and serious consideration given to alternate explanations.
AIRSLUG: A Fortran Program for the Computation of Type Curves to Estimate Transmissivity and Storativity from Prematurely Terminated Air‐Pressurized Slug Tests
Authors: Greene Earl A. , Shapiro Allen M.
Published: August 2005

The Fortran code AIRSLUG can be used to generate the type curves needed to analyze the recovery data from prematurely terminated air‐pressurized slug tests. These type curves, when used with a graphical software package, enable the engineer or scientist to analyze field tests to estimate transmissivity and storativity. Prematurely terminating the slug test can significantly reduce the overall time needed to conduct the test, especially at low‐permeability sites, thus saving time and money.
Probabilistic Analysis of Monitoring Systems for Detecting Subsurface Contaminant Plumes
Authors: Warrick A.W. , Younga M.H. , Wierenga P.J.
Published: August 2005

We study the probabilities that monitoring systems will be capable of detecting subsurface contaminant plumes. The analysis is an extension of previous research which focused on detection of ore bodies and contaminant releases to the subsurface using probabilistic models; the previous research assumed that releases to the subsurface are elliptical in shape, and that detections are absolute when a monitoring point intercepts a release. New features are introduced into the analytical framework that include irregular, rather than regular, sampling arrays, as well as nonuniform probabilities of a release occurring at a particular location of the site. These features allow the user to optimize the location of sampling devices based on site knowledge, by concentrating monitoring locations where a release is believed more likely. The stratified Monte Carlo approach used in this paper is tested on a number of cases with uniform and nonuniform sampler distribution and release probabilities. The results provide statistical probabilities that one is capable of finding releases of different sizes with a system of monitoring points.
Methodology for the Study of Unexploited Aquifers with Thermal Waters: Application to the Aquifer of the Alhama de Aragon Hot Springs
Authors: Sanz Eugenio , Yelamos Javier G.
Published: August 2005

A methodology for the study of thermal waters in unexploited aquifers is proposed. This methodology has been applied to the Alhama Aquifer, which is the origin of the most important thermal springs of the Iberian Peninsula. A conceptual model was made of the aquifer by integrating data such as (1) the geometry at depth (on the basis of deep geophysics) and at the surface (from conventional geological maps); (2) hydrographic analysis of the aquifer discharge; (3) a study of the recharge by classic hydrometeo‐rological methods; and (4) conventional and isotopic hydrochemistry. In addition to the hydraulic regional parameters it provides, the model explains the origin of the Alhama springs in terms of simple circulation at a depth of some 900 m and a normal geothermal gradient (3°C/100 m), with no requirement of contact with a source of heat at the bottom of the aquifer.
Type Curves to Determine the Relative Importance of Advection and Dispersion for Solute and Vapor Transport
Authors: Garges John A. , Baehr Arthur L.
Published: August 2005

The relative importance of advection and dispersion for both solute and vapor transport can be determined from type curves for concentration, flux, or cumulative flux. The dimensionless form of the type curves provides a means to directly evaluate the importance of mass transport by advection relative to that of mass transport by diffusion and dispersion. Type curves based on an analytical solution to the advection‐dispersion equation are plotted in terms of dimensionless time and Peclet number. Flux and cumulative flux type curves provide additional rationale for transport regime determination in addition to the traditional concentration type curves. The extension of type curves to include vapor transport with phase partitioning in the unsaturated zone is a new development. Type curves for negative Peclet numbers also are presented. A negative Peclet number characterizes a problem in which the direction of flow is toward the contamination source, and thereby diffusion and advection can act in opposite directions. Examples are the diffusion of solutes away from the downgradient edge of a pump‐and‐treat capture zone, the upward diffusion of vapors through the unsaturated zone with recharge, and the diffusion of solutes through a low hydraulic conductivity cutoff wall with an inward advective gradient.
Use of Multiple Isotope Tracers to Evaluate Denitrification in Ground Water: Study of Nitrate from a Large‐Flux Septic System Plume
Authors: Aravena Ramon , Robertson William D.
Published: August 2005

This study explores the use of multiple isotopic tracers to evaluate the processes involved in nitrate attenuation in ground water. δ15N and δ18O are used to provide information about the role of denitrification on nitrate attenuation, and δ34S, δ18O, and δ13C are used to evaluate the role of reduced sulfur and carbon as electron donors for nitrate reduction. The focus of this study is a zone of significant NO3−1 attenuation occurring in a sand aquifer impacted by septic system contamination. The NO3−1 pattern, the ground water flow system, and changes in other chemical parameters suggest that the NO3−1 depletion is caused by denitrification. This is supported by the nitrate δ15N and δ18O data which both show significant isotopic enrichment as NO3−1 depletion proceeds along the flow path. The increase of sulfate and dissolved inorganic carbon observed in the zone of nitrate attenuation suggests that reduced sulfur in addition to carbon is also involved in denitrification. This is supported by a trend toward depleted sulfate δ34S and δ18O values in the zone of sulfate increase, which reflects the input of sulfate formed by the oxidation of biogenic pyrite present in the aquifer sediments. The trend toward depleted δ13 values in the zone of increasing dissolved inorganic carbon reflects the input of organic carbon into this carbon pool. Chemical mass balance indicates that carbon is the dominant electron donor; however, this study demonstrates the effectiveness of using multiple isotopic tracers for providing insight into the processes affecting nitrate attenuation in ground water.
Imaging the Water Table by Filtering Self‐Potential Profiles
Authors: Birch F.S.
Published: August 2005

In suitable cases, digital filtering of self‐potential anomalies produces images of the water table. Two hypothetical cases and four field examples from New Hampshire yield images in reasonable agreement with known water tables. Filtering for a sheet of dipolar sources (that is, the water table) would be a useful addition to routine interpretation of self‐potential data.
Solute Transport Processes in a Highly Permeable Fault Zone of Lindau Fractured Rock Test Site (Germany)
Authors: Himmelsbach Thomas , Hbtzl Heinz , Maloszewski Piotr
Published: August 2005

The results of field tracer experiments performed in the Lindau fractured rock test site (southern Black Forest, Germany) and subsequent modeling are presented. A vertical, hydrothermally mineralized fault zone, with a permeability much greater than the surrounding granite mass, lies beneath a planned dam site. A dense network of boreholes and tunnels were used to investigate scaling effects of solute transport processes in fractured rock. A series of tracer experiments using deuterium and dye tracers (uranine, eosine, and pyranine) were performed over varying distances and under different testing procedures, resulting in different flow field conditions. Large‐scale tracer experiments (21 to 346 m) were performed under natural flow field conditions, while small‐scale tracer experiments (11 to 16 m) were performed under artificially induced radial‐convergent and injection‐withdrawal flow fields. The tracer concentration curves observed in all experiments were strongly influenced by the matrix diffusion. The curves were evaluated with the one‐dimensional single fissure dispersion model (SFDM) (advective‐dispersive transport in the fractures coupled with diffusive transport in the adjacent rock matrix) adjusted for the different flow field conditions. The fitting model parameters found determined the fracture aperture, and matrix and fissure porosities. The determined fracture aperture varied between the sections having different hydraulic conductivities (100 to 270 um and 430 to 580 um, respectively). The determined values of matrix porosity (3 to 7%) seemed to be independent of the scale of the experiment. The modeled matrix porosities agreed well with values determined in independent laboratory investigations of drill cores using mercury porosimetry. In situ fissure porosity, determined only in small‐scale experiments, was independent of the applied geometry of the artificially induced flow fields. The dispersivities were found to be independent of the scale of experiment but dependent on the flow conditions. The values found in forced gradient tests lie between 0.2 and 0.3 m, while values in experiments performed under natural flow conditions were one order of magnitude higher.
Hydrogeochemical Interaction Between a Wetland and an Unconfined Glacial Drift Aquifer Southwestern Michigan
Authors: Kehew Alan E. , Passero Richard N. , Krishnamurthya R.V. , Lovett Cole K. , Bettsc Marilyn A. , Dayharsh Brent A.
Published: August 2005

In the glacial topography of southwestern Michigan, the water table does not always conform exactly to the land surface and flow‐through wetlands, those with both ground water recharge and discharge, are common. The W‐l wetland in Cass County, Michigan, a flow‐through system, shows a distinct contrast between upgradient and downgradient ground water quality. Ground water discharging into the wetland is oxic, has up to 40 mg/L NO3‐N derived from fertilizer and hog manure application to corn fields, and has major ion concentrations typical of the shallow unconfined aquifer in the area. In contrast, shallow ground water that originates as recharge from the wetland forms a plume extending downgradient that can be identified by isotopic enrichment in 18O and deuterium resulting from evaporation in the wetland prior to recharge and by distinct chemical characteristics similar to the wetland surface water (low conductivity and alkalinity, low concentrations of sulfate, nitrate and dissolved oxygen and high concentrations of ammonia, and DOC). As the wetland surface water infiltrates into the unconfined aquifer, conductivity and alkalinity increase due to carbonate mineral dissolution and iron concentrations increase as ferric iron in the aquifer solids serves as an electron acceptor in microbially mediated reactions. The other chemical characteristics, including the lack of nitrate, persist in the flow system for significant distances downgradient from the wetland.

The chemical and isotopic composition of shallow ground water around wetlands can be used to spatially delineate areas of ground‐water discharge to the wetland and ground water recharge from the wetland, thereby providing a supplemental method to the use of sometimes inconclusive hydraulic head data in the determination of wetland recharge‐discharge function. In this study, the chemical and isotopic data confirm that the water table does not replicate surface topography around closed depressions in the landscape.
Incorporation of Total Stress Changes into the Ground Water Model SUTRA
Authors: Reeves Howard W. , Thibodeau Peter M. , Underwood Robert G. , Gardner Leonard R.
Published: August 2005

To model ground water flow in a shallow aquifer underlying a salt marsh, the impact of total stress changes due to tidal loading of the marsh surface on the piezometric head within the aquifer must be considered. If the deformation of the porous medium is negligible, a ground water flow model may be modified to account for the changing total stress. The incorporation of these modifications into the U.S. Geological Survey (USGS) numerical model SUTRA is discussed, and example problems for which analytic solutions are available are presented to demonstrate the behavior and validity of the modified model. In addition, the form of the specific pressure storativity term used in the SUTRA model is discussed and modifications of this form are suggested.
Using Ternary Diagrams to Characterize Transport and Attenuation of BTX
Authors: Lipson D. , Siegel D.I.
Published: August 2005

During the past decade or longer, large amounts of data on the concentrations of dissolved aromatic hydrocarbons have been obtained from routine monitoring of leaky underground storage tanks (USTs). Commonly, aromatic hydrocarbon concentration data is interpreted only within the context of regulatory maximum allowable concentration levels. We show in this paper how ternary diagrams can clearly characterize the physical and chemical controls governing the fate and transport of aromatic hydrocarbons in ground water from routine monitoring data.

The results of type mathematical modeling experiments for BTX solute transport show that changes in BTX concentrations, when plotted as proportions on ternary diagrams, form clear “trajectories” documenting major attenuation or transport processes. For example, BTX concentrations affected by biodegradation form a trajectory from the source BTX location on the ternary diagram to the benzene apex. In contrast, BTX concentrations affected by volatilization form a trajectory trending from the source to the xylene apex. Ternary diagrams are easy and effective tools to determine from routine monitoring data (1) whether proposed natural attentuation processes are in fact present, and (2) the efficiency of different remediation efforts used to clean up UST sites.
The Effect of Measurement Error on Estimating the Hydraulic Gradient in Three Dimensions
Authors: Silliman S.E. , Mantz G.
Published: August 2005

Based on a series of analyses of published data sets, it was observed that there is a consistent problem in the estimation of the vertical component of the hydraulic gradient. In most cases investigated, data collected for a single field site led to individual estimates of the orientation of the gradient that fell close to both +90 degrees and ‐90 degrees relative to the horizontal plane (i.e., the gradient was estimated to be oriented both vertically upward and vertically downward at the same site). Being consistent across most field sites analyzed, but inconsistent with our basic knowledge of hydrology (the impact of heterogeneity is distinct from the behavior presented here), alternative explanations for these observations were sought. Analysis using a simple numerical study showed that this behavior could be attributed to the presence of measurement error in the field data. The consistency of the field observations with the numerical study shows that errors in measuring the elevation of water in a well or piezometer may result in estimates of the vertical component of the gradient that are unreliable, effectively being measures of the difference in measurement error among wells. It is noted that this measurement error is in addition to local variations in the vertical component of the gradient that are related to heterogeneity or transients in the flow field. A formula is presented for the standard deviation of the error of the estimated vertical gradient as a function of both the measurement error and the relative location of the data points used in completing the estimate.
Field and Laboratory Evaluation of a Diffusive Emitter for Semipassive Release of PCE to an Aquifer
Authors: Arildskov N.P. , Devlin J.F.
Published: August 2005

In controlled field experiments or model aquifers, it is sometimes desirable to introduce solutes below the water table without perturbing the flow system. Diffusive emitters offer a means of achieving that goal. In this study, two laboratory experiments were conducted to evaluate nylon tubing as a diffusive emitter for tetrachloroethene (PCE). The initial approach was to pump a saturated aqueous PCE solution through a piece of nylon tubing immersed in a flow‐through contactor vessel. Millipore water was pumped through the contactor vessel at a constant rate. Due to PCE diffusion through the nylon, a steady‐state concentration in the contactor vessel eventually developed. The process was well described by a computer model that accounted for retarded diffusion through the nylon. In a second experiment, pieces of nylon tubing were exposed to a relatively low concentration of PCE in water for 10 days in gently rotated hypovials. With the aid of a second diffusion model, the bulk diffusion coefficient (lumped with the retardation factor) was obtained from the concentration history of the solution. With the different experimental conditions taken into account, there was reasonably good agreement between the bulk diffusion coefficients in the two experiments (a factor of 3.5 difference). The results were used in the field design of a semipassive release system. Evaluation of this system showed a lower than expected steady‐state concentration of PCE inside the releasing wells. The difference is likely due to lower temperature, variable PCE concentrations in the nylon tubing, and nonideal mixing in the wells. The work has shown that laboratory derived diffusion coefficients for polymeric materials are likely to be larger than, but within an order of magnitude of, the effective diffusion coefficients exhibited by emitters in the field. Nevertheless, with temperature corrections taken into account and proper well development, these values could be used to design emitters that would suit most practical applications.
Problems Associated with Estimating Ground Water Discharge and Recharge from Stream‐Discharge Records
Authors: Halford Keith J. , Mayer Gregory C.
Published: August 2005

Ground water discharge and recharge frequently have been estimated with hydrograph‐separation techniques, but the critical assumptions of the techniques have not been investigated. The critical assumptions are that the hydraulic characteristics of the contributing aquifer (recession index) can be estimated from stream‐discharge records; that periods of exclusively ground water discharge can be reliably identified; and that stream‐discharge peaks approximate the magnitude and timing of recharge events. The first assumption was tested by estimating the recession index from stream‐discharge hydrographs, ground water hydrographs, and hydraulic diffusivity estimates from aquifer tests in basins throughout the eastern United States and Montana. The recession index frequently could not be estimated reliably from stream‐discharge records alone because many of the estimates of the recession index were greater than 1000 days. The ratio of stream discharge during base flow periods was two to 36 times greater than the maximum expected range of ground water discharge at 12 of the 13 field sites. The identification of the ground water component of stream‐discharge records was ambiguous because drainage from bank‐storage, wetlands, surface water bodies, soils, and snowpacks frequently exceeded ground water discharge and also decreased exponentially during recession periods. The timing and magnitude of recharge events could not be ascertained from stream‐discharge records at any of the sites investigated because recharge events were not directly correlated with stream peaks. When used alone, the recession‐curve‐displacement method and other hydrograph‐separation techniques are poor tools for estimating ground water discharge or recharge because the major assumptions of the methods are commonly and grossly violated. Multiple, alternative methods of estimating ground water discharge and recharge should be used because of the uncertainty associated with any one technique.
Microbial H2 Cycling Does Not Affect δ2H Values of Ground Water.
Authors: Landmeyer James E. , Chapelle Francis H. , Bradley Paul M.
Published: August 2005

Stable hydrogen‐isotope values of ground water (δ2H) and dissolved hydrogen concentrations (H2(aq)) were quantified in a petroleum‐hydrocarbon contaminated aquifer to determine whether the production/consumption of H2 by subsurface microorganisms affects ground water δ2H values. The range of δ2H observed in monitoring wells sampled (−27.8 %c to −15.5 %c) was best explained, however, by seasonal differences in recharge temperature as indicated using ground water δ18O values, rather than iso‐topic exchange reactions involving the microbial cycling of H2 during anaerobic petroleum‐hydrocarbon biodegradation. The absence of a measurable hydrogen‐isotope exchange between microbialy cycled H2 and ground water reflects the fact that the amount of H2 available from the anaerobic decomposition of petroleum hydrocarbons is small relative to the amount of hydrogen present in water, even though milligram per liter concentrations of readily biodegradable contaminants are present at the study site. Additionally, isotopic fractionation calculations indicate that in order for H2 cycling processes to affect δ2H values of ground water, relatively high concentrations of H2 (>0.080 M) would have to be maintained, considerably higher than the 0.2 to 26 nM present at this site and characteristic of anaerobic conditions in general. These observations suggest that the conventional approach of using δ2H and δ18O values to determine recharge history is appropriate even for those ground water systems characterized by anaerobic conditions and extensive microbial H2 cycling.
Stream and Fluvial Plain Ground Water Interactions: Rescaling Hydrogeologic Thought
Authors: Woessner William W.
Published: August 2005

Management of near‐channel ground water and surface water to maintain stream health and flood plain ecological function requires hydrogeologists to refocus their conceptual models of water exchange between the aquifer and stream. The high hydraulic conductivity fluvial plain directs ground water flow down‐plain where it exchanges with the stream channel creating gaining, losing, flow‐through, and parallel‐flow reaches. The resulting complex flow system requires consideration when profiles representing ground water flowpaths are constructed. In addition to interaction at the scale of the fluvial plain, exchange of ground water and surface water within and immediately adjacent to the stream channel creates hyporheic zones. The physical and bio‐geochemical extent of these zones depends on the head distribution and ground water flow directions, stream hydraulics, and channel bed conditions, and magnitudes and distributions of hydrogeologic parameters. Simulated conceptualizations of flow dynamics caused by slight increases in hydraulic potentials at the surface water‐stream bed interface indicate stream‐ground water mixing could occur to a depth of 1.7 m below the channel. Rescaling of traditional hydrogeologic approaches to include the fluvial plain and channel scale will result in opportunities to expand hydrogeologic research and participate in interdisciplinary research teams attempting to decipher and manage fluvial systems.
CRAFIT: A Computer Program for Calibrating Breakthrough Curves of CRAFLUSH, a One‐Dimensional Fracture Flow and Transport Model
Authors: Toran Laura
Published: August 2005

This Computer note presents a program called CRAFIT, which automates trial and error curve fitting of breakthrough curves for CRAFLUSH, a one‐dimensional fracture flow and transport code. CRAFIT is useful for modeling column experiments where the source function is well‐known but fracture geometry and matrix are to be characterized. CRAFIT is demonstrated for curve fitting with three unknowns and five unknowns, and found a single best‐fit solution for each case.
Hydraulic Characterization and Design of a Full‐Scale Biocurtain
Authors: Hyndman David W. , Dybas M.J. , Forney L. , Heine R. , Mayottee T. , Phanikumar M.S. , Tatara G. , Tiedje J. , Voice T. , Wallace R. , Wiggert D. , Zhao X. , Criddle C.S.
Published: August 2005

This paper deseribes the design and hydraulic characterization of a cost‐effective biocurtain that is currently being used to remove carbon tetrachloride from an aquifer in Schoolcraft, Michigan. Novel aspects of the design are the use of closely spaced wells to recirculate solutes through a biocurtain, well screens spanning the vertical extent of contamination, and a semipassive mode of Operation, with only six hours of low‐level pumping per week. This design was developed by coupling flow and transport sim‐ulations with a cost optimization algorithm, based on initial hydraulic conductivity data and system design constraints from a previous pilot‐scale experiment adjacent to the current site, The hydraulic conductivity of the site was characterized using permeameter analysis on more than 200 samples from continuous well cores that were collected during well Installation. The subset of availablc conductivity data was used to predict tracer transport through the biocurtain during System Operation. Observed tracer conecntration arrival histories during initial system Operation confirmed model predictions. Modeling also established that closely spaced wells operated for brief periods each week could effectively deliver the agents needed for remediation across the biocurtain. This was confirmed during long‐term Operation of the System, which has resulted in highly efficient contamination degra‐dation. The delivery well design methodology is expected to be broadly applicable at other sites where flow can be recirculated between a series of delivery wells.
Ownership of Mine‐Tunnel Discharge
Authors: Parry W.T. , Forster Craig B. , Solomon D. Kip , James Laurence P.
Published: August 2005

Water discharging from numerous tunnels constructed during mining in the Wasatch Mountains near Salt Lake City, Utah, flows into nearby creeks. Disputes over ownership of water feeding the creeks have resulted in extensive litigation. In the course of a legal dispute over ownership of outflow from the Kentucky‐Utah (K‐U) Tunnel we evaluated the patterns and rates of ground water flow using an integrated study of the geology, chemistry, isotopes, and chlorofluorohydrocarbon (CFC) composition of the water. A sequence of sedimentary rocks with a range of hydraulic conductivity values has been folded, faulted, intruded by igneous rocks, and then eroded to create the rough topography of the Wasatch Mountains. The similarity of composition among tunnel discharge, springs, and base flow in the creek indicates that the creek is fed by ground water circulating in local, shallow flow systems. Results of numerical simulations of ground water flow indicate that the K‐U Tunnel likely intercepts ground water that, in the absence of the tunnel, would ultimately flow in the subsurface to Big Cottonwood Creek. CFC and tritium contents of the water indicate flow weighted average ground water travel times range from four to 23 years and support our conclusion that water discharging from the tunnel is moving within a shallow ground water flow system. Despite sparse data, the scientific understanding was deemed sufficient for the judge to rule that owners of the surface water also own the tunnel discharge because, in the absence of the tunnel, this water would supply the stream.
Generating Two‐Dimensional Fields of Autocorrelated, Normally Distributed Parameters by the Matrix Decomposition Technique
Authors: El‐Kadi Aly I. , Williams Stan A.
Published: August 2005

This paper introduces a computer program that uses matrix decomposition to generate two‐dimensional fields of normally or log‐normally distributed parameters (e.g., hydraulic conductivity). The input data for the program consists of a set of x, y‐coordinate locations, and parameters representing the statistical distribution of the parameter of interest. The program computes the covariance matrix for the set of locations and decomposes the matrix into a lower‐triangular matrix. The decomposed matrix is then used to estimate a set of values for the parameter of interest. A seed number that changes automatically is incorporated into the program to generate different realizations of the parameter.