Environmental Engineering Reference
In-Depth Information
station, it is within reason that gasoline contamination may be found. Also, and just as
important as the initial field characterization, is the ongoing history of a site. This can be
as fundamental as a field map indicating where the sample points are located to as
complex as the field sample history plotted as a thread over time with reference to field
soil characteristics and hydrology.
The biggest mistake made in obtaining the history of an area is the assumption that it
was not or could not have been used for a specific or general activity that would lead to
contamination. These assumptions are often made by looking at the area as it is presently
and seeing no indication of human activity. Of course this view leaves out the possibility
that somewhere below the surface is information about previous uses, which may be
indicated by the occurrence of some common soil components. The occurrence of higher
than normal levels of elemental carbon may indicate the existence of campfires or other
burning in the area. This might be caused by normal occurrences, but may also indicate
human habitation. Higher than expected levels of phosphorous in soil may indicate the
same thing.
Thus, exploration of the history of an area must be done with an open mind, and it
must never be assumed that the area is not and never has been contaminated. The most
unlikely fields, often remote from populated areas, are contaminated in one way or
another. A small area enclosed in trees in a remote field on a farm was found to be an
area in which a farmer had dumped both empty and partially filled containers of excess
agricultural chemicals, including toxic compounds, some dilute and some concentrated.
Such an area is a source of contamination to surrounding land and water supplies.
Another remote field surrounded by trees was found to contain a pit being used as a
dump. The area was both remote from a population center and screened from surrounding
roads by the trees. Gullies are commonly used as places to dump unwanted materials.
Often this is done for two purposes. One is a mistaken idea that this activity will decrease
erosion and slow or stop the development of the gully. The other reason is that the
material is not visible to the casual passerby. Even if the discarded material is buried it
will be exposed later when further erosion has occurred.
In terms of human occupation, some chemicals are commonly found, that were used in
earlier times but would be restricted today. A simple example is arsenic, which although
still commonly used in small amounts, was previously used much more extensively. The
same is true for lead, which was commonly used for water pipes and in paint. Both of
these elements, in various combinations, may be found in soil on which humans have
built towns and businesses. Thus these chemicals may be present in appreciable amounts
even if there is no indication that someone is living on or using the land at the present
time.
It is also not safe to assume that contamination must be only at the surface or at a
certain depth and no deeper. Material becomes buried for all kinds of reasons and by all
kinds of activities, and so all sources of information about an area must be investigated,
including historical accounts of activities, such as battles and settlements, that may have
been located in the area.
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