Traps, Mistakes, and Errors - Field Sampling: Principles and Practices in Environmental Analysis - page 283

characteristics, maintaining sample integrity, and observing safety rules will be three
more problems associated with inexperienced samplers. It is hoped that only one of these
is the major problem and can easily be rectified. Unfortunately, several of these may
occur in the same sampling event.
For the inexperienced samplers problems start with not finding the correct field, and it
is often the case that inexperienced samplers will sample the wrong field. However, this
can also happen with trained personnel if they are not careful. Often fields and their
extent are not easily recognizable. They will not have GPS references associated with
them. Personnel must rely on tree lines, streams, roads, buildings, and their relationship
to each other to find the correct field.
Assuming the person finds the correct field, how is he or she to set up the sampling
grid? Experienced samplers will be able to accurately judge a grid in a field by picking
out reference points around the field. Inexperienced samplers will take all their samples
from a relatively small, unrepresentative area in a large field. If multiple grids are to be
sampled and multiple subsamples taken from each grid, then such persons will fail to
sample all the grids appropriately. Upon completion of sampling the position of the
samples in the grided area will be unknown.
If samples are not taken from representative places in the field, are taken to different
depths at different places, or are not taken in the prescribed place in the field, the analysis
of these samples will be accurate but may not be representative of the field. These
eventualities will come about because areas are hard to get to, it is harder to insert the
sampler in some places than in others, and some designated places in the field will not be
found.
Another concern is that samplers understand environmental factors affecting sampling.
Often variations in layers and direction of movement of the medium being sampled are
not taken into account. This leads to mixing of samples from different layers in one
sample container. Other mistakes would be not noting changes in layer thickness or
density in the project notebook and not taking these into consideration in obtaining the
sample. For instance, if the A horizon is specifically being sampled and it becomes thin
in an area, it is not acceptable to include the B horizon in the sample just to make it the
same depth of other sample cores. In this case, this variation needs to be detailed in the
project notebook so that later evaluation of variations in the A horizon and how they
affect sampling and analytical results can be made.
The inexperienced sampler will often not be careful in maintaining the integrity of the
samples. This may mean that the sampling tool is not cleaned between samples, that care
is not taken in getting all the sample in the container, or that the container is not sealed or
is not placed in the proper transportation box. It might also mean not taking care to
protect the sample from heat, cold, light, and contamination after sampling or not
transporting it rapidly to the analytical laboratory. An additional problem with the
inexperienced sampler is in not being careful to make sure that all data are carefully
recorded in the project notebook. Careful recording of field notes is essential in later
interpretation of analytical results and applying them to the remediation of a field
problem. These notes are also essential in deciding if data are correct and if extraneous or
suspicious data need to be kept or discarded. This is especially important during
statistical analysis of analytical results.