Management of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 220

3.2.1 Fight against point-source pollution
Two types of action are possible. If water circulates rapidly in the aquifer,
as is the case in karst systems, qualitative monitoring can predict when the
pollution plume will reach catchment areas. Pumping can then be stopped
as the wave of pollution passes through.
If circulation is slow, the aquifer must be cleaned-up. Procedures are
varied, depending on whether the pollutant is fl oating at the surface of
the aquifer or is spreading throughout it entire cross-section. One can,
for example, create a hydraulic barrier by injecting water into the aquifer
around the contaminant, and then pump the polluted water. The injection of
reactants or solvents may be necessary. Volatile pollutants can be mobilized
by injecting air into the aquifer. One can also, for pollutants less dense than
water, skim the surface of the aquifer by creating a cone of depression
through pumping, at the surface of which a second pump can recover
the substance to be eliminated (Figure 114). Biodegradation processes are
used for certain organic products, by injecting bacteria and favoring their
development in the aquifer through the addition of nitrates.
Figure 114 Example of aquifer cleaning-up through skimming.