Characteristics of the Environment - Field Sampling: Principles and Practices in Environmental Analysis - page 23

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Characteristics of the Environment
In order to successfully sample a portion of the environment one must understand the
characteristics and dynamics of the portion of the environment being sampled. It is also
critical that the relationship and interaction between the specific part of the environment
being sampled and the rest of the environment be understood. The term successful sample
refers to a sample that truthfully and accurately describes the characteristics of the part of
the environment sampled at that particular time. In addition to using the results of a
sample analysis to predict the future of a particular component or contaminant in an
environment, its relationship to all parts of that environment must be understood.
It might be assumed that the lithosphere is inert and impenetrable to water and
contaminants. Sandstones can contain large amounts of water, however, which can move
through it at significant rates. Even bedrock, such as limestone and shale, can contain
numerous cracks that allow ready movement of water and contaminates. It is important to
know not only where a component is at a given time, but also where that component may
move to in the future and how a particular environment may change a contaminant.
Another example is the atmosphere, which can affect sampling in three ways,
particularly in windy conditions. It can remove contaminants from a contaminated field,
thus changing their concentration. It may also deposit contaminants, including particulate
matter, such as contaminated silt and clay particles, on a field. To a lesser extent it can
also move sand-sized particles from one location to another. Thus, wind can
recontaminate an area or a field that has been remediated. Wind can carry contaminants
long distances, and so its effects can be widespread.
A third example is water, which may be seen as a nuisance when it rains or when a
river floods and covers a field that is to be sampled. Rain can leach contaminants deep
into a soil or through a soil and into the water table. If this happens, water from wells in
and around the field will need to be sampled and analyzed. Flooding can wash away
contaminants, spreading the hazard. It may also mix contaminants with more soil or
cover a contaminated area with clean soil that must be removed to effect remediation.
While the soil is saturated with water it becomes anaerobic and thus changes the chemical
and biological condition of the contaminants. For these reasons water is an extremely
important factor in sampling. If contaminants are being carried by water, sampling the
water itself will become an important sampling activity.
It might be assumed that soil is a homogeneous mixture with a well-defined movement
of air, water, and contaminants when water moves through it. Soil has horizons of
differing composition, however, which allow differential movement of water downward
through the soil. Some horizons may cause water to move horizontally rather than
vertically, thus causing contaminants to be found in unexpected places.