Geology Reference
In-Depth Information
Figure 104 Difference in the design of a catchment area protection, according to its recharge
mode.
The defi nition of protection zones is therefore currently a large source
of work for specialized hydrogeologic and environmental consulting fi rms.
For example, in a porous environment, the expert must have data on the
geometry of the aquifer (limits, thickness, storativity), on its piezometry,
on its hydrodynamic characteristics (transmissivity, permeability), on its
physico-chemistry over time. The expert therefore requires geophysical
surveys, exploration drilling, piezometric surveys, pumping tests, and
dating and analyses of the water. In heterogeneous (fractured or karst)
environments, there is the additional requirement of tracer or multi-tracer
tests in order to determine the residence times for water infi ltrated in various
zones of the catchment basin.
4.1 Immediate protection zone
The immediate protection zone (or immediate zone) is a limited area
intended to protect the catchment system itself, within which all activities
aside from water extraction are forbidden. The land parcel must be entirely
owned by the community. An immediate zone must not be a storage area
for streetlights, fi rewood, sewer-cleaning vehicles, or rabbits being breeded
for hunting! (all examples encountered in Southern France).
This zone does not not exempt from construction standards: tubing
cemented to the non-water-bearing cover and the impermeable units
separating aquifers, impermeable slab foundation, surrounding rim higher
than the ten-year fl ood level….
The constructed catchment system (gallery, tank, borehole, well) must
prevent public access with a building closed by a locking metal door.
The size of the immediate zone is a function of the nature of the aquifer:
a zone of a few m 2 for an artesian well, or of 10 m x 10 m for a superfi cial
unconfi ned aquifer. The size is generally dictated by the size of the catchment
construction: a classic point-source catchment requires only a 10 m x 10 m
zone, a small spring catchment with an access gallery of 20 m might have a
perrimeter measuring 10 m x 40 m, and a large catchment fi eld such as the
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