The Causes and the Control of Selective Pollution of Shallow Wells by Coliform Bacteria, Imo River Basin Nigeria

Abstract

The variability of water quality due to fecal coliform bacteria among shallow wells (37–67 m deep) in Aba northwest and Owerri west flank of the Imo River basin Nigeria surpassed surface explanation. This is because the communities have similar human and animal waste disposing habit. Analytical results show that six out of ten wells (60%) have 40–70FC/100 ml of water exceeding the 10FC/100 ml of water allowable by the world health organization (WHO). The pollution is attributed predominantly to the absence of toilet facilities in automobile mechanic villages, and transit grazing of cattle in the area. Uphole refraction and vertical electric sounding revealed presence of highly weathered topsoil to an average depth (18 m), often with gravel bed. Water table is 16–21 m, fluctuating below and above the weathered base. Results implicate the coliform polluted shallow wells as those located in areas where water table (WT) is above weathered base and coincides with the base of “khaki” colored gravel bed. As a result, safe depth of shallow wells is obtained as: WT+48 m at locations were weathered base is above WT, and WT+66 m at locations were weathered base is below WT, for a total cased depth ranging from 60 m (200 ft) to 85.4 m (280 ft). In the absence of adequate treatment, the polluted wells may be closed. Auto mechanic villages without toilet facilities, transit grazing near streams and residential areas, poorly constructed septic tanks may be prohibited by law, and the practice of mechanic villages’ concept must be environmentally friendly to be sustainable.