Examining the ultraviolet optical screening tool as a viable means for delineating a contaminated organic sediment

Abstract

Rapid and accurate delineation of contaminated sediments in marine environments is critical for the effective assessment of site risks and the development of appropriate remedial action plans. In this study, a new application of the ultraviolet optical screening tool (UVOST) equipped with electrical conductivity measurement (UVOST-EC) is proposed to delineate a water-covered sediment contaminated with dioxins and furans in a decommissioned pulp and paper wastewater stabilization basin. Bench scale experiments are presented that were used to develop a UVOST-EC interpretation method for delineating between two different sediment types present in the basin: an anthropogenically derived organic rich contaminated sediment (“black sediment”) and a naturally occurring grey organic silt sediment with marine provenance (“grey sediment”). The method involves comparative analysis of fluorescence and electrical conductivity signatures between the two sediments. Results indicate that each sediment type presents unique “signatures” related to fluorescence and electrical signals which corresponds to variability in their physio-chemical structure. Almost 100 UVOST-EC tests performed at the study site were paired with ex situ physical gravity core measurements of the black sediment to test the accuracy of the UVOST-EC-based method. A statistical analysis at seven sample “cluster” sites (i.e. multiple sub-samples within a defined area) indicated that the mean of sediment thickness obtained by the UVOST-EC measurement technique at a given site were not significantly different (p = 0.05) from measurements derived from sediment gravity core measurements. The UVOST-EC-based sediment thickness delineation method reliably determined the thickness of the dioxin and furan contaminated sediments as compared to gravity core determination for the sediment in this study. Application of this approach to other studies should be assessed in a similar manner. The UVOST-EC method offers health and safety, cost, logistics, and data interpretation benefits.