bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial Estimation of Transmissivity Using Artificial Neural Network
Authors: Mukhopadhyay Amitabha 
Published: August 2005

AbstractThe spatial interpolation of transmissivity and other hydrogeological parameters, based on data measured or observed at well locations, is necessary for the numerical simulation of various ground water flow and transport problems. The application of artificial neural network technology for this purpose has been investigated for the transmissivity of the Dammam Formation Aquifer in Kuwait. It has been found that reasonable estimates of this parameter can be obtained with the help of a network that uses the location coordinates, altitude of the top of the Dammam Formation, and logarithm of the total dissolved solids content of the ground water of the aquifer as the input neurons, and the logarithm of the transmissivity value as the output neuron. A better estimate is obtained with a model that takes into account the information on the occurrence of circulation loss in the Dammam Formation. This information, however, can only be obtained at a site where a well has penetrated the Dammam Formation, and unlike the altitude of a stratigraphic horizon and total dissolved solids content, cannot be extrapolated with any certainty away from a well site. This model, therefore, has limited value in estimating the transmissivity of the Dammam Formation. The artificial neural network models are found to give better estimates of transmissivity of the Dammam Formation in Kuwait when compared with the more commonly used kriging model.
A Heuristic Model of Aerobic Biodegradation of Dissolved Hydrocarbons in Aquifers
Authors: Ma Yang , Kemblowski Marian W. , Urroz Gilberto E. 
Published: August 2005

AbstractIn this paper, we present a heuristic model of mixing and aerobic degradation based on a conceptual understanding of the mixing process in heterogeneous media, rather than on a rigorous derivation from the stochastic transport equations. The mean‐behavior, heuristic approach, with a uniform velocity field, was used to reproduce organic plume behavior from a previously published simulation for random pore water velocity fields. The heuristic model presented herein requires that the mixing coefficient be calibrated to explain field data; therefore, in that sense, the model is not predictive. The numerical model uses a modified form of a particle tracking model to account for multispecies transport. Transport simulation includes a random‐walk component, while biodegradation is simulated with Monod kinetics. Numerical simulations are presented for nonreactive transport in homogeneous media, and for reactive transport in heterogeneous media. A sensitivity analysis of the model is performed to determine the effect of the mixing coefficient in the model.
Mass‐Transfer Limitations for Macroscale Bioremediation Modeling and Implications on Aquifer Clogging
Authors: MacDonald Thomas R. , Kitanidis Peter K. , McCarty Perry L. , Roberts Paul V. 
Published: August 2005

AbstractIn engineered in situ bioremediation, substrates are injected into the subsurface to stimulate microbial metabolism and growth. Models are useful in the design and optimization of such systems, such as in devising strategies to prevent clogging of soil by large bacterial populations around wells. Such models are macroscale, i.e., they do not resolve pore‐scale variability; rather, substrate and biomass concentrations are bulk averages that vary from block to block. These models give unrealistic predictions, in that they predict monotonically increasing biomass growth everywhere except where the limiting substrate concentration is very small. This work examines the possibility of biofilm mass‐transfer limitations at the pore scale using both the traditional biofilm model as well as previously published results from an upscaling model. Results from the biofilm model suggest that limitations on biofilm growth due to mass‐transfer resistance could be significant in coarse‐grained soils with adequate substrate availability. The upscaling approach confirms this result. While these two approaches do not yield identical results, both do agree that coarser grain sizes tend to cause greater mass transfer resistance. These are the conditions most likely to occur near injection well screens of an enhanced bioremediation system, where clogging is most commonly observed. The upscaling approach also indicates that the degree of mass transfer resistance is reduced at higher ground water velocities, which are also most commonly observed near well screens. These results could be useful for improving macroscale bioremediation models to more accurately predict rates of biomass growth and aquifer clogging.
Effects of Shear Detachment on Biomass Growth and In Situ Bioremediation
Authors: MacDonald Thomas R. , Kitanidis Peter K. , McCarty Perry L. , Roberts Paul V. 
Published: August 2005

AbstractThe dispersed growth model incorporating Monod kinetics has often been applied to simulate enhanced in situ bioremediation of contaminants. The dispersed growth model might not adequately address the impacts of the growth of large bacterial populations that can often have the unwanted effect of clogging the porous media. Two mechanisms that could affect model predictions of biomass are biofouling and biomass detachment due to shear stress. A mathematical model was developed to evaluate the potential impact of shear detachment on biomass distribution and the prediction of contaminant biodegradation by comparing the impact of both shear detachment and biofouling together with that of biofouling alone. The results of this examination can aid in designing a system for in situ bioremediation using computer simulations and in evaluating a system's ability to meet remediation goals. The model simulations indicate that shear detachment of biomass can be an important process to include in model simulations used to predict the effectiveness of a bioremediation system and the time before significant clogging occurs.
Improved Piezometer Construction and Sampling Techniques to Determine Pore Water Chemistry in Aquitards
Authors: Wassenaar Leonard I. , Hendry M. Jim 
Published: August 2005

AbstractDue to extremely slow water recovery rates in aquitards and high contamination potential from sealing materials, installation of piezometers in aquitards for geochemical studies requires specialized construction and careful sampling techniques. Few methods have been demonstrated for obtaining representative ground water samples for geochemical parameters from piezometers in aquitards. Here we implement and evaluate an aquitard piezometer installation and ground water chemistry sampling strategy and show that the use of an inert gas pocket in piezometer construction can be used to delay seal contamination for at least three years and avoid oxygenation and disturbance of downhole redox conditions. Major ion analyses did not change appreciably through the standing water columns in the aquitard piezometers over time; however, reliable measurements of typically unstable geochemical parameters (dissolved oxygen, pH, and oxidation‐reduction potential) were best obtained using downhole, in situ instrumentation, provided there was at least 2 to 10 m of standing water in the piezometer.
Impacts of Irrigated Vegetable Agriculture on a Humid North‐Central U.S. Sand Plain Aquifer
Authors: Kraft G J. , Stites W. , Mechenich D.J. 
Published: August 2005

AbstractWe determined the impacts of irrigated vegetable agriculture on ground water quality in a 29 km2 portion of the Wisconsin central sand plain (WCSP). Vegetable fields cover 22% of the study area and are used for growing potatoes, sweet corn, snap beans, peas, field corn, and soybeans. We found that contaminant plumes from fields underlay about 54% of the area. Plumes were 3 to >16 m thick and in places occupied the entire aquifer thickness. Impacted ground water retained the chemical signature observed under fields, and compared with unimpacted ground water, had elevated NO3‐N (median 13.7 mg L−1 impacted vs. 0.5 for unimpacted) and Cl (median 23 vs. 2.0 mg L−1) and 1.4 to 2.5 times the Ca, Mg, K, Na, and SO4. NO3‐N detections exceeded 10 mg L−1 in 58% of impacted monitoring wells compared with none of the unimpacted wells. Evidence of denitrification was observed, but rarely. Residues of the pesticides alachlor, atrazine, carbofuran, metolachlor, and metribuzin were detected, but usually at summed concentrations of <1 μg L−1 outside of fields. The maximum observed sum of pesticide residues was 8 μg L−1. Not all potential pesticide residues were detectable by the analytical method.Agricultural impacts limit the aquifer's value as a source of potable water, because wells are unable to tap unimpacted ground water through much of the area. Results of this study are generally applicable to other humid sandy areas in the north‐central United States and elsewhere. Impacts might be more severe elsewhere because the agricultural land use is frequently denser and ground water flowpaths are longer.
Laboratory Investigation of Surfactant‐Enhanced Trichloroethene Solubilization Using Single‐Well, “Push‐Pull” Tests
Authors: Field J.A. , Istok J.D. , Schroth M.H. , Sawyer T.E. , Humphrey M.D. 
Published: August 2005

AbstractThe objective of this study was to evaluate the ability of the single‐well, “push‐pull” test to characterize the enhanced solubilization of trichloroethene (TCE) by a hexadecyl diphenyl oxide disulfonate (DOWFAX) surfactant. Batch solubilization experiments indicated a linear relationship between TCE solubility and DOWFAX concentration characterized by weight‐ and molar‐solubilization ratios of 0.26 and 1.25, respectively. Laboratory push‐pull tests were performed in wedge‐shaped physical aquifer models to simulate the alternating radially divergent/convergent flow field in the vicinity of an injection/extraction well. Experiments were conducted in a TCE‐free sediment pack and in a sediment pack initially containing liquid TCE with an initial saturation of ∼ 5% of the total pore volume. In an experiment conducted in the absence of DOWFAX, maximum TCE concentrations during the extraction phase were ∼ 0.6 g/L. In contrast, in an experiment conducted with 13.5 g/L active DOWFAX, TCE concentrations during the extraction phase increased to ∼ 3.2 g/L and TCE mass recovery increased by a factor of ∼ 3. Two additional experiments conducted with DOWFAX in the same sediment pack yielded smaller maximum TCE concentrations and mass recoveries. The increased density of injected DOWFAX solutions due to TCE solubilization resulted in significant sinking of injected solutions and an accumulation of DOWFAX and TCE at greater depths in the sediment pack; however, no mobilization or sinking of liquid TCE was observed. The results indicate that push‐pull tests can provide useful information on surfactant enhanced solubilization of nonaqueous phase liquids in the subsurface.
Laboratory and Field Investigation of Surfactant Sorption Using Single‐Well, “Push‐Pull” Tests
Authors: Istok J.D. , Field J.A. , Schroth M.H. , Sawyer T.E. , Humphrey M.D. 
Published: August 2005

AbstractSorption to aquifer sediments can limit the effectiveness of surfactants injected to solubilize residual nonaqueous phase liquid contaminants in the subsurface. The objective of this study was to evaluate the ability of the single‐well, push‐pull test to characterize sorption of linear alkylbenzene sulfonate (LAS) and hexadecyl diphenyl oxide disulfonate (DOWFAX) surfactants to natural aquifer sediment in situ. Batch sorption isotherms for both surfactants exhibited Langmuir‐type sorption behavior with larger apparent sorption maxima for LAS than for DOWFAX. However, numerical transport simulations based on batch sorption isotherms were unable to predict the retardation and chromatographic separation of LAS homologs and conservative transport of DOWFAX observed during laboratory and field push‐pull tests, indicating that the single‐well, push‐pull test method can more accurately describe in situ surfactant sorption and transport behavior than batch sorption isotherms.
Effect of Shallow Penetration and Streambed Sediments on Aquifer Response to Stream Stage Fluctuations (Analytical Model)
Authors: Zlotnik Vitaly A. , Huang Huihua 
Published: August 2005

AbstractAn analytical model of stream‐aquifer interaction is proposed that considers the effects from a small degree of aquifer penetration and low‐permeability sediments on the head response to an arbitrary stream‐stage hydrograph. Aquifer sections under the stream and beyond are considered in a single model. The model of ground water flow in the aquifer is based on the Dupuit assumptions corrected for leakage from the stream. The model can use stream‐stage hydrographs in both analytical and tabular forms. The nondimensional linear boundary value problem is solved for hydraulic head in the aquifer using numerical Laplace transforms and a convolution algorithm. The proposed solution is used to assess the impact of shallow penetration and low‐permeability streambed sediments on head responses by comparison with available solutions which neglect these factors.
Modeling Analysis of Ground Water Recharge Potential on Alluvial Fans Using Limited Data
Authors: Munévar Armin , Mariño Miguel A. 
Published: August 2005

AbstractA modeling approach is developed to evaluate the potential for artificial recharge on alluvial fans in the Salinas Valley, California, using limited data of soil texture, soil hydraulic properties, and interwell stratigraphy. Promising areas for surface recharge are identified and mapped on a broad‐scale using soil surveys, geologic investigations, permeability tests, and seasonal ground water response to rainfall and runoff. Two‐dimensional representations of the vadose zone at selected sites are then constructed from drillers’logs and soil material types are estimated. Next, hydraulic properties are assigned to each soil material type by comparing them to laboratory‐tested cores of similar soils taken from one site. Finally, water flow through the vadose zone is modeled in two dimensions at seven sites using a transient, finite‐difference, variably saturated flow model. Average infiltration rates range from 0.84 to 1.54 cm/hr and recharge efficiency, the percentage of infiltrated water that reaches the water table, varies from 51% to 79%. Infiltration rates and recharge efficiency are found to be relatively insensitive to recharge basin ponding depth due to the thickness of the vadose zones modeled (31 to 84 m). The impact of artificial recharge on the Salinas Valley ground water basin is investigated by simulating the regional ground water response to surface spreading and streamflow augmentation with a recently calibrated, finite‐element, ground water‐surface water model for the basin. It was determined that a combined approach of surface recharge and streamflow augmentation significantly reduces the state of ground water overdraft and, to a lesser extent, reduces the rate of sea water intrusion.
Role of Macropores in Solute Transport under Ponded Water Condition Produced by Laboratory Simulated Intense Storms
Authors: Iqbal Mohammad Z. 
Published: August 2005

AbstractSoil macropores are widely studied because they are known to serve as avenues for rapid contaminant transport. Currently, it is understood that a macroporous medium develops regions of mobile and immobile water during flow. Consequently, solutes in the mobile phase bypass a considerable portion of the medium, thus limiting their natural attenuation. It is, however, not adequately documented in the literature what role the macropores play during intense rain events that result in variable ponding depths.Macropore flow under ponded water conditions was studied on two undisturbed soil columns taken from the loam soils of northeastern Iowa, U.S. The columns were placed on a four‐segment outflow collector system. A slug of water labeled with Br was applied to the columns followed by simulation of 58 mm of rain on column 1 and 53.6 mm on column 2, in one hour, 30 minute, and 15 minute events. During the highest intensity rain event (15 minutes), the total volume of water that exited through the bottom of segments 1,2, 3, and 4 were 21.6%, 34.5%, 28.5%, and 15.4% in column 1, and 1.3%, 15.9%, 72.2%, and 10.5% in column 2, respectively. As the intensity of rain was increased from one hour to the 15 minute event, the total bromide mass recovery increased from 45% (29.2 mg) to 57% (36.9 mg) of the total application (65 mg) for column 1, and from 51 % (33.2 mg) to 59% (38.2 mg) for column 2, respectively. Finally, an examination of dye‐stained high flow regions in column 1 demonstrated that macro‐porosities made approximately 20% of the total cross‐sectional area of the column.These results suggest that solute transport behavior in macroporous soils can be impacted by ponding depths, and intense rain events can severely restrict contaminant degradation in soils.
Use of Combined Shewhart‐CUSUM Control Charts for Ground Water Monitoring Applications
Authors: Gibbons Robert D. 
Published: August 2005

AbstractStatistical properties of combined Shewhart‐CUSUM control charts are examined in terms of the site‐wide false positive rate, false negative rate, and average run length (i.e., the average number of sampling events that it takes to detect a significant exceedance). The effects of multiple comparisons (i.e., multiple monitoring wells and constituents), verification resampling, background sample size, and background updating are incorporated into the analysis. The effects of (1) verification resampling plans including no resampling, pass one resample, pass one of two resamples, and pass two of two resamples; (2) background sample sizes (n = 8,12,16,20, and 24); and (3) multiple comparisons (k = 1 to 500 future comparisons) were examined. In addition, various alternative control limit factors (h = SCL= 4.5, 5.0,5.5, and 6.0) were considered, where the control limit is x + hs. Results of simulations revealed that it is possible to balance site‐wide false positive and false negative rates at low levels using combined Shewhart‐CUSUM control charts. The results revealed that it is important to select the appropriate multiplier, verification resampling plan, number of background samples, and number of intervening samples prior to updating background.
Analysis of the Quality of Parameter Estimates from Repeated Pumping and Slug Tests in a Fractured Porous Aquifer System in Wonju, Korea
Authors: Lee Jin‐Yong , Lee Kang‐Kun 
Published: August 2005

AbstractPumping and slug tests are widely used, relatively simple methods for estimating hydraulic conductivity and storage coefficient. This study tested the reproducibility of pumping and slug tests in estimating aquifer parameters in fractured or fractured porous media. The continuum concept is applied to represent the hydraulic properties by the conventional conductivity and storage coefficient. Repeated tests show discrepancies wider than can be attributed to probable measurement errors or incomplete curve fitting. The sources of discrepancy include turbulent head loss in an observation well, pumping well location, data acquisition period (pumping or recovery), selection of analysis method, test initiation mechanism, applied initial displacement, and selection of data segment for analysis. When we employ a specific test practice or choose a specific analysis method or data segment for the analysis, the resulting parameter estimates show characteristic patterns of distribution with respect to the mean value. This study analyzes the patterns and discusses how to improve the reliability of the parameter estimation.
Application of Flowmeter and Depth‐Dependent Water Quality Data for Improved Production Well Construction
Authors: Gossell M.A. , Nishikawa T. , Hanson R.T. , Izbicki J.A. , Tabidian M.A. , Bertine K. 
Published: August 2005

AbstractGround water production wells commonly are designed to maximize well yield and, therefore, may be screened over several water‐bearing zones. These water‐bearing zones usually are identified, and their hydrogeologic characteristics and water quality are inferred, on the basis of indirect data such as geologic and geophysical logs. Production well designs based on these data may result in wells that are drilled deeper than necessary and are screened through zones having low permeability or poor‐quality ground water. In this study, we examined the application of flowmeter logging and depth‐dependent water quality samples for the improved design of production wells in a complex hydrogeologic setting. As a demonstration of these techniques, a flowmeter log and depth‐dependent water quality data were collected from a long‐screened production well within a multilayered coastal aquifer system in the Santa Clara‐Calleguas Basin, Ventura County, California. Results showed that the well yields most of its water from four zones that constitute 58% of the screened interval. The importance of these zones to well yield was not readily discernible from indirect geologic or geophysical data. The flowmeter logs and downhole water quality data also show that small quantities of poor‐quality water could degrade the overall quality of water from the well. The data obtained from one well can be applied to other proposed wells in the same hydrologic basin. The application of flowmeter and depth‐dependent water quality data to well design can reduce installation costs and improve the quantity and quality of water produced from wells in complex multiple‐aquifer systems.
Sensitivity Study on Hydraulic Well Testing Inversion Using Simulated Annealing
Authors: Nakao Shinsuke , Najita Julie , Karasaki Kenzi 
Published: August 2005

AbstractCluster variable aperture (CVA) simulated annealing has been used as an inversion technique to construct fluid flow models of fractured formations based on transient pressure data from hydraulic tests. A two‐dimensional fracture network system is represented as a filled regular lattice of fracture elements. The algorithm iteratively changes element apertures for a cluster of fracture elements in order to improve the match to observed pressure transients. Aperture size is chosen randomly from a list of discrete apertures. The cluster size is held constant throughout the iterations. Since hydraulic inversion is inherently nonunique, it is important to use additional information. We investigated the relationship between the scale of heterogeneity and the optimal cluster size and shape to enhance convergence of the inversion and improve the results. In a spatially correlated transmissivity field, a cluster size corresponding to about 20 % to 40 % of the practical range of the spatial correlation is optimal. Inversion results of the Raymond test site data are also presented and based on an optimal cluster size; the practical range of the spatial correlation is estimated to be 5 to 10 m.