Interpretation of Gas Chromatographic Data in Subsurface Hydrocarbon Investigations

Capillary column gas chromatography (GC) is extremely useful in investigations of subsurface contamination by petroleum hydrocarbons. Fluid samples collected from observation wells are evaluated by GC methods to detect and analyze petroleum hydrocarbons in dissolved and liquid phases. The presence, types and concentrations of many petroleum‐derived hydrocarbons dissolved in ground water can be determined. GC analysis can also be used to determine the composition of liquid hydrocarbon products, including gasoline, distillates and heavier oils. The degree of degradation of sampled liquid hydrocarbon product can be estimated from GC information, and this information can be helpful in estimating the length of time the product has been in the subsurface. Determination of the hydrocarbon source and migration path can be made from GC analysis of fluid samples collected at two or more locations. This paper is intended to demonstrate interpretative techniques that can be used by hydrogeologists to facilitate the detection, identification and mitigation of subsurface hydrocarbons.