Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 135

This sampling must be three-dimensional (i.e., surface and subsurface water samples are
taken). Atmospheric samples should be taken at various altitudes. The sampling should
be as random as possible, but with attention to the different zones occurring in the area.
Differing zones are produced by strong currents of a river or in currents induced in a
lake by a river, and they do not give a true picture of the state of the whole river or lake.
Similarly, atmospheric samples taken at one altitude downwind from a pollution source
do not give an adequate picture of the pollution. The same can be said for samples taken
only upwind or away from entering water sources.
Here again sample size and uniformity of size are important, particularly if
comparisons are to be made between samples. The same can be said for samples in which
some regulatory criteria in terms of pollutant concentration are to be met [21-23].
5.12.7. Monitoring Wells
Where is the water in the field going? Not only is it necessary to sample the soil or the
regolith, it is also essential to know where either rainwater or surface water goes when it
enters from adjoining areas and exits a contaminated site. It is assumed that incoming
water cannot be contaminated, but this must be verified. Incoming water is compared to
both the water in the contaminated site and the water exiting the contaminated site in
order to be sure of what is happening to the contaminant. Even if it seems that all the
water in the area stays in place or just flows over the top of the soil it is still essential to
keep track of it and its condition in and around the contaminated site.
To keep track of water and its condition, contamination, and movement, it is essential
that wells be installed at the contaminated site. The most logical location is downstream
from the contamination. It is essential to also have wells on all sides and upstream,
however. These wells need to be sampled frequently throughout the sampling and
remediation in the area. Keep in mind that well monitoring is recommended and
sometimes required, even if the material at the site is to be removed for remediation or
cleaning at some other site. Also, such monitoring wells are monitored for a period of
time after the site has been certified as being clean [24].
5.12.8. The Number of Samples Needed
Methods for estimating the total number of samples needed to obtain a representative
sample are presented in Chapter 6.
5.13. SAMPLE HANDLING
Sample locations can be chosen before actually going to the field. When in the field it is
sometimes tempting to move the sampling site if it is in the middle of a tuft of grass, on
top of a rock, or under a layer of plant residues. As much as possible, the site should not
be changed. Take the sample near to the plant or under the rock, or take plant residue, if
at all possible. Rocks or plant material occurring in the sample when it is removed from
the soil should be left with the sample rather than being picked out. To maintain sample