bluuebunny/crossref_metadata_2025_split huggingface dataset:
Joint Management of Surface and Ground Water Supplies
Authors: Başaǧaoǧlu Hakan , Mariňo Miguel A. 
Published: August 2005

AbstractA management model is developed to determine optimal water allocation policies for hydraulically connected time‐variant surface and ground water supplies in a hypothetical system. The system involves a multipurpose reservoir, a hydraulically connected stream and aquifer, agricultural plots, water supply and observation wells, and an artificial recharge zone. The model minimizes deviations from a set of rule curves defined for storage in the reservoir and along the stream course, so as to consider possibilities for storage of excess water in wet periods and its distribution in subsequent dry periods. The hypothetical system is divided into components which are subsequently integrated using numerically generated response functions that relate the systemis behavior to various system excitations. The management model is formulated and solved for monthly time steps, which include both dry and wet conditions, to determine reservoir release, pumpage rate from supply wells, artificial recharge rate, water diversion from reservoir and stream to the demand area, and storage both in the reservoir and along the stream course at an optimal level in each time step over a six‐month planning horizon. Furthermore, sensitivity analysis of the management plan with respect to potential use of ground water supplies is performed to analyze the latter's impact on operating policies.
Determining the Hydraulic Conductivity Spatial Structure at the Twin Lake Site by Grain‐Size Distribution
Authors: Indelman Peter , Moltyaner Greg , Dagan Gedeon 
Published: August 2005

AbstractConcentrations of a radiotracer were measured continuously in observation wells in a Held test conducted in the sandy aquifer at the Chalk River site. These measurements were used recently (Dagan et al. 1997) to assess the values of the parameters characterizing the spatial distribution of logconductivity (mean, variance, and horizontal and vertical integral scales).Soil samples were taken independently from a few wells and the grain‐size distributions were determined by sieve analysis. The aim of the present study is to infer the aforementioned parameters’values of logconductivity with the aid of grain‐size distributions. A Carman‐Kozeny‐type formula was used to derive the sample hydraulic conductivity and a geostatistical analysis to infer the parameters characterizing the logconductivity spatial distribution. The agreement for the results based on the two methods was quite satisfactory in view of the various approximations adopted by the two methodologies.
Phosphate Plume Persistence at Two Decommissioned Septic System Sites
Authors: Robertson W.D. , Harman J. 
Published: August 2005

AbstractLong‐term monitoring of two well‐characterized, oxidizing septic system plumes (Langton and Long Point 2 sites) over periods extending two to four years after decommissioning, has revealed that ground water PO 43− concentrations (0.4 to 5 mg/L P) have persisted at levels virtually unchanged from those observed during active sewage loading. In addition, the frontal part of the PO43− plume at the Long Point 2 site can be observed to continue to advance during the decommissioned period. At the Langton site, where an active regional ground water flow system is present, all major plume solutes (Na+, Ca2+, Cl−, NO 3−) returned to background values within one year of decommissioning, with the exception of PO43−.This evidence suggests that phosphate behavior in the ground water zone at these sites is dominated by sorption reactions that are both rapid and reversible. Thus, if septic system phosphorus is not retained in the vadose zone, but is transported into the ground water zone, it has the potential to be persistent and to be mobile enough to constitute a threat to downgradient surface water environments. This evidence also shows that when a septic system is decommissioned, if an oxidizing PO43− plume is present, downgradient P loading is not likely to diminish for many years thereafter.
Importance of Rock Matrix Entry Pressure on DNAPL Migration in Fractured Geologic Materials
Authors: Slough KJ. , Sudicky E.A. , Forsyth P.A. 
Published: August 2005

AbstractThe capillary pressure versus saturation relationship for various carbonate rocks exhibits a wide range of entry pressures depending on the depositional and diagenetic environment of the rock. The results of a numerical study are presented that focus on the effect of the DNAPL entry pressure of the porous rock matrix on the migration of DNAPL within the fracture network of carbonate rocks. Representative numerical experiments involving the release of DNAPL into a single vertical fracture terminating within a porous carbonate rock that was assigned a variety of measured capillary pressure versus saturation relationships showed that the volume of DNAPL that entered the rock matrix increased dramatically as the entry pressure of the rock matrix decreased. Simulations of a DNAPL‐contaminated site located on fractured carbonate bedrock in southern Ontario are also presented which highlight the sensitivity of the extent of the zone of DNAPL contamination within the bedrock to the capillary pressure curves assigned to the rock matrix. One scenario presented demonstrates that the penetration depth and horizontal extent of the zone of DNAPL contamination within the bedrock can be large if the carbonate rock has a high entry pressure, because much of the DNAPL flow is restricted to the fracture network. Another case involving a lower entry pressure for the rock matrix produced a smaller zone of DNAPL contamination, but the bulk of the DNAPL was contained in the rock matrix. The results for both cases suggest that attempts at DNAPL‐zone restoration in fractured rock using technologies that are available today would be problematic.
Post Audit of a Numerical Prediction of Wellfield Drawdown in a Semiconfined Aquifer System
Authors: Stewart Mark , Langevina Christian 
Published: August 2005

AbstractA numerical ground water flow model was created in 1978 and revised in 1981 to predict the drawdown effects of a proposed municipal wellfield permitted to withdraw 30 million gallons per day (mgd; 1.1 × 105 m3/day) of water from the semiconfined Floridan Aquifer system. The predictions are based on the assumption that water levels in the semiconfined Floridan Aquifer reach a long‐term, steady‐state condition within a few days of initiation of pumping. Using this assumption, a 75 day simulation without water table recharge, pumping at the maximum permitted rates, was considered to represent a worst‐case condition and the greatest drawdowns that could be experienced during wellfield operation. This method of predicting wellfield effects was accepted by the permitting agency.For this post audit, observed drawdowns were derived by taking the difference between pre‐pumping and post‐pumping potentiometric surface levels. Comparison of predicted and observed drawdowns suggests that actual drawdown over a 12 year period exceeds predicted drawdown by a factor of two or more. Analysis of the source of error in the 1981 predictions suggests that the values used for transmissivity, storativity. specific yield, and leakance are reasonable at the wellfield scale. Simulation using actual 1980–1992 pumping rates improves the agreement between predicted and observed drawdowns. The principal source of error is the assumption that water levels in a semiconfined aquifer achieve a steady‐state condition after a few days or weeks of pumping. Simulations using a version of the 1981 model modified to include recharge and evapotranspiration suggest that it can take hundreds of days or several years for water levels in the linked Surficial and Floridan Aquifers to reach an apparent steady‐state condition, and that slow declines in levels continue for years after the initiation of pumping. While the 1981 “impact” model can be used for reasonably predicting short‐term, wellfield‐scale effects of pumping, using a 75 day long simulation without recharge to predict the long‐term behavior of the wellfield was an inappropriate application, resulting in significant underprediction of wellfield effects.
Time‐Related Capture Zones for Contaminants in Randomly Heterogeneous Formations
Authors: Guadagnini Alberto , Franzetti Silvio 
Published: August 2005

AbstractPrediction of solute travel distance based on homogeneous and isotropic hydraulic conductivity may lead to substantial differences in the actual travel distance in a heterogeneous system. The effect of randomly varying hydraulic conductivity on the spatial location of time‐related well capture zones for a nonreactive tracer in a confined aquifer with uniform base flow is considered. A numerical Monte Carlo procedure is used in conjunction with fast Fourier transform‐based spectral methods. The log hydraulic conductivity field is assumed to be Gaussian and stationary, with isotropic exponential autocovariance. Various degrees of domain heterogeneity are considered, and stability and accuracy of the numerical procedure are examined. The total probability that a particle injected at a point in the aquifer is extracted by the well within a given time is identified. The concept of probabilistic isochrone, which is the boundary of a given time‐related capture zone, is introduced. A simple analytical model that extends the deterministic capture‐zone model for uniform media is derived, by taking into account the effect of random variations of hydraulic conductivity. Knowledge of the spatial pattern of probabilistic isochrones allows reconstructing the breakthrough curve at the well for solute injections at selected locations in the aquifer.
Ground Water Salinization Caused by Residual Neogene and Pliocene Sea Water‐An Example from the Judea Group Aquifer, Southern Israel
Authors: Rosenthal E. , Weinberger G. , Kronfeld J. 
Published: August 2005

AbstractThe Judea Group Aquifer of late Albian‐Turonian age is mainly composed of karstic limestone and dolomite. In the western part of Israel it is known as the Yarkon‐Taninim ground water basin. The study area is located in the southern part of the basin. Fresh ground water (46 to 200 mg/L Cl) flows northward from the south and southeast. Saline ground water (1200 to 8350 mg/L Cl), which occurs irregularly in the midst of this flowpath, severely jeopardizes the development and exploitation of this aquifer. By defining the hydrochemical typology and applying mass balance considerations, it was found that the saline water is derived from two endmembers designated as the “Lahish” and “Hazerim” water types. The Lahish water type is generally responsible for salinization of the lower portion of the Judea Group Aquifer. It apparently evolved from transgressing Messinian sea water which penetrated inland through prior incised Neogene erosional channels. Upon inundation, it dissolved halite and gypsum from the Mavqi'im Formation. This was followed by massive bacterial reduction of sulfates in the presence of oil. The Hazerim water type infiltrated into the Judea Group Aquifer through the overlying Avedat and Mt. Scopus rock successions. It appears that the Hazerim water developed from the transgressing Pliocene sea which percolated through these low‐permeability rock units. Subsequent rain percolated through these formations, dissolved evaporites that are mainly concentrated in the shallow layers and mixed with residual sea water of Pliocene age, which became more diluted over time. Geological studies revealed that during the Neogene age, the back‐cut incision of channels into the Coastal Plain facilitated inland ingression of the sea and dissolution of evaporites. The Pliocene marine transgression deposited a thick sequence of clay that sealed the underlying beds. This process resulted in trapping and pressurizing the saline water landward along pre‐existing fault lines. These findings contribute to the formulation of an updated ground water exploitation scheme that avoids subsurface fault systems, which act as conduits of brines. The geological processes occurred during the Neogene and Pliocene. This case study could help solve similar problems in the eastern Mediterranean region which experienced similar geological events.
Model Calibration with Multiple Targets: A Case Study
Authors: Kim Kangjoo , Anderson Mary P. , Bowser Carl J. 
Published: August 2005

AbstractMultiple calibration targets were used to calibrate a two‐dimensional finite‐difference model of a ground water lake system. The calibration targets included (1) steady‐state head data, (2) transient head data, (3) head gradients, and (4) flowpath information. Because calibration was sensitive to the ratio of horizontal to vertical hydraulic conductivity, four models, each with different assumptions about anisotropy, were developed. All four models produced acceptable calibration to either heads or flowpath, but only one model was well calibrated to all targets. In that model, stratification of the upper aquifer was represented by introducing several dipping layers of low permeability. This allowed the use of a small ratio of horizontal to vertical anisotropy for individual layers but produced a large effective anisotropy for the upper aquifer as a whole.
Analytical Modeling of Aquifer Pollution Caused by Solid Waste Depositories
Authors: Rudakov Dmitry V. , Rudakov Victor C. 
Published: August 2005

AbstractAn analytical model to assess the risk of ground water pollution caused by leaks from surficial depositories containing water‐soluble toxic substances is presented. The proposed model includes two stages of pollutant migration: (1) predominantly vertical transport through a low‐permeability protective soil layer above the aquifer, and (2) two‐ or three‐dimensional transfer of the pollutant in ground water flow. Convection, longitudinal and transverse dispersion, sorption, and pollutant decay are taken into consideration both for the soil layer and the aquifer. Corresponding boundary problems are formulated and solved. The exact solutions allow us to estimate the possibility of toxic substance percolation into the aquifer and the expected intensity of this process, and to simulate pollution zone formation in ground water and possible material flow to a nearby surface water body. The calculations showed good numerical accuracy and the practical convenience of the model for monitoring and predicting ground water pollution near landfills and depositories of industrial solid waste.
Hydraulic and Geochemical Performance of a Permeable Reactive Barrier Containing Zero‐Valent Iron, Denver Federal Center
Authors: McMahon P.B. , Dennehy K.F. , Sandstrom M.W. 
Published: August 2005

AbstractThe hydraulic and geochemical performance of a 366 m long permeable reactive barrier (PRB) at the Denver Federal Center, Denver, Colorado, was evaluated. The funnel and gate system, which was installed in 1996 to intercept and remediate ground water contaminated with chlorinated aliphatic hydrocarbons (CAHs), contained four 12.2 m wide gates filled with zero‐valent iron. Ground water mounding on the upgradient side of the PRB resulted in a tenfold increase in the hydraulic gradient and ground water velocity through the gates compared to areas of the aquifer unaffected by the PRB. Water balance calculations for April 1997 indicate that about 75 % of the ground water moving toward the PRB from upgradient areas moved through the gates. The rest of the water either accumulated on the upgradient side of the PRB or bypassed the PRB. Chemical data from monitoring wells screened down‐gradient, beneath, and at the ends of the PRB indicate that contaminants had not bypassed the PRB, except in a few isolated areas. Greater than 99 % of the CAH mass entering the gates was retained by the iron. Fifty‐one percent of the CAH carbon entering one gate was accounted for in dissolved C1 and C2 hydrocarbons, primarily ethane and ethene, which indicates that CAHs may adsorb to the iron prior to being dehalogenated. Treated water exiting the gates displaced contaminated ground water at a distance of at least 3 m downgradient from the PRB by the end of 1997. Measurements of dissolved inorganic ions in one gate indicate that calcite and siderite precipitation in the gate could reduce gate porosity by about 0.35 % per year. Results from this study indicate that funnel and gate systems containing zero‐valent iron can effectively treat ground water contaminated with CAHs. However, the hydrologic impacts of the PRB on the flow system need to be fully understood to prevent contaminants from bypassing the PRB.
The Effects of Bag Type and Meter Size on Seepage Meter Measurements
Authors: Isiorho Solomon A. , Meyer John H. 
Published: August 2005

AbstractSeepage meters provide a useful, inexpensive method of measuring seepage flux through unconsolidated sediments in lakes, reservoirs, and stream channels. In the literature, the bag type used is usually not indicated, and its effect on seepage measurement has not been evaluated. The effects of bag type and seepage meter size have been evaluated in a laboratory setting.A sandbox 100.4 (L) × 76.2 (W) × 24 (H) cm size was half filled with coarse sand and water to a depth of 10 cm. Four seepage meters and two bag types (balloon and condom) were used in the seepage measurements.There was no significant difference between the seepage measurements obtained from the two bag types. A two‐sample t‐test (df=56, Wt‐sat=2.58, alpha=0.01, p=0.0013) failed to reject the null hypothesis of similarity between measurements from the two bag types. The seepage measurements from four seepage meters were similar with no significant difference; however, the smaller diameter seepage meters had a greater variance.
Multiple Geochemical and Isotopic Approaches for Assessing Ground Water NO3− Elimination in a Riparian Zone
Authors: Mengis M. , Schif S. L. , Harris M. , English M. C. , Aravena R. , Elgood RJ. , MacLean A. 
Published: August 2005

AbstractDuring the last 40 years, nitrate (NO3−) has become one of the most common ground water contaminants. Stream riparian zones are considered important ecological ecotones that decrease the NO3− load of ground water discharging into streams. This study uses NO3−/Cl− ratios, natural abundances of15N and18O in NO3−, and an in situ15NO3− tracer experiment to evaluate NO3− reducing processes occurring in ground water within a narrow grassed buffer strip bordering a stream in an agricultural watershed. The NO3−/Cl− ratios (1.9‐0.0 [M/M]) indicate that both NO3− consuming processes and mixing of two ground water flow regimes with different NO3− loads contribute to the drop observed in ground water NO3− concentrations within the riparian zone. δ15N and δ18O of the ground water NO3− within the riparian zone (δ15N = 5.1 to 48.8 %c; δ18O = 1.1 to 17.8 %c) were enriched compared to the ground water below the adjacent cultivated field (δ15N = 3.8 to 10.1 %0; δ18O = 0.5 to 6.2 %c). A significant linear relationship (r2=0.97) between ground water δ15N and δ18O in NO3− was found, which is consistent with NO3− consumption by microbial denitrification. The estimated enrichment factors for15N are a factor of 1.5 higher than for18O. The in situ15NO3− tracer experiment conclusively confirmed that denitrification is occurring within the ground water of the riparian zone and demonstrates that denitrification rates can be directly measured in situ.
Numerical Modeling of Perched Water Under Yucca Mountain, Nevada
Authors: Hinds Jennifer J. , Ge Shemin , Fridrich Chris J. 
Published: August 2005

AbstractThe presence of perched water near the potential high‐level nuclear waste repository area at Yucca Mountain, Nevada, has important implications for waste isolation. Perched water occurs because of sharp contrasts in rock properties, in particular between the strongly fractured repository host rock (the Topopah Spring welded tuff) and the immediately underlying vitrophyric (glassy) subunit, in which fractures are sealed by clays that were formed by alteration of the volcanic glass. The vitrophyre acts as a vertical barrier to unsaturated flow throughout much of the potential repository area. Geochemical analyses (Yang et al. 1996) indicate that perched water is relatively young, perhaps younger than 10,000 years. Given the low permeability of the rock matrix, fractures and perhaps fault zones must play a crucial role in unsaturated flow. The geologic setting of the major perched water bodies under Yucca Mountain suggests that faults commonly form barriers to lateral flow at the level of the repository horizon, but may also form important pathways for vertical infiltration from the repository horizon down to the water table. Using the numerical code UNSAT2, two factors believed to influence the perched water system at Yucca Mountain, climate and fault‐zone permeability, are explored. The two‐dimensional model predicts that the volume of water held within the perched water system may greatly increase under wetter climatic conditions, and that perched water bodies may drain to the water table along fault zones. Modeling results also show fault flow to be significantly attenuated in the Paintbrush Tuff non‐welded hydrogeologic unit.
Analysis of Convective Heat Transfer in Deformed and Stratified Aquifers Associated with Frasch Thermal Mining
Authors: Williams Daphne D. , Lee Ming‐Kuo , Crawford Joe E. , Tyree Philip O. 
Published: August 2005

AbstractThis paper presents numerical experiments designed to simulate heat transfer in deformed, stratified geologic formations during Frasch thermal mining operations in the Delaware Basin. In such operations, superheated water (163°C) is injected into permeable ore zones to melt and mobilize sulfur. The efficiency of Frasch mining depends largely on various aspects of hydrologic controls and geologic factors, such as directing heat flow toward target areas and minimizing heat dissipation through advection and conduction in ore zones. Numerical modeling techniques were used in the search of an optimum thermal mining strategy for maximum sulfur recovery in various geologic settings present at the Culberson Mine, west Texas. The sample calculations illustrate heat transfer patterns in inclined, folded, and fractured geologic formations. Important results presented include the controls of geologic structures on directions and rates of heat transfer and ground water flow, a display of field evidence for the occurrence of thermal convection in permeable ore zones, and a depiction of heat transfer during a thermal mining operation proceeding down‐dip along an inclined geologic unit. Modeling results and field data strongly support the hypothesis that thermal convection occurs and controls the heat transfer process in inclined ore zones. Simulations further suggest that the current thermal mining practice, which proceeds down‐slope along an inclined ore zone, may result in lowered ultimate sulfur recovery. In this mining approach most heat migrates up‐slope where the rock's permeability is enhanced by previous sulfur extraction, rather than down‐dip toward the target area.