NAPL Source Identification Utilizing Data From Laser Induced Fluorescence (LIF) Screening Tools Check Access

Spectroscopists discovered that polycyclic aromatic hydrocarbons (PAHs) were particularly efficient at fluorescing when excited by ultraviolet (UV) light. This phenomenon can be utilized for environmental investigation because a variety of PAHs are present in hazardous media such as non-aqueous phase liquids (NAPLs). Laser Induced Fluorescence (LIF) relies on this principle, using UV or visible laser light to excite PAH molecules present in NAPLs and log fluorescence with depth; this allows the distribution and extent of NAPL to be characterized semi-quantitatively within the subsurface. Depending primarily on laser excitation wavelengths, three tools are commercially available. Rapid optical (ROST^®) and ultraviolet optical screening tools (UVOST^®) are very similar and used for most fuels and oils. The tar green optical screening tool (TarGOST^®) is designed for heavy products/hydrocarbons such as coal tar, creosote and bunker C, materials challenging for UV LIF tools. This chapter focusses on waveforms from the LIF tools that are related to NAPL source identification, providing three case studies to illustrate how LIF tools can be used for source identification in a site investigation.