FORENSIC ENVIRONMENTAL GEOCHEMISTRY - DIFFERENTIATION OF FUEL-TYPES, THEIR SOURCES AND RELEASE TIME

During the evolution of organic and petroleum geochemistry, attention has focused mainly on investigation of either the gaseous or high mole cular-weight hydrocarbons. Characterization of novel and environment-s pecific 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 recons tructing geologic events can also be used with some modification for c haracterizing current processes affecting fugitive crude oil and its r efined products that have impacted the environment and become an ecolo gic 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 m uch of each fuel is mixed in the plume. These requirements can be acco mplished 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 Environ mental 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 app lication of certain methods for differentiating various petroleum deri vatives based on fuel-specific hydrocarbon patterns, some of which hav e not been described extensively in the organic geochemistry literatur e or applied for site investigations. A detailed description is provid ed for alkylcyclohexane distribution patterns in petroleum products an d their use for differentiating various hydrocarbon fuels and solvents in environmentally altered samples. A case history illustrates applic ation of the simulated distillation technique for estimating the relat ive proportion of individual fuel types in a binary mixture. We also d escribe how fuel additives can be used as tracers for estimating resid ence time in the environment and time of manufacture of gasoline. The methodology summarized here has been used in numerous environmental ca ses throughout the U.S.A. and has provided critical evidence in resolv ing legal disputes relating to the source of environmental contaminant releases and possible responsible parties. (C) 1997 Elsevier Science Ltd. All rights reserved.