Source Identification of Petroleum Derived Contaminants in Groundwater

Petroleum derived constituents are among the most common contaminants in groundwater. Source identification is often conducted to better understand the sites and/or to determine the responsible party(s). One of the commonly used methods to identify source(s) of petroleum contaminants in groundwater uses ratios of diagnostic compounds. Typically, the selection of compound pairs for the ratios is based on one hypothesized weathering mechanism. The conclusions drawn based on such analyses can be misleading. As multiple weathering processes (i.e., evaporation, dissolution, biodegradation, etc.) can be occurring simultaneously at a site, the ratios are often influenced by other weathering mechanisms.

This paper presents three case studies to demonstrate that how source identification is conducted with a screening assessment to select paired compounds and a vigorous procedure for data evaluation. The three case studies cover three commonly encountered spill scenarios: gasoline, diesel and mixed sources. The diagnostic compounds were selected by considering laboratory analytical methods, levels of concentration, physical and chemical properties, and biodegradation potential. The pairs were categorized into two groups: primary and secondary. The ratios of paired compounds with similar physical, chemical properties and biodegradation potential were used as primary evidence for source identification. The ratios that consider one or more weathering factors were used as secondary constraints to cross check the conclusions drawn based on the primary group. Advanced statistical analyses such as cluster analysis and principal component analysis were also employed to enhance data evaluation. The results of these three case studies show that source identification is achievable with the appropriate forensic approach.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California