Characterizing Aquifers - Hydrogeology: Objectives, Methods, Applications - page 142

Figure 77 Recharge of an aquifer by a river and by the surrounding hills.
6.1.4 Decline of water quality during exploitation. Example
of the Pinchinade graben, (Mouans-Sartoux, Alpes-
Maritimes) (Reynaud et al., 1999)
The exploitation of a well in a Jurassic limestone graben within the
gypsiferous Provençal Keuper clays demonstrates a decline in quality of
the extracted water over time, when drawdown exceeds 30 m (Figure 78).
The nitrate content of the water decreases; its sulfate content increases.
The infl ows to the pumping well change: initially, pumping mobilises
recent water, easily infi ltrated through limestone. This water has leached
the graben's soil (nitrates). The restricted size of the reservoir imposes a
lateral realimentation by older water having resided in gypsiferous clays
(sulfates), but devoid of shallow tracers (nitrates).