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Proposed National Environmental Standard for Assessing and Managing Contaminants in Soil

• Executive Summary
• Introduction
• Part 1: The Proposed NES for Assessing Contaminants in Soil
  • What is the Problem?
  • What are the Options?
  • The Proposed NES for Assessing and Managing Contaminants in Soil
  • Costs and Benefits of the Proposed NES
  • What Happens Next?
• Part 2: Implementing the Proposed NES
  • Implementing the Proposed Standard
  • Soil Guideline Values
• Appendix 1
• Appendix 2
• Appendix 3
• Appendix 4
• Abbreviations / Glossary
• References

8      Soil Guideline Values

This section describes what SGVs_(health) are, how they have been derived, and how they are to be applied. It is expected that if the national environmental standard is implemented, the SGVs_(health) provided in tables 6–8, and the method for deriving site-specific SGVs_(health), will be incorporated into the NES.

8.1    What are SGVs_(health)?

SGVs_(health) are threshold concentrations for 12 contaminants in soil, calculated for five generic land-use exposure scenarios at which the exposure is judged to be acceptable because any adverse effects on human health for most people are likely to be no more than minor.

The generic exposure scenarios are described in Appendix 1.

8.1.1   The function of SGVs_(health)

SGVs_(health) perform two functions:

1. Health-based trigger values – SGVs_(health) represent a human health risk threshold above which:
   • the effects on human health may be unacceptable over time
   • further assessment of a site is required to be undertaken.
2. Remediation targets – SGVs_(health) represent the maximum concentrations of contaminants at or beneath which land is considered “safe for human use” and the risk to people is considered to be acceptable.

SGVs_(health) do not necessarily provide protection for the natural environment (eg, soil invertebrates and plants) whose SGVs_(health) may be significantly lower.

The relationship between human health risk thresholds (SGVs_(health)) and effect thresholds (as defined under the RMA) is shown in figure 6.

Figure 6: Relationship between human health risk, SGVs_(health) and the RMA effects thresholds

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8.2    Soil guideline values – SGVs_(health)

SGVs for 12 metals and semi-volatile organic compounds are presented in tables 7, 8 and 9. The values have been rounded to two significant digits.

The values are purely for the protection of human health. The SGVs_(health) contained in the proposal are not to be promoted as desirable soil quality criterion nor as levels up to which contamination may be allowed to occur.

The SGVs_(health) for chromium III and copper range to in excess of a hundred thousand milligrams per kilogram soil (>10⁵ mg/kg), indicating a minimal threat to human health from the presence of these contaminants. These levels are well in excess of concentrations that are phytotoxic, ie, affecting plant health. Although phytotoxicity is beyond the scope of this proposal, if these contaminants are present at excessive concentrations it is questionable whether the land is fit for the intended purpose. This would need to be considered on a site-specific basis.

The SGVs_(health) for cadmium shown in table 9 is the proposed value (at a pH of 5) derived using Joint Expert Committee on Food Additives (JECFA) tolerable daily intake, as recommended in the Draft Toxicological Intake Values for Priority Contaminants in Soil (MfE, 2010a).

The SGVs_(health) proposed for cadmium would be reviewed if a future meeting of the JECFA of the Food and Agriculture Organization and the World Health Organization recommends a more conservative tolerable daily intake, in line with that adopted by the European Food Safety Authority.

The SGVs_(health) for cadmium in table 8 show cadmium SGVs_(health) for soil pH values 5–8 in a residential or rural residential scenario. Where the pH of the soil is measured, SGVs_(health) can be determined using this table. Where soil pH is not measured, the default is the SGVs_(health) at a pH value of 5.

Figure 7 shows the dependence of cadmium SGVs_(health) on pH. The 50 per cent produce curve is shown for reference purposes only.

Table 7: Summary of soil guideline values for inorganic substances (mg/kg)

1    Default value is for pH 5.  See table 8 for SGVs at other soil pH values.
2    Values for Joint Expert Committee on Food Additives tolerable daily intake of 2 µg/kg bw/day.
3    The SGVs_(health) for boron, chromium III, and copper represent levels well in excess of concentrations that would affect the health of plants.
NL = No limit.

Table 8: Summary of soil guideline values for organic compounds (mg/kg unless shown otherwise)

Table 9: Cadmium soil guideline values for soil pH values 5–8 (mg/kg)

Notes: Where pH is not measured, the SGVs_(health) at a pH value of 5 should be used.

Figure 7: Dependence of cadmium soil guideline value on pH (50% produce is shown for reference purposes only)

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Figure 7 shows the dependence of cadmium on pH in a graph with the soil guideline value in mg/kg on the y axis and soil pH on the x axis. The soil guideline values for the 10 per cent produce scenario from Table 9 and the 50 per cent produce scenario are plotted against pH values.  The graph shows that as soil pH increases so does the soil guideline value for both scenarios. The 50% produce land use scenario (shown for reference purposes only) soil guideline values are more conservative than the 10% scenario and increase at a reduced rate.

8.3    The SGV application framework

A decision tree that guides applying SGVs_(health) is set out in figure 8. This flowchart sets out nine steps in determining whether the risk from soil contaminants is unacceptable and if so, the further steps to manage the risk from that contamination. If this proposal is approved, a modified and expanded version of this section is likely to form part of the user’s guide.

Figure 8: Decision tree for applying SGVs_(health): basic steps

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The process is typically iterative, with more information gained at each review step which might send the process back to an earlier step. However, it is also possible to short-circuit the process at an early stage by simply choosing to go directly to the management or remediation stages, if site-specific risk assessment is considered unwarranted.

Step 1 – Site identified

A site is identified as possibly having hazardous substances on or in it. Land may be identified through a variety of ways including: regional councils HAIL survey; information provided in resource consent applications for subdivision, development or land-use change; enquiries to councils from landowners and/or neighbours, complaints, and through council responses to unauthorised discharge events.

For guidance on identifying and prioritising sites refer to:

• Identifying, Investigating and Managing the Risks Associated with Former Sheep-dip Sites: A Guide for Local Authorities (MfE, 2006a)
• Contaminated Land Management Guideline No. 3: Risk Screening Systems (MfE, 2004a)
• The Hazardous Activities and Industries List (Appendix 4).

Step 2 – Does land need to be investigated?

Sufficient information is gathered to determine whether further investigation is warranted, via a preliminary study as defined in Contaminated Land Management Guideline No. 1 (MfE, 2003a). An essential part of the preliminary study is to develop a conceptual site model as set out in Contaminated Land Management Guideline No. 5 (MfE, 2004b). The conceptual site model should set out receptors and exposure pathways for the particular land use or proposed land use.

For further guidance on determining whether further investigation is required and on developing a conceptual site model refer to:

• Contaminated Land Management Guideline No. 1: Reporting on Contaminated Sites in New Zealand
• Contaminated Land Management Guideline No. 5: Site Investigation and Analysis of Soils.

Step 3 – Does site exceed SGVs_(health)?

Carry out a further investigation involving sampling. The results are compared against SGVs_(health) and the conceptual site model should be updated as required, based on additional information from the investigation. Sampling should be carried out in accordance with CLMG5. For further guidance on sampling and analysis and determining whether land exceeds SGVs_(health) refer to:

•  Contaminated Land Management Guideline No. 5: Site Investigation and Analysis of Soils.

Step 4 – Risk is acceptable

If the site complies with the SGVs_(health) for the particular land use (and conceptual site model), then the risk from hazardous substances in or on the site is considered acceptable for the current land use without restrictions. Compliance with SGVs_(health) is deemed as sufficient proof that land does not have, or is not reasonably likely to have, hazardous substances on or in it, at levels that would lead to unacceptable adverse effects on human health under that particular land use.

Step 5 – Is a site-specific investigation warranted?

If the site does not comply with the SGVs_(health), then decision options include:

1. carrying out a site-specific exposure assessment to better quantify the actual risk – go to Step 6
2. remediating the site to reduce the hazard (ie, reduce the concentration of the contaminants) – go to Step 8
3. managing the site to prevent access to or exposure to the hazard (ie, interrupt the exposure mechanism(s) or pathway(s)) – go to Step  8.

The factors to consider in making this decision are contained in Appendix 2.

Step 6 – Assess site-specific exposure

A site-specific analysis will quantify the risk, taking into account the actual site parameters and whether the generic exposure parameters used to derive the SGVs_(health) are too conservative for the site or not conservative enough. If carried out numerically, site-specific SGVs_(health) will be derived using the methodology in Appendix 2 with varied exposure parameters. There are limits, however, as to what can be varied.

For further guidance on assessing site-specific exposure, refer to Appendix 2.

Step 7 – Determine whether land exceeds site-specific SGVs_(health)

If the site complies with the site-specific SGVs_(health), then the risk from hazardous substances in or on the site is considered acceptable for the current land use without restrictions as in Step 4. However, if the site does not comply, the risk is considered unacceptable and the risk must be managed as in Step 8.

For further guidance on determining whether land exceeds SGVs_(health) refer to:

• Contaminated Land Management Guideline No. 5: Site Investigation and Analysis of Soils.

Step 8 – Decide how to manage risk

It may be decided that some form of management is the best approach (because the additional expense of a site-specific assessment is not worth it, or the site is clearly contaminated and will require management regardless of a further site-specific assessment or it has failed a site-specific assessment). In that case the next step is to weigh up the available management options. These options could be remediation of the soil, containing the soil in some way to prevent or limit access, or (if appropriate to the circumstances) by restricting behaviour to ensure that people are not at an unacceptable level of risk (see figure 9). These and other options are discussed further in Contaminated Land Management Guideline No. 5; see also the sheep-dip guide (MfE, 2006a).

Figure 9: Methods for managing the risks from contaminants in soil

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Step 9 – Manage the risk

If the site is remediated, and validated to demonstrate it complies with generic or site-specific SGVs_(health), it is deemed that the risk is acceptable for current land use without restrictions. The remediation of a site should be subject to controls to protect off-site and on-site receptors; these controls should be formalised through resource consents held for the duration of the remediation.

If the land remains un-remediated and exceeds SGVs_(health), other management action (eg, containment, behavioural modification) is to be put into effect to ensure the risk to human health is acceptable for current land uses. Any maintenance or restrictions to land use need to be made legally binding through conditions of resource consent, or non-regulatory advice.

Reporting

The process of identifying, investigating and managing risks associated with contaminants in soil should result in the land investigator preparing a report that documents their work for their client and/or intended audience. Contaminated Land Management Guideline No. 1 identifies five reporting stages:

• preliminary site investigation report
• detailed site investigation report
• site remedial action plan
• site validation report
• ongoing monitoring and management plan.

These stages may be reported together or separately, and not all sites will need to report all stages.

For further guidance on reporting on contaminated sites including checklists for each stage of reporting refer to:

• Contaminated Land Management Guideline No. 1: Reporting on Contaminated Sites in New Zealand.

Information management

Where reports on soil contaminants are submitted to regulatory authorities (regional councils and territorial authorities), this information should be held on the property file. The land to which the information applies should be classified and information on the site reported and made available to the public in general accordance with Contaminated Land Management Guideline No. 4.

For further guidance on local government recording and reporting:

• Contaminated Land Management Guideline No. 4: Classification and Information Management Protocols (MfE, 2006b).

Table 10: Application of existing guidelines within the application framework

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