Assessing recharge mechanisms of the Pampa del Tamarugal Aquifer in northern Chile's Atacama Desert

ASSESSING GROUNDWATER RECHARGE MECHANISMS IN THE PAMPA DEL TAMARUGAL BASIN OF NORTHERN CHILE’S ATACAMA DESERT Richard Scott Jayne, M.S. Department of Geology and Environmental Sciences Northern Illinois University, 2015 Ryan M. Pollyea, Director Northern Chile’s Atacama Desert is one of the driest inhabited regions on the planet. The Pampa del Tamarugal Basin is located within the Atacama Desert and is home to ~300,000 people, yet this region receives little to no rain (<5 mm/yr). However, despite the lack of rain, there is a large source of fresh water in the Pampa del Tamarugal Aquifer (PTA). The PTA is heavily relied upon for municipal, agriculture, and industrial uses. The source of water for the PTA is widely accepted to originate in the high Andes to the east, but the magnitude and mechanism for this recharge remains poorly understood. This study utilizes a 2-D numerical model that takes into account the complex geology and geothermal gradient in this region to further understand regional scale fluid flow within the Pampa del Tamarugal Basin. The results indicate that shallow fluid flow only recharges Salar de Huasco on the eastern edge of the model domain while deep, hydrothermal fluid circulation recharges the PTA and is also responsible for salar formation in the western portion of the basin. NORTHERN ILLINOIS UNIVERSITY DE KALB, ILLINOIS DECEMBER 2015 ASSESSING RECHARGE MECHANISMS OF THE PAMPA DEL TAMARUGAL AQUIFER IN NORTHERN CHILE'S ATACAMA DESERT BY RICHARD SCOTT JAYNE ©2015 Richard Scott Jayne A THESIS SUBMITTED TO THE GRADUATE SCHOOL IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE MASTER OF SCIENCE DEPARTMENT OF GEOLOGY AND ENVIRONMENTAL SCIENCES Thesis Director: Ryan M. Pollyea ACKNOWLEDGEMENTS There are many people whom I would like to thank that made this work possible. First, I would like to thank my advisor Dr. Ryan Pollyea for his guidance, encouragement, and support from the very beginning of this research. Thank you for all the extra time you spent helping me along the way from understanding governing equations to editing abstracts. I would also like to thank my other committee members Dr. Justin Dodd and Dr. Philip Carpenter for their support and willingness to help throughout this endeavor. I can’t forget the support my family has given me throughout this process, especially my wife, Elsbeth and of course our dog Juniper. I couldn’t have done this without the assistance of some fellow graduate students, Elizabeth Olson and Jason Coenen. Finally, I would like to acknowledge the sources of funding that made this research possible: the Geological Society of America Graduate Student Grant and the NIU Department of Geology and Environmental Geosciences Goldich Fund. TABLE OF CONTENTS LIST OF TABLES . v LIST OF FIGURES. vi CHAPTER 1. INTRODUCTION . 1 Hypothesis and Study Objective . 5 Study Area & Geologic Setting . 7 Climate . 12 2. METHODS . 15 Code Selection . 16 Transect Geology & Model Domain . 18 Source Terms . 21 Building the Mesh . 24 Boundary and Initial Conditions . 25 Transient Simulations . 28 3. REULTS AND CONCLUSIONS . 29 Results . 29 Discussion . 33 Salar de Huasco . 40 Pica . 43 Western PdT Basin . 45 Summary . 46 Conclusions . 48 REFERENCES . 50 LIST OF TABLES Table Page 1. Lists all geologic formations within the model domain with their corresponding physical parameters and sources . 20 LIST OF FIGURES Figure Page 1. Tarapacá Region of northern Chile . 2 2. Two different conceptual models for groundwater recharge into the Pampa del Tamarugal Aquifer (PTA) . 4 3. Basin-Scale Fluid Flow . 6 4. The Tarapacá Region in northern Chile is comprised of four morphotectonic units. 8 5. Generalized geology through transect A-A’ (Figure 4) . 13 6. Elevation profile for transect A-A’ . 23 7. Boundary conditions (A) and generation terms (B) utilized for this study . 26 8. Initial hydraulic head (A) and temperature (B) distributions . 27 9. Simulated temperature profiles for transect A-A’ . 30 10. Meteoric water saturation within the model domain ranges from 0.00 – 1.00 at discrete time steps . 31 11. Model results for meteoric water saturation and hydraulic head contours at 1,000,000 years . 32 12. Meteoric water saturation and temperature contour intervals for model simulations (A) 100,000 and (B) 1,000,000 years . 38 13. Meteoric water saturation and hydraulic head contours at 1,000,000 years . 39 14. Meteoric water saturation and hydraulic head contours at 1,000,000 years . 41 15. Meteoric water saturation and hydraulic head contours at 1,000,000 years . 42 16. Fluid flow paths within the model domain correspond with different time scales . 47 CHAPTER