Complex NAPL Site Characterization Using Fluorescence Part 2: Analysis of Soil Matrix Effects on the Excitation/Emission Matrix

Abstract

Commercially available cone penetrometer (CPT)fluorescence based sensor platforms have been used to detect non-aqueous phase liquids (NAPLs), such as petroleum oils and lubricants, in situf or more than a decade. These approaches have also been used to detect dense non-aqueous phase liquid (DNAPL) source zones by detecting commingled oilsfuels, and naturally occurring organic materials entrained by DNAPLs and carried to depths below the water table. Several neat NAPLs and mixtureswere added to various soil types and analyzedfor specific fluorescence characteristics to determine the optimal excitation source for site characterization efforts. Using excitationlemission matrices (EEMs), we demonstrate that an optimized excitation wavelength can be determinedfor specific fiuowphores within the NAPL mixtures, and that available systems can be ranked based on the specific contaminant and site soil types. An optimal excitation wavelength yields the maximum fluorescence within an EEM spectrum. We ranked commercially available cone penetrometer fluorescence detection systems according to the potential for ease of detection based on maximum fluorescence response. When soils were added tocomplexNAPLmixtures,analytefluorescence emissionwasattenuatedinpreferential portions of the EEM, leading to differences in the optimal excitation source wavelength. Furthermore, impure silica-containing minerals impact the emission signal, potentially leading to incorrect conclusionsf or several commercially available systems. Our find ings suggest that afrequency-agile (e.g., tunable excitation source) probe system would be superior to any other system commercially available, provided the system would be relatively easy to operate and would have rapid in-situ EEM generating capabilitiesfo r optimization in the field.

Keywords:

• NAPL
• DNAPL
• site characterization
• fluorescence
• excitation/emission matrices

Additional information

Notes on contributors

MARK L. KRAM

Address correspondence to Mark L. Kram, Bren School of Environmental Science and Manage ment, 2324 Bren Hall, University of California, Santa Barbara, CA 93106, USA. E-mail: mkram@ bren.ucsb.edu