Stratified sampling is commonly used in a location which is known to have contaminants heterogeneously distributed. This is therefore the most common approach to sampling. In this type of sampling, the site is sub-divided into smaller areas, each of which is fairly homogeneous,and thus more accurate sampling can take place. Each sub-area is then randomly sampled. The sub-dividing of the site can be carried out either to give equal areas, or be related to known features within the site (see Figures 3.2(c)and 3.2(d),respectively)