Proceedings of the 11 th International Conference on Environmental Science and Technology Chania, Crete, Greece, 3 – 5 September 2009 DELINEATION OF WELL HEAD PROTECTION AREAS USING STOCHASTIC ANALYSIS APPROACH N. THEODOSSIOU* and E. FOTOPOULOU Faculty of Civil Engineering, School of Technology Aristotle University of Thessaloniki, GR 541 24 Thessaloniki, Greece *e-mail: niktheod@civil.auth.gr EXTENDED ABSTRACT The determination of wellhead protection areas is a matter of major importance especially for wells supplying water for domestic use, since it allows water resources managers and local authorities to impose measures over the development of agricultural or industrial activities that could somehow affect the quality of groundwater. One of the main problems although, for the rational and effective determination of these protection areas is the fact that their delineation is based on parameters generally characterised as uncertain. Typical examples of these parameters are the hydrogeological characteristics of the aquifer and their special distribution. In this paper an investigation, using computer-based mathematical models, of the implications of uncertainty on the estimation of the hydrogeological parameters that affect the delineation of wellhead protection areas is performed. The applied approach is used for the estimation of the hydraulic conductivity of the material sets that comprise the aquifer, a parameter that is characterized by uncertainty in most groundwater simulation problems. This investigation is based on a stochastic simulation of the problem of pollutant transport in groundwater systems. The spatially distributed parameter randomization required for the stochastic simulation is performed using Markov Chains to formulate the equations used to estimate the distribution of these material sets. The entire process is performed using the software package T-Progs which is a module that performs transition probability geostatistics to generate multiple equally probable models of aquifer heterogeneity, and the well-known computer software ModFlow 2000 for the simulation of groundwater flow. As a result of a series of possible realisations of the soil material distribution over the aquifer, a respective number of capture zones is formulated. The similarity and the differences of these capture zones are depended on the level of uncertainty of the stochastic parameters. The overall capture zone, that is the one that includes all the others, is characterised as the wellhead protection area under the specific conditions of uncertainty. KEYWORDS: wellhead protection areas, stochastic analysis, groundwater protection, water pollution, water resources management A-1440