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Geoenvironmental impact of Okpara coal mine, Enugu, Southeastern Nigeria

G. U. Sikakwe, B. E. Ephraim, T. N. Nganje, E. E. U. Ntekim and E. A. Amah

Water, sediments and mine dumps samples were collected around the Okpara coal mine in Enugu area of southeastern Nigeria, for analysis for physicochemical parameters, inorganic ions/salts, and heavy metals abundance. The intension was to investigate the impact of coal mining activities on the geoenvironment. The measured pH range of 2.84– 6.05 qualifies the water as acidic to moderately acidic, and consequently unsuitable for human, vegetation, aquatic life and wildlife. The SO4 2– ion, which is an indicator for acid mine drainage (AMD) pollution in most mine waters, displayed moderate concentrations, thereby implying insufficient pyritization. On the other hand, the excessive concentration of NO3 – and PO4 3– in the water calls for concern as it renders the water prone to eutrophication and numerous potential health risk, especially for pregnant women and infants. Heavy metal results show that iron comprised the most abundant metal in all the media sampled. This similarity in trend for the three media supports the idea of Fe being the element of main interest. In the sampled water, aluminum, iron manganese and nickel are respectively higher by 21.50, 17.13, 16.75 and 2.55 times the maximum allowable limits for the relevant chemical specie in the Nigerian Standard for Drinking Water Quality (NSDWQ). This excessive Al, Fe, Mn and Ni, coupled with the generally acidic nature of the water portend doom for the ecosystem. In particular, acid and iron polluted waters are not favourable for fish growth and survival of other aquatic biota. Also, acidic and ferruginous waters are responsible for the corrosion of mine plants and equipment, formation of scales in delivery pipes as well as pollution of mine surface environments, thereby also affecting the surface ecology. Additionally, high iron composition of sediments and mine dumps imply precipitation of ferric hydroxide which, if unchecked, may result in the complete layering of stream bottom, filling in crevices in rocks and making substrates unstable and unfit for habitation by benthic organism. Evaluation of the comparative abundance of the inorganic ions/salts (Ca, Mg, Na, K) and heavy metals in the water, sediments and mine dumps revealed that these components are much more concentrated in the sediments and mine dumps than in the water. The danger in this is that the sediments and mine dumps serves as a pool that can release toxic heavy metals into the water column by various processes of remobilization.