Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 3/5)
Character Range: 2030228–2033233

reviewing site contamination history, identifying all past and present contaminating activities and associated potential contamination
    * reviewing available information about local and regional geology and hydrogeology
    * identifying aquifers and confining layers, groundwater flow domain, potential receptors
    * identifying natural geochemistry of the groundwater system
    * sampling of site groundwater monitoring wells and identifying seasonal trends in groundwater quality
    * comparing site data with relevant GILS.
The purpose of Tier 1 assessment is to determine whether further assessment is required. It includes a comparison of monitoring data from the site with relevant GILs (such as those listed in Table 1C Groundwater Investigation Levels in Schedule B1). The relevant GILs should be selected on the basis of the environmental values identified in the conceptual site model.
Exceedence of Tier 1 criteria is generally used to determine whether there is a need to collect more data and/or progress to a Tier 2 assessment. An assessment of the significance of exceedences may be necessary where they are marginal or present over a limited area. Under some circumstances further assessment of contaminants exceeding Tier 1 criteria may not be conducted (e.g. where the extent of the exceedence and cost of remediation is small and further assessment is not cost-effective). Where further assessment of contaminants exceeding Tier 1 criteria is not proposed, a clear and transparent explanation should be provided.

This means that a groundwater sample from a monitoring well with contaminant levels above the GILs will trigger further investigation rather than initiate remedial action. However, site-specific consideration should be given to water quality impacts that cause variations from ambient water quality even when GILs are not exceeded. This is because individual jurisdictions may operate protective strategies for groundwater that require action at levels below the GILs or whenever levels of contaminants above ambient background are detected. Such issues are the responsibility of jurisdictions.

    3.4.2         Tier 2
A Tier 2 assessment is typically required when one or more contaminants are present at the site at levels that exceed Tier 1 guidance criteria, or if there are no appropriate Tier 1 criteria, or if there are unresolved and significant uncertainties identified in the Tier 1 assessment.

Tier 2 assessment includes consideration of the site-specific conditions and the modification of Tier 1 generic GILs according to the site conditions, including actual exposure. For example, the toxicity of some metals (Cd, Cr III, Cu, Pb, Ni and Zn) to freshwater biota is known to reduce with increasing water hardness (ANZECC & ARMCANZ 2000). The AWQG are conservatively presented on the basis of low hardness (30 mg/L CaCO3) and the relevant GILs may be modified for increased levels of hardness according to the algorithm presented in ANZECC & ARMCANZ