Rehabilitation and closure ecological risk assessment for Ranger Uranium Mine: Documentation of initial problem formulation activities

Department of the Environment, 2013

Internal Report 624
R Bartolo, S Paulka, R van Dam, S Iles  & A Harford

Executive summary

Initial conceptual models (causal maps) of potential stressors and their pathways have been developed as part of the problem formulation phase of the ecological risk assessment focused on closure and rehabilitation of Ranger Uranium Mine. The conceptual models were drafted during a two day workshop with stakeholders who formed breakout groups around four themes (aquatic ecosystems; terrestrial ecosystems (Ranger Project Area); terrestrial ecosystems (landscape); and people), and were subsequently reviewed by a small review group and finalised by the breakout groups.

Components of the problem formulation that were undertaken include:

  • Setting the spatial and temporal scales that are the focus of the ecological risk assessment. There are three temporal phases: i) decommissioning; ii) stabilisation and monitoring; and iii) post-closure. The five spatial scales defined are: i) the Ranger mine site (disturbed footprint); ii) the Ranger Project Area (RPA); iii) Magela Creek catchment; iv) Kakadu National Park; and v) the Alligator Rivers Region (ARR).
  • Identify the key sources, stressors and ecological assets that will be examined for the decommissioning, stabilisation and monitoring, and the post-closure phases of Ranger uranium mine’s closure. The values are documented in Pollino et al. (2013).
  • Determine the ecological assessment endpoints. Numerous assessment endpoints were developed for the four themes.

For aquatic ecosystems three assessment endpoints were developed for both the on-site and off-site environment reflecting their different management goals:

  1. Off-site water quality meets agreed closure criteria specified for water quality.
  2. Habitat diversity of off-site aquatic ecosystems are comparable to the agreed reference condition.
  3. Biodiversity (structure and function) of off-site/on-site aquatic ecosystems are comparable to the agreed reference condition.
  4. On-site water quality is on a trajectory towards meeting agreed closure criteria specified for water quality on-site.
  5. Habitat diversity of on-site aquatic ecosystems is on a trajectory towards meeting agreed closure criteria.
  6. Biodiversity (structure and function) of on-site aquatic ecosystems are on a trajectory towards meeting agreed closure criteria.

The biodiversity assessment endpoints are proposed and not finalised as the ecological processes and functions that were identified during the workshop have not been drafted as conceptual models. The ecological processes and functions will be addressed in the near future by the Closure Criteria Working Group (CCWG).

For terrestrial ecosystems (RPA) three assessment endpoints were developed:

  1. Erosion characteristics of the rehabilitated landform meet agreed closure criteria.
  2. Wildlife on the rehabilitated site is on a trajectory towards meeting agreed closure criteria.
  3. Vegetation on the disturbed sites of the RPA is on a trajectory towards meeting agreed closure criteria.

For terrestrial ecosystems (landscape) two assessment endpoints were developed:

  1. Habitat diversity and ecosystem function within the landscape of the Magela Creek sub-catchment and broader Kakadu National Park is comparable to an agreed reference condition.
  2. Aesthetic values meet the expectations of the stakeholders in the ARR.

For people four assessment endpoints were developed:

  1. Landform is able to be accessed, and is readily traversable, by people.
  2. Presence of culturally important species at right time and abundance.
  3. Landform, vegetation and water bodies on-site meets agreed cultural closure criteria.
  4. Return of traditional practices (e.g. burning, harvesting).

Develop conceptual models for the above-mentioned closure phases of the Ranger mine site:

  • The aquatic ecosystems breakout group drafted one large conceptual model that included all sources, stressors, pathways, measurement points and assessment endpoints during the workshop. This large model needed to be reduced into ten sub-models in order to define differences in the pathways to measurement endpoints for each of the stressors.
  • The terrestrial ecosystem (RPA) breakout group drafted four conceptual models during the workshop, with three being reviewed post workshop. The fourth model not revised to date, focused on ‘protection of human health’. The human health model will be dealt with separately in the future, combining it with the human health model drafted by the people group.
  • The terrestrial ecosystem (landscape) breakout group drafted three conceptual models during the workshop. These have been revised to two conceptual models as the sources and stressors were similar between two of the models that were output from the workshop, and review of the assessment endpoints indicated that the models were quite similar.
  • The people breakout group drafted two conceptual models – one for cultural landscape and the other for human health. Currently, the group has focused on refining the cultural landscape model. The human health model will be dealt with separately in the future as discussed above. The original cultural landscape model, drafted during the workshop, has been split into four separate conceptual models, to reflect the revised assessment endpoints.

Communicate and document the outcomes from the problem formulation phase:

  • A report was produced by Pollino et al. (2013) which details background material, and the values and draft conceptual models produced during the workshop. These are not reported in detail here.
  • Revision of the conceptual models presented here and communication is ongoing.
    Part of the problem formulation phase project included the development of an analysis plan (design, data needs, and methods for undertaking the risk analysis phase of the assessment), which was undertaken and reported by Pollino et al. (2013). It is recommended that the AS/NZS ISO 31000:2009 generic framework for risk management be adopted as it is considered best practice. The US EPA ecological risk assessment guidelines (US EPA 1998) can be used in conjunction with the ISO risk management standard. Pollino et al. (2013) recognise there are many approaches for undertaking risk analysis, but they focused on Bayesian networks, a recommended approach in the ISO/IEC 31010 Standard which supports the risk management standard (it is focused on risk analysis techniques). Bayesian networks have also been identified as a potential tool by Energy Resources Australia (ERA).