Introduction to Field Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 3

An essential question to ask is what do we wish to accomplish by sampling this field.
In order to be able to answer this question we need to know about the environment so that
we know we are getting a sample that will give us the answers we need. We walk
outdoors, breathe the air, feel the rainfall, and feel our feet on the ground. It is easy to
take all this for granted and not consider the various characteristics of these and other
components of the environment and how they may affect a field sample.
To obtain the needed information the general and specific characteristics of the field
must be known. It is also important to know how the field is related to the rest of the
environment. For example, does water move into, on, through, or under the field? Is the
area being used (or has it been used in the past) mainly for manufacturing or agriculture?
Is the field low-lying and thus receiving inputs from surrounding areas, or is it high and
eroding? All possible and probable interactions of the field with the surrounding
environment must be taken into consideration.
The specific type or types of materials contained in the field must be known. Without
this information samples from a landfill might be mistaken for samples from a cornfield.
What is the source of the material? Is it the natural soil or has it been brought in as fill
from some other place? Imported material may unknowingly be contaminated and thus
add to the sampling problem.
More specifically, what are the characteristics of the medium (for instance, soil) to be
sampled? Is it a sandy soil that has little ability to retain water and chemicals, or is it clay,
which has high retentive capacity? Is there only one component, or are there several
components of interest present? What are the characteristics of the components? Are they
soluble or insoluble in water, toxic or carcinogenic, volatile or nonvolatile, flammable or
nonflammable? This information is added to the general information to obtain all the
information important to the sampling plan.
A visual evaluation of the present condition of the field, obtained by walking around its
perimeter, is important in assessing the situation. Is the field bare or planted, or does it
have weeds on it? What is its slope? Is there evidence of erosion? What are the
surrounding structures like and what is their relationship to the field? What is its
physiography? All these are noted and recorded while walking around the field.
As much information as possible about the background or history of the field is
obtained next. In how many different ways has it been used in the past? Do any of these
past uses impact the sampling plan? Are there likely to be pipes, tanks, or electrical or
communication cables buried in the field? All of this type of information needs to be
obtained and added to the other information before sampling is begun.
The understanding gained during the above activities provides information about how
extensive and intensive the sampling needs to be. If one or more of the contaminants is
volatile, soluble, or mobile the extent of the contamination will be greater than it would
be for an immobile contaminant. A contaminant soluble in water and carrying a negative
charge (anion) would be expected to move further and possibly contaminate water
supplies. This calls for a more extensive sampling plan. A low solubility contaminant
may remain in a restricted location for long periods of time and not constitute a hazard to
surrounding areas, thus calling for less extensive sampling. Putting this all together
allows for understanding the sampling requirements necessary for a successful
investigation [1].