Introduction to Field Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 13

media, including soil, rock, and fractured rock. Such models can be invaluable in
developing an effective sampling and remediation plan. Models are only as good as the
data used in them, however. Of particular concern are areas in which water moves
through layers of different media or rock that have significantly different hydraulic
conductivity (K) and effective porosities (theta; θ ). It is also good to keep in mind that the
contaminant may affect both K and theta by changing the viscosity of water, which in
turn changes the way it moves through the environment. Modeling is treated further in
Chapter 7.
1.9. SAMPLE HANDLING
Once the sample is obtained it will be analyzed. Some analytical data, such as pH, will be
obtained in the field, while other needed data will require sophisticated laboratory
analysis. This means that samples will need to be placed in suitable containers and
labeled. Labeling is critically important because a sample that arrives at the analytical
laboratory without a label is useless. This means the time and effort used in obtaining and
transporting the sample is lost. A more costly result is that the sample usually cannot be
replaced and thus the data it contained are lost; that is, by the time the problem is found
some time has elapsed and so a subsequent sample will not be the same as the previously
taken sample. Sometimes this may not be a problem, but in other cases significant
changes in the sampling area may have occurred. For instance, a heavy rainfall might
change the concentration or distribution of the contaminant.
Depending on the type of sample, the type of component, the analytical laboratory
specified, sample handling, storage, and transport procedures must be followed. Some
samples may be dried, some must be sealed in their original condition, and some must be
kept at a specific temperature between sampling and analysis. During these operations the
sample must be safely handled, stored, and transported in such a manner that the
constituent or contaminant of interest is not lost or its concentration changed. These
conditions must be not only followed, but also recorded and verified using chain of
custody forms.
Once samples are in the analytical laboratory they will be handled in an appropriate
manner for the contaminant of interest. It is important for the people in charge of and
actually doing the sampling to have some idea of what happens to samples in the
analytical laboratory, because what happens there can affect what happens both in the
field and during sampling (and vice versa) [11]. Specific examples of this type of
interaction will be presented in Chapter 11.
1.10. WHAT IS PRESENT?
In any sampling it is always good to know what is present or likely to be present in the
sample. This is important for three reasons. The components present or likely to be
present will determine what sampler and what sample container is used. They will also
determine what safety precautions need to be taken in both the field and the laboratory.