Laser cone spotlights on-site screening

contamination data, ranging from the latest GeoprobeTM percussion samplers and site GC laboratories to the in situ hydrocarbon detection cones – the Laser Induced Fluorescence (LIF) and Mercury Lamp (ML) probes. Paul Jacobs, Head of the Cone Testing Department at Fugro, explains how the latest LIF cone system allows continuous detection of HC contamination as well as continuous identification or speciation of the contaminant.

Many different types of in situ techniques have been developed over the last decade. The LIF and ML cones can be deployed from normal static CPT rigs. The LIF cone can now also be deployed from the Geoprobe TM percussion samplers allowing better access on congested sites.

Although Fugro operates on-site laboratories to test and process samples faster, and discrete soil samplers to

provide better quality samples, these services do not provide continuous real-time data on in situ contamination. The LIF and ML cones provide real-time data on the extent and amount of hydrocarbon contamination. As well as providing semi-quantitative data on contaminant levels the LIF provides realtime HC contaminant identification, whether the contaminant source is petrol, diesel, etc.

The detection limits of the LIF and ML are directly related to the power of the source of light, ie the number of photons they deliver into the soil, or “more light in, more light out.” Although both the LIF and ML cones use UV light, the power of the light delivered by the LIF is magnitudes higher than that delivered by the ML.

The latest LIF system can now provide continuous fuel/product identification without halting the LIF cone’s

penetration. Data is collected every one second or 20mm during penetration and the spectrum of light fluorescing from the contamination is collected at multiple wavelengths (colours).

The distribution of wavelengths (colours) intensity is a unique “fingerprint” to the type of HC contaminant being probed. To identify the type of contaminant during the test the collected “fingerprint” is compared with the library of standard HC products, such as petrol, diesel, jet fuel, coal tar, creosote and when a match is made the system displays which library contaminant has been found in the ground.

This is performed in real time and before the next one-second reading. The system can be set to search for non-standard HC products which may be used in chemical processes and if a client provides specimens of stored HC matter prior to the LIF investigation then a site specific library is created and used during

the fieldwork.