Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 107

5
Sampling
When sampling, local rules apply.
N o single, simple set of guidelines is applicable to all sampling
situations.
G eneral sampling principles will need to be adapted for each field
and sampling situation.
When sampling, it is important to first keep general sampling basics in mind. The most
important of these is that the environment changes over distance and time. The second is
that information about a field may be obtained either without (noninvasive) or with
(invasive) sampling; in either situation, it is essential to know beforehand from where the
samples are to be taken. This information is essential because it is used when relating the
sample to the whole environment. It is also critical if we wish or need to sample this same
field again at a later date or to remediate it. All data must be readily available, and thus it
is essential to have a place to put field data, such as a map of the area, a project notebook,
a computer, or all three.
Data about a field can be obtained by both noninvasive and invasive sampling.
Noninvasive sampling is carried out using ground-penetrating radar (GPR), remote
sensing, or other noninvasive technologies. Invasive sampling is accomplished using
hand- or machine-driven samplers that extract a portion of the medium about which we
wish to obtain information. The sample thus obtained is subjected to laboratory analysis.
Both methods are valuable and sometimes essential in field sampling. Both have
limitations, and the best sampling results are obtained when all ways of investigating the
medium of concern are used. In all cases knowing the location of sampling activities is
essential. Determining the location is best done using a global positioning system (GPS).
Because of its importance, GPS will be discussed before examining either noninvasive or
invasive sampling.
In many cases noninvasive sampling is done before invasive or physical samples are
taken, mainly because these methods show surface and subsurface features affecting the
invasive sampling pattern. In some cases these methods are necessary for the safety of
sampling personnel and buried utilities. They will thus be used to develop the invasive
sampling plan. Because they will be used first they will be discussed before discussing
actual invasive sampling.
Data obtained by all sampling methods can be combined in a geographical information
system (GIS). Combining data allows them to be both stored and displayed on maps of
the area of interest (e.g., thematic maps). As many or as few data as needed can be
displayed at one time. Additionally, a GIS system can relate data obtained from sampling