Forensic Environmental Geochemistry: differentiation of fuel-types, their sources and release time

Abstract

During the evolution of organic and petroleum geochemistry, attention has focused mainly on investigation of either the gaseous or high molecular-weight hydrocarbons. Characterization of novel and environment-specific compounds has enriched our understanding of paleoenvironments, fossil biota and the alteration processes leading to the formation of energy resources. The “fingerprinting” methods developed for reconstructing geologic events can also be used with some modification for characterizing current processes affecting fugitive crude oil and its refined products that have impacted the environment and become an ecologic threat. In order to identify the source of the escaped hydrocarbon products, it is often essential to determine (a) what fuel types the hydrocarbons represent, (b) when the release(s) occurred and (c) how much of each fuel is mixed in the plume. These requirements can be accomplished by the combination of specialized analytical procedures used in standard contamination characterization with methodology developed in organic geochemistry, a combination we refer to as Forensic Environmental Geochemistry. The synopsis provided in this paper is concerned specifically with the light (naphtha) and middle distillate (kerosene-diesel) products in the C 3–C 25 hydrocarbon range. We demonstrate application of certain methods for differentiating various petroleum derivatives based on fuel-specific hydrocarbon patterns, some of which have not been described extensively in the organic geochemistry literature or applied for site investigations. A detailed description is provided for alkylcyclohexane distribution patterns in petroleum products and their use for differentiating various hydrocarbon fuels and solvents in environmentally altered samples. A case history illustrates application of the simulated distillation technique for estimating the relative proportion of individual fuel types in a binary mixture. We also describe how fuel additives can be used as tracers for estimating residence time in the environment and time of manufacture of gasoline. The methodology summarized here has been used in numerous environmental cases throughout the U.S.A. and has provided critical evidence in resolving legal disputes relating to the source of environmental contaminant releases and possible responsible parties.