Cone
Penetrometer Technology
(CPT)
Description
Cone
penetrometer technology (CPT) is a method of providing real-time
data for use in characterizing the subsurface, as opposed to older
methods of
analyzing subsurface conditions in the laboratory. It consists of a
steel cone
that is hydraulically pushed into the ground at up to 40,000 pounds of
pressure. Sensors on the tip of the cone collect data. Standard cone
penetrometers collect information to classify soil type by using
sensors that
measure cone-tip pressure and friction. CPT is often used in
conjunction with
Hydropunch tests, which use the CPT holes to extract groundwater
for laboratory analysis. An innovation of the CPT (i.e., the wireline
CPT)
allows multiple CPT tools to be interchanged during a single
penetration,
without withdrawing the CPT rod string from the ground.
Initially
developed to collect information about soil characteristics, as sensor
technology was developed CPT also became a platform for collecting
information
about a variety of contaminants.
Recent advances in sensor technology have expanded cone penetrometer
capabilities to detect the presence of petroleum hydrocarbons.
Sensors are being tested or demonstrated for the detection of other organics,
compounds, metals, radioactivity,
explosives, and soil moisture.
Generally,
the advantage of using CPT is that sampling costs less and is
faster than
shipping samples to a laboratory. CPT locations can be altered as
results are
analyzed, thus providing the operator with increased flexibility. It
should be
noted, however, that when certain sensors are used, results may have to
be validated
by laboratory analysis.
Limitations
and Concerns
CPT
cannot be used at some sites due to high soil density.
Most
sensors are now used as screening tools that provide initial site
characterization data. The data is confirmed by collecting samples that
are
analyzed in the laboratory. This is due to limitations in sensor
technology,
and it will likely diminish in importance as the technology improves.
CPT
is useful on sites that contain unconsolidated sediments (e.g., soil
and clay
that are not cemented together). On the other hand, sites with large
boulders,
rock or cemented layers are difficult to penetrate.
CPT
sensors, such as lasers, that require a lens may be hampered by fouling
of the
lens due to a reaction to dust.
Decontamination
may be necessary if the CPT comes into contact with contaminated
material.
Applicability
CPT
is a characterization tool used to identify the geologic, hydrologic
and chemical features of a site. It can be applied to all sites. It is
not
contaminant specific. CPT is generally applied to depths up to 150
feet, but it
has been used as deep as 300 feet.
Technology
Development Status
CPT
was introduced in 1934 in the Netherlands. Actual electrical
measurement
sensors were not developed until 1948, and they were not widely used
until the
1960s. By the 1980s, the cone penetrometer was commonly used for
geo-technical
applications, with at least a dozen companies routinely providing the
technology. Research was initiated in the late 1980s to develop other
sensors.
Web
Links
http://www.frtr.gov/site/3_3_1.html
http://www.epa.gov/esd/cmb/site/pdf/papers/sb125.pdf
http://clu-in.org/characterization/technologies/dpgeotech.cfm
Other
Resources and Demonstrations
See
the descriptions of SCAPS,
X-ray
Fluorescence (XRF), Laser-induced
Fluorescence (LIF), and Raman Probe.
A
successful demonstration was performed at Sandia National Labs (SNL) in
New
Mexico using an integrated Laser Induced Breakdown Spectroscopy (LIBS)
and Cone
Penetrometer Technology (CPT) system to rapidly analyze (currently less
than 24
hours) the heavy-metals
content of the subsurface soils. The CPT-deployed LIBS using a
high-energy
laser pulse. The soil absorbs the energy and heat. Elemental analysis
is
conducted via an optical fiber. The CPT/LIBS system was successfully
demonstrated. (LIBS technology developed by Los Alamos National
Laboratories
was successfully field tested to detect chromium and beryllium in
surficial
soils. However, one of the shortcomings of LIBS is the calibration/data
analysis procedure requires a knowledge of soil type prior to effective
LIBS
analysis).
See
http://www.osti.gov/bridge/servlets/purl/491995-LAQZsj/webviewable/
for a description of a cone penetrometer with a Raman probe used at
Hanford
underground tanks.
See http://www.osti.gov/bridge/servlets/purl/585514-XNxjsb/webviewable/ for determining migration and distribution of contaminants using multiple sensors on the cone penetrometer.