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Gregg In Situ, Inc. conducts Ultra Violet Induced Fluorescence (UVIF) Cone Penetration Tests using a UVIF module that is located behind the standard piezocone, Figure UVIF.  The ultra violet induced fluorescence cone works on the principle that polyaromatic hydrocarbons (PAH’s), mixed with soil and groundwater, fluoresce when irradiated by ultra violet light.  Therefore, by measuring the UVIF intensity of the soil and groundwater the lateral and vertical extent of polyaromatic hydrocarbon contamination in the ground can be determined.

The UVIF module uses principles of fluorescence spectrometry by irradiating the soil with ultra violet light.  The hydrocarbon molecules absorb the UV light energy during radiation and immediately re-emit the light at a longer wavelength.  This re-emission is termed fluorescence.  The difference between the excitation (250 nm) and emission (275-550 nm) wavelengths is called the Stokes shift.  Specific hydrocarbon compounds can be identified by the magnitude of their Stokes shift, Figure EWL.

Figure UVIF

In general, as the number of aromatic rings increase the fluorescent response shifts toward longer wavelengths.  Therefore, lighter compounds tend to fluoresce at shorter wavelengths and heavier compounds fluoresce at longer wavelengths.

The UVIF module contains a fiber optic cable that captures the emitted radiation and sends it to an amplifier at the surface so the intensity can be recorded. 

The UVIF data is displayed in graphical form along with soil behavior type and other calculated parameters with the corresponding CPT plot.

Figure EWL (After Fontana, 1994)