*5.2. The Cretaceous Unit*

– – – The Cretaceous limestone hosts an unconfined aquifer (# 111, 120, and 130) with a hydraulic head up to +8 masl. The water table annual fluctuation is around 0.60 m. Hydrochemical data indicate that Cretaceous limestone is contaminated with seawater. Chlorides range from 16.4–36.5 mmol/L and sodium from 11.8–28.1 mmol/L; the sodium/chloride molar ratio ranges from 0.72–0.77. In this aquifer, passive seawater encroachment could take place, which means that the head is above sea level, and groundwater still flows seawards. However, as the water was found brackish since the early 1950s, seawater intrusion seems to be happened in a previous geological time. Due to the Pleistocene sea level rise and, mainly, the last 12 ka and the fact that limestone is intensively fractured, the seawater intruded 9 km inland.
