Some simple procedures for the calculation of the influence radius and well head protection areas (theoretical approach and a field case for a water table aquifer in an alluvial plain)

The paper describes some simple methodologies for the delineation of well-head protection areas, together with an overview of the main regulations published in Italy and Europe. Starting from a general explanation of the main parameters, like the radius of influence and the zone of capture in homogeneous isotropic aquifers, basic methodologies suggested in the literature are then illustrated. Different criteria are involved: from the simple 200 m radius, to more complex analytical and numerical simulations. Five different approaches are applied and compared, to a well field in a water table aquifer along a river. Results have shown that, while simpler methods can be satisfactory at a first stage of the study, they fail to account correctly, for local heterogeneities. On the other hand the more accurate description of the aquifer obtained with a full numerical model requires extensive time, expertise and amount of data, that are not always available in case of small water supply systems. As many Authors have underlined, one of the most effective outcome of the numerical tool, lays in the capability to increase our knowledge on the groundwater dynamics of the system and the amount of the sustainable yield.