Impact of artisanal small-scale (gold and diamond) mining activities on the Offin, Oda and Pra rivers in Southern Ghana, West Africa: A scientific response to public concern

The surface water systems of Ghana serve as a major source of drinking water, besides other multi-purpose benefit of hydro-electrical power generation and transportation. Thus, the dependence and benefits from such resources are of national interest. For instance, the Pra river of the South-Western surface water system of Ghana was a major consideration for a projected 5 billion m(3) water demand in the year 2020 and “African Water Vision 2025”. In recent times, the colour state of the Pra river and similar surface water bodies of the Offin and Oda rivers has attracted intense public discussion. The prime issue relates to incessant illegal artisanal gold/diamond mining on or along these rivers. In order to assess the state of these rivers, water samples were taken, and analysed at the Council of Scientific and Industrial Research Laboratory (CSIR, Accra-Ghana) to investigate their physico-chemical quality. The research objective was to assess the extent of their water pollution by measuring physico-chemical parameters of turbidity, colour, pH and content of selected metals. A total of 18 preserved bottled samples [(5 from Offin river and 2 boreholes), 5 from Oda river and 5 from Pra river and 1 borehole)] were analysed, and results compared with portable water standards as defined by the WHO and CSIR (GS-175-1) of Ghana. Results on turbidity, colour, mercury and iron from the river and water samples generally exceed WHO or GS-175-1 limit. The Pra river recorded the most alarming result; range for turbidity (2,010 to 2,745 NTU), colour (3,000 to 4,500 Hz), total suspended solutes (2,240 to 2,570 mg/L) and total dissolved solutes (97.80–99.60 mg/L, excluding 319.00 to 25,440 mg/L). The Oda river shows lowest parameter values among the three rivers, as the areas have been dormant from illegal gold mining for 5 years. Current data suggests polluted river bodies and boreholes, and that none of these water resources meets the portable water consumption criteria unless treated prior to usage. As the current state of the water bodies may incur higher cost of water treatment or purification, an integrated water governance under Ghana's Ministry of Water Resource, Work and Housing, and the Minerals Commission and Environmental Protection Agency are recommended for the management of these valuable water resources.