bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Impact of Ion Exchange Processes on Subsurface Brine Transport as Observed on Piper Diagrams
Authors: Cates David A. , Knox Robert C. , Sabatini David A. 
Published: August 2005

AbstractAn experimental study was conducted to assess how ion exchange processes, which occur during subsurface transport of oilfield brines, manifest themselves on graphical water quality diagrams. Concentrated brine soil column studies indicated sodium in the brine solution is able to exchange for calcium and magnesium on the soil, thereby retarding transport of sodium relative to the average ground‐water velocity and resulting in the development of a “hardness halo” at the leading edge of the brine plume. In this zone, calcium and magnesium concentrations exceed the values for both the brine and the fresh ground water. The hardness halo manifests itself as a characteristic deviation away from the mixing lines on the Piper diagram. Initially, the hardness halo causes concentrations to plot left of the fresh‐water end member in the cationic triangle. Chloride domination in oilfield brine causes concentrations to plot in the lower right corner of the anionic triangle almost immediately. After the hardness halo passes through the column, the sampling results show a characteristic pattern of movement parallel to the mixing line in the cation triangle or along the (decreasing) hardness axis of the upper diamond of the Piper diagram. The laboratory results were similar to those exhibited by monitoring well samples taken at a field site involving oilfield brine contamination. The results of this study show the Piper diagram to be potentially useful for early detection of brine contamination episodes.
Determining an Optimal Sampling Frequency for Measuring Bulk Temporal Changes in Ground‐Water Quality
Authors: Moline G. R. , Beauchamp J. J. , Wright T. 
Published: August 2005

AbstractIn the Data Quality Objectives (DQO) process, statistical methods are used to determine an optimal sampling and analysis plan. When the DQO decision rule for instituting remedial actions is based on a critical change in water quality, the monitoring program design must ensure that this change can be detected and measured with a specified confidence. Usually the focus is on the change at a single monitoring location and the process is limited to addressing the uncertainty inherent in the analytical methods and the variability at that location. However, new strategies that permit ranking the waste sites and prioritizing remedial activities require the means for assessing overall changes for small regions over time, where both spatial and temporal variability exist and where the uncertainty associated with these variations far exceeds measurement error. Two new methods for assessing these overall changes have been developed and are demonstrated by application to a waste disposal site in Oak Ridge, Tennessee. These methods incorporate historical data where available and allow the user to either test the statistical significance of a linear trend or of an annual change compared to a baseline year for a group of water quality wells.
Enhancing Data Worth of EM Survey in Site Assessment by Cokriging
Authors: Parks Kevin P. , Bentley Laurence R. 
Published: August 2005

AbstractGround‐water chemistry data from wells are cokriged with ground conductivity measurements to quantitatively describe ground‐water chemical quality at a site. The cokriged estimates are shown to be superior to both simple rescaling of ground conductivity by a linear regression model and to interpolation of ground‐water chemistry data from wells using ordinary kriging. By extending the use of geophysical measurements in this way, significant cost savings in site assessment can be realized and the geophysics will have more data “worth.”
Hydrogeological Investigations in Northwestern Yucatan, Mexico, Using Resistivity Surveys
Authors: Steinich Birgit , Marin Luis E. 
Published: August 2005

AbstractEight Schlumberger soundings and four Wenner anisotropy measurements were conducted in the northwestern section of the Yucatan Peninsula for hydrogeological investigations of a karst aquifer. This system is influenced by a circular high permeability zone (Ring of Cenotes) probably related to the Chicxulub Impact Crater. Schlumberger soundings and Wenner anisotropy measurements show that the karst aquifer can be modeled as an electrically anisotropic medium. Anisotropy is related to preferential permeability directions channeling ground‐water flow within the aquifer. Directions of maximum permeability were determined using Wenner anisotropy measurements. Electrical soundings were conducted at different sites near the Ring of Cenotes. Resistivity values decrease toward the Ring of Cenotes supporting the hypothesis that selected segments of the Ring have high permeability. Several soundings were conducted in order to study lateral permeability variations along the Ring. A high permeability section can be identified by low resistivity models and is related to a zone of high cenote density. A low permeability section of the Ring was found showing high resistivity models. This zone overlaps with an area of low cenote density. Electrical soundings were used to determine the depth of the fresh‐water lens; the interface was detected along two profiles perpendicular and parallel to the Ring of Cenotes resulting in a depth that ranged from 18 m near the coast up to 110 m in the southeastern part of the study area. The predicted depths of the interface using electrical methods showed a good correlation with Ghyben‐Herzberg and measured interface depths at some sites. Discrepancies between calculated and interpreted interface depths at two sites may be explained by horizontal‐to‐vertical permeability anisotropy.
Multidimensional Water Flow in a Low‐Level Waste Isolation Barrier
Authors: Nichols William E. , Meyer Philip D. 
Published: August 2005

AbstractAn analysis was conducted of multidimensional subsurface moisture flow in a hypothetical low‐level radioactive waste disposal facility. The key design feature examined in the analysis was a sloping sand/gravel capillary barrier designed to route natural infiltration around a concrete vault. Three barrier slopes (1:25, 1:10, and 1:5) and three sand/gravel property combinations were considered. The slopes and material property combinations were selected to represent a range in barrier effectiveness. The porous media flow code used for this analysis was VAM3DCG, a three‐dimensional, finite‐element code which was able to use nonorthogonal grid discretizations and employed robust, efficient numerical techniques. Three‐dimensional modeling demonstrated that flow in the hypothetical design exhibited cross‐slope flow because of the pressure gradient produced in the third, cross‐slope dimension. Barrier effectiveness was shown to be highly sensitive to the sand/ gravel material properties. Barrier slope was less important, especially for the effective material combinations. The presence of three‐dimensional flow could be important in a performance assessment if the quantity of water predicted to breach the capillary barrier by a two‐dimensional model were different from that predicted by a three‐dimensional model. Comparative modeling demonstrated that a two‐dimensional analysis resulted in underestimation of barrier effectiveness. For the considered design, two‐dimensional modeling is a conservative, yet reasonable, approach in a performance assessment application.
Measuring Rates of Biodegradation in a Contaminated Aquifer Using Field and Laboratory Methods
Authors: Chapelle Francis H. , Bradley Paul M. , Lovley Derek R. , Vroblesky Don A. 
Published: August 2005

AbstractRates of biodegradation were measured in a petroleum hydrocarbon‐contaminated aquifer using a combination of field and laboratory methods. These methods are based on tracking concentration changes of substrates (both electron donors and acceptors) or final products of microbial metabolism over time. Ground water at the study site (Hanahan, South Carolina) is anoxic, and sulfate reduction is the predominant terminal electron accepting process. Laboratory studies conducted with sediment cored from the site showed that 14C‐toluene was mineralized to 14CO2 with a first‐order degradation rate constant (ktol) of ‐0.01 d−1 under sulfate‐reducing conditions. Under nitrate‐amended, Fe(III)‐amended, or nonamended (methanogenic) conditions, toluene was not significantly mineralized. 14C‐Benzene was degraded at low but measurable rates (kben= ‐0.003 d−1) under sulfate‐reducing conditions whereas degradation under methanogenic conditions was negligible. These results illustrate the extreme sensitivity of laboratory‐measured biodegradation rates to terminal electron‐accepting conditions, and show the necessity of carefully matching experimental conditions to in situ conditions. Concentration decreases of toluene along aquifer flowpaths, when the uncertainty of ground‐water flow velocities was considered, indicated ktol values ranging from ‐0.0075 to ‐0.03 d−1. Concentration decreases of sulfate and concentration increases of dissolved inorganic carbon (DIC), when normalized for assumed stoichiometric oxidation of toluene coupled to sulfate reduction, yielded a kso4 range of ‐0.005 to ‐0.02 d−1, and a kDIC value range of +0.00075 to +0.003 d−1. Because both laboratory and field methods have numerous sources of uncertainty, a combination of these methods is the most appropriate procedure for evaluating biodegradation rate constants in contaminated ground‐water systems.
Industrial Contamination of a Municipal Water‐Supply Lake by Induced Reversal of Ground‐Water Flow, Managua, Nicaragua
Authors: Bethune David N. , Farvolden R. N. , Ryan M. Cathryn , Guzman Andres Lopez 
Published: August 2005

AbstractLaguna Asososca, a large ground‐water‐fed volcanic crater, is an important source of municipal water supply for the city of Managua. In 1990, after 65 years of pumping at increasing rates from the crater, the gradient between the Laguna and the highly contaminated Lake Managua had potentially reversed, leading to a scenario where the Laguna was possibly drawing in contaminated ground water from Lake Managua and/or a highly contaminated aquifer below an industrial area located between the Laguna and Lake Managua. A drilling and sampling program undertaken between 1990 and 1992 found: (1) four synthetic organic chemicals in the Laguna (methylene chloride, chloroform, 1,3‐dichlorobenzene and 1,4‐dichlorobenzene), (2) numerous other synthetic organic chemicals near Laguna Asososca in the ground water below the industrial area, and (3) no evidence of Laguna Asososca drawing water from Lake Managua. It appears that the Laguna Asososca capture zone extended into the industrial area but not as far as Lake Managua. Ground‐water flow modeling of the regional ground‐water flow system was consistent with the field interpretation. Estimates of the relative mobilities of the synthetic organic chemicals indicated that the chemicals found in the water of Laguna Asososca likely represented the mobile leading edge of a contaminant plume emanating from the industrial area. The simplest and most effective solution to mitigate contamination of Laguna Asososca is to maintain its water level above that of Lake Managua by reducing its pumpage to about 50% of the 1990 rate.
Gas Partitioning of Dissolved Volatile Organic Compounds in the Vadose Zone: Principles, Temperature Effects and Literature Review
Authors: Washington John W. 
Published: August 2005

AbstractEnthalpy and entropy of volatilization from dilute aqueous solutions for 26 volatile organic compounds (VOCs) have been determined using Henry's Law values reported in published literature. Based on the linearity of van't Hoff plots, for the temperature ranges common in soils, the differences in heat capacities of volatilization for reactants and products are very small for the VOCs studied.When volatile solutes such as VOCs are present in soil water, soil‐gas concentration often nearly is in equilibrium with the dissolved solute. Setchinow salting coefficients are linearly related to dissolved partial molar volumes for halogenated aliphatic compounds. Based in part on approximations from this linear relationship, equilibrium deviations from Henry's Law behavior for dilute VOC concentrations due to capillary tension or the presence of ionic solutes are small for common soil conditions.Since gas/water partitioning of VOCs if temperature‐sensitive and since annual soil moisture and temperature patterns vary geographically in documented fashion, geographically specific temporal patterns in soil‐gas VOC concentrations are predictable in vadose zones containing dissolved VOCs. A U.S. map depicting these general soil‐moisture and temperature patterns is provided. Gas concentrations in vadose zones containing dissolved VOCs tend to increase with increasing temperature and decreasing moisture content due to equilibrium partitioning effects.Diagrams useful for understanding the results of soil‐gas surveys and the efficacy of various remediation options are provided. The effect of bubbles in VOC water‐sample vials on aqueous concentrations is shown to be very small. The effect of head‐space volume of soil samples on estimated soil‐gas concentrations can be large.
Optimum Hydraulic Conductivity to Limit Contaminant Flux Through Cutoff Walls
Authors: Devlin J. F. , Parker B. L. 
Published: August 2005

AbstractCutoff walls are becoming increasingly attractive options for the control of solute migration from long‐term sources of contamination. The main advantage of low permeability enclosures is that they restrict advective transport of solutes away from the source. However, with high concentration source zones surrounded by cutoff walls, there exists the potential for notable mass fluxes outward due to diffusive transport. This paper shows, through the use of the steady‐state flux equations, that there is an optimal range of hydraulic conductivities for barrier materials which permit the outward diffusive flux to be counter balanced by an inward advective and dispersive flux. This concept of designing optimum contaminant containment using an inward advective flux to counter the outward diffusive flux is valid for sealable joint sheet pile walls, bentonite‐slurry walls and clay liners, but not synthetic membrane materials with extremely low hydraulic conductivities. The effective diffusion coefficient for the common chlorinated organic solvents such as TCE in water‐saturated clayey materials is approximately 1 × 10−6 cm2/sec, resulting in an optimum hydraulic conductivity ranging from 1 × 10−6 to 1 × 10−8 cm/sec. This range in hydraulic conductivity is within the range of common barrier materials but not the lowest achievable. The steady‐state concentration profile in a slurry cutoff wall can result in a substantial amount of contaminant mass stored within the wall which will need to be considered over the long term or dealt with during site remediation. Large inward advective fluxes reduce the total chemical mass stored within the low permeability barrier material.
A Hydrogeologic Model of Samana Cay, Bahamas, and Its Implications for the Columbus Landfall Question
Authors: Valdés José J. 
Published: August 2005

AbstractSamana Cay, Bahamas, is a leading candidate among the sites proposed as the first landfall of Columbus in the New World. One main point of contention against this identification is that Samana lacks a feature matching the laguna observed by Columbus in the middle of his landfall island. However, this argument has failed to consider the paleogeographic aspects of the problem. A hydrogeologic computer model suggests the existence of a sizable surface‐water feature in the medial interior of Samana Cay under conditions theorized to have been present when Columbus arrived in the Bahamas. This feature may correspond to the laguna described by Columbus.
Pentachlorophenol Reductive Dechlorination in an Interceptor Trench: Temperature Effects
Authors: Cole Jason D. , Woods Sandra L. , Bricker Timothy R. 
Published: August 2005

AbstractPentachlorophenol‐acclimated methanogenic consortia were incubated at temperatures of 5, 10, 21, and 31° C in physical models of an interceptor trench. Four identical 5.4 cm diameter brass columns packed with a uniform pea gravel were operated with a 2 day hydraulic retention time in a continuous upflow mode. The columns were fed 25 or 50 mg of acetate per liter, 0.32 or 4.0 μM pentachlorophenol, and a dilute vitamin and nutrient mixture. In the columns operated at 31 and 21° C, pentachlorophenol was reductively dechlorinated at the ortho positions to form 2,3,4,5‐tetrachlorophenol and 3,4,5‐trichlorophenol. 3,4,5‐Trichlorophenol was the sole degradation product observed in the effluent. The lag period prior to pentachlorophenol biotransformation increased with decreasing temperature. At 31° C, a lag of 72 hours was observed; at 21° C the lag was 120 hours; and at 10° C the lag was 744 hours. No biodegradation of pentachlorophenol was observed at 5° C within an 888 hour period. Conversion of pentachlorophenol to 3,4,5‐trichlorophenol was complete within the first 7.6 cm of the column at 31 and 21° C. Loss of 90% of the pentachlorophenol was observed over the 30 cm column at 10° C. An interceptor trench inoculated with a temperature‐ and pentachlorophenol‐acclimated methanogenic consortia has the potential to anaerobically biotransform pentachlorophenol at temperatures as low as 10° C.
Investigation of Possible Extra Recharge During Pumping in Nottingham Aquifer
Authors: Jiao Jiu J. 
Published: August 2005

AbstractApproaches to investigate possible recharge during a pumping test period are demonstrated by analyzing the pumping test data from the Nottingham aquifer, UK. The pumping lasted more than 200 days and the data for different observed periods are used to obtain aquifer parameters. If recharge is ignored, estimated transmissivities and storativities change progressively with the observation time. This indicates that a gradually added new source may be involved. Then the observed data in both pumping and recovery periods at one of the pumping sites are matched by the data calculated from the Theis equation. The match is very good except near the end of the recovery period. It shows that the real drawdown recovered more quickly than predicted by the model, indicating that the aquifer obtained extra recharge from other sources. The match between the observation and the model is improved by including a fixed‐head boundary or leakage in the model. The recharge to the aquifer is estimated to be 19% and 34% of the pumpage at the end of pumping, depending on the method used. The real source of the additional recharge is not clear; it could be from the surface water in the unconfined area, the storage of the aquitard, the compaction of the aquitard, or a combination of the three. This requires further hydrogeological investigation.
Environmental Isotope Characteristics of Landfill Leachates and Gases
Authors: Hackley K. C. , Liu C. L. , Coleman D. D. 
Published: August 2005

AbstractThe isotopic characteristics of municipal landfill leachate and gases (carbon dioxide and methane) are unique relative to the aqueous and gaseous media in most other natural geologic environments. The δ13C of the CO2 in landfills is significantly enriched in 13C, with values as high as +20 ‰ reported. The δ13C and δD values of the methane fall within a range of values representative of microbial methane produced primarily by the acetate‐fermentation process. The δD of landfill leachate is strongly enriched in deuterium, by approximately 30 ‰ to nearly 60 ‰ relative to local average precipitation values. This deuterium enrichment is undoubtedly due to the extensive production of microbial methane within the limited reservoir of a landfill. The concentration of the radiogenic isotopes, 14C and 3H, are significantly elevated in both landfill leachate and methane. The 14C values range between approximately 120 and 170 pMC and can be explained by the input of organic material that was affected by the increased 14C content of atmospheric CO2 caused by atmospheric testing of nuclear devices. The tritium measured in leachate, however, is often too high to be explained by previous atmospheric levels and must come from material buried within the landfill. The unique isotopic characteristics observed in landfill leachates and gases provide a very useful technique for confirming whether contamination is from a municipal landfill or some other local source.
Applicability of Slug Interference Tests for Hydraulic Characterization of Unconfined Aquifers: (2) Field Test Examples
Authors: Spane F. A. , Thorne P. D. , Swanson L. C. 
Published: August 2005

AbstractSlug interference testing may be particularly useful for characterizing hydraulic properties of aquifer sites where disposal of contaminated ground water makes pumping tests undesirable. The design, performance, and analysis of slug interference tests for two field test examples are presented. Results were compared with standard constant‐rate pumping tests. The comparison indicates that slug interference tests provide estimates comparable to those obtained from short duration pumping tests for the determination of transmissivity, storativity, and vertical anisotropy.The close agreement in hydraulic property values obtained using the two test methods suggests that slug interference testing, under favorable test conditions (for example, observation well distances ≤ 30 m), can provide representative aquifer characterization results. The quality and extent of test data obtained also indicate the potential use of slug interference testing for three‐dimensional hydrologic characterization investigations, when conducted using multilevel monitoring facilities.
A BEM Code for Ground‐Water Problems in Multizoned Domains with Normal Boundary Flux Discontinuities
Authors: Fidelibus C. , Lenti V. 
Published: August 2005

AbstractA numerical code which utilizes the boundary element method (BEM) for solving steady‐state ground‐water flow problems is illustrated. The paper concentrates on accuracy in studying the situations which are generally considered to involve some mathematical difficulty, such as zoned domains and flux discontinuities. A numerical BEM code is proposed, the main feature of which involves accurately calculating flux discontinuities using a structure particularly flexible in multizoned domains. Two examples are reported, the results of which are comparable with those available in the literature.
Boundary Condition and Soil Attribute Impacts on Anionic Surfactant Mobility in Unsaturated Soil
Authors: Allred Barry , Brown Glenn O. 
Published: August 2005

AbstractSurfactant mobility in unsaturated soil will impact the effectiveness and efficiency of using these compounds for in situ environmental remediation above the water table. For this reason, transient unsaturated column tests were used to study the influence of boundary conditions and soil attributes on anionic surfactant transport. In these tests, aqueous surfactant solutions were injected into the inlet of horizontally mounted soil columns. Two commercial anionic surfactants were used, an alkyl ether sulfate (AES) and a linear alkylbenzene sulfonate (LAS).The overall study was divided into two parts. First, boundary condition effects including injected surfactant solution concentration, initial moisture content, and surfactant application rate were investigated. Increasing the injection solution concentration increased anionic surfactant mobility in the column while changes in the initial soil moisture content and surfactant application rate had no significant impact. Second, the impacts of soil attributes such as texture, dominant exchangeable cation, and resident organic matter were measured. With respect to texture, mobility was found to be greater in a sandy soil as compared with two loamy soils. Both surfactants, especially LAS, were found to be more mobile in a Na+ dominated soil rather than one dominated by Ca−2.The absence of soil organic matter increased LAS mobility.