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Improved Finite Analytic Methods for Solving Advection-dominated Transport Equation in Highly Variable Velocity FieldCuifeng, Wei 28 April 1995 (has links)
Solute transport studies frequently rely on numerical solutions of the classical advection-diffusion equation. Unfortunately, solutions obtained with traditional finite difference and finite element techniques typically exhibit excessive numerical diffusion or spurious oscillation when advection dominates, especially when velocity field is highly variable. One recently developed technique, the finite analytic method, offers an attractive alternative. Finite analytic methods utilize local analytic solutions in discrete elements to obtain the algebraic representations of the governing partial differential equations, thus eliminating the truncation error in the finite difference and the use of approximating functions in the finite element method. The finite analytic solutions have been shown to be stable and numerically robust for advection-dominated transport in heterogeneous velocity fields. However, the existing finite analytic methods for solute transport in multiple dimensions have the following disadvantages. First, the method is computationally inefficient when applied to heterogeneous media due to the complexity of the formulation. Second, the evaluation of finite analytic coefficients is when the Peclet number is large. Third, the method introduces significant numerical diffusion due to inadequate temporal approximation when applied to transient problems. This thesis develops improved finite analytic methods for two-dimensional steady as well as unsteady solute transports in steady velocity fields. For steady transport, the new method exploits the advantages of the existing finite analytic and finite difference methods. The analytically difficult diffusion terms are approximated by finite difference and numerically difficult advection and reaction terms are treated analytically in a local element in deriving the numerical schemes. The new finite analytic method is extended to unsteady transport through application of Laplace transformation. Laplace transformation converts the transient equation to a steady-state expression that can be solved with the steady version of the improved finite analytic method. Numerical inversion of the transformed variables is used to recover solute concentration in the physical space-time domain. The effectiveness and accuracy of the new finite analytic method is demonstrated through stringent test examples of two dimensional steady-state transport in highly variable velocity fields. The results clearly demonstrated that the improved finite analytic methods are efficient, robust and accurate.
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Effects of water table management on water quality and strip cropped corn-soybean yieldsMejía, Manuel. January 1997 (has links)
No description available.
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Groundwater contamination by arsenic in Bangladesh : causes, consequences and solutionsUddin, G.M. Saleh. January 2001 (has links) (PDF)
Bibliography: leaves 106-114.
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Kinetic modelling of Fenton-mediated oxidation: reaction mechanism, applications,and optimization.Duesterberg, Christopher Ku, Civil & Environmental Engineering, Faculty of Engineering, UNSW January 2007 (has links)
The ever-increasing detection of harmful organic and inorganic compounds in habitable areas throughout the world has led to mounting research into applications and techniques for the treatment of contaminated soils, surface and groundwaters, and chemical and industrial wastewaters. Chemical oxidation technologies, in particular Fenton-based remediation systems, have exhibited considerable potential for the effective treatment and remediation of such contaminated waters and soils. The use of Fenton-based oxidation systems for the treatment of contaminated waters and wastewaters warrants the development of kinetic models capable of accurately simulating system behaviour. In this thesis, the kinetics of Fenton-mediated oxidation systems and kinetic models based on its governing reaction mechanism are investigated in order to highlight those parameters and conditions that effect Fenton chemistry and oxidation performance, and to demonstrate the application of such kinetic models to design and improve treatment systems. Experimental and simulated data describing the oxidation of formic acid by Fenton's reagent at low pH (3 to 4) and under a variety of initial conditions, operating regimes, and solution environments supports a proposed reaction mechanism that nominates the hydroxyl radical (OH) as the active oxidizing intermediate in Fenton-based oxidation systems. Laboratory experiments demonstrate that formic acid oxidation is inhibited in the presence of oxygen, and model simulations of these systems reveals that such behaviour is due to the effect organic radical intermediates and/or by-products have in assisting or hindering the redox cycling of the catalytic iron species. The critical role that iron redox cycling plays in affecting oxidation performance is further highlighted by experimental and simulated studies at alternate pHs and using different target organics, including those that react directly with iron in a redox capacity. Experiments at pH 4 reveal an increase in the redox cycling of iron and improved oxidation performance compared to pH 3 as the higher pH favours the superoxide radical, a stronger reductant than the hydroperoxyl radical that predominates at pH 3. Other laboratory and modelling studies on the Fenton-mediated oxidation of certain aromatic compounds highlight the manner in which quinone and quinone-like compounds, being added directly or generated as oxidation by-products, can improve oxidation performance via redox reactions with iron. Further simulations reveal the type of practical design and operating information kinetic models can provide for treatment processes, though it is noted an appropriate understanding of the oxidation mechanism of the target species is necessary for the accurate application of the model.
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A catchment approach to managing agricultural pesticides in the environment : a case study with the herbicide atrazinePopov, Vladislav H., University of Western Sydney, College of Science, Technology and Environment, School of Environment and Agriculture January 2005 (has links)
Surface water quality of the Liverpool Plains (NSW), a series of floodplains comprising the floodplain of the Mooki River, is poor despite the introduction of conservation tillage that has reduced soil erosion and, with it, the transport of sediment, nutrients and chemicals to streams.The aim of this thesis was to provide a basis for recommending the possible wider use of biofilters, by determining their effectiveness in reducing pollutant (mainly atrazine) transport at multiple scales in the Liverpool Plains, quantifying the importance of relevant processes, including the capacity of soil biofilters to degrade the retained pollutants, and evaluating the effect of pollutants on the biofilter vegetation. These objectives were explored in two sub-catchments within the Liverpool Plains, namely Big Jacks Creek and the Blackville.Soils are predominantly vertosols that crack deeply on drying, resulting in initially high infiltration rates on wetting and high water holding capacity. Field monitoring revealed that biofilters such as grassed waterways, natural grasslands or vegetated filter strips (VFS) positioned at multiple catchment scales can significantly reduce pollutant concentrations in runoff. The use of biofilters is discussed, along with other best management practices that will be needed to manage pesticide loads both at source and in the transport pathway. / Doctor of Philosophy (PhD)
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Radon-222 as an in situ partitioning tracer for quantifying nonaqueous phase liquid (NAPL) saturations in the subsurfaceDavis, Brian M. 30 January 2003 (has links)
This study investigated the use of radon-222 as an in situ partitioning tracer for
quantifying nonaqueous phase liquid (NAPL) saturations in the subsurface.
Laboratory physical aquifer models (PAMs), field experiments, and numerical
simulations were used to investigate radon partitioning in static (no-flow) experiments
and in single-well, 'push-pull' tests conducted in non-contaminated and NAPL-contaminated
aquifers. Laboratory push-pull tests in a wedge-shaped PAM and field
push-pull tests in a NAPL-contaminated aquifer showed that radon was retarded in the
presence of NAPL, with retardation manifested in increased dispersion of radon
extraction phase breakthrough curves (BTCs). An approximate analytical solution to
the governing transport equation and numerical simulations provided estimates of the
radon retardation factor (R), which was used to calculate NAPL saturations (S[subscripts n]).
Laboratory static and push-pull tests were conducted in a large-scale
rectangular PAM before and after NAPL contamination, and after alcohol cosolvent
flushing and pump-and-treat remediation. Radon concentrations in static tests were
decreased due to partitioning after NAPL contamination and increased after
remediation. Push-pull tests showed increased radon retardation after NAPL
contamination; radon retardation generally decreased after remediation. Numerical
simulations modeling radon as an injected or ex situ partitioning tracer were used to
estimate retardation factors and resulted in overestimations of the likely S[subscripts n] in the
PAM. Radon partitioning was sensitive to changes in S[subscripts n] in both static and push-pull
tests. However, the test results were sensitive to test location, sample size, test design,
and heterogeneity in S[subscripts n] distribution.
Numerical simulations of hypothetical push-pull tests conducted in a NAPL-contaminated
aquifer were used to investigate the influence of homogeneous and
heterogeneous S[subscripts n] distributions and initial radon concentrations on radon BTCs and
resulting S[subscripts n] calculations. Both of these factors were found to affect radon BTC
behavior. A revised method of plotting and interpreting radon BTCs combined with
numerical simulations modeling radon as an in situ partitioning tracer (incorporating
initial radon concentrations into the model as a function of S[subscripts n]) were used to re-analyze
laboratory and field push-pull test BTCs. This method reduced the overestimation of
calculated S[subscripts n] values from laboratory tests. / Graduation date: 2003
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Abiotic and biological transformation of TBOS and TKEBS, and their role in the biological transformation of TCE and c-DCEVancheeswaran, Sanjay 10 June 1998 (has links)
At Site-300, Lawrence Livermore National Laboratory (LLNL), CA,
trichloroethene (TCE) is present along with tetraalkoxysilanes such as tetrabutoxysilane
(TBOS) and tetrakis(2-ethylbutoxy) silane (TKEBS), as subsurface contaminants.
Intrinsic transformation of TCE to cis-dichloroethene (c-DCE) was observed in the
groundwater at locations co-contaminated with TBOS or TKEBS. Attenuation of TBOS
and TKEBS by abiotic hydrolysis and biological mineralization and the role played by
TBOS and TKEBS in driving the TCE transformation were investigated.
Under abiotic conditions, TBOS and TKEBS were found to slowly hydrolyze to
1-butanol and 2-ethylbutanol, respectively, and silicic acid. Hydrogen was produced as
a result of the fermentation of the alcohols to the corresponding acids, and then
subsequently to carbon dioxide. The hydrogen likely served as the electron donor for the
microbially-mediated reductive dechlorination of TCE.
The rates of hydrolysis of TBOS and TKEBS were determined and typical rates
at pH 7, 30��C and 28 ��M initial concentration, were 0.32 and 0.048 ��/day,
respectively. The TBOS hydrolysis reaction was observed to be acid and base catalyzed
and independent of temperature from 15 to 30��C. All hydrolysis experiments were
conducted at concentrations above the solubility limit of TBOS and TKEBS and the rate of hydrolysis increased with concentration of TBOS or TKEBS. An aerobic microbial culture from the local wastewater treatment plant that could grow and mineralize the alkoxysilanes was enriched. The enriched culture rapidly hydrolyzed TBOS and TKEBS and grew on the hydrolysis products. The microorganisms grown on TBOS cometabolized TCE and c-DCE. TCE and c-DCE degradation was inhibited by acetylene indicating the stimulation of a monooxygenase enzyme. Acetylene did not inhibit the hydrolysis of TBOS. / Graduation date: 1999
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Simulating the effects of a capillary barrier using the two-dimensional variably saturated flow model SWMS-2D/HYDRUS-2DHeiberger, Thilo Stefan 20 May 1996 (has links)
Graduation date: 1997
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Monitoring potential groundwater contamination due to agricultural production in Lane County, OregonGatchell, Lance O. 06 June 1996 (has links)
Graduation date: 1997
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Assessment of variability and monitoring methods for leaching under cover crop managementHess, Mario 16 May 1995 (has links)
The contamination of ground water resources represents a serious
problem and a prominent threat to the health of our society. This study
focuses on the leaching of inorganic anions as a function of agricultural
practices under natural field conditions. In order to enhance the
understanding of such leaching processes, this thesis evaluates the spatial
variability of the leaching characteristics of a site, the factors controlling
percolation, and the use of a cereal rye cover crop to reduce nitrate leaching.
Thirty-two Passive Capillary Wick Samplers (PCAPS) and 32 suction
cups were installed at a depth of 120 cm under row crop produced in a
Woodburn Variant loam (fine-loamy mixed mesic Aquultic Argixeroll).
Significant correlation for the water flux was seen at the 2.0 m distance,
beyond which values were uncorrelated. No spatial correlation was seen in
hydrodynamic dispersion coefficients. Percolation was independent of field saturated
hydraulic conductivity, while the quantity of incident water was
strongly correlated with percolation. The occurrence of preferential flow
affected the leaching process as documented by solute breakthrough ahead of
the main solute peak. Rates of nitrogen fertilizer application were
proportional to observed nitrate leaching losses. The cover crop significantly
reduced the amount of nitrate leaching at all N fertilizer application rates. At
the recommended rate, nitrate-N concentrations were lowered on average
from 22.2 to 9.9 mg/l; cumulative N mass losses were cut by 62% due to plant
uptake by the cover crop. The study demonstrated the importance of
conducting long-term field experiments under natural conditions to
accurately assess leaching processes. / Graduation date: 1996
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