Cone penetrometer based on time domain reflectometry and laser induced fluorescence for contaminated site investigation

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4. Cone penetrometer based on time domain reflectometry and laser induced fluorescence for contaminated site investigation

The rapid characterization of soil and groundwater contamination is always a focus of environmental geotechnics, which stimulates the development of some advanced site characterization tools. This paper developed a novel cone penetrometer to identify soil ionic contaminants, groundwater dissolved organic matters (DOMs), and polycyclic aromatic hydrocarbons (PAHs) based on laser-induced fluorescence (LIF) and time domain reflectometry (TDR). The characteristic excitation wavelengths (325 nm) for defining the presence and extent of groundwater DOMs were found using excitation-emission-matrix spectra. On the other hand, to increase the detection depth of previous TDR penetrometers, the TDR module configuration (non-conductor shaft diameter and core material) was improved based on a spatial weighting analysis of the electromagnetic field using a seepage analysis software. Then, an integrated cone penetrometer consisting of a LIF module (two downhole ultraviolet lights to induce fluorescence and one industrial endoscope behind a sapphire window to capture the underground images) and a TDR module (four semicircle-shaped conductors circled PEEK shaft) was developed. Finally, the proposed novel penetrometer innovatively realized in-situ detection of groundwater DOMs based on 325 nm laser-induced fluorescence. The soil ionic contaminants and PAHs could also be characterized by electrical conductivity from TDR waveforms and fluorescence intensity from 275nm laser inducing respectively. The tool, successfully applied to a 30m-depth contamination detection in Woqishan Landfill, could hammer complex scenarios like landfills and petrochemical contaminated sites.

9th International Congress on Environmental Geotechnics (ICEG2023)

Advances in Geoenvironmental Field Characterization