Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 126

random sampling not related to the position of the material in the environment but to the
amount of disturbance the material is subject to during the cleaning process.
The fourth detailed sampling situation occurs with bio- or phyto-remediation. In this
case the field will need to be sampled several times to ascertain if remediation is
progressing as planned and if additional steps need to be taken, and to certify that
remediation has been completed. In this case, sampling sites will initially be randomly
assigned or sited. Subsequent sampling will take place at or near these originally
designated sampling sites, however. Final sampling before designating the area as clean
should involve a few additional random sites to assure cleanliness.
There are several possible approaches to the detailed sampling plan. One is to make it a
totally random three-dimensional sampling. A potential problem with this approach is
that picking random sites to sample may have sampling occurring in many areas in which
you are certain there is little or no contamination. Another possibility is that you may
obtain less information about a particular field when multiple samplings are called for.
Another approach is to produce an imaginary three-dimensional grid of an area, each
grid of which will be sampled. Such a grid has been superimposed on the maps shown in
Figures 5.3 and 5.7. Note that in each case the position and limits of each field have been
unequivocally located with the longitude and latitude of the four corners of the field.
Another approach would be only to sample within randomly selected grids in the
girded area. Subsequent samples can again be taken randomly within the given grid.
Another possibility would be to take individual grid elements and apply them randomly
to the field. For instance, grid element 15 α βγ (see Figure 5.9) would be applied (with
their own individual designations) to random areas in the field to designate places in
which sampling is to occur [4]. It is important to remember that the grid is three-
dimensional and that every sampling event must include samples from all three
dimensions. (See Figure 5.9.) The fourth dimension will be determined by sampling at
different times.
It is often the case that the soil and underlying regolith is composed of several layers of
differing composition. These layers have different densities and may be at different
depths across the contaminated site. Such layers may need to be sampled specifically, and
the samples taken will need to contain the same amount of contaminated material. This
will necessitate sampling at different depths at different points across the contaminated
field. It will also necessitate taking a larger sample in some cases (low bulk density), or
smaller samples in other areas and at other depths (high bulk density strata; see Chapter
2) [11].
5.11. TOPOGRAPHY
A totally random sampling plan has the advantage of removing bias from the sampling.
In many situations, however, the topography of the landscape (see Chapter 2), including
that of the bottoms of bodies of water, affects the level, depth, location, and concentration
of the component of interest. For this reason, it is important that topography be taken into
consideration when the sampling plan and sampling sites are chosen. A sloping field