Evaluation of Tiered Environmental Forensic Methods for Petroleum Derived Light and Middle Range Distillates

Abstract

Environmental forensics of crude oil releases to the environment has been a topic of considerable research in recent years. However, less study has been conducted to develop and employ environmental forensic strategies for light and middle range distillates released to the environment. Complex molecular structures allow certain petroleum biomarkers to be quite recalcitrant to changes in their molecular structure from environmental processes such as weathering, making these biomarkers common target analytes for crude oil environmental forensics studies. However, refining and weathering processes remove a significant amount of commonly analyzed biomarkers from light and middle range distillates, presenting challenges for environmental forensic studies.

A tiered environmental forensics strategy was developed to attempt to identify diagnostic compounds and ratios that are most beneficial for application in light and middle distillate chemical fingerprinting. Samples were collected from a Study Site that was evidently contaminated by multiple sources. Contaminated groundwater and light non-aqueous phase liquid (LNAPL) samples were collected for laboratory analysis from various areas of the Study Site. Additionally, fresh gasoline and diesel samples were collected directly from the on-site fuel dispensers and analyzed as reference samples.

Distribution patterns of C3-alkylbenzene compounds proved valuable for linking the light distillate contaminant plume at the Study Site to the reference sample. C3-alkylbenzenes were found to be a beneficial target analyte compound group for environmental forensics studies on sites contaminated by light distillates due to the recalcitrant nature of this compound group. Further, analysis of diagnostic ratios of certain analyte pairs with similar solubility and chemical properties was sufficient to confirm the source of light distillate contamination across the Study Site, supporting the defensibility of the light distillate study methodology. The distinct distribution and diagnostic ratios of the biomarker sesquiterpanes compound group and alkylated PAHs were used to differentiate LNAPL collected from a contaminated portion of the Study Site to the fresh diesel reference sample. The LNAPL collected at the Study Site was determined to have originated from a different crude oil feedstock source and/or refining process than the fresh diesel reference sample.