identifying the type of contamination, tracing it back to its source, and occasionally fingerprinting to identify a specific source. It is useful in both remediation and litigation. It involves all aspects of site characterization and it requires an accurate conceptual site model.

In most cases involving petroleum or petrochemicals we usually start with a basic GC/FID chromatogram as a screening tool for characterization. From there, an investigation may involve chemical ratios, GC/MS precision identification and quantification, or stable isotope analysis.

As with any fingerprinting there must be a comparison fingerprint or suite of chemicals to evaluate against. We will discuss some sources of information for obtaining these comparisons and identify some key compounds and ratios that will guide the effort. Petroleum sources, formulation, refining, alterations and degradations each play a key role in selecting a reliable forensic strategy.