ESTCP Project #1011, Rhizosphere
Final Report
Sample Analysis. Composited samples taken from the soil socks were analyzed for
petroleum by several approaches to characterize the petroleum fractions in the soil. Total
petroleum hydrocarbon (TPH) data are expressed as a concentration of mass of petroleum per
mass of soil. Although this approach measures an integrated value of the total amount of
petroleum products present, you cannot distinguish among specific compounds, degree of
weathering, or degradation in the form in which TPH is usually expressed. We therefore used
TPH in conjunction with more specific methods to determine contaminant degradation and the
time-related depletion of specific fractions. The approaches are described below. Details of
analytical methods are given in Appendix A of this document and in our Demonstration Plan in
section 5.4 "Sampling Plan" and Appendix D "Sampling and Analysis Plan for Annette Island
and Campion."
For semi-volatile TPH and FSH analyses, soil samples are extracted in n-pentane, passed
through an open silica column, and fractionated into aliphatic hydrocarbons (F1 fraction) and
aromatic hydrocarbons (F2 fraction) using open tubular silica gel chromatography techniques.
The resulting extracts are analyzed for TPH and FSH and, for selected samples, for PAHs.
Total Petroleum Hydrocarbons (TPH). High-resolution gas chromatography using flame
ionization detection (HRGC/FID) yields a chromatogram such as those shown in Figures 16
through 20 (see Appendix A for a description of the HRGC/FID technique). These
chromatograms show relative amounts of petroleum compounds as they differentially elute from
a chromatographic column. Integrating the area under the curve and between two defined
retention times provides a measure of TPH. TPH data are generally provided as a single, numeric
concentration value, such as mg/kg or ppm; thus, much of the data contained in the
chromatogram is lost because a numeric TPH value gives no qualitative information about the
distribution of fractions. Nonetheless, when monitored over time, TPH data can show, in general,
if concentrations of petroleum products are decreasing. To rely mainly on TPH as a monitoring
tool, you must assume homogeneity of initial concentrations or have large concentration
changes.
Fingerpirnting (Fuel Types and Weathering). With experience, the same chromatograms used
for obtaining TPH values can be compared to typical curves of known products and provide
information about types of petroleum products and degree of weathering. Figures 16 through 20
show typical curves for petroleum product types.
Fraction-specific hydrocarbons (FSH). Fraction-specific hydrocarbons (FSH) are based on the
concept that petroleum consists of a very large number (~104) of individual compounds. The
distribution of broad classes of these compounds is reasonably representative of different types
of petroleum products, such as diesel or bunker C. A combination of distillation and blending of
the distillates are used to obtain petroleum products. Consequently, rather than being a set
percentage of different compounds, petroleum products are combinations of various distillation
fractions that are blended together to provide a product that meets performance guidelines.
Chemically, various fractions of petroleum compounds behave similarly and, hence, can be
grouped together. Chemical similarities influence both extraction from soil and also the potential
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