Groundwater contamination in Agbowo community, Ibadan Nigeria: Impact of septic tanks distances to wells

In Nigeria, inadequate supply of pipe borne water is a major concern; hence many homes have wells as a source of water for household uses. The groundwater of forty wells in Agbowo community was assessed for Total Aerobic Bacteria Counts (TABC) and Total Coliform Counts (TCC). The location and distances of wells from septic tanks were determined using the Global Positioning System (GPS) device and a tape rule respectively. All the wells sampled had high TABC (4.76 +/- 1.41 log CFU/mL) and TCC (2.29 +/- 0.67 log CFU/mL) counts which exceeded the international standard of 0 per 100 mL of potable water. There were no significant differences in the bacterial counts between covered and uncovered wells (p> 0.05). The mean distance (8.93 +/- 3.61m) of wells from the septic tanks was below the limit (15.24 m or 50 ft) set by United State Environmental Protection Agency (USEPA). TABC increased with a decrease in distance between the wells and septic tanks though not significant (p< 0.05). A very weak positive correlation (r(2) = 0.021) ensued between the distance from septic tank and CC, while a weak negative correlation (r(2) =. 0.261) was obtained between the TCC and TABC. This study accentuates the need to set standards for the siting of wells from septic tanks while considering all possible sources of well contamination as well as treatment of ground water before use.