Διερεύνηση της ρύπανσης από υδρογονάνθρακες στα υπόγεια νερά των νεοτεταρτογενών στρωμάτων του Θριάσιου Πεδίου

Abstract

The Thriassio Plain, located in Western Attica, was a cultural cradle of the antiquity. The current urban and industrial development has been accomplished against the natural sources, such as groundwater. The Thriassio Plain, as well as other urban-industrial regions of Greece, is a typical example not only of the uncontrolled exploitation of the underground water, but also of the degradation of the quality of life due to pollution of the aquifer. This study involves the pollution of the aquifer system of the Thriassio Plain, by various dangerous pollutants coming mainly from light oil fractions, such as a) benzene, toluene, ethylbenzene, and xylenes- known as BTEX, b) the methyl- tertiary-butyl-ether (ΜΤΒΕ), a gasoline additive, which was used up to a few years ago, and c) the seventeen basic polycyclic aromatic hydrocarbons (PAHs) which are products of oil combustion or heavier oil fraction leakages. The US Environmental Protection Agency (USEPA) has characterized the BTEX and some heaviest members of the PAHs, as priority pollutants, for which a maximum allowed concentration in drinking water has been established. The European Union has only included benzene and the same PAHs as USEPA among the hazardous water pollutants. So far, both Agencies have not established regulations for the target pollutants in groundwater. The sampling and identifications at the studied area lasted three years, covering two seasons per year: spring (in May), following the winter rainy period, and autumn (in November), following the summer drought. During sampling, the depth of the groundwater level was measured and converted to an absolute altitude of the piezometric surface. The results were then illustrated on a piezometric surface estimation map through a Geographical Information System (GIS). By studying the piezometric curves, the calculated hydraulic gradient and the spatial distribution of the pollutants, some conclusions came up about the “fate” of the target analytes within the aquifer. During each sampling period, the basic parameters of the groundwater quality, such as salinity, electrical conductivity, dissolved oxygen and pH, were measured. The laboratory determination then followed, which included: a) for the BTEX and the MTBE, preparation of the groundwater samples with Solid Phase Micro Extraction (SPME), and determination with Gas Chromatography – Mass Spectrometry (GC-MS) b) for the PAHs, preparation of the groundwater samples using Solid Phase Extraction (SPE), and determination with High Performance Liquid Chromatography (HPLC) coupled with Photo Diode Array detector. The results were illustrated on GIS maps, providing an estimation of the spatial distribution in the aquifer of each target analyte. The concentration values of the pollutants in association with their spatial distribution, leads to the assessment that the aquifer has been polluted in varied degree. The maximum concentrations were observed in November, all through the three year period. In spring, following water level rise, the BTEX and MTBE concentrations reduce significantly, to much lower levels than the allowed limits. ....................................................................................................................................................