**1. Introduction**

Our study area is the Thriassion Plain, in the Attica Prefecture, located 25 km west of Athens. It covers a surface of 480 km<sup>2</sup> , characterized by a relatively smooth relief with altitudes up to 100 m and comprises the town of Aspropyrgos, Eleusis (pronounced Elefsis) and Magoula (Figure 1). The broader area is a historical and cultural landmark of Greece since prehistory. In the period 1965–1995, the area experienced a rapid unprogrammed, industrialization, which, in combination with the lack of environmental infrastructures, resulted in generation and accumulation of urban and industrial wastes, natural resources degradation and environmental hazards [1–3], turning the area into one of the most polluted Mediterranean regions. The drainage receptor of the study area is the Gulf of Eleusis, a semi enclosed embayment within the Saronikos Gulf, one of the most important areas in terms of the ecological status- and climate change-related coastal hazards [4,5] and biomonitoring [6] in the Eastern Mediterranean Sea. The Gulf of Eleusis and the Saronikos Gulf represent the seaward boundary of the metropolitan area of Athens and Piraeus whereas within the Thriassion Plain some of the biggest industrial installations of the country exist, such as oil refineries, steel mills and cement factories, and shipyards. The industrialization and land use changes have affected the sea bottom sediments [7–9], the soil [10,11], and the water column dynamics of the Gulf of Eleusis [12,13] which is the final receptor of human activities in the plain [14–17]. Among the industries involved with oil refining, processing and transport, the Refinery of Aspropyrgos (known as ELPE), the Refinery of Eleusis, and the relics of a petroleum recycling unit (CYCLON), along with the Military Airfield may potentially be responsible for hydrocarbon leakages to the groundwater, which is used in industries and for irrigation of agricultural lands. The first evidence of groundwater contamination from hydrocarbons was reported by Kounis et al. [18]. Ever since, the presence of aliphatic and PAHs pollution in coastal marine waters and tissues was documented [19] while some groundwater oil-remediation was merely reported for the area of the Refinery of Aspropyrgos [20].

**Figure 1.** The study area.

The present study investigates the potential groundwater pollution from BTEX (benzene, toluene, ethylbenzene and xylenes) within the complex aquifer system of the Thriassion Plain. It was carried out by the National and Kapodistrian University of Athens and supported by the General Secretariat of Research and Technology. The research was considered of critical importance by the Local Authorities because it provided feedback to the environmental management of the area as well as a starting point for further investigations necessary to address the complex pollution issues of the region.
