Environmental Sampling Design - Fundamentals of Environmental Sampling and Analysis - page 48

When will we collect the data?
Where will we collect the data?
How will we collect the data?
How will we determine whether we have collected a sufficient volume of
data?
How will we determine whether the collected data are valid?
How will we determine whether the collected data are relevant?

3.1.2 Basic Considerations of Sampling Plan

In developing a sampling plan to formulate the number and location of samples (how
many, where, and when), four primary factors need to be considered (Gilbert, 1987,
Fig. 3.3). Of these four factors (objectives, variability, cost factors, nontechnical
factors), a project objective is probably the determining factor in sampling design.
For example, sampling efforts in water quality monitoring will be very different
depending on whether the objective is for trend analysis or baseline (background)
type investigation. The former needs a long-term but less frequent sampling scheme,
while the latter requires more samples and perhaps a one-time sampling event. The
project objective with regard to the required data quality also affects the number of
samples to be collected. In other words, the sample number will increase
significantly as the allowable margin of error is reduced. Environmental variability
or the spatial/temporal patterns of contamination is another important consideration.
The variations in different environmental matrices will be further discussed in
Section 3.2, and the sampling approaches to address such variations in order to
obtain ''representative'' samples will be discussed in Section 3.3.

1. Objectives
-

3. Cost factors
Sampling cost
Analytical cost
Fixed vs. minimum cost

Baseline monitoring

-
-
-

- Trend detection

- Search for hot spot

How many?
Where & When?

- Margin of error allowable

4. Nontechnical factors
- Sampling convenience
- Accessibility
- Availability of resource
- Regulations

2. Variability
Spatial variation
Temporal variation

-
-

Figure 3.3 Criteria for selecting a sampling plan

Expenses associated with sampling and analysis should certainly be a
consideration in all environmental projects. The cost-effectiveness of a sampling
design should be evaluated in the design stage so that the chosen sampling design
will achieve a specified level of data quality at a minimum cost or, an acceptable
level of data quality at a prespecified cost. Last but not least important thing is that