Questo sito utilizza cookie di terze parti per inviarti pubblicità in linea con le tue preferenze. Se vuoi saperne di più clicca QUI 
Chiudendo questo banner, scorrendo questa pagina, cliccando su un link o proseguendo la navigazione in altra maniera, acconsenti all'uso dei cookie. OK

A numerical model for simulating the transport of reactive groundwater contaminants

A contaminant discharged into an aquifer can have a significant impact on the quality of the subsurface water resources. Transported by the groundwater, the contaminant can pollute withdrawal sites at pumping wells, and may reappear at the surface, emerging from springs and seepage faces. Due to the relative inaccessibility of the groundwater and the complexity of the processes involved, it is difficult to predict the extent and impact of the contamination using solely experimental techniques. Numerical modelling has been found to be one of the most effective techniques for predicting the effects, extent and impact of groundwater contamination, remediation and protection of groundwater resources. In this study, a numerical model for simulating the flow and transport of reactive groundwater contaminants has been developed. The flow properties were derived from the Darcy and mass conservation equations that gave velocity distributions required by the contaminant transport equations to determine the spatial and temporal variation of concentration. The governing equations were discretized by integrated finite differences method. The transport equation was solved by operator-splitting technique. The kinetic reaction part was implemented by the linear integrated method. The model was validated using analytical solutions available in literature for uniform velocity cases. The various modules for solving the governing equations were implemented in the object-oriented computer codes. A comparison between model results and analytical solutions show that the numerical solution trails the analytical solution with increasing time. This is attributed to the propagation of the truncation error associated with the numerical method used. Experiments on hydrodynamic control and varying aquifer properties have been done to further show the model’s usefulness in water quality management. From the hydrodynamic experiment, it was established that it is possible to effectively use a pump-treat and inject strategy to protect a production well from an up-gradient source. Another experiment conducted using the model aimed at predicting the rate of contaminant transport through different aquifer materials. Aquifer materials were characterized by using the values of their hydraulic conductivities obtained from literature. Breakthrough curves were obtained for both continuous and accidental pollution cases. It was found that the rate of contaminant transport process increases with increase in the value of hydraulic conductivity. The numerical model developed will aid in understanding the subsurface flow and transport processes and may also have pedagogic uses especially in the field of groundwater hydrology and engineering.

Mostra/Nascondi contenuto.
1 Chapter 1 INTRODUCTION 1.1 Background to the study A contaminant discharged into an aquifer can have a significant impact on the quality of the subsurface water resources. Transported by the groundwater, the contaminant can pollute withdrawal sites at pumping wells, and may reappear at the surface, emerging from springs and seepage faces. Moreover, the pollutant can interact with the fluid and solid phases of the porous media through a wide variety of processes, including chemical diffusion, mechanical dispersion, advection, chemical reaction, sorption, decay and degradation (Putti et al., 1994; Masters, 1991). Due to the complexity of these processes, it is difficult to predict the extent and impact of the contamination using solely experimental techniques. In addition, due to the relative inaccessibility of aquifers, slow pace of subsurface processes and high expenses involved in performing actual groundwater experiments, models are developed and used to study groundwater resources. Further, numerical modelling has been found to be one of the most effective techniques for predicting effects of groundwater contamination, remediation and protection of groundwater resources. (EPA, 2004; Jorgensen, 1991; Kinzelbach et al., 2002) Contamination of the groundwater can occur from point sources or non-point sources, which implies that there is no single universal method of controlling groundwater pollution. Further still, the contaminants can be organics, trace metals, or radionuclides. A full understanding of the fate and transport processes of these contaminants is complicated by numerous factors such as heterogeneity and anisotropy, scale of

International thesis/dissertation

Autore: Joshua Sangoro Contatta »

Composta da 133 pagine.

 

Questa tesi ha raggiunto 63 click dal 13/10/2009.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.