Hydrochemical impact of a gravel pit on ground waters
A gravel pit can exert two different types of hydrochemical impacts on downstream groundwaters : a nature impact and an artificial impact caused by accidental pollution. The first impact was studied in the case of gravel pits of the Rhenan Alsatian aquifer. The water quality of two deep graves pits (one of them is still exploited) was closely observed in the experimental field at la Wantzenau (north eastern France, north of Strasbourg). The artificial impact was simulated with a mathematical modelisation. Water samples of gravel pits and upstream and downstream groundwaters were analysed. As a result, the presence of the gravel pits does not after the downstream groundwater quality. In particular, no influence was observed on the quality of water pumped at a station situated 300 meters away from the gravel pits. On the contrary, the accidental pollution of an aquifer - from or through - a gravel pit remains quite a problem. A mathematical modelisation of the hydrochemical exchanges between the aquifer and the gravel pits was set up. The preliminary adjustment of the model was carried out on the propagation of the chloride ion, which behaves as a natural tracer. The issue of this first step authorized a simulation of different cases of fictitious chemical contamination of the water pumped at the station.