Open Cut » Environment
Final voids resulting from open cut mining present special problems with respect to rehabilitation. The project aims to develop appropriate low cost, low maintenance, technology for rehabilitating acid water to treat the standing bodies of water now forming lakes in final voids in many parts of Australia. It is planned to use these voids for aquaculture after rehabilitation.
Field trials are being conducted at Collie in Western Australia. A study site, Ewington Open Cut No 2, is being used for manipulations to test the application of the technology. Although the studies will be carried out in Western Australia the results will be applicable to similar areas throughout Australia.
A staged approach has been adopted and the current report is for Stage II of the research program. This was aimed at initiating field manipulation studies at the study site.
A series of simultaneous or sequential investigations have been incorporated into the program:
- Geology, geochemistry and hydrogeology of the area
- Amelioration of acid run off from coal mine dumps
- Passive mine drainage treatments and aquatic vegetation strategies
- Bacterial strategies for increasing pH in acidic voids
- Fish and crustacean acid tolerance and restocking of the lakes
The research completed includes a review of the geological setting of the Collie Basin, with respect to the Ewington Open Cut No 2 lake area. It focuses on the work on subsurface geology, hydrogeology and geochemistry of study site. Considerable progress was made in the revegetation experiments. These are aimed at determining appropriate species for rehabilitation on difficult acidic sites, comparing effects on survival of various substrates placed immediately around seedlings of each of three plant species, establishing and growing plants in 'hotspot' overburden soils, comparing plant species responses to pot growth in Collie soils and determining whether any toxic materials are taken up by the plants. Limnological surveys of Ewington Open Cut No 2 and Stockton Lake were conducted and an experimental passive mine drainage treatment system was set up. It was concluded that the water quality of both lakes remains fairly stable throughout the year, and the use of the filamentous algae for removing heavy metals appears promising. Studies of bacterial strategies for increasing pH in acidic voids indicate that there is little organic matter (typically less than 10%), waters are unproductive, with low biomass and phytoplankton and biofilm. Further work is necessary to identify the source of the C and the acidity.
The presence of marron in Ewington Open Cut No 2 capable of reproducing was identified in Stage I. Further studies supported these results. Trials showed that marron do survive extended exposure to pH of 3.0 or less. A preliminary acid tolerance trial has been conducted with marron the results of which suggest that marron have a higher pH tolerance than reported for other species of freshwater crayfish. Of special interest was the discovery of small frogs and at least two species of freshwater crayfish present in considerable numbers in the waters in the Ewington Open Cut No 2 void. This was both unexpected and exciting because it suggests that these species have a high tolerance to the low pH waters, and increases the possibility that these voids may be suitable for aquaculture.