Agriculture Reference
In-Depth Information
4.1.2 Analytical methods
4.1.2.1 EPA method 418.1
The most common method in use today, which is based on the EPA's method 418.1 which
was adjusted for soils, is costly and time-consuming. Briefly, the sample is brought to the
laboratory and a specific extraction technique is applied using Freon 113
(trichlorotrifluoroethane). The TPH level is then determined in the solvent by Fourier
transform infrared (FTIR) spectrophotometer. This method necessitates careful shipping of
the samples to the laboratory (e.g., cooling conditions and use of special quartz tubes) and
several replications to precisely establish the chemical analysis. Measuring one sample can
cost about $50 and the results cannot provide information in a near-real-time domain.
Consequently, in obtaining a reliable spatial pattern of the contaminated area, many
samples are required to generate useful information that will facilitate the rehabilitation or
precautionary processes. This method can only be used for quantification of TPH and not
for identifying PHCs type.
4.1.2.2 Gravimetric
Hydrocarbons are removed from the sample by an extraction solvent, the solvent is weighed
before and after the extraction, and the difference in weight expresses the TPH. This method
is analogous to weighing a battleship with its captain, then subtracting the weight of the
battleship in order to find out the weight of the captain: while it is relatively inexpensive, it
is highly inaccurate.
4.1.2.3 EPA method 8440
Hydrocarbons are extracted from the sample with CO
2
at very high pressure (340 atm), at
80
o
C for 30 min. After extraction, TPH is determined by FTIR spectrometry and compared to
a calibration model (similar to method 418.1). This method is not only expensive but it is
also dangerous due to the high pressures involved.
4.1.3 TPH field methods
The abovementioned laboratory methods are costly and time-consuming, and usually
cannot be implemented in a real-time domain at the contaminated site. Samples need to
be transported to the laboratory in a cooled container and there is a waiting period
before results are reported. In addition to the laboratory tests, a few field-measurement
kits are available. The seven field-measurement devices listed below were tested at the
Navy Base Ventura County site in Port Hueneme, California by Tetra Tech EM Inc.
(2000):
CHEMetrics, Inc.: RemediAid™ Total Petroleum Hydrocarbon Starter Kit
Wilks Enterprise, Inc.: Infracal® TOG/TPH Analyzer, Models CVH and HATR-T
Horiba Instruments, Inc,: OCMA-350 Oil Content Analyzer
Dexsil® Corp.: PetroFLAG™ Hydrocarbon Test Kit for Soil
Environmental Systems Corp.: Synchronous Scanning Luminoscope
siteLAB® Corp.: Analytical Test Kit UVF-3100A
Strategic Diagnostics, Inc.: EnSys Petro Test System
These field tests, making use of several technologies, are summarized in Table 2.
