Open Cut » Environment
Coal has been mined from Collie Basin from the 1890's. The Collie Basin is a tectonic depression in the Yilgarn block with large areas of permian sediments. Following the Second World War, open cut mining was introduced. As a result Collie now has several open pits filled with water fed by the aquifer as well as surface flow. The waste rock and the tailing piles surrounding the voids continue to be a source of Acid Mine Drainage (AMD). Oxidation of pyrite continues to produce acidity and pyrite oxidation has been studied extensively.
The impetus for this current program of research arose from problems currently being experienced in Stockton Lake, Collie. Stockton Lake is a disused open cut coal mine that was closed down in 1957 and it subsequently filled with water. The surface area of the lake is about 14.95 ha and it is a popular recreation site for activities such as water skiing and swimming.
In November 1994 at a Collie Coal Mines Rehabilitation Committee meeting an acidity survey was released which showed that the Stockton Lake acidity level was very low, pH 3.7-4.0. Values of 3.1-3.4 were also measured in the Lake earlier in the year. These values are well outside public health guidelines (6.5-8.5 for recreation waters).
This is not a new situation as Stockton was reported as having a pH of 4.0 in 1978. Two attempts were subsequently made by the Department of Conservation and Land Management to use chemical methods (lime and then caustic soda) to raise the pH in the lake, without success. Adjacent to Stockton Lake on the south side is an apparently separate area we have called Stockton tailings pond. It had a very low pH (about 2) and the water was brown in colour. This was thought to probably be the result of rain water seepage through nearby mining spoil dumps.
To examine this problem a small team was set up to develop a program of research aimed at developing low cost, and low maintenance, technology for rehabilitating acid water to treat the standing bodies of water now forming lakes in final voids as a result of seepage, run-off and residual effluent drainage. The studies were to provide technology and guidelines for treatment of the acidic water in the voids, and also recommendations as to approaches for stocking such water bodies with crustaceans and fish species for aquaculture. The idea was to develop a sustainable maintenance free ecosystem, which would stabilise the pH and also provide food and habitat for the fish, crustaceans and other animals suitable for aquaculture.
A staged approach was adopted, and a series of simultaneous or sequential investigations was incorporated over the three, one year, stages of the program:
- Geology, geochemistry and hydrogeology of the area
- Low cost water pumping techniques
- 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 program was conducted by a research team comprising staff from three tertiary institutions (Curtin University of Technology, Edith Cowan University and the South-West College of TAFE), two coal mining companies (The Griffin Coal Mining Company Ltd and Wesfarmers Coal Pty. Ltd.), and two government departments (Conservation and Land Management, Department of Minerals and Energy). The Program Leader was Adjunct Professor Bruce Phillips from Curtin University of Technology.
No attempt was made during this research project to rehabilitate Stockton Lake. However, field manipulations were undertaken at smaller, disused mining voids and Ewington No 2 Open Cut was selected and used as the main experimental site in all three stages of the study.
Although the studies were carried out in Western Australia, the results are applicable to similar areas throughout Australia and overseas. This report summarises the findings of Stages I, II and III of the program undertaken from 1997 to 2000. More detailed data can be obtained by ordering ACARP Reports for C6005, C7008 and C8031.