EFFECTS OF MINING ACTIVITIES AT BULYANHULU GOLD MINE (BGM) ON THE WATER QUALITY OF BULYANHULU RIVER: SHINYANGA - TANZANIA

Abstract

This study assessed the effects of mining activities at Bulyanhulu Gold Mine (BGM) on the water quality of Bulyanhulu River in Tanzania. Potential pollutants were identified, quantified and their spatial distribution determined along different sampling points upstream and downstream the mine. The water quality of the river and groundwater in the area is of importance as the water is used for agriculture and domestic purposes. Grab samples were collected from Bulyanhulu River, shallow wells, Effluent Control Ponds (ECP’s) and boreholes during the period January-March 2008 and analyzed for Temp, pH, EC, SO42+, Fe, Ni, Ag, As, Hg, CN-, NO3- and Zn according to Standard methods. The pH values in water samples were 6.3 ± 1.4 in ECP, 7.0 ± 0.2 in river, 5.9 ± 0.4 i n boreholes and 5.2 ± 0.3 in wells. The conductivity in ECP, river, boreholes and wells sample were 1969 ± 470 μS/cm, 207 ± 46 μS/cm, 1023 ± 497 μS/cm and 203 ± 112 μS/cm respectively. The mean SO42+ concentrations in ECP, river, boreholes and well sample points were 1014 ± 353 mg/l, 70 ± 30 mg/l, 497 ± 205 mg/l and 181 ± 0 mg/l. The temperature values were 26 ± 1 °C for ECP, 24 ± 1 °C for the river, 25 ± 1°C for boreholes and 24 ± 1 °C for wells. Values of NO3- for ECP were 5 ± 1 mg/l, 4 ± 2 mg/l for river, 5 ± 3 mg/l for boreholes and 4 ± 3 mg/l for wells. Results for Ag were 0.1 ± 0.1 mg/l for ECP, 0.1 ± 0 mg/l for the river, 0.1 ± 0 mg/l for boreholes and <0.005 mg/l for wells. Results for Ni were 0.7 ± 0.3 mg/l for ECP, 0.4 ± 0.3 mg/l for the river, 0.04 ± 0. 03 mg/l for boreholes and 0.2 ± 0.1 mg/l for wells. Concentrations of Fe for ECP were 7.2 ± 3 mg/l, 2.9 ± 0.13 mg/l for the river, 0.3 ± 0.4 mg/l for boreholes and 0.2 ± 0.13 mg/l for wells. Concentrations of Zn in ECP, river, borehole and well samples were 13.0 ± 7.0 mg/l, 1.8 ± 0.8 mg/l, 4.0 ± 2.0 mg/l and 2.5 ± 0.8 mg/l. Water quality of the Bulyanhulu River, shallow wells and monitoring boreholes were compared against Tanzanian maximum permissible concentration and WHO drinking water quality guidelines while Effluent Control Pond values were compared against the Tanzanian effluent discharge maximum permissible concentration guidelines. The concentrations of As, Hg and CN- were low (below method detection limit ). The high concentrations of these param eters could be attributed to weathering of sulphide ore bodies, chemicals used in the process plant, decomposition and leaching of discarded batteries and old metal scraps in mine areas. These elements could relatively have high toxicological effects in the environment, biota and health hazards to human beings especially in the mining communities. It was concluded that, the water quality of the river is polluted with respect to Ni, Fe and slightly by Zn and was therefore, considered not suitable for human consumption. Groundwater quality was affected by mining activities with respect to pH, EC, SO 42+, Ni and Zn however; EC and SO42+ affected the boreholes more. The ECP’s showed highest mean concentrations of all elements studied. It is therefore, recommended to treat the effluents in the ECP’s by precipitating out metals thus reducing their mobility through seepage. The existing monitoring Programme for BGM needs improvement.