Presampling - Field Sampling: Principles and Practices in Environmental Analysis - page 69

3.7.3. Water Sampling
Several types of water sampling are common. Surface waters and wells are sampled by
simply filling a sampling bottle or with water pumped out of a well. Sampling bottles can
simply be dipped into surface waters to obtain a sample. For pumped water it is common
to clean the outlet, sometimes even to try to sterilize it, and allow some water to run for a
period of time before taking the sample. Obtaining water from various depths is usually
done with a sampler that is similar to the powder sampler described above. It will have a
valve that works such that when it is at the required depth the valve is opened and a
sample taken. The valve is then closed and the sample retrieved.
3.7.4. Sediment Samplers
The bottom of bodies of water is saturated with water. Taking a sample of this material
requires a sampler that can retrieve both the solid and the water. The sampler bottom is
open when it enters the sediment and is then closed to retrieve the sample. An even more
complicated and specialized sampler is required when the sample pressure must be
maintained [10].
3.7.5. Air Sampling
Air can be sampled using an evacuated sampling container. When the container is opened
the surrounding air moves into the container. Other methods include pumping air into a
container by various means. Pumping air always carries the risk of the pump
contaminating the air sample. On the other hand, negative pressure can be used to move
air into a container without contamination. Figure 3.7 shows a number of sample
containers, including an air sample container, that can be evacuated.
3.8. OTHER SOIL SAMPLING CONSIDERATIONS
At this point the number of samples and the number of grids from which they should be
obtained is not known. Only after the transect sampling has been done and the analytical
results reviewed can this decision be made. There are some things that can be decided
upon at this point, however.