Industry-specific guideline documents developed by the Ministry for the Environment (MfE) in the 1990s contain valuable information to guide development of contaminated land conceptual site models and source pathway receptor linkages. They also include risk based assessment criteria applicable when assessing contaminated sites for media and pathways that are not covered by or cannot be developed through the National Environmental Standard for Assessing and Managing Contaminants in Soil to Protect Human Health (NESCS) Methodology.
Anna Lukey and Kevin Tearney from SLR Consulting discuss their recommendation that the industry guideline documents become go-to references for contaminated land practitioners and regulatory authorities, and that a refresh of the guidelines is prioritised by MfE or the Environmental Protection Authority.
Against the backdrop of global risk-based corrective action (RBCA) principles, the 1990s were a prolific time for the Ministry for the Environment (MfE) to publish guidelines.
Several risk-based industry specific guideline documents were produced by MfE in this period. Industries were selected based on the understanding of the relatively high risk posed by contamination and numbers of sites associated with the industries. These included petroleum (oil industry), gasworks and timber treatment. Sheep dip guidelines were produced in mid-2000s.
The guideline documents present detailed discussions of industry practice, the contaminants associated with these industries, their fate and transport in the environment, sampling and analysis strategies and risk management advice. The level of detail is often greater than offered in The Contaminated Land Management Guidelines (CLMG) No.5.
The benefits of industry guidelines
The industry guidelines documents also include risk-based guideline values, derived using various assumptions for different land use scenarios. They cover exposure of contaminants through ingestion, inhalation and adsorption for various media (soil, groundwater and air) and receptors based on land use. Risk-related assumptions and guideline number calculations based on internationally accepted values and methodologies are documented for transparency. These assumptions are typically conservative, although it should be noted that for non-threshold substances (which have the potential to cause cancer at any level of exposure), MfE adopted a risk level of 1x10-5 to calculate guideline values in New Zealand, which has been taken through to the methodology. The USEPA for example, use a more conservative value (10-6). The guideline values are considered first cut or Tier 1 numbers.
These guideline documents have been used extensively by contaminated land practitioners since the 1990s to develop Conceptual Site Models (CSM) and to inform source-pathway-receptor linkages (SPR). The Tier 1 guideline values are then used to assess the risk posed to human health and the environment from a contaminated site and to determine risk management, including administrative controls, physical remediation, and/or further assessment using site specific exposure scenarios (Tier 2 or Tier 3 risk assessment).
A common misperception
Since the introduction of the National Environmental Standard for Assessing and Managing Contaminants in Soil to Protect Human Health (NESCS) in 2012 and revision of companion CLMG documents, we note a perception amongst practitioners that the industry specific guidance documents are no longer relevant or applicable. This may be due in part to CLMG1 which states that MfE industry specific guideline criteria have been largely superseded by the soil contaminant standards derived by the methodology.
However, CLMG1 references the industry guideline documents and notes that Suitably Qualified and Experienced Practitioners (SQEPs) should be familiar with their contents. CLMG2 also includes reference to the Tier 1 values within these guideline documents and provides validity through their inclusion, albeit with the proviso that the methodology should be used where appropriate.
The methodology does have limitations however, including:
- It covers standards for soils in relation to human health only. Pathways comprise dermal exposure and soil ingestion and produce consumption. Inhalation of particulates and volatiles are not included. There are other media and exposure routes that may need to be investigated to fully develop a CSM and to understand risk posed by potentially complete contamination exposure pathways to human health, including groundwater, surface water, sediment and soil vapour and the contaminants of concern. Risk-based guidelines and other information are presented in the industry specific guideline documents which can be used to develop the CSM and SPR linkages for exposure from media other than soil.
- The methodology does not provide soil criteria for protection of surface water or groundwater quality. These criteria are provided in guidelines developed for the oil industry, which for groundwater is based on potability.
- The methodology does not cover the inhalation of volatile contaminants in any detail and has not derived any standards for volatile contaminants. This SPR linkage is covered in the oil industry guidelines. The widespread use and acceptance of these risk-based values demonstrate the continued applicability of the oil industry guidelines.
- Industry specific guidance also provides detail around specific pathway assessments and criteria, including criteria for the dominant pathway and different soil types and depth, which are useful when using a tiered assessment approach.
Industry guidelines should be used too
With the introduction of the NESCS and the associated focus on soil quality in relation to human health based on a lookup table of numbers, we are concerned that knowledge and use of the industry specific guidelines may lessen, leading to a diminished understanding of the risk assessment process for contaminated land. The industry guidelines include valuable information on historic site layout and processes, contaminants of concern and which media to sample. This level of detail is important when planning an investigation as it ensures the most appropriate areas are sampled for the appropriate analytes.
In relation to the risk-based guideline values themselves, these are still valid and applicable when assessing contaminated sites for media and pathways that cannot be developed through the methodology.
Given the ongoing relevance and validity of aspects of the guideline documents, we strongly recommend that they again become go-to references for contaminated land practitioners and regulatory authorities, and that a refresh of the guidelines is prioritised by MfE or the Environmental Protection Authority. Quality decision making is the goal.
About the authors
Anna Lukey, Technical Director, SLR Consulting
Years in the industry: 28
Anna is an environmental professional working in the contaminated land field. She has direct experience both in industry organisations and for environmental consultancies, both global and New Zealand owned.
Kevin Tearney, Technical Director, SLR Consulting
Years in the industry: 35+
Kevin is a geoscientist with over 35 years of international environmental consulting experience covering hydrogeological assessments, environmental baseline studies, environmental due diligence, and soil and groundwater contamination investigation, risk assessment, remediation and site management.
