Analytical and geophysical assessments of heavy metals dispersion from an automobile mechanic village and its pollution prevention

This paper assesses metal dispersion from Nekede mechanic village (MV) in the lower Imo River basin Nigeria, to introduce the concept of environmentally friendly MV. Analysis of composite soil samples derived from three replicates collected at each measurement point using atomic absorption spectrophotometer was carried out. Mean values (mg kg-1) above the background, 0-200m from the MV are Pb, 853±572; Mn, 604±531; Cu, 137.3±202; Fe, 17713±4770; Cd, 3.4±12.8; Zn, 444±190, and Ni, 29.4±35.2 measured in the direction of drainage. The dispersion rates (mgkg-1/m) are Fe, 197; Pb, 12.9; Mn, 6.7; Zn, 4.9; Cu, 1.5; Ni, 0.3; and Cd, 0.04. Concentration and dispersion rates were confirmed by metal depth ratio (MDR), and metal distance ratio (MDsR). Electrical resistivity profiling showed metal dispersion to 350 m from the MV, representing a safe distance for farming in the direction of drainage. Both uphole refraction seismic and vertical electric sounding (VES) showed a weathered base (WB) average 18m, consisting of sand and gravel bed (GB). Water table (WT) at 16-21m fluctuates below and above the WB, showing that shallow wells located in areas where WT is above WB, and overlain by GB may easily be polluted by heavy metals. As a result, safe depth of shallow wells is: WT+48m were WB is above WT, and WT+66m were WB is below WT. Relatively higher elevation and slope (1:20) of the MV indicates greater metal dispersion dynamics. Pollution prevention model designs of infiltration basin and shallow water well are presented.