Investigation Of Geo-Environmental Hazards And Reclamation Of Abandoned Borrow Pits, South - Eastern, Nigeria

ABSTRACT

Geo-environmental hazards associated with active and abandoned borrow pits are on the increase following rising trend in road construction. This situation presents a major challenge to Citizens, Environmentalists and Governments. Several highway failures have been directly linked to the action of erosion initiated by active or abandoned borrow pits situated close to roads. This study investigated environmental hazards and reclamation requirements associated with abandoned borrow pits in parts of Owerri area, south-eastern, Nigeria. On-sites environmental assessment conducted by direct measurements and supported with photographs showed prevalence of landslides, gully erosion, structural failure, possibility of accidents and threat to ecosystem as well as biodiversity. There is significant threat to groundwater and general environmental safety. A detailed investigation of the Ihiagwa and Emekuku pits revealed poor pit safety factor and high probability of sliding indicative of danger zones, angle of slope 70° - 80°, depth of the pit is 10 m (33 ft) and 21.3 m (70 ft), and pit distance to the road is 15 m and 30 m for Ihiagwa and Emekuku respectively. Geotechnical results show average values of maximum dry density (MDD) and optimum moisture content (OMC) in the two locations is 1.89 mg/m3 and 14% respectively. The average Plasticity index (Ip) of the soil samples was 19.7% while average of shear strength was 97.65 KN/m2 . Results of grain size distribution for the two sites show the lateritic soil as sandy with percentage of Clay-silt as 23 and 54 for Emekuku and Ihiagwa respectively. This implies that the lateritic soil is plastic, and can be generally described as cohesive, and suitable as road fill material for which it is being used. Resistivity measurements at the two sites show sandy topsoil 0.43 m and 0.57 m, followed by sandy (lateritic) overburden 3.62 m and 19.17 m representing the borrow material, indicating water table at depth 40.43 m and fluctuates between 47.78 m and 64.81 m for Ihiagwa and Emekuku respectively. It is recommended that borrow pits be professionally sited and fenced, to reduce accidents while in-use. Nigerian mining laws on reclamation of borrow pits must be enforced. Reclamation shall be part of the borrow pit contract agreement. Communities must insist on reclamation of borrow pit after mining with the borrow pit operators. Proper reclamation of borrow pits is by earth-moving, filling the pit with soil and moving land area next to the pit using bulldozer. This is followed by compaction of the earth material, with in-situ and laboratory testing to achieve the original geotechnical ground condition as measured. An agreement to pit reclamation must be signed by the borrow pit operators with the appropriate government agency before a borrow pit site will be opened. Host community of the borrow pit will be empowered in the agreement to follow up the reclamation exercise soon after the mining operation. Warning signs are to be placed at strategic locations from 500 m to the very location of a borrow pits. This will help to control movement and reduce accidents particularly to farmers and cattle grazers. Reclaimed borrow pit site is turned green for farming or used as recreation parks. It will promote a self-sustaining environment which attracts wildlife; improves ecosystem services and environmental quality.