Arsenic Intensity Risk Assessment at AngloGold Obuasi Goldmine, Ghana, West Africa: Using Sorption and Geotechnical Factors

Abstract

This research evaluated arsenic (As) intensity risk using sorption and geotechnical factors in the AngloGold Obuasi mine environment in Ghana. Water samples from tailings dam boreholes and surface stream were analysed for As contents over a time period of 24 months and over a distance of about 9 km respectively, under closed conditions, where there are no more discharges of waste. The porosity and bulk density of the subsurface material were also determined. Data generated from the mass-time and mass-distance analysis were used to establish As intensity risk assessment model based on documented global As impact data. From the model, a period of about 4 years is required in monitoring boreholes and a distance of about 12 km is required along the stream profile for As concentration to reduce from the maximum value of about 2.50 mg/l to 0.01 mg/l. Using the porosity, bulk density and combined degradation properties of the monitored media of the mobile As, the estimated retardation factor was 1.96 and the solute velocity estimated to be 1.53 × 10 -7 ms -1 in the borehole environment, and 1.074 and 9.25 × 10 -1 ms -1 along the streambed, respectively. This study shows that the pollution risk assessment model can be used to spatially estimate exposure to As contamination in the environment, while the transport characteristics can be used to determine clean-up criteria for effective As remediation in drainage.