A Simulation of One Dimensional Contaminant Transport

In this note we present some simulations and some analytical solutions, in closed form, of the advection dispersion equation in one-dimensional domain. These solutions are obtained for not-conservative solutes by considering time-dependent, third type (Robin) boundary condition for first order reaction and linear equilibrium absorption. The Robin boundary condition models a combined production-decay function. The model is useful to describe sources as the contaminant release due to the failure of an underground pipelines or radioactive decay series. The developed analytical model gives rise to analytical solutions not present in the literature. Further, we remark that, for particular values of the rate constants involved in the model, our results furnish values which are in agreement with results present in the literature

Landfill Leachate Production and Gas Generation Numerical Model

Numerous processes occur in landfills which lend themselves to modeling. Many of the processes are mutually interdependent. An unsteady numerical model is developed combining the major processes. The three-dimensional moisture transport equations and boundary conditions are solved using an implicit finite difference scheme. The boundaries are determined through a two-dimensional runoff model for the landfill surface and a one-dimensional leachate liner flow model at the bottom of the landfill. The runoff model accounts for evapotranspiration, runoff, infiltration, and leachate recirculation. Richard\u27s equation is solved for saturated and unsaturated vertical flows and Darcy\u27s Equation is solved for lateral flow between adjacent saturated landfill cells. Results of the moisture flow are used to solve contaminant production and transport equations. Contaminant production uses moisture flow and previous leaching history to generate source terms. The source terms and recirculated contaminants are used to implicitly solve contaminant transport equations which account for advection, diffusion, and dispersion of the contaminant. Landfill temperatures are predicted by solving an energy equation implicitly. Temperatures are combined with moisture content and gas production history to determine gas generation. The model is applied to three Wisconsin lysimeters and a Kentucky landfill to demonstrate the simulation of leachate and contaminant production and transport. Comparison to the HELP water balance model is also done for a Wisconsin lysimeter. The model is also applied to an existing landfill to demonstrate the gas generation portions of the model

Application of PHREEQC on solute transport in groundwater

With increasing groundwater contamination, the study of contaminant transport is becoming more and more important. Since chemical reactions occur simultaneously with contaminant transfer, these two aspects should be coupled in one model. PHREEQC is a simulation software package for modeling chemically reactive transport processes in natural and underground water bodies. PHREEQC was applied to simulate the processes of cation exchange and kinetic redox transformations with 1D groundwater flow. The results show that PHREEQC can successfully simulate complex geochemical reactions coupled with steady water flow. However, for the simulation of multi-dimensional groundwater flow and contaminant transport, it is necessary to couple PHREEQC with other groundwater flow and species transport models

Simulation of solute transport in 3d porous media using random walk particle tracking method

Random walk particle tracking (RWPT) method provides a computationally effective way to characterize solute transport process in porous media. In this work, an object-oriented scientific software platform OpenGeoSys (OGS) was adopted for the simulation and visualization of the complex behavior of particles. Finite element method is used for the calculation of the velocity field which is necessary for the determination of the displacement of the particles through space. The RWPT method has been used in the simulation of the hydraulic process, diffusion and dispersion as it is proved to be well suitedfor such studies. In this work, efforts were taken to search for the solutionto simulate the retardation and decay processe in order to investigate the effects that appear in the contaminant plume evolution. Expressions for the effective coefficients governing the solute transport are derived for retardation model, based on a two-rate sorption-desorption approach. The RWPT model was first verified by a benchmark test of solute transport in a one-dimensional homogeneous media to analysis the accuracy of the method with comparison to the analytical solution. The analysis was the next ended to applications witht hree-dimensional homogeneous aquifer. This method can be used as a tool to elicit and discern the detailed structure of evolving contaminant plumes

A Web-Based High Performance Simulation System for Transport and Retention of Dissolved Contaminants in Soils

Groundwater, the major source of human drinking water, is susceptible to contamination from industrial and agricultural activities. This research develops a web-based simulation system of remote high performance computing model for contaminant transport and retention in soils. A three-dimensional advection-dispersion-reaction MRTM model, based on previous experimental and theoretical studies, is proposed to analyze the transport and retention of chemical contaminants in groundwater flowing through soils. Since three-dimensional experiments are difficult to implement and verify, this simulation system provides scientists an alternative to trace the contaminant movement in soils outside laboratories. The alternating direction implicit (ADI) algorithm is used in this study to reduce the computational complexity. Although the ADI method is very efficient to solve the governing advection-dispersionsorption equations in the three-dimensional MRTM model, achieving higher order accuracy with different boundary conditions remains a difficult research topic. This research develops a new numerical scheme to achieve second-order accuracy with the Neumann-type boundary conditions. Furthermore, parallel computing is used to achieve high performance using powerful multiprocessor computers. A web-based simulation system provides users a friendly interface for remote access to the system through Internet browsers, so as to utilize remote computing resources transparently and efficiently. In the client-side computing one-dimensional MRTM simulation system, the legacy code written in FORTRAN and C are wrapped and reused with Java code, which provides the web-based graphic user interface (GUI). The server-side computing three-dimensional MRTM simulation system integrates the remote high performance computing resources, database management systems, online visualization functionality, and web-based userriendly GUIs. Given access to the Internet, users can execute and manage remote high performance computing jobs anywhere anytime, even through a web browser from a laptop personal computer

Development of a Combined Quantity and Quality Model for Optimal Management of Unsteady Groundwater Flow Fields

Presented are alternative techniques for including conservative solute transport within computer models for optimizing groundwater extraction rates. Unsteady two-dimensional flow and dispersed conservative solute transport are assumed. Comparisons are made of the practicality of including modified forms of implicit and explicit finite difference solute transport equations within optimization models. These equations can be calibrated and subsequently used within a MODCON procedure. The MODCON modelling procedure consists of an integrated series of five optimization or simulation modules. The procedure is applicable for either an entire aquifer system or for a subsystem of a larger system. The first module, A, computes physically feasible recharge rates across the boundaries of the modelled subsystem. Module B computes optimal extraction rates without considering groundwater quality. Module C uses method of characteristics simulation to compute solute transport that would result from implementing the pumping strategy of model B. Module D uses linear goal programming and nonlinear solute transport equations to calibrate linear coefficients. It attempts to duplicate the solute transport predicted by module C. Calibration is performed because coarsely discretized implicit or explicit solute transport equations may not be as accurate as the method of characteristics. Module E includes appropriate calibrated equations of module D as well as the flow equations of module B. It computes an optimal pumping (extraction or recharge) strategy that can satisfy future groundwater contaminant concentration criteria. Testing of the validity of this optimal pumping strategy is subsequently accomplished using module C. If necessary, one may cycle through modules C, D and E until convergence is obtained--until concentrations resulting from implementing the strategy of E are demonstrated to be acceptable

Numerical investigation of airborne contaminant transport under different vortex structures in the aircraft cabin.

Airborne contaminants such as pathogens, odors and CO2 released from an individual passenger could spread via air flow in an aircraft cabin and make other passengers unhealthy and uncomfortable. In this study, we introduced the airflow vortex structure to analyze how airflow patterns affected contaminant transport in an aircraft cabin. Experimental data regarding airflow patterns were used to validate a computational fluid dynamics (CFD) model. Using the validated CFD model, we investigated the effects of the airflow vortex structure on contaminant transmission based on quantitative analysis. It was found that the contaminant source located in a vorticity-dominated region was more likely to be "locked" in the vortex, resulting in higher 62% higher average concentration and 14% longer residual time than that when the source was on a deformation dominated location. The contaminant concentrations also differed between the front and rear parts of the cabin because of different airflow structures. Contaminant released close to the heated manikin face was likely to be transported backward according to its distribution mean position. Based on these results, the air flow patterns inside aircraft cabins can potentially be improved to better control the spread of airborne contaminant

Modelling and simulation framework for reactive transport of organic contaminants in bed-sediments using a pure java object - oriented paradigm

Numerical modelling and simulation of organic contaminant reactive transport in the environment is being increasingly relied upon for a wide range of tasks associated with risk-based decision-making, such as prediction of contaminant profiles, optimisation of remediation methods, and monitoring of changes resulting from an implemented remediation scheme. The lack of integration of multiple mechanistic models to a single modelling framework, however, has prevented the field of reactive transport modelling in bed-sediments from developing a cohesive understanding of contaminant fate and behaviour in the aquatic sediment environment. This paper will investigate the problems involved in the model integration process, discuss modelling and software development approaches, and present preliminary results from use of CORETRANS, a predictive modelling framework that simulates 1-dimensional organic contaminant reaction and transport in bed-sediments

A 3-dimensional finite element method for groundwater flow and containment transport

A code was written to model groundwater flow and to solve for contaminant transport in variably saturated porous media using the Finite element method. The numerical code was written in FORTRAN 77. The GWGRID program was used for mesh generation. This numerical model was applied to two nuclear waste sites; Two test cases were run. The first one was the Savannah River Site, located in Aiken, South Carolina (SRS). The SRS has been storing radioactive waste material for several decades. Numerous studies as well as field data for the properties of the surrounding soil and contaminant presence have been conducted. Results of a two dimensional case were compared with the three dimensional case for a period of fifteen years; The second test case was the Yucca Mountain Repository Site (YMP), which is being evaluated as a future site for storing radioactive nuclear-waste. Results from the 3-D simulation were compared to results from a two-dimensional model. This simulation was run for a period of ten thousand years; The purpose for running the 3-D simulation was to get more realistic results than the 2-D calculations. The simulations were mainly run on the Convex and the Cray computer. The results seem to be fairly accurate as compared to the work done at the sites