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ABSTRACT RUDD, HAYDEN. Assessing the Vulnerability Of ABSTRACT RUDD, HAYDEN. Assessing the Vulnerability of Coastal Plain Groundwater to Flood Water Intrusion using High Resolution Mass Spectrometry. (Under the direction of Dr. Elizabeth Guthrie Nichols). Communities in the North Carolina Coastal Plain (NCCP) depend on safe and reliable groundwater for private well use, agriculture, industry, and livelihoods. Although storm intensity and frequency are predicted to increase in coastal areas, the risk of surficial and confined aquifer contamination from extreme storms is not understood. In September 2018, Hurricane Florence caused extensive flooding across the NCCP for several weeks. The North Carolina Department of Environmental Quality (NCDEQ) Groundwater Management Branch had just completed sampling of some wells in their monitoring network when Hurricane Florence made landfall. NCDEQ returned to these wells, particularly those flooded by Hurricane Florence, for post-flood sampling. These groundwater samples were analyzed by NCDEQ for regulated semi-volatile organics with few to any detections of regulated organic contaminants. NCDEQ provided NC State the same sample extracts for analysis by high resolution mass spectrometry (HRMS). This research reports on the non-targeted and suspect-screening HRMS analyses of groundwater from nested monitoring wells. Some monitoring well sites experienced flooding during the study period, and some did not. The goal of this research was to advance our understanding of coastal aquifer susceptibility to flooding by producing the first comprehensive organic chemical profiles of coastal aquifers and by determining if aquifers have distinct organic chemical profiles that change after flooding events. This study used HRMS analyses to produce the first comprehensive organic chemical profiles of 11 aquifers in the coastal plain. The mean total chemical feature count per groundwater sample was 5,207 (±1,088). Across all groundwater samples, a total of 396 unique chemicals were tentatively identified using the NIST 20 mass spectral database (M1). The deepest confined aquifer, Lower Cape Fear, had significantly more chemicals of environmental concern (ToxCast) than the Surficial aquifer, and eight ToxCast chemicals had higher detection frequencies in deeper, confined aquifers than more shallow or surficial aquifers. Detected ToxCast chemicals ranged from very water soluble to very water insoluble. Finally, chemical profiles of flooded wells, in confined and surficial aquifers, had several regulated organic compounds that were not detected prior to flooding. The mechanisms by which organic chemicals of variable solubilities transport to confined aquifers merits further research. Overall, HRMS analyses suggest the intrusion of new water to confined aquifers as indicated by the detection of anthropogenic chemicals. © Copyright 2021 by Hayden Rudd All Rights Reserved Assessing the Vulnerability of Coastal Plain Groundwater to Flood Water Intrusion using High Resolution Mass Spectrometry by Hayden Rudd A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Natural Resources Raleigh, North Carolina 2021 APPROVED BY: _______________________________ _______________________________ Dr. Elizabeth Guthrie Nichols Dr. Damian Shea Committee Chair _______________________________ Dr. David P. Genereux BIOGRAPHY Guided by a childhood filled with outdoor activities and a love of science, I chose to study chemistry and environmental studies at Furman University. As an undergraduate Beckman Scholar, I worked in Dr. Brian Goess’s organic synthesis laboratory developing a novel synthesis pathway of hibiscone B – a natural product with chemotherapeutic properties. Working in Dr. Goess’s laboratory reaffirmed my interest in career as a research scientist as well as my desire to pivot my research efforts towards environmental challenges. This realization led me to the AmeriCorps CivicSpark program after college. CivicSpark is a national service program aimed at building the ability of local governments to address resiliency and sustainability issues by placing Fellows with local government organizations. I was stationed with the San Luis Obispo (SLO) County Water Resources Division and tasked with helping the Division address severe drought conditions and depleting groundwater supplies. Through my time serving in AmeriCorps, I witnessed the challenging issues that arise from the essential but often underappreciated relationship between humans and water resources; I decided to focus my future career efforts in hydrological research that would inform and improve water resource management. This led me to my pursuit of a M.Sc. in Natural Resources with a focus in Hydrology under the advisement of Dr. Elizabeth Guthrie Nichols, who shares my interest in research that advances sustainable management of local groundwater resources. ii ACKNOWLEDGMENTS I would like to thank the North Carolina Department of Environmental Quality Groundwater Management Branch for collecting, extracting, and sharing the groundwater samples used in this study as well as for their general assistance on this project. I would also like to thank Statera Environmental, Inc. for allowing the use of their laboratory and for their assistance on this project. Finally, I would like to thank my committee members for their support in the execution of this project and thesis. This study was funded by the United State Department of Agriculture Exploratory Research Grant (grant number #12762841). iii TABLE OF CONTENTS LIST OF TABLES ......................................................................................................................... v LIST OF FIGURES ...................................................................................................................... vi Chapter 1: Introduction .............................................................................................................. 1 Chapter 2: Methods ..................................................................................................................... 5 2.1 Sample Sites .................................................................................................................... 5 2.2 Sample Collection, Extraction, and Analysis ................................................................. 5 2.3 Data Analysis .................................................................................................................. 7 2.4 Quality Control ............................................................................................................... 8 Chapter 3: Results ...................................................................................................................... 10 3.1 Chemical Counts by Aquifer ........................................................................................ 10 3.2 Chemical Features, TICs, and ToxCast Chemicals by Depth ....................................... 13 3.3 Tentatively Identified Chemicals by NIST 20 Mass Spectral M1 ................................. 15 3.4 NIST 20 TICs Matched to USEPA’s ToxCast Chemical Database ............................. 17 3.5 TICs and ToxCast Chemicals in Flooded Wells ........................................................... 20 Chapter 4: Discussion ................................................................................................................ 29 4.1 HRMS Analyses of Groundwater ................................................................................. 29 4.2 Chemicals of Emerging Concern as Co-tracers ............................................................ 30 4.3 Chemical Fingerprinting ............................................................................................... 32 4.4 Groundwater Vulnerability to Extreme Storms ............................................................ 33 4.5 Limitations and Advancement ...................................................................................... 34 Chapter 5: Conclusion ............................................................................................................... 35 References ................................................................................................................................... 37 Appendix ..................................................................................................................................... 42 Appendix A: Supplemental Tables and Figures ................................................................. 43 iv LIST OF TABLES Table 1 Mean counts for chemical features, TICs, and ToxCast chemicals (+ one standard deviation) by aquifer. ................................................................................. 11 Table 2 HRMS detections of compounds regulated by NC groundwater standards rule 15A NCAC 02L .0202 .............................................................................................. 12 Table 3 HRMS detections of regulated compounds (NC groundwater standards rule 15A NCAC 02L .0202) in each aquifer. .......................................................................... 12 Table 4 The 15 most prevalent TICs (90% match factor) across all samples and number of well extracts in which the TIC was detected. ....................................................... 16 Table 5 ToxCast 90 results for groundwater samples from the Snow Hill nested well site. 21 Table 6 ToxCast 90 results for groundwater samples from the Falkland
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