Presented at the International Conference on New Water Culture of South East European Countries-AQUA 2005, 21–23 October 2005, Athens, Greece. Groundwater hydrochemistry at Balkan coastal plains — the case of Marathon of Attica, Greece Maria Psychoyou*, Theologos Mimides, Spiros Rizos, Anastasia Sgoubopoulou Agricultural University of Athens, 75, Iera Odos, 118 55, Athens, Greece Tel. +30 2105294082, 2105294072, 2105294025; Fax +30 2105294081; email: lhyd4psm@aua.gr Received 1 February 2006; revised accepted 11 April 2006 Abstract The expansion of irrigated agriculture and the overexploitation of groundwater aquifers are leading to seawater intrusion and severe deterioration of groundwater quality at coastal areas. The shortage of good quality water resources constitutes an important threat for the maintenance of productivity of crops and soil protection. In the region of Marathon in Attica, an area with fast urbanization and intense agricultural activity, a network of 56 observation boreholes for monitoring water level and the qualitative characteristics of groundwater was installed. The values of EC, pH, Eh, as well as main anions and cations were determined twice, at the end of rainy and dry periods. Severe deterioration of water quality, due to high salt loads, was recorded, especially in areas very close to the sea. The possible risk for the crops and the soil, deriving from irrigation use of groundwater, was estimated. In certain regions, increased nitrate concentrations were observed due to intense use of fertilizers. The recent prevailing groundwater quality status was compared to that of the previous decade, revealing no significant further degradation of the coastal aquifer, except for some sub-areas. Keywords: Groundwater; Coastal aquifer; Seawater intrusion; Nitrate 1. Introduction The expansion of irrigated agriculture and the intensive agricultural activities induce the risk of groundwater quality degradation through high groundwater pumping rates and overex- ploitation of the aquifers, leading to seawater intrusion in the coastal aquifers. The use of poor quality water for irrigation reduces crop produc- tivity and can alter soil physicochemical proper- ties causing soil degradation [1,2]. About 25 million hectares, more than 10% of the world’s irrigated area, are severely affected by yield- suppressing salt built up [3]. The magnitude and intensity of soil salinization increased rapidly in the second half of the 20th century [4]. In recent years, nitrate pollution of ground- water has become an important environmental *Corresponding author. Desalination 213 (2007) 230–237 doi:10.1016/j.desal.2006.04.088 0011-9164/06/$– See front matter © 2007 Elsevier B.V. All rights reserved.