Numerical modeling of the seasonal variation of the groundwater quality in the aquifer Magra River, Italy

The aquifer of the Magra river is the main source of drinking water, industry and agriculture in the area of La Spezia (NW of Italy). However, the groundwater suffers from a high vulnerability to the problems of over­exploitation and pollution. In order to control these constraints, a hydrodynamic and transport modeling was achieved using by MODFLOW/GMS7.1 after the establishment of the conceptual model of the system and the definition of the limits conditions. The model is calibrated in steady state and transient considering the period 2004-2011. The calibration of model has shown the importance of the Magra river flows in the water balance of the aquifer, these contributions participates up 66% of the inputs to the Magra aquifer. In addition, the transient calibration shows a seasonal variation of the piezometry. the piezometric amplitude difference can reach 2 m in water catchment areas. This variation was also observed in the analysis of some chemical elements water of Magra groundwater such as Cl, SO4 and also for total dissolved solids (TDS). In order to control this phenomenon, we developed a model of transport by MT3DMS/GMS. The identification of the contamination sources during the conceptual model elaboration is very important in the process of the quality of groundwater modeling. It was necessary to define the presence of multi- sources of groundwater contamination environment: from river and boundaries (NE side). The choice of the period of the reference for calibration of the model is based on well sinks monitoring the level and the quality of groundwater Magra basin. These wells are themselves the catchments of resources in this area. These measuring points offer a series of measurements of groundwater levels and the concentration of certain chemical elements (SO4 , Cl, TDS). The results show a strong correlation between on the one hand physic - chemical parameters, and on the other hand between these parameters and the hydrodynamic behavior of the aquifer. The seasonal variation of the groundwater quality is reproduced by managing a suitable stress period in MTD module. The Dispersivity and effective porosity were calibrated and are respectively about of 4 m and 11-29%. The simulations showed that the transport in the hydrogeological Magra aquifer is influenced by advection rather than diffusion-dispersion.