Environmental Engineering Reference
In-Depth Information
13.7.4.
In situ tracer test
This last example shows the results of a three-dimensional numerical simulation
of an
in situ
tracer test around a pumping well [BIV 93]. The site studied and
discretization are identical to those of the previous example, but here five finite
element layers mesh the depth of soil.
The tracer is injected (at point
i
in Figure 13.10) at the surface for about 30
minutes. At steady state, all the water flows converge towards the pumping well
(noted
p
in Figure 13.10).
Figure 13.12 presents the restitution curves of the tracer at the pumping well at
different depths. Figure 13.13 shows the maps of tracer concentration (in ppb = 10
-9
)
in the mobile water at three different times in a vertical cross-section between the
injection place and pumping wells.
Finally, Figure 13.14 gives the same results for the upper surface layer and two
vertical cross-sections (one between the injection wells and pumping wells; the
other perpendicular to it), seen from beneath the surface. We can again see the
importance of three-dimensional effects and observe the results of the mechanical
dispersion.
5
Concentration (ppb)
z = -24.5 m
4
z = -31.0 m
z = -37.5 m
z = -44.0 m
3
2
z = -50.5 m
1
z = -57.0 m
0
T (h)
0
12
24
36
48
Figure 13.12.
In situ tracer test: restitution curves according to depth
