Title Page
ABSTRACT
국문 초록
Contents
CHAPTER 1. INTRODUCTION 14
CHAPTER 2. SITE DESCRIPTION 15
2.1. Site History 15
2.2. Site Topography and Geology 16
2.3. Climate and Hydrology 18
CHAPTER 3. SAMPLING AND ANALYTICAL METHODS 21
3.1. Collection and Analysis of Sample 21
3.2. Principal Component Analysis (PCA) and Clustering 23
3.3. Trend Analysis (Mann-kendall test and Sen's Slope) 23
CHAPTER 4. RESULTS 26
4.1. Contamination Status 26
4.2. Groundwater Geochemistry and Redox Condition 28
4.3. Governing Factors for BTEX Concentrations and Hydrochemical Groups 32
4.4. Trend Analysis of Contaminants Concentration 37
4.4.1. BTEX and TPH Concentration 37
4.4.2. BTEX Mole Fraction 39
4.4.3. BTEX Molar Ratios 39
4.5. Oil Fingerprinting Analysis 40
4.6. Compound Specific Isotopes Analysis (CSIA) 41
CHAPTER 5. DISCUSSION 43
5.1. Biodegradation of BTEX under Reducing Condition 43
5.1.1. Water Chemistry Affected by BTEX Degradation 43
5.1.2. Difference of BTEX Biodegradation Rates Depending on Redox Condition 46
5.1.3. Compound Specific Isotope Analysis 47
5.2. Contaminant Sources Identification 47
5.2.1. Previously Reported Potential Contamination Sources 47
5.2.2. Water Chemistry Differences by Zones 48
5.2.3. Oil Fingerprinting 51
CHAPTER 6. CONCLUSION 52
REFERENCES 54
Table 1. Summary of the geochemical parameter and contaminants results in Sep. 2021 and Aug. 2022 (n=36). 28
Table 2. Results of Mann-Kendall test (2004~2021 annual average concentration, n=2,100) 37
Table 3. Results of Mann-Kendall test (2004~2021 annual average mole fraction, n=1,544) 39
Table 4. Results of oil fingerprinting analysis and concentration of TPH and BTEX in Aug. 2022. 41
Table 5. Reaction equations and Gibbs free energy for benzene biodegradation with different electron acceptors. 44
Table 6. First-order decay rates of BTEX along redox conditions (/day) 46
Table 7. BTEX solubility at 10 °C 48
Table 8. BTEX concentration ratios in oil products in South Korea 49
Figure 1. (A) Location of study area (red box), (B) geological ma, (C) location of wells in study area (red dot: water chemistry analyzed wells, white dot: other wells) and... 17
Figure 2. Average monthly temperature and rainfall of the study site in 2021 (dark grey) and 2022 (grey). Sampling points are plotted in red letters. 19
Figure 3. Well altitude shows as line graph and elevation levels in 2021 (Measured 13 times). The subway tunnel's elevation level is 7.15 m and 7.21 m height 20
Figure 4. (A) The total concentration of BTEX using the larger circle with the larger concentration, (B) The TPH concentration in Sep 2021. In (A), the colors in... 26
Figure 5. The mole fraction of contaminant by year is plotted by Zone 1 and Zone 2. (A) Benzene (n=956), (B) Xylene (n=956). 27
Figure 6. The ionic composition of groundwater samples with the contaminant concentration: (A) BTEX, (B) TPH in 2021 and 2022 (n=36). 30
Figure 7. BTEX concentration vs. Fe, Mn, NO₃, SO₄, and HCO₃ in 2021 and 2022 (n=24). 31
Figure 8. Result of PCA for groundwater samples in 2021 (n=18): Loading plot for 14 variables and 5 supplementary variables for contaminant concentrations. (B: Benzene; T:... 33
Figure 9. Factor score plot of groundwater samples with BTEX concentration and clustering group. 34
Figure 10. Dendrogram for clustering analysis result in 2021. 35
Figure 11. Plot of well points which has different colors for each group. 36
Figure 12. BTEX concentrations by year in (A) Zone1 (n=2,119) and (B) Zone2 (n=1,179). 38
Figure 13. Statistically significant increased or decreased (p-value 〈0.05) of (A) Benzene/Toluene molar ratios (n=213) and (B) Toluene/Ethylbenzene molar ratios (n=... 40
Figure 14. Chromatograms obtained from groundwater samples in Aug. 2022. 41
Figure 15. δ¹³C of BTEX vs. δ²H of BTEX obtained from groundwater samples (Sep. 2021 and Aug. 2022, n=26) and δ¹³C of BTEX obtained from JP-8 oil (vertical line) 42
Figure 16. Alkalinity vs. Calcium as normality with 1:1 alkalinity-Ca line (dashed) (2021 and 2022, n=36) 45
Figure 17. Changes of the concentrations of BTEX and TPH concentration from 2004 to 2021. (A) PW-3 (n=200), (B) BH-34 (n=325) and (C) PW-4 (n=200).... 50