Final Report

CONTAMINANT TRANSPORT

IN

COASTAL AQUIFERS

By

Yuan Ding Yong Peng

Department of Civil and Environmental Engineering

New Jersey Institute of Technology Newark, NJ

Submitted To

New Jersey Department of Environmental Protection Division of Science, Research and Technology

Trenton, New Jersey

April 2009

Contract Number SR02-035

ii

Research Team

Department of Civil and Environmental Engineering New Jersey Institute of Technology

Paul C. Chan, Ph.D., Professor Yuan Ding, Ph.D., Associate Professor Robert Dresnack, Ph.D., Professor John R. Schuring, Ph.D., Professor Yong Peng, Ph.D.

iii

ABSTRACT

CONTAMINANT TRANSPORT IN COASTAL AQUIFERS

Coastal aquifers are distinguished from other aquifers because of tidal effects which

cause complicated groundwater flow and contaminant transport phenomena in regions

immediately adjacent to the coast. This study is designed to address the significance of

tidal influence on contaminant transport by focusing on one-dimensional homogeneous

coastal aquifers.

This study formulates a conceptual model and corresponding flow and transport

equations, analyzes coastal boundary conditions, solves numerically the transport

equation, and uses experiments to verify the numerical results.

Results of the numerical and experimental studies conclude that tides can have a

significant impact on contaminant transport, especially when under unconfined aquifer

conditions, subject to moderate to high tidal amplitude, with low groundwater flow

velocity in the aquifer, and within areas adjacent to the coastal boundary. Quantitatively,

under these favorable conditions, contaminant discharge can be enhanced by tides by a

factor of two or three during the early stages of discharge, and the enhanced discharge

can still be substantial during later stages by 30 to 50 percent. When the groundwater

flow is close to stagnant, as demonstrated in the case study, the tidal impact is most

apparent, resulting in significant discharge tens of years ahead of the case without tides.

iv

TABLE OF CONTENTS

Chapter Page

1 INTRODUCTION .................................................................................................. 1

1.1 Contamination Problem in Coastal Waters .................................................... 1

1.2 Limitations in Previous Studies...................................................................... 3

1.3 Objective and Scope of Study ........................................................................ 4

2 LITERATURE REVIEW ....................................................................................... 6

2.1 Groundwater Dynamics in Coastal Aquifers.................................................. 6

2.2 Contaminant Transport in Coastal Aquifers................................................... 13

2.3 Study Approaches........................................................................................... 18

3 PROBLEM FORMULATION AND SOLUTION................................................. 22

3.1 Conceptual Model of the Research Problem.................................................. 22

3.2 Flow and Transport Equations........................................................................ 25

3.2.1 Groundwater Flow Equation................................................................. 25

3.2.2 Contaminant Transport Equation.......................................................... 26

3.2.3 Tides...................................................................................................... 27

3.2.4 Initial Condition.................................................................................... 29

3.2.5 Influent Boundary Condition ................................................................ 29

3.2.6 Contaminant Input ................................................................................ 31

3.3 Coastal Boundary Conditions and Baseline Selection ................................... 32

3.3.1 Coastal Boundary Conditions ............................................................... 32

3.3.2 Baseline Selection................................................................................. 34

3.3.3 Solutions to the Baseline Problem ........................................................ 35

v

TABLE OF CONTENTS (Continued)

Chapter Page

3.3.4 Discussion and Conclusion to Baseline Selection ................................ 56

3.4 Numerical Solution......................................................................................... 58

3.4.1 Development of a Finite Difference Solution....................................... 59

3.4.2 Accuracy and Convergence of Numerical Solution.............................. 65

4 EXPERIMENTAL STUDY.................................................................................... 77

4.1 Experimental Setup ........................................................................................ 77

4.1.1 Experimental Scale ............................................................................... 77

4.1.2 Experimental Facility............................................................................ 80

4.1.3 Porous Medium..................................................................................... 83

4.1.4 Experiment Equipments and Procedures .............................................. 84

4.2 Experimental Results...................................................................................... 87

4.2.1 Experiment Consistency Tests.............................................................. 89

4.2.2 Experimental Study of Boundary Conditions ....................................... 109

4.2.3 Results of Unconfined-Condition Experiments .................................... 118

4.2.4 Results of Confined-Condition Experiments ........................................ 137

4.3 Summary of Experimental Study ................................................................... 168

4.3.1 Summary of Experimental Results ....................................................... 168

4.3.2 Application of Experimental Results .................................................... 170

5 NUMERICAL STUDY .......................................................................................... 171

5.1 Tide Induced Groundwater Table Fluctuations.............................................. 171

5.2 Tide Induced Contaminant Transport Fluctuations........................................ 174

vi

TABLE OF CONTENTS (Continued)

Chapter Page

5.3 Tidal Influence under Unconfined Condition................................................. 180

5.3.1 Effect by Tidal Amplitude .................................................................... 180

5.3.2 Tidal Effect with Different Flow Velocity............................................ 186

5.3.3 Tidal Effect with Different Retardation................................................ 201

5.3.4 Tidal Effect with Different Decay ........................................................ 212

5.3.5 Tidal Effect with Different Aquifer Dimension.................................... 222

5.4 Tidal Influence under Confined Condition..................................................... 233

5.5 Case Study ...................................................................................................... 258

5.6 Summary of Numerical Study ........................................................................ 265

6 DISCUSSION AND CONCLUSIONS .................................................................. 270

6.1 Summary and Discussion ............................................................................... 270

6.2 Conclusions .................................................................................................... 271

APPENDIX A DERIVATION OF THE ANALYTICAL SOLUTION...................... 274

APPENDIX B FIELD APPLICATION OF NUMERICAL SIMULATIONS............ 279

REFERENCES ............................................................................................................. 287

vii

LIST OF TABLES

Table Page

3.1 Analytical Solutions of the Baseline Problem .................................................. 36 3.2 Parameter Values Used in Boundary Condition Study..................................... 39 3.3 Convergence Test for the Case without Tides (T=1.5)..................................... 69 3.4 Convergence Test for the Case with Tides (T=1.5).......................................... 70 4.1 Aquifer Parameter Values Considered in Prototype and Model....................... 80 4.2 Cases Considered in the Unconfined-Condition Experiments.......................... 88 4.3 Cases Considered in the Confined-Condition Experiments.............................. 88 4.4 Calibration of the Numerical Model Based on Case B20X...........................