The Exploitation of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 187

Figure 99 Conductimetry study of the saltwater intrustions in the coastal dunes of Dakar
(Senegal) (from Diouf et al., 1997).
conductivity probes enabling the regular acquisition of vertical profi les. This
enables the drawing up of isoconcentration maps allowing the monitoring
of an eventual marine intrusion's evolution.
Salinity is not, however, always linked to a marine intrusion. The
leaching of continental evaporites can also increase the NaCl concentration
of water. The bromine content can differentiate the two types of water.
Indeed, the Br - /Cl - ratio (in 10 3 meq·L -1 ) is near 1.53 for sea water, and
between 0.7 and 1. 2 for evaporites (Edmunds, 1996) (see chap. B3-6.1.3a).
4.1.2 Treatment
The intrusion of sea water can be limited by artifi cially raising the piezometric
surface downslope of the pumping zone, either through damming or grout
curtains, or by returning water to the aquifer (Figure 100). The town of
Orange (California, USA) relies on 28 wells used to inject treated wastewater
and water from deeper reservoirs, in order to create a hydraulic barrier
protecting the Fountain Valley aquifer from marine intrusions.