Final Void Water Quality Enhancement - Stage 1

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 1 of the research program. This was essentially an exploratory and laboratory approach. In Stage II the emphasis of all sub-projects will be on initiating field manipulation studies at the study site.

A series of simultaneous or sequential investigations have been incorporated into the program:

1. Geology, geochemistry and hydrogeology of the area
2. Low cost water pumping techniques
3. Amelioration of acid run off from coal mine dumps<
4. Passive mine drainage treatments and aquatic vegetation strategies
5. Bacterial strategies for increasing pH in acidic voids
6. 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. A surface geology map of the area was produced and the hydrogeology of the area was reviewed. Based on the available data a groundwater level contour map of the area has been prepared. A desk top study of power sources showed that the most viable option for the trials in the Collie Basin was the use of mains off-peak power. 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. Limnological surveys of Ewington Open Cut No 2 and Stockton Lake was 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 sulphate reducing bacterial activity in the sediments, and although additions of organic matter to cores taken from the sediment suggest that the approach is likely to be successful, the mechanism for that apparent success is not understood and will need further experimentation before field trials are possible.

A preliminary trial aimed at demonstrating that marron reproduction can be successfully performed in a rearing system established at the collie TAFE Centre was conducted, and marron fingerlings were obtained. 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.