QUALITY ASSESSMENT OF GROUNDWATER WELLS PROXIMAL TO POLLUTED STREAMS ACROSS ONDO TOWN, NIGERIA.

Abstract

This study aimed at assessing the quality of groundwater wells domiciled close to pollution receiving streams in Ondo town. Thirty (30) water samples; from fifteen (15) wells and fifteen (15) closely associated streams across the town were collected for the study. Water samples were tested for Temperature, pH, Turbidity, Total Dissolved Solids and Electrical Conductivity following appropriate measuring techniques. Microbial analyses were also carried out on water samples to determine the Total Coliform Count and presence of Faecal Coliforms using appropriate growth media and standard techniques. Atomic Absorption Spectrometry (AAS) was also used to screen for four selected heavy metals; Aluminium, Cadmium, Lead, and Chromium in the same sampled water. The work was carried out both in dry and rainy seasons for comparative analyses. Out of the fifteen wells sampled, 86.6% (13) had concrete rings while 13.3% (2) had no concrete rings. 80% (12) of wells were covered while 20% (3) had no covering. Percentage of wells sited in areas with cemented floor covering was 26.6% (4), while 73.3% (11) had no cemented floor covering around them. 60% (9) of the wells were located up-gradient to streams while 40% (6) were located down-gradient to the stream. Aside for Temperature and pH, the mean values of other physicochemical parameters like Turbidity (111.47/ 68.77 NTU), Total Dissolved Solid (474.6/ 68.77mg/l), and Electrical Conductivity (822.31/816.79 μS/cm) in the dry and rainy season respectively were above the highest desirable limit according to WHO standard. The highest total coliform (T.col) was recorded at 11,200 (Cfu/100ml) and 11,300 (Cfu/100ml) during the dry and rainy season respectively. The Faecal coliform count was also very high with 8,400 (Cfu/100ml) and 12,100 (Cfu/100ml) for dry and rainy seasons respectively. This study also revealed the highest level of Aluminium (1.632mg/l), Cadmium (0.820mg/l), Lead (0.079mg/l) and Chromium (0.079) concentrations during the rainy season to exceed maximum permissible levels recommended by World Health Organisation. Results from the concentration of well water parameters between dry and rainy seasons shows that there were no significant difference (P ≤ 0.05) in parameter recorded between the two seasons except for Temperature and Faecal coliform. The correlations of water parameters between streams and wells in the dry season were positive, with varying levels of significance. Also, all water parameters between streams and wells in rainy season showed positive correlation except Total coliform (-0.821). Faecal coliform (-0.680) and Chromium (-0.408) concentration showed negative correlation. The major outcome of this research revealed that most of the well water sampled failed quality assessments. Wells in Oke gbogi, Losunla, Odojomu, Lisaluwa, and Olorunsola were observed to have highest contamination levels above WHO permissible standards. The positive correlations between wells and polluted streams parameters showed that distances contributed significantly to well contamination.