Risk Assessment at Abandoned Tin Mine

The Sungai Lembing abandoned tin mining and processing activities 77 years lease to mine the area have resulted in the production of hazardous wastes, which contain high residual concentrations of heavy metals. Heavy metals (As, Pb, Zn, Cu, Cr and Ni) contained in the tailings are mobilised, migrate to the surroundings and cause severe and widespread contamination of soils, surface and ground waters and to river. For the purpose of this study, eight holes were drilled using hand auger, and sampling of contaminated soil was conducted at different depths and collected samples from surface for the tailings. The concentrations of heavy metals in this area exceed the limit allowed by Dutch list and Kelly Indices. Results showed that the concentrations of heavy metals in contaminated soils range between 101.71 mg/kg for Cr and 250311.4 mg/kg for Pb. Meanwhile, the maximum concentration of heavy metals in tailing deposits is 151839.32 mg/kg for Pb near the main potential sources of pollution (i.e. near the abandoned processing structure), and the minimum concentration is 96.04 mg/kg for Cr. The results suggest that there is a vital increase of heavy metal risk in this area. Polluted heavy metals dispersion (for examples from historical and active tailings impoundments and waste rock dumps), are mainly associated, at this site, with water transportation of mine waste through the flowing streams. Control measures of pollution routes and remediation measures at the site are urgently required