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This work represents a contribution to the protection techniques of karst aquifers against groundwater pollution. The paper sets out the methodology being introduced for the protection of the karstic system that gives rise to five (5) major groups of springs and supplies fourteen (14) pumping wells near Agyia Chania (Crete, Greece). Starting from a geological and hydrogeological survey of the area, the work presents a vulnerability assessment of the karstic aquifer based on the application of three index-based methods (EPIK, PRESK and DRISTPI). The protection zones for the discharge area of the aquifer were delineated through an integrated geomorphological approach and groundwater flow modeling. At first, the risk of polluting substances migration from ground surface to groundwater was considered based on the spatial distribution of vulnerability. Following this, the vulnerability was evaluated in the saturated zone, where the attenuation mechanisms of contaminants were reducing due to the raised flow velocity. The groundwater flow and contaminant transport processes was considered using the MODFLOW code. Next, the data from the vulnerability mapping and the groundwater flow simulation were merged into an integrated assessment to delimit the protection zones for the water abstraction points. The vulnerability assessment outlines zones of high vulnerability in the SE part of the area, far away from the discharge zone of the aquifer and the water abstraction points. These zones are associated with an intensive infiltration process via carbonate formations. Protection Zone I was delineated 20 m around the water abstraction points, and it should be excluded from any anthropogenic activity. Protection Zone II coves part of the very high and high vulnerability zones defined by the DRISTPI method (located upwards of the water abstraction points), as well as an area downwards of springs and wells, where the flow path lines which demonstrate the subsurface travelling time of 50 days are projected to the ground surface. Protection Zone III extends outside Zone Ι and Zone ΙΙ, up to the limits of the hydrogeological or hydrological basin, whichever is larger. It includes the entire capture zone (i.e., the surface and underground catchment area) that feeds the water abstraction points. In this manner the protection zones include the entire contributing area to water abstraction points, not just the ground surface recharge zone.

Five major groups of springs and more than ten pumping wells comprise the main discharge outlets of Agyia karstic aquifer (W. Crete, Greece). The mean annual discharge of the springs is 76 9 10 6 m 3 , while 12 9 10 6 m 3 of water are pumped annually from Myloniana and Agyia's well fields for public water supply and irrigation. The area is almost composed of entirely karstified carbonate rocks (limestones with dolomites), and karstic drainage contributes to infiltration and replenishment of the aquifer. The present work studies the groundwater flow system in the region to investigate the impact of intensive exploitation of the aquifer especially during dry periods (low water table conditions). Due to the lack of sufficient hydrogeologic data, a part of the aquifer extending upwards of Agyia springs was chosen for building the conceptual and numerical model. The groundwater flow was simulated by establishing a reproduction of the measured water heads in the field and the springs discharge. The appropriate set of boundary conditions and the repetition of the model's verification in different dry periods resulted in a sufficiently reliable model. This can be used as a tool to assess different water resource management options during dry periods, when the demand for water is high.

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