Introduction to Field Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 14

For the laboratory it is also good to know the likely concentration of the contaminants,
because some analytical' procedures may be sensitive to components other than those of
primary interest present in the sample. This could mean over- or underestimation of the
level of contamination of interest, which would in turn affect the sampling and
remediation plan.
Part of this information will be obtained by a thorough investigation of the history of
the field. For instance, the types and concentration of components will be different if the
field is or has been used for agriculture, manufacturing, housing, or a municipal dump.
The length of time a field is used for a particular activity will often indicate the level of
contamination likely to be found.
The occurrence of either an inorganic and organic toxic component in a soil sample,
however, is not necessarily an indication of contamination. All soils naturally contain low
levels of compounds that are toxic in high concentration. For example, all soil contains
low levels of such things as lead and arsenic. The analysis of humic materials may result
in finding many simple organic compounds, including phenols, alcohols, acids, and
aromatic compounds. Thus in a high-sensitivity gas chromatographic/mass spectral
analysis of soil or water extracts a low level of a wide variety of organic compounds
should be expected to be found [12]. When evaluating the results of soil analysis it is
critical to look at the occurrence of toxic compounds, their concentrations, and the natural
occurrence of these same compounds in similar but uncontaminated soils.
1.11. ANALYTICAL METHODS
Samples will be analyzed in several different ways using three different methodologies.
Some samples (e.g., transect samples) will be analyzed for some components using rapid
methods designed to determine the extent, width, breadth, and depth of contamination.
These analyses may be done in the field as the samples are taken or at the field office
laboratory. Samples from detailed sampling will be analyzed for some characteristics in
the field or at the field office laboratory, but most analysis will be done at a commercial
laboratory.
Those samples sent to the commercial laboratory will be treated in a manner
appropriate for the contaminant or component that the organization submitting the sample
wishes to know about. This is important because samples to be analyzed for metals will
be treated differently from samples to be analyzed for organic contaminants, and the two
procedures are not compatible. A sample extracted for metals cannot subsequently be
used for the analysis of organic contaminants and vice versa.
It is advisable to use the same procedures, analytical methods, and analytical
laboratory for all samples. For example, it is not advisable to change the method of
determining soil pH in the middle of the sampling plan. For some extraction procedures
slight changes in the way the procedure is carried out can make a significant difference in
the analytical results. The results will be more consistent, and it will be easier to interpret
them if they are all carried out the same way and are sent to the same laboratory [13].