4 The Hierarchy of Guideline Values
Determining the order in which available guideline values should be used when assessing a contaminated site is not a simple matter, resulting in uncertainty as to which criteria to use in which circumstances.
To help alleviate this uncertainty the Ministry for the Environment compiled a derivation Methodology for health-based standards to apply to soil contaminants in New Zealand (Ministry for the Environment, 2011). Soil contaminant standards for a group of 12 priority contaminants were derived under a set of five land-use scenarios that are legally binding as gazetted under the National Environmental Standard for Assessing and Managing Contaminants in Soil to Protect Human Health.
The ‘soil contaminant standards’ are intended to supersede the ‘soil acceptance criteria’ used in previous New Zealand guidelines and comprise the following priority contaminants: arsenic, boron, cadmium, chromium, copper, inorganic lead, inorganic mercury, benzo(a)pyrene, DDT, dieldrin, dioxin and dioxin-like polychlorinated biphenyls (PCBs), and pentachlorophenol (PCP).
To help contaminated site practitioners prepare and review contaminated site assessments for contaminants that are not part of the group of priority contaminants and for purposes other than protecting human health, a hierarchy of guideline values contained in the reference documents has been established. The hierarchy is intended to provide guidance to preferred guideline values that should be used when assessing a contaminated site, and is provided in the form of a hierarchy of documents containing the guideline values. Not all guidelines values contained in a reference document are included (Table 2).
The hierarchy has been developed according to the following principles.
- The New Zealand guideline values should be used in preference to guideline values from other nations or jurisdictions.
- Guideline values using a risk assessment methodology to establish guideline values (risk-based guideline values) should be used in preference to those that present threshold values.
Following these principles an overall hierarchy of reference documents has been established. This hierarchy, in order from most to least preferred, is:
- New Zealand derived risk-based guideline values
- rest of the world derived risk-based guideline values, with preference given to those that employ risk assessment methodologies and exposure parameters consistent with that already used in New Zealand
- New Zealand derived threshold values
- rest of the world derived threshold values.
This hierarchy has been developed for the following reasons.
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New Zealand documents have been developed using international best practice at the time. They have been through substantial national and international peer review, and are accepted by national and local government and industry. In some cases they also reflect exposure pathways common in New Zealand (eg, consumption of home-grown produce) that are often omitted from international documents.
- On the one hand, some countries have been addressing contaminated site issues for much longer than New Zealand and have invested heavily in the development of methodologies for deriving guideline values. Indeed, some of these methodologies have been used in the derivation of some New Zealand guideline values. On the other hand, internationally derived guideline values are likely to contain regulatory and social assumptions that are not necessarily applicable in the New Zealand context, and therefore these values should be used only in the absence of New Zealand values.
4.1 The hierarchy of documents
To assist in the selection of the appropriate guideline values for a given environmental media and/or purpose, a hierarchy of reference documents containing guideline values is established separately for those documents that contain guideline values for soil and water. Further differentiation of documents within those groupings is made on the basis of protection (eg, human health, ecological receptors). However, users should note that different parameters and, in some cases, pathways of exposure, are used to derive the guideline values from different jurisdictions and users should refer to the original documents to ascertain the applicability of a selected guideline value. Where multiple guideline values in a given reference document exist (eg, ANZECC and ARMCANZ, 2001), users should refer to Table 2 for the guideline values to which the hierarchy applies.
Table 5: Hierarchy of documents containing guideline values for soil
View the hierarchy of documents containing guideline values for soil (large table)
Table 6: Hierarchy of documents containing guideline values for surface water, groundwater and sediment
It is important to note that a hierarchy is not established for the guidance documents within each category - the documents are listed alphabetically. Final selection of the appropriate criteria should be conducted according to the principles outlined in section 5. Particular attention should be given to the selection of guideline values for residential land use, as New Zealand, UK, Canadian and Dutch criteria are the only ones that include produce consumption as a pathway of exposure in this scenario.
If a reference document and its guideline values are not found in the database, this does not necessarily mean these criteria cannot be used in assessing a contaminated site. Guideline values from overseas jurisdictions can be used as long as:
- the hierarchy established in this guideline document is followed
- the user can demonstrate that the methodology used to derive the guideline values is consistent with New Zealand risk-based methods, or justify the appropriateness of using values based on different derivation methodologies for the particular site under consideration
- the exposure pathways on which the criteria are based are those that operate at the site being assessed.
Users should apply this hierarchy in selecting appropriate guideline values in the assessment of any contaminated site (see section 5). If, for any reason, users deviate from the hierarchy established above, the reasons for the deviation should be given and fully documented within the contaminated site investigation report. The minimum information requirements of site investigation reports have previously been outlined (see Contaminated Site Management Guideline No. 1: Reporting on Contaminated Sites in New Zealand (Revised 2011) (Ministry for the Environment, 2001).
While this document and the EGV database have been developed as a tool for contaminated site practitioners, users should ensure they are conversant with the derivation of any guideline value referenced in a contaminated site assessment.
4.2 EGV database
The guideline values presented in the reference documents listed in this guideline (Table 1) and included in the EGV database are listed in Table 2. The database is designed to provide users with a rapid and user-friendly means by which criteria can be accessed. In addition, criteria from the database will be displayed in keeping with the hierarchy established; that is, where available, New Zealand risk-based criteria will be displayed before any other criteria. However, it is important that the database is not used solely as a series of look-up tables without the users being conversant with the principles and assumptions underlying the derivation of the criteria.
Users of the database should not assume that the criteria contained in the EGV database have not been superseded. Users therefore need to acknowledge this in their use of guideline values from the database, or confirm the status of the value with the organisation responsible for publishing it.
Last updated: 19 October 2011
