Characterizing Aquifers - Hydrogeology: Objectives, Methods, Applications - page 137

and x is the distance between the pumping well and the piezometer in
question (in m).
This method can be illustrated by a pumping test in the alluvial aquifer
of the Loup river (Alpes-Maritimes), over 14 days (Figure 73). The test
was performed in a well 9 m deep, with a discharge of 45 m 3 ·h -1 , and the
water table height was monitored in the pumping well and in 4 peripheral
piezometers, at distances, respectively, of 76 m (P1), 112 m (P2), 107 m (P3),
and 260 m (P4).
The curves show the drop in water level of the pumping well during
pumping, and the different reactions in each piezometer. The latter are
not proportional to their respective distances from the well, and reveal the
horizontal heterogeneity of the alluvial aquifer.
The fi rst rectilinear portion of the curves allows the calculation of the
aquifer's characteristic parameters, leading to the values in the following
table (Table 11).

Table 11 Characteristic Parameters of the Alluvial Loup Aquifer (Alpes-Maritimes).

Point Transmissivity T (m 2 ·s -1 ) Storativity S (%)

Pumping well 0.47.10 -2

P1 2.32.10 -2 2.33.10 -2

P2 2.59.10 -2 4.93.10 -2

P3 1.53.10 -2 7.20.10 -2

P4 2.36.10 -2 2.96.10 -2

The curves then present commonly encountered variations for pumping
tests, fi rst a doubling of the slope, then stabilisation before the pumping
was stopped.
The doubling of the slope (beyond point i on the fi gure) indicates the
existence of an impermeable lateral barrier, probably one of the banks of
the fi lled-in channels within which is established the alluvial reservoir. The
image well method allowed an estimate of the limit's distance at between
230 m and 450 m, depending on the point under consideration (well or
piezometer), which is totally compatible with the known geologic structure
and with the superfi cial extent of alluvium.
The fi nal stabilization is characteristic of a lateral infl ow front at a
set level, represented by the Loup River, which is closely linked to its
accompanying aquifer.

6 WATER ANALYSES

Natural physical, chemical, isotopic, or microbiological tracers are a
powerful tool in understanding groundwater. Indeed, at any observation