Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p14
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 14/117)
Character Range: 384647–387657

usually a maximum of four, into a single well-mixed sample for analysis. The subsamples should be preferably composited in the analytical laboratory.

Compositing can be cost-effective where the analysis costs are large relative to sampling costs. However, its use should be considered with caution because of the potential for individual high results to be masked by low results. Composite sampling is not recommended for site-specific health and ecological risk assessments. Its use is also dependent on there being no safety concerns or potential biases (for example, loss of volatile compounds) associated with the compositing process.

The SAQP should clearly state the qualifiers applying to selection of subsamples for a composite sample. Care should be taken to take the subsamples from the same soil horizon or stratum.

Composite sampling is not suitable for clay or fine-grained soils as subsamples are difficult to mix adequately. Consideration should be given to the moisture content of the soils to be sampled as subsamples are mixed without drying whereas laboratory results are reported in terms of dry weight.

Where non-volatile contaminants are present (for example, metals or heavy oils such as heating oils), composite sampling may be adopted as a cost-effective method for achieving low resolution data for screening purposes. Composites may also be useful in conjunction with other sampling designs or when the objective is to estimate the population mean and information on spatial or temporal variability is not needed (e.g. for characterisation of stockpiled materials).

Composite sampling is not suitable for the assessment of pH, volatile substances and semi-volatile substances such as OC/OP pesticides and lower molecular weight PAHs. A good understanding of the site history and the potential contaminants of concern are therefore a necessary precursor to adopting a composite sampling approach.

Where composite sampling has been used, the relevant assessment level should be divided by the number of subsamples in the composite and compared with the laboratory result. Further information may be found in AS 4482.1-2005 and SA EPA (2005).

6.3              Selecting a sampling design
Source: US EPA (2002)
The site should be subdivided into assessment areas based on the information collected in the preliminary site investigation (site history, local geology and hydrogeology and site conditions) and anticipated exposure areas (for example, size and location of proposed residential lots) and the sampling design selected according to the characteristics of the different sub-areas and the DQOs.

In general, when the source of contamination is known or is suspected to be limited to a specific area, sampling points are located relative to the suspected source(s) using judgemental sampling stepping out from the suspected source location, or systematic grid sampling centred on that location.

Specialised professional advice should be sought in developing sampling plans