Assessment of groundwater pollution in relation to heavy metals of the alluvial aquifer of Thriasion Plain (NW Attica)

Abstract

In this study the hydrogeological and hydrochemical characteristics of Thriasion Plain are presented focusing mainly on the presence of heavy metals in the alluvial aquifer. Two main aquifer systems exist in the study area: a) the karst aquifer hosted in the karstified carbonate formations, which structure the bedrock and the margins of the alluvial basin and b) the phreatic aquifer within the Quaternary deposits of the Thriasion Plain. Coastal and submarine groundwater discharges show the direct connection of the aquifers with the sea causing intense salinization in both aquifers. The phreatic aquifer is characterized by high levels of TDS (483 – 13,067 mg/l) and correspondingly high degree of hardness (15.7 to 165.7 odH). High concentrations of Na+, Cl-, SO4 2-, NO3 -, NH4 + and PO4 3- reflect the diverse anthropogenic influences on the aquifer. The strong presence of heavy metals, Cd, Cu, Fe, Mn, Ni, Pb, Sr and Zn has been determined in the most of the samples. Their origin is associated with geogenic factors, such as the occurrences of bauxites, oxides derived from the alteration of rocks, especially shischts, organic matter within the Plio-Pleistocene sediments of the region, as well as with intense pressures from anthropogenic activities. In some cases the groundwater is improper not only for human consumption but also for many other uses.

Advances in the Coastal and Submarine Groundwater Processes: Controls and Environmental Impact on the Thriassion Plain and Eleusis Gulf (Attica, Greece)

“…Its connection to the Saronikos Gulf is through two shallow channels of 8 m in depth at the western end and 12 m in depth at the eastern end, respectively. This area has been degraded environmentally due to uncontrolled agricultural and industrial development during recent decades [30][31][32][33].…”

“…Groundwater response was 2 cm after a time lag (tlag) between the high tide and the peak of the groundwater level, tlag = 36 h. Tidal period was 24 h, and the tidal amplitude was 8 cm. The hydrogeological conceptual model that was proposed so far [30,[46][47][48] suggested the existence of two unconfined aquifers in the plain: (i) the upper one, which occurs in the Pleistocene-Holocene deposits, and (ii) the lower one in the Mesozoic carbonate rocks, which both discharge at the shoreline of Aspropyrgos and Eleusis Cities. A mathematical model, based on the previous conceptual model, failed to describe the hydrogeological regime of the plain.…”

“…The Na/Cl molar ratio is between 0.73-0.87, and the chlorides are between 12-205 mmol/L. In the western, eastern, and the northern parts of the study area where carbonate outcrops, saline groundwater was found 8 to 9 km inland, with total dissolved solids (TDS) between 1500-6000 mg/L and the chlorides between 15-90 mmol/L [29][30][31][32][33][46][47][48][49]. Groundwater flows SW with hydraulic gradient 1% .…”

“…On the contrary, in the carbonate aquifers, EC values remain at high elevations, and an increase of chlorides has been observed in almost all the wells of this aquifer, e.g., # 120, 118, 18A, etc. [29][30][31]. In Figure 8, the TDS versus distance from sea graph is shown.…”

Υδρογεωλογικό Καθεστώς Λεκάνης Θριασίου Πεδίου Με Έμφαση Στα Γεωυδραυλικά Χαρακτηριστικά Των Υδροφόρων Οριζόντων Και Στην Ποιότητα Των Υπογείων Υδάτων

“…Φρέσκο υπόγεια νερό υπήρχε στους Πλειστοκαινικούς υδροφορείς 18 Ka BP και τα παρακείμενα θαλάσσια στρώματα είχαν κατακλυσθεί από φρέσκο νερό μέχρι το βάθος των 100-120 μ. Η γρήγορη αύξηση της στάθμης της θάλασσας κατά τη διάρκεια του Ολόκαινου (Poulos et al 2009, Lambeck 1996, Καμπούρογλου 1989, Kraft et al 1980 οδήγησε στην εισβολή θαλασσινού νερού μέσω των χαμηλών υψομετρικά περιοχών των πεδιάδων και των θαμμένων ποτάμιων κοιλάδων καθώς και μέσω των ανθρακικών σχηματισμών. Με αυτό τον τρόπο, το υφάλμυρο νερό συναντάται σε απόσταση 7-8 χιλιόμετρα από την σημερινή ακτογραμμή (Kyriazis et al 2013, Christides 2011, Παρασχούδης 2002, Μιμίδης 2002, Λιονής 1992). Η εναπόθεση μεγάλου πάχους στρωμάτων κόκκινης/κοκκινωπής/καφέκόκκινης αργίλου κατά τη διάρκεια του Πλειστόκαινου-Ολοκαίνου ήταν καθοριστικής σημασίας.…”