A tiered approach to distinguish sources of gasoline and diesel spills.

Approximately 11% and 25% of annual Canadian oil spill accidents are gasoline and diesel spills, respectively. Gasoline and diesel spills are a challenge to conventional environmental forensic techniques because refinery processes remove most of the higher molecular weight biomarkers. This study presents a tiered environmental forensics strategy that includes such information as site operational history, geology/hydrogeology, GC/FID pre-screening, volatile GC/MS, semi-volatile GC/MS, and GC/MS selected ion monitoring (SIM) chromatograms for fingerprinting of gasoline and diesel spills. GC/FID pre-screening analysis identified the presence of two individual gasoline and diesel plumes at a fuel service station (study site). The gasoline plume is present between the upgradient fuel underground storage tanks (USTs) and the downgradient diesel plume, suggesting that the diesel impacts to groundwater may not be originated from the current UST leakage. Similar distribution of C3-alkylbenzenes (the most stable chemicals in gasoline) and the consistent diagnostic ratios of the analyte pairs with similar solubility indicate that the source for the dissolved gasoline constituents in the gasoline impacted zone likely originated from a gasoline leakage from the current USTs on the study site. In the diesel impacted zone, the distinct distribution and diagnostic ratios of sesquiterpanes (biomarkers for diesel) and alkylated PAHs confirm that the diesel plume originate from different crude oil sources than the current USTs.