Dissertation committee:
Τριμελής Συμβουλευτική Επιτροπή
Επιβλέπουσα: Αριάδνη Αργυράκη, Καθηγήτρια, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος ΕΚΠΑ
Μέλη: Εμμανουήλ Δασενάκης, Καθηγητής, Τμήμα Χημείας ΕΚΠΑ
Δημήτριος Δερματάς, Καηγητής Σχολή Πολιτικών Μηχανικών ΕΜΠ
Επταμελής Εξεταστική Επιτροπή
Επιβλέπουσα: Αριάδνη Αργυράκη, Καθηγήτρια, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος ΕΚΠΑ
Μέλη: Εμμανουήλ Δασενάκης, Καθηγητής, Τμήμα Χημείας ΕΚΠΑ
Δημήτριος Δερματάς, Καθηγητής, Σχολή Πολιτικών Μηχανικών ΕΜΠ
Κωνσταντίνος Βουδούρης, Καθηγήτής, Τμήμα Γεωλογίας ΑΠΘ
Ευστράτιος Κελεπερτζής, Επίκ.Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, ΕΚΠΑ
Μαρία Περράκη, Καθηγήτρια, Τμήμα Μεταλλειολόγων Μηχανικών, ΕΜΠ
Εμμανουήλ Σκούρτσος, Αναπλ.Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος ΕΚΠΑ
Summary:
The present thesis aims to investigate the factors contributing to the qualitative degradation of porous aquifers linked to ultramafic rocks. It aims to assess the extent of geogenic and anthropogenic influence on hexavalent chromium (Cr(VI)) enrichment in groundwater. Additionally, the research intends to estimate natural background levels of chromium and other major contaminants, providing a baseline for comparison. Within such a framework, a total of 154 samples were collected during the wet and dry seasons of 2017 and 2018 from five different areas, Loutraki basin, Northeast Peloponnese, Schinos basin, Northeast Peloponnese, Messapia basin in Central Evia, Thiva sub-basin in Assopos basin and Oinofyta sub-basin in Assopos basin. The suitability of groundwater for various purposes was evaluated according to legislation upper limits, and a health risk assessment has been conducted with focus on chromium toxicity.
The main anthropogenic pressures identified include wastewater discharges from urban, agricultural, and industrial sources, as well as the impact of sea water intrusion in coastal zones. Hydrochemical analyses in distinct regions unveil a spectrum of water types, ranging from pristine conditions in Loutraki to varying degrees of anthropogenic influence in Schinos, C.Evia, Thiva, and the industrial area of Oinofyta.
Loutraki's groundwater remains mostly pristine, yet contamination from septic tanks in peripheral urban areas is identified. In Schinos, indicators of sea water intrusion, such as increasing electrical conductivity (EC) values and elevated chloride (Cl-) and sodium (Na+) concentrations, manifest toward the coastal zone. C.Evia exhibits elevated concentrations of sulphates, chlorides, and nitrates, indicative of potential anthropogenic influence. Thiva experiences salinization in its northern part, evident through heightened EC values and concentrations of sulphates, chlorides, and sodium. Oinofyta, an industrial area, demonstrates intense salinization, with chloride concentrations up to 812 mg/l, strongly suggesting industrial wastewater discharges as a primary source. According to N isotope analysis and Bayesian mixing modeling, in Schinos the main anthropogenic source of NO3- is manure sewage (MS) and to a lesser extent chemical fertilizers (CF). In C. Evia, both MS and CF contribute almost equally to NO3- occurrence in groundwater. In Thiva, the main anthropogenic sources of NO3-are CF which is in accordance with the high percentage of agricultural land use comparatively to the other areas.
Hexavalent chromium contamination emerges as a significant issue, with concentrations surpassing natural background levels in all areas. In particular, In all the areas except from Loutraki, Cr(VI) concentrations greater than 90 μg/l were measured (up to 430 μg/L in Schinos, 96 μg/l in C.Evia , 164 μg/l in Thiva and 11.7 mg/l in Oinofyta). In Thiva, Cr(VI) is correlated positively with Na+, Cl- and SO42-, in C.Evia, Cr(VI) is correlated positively with SO42- while in Oinofyta area Cr(VI) is positively correlated with Cl- and SO42-. The aforementioned correlations indicate that Cr(VI) in these areas can also be of anthropogenic origin. This is further supported by the identification of Fe-oxide spherules with Fe2O3 ranging from 63.2 to 77.2%, Cr2O3 ranging from 11.4 to 24% and MnO, NiO, SiO2, Al2O3 and CaO in trace amounts in these areas. Therefore, the 'polluter-pays' principle could act as an applicable framework, emphasizing the responsibility of operators for the costs associated with preventive or remedial measures.
Established threshold values for total chromium in each aquifer provide regulatory benchmarks, guiding permissible concentrations. The threshold value for total Cr for Loutraki aquifer is 36 μg/l , for Schinos 69 μg/l , for C.Evia 44 μg/l and for Thiva 38 μg/l. In Loutraki, a significant percentage of the samples, varying from 20% to 40% have poor to very poor quality for drinking water purposes. It has to be mentioned that the particular wells are not used for drinking water purposes but they contribute to the overall quality of the groundwater system. In Schinos, C.Evia and Thiva the majority of groundwater samples are poor to unsuitable for drinking water purposes. Regarding the use for agricultural purposes, only Loutraki aquifer has good to excellent suitability whereas in the other areas a percentage ranging from 10 to 40% has poor to very poor quality for crop irrigation.
In Loutraki groundwater body where the aquifer is exploited for drinking water supply, the non-carcinogenic health risk caused by Cr(VI) is within the acceptable level through drinking water ingestion pathway for adults. Nevertheless, children face a medium non-carcinogenic risk than adults owing to their lower body weight. The carcinogenic risk is high and very high for the adults and children respectively. For Schinos, C.Evia and Thiva, the non-carcinogenic health risk caused by Cr(VI) is medium to high for adults and high for children and the carcinogenic health risk is high and very high for adults and children respectively.
The conclusions of the present thesis contribute significantly to the multifaceted challenges of groundwater quality management. The findings underscore the necessity for region-specific strategies and ongoing monitoring to ensure sustainable groundwater use and environmental preservation.
Keywords:
hexavalent chromium, groundwater, natural background level estimation, geogenic chromium, health risk assessment, drinking water, Loutraki, Central Evia, Psachna, Thiva, Oinfofyta, water uses, water management, groundwater pollution, nitrogen isotopes, nitrate pollution
