Laser-Induced Fluorescence (LIF) for High-Resolution Site Characterisation (HRSC) and delineation of LNAPL source zones - Webinar #3

Rapid, precise delineation of petroleum LNAPLs using laser-induced fluorescence (LIF) for improved LNAPL conceptual site models and in-situ remediation plans

Legion Drilling recently hosted a webinar featuring Randy St Germain from Dakota Technologies, focusing on Laser-Induced Fluorescence (LIF) Technology and the application of the Ultra-Violet Optical Screening Tool (UVOST) for High-Resolution Site Characterisation (HRSC) and more specifically petroleum LNAPL source zone delineation.

Contaminated Land Investigation, Direct Sensing, High Resolution Site Characterization (HRSC), Laser Induced Fluorescence (LIF), LNAPL Conceptual Site Model

What is Laser-Induced Fluorescence (LIF)?

Laser-Induced Fluorescence (LIF), and the UVOST system in particular, is considered one of the most powerful tools for identifying and delineating petroleum hydrocarbon LNAPLs. It enables rapid identification of fluorophore molecules, such as polycyclic aromatic hydrocarbons (PAHs), at the centimetre scale. The application of UVOST is particularly encouraged in sites impacted by petroleum hydrocarbon fuels such as petrol, diesel, kerosene-type jet fuel and crude oil, addressing the limitations of conventional investigation methods.

The major benefits of UVOST include its ability to provide detailed and efficient site characterization, rapid identification of LNAPLs, precise delineation of source zones, real-time data visualisation, and reduced project durations. LIF technology has been successfully applied worldwide for approximately 30 years, offering insights into LNAPL type, weathering degree, and subsurface conditions.

Legion Drilling, with a decade of experience, pioneers High-Resolution Site Characterisation (HRSC) services in Australia. They operate from locations in Brisbane, Sydney, and Townsville, providing cost-effective and sustainable solutions through the application of UVOST.

More about the Laser-Induced Fluorescence (LIF) technology

The power of Laser-Induced Fluorescence (LIF) technology lies in its ability to use a laser source to excite molecules in subsurface contaminants and environmental dyes, producing characteristic absorption and emission spectra. UVOST, as other LIF systems, uses a sapphire window to transmit laser pulses into the geological medium and measures the fluorescence response at four wavelengths (350 nm, 400 nm, 450 nm, and 500 nm).

Advanced log interpretation is crucial for understanding UVOST data, considering factors such as NAPL characteristics, geological features, and the analysis of multi-wavelength waveforms. It should be emphasised the importance of adapting field plans based on real-time data and the combination of UVOST with other tools for comprehensive site characterization.

The Legion Drilling webinar #3, featuring Randy St Germain from Dakota Technologies as the presenter, focused on Laser-Induced Fluorescence (LIF) and the application of the Ultra-Violet Optical Screening Tool (UVOST) for delineating petroleum LNAPL source zones. The webinar delved into the intricacies of LIF tools, justifying the existence of different systems (UVOST, TarGOST, DyeLIF) due to the vast variations in the chemistry of light NAPLs (Non-Aqueous Phase Liquids). The UVOST, specifically designed to handle crude oil and refined fuels like diesel and petrol, was highlighted as a powerful tool for this purpose.

Randy St Germain elucidated the chemical variations in fuels. He explained the principles behind fluorescence, detailing how different polycyclic aromatic hydrocarbons (PAHs) in fuels fluoresce at different wavelengths, allowing for their identification.

The discussion extended to the importance of waveforms in interpreting data, emphasizing that different fuels exhibit distinct fluorescence behaviours. The UVOST response at multiple channels (including the UV ‘blue’ channel, sensitive to smaller PAHs, and the ‘red’ channel, sensitive to larger PAHs) were shown to be crucial in differentiating fuel LNAPLs during the analysis. A reference emitter (RE) was introduced as a calibration tool, helping standardise measurements across different sites. St Germain underlined the significance of interpreting the %RE (reference emitter) values, cautioning that the interpretation should consider the specific characteristics of each fuel type.

The presentation delved into practical applications, showcasing how UVOST performs with different fuel LNAPLs at varying concentrations in soil. Diesel, with its high fluorescence, demonstrated a linear relationship between concentration and fluorescence intensity, whilst petrol exhibited lower fluorescence.

St Germain introduced the concept of lifetime processing to analyse waveforms further. By breaking down waveforms into colour and lifetime components, a more comprehensive understanding of the type and concentration of LNAPLs became possible. The cluster diagrams provided a visual representation of different LNAPLs based on their fluorescence characteristics, aiding in distinguishing various sources in complex subsurface environments.

The presentation also provided insights into challenges and limitations of LIF, such as false positives from fluorescent natural materials and the impact of soil particle size on fluorescence. St Germain emphasised the need for a nuanced interpretation, considering factors like oxygen presence and the evolving chemistry of LNAPLs over time.

Additionally, St Germain discussed the rapid degradation of petrol when subjected to air. The distinct shifting patterns in the LIF signals became crucial indicators for identifying the type of LNAPL present at a site. For instance, gasoline exhibited a chameleon-like quality due to its weathering behaviour, while diesel showcased consistent waveforms over extended periods. St Germain highlighted how, for a specific LNAPL, the waveform shape may remain constant regardless of the signal size. Detailed insights were provided into the interpretation of LIF signals, especially in cases of small signals indicating low concentrations of LNAPL. St Germain stressed the necessity of closely examining waveforms for extended lifetimes and any blue shifts, as these could signify the presence of LNAPL.

The webinar included an exploration of complex field LIF logs, showcasing variations in the fluorescence patterns. St Germain explained the challenges of interpreting such LIF logs, pointing out the need to differentiate between weathering patterns and potential mixing zones. The presentation also touched on the significance of using multiple types of information. The presenter shared a case study where soil core samples confirmed LIF interpretations, emphasising the importance of validating results with additional techniques. He showcased the effectiveness of LIF in identifying small veins of LNAPL, highlighting the potential challenges in sampling adjacent to wells and the need for careful control of localised heterogeneity.

The webinar concluded with a discussion on plotting LIF data, incorporating multiple logs, and addressing the complexities of heterogeneous sites. St Germain provided valuable insights into the challenges posed by site variability and the importance of controlling sample locations for accurate comparisons.

In the upcoming sessions, the presenter promised to delve into breaking down LIF signatures into separate bodies, exploring core photography, and revealing intriguing findings related to activated carbon (BOS 200)'s interaction with petrol. Overall, the Legion Drilling webinar delivered valuable information on the practical applications and nuances of LIF using UVOST for LNAPL source zone delineation, emphasising its benefits, capabilities, and the importance of accurate data interpretation for effective site management and remediation strategies.

Check out other webinars organised by Legion Drilling here.