Preventing environmental impacts on streams from mining
With an annual value of $1.5 billion (excluding petroleum) mining is an important part of the New Zealand economy.
However mining can also have significant environmental impacts and it is therefore vital that it is managed in a way that ensures environmental sustainability.
Landcare Research has been key in establishing a framework to assist with planning of future mine developments on the West Coast and in Southland. It has been developed as part of a collaborative research programme involving research on rock geochemistry, aquatic chemistry, freshwater ecology, aquatic toxicology and management, and remediation techniques and is intended to provide consistency and transparency in decision making for proposed mining operations, specifically around minimising impacts on streams.
It has been developed in conjunction with stakeholders and end-users including DOC, regional councils, consultants and mining companies.
‘The great advantage for business is that this framework is intended to streamline the processes when they’re investigating the feasibility of mining. They will have confidence that if they follow this framework then the relevant regional council will have the required information. Therefore, it saves them significant time and money,’ lead researcher Jo Cavanagh says. The framework is a flowchart outlining a series of steps to determine the likelihood and extent of impacts on aquatic systems from mining – and underlying detailed information. Water quality is the key parameter enabling prediction of the likely ecological impact and selection of management or remediation options. While the framework is intended for new mining operations, the information is also relevant to existing mining operations or when selecting remediation options for historic mining operations.
The potential for ecological impact is based on the likely downstream water quality arising from mining operations. The water quality can be predicted by considering background and regional geology, geochemical analysis of rocks and water quality, and quantity of the receiving system.
The level of potential ecological impact associated with various water qualities has been determined using a combination of biological surveys and toxicity testing.
Information on likely downstream water quality is combined with information on the likely ecological effects to determine whether, for the specific operation, any potential impact is acceptable or not. This information can be used internally by mining companies when planning their operations, or in a regulatory context such as during the consenting process.
‘We’re not making a value judgement on what is environmentally acceptable and what is not,’ Dr Cavanagh says.
‘We’re simply providing information – people can debate the details.
‘If it’s not acceptable then the framework offers different options for management of remediation, and there is guidance on what sort of monitoring should be undertaken to validate whether the system is working.’
Mitigation or prevention of poor quality mine drainage can be achieved through appropriate management of waste rock and tailings (operational management) and /or treatment of mine drainage through active or passive remediation systems.
The framework does not establish explicit ‘acceptable’ water quality criteria because these are likely to be different at different sites and because there are social, economic and cultural factors that may also influence decision making. Instead, the framework provides a robust scientific basis for this decision to be made by end-users during consultation processes.
‘The framework could even indicate at a very early stage that a project is not worth continuing because of potential financial or environmental costs,’ she says
The framework includes details on predicting downstream quality for mine operations on the West Coast and in Southland and specific information on four mine types: coal – potentially acid forming (PAF), coal – non-acid-forming (NAF), gold – alluvial, and gold hard rock.
For each of these groupings a more detailed discussion of the likely water quality, potential ecological impact and options for management and remediation to reduce aquatic impacts is provided. In addition, information on monitoring requirements, determination of the acceptable level of impact and consideration of the impact of extreme events on mining operations is provided.