Presampling - Field Sampling: Principles and Practices in Environmental Analysis - page 64

Often historical information about a site is not as complete as one might wish. It is not
unreasonable to talk with people who have worked on various projects that were carried
out at the field and with people living around the area. Sometimes some surprising
activities can come to light during this investigative phase.
The purpose of this phase of investigation is to understand the sampling needs, provide
proper safety for workers, and avoid unpleasant surprises. The potential depth and extent
of sampling will be indicated during this phase, as will the type of sampler or samplers
needed. The types of samplers used will depend on the composition of the field, the type
of component to be determined, and the depth of sampling. In a field requiring small
numbers of shallow samples a hand sampler capable of sampling 3 meters deep may be
sufficient. If more or deeper sampling is required, powered samplers or drills may be
needed [6].
Without knowing the history of the field it is hard to anticipate such safety needs as
what or how much protective and emergency equipment is needed. Will safety glasses
and work boots be sufficient or will more sophisticated coveralls, rubber gloves,
respirators, and so on be needed? There is also an economic aspect to knowing the history
of the field in that the amount of safety equipment needed will change, depending on the
level and the type of contamination. If there is no contamination and the sampling is for
other purposes, minimal safety protective and emergency equipment will be needed [7,
8].
Another aspect of obtaining the history of the field is to avoid unpleasant surprises.
One such surprise might be discovering underground tanks containing unknown waste.
Another might be discovering unsuspected contaminants that affect the sampling and
remediation plans. It is far less expensive to know about these beforehand than to have to
contend with them later.
One last piece of information to obtain is to identify all possible sources of
contamination or pollution. Sources may be point sources, so that the exact location of
the source of the contamination, such as a spill of fuel oil from a tank car, can be
pinpointed. The other is the nonpoint source. In this case the contaminant may be spread
out over a large area, such as an agricultural field of several hundred acres. This diffuse
material may wash off the soil surface and be concentrated in low areas or bodies of
water. It is much easier to find, identify, sample, and remediate point sources of
contamination than nonpoint sources, but it is essential to identify all possible sources as
early as possible.
Surprises in the Field
At one cleanup field that I was assured had been previously investigated, I
found an unpleasant surprise, which is the one thing I do not wish to find at a
field. I attempted to take a soil sample only to encounter a board 5 cm under
the surface. Five cm deeper I found a brick, and under that a large rock. I was
immediately concerned. What had been dumped in this area? If it was fill, the
question was, from where? Was the fill clean to begin with? Had this been a
dump at one time? It turned out that relatively clean fill had been used. This is