Now that I know what UVOST is; How does it work??

The Direct-Push system (Geoprobe) drives the optical probe into the subsurface. The UVOST sends UV light through optical fibers that are strung through direct push steel rods. The light reflects off a small parabolic mirror within the probe and exits through a sapphire window on the probe’s face. As the probe is advanced, soil sliding past the window becomes exposed to UV light. Contaminants within the exposed media will “emit” a signal response. The signal response is then transmitted through a fiber line and is analyzed at the surface. The specific analysis is interpreted and displayed instantaneously in graphical and numerical form on a fluorescence vs. depth (FVD) log. Since hydrocarbons fluoresce at different wavelengths, individual wavelengths provide distinct waveforms. These unique patterns are the ‘fuel signatures’ of the petroleum hydrocarbon within the soil matrix and can be used to differentiate differing petroleum contaminants (such as diesel, gasoline, Bunker C, etc).

The figures below show the concept of waveform generation and the transition to the 'fuel signature.'