Environmental Engineering Reference
In-Depth Information
Traditional drilling and sampling are still the main approach used to conduct an
environmental characterization of a given site. However, a rich set of standards has
been developed by the ASTM [AST 98], defining specific drilling and sampling
protocols to ensure that quality samples (for both soil and water) are obtained for
environmental investigations.
Unlike previous standards that have focused on the sampling method, the
protocol for these new standards ensures that the chemical characteristics of the
samples are not altered and that clean areas of the sub-soil are protected. Factors
such as contamination, volatilization and preservation of samples are of prime
importance in these standards.
A major difference between traditional geotechnical and geoenvironmental
investigations is the need to define a detailed ground stratigraphy. Indeed,
contaminants generally move along paths of least resistance, and the narrow and
permeable channels usually guide their movements [WEB 96]. It is important to
define these pathways. However this task is difficult to accomplish using
conventional drilling and sampling because the volume investigated is often small,
sampling is generally slow, and the cost of removal is high. In addition, traditional
drilling and sampling brings contaminated materials to the surface that often needs
to be handled as “hazardous or toxic waste”. Accordingly, methods of investigation
have been developed so that a better characterization can be executed in a faster way
at lower cost and without generating waste spoils.
Direct penetration technologies are particularly responsive to the need for faster
and less expensive investigations. These technologies are mostly derived from the
cone penetrometer test (CPT). The cone penetration test is fast, economical, easily
reproducible and provides accurate data that can be used to determine the
stratigraphy and geotechnical parameters of a given site. Thus, it provides a much
more rapid and effective approach by which to describe the stratigraphy of a site
without bringing polluted materials to the surface and eliminating the need for
treatment and storage of materials that can be dangerous.
The most attractive aspect of cone penetrometers, however, is the ability to
incorporate other types of sensors to measure further geoenvironmental parameters
in addition to penetration resistance. One example is the resistivity sensor. Other
probes have been developed, such as sensors that enable the measurement of pH and
temperature, radar probes (GPR or ground penetrating radar) and gamma probes.
Such probing technologies have been successfully adapted to the CPT including a
new class of probes based on the use of fiber optics and light absorbance or
fluorescence as a signal.
