4.20 Review of monitoring programs

As noted above, monitoring is the means by which mining companies and stakeholders can assess the effectiveness of management measures, verify or adjust predictions made early in a project, and develop improved management practices. With this in mind, leading practice monitoring should be regularly reviewed in the light of changes to ensure that objectives are being met. The changes may be internal (adjustments within the organisation or operation) or external (broader regional or community adjustments).

Examples of changes that should trigger a review of monitoring programs in the mining industry are:

  • changes to the mine plan (for example, expansion or contraction of the operation)
  • changes in the type of mining (such as from open-cut to underground) or in the ore mined and processed on the site (such as from oxide to sulphide)
  • extreme events that cause the company to adjust the assumptions on which planning has been based and risk assessed
  • a significant incident at another mine site of a similar type or in the same region (for example, deaths of flora or fauna or community health impacts)
  • changes within the local community as the mine matures through its life cycle (for example, demographic stabilisation following periods of substantial population expansion).

Importantly, the findings of monitoring programs should be used to inform and, if necessary, modify management decisions and practices.

Collapsed - Case study: Upgrading monitoring systems to inform water management

The Ranger uranium mine, operated by Energy Resources of Australia (ERA) Ltd, is situated next to Magela Creek, east of Darwin in the Northern Territory. It is separate from but surrounded by the World Heritage listed Kakadu National Park.

The climate of the area is tropical monsoonal, with an average rainfall of about 1,600 mm per year, falling mainly in the wet season between October and April. The concentration of heavy rains over a relatively short period presents a significant challenge to the mining operation: it must manage its water inventory to ensure that releases of water from the site do not compromise natural and cultural values and that the downstream environments of Kakadu National Park remain protected.

In the past, the release of site catchment run-off water (not process water or seepage water from mineralised material) was permitted, depending on results from routine weekly grab samples, biological testing in specific cases, and a conservative predictive model designed to assess the suitability of release conditions in line with meeting formal water-quality objectives. While successfully protecting the environment, this approach to water management resulted in substantial volumes of water being unnecessarily stored on site and subsequently requiring further treatment. The efficiencies that could be realised by using a real-time monitoring system to identify optimal opportunities for water releases and to monitor responses in receiving water quality were clear.

Continuous monitoring of surface water quality for pH, electrical conductivity (EC) and turbidity in the receiving waters of Magela and Gulungul creeks upstream and downstream of the Ranger mine has been conducted independently by the Australian Government’s Supervising Scientist Division (SSD) since 2005. Since 2007, ERA has progressively installed continuous monitoring stations at key onsite locations to enable real-time monitoring of data at key release points from the mine site. ERA has also installed an array of monitoring stations in the creeks adjacent to the mine site to assist with water management decision-making in real time. This monitoring is done in addition to statutory grab sampling for monitoring water quality in the main mine site catchments. The Northern Territory Government conducts a grab sampling monitoring program for specific analytes to check field parameters and laboratory results against those reported by the operator.

EC is a demonstrated proxy for magnesium (Mg), for which local water-quality objectives have been derived from the ecotoxicological response testing of six sensitive local aquatic species. Given the dynamic nature of water flows during the wet season, the behaviour of EC is best described by a pulse (event-based) exposure regime. It was thus recognised that traditional ecotoxicological end points based on long-term (chronic) exposure might not provide the most appropriate management framework. Accordingly, water-quality objectives spanning pulse exposure durations ranging from short term to chronic have been developed for continuously monitored EC (Figure 6). Figure 7 shows a practical example of the application of the EC pulse exposure magnitude and duration curve shown in Figure 6. A maximum peak in EC was detected at the monitoring site in Magela Creek downstream of the Ranger mine during 2009–10. In this example, the EC pulse exposure limit as inferred from the exposure limit curve is 174 μS/cm for a pulse duration of 8 hours.

The pulse duration is defined by the period of time for which EC is above the chronic 72-hour limit of 42 μS/cm. The maximum EC recorded during this event was 89μS/cm, which is only 51% of the EC pulse exposure limit (derived from Figure 6) for this event duration.

Figure 6: Water quality objectives for continuously monitored EC
Water quality objectives for continuously monitored EC

Figure 7: Practical application of EC pulse exposure magnitude and duration curve shown in Figure 6
Practical application of EC pulse exposure magnitude and duration curve shown in Figure 6

The interpretative framework for assessing the possible effects of short-duration pulses of elevated EC (Mg) waters was formally incorporated into the statutory monitoring regime for the Ranger mine in December 2013. This was an Australian first for the implementation of an event- based water-quality assessment framework, and is one of the few examples internationally of this type of approach. Water-quality objectives are currently being developed for continuously monitored turbidity.

Online telemetry enables the immediate notification of events (via mobile phone SMS) to key staff, allowing the operator and regulators to commence timely investigations into the cause of an EC pulse, whether it be from a natural or mine-derived source. An important attribute of the continuous monitoring system is that it provides the ability to quickly distinguish differences between the upstream and downstream sites, and intermediate monitoring sites are used to identify the location of specific input sources from the mine. Adaptive management by the mine operator, using the feedback from the continuous monitoring system, of the rate and time of discharge of site run-off water ensures that the water quality in receiving surface waters downstream of the mine site remains within acceptable levels, protecting the receiving environment. The outputs from the SSD surface water quality and biological monitoring programs are posted on the SSD’s website to provide ongoing assurance reporting to stakeholders and the general public.1

All monitoring by the SSD is completely independent of that done by the mining company and the Northern Territory Government regulator. However, the data is regularly shared between the three entities in order to aid interpretation, promote transparency and achieve the implementation of leading practice monitoring methodologies for this sensitive environment.

The long record of macro-invertebrate and fish community data from the biological monitoring program conducted by the SSD shows that, despite some changes in water quality having occurred, the biodiversity in water bodies on the mine site has not been adversely affected.

Because of this lack of demonstrated effect, the current water-quality record, including that provided by the continuous monitoring system, will be able to be used to derive water-quality closure criteria to protect the environment following rehabilitation of the Ranger site.

The long record of macro-invertebrate and fish community data from the biological monitoring program conducted by the SSD shows that, despite some changes in water quality having occurred, the biodiversity in water bodies on the mine site has not been adversely affected.

Because of this lack of demonstrated effect, the current water-quality record, including that provided by the continuous monitoring system, will be able to be used to derive water-quality closure criteria to protect the environment following rehabilitation of the Ranger site.

Footnotes

1 Supervising Scientist, Department of the Environment, http://www.environment.gov.au/science/supervising-scientist/monitoring.

Collapsed - Case study: Environmental evaluation of QAL’s red mud dam and receiving waters

The Queensland Alumina Limited (QAL) refinery, one of the largest alumina refineries in the world, is on the coast at Gladstone, central Queensland. It produces 3.95 Mt/y of smelter-grade alumina using the Bayer process. The QAL site (Figure 8) comprises the refinery (which is situated within 90 hectares of land and is bounded by buffer land, communities to the south and west, and coastal waters to the east and north), wharf facilities, boiler ash residue areas and a red mud dam (RMD). QAL operates within and adjacent to the Great Barrier Reef World Heritage Area.

Figure 8: QAL refinery and red mud dam
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Note: The Great Barrier Reef World Heritage Area covers the QAL red mud dam area and South Trees Inlet.

Alkaline bauxite mud residue (red mud) slurry is transported via pipeline from the refinery to the RMD for neutralisation with seawater. The neutralised red mud and associated precipitates are separated in a clarifier, and the thickened solids fraction is pumped to one of two residue disposal areas (RMD1 and RMD2). The clarifier overflow is directed to a decant pond within RMD2.

Discharge from RMD2 is via a gabion spillway structure, for aeration, into an open maze, which assists in the removal of suspended solids. From there, the discharge flows initially through an underground pipe to an open channel and then directly to South Trees Inlet via two diffusers at a continuous flow of 130,000—150,000 m3/day (Figure 9).

Figure 9: QAL’s red mud dam
QAL’s red mud dam

In 2010, following a series of incidents involving low dissolved oxygen in discharge waters, QAL installed aerating paddles in the open discharge channel to remedy the situation. In addition, in consultation with the Australian Institute of Marine Science, QAL developed a comprehensive environmental evaluation of impacts on the receiving aquatic environment of discharges from RMD2. The evaluation of RMD2 and South Trees Inlet used a leading practice integrated approach to gather multiple lines of evidence. The approach included:

  • physicochemical assessment (water and sediment quality)
  • biological characterisation using next generation genomic (DNA pyro-sequencing) techniques
  • direct toxicity assessment of the RMD2 discharge
  • hydrodynamic and water-quality modelling of RMD2 discharge dispersion and dilution in South Trees Inlet
  • biological impact assessment (bioaccumulation, biochemical and histopathological investigation of oysters and mud crabs)
  • the development of environmental values and water-quality objectives for South Trees Inlet.

Physicochemical assessment identified a number of elements (aluminium, gallium, molybdenum and vanadium) as fingerprints of the RMD2 discharge in water and sediment.

The results from the genomics characterisation showed that bacterial populations were significantly different in the RMD2 decant pond, the maze and the receiving environment and between summer and winter (Figure 10). These results showed that bacterial populations in South Trees Inlet were not being affected by the RMD2 discharge. The study also identified that the low dissolved oxygen levels measured in the decant pond were due to a high level of activity of sulphate-reducing bacteria, together with a range of heterotrophic bacteria.

Figure 10: Spatial separation of bacterial populations, revealed by principal coordinates (PCO) analysis of the genomics data
Spatial separation of bacterial populations, revealed by principal coordinates (PCO) analysis of the genomics data

The direct toxicity assessment showed no toxicity to six marine species from five trophic levels at 100% concentration of RMD2 discharge water. While this result showed that there was no need for operational dilution of the discharge, the dilution that does occur at the diffuser within the South Trees Inlet provides an additional level of protection for the marine ecosystem of the inlet.

The biological impact assessment included an investigation of bioaccumulation of fingerprint elements, together with biochemical and histopathological investigations of oysters and mud crabs collected within 500 metres of the RMD2 diffusers in South Trees Inlet and at a reference estuary 13 km south (Colosseum Inlet). The results showed no significant differences between the two sites; a minor observed alteration in histopathology was attributed to freshwater flows resulting from floods before the evaluation.

The results from the multiple lines of evidence evaluation described here have allowed QAL to demonstrate minimal impact on the receiving environment of South Trees Inlet, and no measurable environmental harm.

Overall, the findings have resulted in significant improvements to the monitoring program, including:

  • the installation of continuous water-quality monitoring buoys at the RMD outfall, upstream and downstream
  • the implementation of a more robust near-field monitoring program
  • the reconciliation of far-field and near-field monitoring programs, resulting in a more comprehensive and cost-effective program.

Ongoing work is being done to develop new marine water toxicity testing methods for tropical Australian marine species, including the derivation of regionally relevant water-quality guideline trigger values for several key contaminants (such as aluminium).

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