Environmental Engineering Reference
In-Depth Information
thus necessary to used the same sampler and take the same amount of sample each time.
This is true for both surface and subsurface samples.
Note that samples for volatile organic compounds (VOCs) analysis are handled very
differently. Samples must be taken, handled, and contained in such as way as to minimize
the loss of sample components. Some procedures call for the sample container to be filled
to the top, leaving as little headspace as possible. The container is then sealed with a top
that is proven to prevent leakage of VOCs. Other procedures will require more or less
sample, depending on the sampling, container, and analytical methods used. The
analytical laboratory can provide specifics as to sample handling, the amount of sample,
and the container needed for the specific VOCs being sampled and analytical methods to
be used.
When the sample arrives at the analytical laboratory it will be ground, sieved, and
mixed. A subsample of this mixture is usually on the order of 1 to 10 g, although larger
samples may be used in some cases. The size of the sample taken from the field thus does
not need to be large. As noted above, however, all samples should be of about the same
size so that observed changes are not due to changes in sample amount, but to the
inherent characteristics of the sample [12, 13]. Sample size can be a trap, and this will be
discussed in further in Chapter 11, along with other traps.
5.8. SAMPLE CONTAINER
Almost every conceivable type and composition of container has been used to contain
contaminated air, water, and soil. Glass bottles or containers are most frequently used for
air and water samples, however, while paper and plastic bags are used for soil samples.
Before deciding on a container material, however, it is essential to know the history of
the field and have a clear idea of the types of contaminants it contains or is suspected to
contain. It is also important to know as far as possible the species of the contaminant that
is of primary interest. For example, when sampling soil for VOCs, bags are not suitable
containers. In this case a glass container will be provided by the analytical laboratory,
along with use and filling instructions. A more complete list of typical containers and
their characteristics is given in Chapter 3 in Table 3.3 and Figure 3.7 [11-13].
5.9. DUPLICATE, SPLIT, AND COMPOSITE SAMPLES
Duplicate samples are taken from the same location and are used to check the accuracy
and precision of analytical methods. In the case of water and air, duplicate samples may
serve this purpose very well. In soil or regolith sampling, duplicate samples are two cores
taken adjacent to each other. These two cores may not be identical, and indeed may be
significantly different from each other. Duplicate soil samples can be different by as
much as 5-10%. If the occurrence of this variation does not cause a problem, duplicate
samples may be useful. If duplicate soil samples give exactly the same analytical results,
the validity of the sampling and analysis is in question.
A single sample split into two subsamples placed in two different containers would
 
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