Identification of weathered multiple petroleum products in contaminated soils by characterizing unresolved complex mixture hump in gas chromatograph data

A new method for identifying the petroleum products in contaminated soils is presented, which characterizes the unresolved complex mixture (UCM) hump in the baseline of gas chromatograph (GC) data. The UCM hump identified in soil data was fitted to the Gaussian function, and characterized according to the time for the maximum point (T_UCM) and the width of the hump (w). Experimental results showed that a UCM hump should be clearly observed in soils when contaminated with petroleum, and that soils contaminated with kerosene, diesel, or some lubricating oils estimated herein should present different characteristic values of T_UCM and w. Even though the environmental weathering of contaminated soils under evaporative conditions might cause variations in these characteristic values, they converged to specific constants depending on the product. The method could also differentiate between multiple petroleum contaminants in soil. Feasibility was evaluated using soils from a military oil storage site that was closed in 1970. The soil contaminants identified by the proposed method corresponded to the historical storage records, suggesting that the UCM hump characterization method could have strong potential in environmental forensics for differentiating products in petroleum-contaminated soils.