The Aosta plain like any intra-ridge alluvial valley, is it hydrogeological system where a multilayer detritic aquifer is recharged by several subwatersheds. In such valleys the preservation of the chemical (mass transfert) and hydraulic (pressure transfert) signals from upstream (input) to downstream (output) can no longer be accepted. Considering the fact that vertical heterogeneities engender hydraulic and chemical discontinuities, in Aosta plain the occurrence of lateral discontinuities in the same sedimentary body. ill hydraulic continuity, should also be taken into account. The geochemical evolution is the result of multiple natural and anthropogenic influences which mark Out the groundwater flows. In the Aosta plain these mechanisms have been set up in space and time by the means of water chemistry and environmental isotopes.