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Published By Lankelma

Lankelma is the foremost contractor for onshore in-situ soil testing in the UK. An acknowledged specialist in CPT, Lankelma also offers a worldwide consultancy and training service.

A.P. van den Berg develops, designs and manufactures geotechnical and environmental soil investigation equipment for onshore and offshore applications. Specialists in CPT systems and equipment.


Gardline Geosciences offers worldwide marine geotechnics, in-house consutancy and services with marine investigations ranging from nearshore to full ocean depth (down to 3000m).

About the Author

Hans Brouwer studied civil engineering at Delft University in The Netherlands. He has worked as a part-time lecturer at Amsterdam Polytechnic and was senior partner in a structural engineering consultancy. He has written a standard textbook in Dutch about the design of building foundations. He now lives in England where he writes technical textbooks in English, hopefully to reach a bigger readership.

Chapter 4

Part 2: Special cones: geo-environmental cones

Hydrocarbon cone

The hydrocarbon cone (Figure 30) is a
testing instrument for the in-situ detection of light, non-aqueous phase liquids (LNAPLs) of hydrocarbons within soils.
Beneath chemical plants, refineries and
petrol stations, hydrocarbons are frequently encountered within the soil in a pure form, either as droplets or as a distinct floating layer. This pure product requires close attention, particularly where mobility is high (ie within the zone of rising and falling groundwater, and within permeable soils).
Mapping and modelling
Where cost effective assessment and remediation is required, the
importance of accurate mapping and modelling of the spatial
distribution and volumes of the contaminants within the soil is high.
The location and presence of hydrocarbons within the soil is particularly
difficult to establish. It is even more difficult to establish the size and
mobility of these layers and the proportions that can be removed by

Traditional methods of hydrocarbon identification and assessment
include chemical soil analysis and measuring the thickness of floating
layers within observation wells. Both methods require boreholes, and
are time consuming and costly. This is because aquifer protection
systems are required and the equilibrium time for monitoring wells can
be significant, with durations of one week and longer not uncommon.
Furthermore, the floating layer in a well represents the mobile part of
the LNAPLs in the soil and not its in-situ location.
The hydrocarbon probe detects, continuously with depth, in-situ, the
presence of total pure product contained within the soil. The system is
pushed into the soil using standard cone penetration testing plant and
The detection of hydrocarbons as a pure product is enabled because
the hydrocarbon mixtures produce fluorescence when they are
irradiated with UV light.   

The cone
The hydrocarbon probe has the appearance of a normal CPT cone.
However, it contains a light source as well as the detection system. The
total diameter of the system is 55 mm.
During the penetration process, measurements are carried out by
illuminating the soil from a UV light source placed behind a window. The
fluorescent light emitted by the hydrocarbons is detected by a photomultiplier
tube in the cone.

Detection limit
The detection limit of the system is set at 50 mg/kg dry weight for a
LNAPL. The intensity of the radiation emitted by the hydrocarbon is an
indication of the concentration of pure product contained within the soil.
The system can also detect other wavelengths for analysis of other
products contained by soils.
The instrument is calibrated. During the test programme, the
occurrence of ‘smearing’ and ‘displacement’ is examined. In practice
however, it has been demonstrated that soil effectively cleans the
probe from hydrocarbons as it passes through the soil.
Displacement of the LNAPL in front of the penetrating probe tip does
occur to a limited extent. This means that the depth at which the LNAPL
occurs in the soil is slightly less than the depth observed by the
hydrocarbon probe. However, this slight variation is considerably less
than drilling-induced disturbance experienced using traditional cable
tool-boring methods of exploration.
Speed and reliability
The speed and reliability with which the method can establish the
presence and extent of LNAPL contaminants means that cost savings
can be obtained. These savings can be made in the reduction of
chemical sampling required and laboratory testing required. Where
necessary, Mostap samples can be obtained to correlate the results
of the hydrocarbon probe and provide samples for subsequent
laboratory testing.
Significantly more exploratory locations can be achieved in less time, in
comparison with traditional sampling methods. Therefore, improved
and more accurate contamination models through contouring and
volume calculation can be achieved. 
The system can also be used for the monitoring of in-situ clean-up
operations. The probe can be used to detect petrol, diesel and motor
oils following calibration. It is also possible to establish whether or not
the LNAPLs can be pumped-off, based on the results of the
hydrocarbon probe.
Typical test results are shown in Figure 31



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