When attempting to differentiate biogenic contribution from petrogenic impact in samples, a typical best first approach is to start by interpreting your routine PHC data.
This includes:
(1) Moisture content: Typical moisture in soils is in the range of 20 to 40%; moisture content values above 50% are a good indicator of high organic soil (such as Peat or Topsoil), suggesting the possibility that biogenic material is present.
(2) Presence / absence of BTEX compounds: While fraction hydrocarbons represent a mixture of compounds and could therefore potentially be non-petroleum in nature, the presence of individual BTEX compounds at the very least suggests that petroleum related impact cannot be ruled out.
(3) Hydrocarbon fractions: Hydrocarbons quantified in the F3 and F4 ranges with no other volatile compounds present are potentially a good indicator of biogenic impact.
(4) Chromatograms: Chromatographic profiles that present as random groups of peaks eluting in the F3 and F4 ranges (C16-C50), without the visual presence of n-alkane peaks or unresolved complex mixtures (chromatographic “humps”), are good indicators of biogenic impact rather than petroleum related
It should be noted that these individual lines of evidence should be consider together, in the context of the project. The more lines of evidence correlate, the more conclusive the conclusion