bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some Analytical and Approximate Darcian Means
Authors: Baker Donald L. , Arnold Mark E. , Scott H. Don 
Published: August 2005

AbstractIn the finite‐difference modeling of unsaturated infiltration by Richards’equation, standard interblock conductivity means like the arithmetic, geometric, and harmonic have been shown to produce flows different from true Darcian by up to orders of magnitude (Warrick 1991; Baker 1995a, 1998). This may have significant impact on models used for contaminant transport of nuclear and other hazardous waste. Previously, it has been impractical to calculate Darcian means in a running model. This paper introduces the analytic solution for Darcian means for the case of an exponential relative conductivity relation, and one possible approximation for general use, a piecewise Brooks‐Corey Darcian (PBCD) mean. It compares the PBCD mean to the arithmetic mean in a modern mass‐conservative numerical model (Celia et al. 1990) for vertical space steps from 0.8 to 105 cm, using soil parameters from Haverkamp et al. (1977). The results demonstrate that even in a model with mass balance good to one part in 108, non‐Darcian flow errors are alive and well, costing up to 50% of the total mass infiltrated with the arithmetic mean and large model space steps. The new PBCD mean reduces that figure to 0.5% for this example soil.
Estimation of Permeability of Disturbed Halite Using Inverse Modeling
Authors: Cardenas M. , LeCompte C. , Cua G. 
Published: August 2005

AbstractThe numerical modeling tool ITOUGH2 was examined to determine its effectiveness in parameter estimation for the small scale seals performance tests (SSSPT) at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico. Gas flow injection tests were performed at various distances inward from the wall of Room D to estimate the effects of creeping of the disturbed rock zone (DRZ) since excavation of Room D and boreholes, and to estimate the amount of healing of the DRZ that has taken place due to an emplaced concrete seal. Salt creeping into an excavation is expected to show increased porosity and absolute permeability values compared to undisturbed halite. Healed halite is expected to show porosity and absolute permeability values comparable to that of undisturbed halite. Single‐phase flow estimates of absolute permeability were made using ITOUGH2. Estimates of DRZ absolute permeability ranged from 10−11 near Room D to 10−21 m2 at the seal. Simultaneous estimates of absolute permeability and porosity were calculated for the disturbed rock zone in halite, and the effects of salt creep and healing were seen in the estimates of porosity and absolute permeability, as evidenced by the differences in absolute permeability and porosity with distance inward from the rib of Room D. Estimate of porosity were 0.04 near Room D, and the locations near the seal showed porosities of around 0.03. ITOUGH2 proved effective in interpreting test data seen in the SSSPT, especially test data with constant injection pressure.
Inferring Ground Water Flow in Fractured Rock from Dissolved Radon
Authors: Cook P. G. , Love A. J. , Dighton J.C. 
Published: August 2005

AbstractGround water radon concentrations have been measured in nested piezometers and an open borehole in fractured, metasedimentary aquifers in the Clare Valley, South Australia. The vertical radon concentration profile within the undisturbed, open borehole appears to indicate the locations of hydraulically active fractures. If radon concentrations within the aquifer are uniform, then the highest radon concentration within the borehole will indicate the location of the highest flow rate into the bore. In relatively short screened piezometers, radon concentrations have been measured both before and after purging. The ratio of radon concentration before to after purging normalizes for variations in aquifer mineralogy, and can be used to quantify the ground water flow rate.
A Numerical Study on the Relationship Between Transmissivity and Specific Capacity in Heterogeneous Aquifers
Authors: Meier Peter M. , Carrera Jesus , Sanchez‐Vila Xavier 
Published: August 2005

AbstractSpecific capacity (Q/s) data are usually much more abundant than transmissivity (T) data. Theories which assume uniform transmissivity predict a nearly linear relationship between T and Q/s. However, linear dependence is seldom observed in field studies. Since hydrogeologic studies usually require T data, many hydrogeologists use linear regression analysis of T versus Q/s data to estimate T values where only Q/s data are available. In this paper we use numerical models to investigate the effects of aquifer heterogeneity on the relationship between Q/s and T estimates. The simulations of hydraulic tests in heterogeneous media show that estimates of T derived using Jacob's method tend to their late‐time effective value much faster than Q/s values. The latter are found to be more dependent upon local transmissivities near the well. This explains why the regression parameters for T versus Q/s data depend on heterogeneity and the‘lateness’of the test period analyzed. Since this effect is more marked in high T zones than in low T zones, we conclude that natural aquifer heterogeneity can explain the convex deviation from linearity often observed in the field. A further result is that the geometric mean of T estimates, obtained from short and intermediate time pumping tests, seems to systematically underestimate effective T (Teff) of heterogeneous aquifers. In the studied simulation cases, the median of the T values or the arithmetic mean yield better estimates for Teff.
On the Use of Semi‐Logarithmic Plots for Baseflow Separation
Authors: Szilagyi Jozsef 
Published: August 2005

AbstractRecession flow has long been considered a composite of exponential terms, where each exponential term represents a different source of water discharged from the watershed. The changing slopes in the semi‐logarithmic plot of the discharge have been considered indicative of the decreasing contribution of surface runoff and interflow to the discharge. The results of this analysis show that the changing slope in the recession plot can be the consequence of baseflow drainage. This can invalidate the semi‐logarithmic baseflow separation technique when applied to some hydrologic settings.
Predicted Retardations of Concentration Fronts Using a Mass‐Balance Approach
Authors: Stoessell Ronald K. 
Published: August 2005

AbstractRegardless of the chemical controls for a pollutant on sediment sorption or release from an immiscible organic liquid, a simple mass balance can be used to predict the retardation of the ground water pollutant front moving downstream from a source of constant composition. The retardation is the ratio of the total molar difference of pollutant across the front to the molar difference in ground water. The mass‐balance approach presented here uses a flushing factor for the entire front. It is implicit in the commonly used retardation factor for pollutants undergoing linear sorption, but does not appear to have been used to predict retardation of concentration fronts involving nonlinear sorption or partitioning in hydrochemical studies. Yet the computations require only limited experimental or field data or the use of an algorithm describing sorption or partitioning of the pollutant. Close agreement was obtained between retardations predicted using the mass‐balance approach and those reported from numerical modeling and column experiments in the literature.
Natural Attenuation of BTEX Compounds: Model Development and Field‐Scale Application
Authors: Lu Guoping , Clement T. Prabhakar , Zheng Chunmiao , Wiedemeier Todd H. 
Published: August 2005

AbstractBenzene, toluene, ethyl benzene and xylene (BTEX) dissolved into ground water and migrated from a light nonaqueous phase liquid (LNAPL) source in a sandy aquifer near a petroleum, oil, and lubricants (POL) facility at Hill Air Force Base (AFB), Utah. Field observations indicated that microbially mediated BTEX degradation using multiple terminal electron‐accepting processes including aerobic respiration, denitrification, Fe(III) reduction, sulfate reduction, and methanogenesis has occurred in the aquifer. To study the transport and transformation of dissolved BTEX compounds under natural conditions, a reactive flow and transport model incorporating biochemical multispecies interactions and BTEX was developed. The BTEX, oxygen, nitrate, Fe(II), sulfate, and methane plumes calculated by the model agree reasonably well with field observations. The first‐order biodegrada‐tion rate constants, estimated based on model calibration are 0.051, 0.031, 0.005, 0.004, and 0.002 day−1 for aerobic respiration, denitrification, Fe(III), sulfate reduction, and methanogenesis, respectively. The results of a sensitivity analysis show that the saturated aquifer thickness, hydraulic conductivity, and reaction rate constants are the most critical parameters controlling the natural attenuation of BTEX at this site. The hydraulic conductivity and aquifer thickness were found to be the key factors affecting the restoration of oxygen, nitrate, and sulfate after their interaction with the BTEX plume. The multispecies reactive transport modeling effort, describing BTEX degradation mediated by multiple electron‐accepting processes, represents one of the few attempts to date to quantify a complete sequence of natural attenuation processes with a detailed field data set. Because the case study is representative of many petroleum‐product contaminated sites, the results and insights obtained from this study are of general interest and relevance to other fuel‐hydrocarbon natural attenuation sites
Simple Probabilistic and Statistical Risk Calculations in an Aquifer
Authors: Şen Zekai 
Published: August 2005

AbstractAn objective methodology is proposed for assessing potential ground water yield on the basis of the randomness inherent in hydrogeological parameters as a result of uncertainty. Randomness is used here in the statistical sense to describe the ground water phenomenon on a regional basis. A systematic approach to selecting aquifer parameters is presented that leads to reliable ground water storage and subsurface flow estimates by incorporating a certain risk level. In addition, the averages of the specific ground water capacity and subsurface flow rate are calculated through a perturbation approach. This study demonstrates that cross‐correlations between basic hydrogeologic variables might underestimate or overestimate model parameter values.Furthermore, the results of aquifer storage and subsurface flow estimates are obtained in the form of probability distribution functions. It is proved that the surface flow rates are presented by a log‐normal distribution. Contrary to conventional point estimate, a simple and objective methodology is proposed in order to obtain the most probable interval estimates. Accordingly, projections of likely future ground water storage and flow rates can be readily calculated.
Skin Localization at Wells Drilled in a Vertical Fault Zone
Authors: Bardenhagen Ingo 
Published: August 2005

AbstractThe efficiency of wells drilled into fractured zones that act as draining conduits in hard rock aquifers can be strongly reduced by skin effects. In such aquifers, skin effects (well losses) can appear in close proximity to the well and/or at the contact between fracture and formation. In this paper it is shown how to locate those skin conditions in the case of two wells that have been drilled in a single vertical fault with infinite conductivity.
Oscillatory Slug‐Test Data Sets: A Comparison of Two Methods
Authors: Weight Willis D. , Wittman Gregory P. 
Published: August 2005

AbstractSlug tests performed in high transmissivity aquifers may exhibit underdamped inertial oscillatory behavior. Analytical methods for oscillatory data have been developed, but are mathematically intimidating. Spreadsheet modeling is helpful because ready adjustments to the equations required to match the well‐response data are quickly applied. A simplified presentation of the Kipp method for the practicing hydrogeologist is presented along with a spreadsheet model. A file containing the type curves is available over the Internet at http://www.mtech.edu from the Geological Engineering home page.Examples from southwestern Montana showing a variety of damping responses and well completions are presented to show how to perform the analysis. Sixteen well responses were modeled using the van der Kamp and Kipp methods, and the outcomes were compared using the two methods with oscillatory responses. Generally, there is good agreement between the methods. Screened wells tend to show more uniform oscillatory behavior, although open‐hole completions can be analyzed with success. Other practical field applications and observations are presented.The theory describing inertial effects has been constrained to confined aquifers, although all aquifers exhibit elastic behavior during the initial disturbance from pumping or instantaneous slug removal.
Estimating Transmissivity from the Water Level Fluctuations of a Sinusoidally Forced Well
Authors: Mehnert E. , Valocchi A.J. , Heidari M. , Kapoor S.G. , Kumar P. 
Published: August 2005

AbstractThe water levels in wells are known to fluctuate in response to earth tides and changes in atmospheric pressure. These water level fluctuations can be analyzed to estimate transmissivity (T). A new method to estimate transmissivity, which assumes that the atmospheric pressure varies in a sinusoidal fashion, is presented. Data analysis for this simplified method involves using a set of type curves and estimating the ratio of the amplitudes of the well response over the atmospheric pressure.Type curves for this new method were generated based on a model for ground water flow between the well and aquifer developed by Cooper et al. (1965). Data analysis with this method confirmed these published results: (1) the amplitude ratio is a function of transmissivity, the well radius, and the frequency of the sinusoidal oscillation; and (2) the amplitude ratio is a weak function of storativity. Compared to other methods, the developed method involves simpler, more intuitive data analysis and allows shorter data sets to be analyzed.The effect of noise on estimating the amplitude ratio was evaluated and found to be more significant at lower T. For aquifers with low T, noise was shown to mask the water level fluctuations induced by atmospheric pressure changes. In addition, reducing the length of the data series did not affect the estimate of T, but the variance of the estimate was higher for the shorter series of noisy data.
Characterizing a Sewage Plume Using the 3H‐3He Dating Technique
Authors: Shapiro Stephanie Dunkle , LeBlanc Denis , Schlosser Peter , Ludin Andrea 
Published: August 2005

AbstractAn extensive 3 H −3He study was performed to determine detailed characteristics of a regional flow system and a sewage plume over a distance of 4 km in a sand and gravel aquifer at Otis Air Base in Falmouth, Massachusetts. 3 H −3He ages increase with depth in individual piezometer clusters and with distance along flowpaths. However, the age gradient with depth (Δt/Δ z) is smaller in the plume than that in the regional waters, due to the intense recharge in the infiltration beds. The 1960s bomb peak of tritium in precipitation is archived longitudinally along a flowline through the main axis of the plume and vertically in individual piezometer clusters. On the eastern side of the sampling area, where water from Ashumet Pond forces plume water deeper into the flow system, 3 H −3He ages are young at depth because the 3 H −3He “clock” is reset due to outgassing of helium in the pond. A reconstruction of the tritium input functions for the regional and plume samples shows that there is no offset in the peak [3H]+[3Hetrit] concentrations for the plume and regional water, indicating that the water from supply wells for use on the base is young. The 3 H −3He ages and detergent concentrations in individual wells are consistent with the beginning of use of detergents and the time period when their concentrations in sewage would have been greatest. Ages and hydraulic properties calculated using the 3 H −3He data compare well with those from previous investigations and from particle‐tracking simulations.
Numerical Modeling of Drainage Schemes in Layered Formations: A Kuwait City Case Study
Authors: Székely Ferenc 
Published: August 2005

AbstractA computer modeling technique is developed to simulate ground water drainage considering a heterogeneous, discontinuous, layered formation with pumping wells screened in several layers and drawdown‐induced recharge/discharge under complex urban hydrological conditions. A composite finite‐difference mesh is used to simulate both the more distant areas (coarse mesh) and the actual drainage site (fine mesh). The skin loss parameters of screens are involved to control the aquifer yield. A pilot drainage scheme is being operated in Kuwait City to eliminate the harmful effects of water table elevation. The scheme involves six multiscreened pumping wells and numerous observation wells. Calibration through computer simulation indicated that the transmissivity exhibits relatively little areal variation, whereas the leakance of partially cemented silty beds and lenses fluctuates significantly over the study area. This heterogeneity effect as well as the induced recharge from various man‐made sources have considerable impact on the drainage efficiency. Skin loss parameters of pumping wells affect the amplitude of drawdown in different aquifer units.
In Situ Redox Manipulation by Dithionite Injection: Intermediate‐Scale Laboratory Experiments
Authors: Istok J.D. , Amonette J.E. , Cole C.R. , Fruchter J.S. , Humphrey M.D. , Szecsody J.E. , Teel S.S. , Vermeul V.R. , Williams M.D. , Yabusaki S.B. 
Published: August 2005

AbstractThe goal of in situ redox manipulation (ISRM) is to create a permeable treatment zone capable of removing redox‐sensitive contaminants from ground water. The objective of this study was to evaluate the effectiveness of one promising ISRM technology: chemical reduction of aquifer sediments by sodium dithionite (Na 2S2O4) injection. The technology was evaluated in intermediate‐scale laboratory experiments designed to investigate the kinetics of Fe(III)‐reduction and dithionite‐disproportionation reactions in a radial flow field over similar transport distances (∼ 7 m) and time scales (∼ 72 hours) as those used in a field trial for remediation of chromate contaminated ground water at the Department of Energy Hanford site in Washington state. Four hundred liters (∼ 1 pore volume) of 0.1 M Na2S2O4 in a 0.4 M K2CO3/0.04 M KHCO3 buffer were injected at a rate scaled to field values. Dithionite breakthrough curves at sampling ports were approximately described by the advection‐dispersion equation with a two‐part reaction model containing first‐order rate coefficients for dithionite reaction with sediment Fe(III) (k1= 0.13 hr −1) and dithionite disproportionation (k2= 0.05 hr −1). Analyses on sediment cores collected from the physical model indicated that substantial Fe(III) was reduced to Fe(II) and that the dithionite‐treated sediment was capable of removing 2 mg/L chromate from ∼ 100 column pore volumes of synthetic ground water. These results indicate that the ISRM technology is a potentially feasible method for removing chromate from Hanford ground water.
TEM Investigations of Aquifers in the Southwest Coast of Taiwan
Authors: Chen Chow‐Son 
Published: August 2005

AbstractA large data set of more than 330 transient electromagnetic (TEM) soundings was collected in the southwest coast of Taiwan. The aims of the study were (1) to define the shallow geoelectrical structure, and (2) locate large bodies of ground water by integrating electrical anomalies and data from more than 140 wells. A one‐dimensional, smooth‐model inversion of TEM data was used, and trend surface analysis of those results was employed to refine the results for interpretation. A resistive zone (15 to 160 ohm‐m resistivity) at elevations 20 to 120 m below sea level in the northern part of the survey area is interpreted as fresh water saturated sand or gravel. The southern part has extremely low resistivity, less than 1 ohm‐m, indicating a widespread sea water intrusion. The divide between these two parts is located at about the middle of the study area. This study demonstrates that TEM investigation can help resolve ambiguities, even in an area with many wells, and thereby increase the likelihood of success in ground water exploration.
Scale Dependency of Hydraulic Conductivity in Heterogeneous Media
Authors: Schulze‐Makuch Dirk , Carlson Douglas A. , Cherkauer Douglas S. , Malik Peter 
Published: August 2005

AbstractVarious types of sediments and rocks were analyzed for the relationship between hydraulic conductivity (K) and scale of measurement No variations of K with scale were observed for homogeneous media such as quartz‐arenites (quartz sandstones). However, hydraulic conductivity increased with scale of measurement in heterogeneous media. The scaling behavior can be described with the equation K = c (V)m, where c is a parameter characteristic of the geological medium that relates to geological variables such as average pore size and pore interconnectivity in porous media, and probably fracture opening and fracture interconnectivity in fractured media. V is the volume of tested material (used as scale measure), and m is the exponent of the relationship (slope of the line on a log‐log plot). The value of the exponent depends on the type or types of flow present. Porous flow media have an exponent of 0.5, multiple flow media an exponent between 0.5 and 1.0, and fracture and conduit flow controlled media an exponent of about 1.0. The more dominant fracture/conduit flow is relative to porous flow, the closer the exponent is to 1.0. K increases with scale up to a rock volume after which the aquifer approaches the properties of an equivalent homogeneous medium and K remains constant with scale. This volume (upper bound of the relationship) is related to the degree of heterogeneity in a medium. It is at a much larger scale in karstic media (if encountered at all) than in nonkarstic and more homogeneous media. Both confined and unconfined aquifers exhibit a similar scale dependence.