Aquifer role in reducing nitrate contamination by means of the dilution process.

The quality of groundwater resources depends on the efficiency with which chemical, physical and biological processes manage to abate the concentration of a certain water-soluble contaminant that leaches vertically into the topsoil and into the unsaturated zone towards the aquifer. Particularly nitrates are greatly water-soluble and they are not subjected to attenuation phenomena in soil and unsaturated zone, like biodegradation, adsorption or precipitation. In case the contaminant reaches the aquifer, one of the phenomena which allows the most significant reduction of contaminant concentration along the flow direction is the process of dilution. This paper is the proposal for a simplified methodology to evaluate the ability of the aquifer to operate a nitrate concentration reduction by means of the dilution process. This ability is directly related with aquifer volumetric flow rate per unit perpendicular to the flow direction (qu) and it increases with qu raise. qu evaluation was carried out for three sample areas in the western sector of the Po Plain (northern Italy). Moreover qu values were compared with the nitrates concentration in groundwater. From this comparison emerges that, on equal terms, low values of the nitrates concentration are present in areas where qu values are high, due to the high dilution rate of the pollutant within groundwater. On the contrary, high nitrate concentrations are present in areas with low qu. Finally, the qu evaluation could allow, especially for studies on regional scale, the localisation of areas more susceptible to groundwater contamination. Moreover this approach can be used as a planning tool with advantages for groundwater management and preservation.