Environmental Engineering Reference
In-Depth Information
photomultiplier tube. The intensity of radiation emitted by the contaminant is an
indication of the product concentration in the soil. An example of a fluorescence
intensity profile of a site polluted with fuel is shown in Figure 12.11. The peaks in
the fluorescence profile correspond to places where there is oil.
Intensity fluorescence signal (output in V)
2
0
4
6
GL 0
-2
-2
Sampling point for
Mineral oil determination
-4
-4
-6
-6
NAPL - layer of
domestic fuel
Sand
Sand
Clay
Silt
Pebbles
SOIL PROFILE
FROM HYDROCARBON PROBE
DESCRIPTION OF
SOIL PROFILE
Figure 12.11.
Profile of the fluorescence intensity of a site polluted with fuel [OLI 94]
When using technologies such as the LFI sensor systems it is important to take
into account the fact that these devices are exploring very small volumes of soil. In
fact, the actual area covered by the excitation energy can be just 10 µm in diameter.
Therefore it is important to take into account the effects of soil properties on
measurement of contaminant. Although research has shown that the soil has little
impact on the shape of fluorescence emission spectra and fluorescence decay time
[SIE 99], it seems clear that soil properties such as grain size have a significant
impact on the intensity of the fluorescence emission associated with a particular
concentration of a contaminant in the sub-soil [API 93, SIE 99]. It is therefore
