Presampling - Field Sampling: Principles and Practices in Environmental Analysis - page 61

both distances and areas can be determined directly from the DOQQ. Software for
manipulating these maps (e.g., MrSID GeoViewer) is available—some of it free—on the
Internet [5].
Digital orthophoto quarter quadrangles are very useful in sampling, and are available at
a minimal cost. Unfortunately they are often hard to find, even on the Internet. One
relatively easy place to find information about DOQQs is the local GIS office. Many
county courthouses will have a GIS office, and personnel doing GIS for the county will
be very helpful in obtaining needed DOQQs. If no county GIS office is available, try the
state GIS office or officer.
When sampling, site positions can be determined using a GPS unit. These site
positions are saved and later loaded into a GIS system. A DOQQ is then also loaded into
the GIS system. The system is then used to generate a map that shows the true location of
sample sites in the field. This map and a GPS unit can be used to locate the sampling sites
at any time in the future. It is also possible to enter other sampling data, such as sample
depth, altitude, vegetation cover, and other information deemed necessary into the GIS
system. These data can also be displayed on the thematic map, and all the data can be
interrelated as needed or desired.
3.4.1. Soil Survey
The soil survey is another invaluable map to have before sampling a field begins. This is
a map of soils in an area, but it also contains additional information about the area it
represents. The soil survey is made up of aerial photographs of an area of the Earth's
surface with the designations of the soils in the field indicated on it, as shown in Figure
1.2 in Chapter 1. Descriptions of the soils, their characteristics, and their suitability to
various uses are also given, as are characteristics of the landscape, such as slope,
buildings, waterways, and roads. This is an extremely useful type of map and source of
information and no field sampling project should be undertaken without having a soil
survey of the area available for ready reference. In situations in which the field sampling
is primarily of water or air a soil survey and associated maps are still useful.
Soil surveys have typically been carried out only in rural areas; that is, they have been
seen as tools for agriculture, particularly in erosion control. In areas of rapid urbanization
older soils maps may show the soils in an area because it was agricultural land when the
map was made. New soils maps attempt to include all land in the soil survey, thus both
the older and newer soils maps can be valuable in a field sampling project.
Field sampling will include sampling a similar uncontaminated field or soil. The soil
survey will be indispensable in finding uncontaminated soils, which are the same as those
in the field under investigation. Such comparison soil samples are essential to be certain
that the analytical results represent an unusual situation in the field of concern. It is often
important to know the base or natural level of a component so that it is not mistaken for a
contaminated level. See Chapter 9 for an introduction to the types of elements and
inorganic and organic compounds likely to be found in soil.
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