Characterizing Aquifers - Hydrogeology: Objectives, Methods, Applications - page 144

Table 12 Principal Isotopes Used in Hydrogeological Prospection.

ISOTOPE Stable Radioactive

in water

18 O recharge elevation
seasonal dephasing
paleorecharge
2 H + 18 O soil evaporation /unsaturated zone/
saturated zone
carbonate/silicate exchange
H 2 S exchange

3 H dating: < 30 years

13 C nature of vegetation
deep/biogenic CO 2 exchange
solide carbonate exchange/dating

14 C dating: < 25,000 years

in solutes

34 S origin of sulfur:
pyrite/evaporite oxidation

36 Cl dating: < 250,000 years

15 N origin of nitrogen:
fertilizers/livestock/sewage
87 Sr origin of mineralization:
bedrock/evaporites/carbonates

6.2.2 Determining an aquifer's catchment basin: example of the
Fontaine de Vaucluse (Blavoux et al., 1992; Malzieu, 1987)

In order to determine the average elevation of a large zone of diffuse recharge
for an aquifer (the Vaucluse system), one selects, in the same geologic,
geomorphological, and climatic context, springs with a well-known recharge
zone (Figure 79). One simultaneously takes samples from these reference
springs and from the spring under study, during the dry season (so as to

Figure 79 Determination of the average recharge elevation of an aquifer.