technique (see Appendix A). For statistical analyses of data, TPH, summed PAHs, and aliphatic
and aromatic fractions were all normalized using a recalcitrant biomarker.
3.6.4 Polycyclic Aromatic Hydrocarbons (PAHs) and Diagnostic Heteroaromatic
Compounds
Using high-resolution gas chromatography mass spectrometry (HRGC/MS; see Appendix A),
mass spectra can be obtained that show peaks corresponding to the molecular fragments of
specific petroleum compounds. Using this approach, we can determine the amounts of individual
polycyclic aromatic hydrocarbons (PAHs). PAHs are various arrangements of fused, aromatic
ring molecules. We can also identify heteroaromatic compounds, which are rings containing
elements in addition to carbon. This approach can be used to specifically identify PAHs that have
been listed by the US Environmental Protection Agency (EPA) as priority pollutants (see Table 6
in Appendix A). Inclusion on this list generally indicates that the compound is carcinogenic.
3.6.5 BTEX
Using appropriate handling, extraction, and analytical methods, we can characterize the volatile
organic compounds (VOCs) benzene, toluene, ethylbenzene, and xylene (BTEX). These
compounds are water soluble and generally have low permissible levels. In field soils, BTEX
compounds are generally the first to leach and to volatilize. Their levels in aged or weathered
contaminated soil may be low. For these sites, BTEX was not considered an issue.
3.6.6 Depletion Monitoring with a Selected Biomarker
For a site contaminated with a relatively uniform type of contaminant, bioremediation
effectiveness can be calculated relative to a compound that is relatively non-degradable. These
recalcitrant or stable compounds are often referred to as biomarkers. As different fractions of the
total suite of petroleum degrade, the relative concentration of the recalcitrant fraction increases.
The compound α,β-hopane (hopane) is often chosen as a biomarker because it appears in many
petroleum compounds and it degrades very slowly. Because it is often cited in petroleum
literature, α,β-hopane is a good choice for TPH degradation normalization studies. The
HRGC/MS method (see Appendix A) used for PAHs is used to quantify hopane.
Using this technique, the percent loss of TPH, FSH, and individual target benzene, toluene, ethyl
benzene, and xylene (BTEX) and PAH compounds can be calculated as follows:
Percent depletion of individual target analytes
(1-[(C1/C2) * (H2/H1)]) * 100
Percent depletion of total petroleum hydrocarbons (TPH)
(1-(H2/H1)) * 100
Where:
C1 = Concentration of analyte in the sample
C2 = Concentration of analyte in the source (time zero)
H1 = Hopane concentration in the sample
H2 = Hopane concentration in the source (time zero)
17
Previous Page
