A.6.4.3 Small-scale (short-range) DH

On a smaller scale, DH results due to intrinsic properties of particles such as density, size, shape, and orientation. Both random and nonrandom distribution of particulates can result in small-scale DH. Since it is not possible to collect particles one by one at random when sampling bulk material, small-scale DH results in GSE. GSE also arises when particles preferentially settle (i.e., finer particles settle at the bottom and larger particles rise to the top of a column). GSE is one of the main contributors to bias in the mean (Smith 2006).

Small-scale (or short-range) DH is common at most environmental sites. For DUs with small-scale DH (and also large-scale DH), it is likely that some parts of the DU consist of a larger number of particulates than other parts. The small-scale DH may cause large variation in analytical results (both for discrete samples and ISM). These observations have resulted in frequent use of lognormal distribution to model data sets originating from environmental studies. With ISM, small-scale DH and GSE are addressed at the sampling locations by collecting increments of appropriate (and practical) sample support.