Over the last few years, a problem has existed along Dawesley Creek due to the release of acid waters with a high concentration of iron and appreciable contents of other heavy metals from the mine area of Nairne Pyrites Limited at Brukunga. This situation appears to have worsened after mining ceased in 1972. Amdel has investigated existing environmental conditions in and around the Brukunga mine, examined methods for treating the acid waters and recommended procedures by which Dawesley Creek could be kept free of polluted waters. The results of these investigations are detailed in Amdel Reports Nos 1015 and 1065. These reports have emphasised providing a solution to the problem particually in the short term. Acid mine drainage (AMD) can be divided into three types, based on the source of the seepage: quarry face seepages, waste dump seepages and tailings dam seepages. The present treatment scheme consists of collecting some of the quarry face seepages and pumping these to the top of the tailings dam. Also, seepages from the toe of the tailings dam are recirculated back to the top of the dam. Since more water is being pumped to the top of the tailings dam than is being released by seepage and evaporation, the level of water in the tailings dam has risen dramatically over the last couple of years. The remainder of the quarry seepages and the waste dump seepages flow into Dawesley Creek and significantly pollute the creek. At conditions of high seepage flow in winter, the quarry seepages pump does not have sufficient capacity and these seepages overflow into the creek. The present scheme must be considered grossly inadequate as Dawesley Creek downstream from the mine is acidic in nature all year. Three basic schemes were considered to have merit in removing polluted water from Dawesley Creek: (a) prevention, (b) evaporation and (c) neutralisation. In all of these schemes, fresh and polluted waters were to be separated, the fresh water being allowed to enter the creek and the polluted waters being collected and treated. In the prevention scheme, in which quarry benches were to be sealed and the acidic waters from the tailings dam were to be continued to be recycled, there is no solution to the AMD collected in the tailings dam. Also, if the mine were to reopen a considerable sum of money would have been wasted on scaling the quarry benches. In the evaporation scheme, in which accumulating acid mine drainage was to be evaporated in ponds, large areas are required for the ponds. In addition, the resulting sludge is acidic in nature and probably will be partially redissolved by rain. Disposal of this sludge will present a much greater problem than the sludge produced from a neutralisation operation (this latter sludge while produced in greater amount, is fixed and would not be redissolved by rain water). Neutralisation of AMD has the advantage that the water treated is of sufficient quality for discharge into Dawesley Creek. If the mine were to reopen, the neutralisation plant would still be required and could be integrated with the new ore treatment plant. The neutralisation scheme puts emphasis on the drying out of the tailings dam in a controlled manner. At present, seepages from this dam represent the largest source of acid mine drainage. In conclusion, neutralisation of the accumulating AMD appears to be the method that: (a) offers the greatest degree of control over the acidity in the polluted water by 'fixing' the pollutants and forming a non-water-soluble sludge (b) offers the greatest flexibility in relationship to the mine reopening (c) provides water of stock and irrigation quality during the months when it is most needed, and (d) is only slightly more expensive than the other schemes that completely remove acidity from the creek. In Amdel Report No. 1015, a modest amount of neutralisation testwork was undertaken. The preferred neutralisation scheme was the addition of alkaline materials in two stages with a calcium carbonate material (caustic mud) added in the first stage and a calcium oxide material (lime) in the second stage. Since that report was written the neutralisation process was given further consideration. In this process, the thickener was replaced by settling lagoons and the use of pH control equipment for lime feeding was found to be unnecessary. While information collected from the above study was sufficient for preliminary cost estimates, it was not sufficient for design or operating purposes. Thus this project, consisting of laboratory studies at Amdel and pilot-plant studies at Brukunga, was aimed at providing this information. In addition, emphasis was placed on studying the feasibility of a neutralisation plant with a minimum amount of operating labour. The present report covers work carried out between April and November 1975, and further refines the flow sheet for the neutralisation process.