Assessment of Hydrological Properties and Proximate Impact of Septic Tank Leachate on Well-water Quality in Two Residential Areas in Ibadan, South-western Nigeria

Aims: To determine the impact of leachate from septic tank on proximate well-water quality in two different residential areas and the variation in the physico-chemical parameters of the well-water that are associated with spatial geographical location.

Study Design: Randomized monthly collection and analysis of well-water over four months in two chosen residential areas.

Place and Duration of Study: Residential houses at Agbowo and Akobo, Ibadan, Nigeria between April and August, 2012.

Methodology: The well-water samples were collected from 30 sites once every month; from different wells located at various perimeters from the septic tanks. The distance between the septic tanks and the wells were measured and the water subjected to physico-chemical analysis and bacteriological assessment to evaluate their qualitative, spatial and temporal variations.

Results: A significant increase (p<0.01) was found in results from coliform counts between dry and wet seasons, while significant decrease (p<0.05) was recorded in the concentration of phosphate, salinity, total dissolved solids and potassium. The distance from the well to the septic tanks exhibited a negative correlation with coliform count (p<0.05), as well as for phosphate, nitrate, chlorine and ammonia (p>0.05). The Discriminant Chi square (X2 = 62.526, p<0.01) and Wilk’s Lambda (0.058) revealed a significant discrimination between the two study sites. Partial Eta Squared value of 0.740, 0.382 and 0.137 were reported for location, proximity of septic tank to well-water site and well depth respectively, showing their degree of contribution to variation in parameters measured.

Conclusion: The results stressed the need to set standards concerning the distance and location of wells from septic tanks/septic tank, while considering spatial and temporal variations in hydrological environment of well-water sites.