Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 1/8)
Character Range: 97679–100761

3                   Application of investigation and screening levels

3.1              Recommended process for assessment of site contamination
The recommended site assessment process is shown in Schedule A of the NEPM. Refer to Schedule B2 for guidance on site characterisation.
Before comparing site data with investigation and screening levels, it is important that  sufficient and appropriate characterisation of the site is carried out to ensure that the comparison is both meaningful and relevant for assessing potential risks to human health and the environment.
A number of cases studies which illustrate the application of the investigation and screening levels in site assessment are included in Section 5 of this Schedule.

3.2              Tier 1 assessment
A Tier 1 (or screening level) assessment comprises a comparison of representative site data with generic investigation levels and/or screening levels for protection of human health and the environment, together with an assessment of any limitations on their use in relation to site-specific conditions. A Tier 1 assessment provides an initial screening of the data to determine whether further assessment is required.

Contaminated sites may contain multiple contaminants in soil and groundwater and the risk posed is affected by site characteristics such as soil properties and the depth to the contamination. The selection of the appropriate investigation and screening levels to apply at a particular site should be determined using professional judgement and with reference to the CSM.

    3.2.1          Comparison with investigation and screening levels
No single summary statistic will fully characterise a site and appropriate consideration of relevant statistical measurements should be used in the data evaluation process and iterative development of the CSM (refer to Schedule B2, Section 4).

The preferred approach is to examine a range of summary statistics including the contaminant range, median, arithmetic/geometric mean, standard deviation and 95% upper confidence limit (UCL). Further information is provided in Section 11 of Schedule B2.

At the very least, the maximum and the 95% UCL of the arithmetic mean contaminant concentration should be compared to the relevant Tier 1 screening criteria. However, where there is sufficient data available, and it is appropriate for the exposure being evaluated, the arithmetic mean (or geometric mean in cases where the data is log normally distributed) should also be compared to the relevant Tier 1 investigation or screening level. The implications of localised elevated values (hotspots) should also be considered. The results should also meet the following criteria:
    * the standard deviation of the results should be less than 50% of the relevant investigation or screening level, and
    * no single value should exceed 250% of the relevant investigation or screening level.
The maximum observed contaminant concentration generally provides a conservative assessment of exposure because if estimated risks from the maximum concentrations