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Any environmental forensic investigation generally revolves around three or four important questions, such as: what is the product; where did it come from; how long has it been there and is it degrading? Many site-or incident-specific factors will determine how these questions are addressed but most will l involve chemical analysis using gas chromatography (GC), GC–mass spectrometry, and stable isotopes. Interpretation of these data for forensic purposes derives from the understanding of oil chemistry, weathering, and naturally occurring organic matter in the environment that exists within decades of petroleum geochemistry literature, which is not commonly used by the majority of environmental investigators but can be very useful in providing additional clues that can be of great use in differentiating oils from different sources.

Environmental forensics has emerged as an important area of environmental studies over the past two decades. One of the major areas of interest in environmental forensic investigations is to determine the origin or point of release of a spilled product. A wide variety of analytics are used to fingerprint the contaminant and potential sources in order to determine whether or not there is any relationship between them. If there are multiple possible sources in the area it may be difficult to narrow it down to a specific source. Furthermore, fingerprinting tools that may be useful with complex mixtures may not be directly applicable to single-component mixtures. In situations such as this, utilization of stable isotopes of the individual compounds becomes a particularly powerful tool for undertaking the correlations. The purpose of this chapter will be to provide a review along with some recent examples of the nature of the stable isotope information that is typically obtained in environmental forensic investigations and how this information may be interpreted. Examples will involve hydrocarbons, chlorinated solvents, and MTBE and BTEX compounds. Techniques will include gas chromatography (GC), gas chromatography–mass spectrometry (GCMS), stable isotopes—both bulk and gas—and chromatography–isotope ratio mass spectrometry (GCIRMS).