Surface water pollution and water quality studies at Prestea Goldfields Limited (P.G.L) Prestea, Ghana.

Prestea is a mining community developed around Prestea Goldfields Limited, which is engaged in mining Suiphide gold ores known to give rise to several environmental problems like air pollution in the form of emissions of arsenic or arsenous oxides, with concurrent production of large amounts of Sulphur dioxide. As a result of extensive mining since 1929 using underground methods, involving about 18 million tons of ore, an estimated 3.5 - 4 million tons of tailings have been left on the surface in the vicinity of both current and historic treatment sites. Since the mine is located in an area of heavy rainfall, incessant rain will flush contaminants from tailings dumps and waste sites into the downstream environment and subsequently into surface waters. Water supply for the population in the area is derived from rivers and streams flowing in the area, supplemented by boreholes and spring water. Not much is known with respect to pollution levels along the rivers and streams which serve as water for domestic uses by settlers along these river banks and around. It therefore became necessary to carry out studies to ascertain the pollution levels of various water resources and to make some suggestions to guide pollution of these waters and uses of them as well. Water sampling was carried out in the rivers and streams. A spring water and well water were also sampled as reference data to ascertain background levels of pollutants. The work highlights activities of the mine and that of the surrounding inhabitants which are likely to result in the pollution of surface waters. It also discusses results of water samples within the area, Sample analysis included determination of parameters like pH, Temperature, Conductivity, Alkalinity, Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Total Solids (TS), Total hardness, Cyanide and Sulphate concentrations among others. Concentrations of some heavy metals were also determined. Based on standards prevailing in the country, which is also the W.R.O standards and other standards available, results were observed to show high amounts of Sulphate resulting from Sulphur dioxide (So2) emissions, from the stack of the nearby processing plant where roasting of the ore takes place. Total Suspended Solids was also high. This was attributed firstly to the tailings being washed by heavy rainfall into the nearby streams and rivers, and secondly to the activities of illegal gold panning by the inhabitants along the river and stream beds. Cyanide from the treatment plant and Mercury used during gold winning by illegal miners also presents pollution problems. Even though the mine is reputed to be using lime in their processing activities which aids the precipitation of metals and settling of suspended solids, yet the fact that most of the streams and rivers subjected to effluent have high suspended solids presupposes that this control measure of lime usage is not enough. From the discussion on the experimental study, it was suggested that, the effluent is impregnated with FeSO4 and retained in a pond before discharge. This will promote the formation of Fe (CN) 2 (that is Fe reacting with CN) which is less toxic and can dissociate easily into Fe, CO2 and CNO (Cyanate) on exposure to air. The FeSO4 will also enhance potency of lime in causing the settling of suspended solids as the effluent flows into the rivers and streams. ‘1n addition, an Environmental Action Plan was suggested with particular reference to groundwater pollution studies in the tailings area This is because, a well near to the current tailings site gave a very low pH (about 5) value, hence the possibility of groundwater pollution in the area.

Source: KNUST