The answer to this question will help us determine the required sampling frequency. There are three types of samples which might be considered at this point. A grab sample is a sample collected at a specific time and place. Grab samples collected at suitable intervals may be used to document variations in time and space. A composite sample is a mixture of samples collected at different times from the same sampling point.
Composite samples are useful for observing average concentrations.
For instance if the discharge permit for a facility specifies an average value over a 24 hour period, composite sampling might be appropriate. Composite samples save analyses time and money. Integrated samples are collected from different points simultaneously. The answers to these questions will help us decide the number of samples, duplicates, and blanks which will be required. Duplicates and blanks are discussed later.