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://www.estcp.org/Technology/ER-9517-VFS.cfm
http://www.estcp.org/Technology/ER-9716-VFS.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.