Environmental Engineering Reference
In-Depth Information
Using this system, a variety of chemical pollutants can be assessed during cone
penetration, including volatile organics, aromatics, chlorinated solvents and dense
non-aqueous organic liquid (DNAPL) [KYL 97, ROS 98]. A specific aspect of this
approach is that qualitative information on the type of contamination can be
obtained from the Raman spectra. Since the Raman signal produced by many
chemical constituents is very low, concentrations of nearly pure product are required
for detection [BRA 95]. Carrabba [GIL 95] also reported the development of a cone
penetrometer-based Raman spectroscopy to examine the feasibility of locating and
identifying NAPL. These tests showed that the optimum Raman wavelength was
dependent on the type of soil.
b)
a)
1500
1500
1000
1000
500
500
0
0
270
280
290
300
270
280
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Wavelength (nm)
Wavelength (nm)
Figure 12.12.
Raman signatures: a) carbon tetrachloride; and b) trichloroethylene [NIS 97]
12.3.2.6.
Visual cone penetrometer
Another interesting
in situ
device is the visual cone penetrometer [HRY 98, SAR
97]. The device uses digital cameras mounted behind miniature sapphire windows in
a cone penetrometer to scan the sub-surface during the penetration of a
penetrometer. Cameras can capture and save images with a visual field up to 20 mm
(measured diagonally) and can operate in black and white or color. The images
collected with the camera can be used to help identify the mineralogy of the soil, to
seek evidence of a change in the type of material, and to provide a continuous and
accurate indication of the size of a grain of soil. This last feature is especially
valuable because a visual cone could potentially be used in conjunction with a laser
probe system to correct the signal intensities observed, for example from
measurements of fluorescence for known effects of soil grain size. The use of a
visual cone can therefore greatly improve the quantitative possibilities of the optical
spectroscopic probes.
12.3.2.7.
Other uses of the CPT
Besides providing a platform for the deployment of a wide variety of site
investigation technologies, the CPT can be used for water sampling or gas analysis.
