Contaminant-transport models ground water

The contaminant transport model, Eq. (28), was solved using the backwards in time alternating direction implicit (ADI) finite difference scheme subject to a zero dispersive flux boundary condition applied to all outer boundaries of the numerical domain with the exception of the NAPL-water interface where concentrations were kept constant at the 1,1,2-TCA solubility limit Cs. The ground-water model, Eq. (31), was solved using an implicit finite difference scheme subject to constant head boundaries on the left and right of the numerical domain, and no-flux boundary conditions for the top and bottom boundaries, corresponding to the confining layer and impermeable bedrock, respectively, as... 

The approach is very commonly used in transport models because mathematically it is relatively easy to incorporate. Goyette and Lewis [28] highlighted the utihty of values in screening level ground water contaminant transport models of inorganic ions with the caution that experimental conditions such as pH, electrolyte composition and soil type are similar to those being modeled. Viotti et al. [29] used values to model phenol transport in an unsaturated soil. Schroeder and Aziz [30] used this approach to account for PCBs sorption into dredged materials. Buczko et al. [31] used the Freundlich approach to model chromium transport in unsaturated zone. 

Falta, R.W., Pruess, K. and Chestnut, D.A., Modeling advective contaminant transport during soil vapor extraction, Ground Water, 31, 1011-1020, 1993. 

To understand the behavior of the movement of the contaminant in ground-water, people solve Eq. (1) forward in time. In solving this equation forward in time, one assumes that the plume is originated from somewhere and will travel through the porous media due to advection and dispersion. The conventional procedure to solve Eq. (1) is to use finite difference or finite element methods. For simple cases, closed-form solutions exist. Quantitative descriptions of the processes forward in time are well understood. Multidimensional models of these processes have been used successfully in practice [50]. Numerical solute transport models were first developed about 25 years ago. When properly applied, these models can provide useful information about transport processes and can assist in the design of remedial programs. 

Finding the source location and the time history of the solute in ground-water can be categorized as a problem of time inversion. This means that we have to solve the governing equations backward in time. Modeling contaminant transport using reverse time is an ill-posed problem since the process, being dispersive is irreversible. Because of this ill-posedness, the problems have discontinuous dependence on data and are sensitive to the errors in data. 

Brown J. G., Bassett R. L., and Glynn P. D. (1998) Analysis and simulation of reactive transport of metal contaminants in ground water in Pinal Creek Basin, Arizona. In Special Issue—Reactive Transport Modeling of Natural Systems (eds. C. I. Steefel and P. van Cappellen). J. Hydrol. 209, 225 - 250. 

The composition of pore waters from contaminated cores 1 and 2 were used to initialize the model (Table 2). Concentrations represent leachate collected from the initial half pore volume of each core. Eluent specified in the transport simulations had the composition of uncontaminated ground water in Table 2. Reactions proposed to describe concentration changes for selected constituents within the cores are based on comparisons between eluent and leachate chemistry and analysis of selected constituents in the core samples. Equilibrium constants and kinetic rates for the reactions were adjusted to give the best fit to leachate concentrations from core 1. The same reactions, equilibrium constants, and kinetic rates were then tested by modeling the concentrations of constituents in leachate from core 2. This geochemical model will be used in the future to simulate evolution of contaminated ground water associated with the Area 4 landfill at the aquifer scale. 

Observations The mass transport models can be used to predict best-case and worst-case scenarios of contaminant transport, but in most cases are not exact predictive tools. Both mass transfer and mass transport models are useful to help establish possible contaminant cleanup strategies and, more generally, to help understand the processes that affect the chemical evolution of ground-waters. 

A major advantage to models such as PRZM or PESTANS is that they are transportable they can simulate a variety of situations with simple changes in weather input and parameters. More Importantly, however, is the fact that in most situations, 90% or more of applied pesticide would have runoff, volatilized, been taken up by the plant, or otherwise decayed before any of it leaches below the root zone. It makes sense, therefore, to develop the capability to predict the fate of pesticides in the root zone, and hence determine the potential for pesticides to contaminate ground water. 

This is the proceedings from a USA/CIS conference organized by the American Institute of Hydrology. Topics include evaluation techniques lor hydrogeologic conditions and extent of ground water contamination, chemical late and transport In die vadose zone, flow modeling, and species migration. 

BIOPLUME II - Computer Model of Two-Dimensional Contaminant Transport Under the Influence of Oxygen Limited Biodegradation in Ground Water (User s Manual Version 1.0 Preprocessor Source Code Version 1.0 Source Code Version 1.0)... 

Zhu, C., Hu, F. Q., and Burden, D. S., 2001a, Multi-component reactive transport modeling of natural attenuation of an acid ground water plume at a uranium mill tailings site. J. Contaminant Hydrology, v. 52, pp. 85-108. 

Pepper, D. W., and D. E. Stephenson. 1995. An Adaptive Finite-Element Model for Calculating Subsurface Transport of Contaminant, Ground Water, vol. 33, no. 3, pp. 486-496. 

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