Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p16
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 16/117)
Character Range: 390735–393655

(which may vary across the site).
When developing a sampling program, consideration should be given to numerous factors including, but not limited to:
    * the likely heterogeneity of any surface fill and underlying geological units
    * whether knowledge of background soil and groundwater quality is required
    * the depth and thicknesses of soil/aquifer units
    * soil properties that affect contamination migration (e.g. texture, moisture content, clay content)
    * physical and chemical nature of the contaminant under investigation (e.g. solubility, volatility and density)
    * the nature of the release (e.g. surface spill, leaking underground pipe, buried waste)
    * the timing and duration of the release
    * the amount of contaminant likely to have been released
    * the possible effects of contaminant migration through the unsaturated zone and when and where the contaminant entered the saturated zone
    * the effects of potential degradation processes
    * the direction and rate of groundwater flow within each aquifer.
If a site is to be subdivided, the size of the subdivided lots should be taken into account when determining the sampling density. While predictions may be made on a 'macro' scale, residents or owners may seek information about their own particular area of land and the risks associated with this land, especially if the potential contamination on the original site was uneven in distribution and type.

The detection of hotspots is an important issue for sites to be used for residential purposes or other sensitive uses where children have regular access to soil or where there is potential groundwater contamination. A greater sampling density is usually required for these sites. The toxicity of the contaminant and the size and magnitude of the potential hotspot(s) needs to be considered in determining the sampling density.

The development of a suitably detailed CSM will inform decisions about the depth of sampling required. For health and ecological risk assessment, the soil strata to which people and other receptors could feasibly be exposed should be adequately sampled. This will result in a weighting towards near-surface sampling unless the history or the nature of the soil and the presence of groundwater suggests it should be otherwise. On residential sites, the maximum excavation depth (such as for a swimming pool) is unlikely to extend beyond three metres, but much deeper soil disturbance may occur on a commercial site.

If dealing with volatile contaminants such as light fraction petroleum hydrocarbons or chlorinated solvents, then vapour transport from depth and through a shallow soil zone may pose a risk. Deeper sampling to determine the nature and extent of the source of the vapours and the risk they represent may be required—refer Section 9.

The risk to groundwater needs to be assessed according to jurisdictional requirements,