Introduction to Field Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 11

sampling, and analytical results. When taking samples it is important to take all four
dimensions into consideration. For instance, it is not sufficient to only take samples from
the surface even if there appears to be no way that the contaminant could have moved
through the surface and into the lower layers. To know what is happening to the part of
the environment being sampled, samples must be taken at various depths and over a
period of time.
1.6.1. Grab Samples
When starting to sample, the first thing people want to do is grab a sample and have it
analyzed. Indeed, there is a type of sample called a grab sample. The sample selected for
grabbing usually looks different from the bulk material, and thus is assumed to be
contaminated. Such a sample might just as well look different because it is
uncontaminated and thus it is not known what this sample represents or how it should be
handled.
There are two further problems with this type of activity. First is a safety issue. It is not
a good idea to go onto a contaminated area without the proper safety equipment. Second,
by the time more systematic sampling is carried out the location of this sample will be
lost, and so the place of this analytical data in connection to other data obtained will be
unknown. There will also be a time difference between this sample and subsequent
samples, further lessening its value. Any information gained will thus be of little or no
value. Grab samples are potentially dangerous and a waste of time and money.
1.6.2. Preliminary Transect Sampling
When all preliminary nonsampling work is completed, some organized preliminary
transect sampling can be initiated. A transect is a straight line passing through the
contaminated or other field of interest. Samples are taken at various sites along the
transect, both surface and subsurface, and include samples assumed to be outside the
contaminated area. A second transect may also be needed if the field contains several
different soil types or areas. This transect is chosen so that all soil types or areas are
sampled.
Preliminary sampling is important because it is the basis for the application of stastical
tools and the development of a realistic, honest, and detailed sampling plan. It is also the
basis for determining the handling of the samples from acquisition to final analysis.
Handling includes the type of sampler used, sample containers, sample labeling, storage,
and transportation. It also provides data needed to determine the type of analysis needed.
1.6.3. Systematic Sampling
On the basis of the historical background and transect sampling a detailed systematic
sampling plan can be developed and carried out. This sampling plan includes the areas to
be sampled and how sampling sites will be determined and designated. The total number
of surface and subsurface samples to be taken will also be part of the plan. Questions
such as whether the surface and subsurface will be sampled at each site or only one and