SUSTAINABLE ENVIRONMENTAL MANAGEMENT MODELS FOR PROPOSED OPEN - PIT MINING OF ILUBIRIN - GBELEJULODA BITUMINOUS SAND, ONDO STATE, NIGERIA

Abstract

This study focused on the development of models for sustainable environmental management of open pit mining of bituminous sands in Ilubirin -Gbelejuloda area of Ondo State. Social-economic data of residents from five neighborhood communities in the study area were collected through face-to-face survey to evaluate the nature and extent of residents’ dependence on the natural environment. Background physico-chemical analyses of three key environmental components of the terrestrial ecosystem in the study area (surface water, soil and bituminous sand) were carried out to determine their baseline characteristics. The potential environmental stressors in the spatio-temporal vicinity of the open pit mine were also identified. 3D geophysical models of geospatial areas likely to be affected by mining were developed based on kriging interpolation of exploratory data using Geographic Information System (GIS) softwares: Google Earth Pro 2017, 2019 and Rockware 16. Slope stability analysis of the projected open-pit was carried out using shear strength parameters of overburden material and bituminous sand core as input parameters. The optimum slope angle of the mine pit was determined by deterministic limit equilibrium and finite element methods using Rocscience RS 2.9 and Geoslope 19 geotechnical software applications. Critical soil management quality indicators for reclamation purpose were determined using Principal Component Analysis (PCA) method with Microsoft Excel-integrated XLSTAT 2018. Empirical models for the soil quality management were developed based on multivariate regression using Statistical Package for Social Sciences (IBM SPSS 20). A strategic and pragmatic two-module management framework model to sustain the quality of the environment was also developed. Results from the socio-economic survey showed that 57% of the sampled respondents were predominantly farmers thus indicating farming as the major source of livelihood. The independent sample t-test of background physico-chemical analyses of surface water showed that dissolved heavy metal concentrations were slightly higher in rainy season than in dry season except for Nickel that has higher dry season value. The soil tests revealed that 70% of sampled topsoil in the area was sandy loam with 69.56% having low plasticity in the silty clay class. The soil metal sequential extraction showed that lithogenic metals were partitioned mainly into the organic matter and residual chemical phases of the soil solid with Lead and Zinc having the highest potentials of mobility. Analysis of Polycyclic Aromatic Hydrocarbons (PAH) in the extracted bitumen revealed that approximately 80% of the samples contained nine out of the sixteen congeners classified as potent source of hazards by the United States Environmental Protection Agency. A stripping ratio (SR) of 3:1 was estimated for the open pit to facilitate sustainable reclamation with an optimum pit slope angle of 29 degrees. Four components of soil quality-management indicators: the exchangeable bases, the organics, soil reaction (pH) and the soil particle size were derived from the PCA. The holdout cross-validated empirical soil quality-management model developed had a generalized best fit of an effect size R2 of 0.758. The Integrated Mine Environmental Management Strategy (IMEMS) framework model developed is recommended to relevant stakeholders (Mine Operators) and decision makers (relevant Government Agencies) to ensure a sustained environmental quality during exploitation and post exploitation of the mineral deposit.