Abstract

A vadose zone leaching, saturated zone mixing, and groundwater flow (VG) model was developed as a "user friendly" model with extensive use of Graphic User Interface and the capability of simulating vertical heterogeneity aquifer. A 1-D finite difference scheme was employed for solving the leaching equation in a vertically heterogeneous vadose zone. The transport processes, including liquid-phase advection, liquid- and vapor-phase dispersion, sorption, and decay of contaminant, were taken into account. The transport processes in all the phases were combined together in one equation under the assumption of the instantaneous linear equilibrium partitioning relationships. This not only provided more consistent formation, but also was computationally more efficient since only one differential equation needed to be solved. The mass-balance principle was used for the mixing calculation within the top portion of the aquifer at the bottom of vadose zone. A 2-D finite difference method was employed for developing a 2-D heterogeneous groundwater flow sub-model. This sub-model provides determination of the contaminant track in the heterogeneous saturated zone, and evaluation of the natural rate of groundwater flow and the risk of contaminant. Soil column tests were performed to test the validity of the model. Three different soil sample sizes of Ottawa quartz sand and 480 ppm saline water as groundwater contamination were used to be validated successfully in a lab steady state soil column study. The important input parameters of soil properties in these simulations were effective porosity, water filled porosity, and bulk density. In the field study at Wood River Junction, RI, the developed model demonstrated its useful performance for evaluating a regional aquifer contaminant site by a good match between simulated data and historical data.

Acknowledgments     

This dissertation is the product of my time and efforts put in to complete my research work at University of Rhode Island. The journey of my academic life at University of Rhode Island contributed significantly to grow my knowledge in environmental engineering. I would like to thank all faculty members that I encountered during this long journey. A special word of thanks is extended to Professor Daniel Wayne Urish for serving as a major professor and his patient reviewing and re-reviewing of the text as well as for his personal advice and constant willingness to help.

I would also like to express my gratitude for the advice and insights provided by committee members Professors Leon T. Thiem and William R. Wright. I thank Dr. Raymond M. Wright for helping me understand advanced hydraulics and modeling knowledge in his lectures.

I must owe my greatest emotional debt to my parents. Especially, my father has encouraged me to complete my studying successfully. My parents have been willing to sacrifice every aspect of their life to look after my brothers, my sisters, and myself. Without the support that my parents have given to me, it would have been impossible to reach this stage.

I thank Dr. Sam B. Lee of Dynamac Co. for his technical advice and for providing the opportunity to work on the VLEACHSM project for heterogeneity of vadose zone leaching problem, which started my study on the subject of heterogeneous underground aquifer system.

I would like to thank my son Michael for all his valuable support from the bottom of my heart. Especially, I thank my wife Youngsin for putting up with me for so long and for loving me so much. Finally, I acknowledge that no feat, great or small, is possible without the grace of God.

Preface

This research is designed to simulate as a whole the underground aquifer system, including vadose zone and saturated zone. It emphasizes vadose zone contaminant transport and its fate in the saturated zone.

The first and second parts (Vadose zone leaching and saturated zone mixing: VLEACHSM 2.0) of the model in this dissertation were developed primarily as a part for a project of the U.S. Environmental Protection Agency Research Program (EPA Contract 68-C4-0031) grant to Dynamac Co. (SI-1-50).

More specifically, this sub-model (VLEACHSM 2.0) had the intention of addressing the following three issues: (1) to develop the program to incorporate vertical heterogeneity of vadose zone, (2) to develop the program capability to handle simulation results graphically, and (3) to develop a Graphic User Interface (GUI) for user friendliness.

Validation of the model evaluates the performance of the model by comparing the simulation results with the results of the soil lab-column studies and also a field application. A sensitivity analysis evaluates the impact of a parameter of longitudinal dispersivity on soil contaminant level and loading to groundwater.

This study is based on the premise the quantitative physical basis of hydrology which is the scientific approach to understanding observed phenomena. The text presents a basic coverage of physical principles and how these allow one to grasp the essential elements of hydrological processes.