Environmental Engineering Reference
In-Depth Information
For water sampling, the sampling point is pushed to the desired depth with the filter
in the closed position. Once the desired depth is reached, a mechanism allows the
pore water to flow inside the probe. In most cases, the water flows directly into the
stems of the CPT and can be pumped or skimmed and analyzed. The Technology
Center at Savannah River (US) has developed a miniature pump that can be installed
at the end of the cone penetrometer. This pump provides discreet semi-continuous
sampling of groundwater during a penetrometer push. By installing these pumps in
the penetrometer, we eliminate the need to withdraw and reintroduce the stem of the
CPT, which results in a considerable gain in the duration of sampling.
Gas samples can also be collected using the CPT. The gas is transferred to the
probe using a gas sampling port located on the CPT probe. Teflon or high-density
polyethylene tubes are used to extract gas from the sampling orifice near the tip of
the analysis instruments' probe. [LIG 95] presented some analytical techniques that
were used with the cone penetrometer system, such as high-speed gas
chromatography equipped with an external detector of acoustic wave. At the
Hanford site (US), several volatiles analyzers incorporated in a CPT were evaluated,
including an infrared spectrometer and a handheld detector incorporating an
acoustic wave sensor. One end of the transfer line was attached to the cone
penetrometer probe and the other end to a gas sampling manifold that splits the gas
flow to each analyzer. In addition to real-time monitoring, the gas can be stored in
Teflon sample bags for a more complete analysis in a laboratory.
12.3.3.
Geophysical methods
The use of direct penetration technology has certainly helped overcome some of
the shortcomings of traditional drilling and sampling. However, the volume of soil
that is assessed is still extremely small. In this respect, geophysical methods,
including electrical methods, can offer a viable alternative because of the advances
made in this field in both technology and date inversion.
For example, inorganic contaminants can be detected by electrical methods
because of their high specific conductivity. The electrical contrast can map the
extent of contamination in all directions. Geophysical methods will not detect low
concentrations of contaminants. Changes from 10 to 20% of dissolved solids in pore
fluids may, however, be detectable under certain conditions. Electrical methods
provide not only a way to directly map the magnitude of non-organic contaminants,
but also provide the direction of flow and evaluation of concentration gradients
[BEN 93]. A good correlation between the chemical data of groundwater and the
results obtained by electrical methods to map areas of contamination by non-organic
products from landfill was reported by [BEN 93]. If there is a mixture of organic
and inorganic, a first approximation of the distribution of organic products can often
