Understanding Coal Pit Lake Resources within the Collie Basin Project

Funding: Department of Water (Western Australia) and Australian Government’s “Water for the Future” initiative

Background

Strategic management of pit lakes as a regional resource and/or liability requires a data collection programme to advise management processes such as environmental and human health and safety. Development of a monitoring and management strategy for pit lakes and connected waters would be made through a review of the various international best practice guidelines.

This study has begun with a literature review of pit lake water quality monitoring strategies. In particular, parameters identified from reviewing existing pit lake datasets and known to be important to pit lake management and eventual modelling will be a focus of a proposed monitoring strategy. A cost-effective and achievable monitoring strategy will be developed, incorporating international best practice and parameters chosen to fill data gaps will be clearly identified. Details of sampling regimes recommended for each selected parameter will be presented. Frequency and timing of sampling will be discussed and recommended.

Collecting bottom water samples using a Kemmerer bottle

Findings

1. Pit lakes can form in open cut mining pits, which extend below the groundwater table. Once dewatering ceases, then groundwater, surface water and direct rainfall contribute to the formation of a pit lake.
2. The current demand for water in WA and its increasing scarcity means that Collie pit lakes represent a potentially valuable resource to both the environment and the community. As a result, a monitoring strategy for these pit lakes is required in order to achieve more stringent demands on pit lake conditions at relinquishment made by state and federal regulation and the desired end uses of local communities.
3. The purpose of this report was to recommend state-of-the-art monitoring design and sampling methodologies for environmental monitoring of pit lakes in the Collie Lake District, south-western Australia.
4. The report gives an overview of regional and international environmental issues related to pit lakes, current national guidelines and best practice international operations and recommendations for monitoring pit lakes aquatic ecosystems. The purpose of monitoring selected indicators and their field sampling and analysis methods and techniques are described. The practical temporal and spatial issues targeting episodic events are also discussed in detail. Strategies for data analysis and reporting are suggested for maximising data value and to enable further monitoring strategy development during long-term monitoring. Based on these general principles of monitoring, quality assurance, health and safety and budget recommendations are included as well.
5. Many metals and metalloids in Collie pit lakes are below detection by ICP-AES methods, yet may be above environment and health background levels. Monitoring of heavy metals and metalloids should be made by ICP-MS to improve detection limits.
6. Although the water in the pit lakes appears to be suitable for a range of end-uses, a comprehensive ongoing water quality and biological monitoring is strongly recommended for these pit lakes in order to better understand whether certain poorly understood parameters are within relevant end use standards and guidelines.
7. Ultimately pit lakes will evolve to become dominated by biological rather than chemical processes; however the consequence of this is unknown. A detailed monitoring program to monitor changes in biological communities is also needed to provide information on whether the pit lakes will be able to provide ecological valuable environments to the region.
8. Little is known about remediation approaches that might be successfully employed to treat water quality issues in Collie pit lakes. Monitoring of pit lakes representative of different rehabilitation and remediation attempts should be made in order to advise which of these approaches may be of use with the predicted, much larger, new pit lakes.
9. Minimum recommended sampling is given in the below table. Major seasons e.g., temperate Summer/Winter or Dry/Wet seasons. *only required if end-use required contact values e.g., swimming and water skiing. πOnly required if end-use requires environmental values e.g., as wildlife habitat.

13. A better knowledge of groundwater near pit lakes; especially with regard to newly forming new pit lakes is essential. This could be achieved through both once-off investigations into catchment backfill characterisation and also from a simple groundwater monitoring program from bores placed close to representative pit lakes.
14. Replication of single depth e.g., surface water samples, are likely a waste of sampling effort and could be dispensed with to reduce sampling and analysis budgets without loss to any monitoring data value. Future monitoring attempts must, however, take into account basic limnological monitoring facets such as water column profiling. Specialised equipment will be required for this as lake water column depth is very great, particularly in the new pit lakes.
15. The quality and quantity of surface discharge from pit lakes also need to be understood through monitoring and the ecological impacts of surface discharges need to be fully investigated.
16. A comprehensive routine monitoring has now been developed (this Report) but still needs to be implemented in the pit lakes for a better understanding of whether or not pit lake water quality will meet end-use criteria for current activities now (e.g., swimming) or proposed activities (e.g., fishing) into the future.

Sampling for fish

Outputs

• Zhao, L. Y. L., McCullough, C. D., Lund, M. A. & Newport, M. (2010). Mine Voids Management Strategy (III): A Monitoring Strategy for Pit Lakes and Connected Waters. Department of Water Project Report MiWER/Centre for Ecosystem Management Report 2010-2, Edith Cowan University, Perth, Australia. 90pp. Unpublished report to Department of Water. PDF