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Wellhead protection zones delineation of the area of Tympaki in Heracleon of Crete with the use of the analytic element model WhAEM

Oikonomou Ioannis

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Summary

The rapid technological and industrial development of recent decades continues to impress the public. On the other hand, both the global destruction of the environment and the growing profits made by the powerful few through technological achievements at the expense of the many poor seem to have no end in sight. The deterioration of surface and groundwater quality is also unavoidable. In recent years, an increase in global temperatures and a decrease in precipitation levels have been observed. At the same time, demand for water resources, whether for drinking or irrigation, is increasing, while environmental regulations are often not respected. This work offers the opportunity — at least in the area of groundwater — to propose measures to preserve or even improve groundwater quality and its proper management through preventive measures such as the designation of wellhead protection areas. The study area is defined as the greater Tympaki area in Heraklion, Crete. This area is mainly used for olive cultivation and other agricultural activities. The potential pollutants threatening the groundwater reservoir therefore include nitrates, pesticides, organic waste, microbial contamination and more. The Alluvial-Pleistocene aquifer in question is located in the –central coastal area of the Messara Basin and covers an area of approximately 50 km² with an average annual rainfall of 474 mm. The WhAEM (Wellhead Analytic Element Model), a deterministic, analytical parametric model, was chosen to model the aquifer. The delineation of protection zones is based on the travel time T. of a potential pollutant to the pumping wells. WhAEM simulates the steady-state groundwater flow for a given aquifer. Various input parameters are required to design protection zones corresponding to 6-month, 1-year, 2-year, 5-year and 10-year travel times for the hydrologic years 2004–05, 2005–06, 2006–07 and 2007–08. These include: a map of the study area, pumping and observation wells, constant pumping rates for each year, annual precipitation rates, hydraulic heads from observation wells for each hydrological year and boundary conditions (sinks, inhomogeneities, horizontal barriers), the latter also defining the model calibration for optimal simulation fidelity. The resulting data show a fairly good convergence of the modeled hydraulic pressure values with the observed values. The errors are considered acceptable, so that the protection zones determined for each hydrological year are meaningful and provide a satisfactory approximation to reality. In summary, the results provide a solid basis for the prevention and protection of boreholes in the study area.

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