Protection of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 199

city of Avignon's catchment system for the Durance aquifer, which relies on
several wells and twenty boreholes, occupies an area of 500 m x 300 m.
The immediate zone and its borders (a radius of 15 m around the
catchment construction) must be deforested, as tree roots damage the
masonry work in catchment galleries, well shaft linings, etc., and therefore
allow the infi ltration of parasitic surface or shallow water. The area must
be maintained: cleared of undergrowth and mowed mechanically (no
herbicides!) every year, and organic debris must be removed.
As much as is possible and necessary, the zone should be fenced off
with an impassable barrier and a locked door. However, catchments at the
foot of a cliff or in the middle of a forest, for example, do not require fences;
in the case of a well in a zone of fl ooding risk with strong currents, it is
preferable to use only barbed wire, as a fence would be likely to obstruct
fl oodwater and be torn down.
4.2 Close protection zone
This zone is defi ned as the zone of signifi cant drawdown in the aquifer.
In France, it is recommended that the zone be drawn to take into
account a residence time of 40 days, supposedly long enough to get rid of
any bacterial contamination.
The close protection zone (or close zone) corresponds, in a continuous
medium and under conditions of mechanical extraction, to the cone of
depression associated with a catchment. In a discontinous environment,
this zone corresponds to the portion of the aquifer within a short mass
transfer time (hours, days).
The close zone has a double protection function: quantitative protection
of the resource, and protection of its quality.
With respect to the quantitative aspect, it requires that any new search
for water within the zone be not recommended: a private entity or a
community should not compete with the community exploiting the same
resource. The community itself can of course increase its production capacity
(reconstruction of catchment systems, drilling of new wells).
With respect to the qualitative function, numerous restrictions and
regulations can be cited. The extraction of material from the ground
(quarries), which modifi es the infi ltration conditions of precipitation, the
creation of new installations classifi ed as environmentally hazardous,
the issuing of building permits with individual sewage treatment, the
installation of open-air livestock housing, of industrial poultry farms, or
of hog farms, are forbidden. The construction of stormwater or wastewater
injection wells, of wastewater or hydrocarbon pipelines, the storage of
radioactive or chemical waste, of fl ammable material and petroleum, of