Complex NAPL Site Characterization Using Fluorescence Part 3: Detection Capabilities for Specific Excitation Sources
Soil & sediment contamination
Non-aqueous phase liquid (NAPL) contaminants comprised of polycyclic aromatic hydrocarbons (PAHs) can be detected using fluorescence spectroscopic methods. Dense non-aqueous phase liquid (DNAPL) contaminant source zones can be delineated using commercially available cone penetrometer (CPT) devices by detecting commingled oils, fuels, and naturally occurring organic materials entrained by DNAPLs and carried to depths below the water table. It has been demonstrated that commercially available CPT
... ially available CPT based fluorescence detection systems can be ranked based on how effectively their excitation source wavelengths induce fluorescence using excitation emission matrices (EEMs). Several neat NAPLs and dilutions with selected DNAPLs were analyzed for specific fluorescence characteristics to determine the optimal excitation source for site characterization efforts. A comprehensive spectral library and corresponding optimization matrix were generated for complex petroleum mixtures. Based on field results documenting successful indirect CPT fluorescence detection of a DNAPL source zone, aviation and diesel fuels were selected from this library, diluted with chlorinated solvents, and evaluated for fluorescence characteristics. Dilution of these complex NAPL mixtures led to changes in the corresponding EEMs. The optimal excitation source for aviation fuel remained relatively constant for each dilution. However, sensitivity for each of the commercially available CPT excitation sources was strongly dependent on diesel concentration, whereby higher energy (lower wavelength) sources yielded improved sensitivity for lower concentrations. Since field concentrations can be highly variable, these observations support the need for multiple wavelength excitation sources for optimal detection capabilities, particularly when diesel fuel is present.