ASSESSMENT OF WELL WATER POLLUTION BY SEWAGE CONTAMINANTS IN AKURE, ONDO STATE, NIGERIA.

Abstract

This study investigated the extent of well water contamination through infiltration of coliform bacteria from sewage pits. This is to establish the possible relationship between sewage pit location and coliform counts of groundwater obtained from household wells in Akure, for both dry and rainy seasons. The Total and Faecal coliform counts of twenty household wells were investigated between the months of March and July with respect to proximity of wells to sewage pits, orientation of wells to sewage pits, and well characteristics (ringed/unringed, elevated/not-elevated, covered/uncovered, cemented/uncemented floor area and soil type). All wells studied were assessed to be vulnerable to contamination with observable differences in characteristics, physicochemical parameters, total coliform counts and faecal coliform counts of their water. With the exception of pH which was higher in the dry season, all other parameters had lower values in the dry season. The pH of the water samples ranged between 5.5 and 7.5 with a mean of 6.23±0.11 in the dry season, while it ranged between 4.7 and 7.2 in the rainy season, with a mean of 5.91±0.14. The temperature ranged between 26.7°C and 29.1°C with a mean of 27.9°C±0.16 in the dry season but in the rainy season, it ranged between 26.7°C and 30.1°C with a mean of 28.5°C±0.20. DO2 values ranged between 0.05mg/l and 5.6mg/l, with a mean of 2.06mg/l±0.35, and ranged between 1.23mg/l and 7.34mg/l with a mean of 3.59mg/l±0.35 in the dry and rainy season respectively. In the dry season, the EC value of the well waters ranged between 0.76 x 102μS/cm and 9.10 x 102μS/cm with a mean of 3.76 x 102μS/cm±62.59 but ranged between 1.32 x 102μS/cm and 1.88 x 103μS/cm in the rainy season with a mean of 5.01 x 102μS/cm±114.95. All well water sampled had coliform counts above the WHO recommended level for drinking water (<1 Cfu/ml). At an average distance of 17.6m from the sewage pits, the mean total coliform counts in water samples for the dry and rainy season were 5.47 x 102Cfu/ml and 1.69 x 104Cfu/ml respectively while the average faecal coliform counts were 4.30 x 10Cfu/ml and 2.93 x 103Cfu/ml for the dry and rainy season respectively. Correlations between coliform counts of water samples and the distances of the wells to sewage pits was positive and not significant for both total (r = 0.279, N = 20, P = 0.12) and faecal coliform (r = 0.265, N = 20, P = 0.13) in dry season, while it was negative and significant for both total (r = -0.167, N = 20, P = 0.04) and faecal coliform (r = -0.112, N = 20, P = 0.04) in the rainy season. The correlation of well depth to the total coliform count (r = 0.399, N = 20, P = 0.23) and faecal coliform counts (r = 0.435, N = 20, P = 0.21) in dry season were positive and not significant at P<0.05. The correlation of these parameters for the rainy season; Total coliform (r = -0.173, N = 20, P = 0.04), faecal coliform (r = -0.192, N = 20, P = 0.03) were however negative and significant at P<0.05. Topography, and distance between wells and sewage pits were prominent factors responsible for well water contamination; as wells that were closer and down-gradient in orientation to the sewage pits had higher coliform counts than wells that were farther and up-gradient in orientation to the sewage pits. The amounts of coliforms found in wells were significantly affected by seasonal variation. It is thus suggested that wells be sited up-gradient and at safer distances away from sanitary systems in the ultimate bid to reduce groundwater pollution and the occurrence of water borne diseases.