Abstract:
The tarsand-bearing communities of Ondo State depend on groundwater in which bitumen is
frequently found filling pores and crevices of host rocks. Several works have been done with
the view to assessing water quality in Eastern Dahomey without emphasizing on the depth of
the groundwater. Hence the study evaluated groundwater quality in selected boreholes and
hand-dug wells with respect to depth. Groundwater samples were collected and analysed for
physicochemical characteristics and heavy metal concentration with respect to depth of the
groundwater. The parameters of interest that were analysed in accordance with standard
methods include E/C, TDS, pH, total hardness, temperature, Cl-, SO42-, NO3-, K+, Fe2+, Mn,
Cd, Cr and Pb. Spatial autocorrelation analysis was conducted on the parameters using the
Moran’s I test in GeoDa®1.8.10 software environment. The spatial pattern of parameters with
positive correlation were determined using Inverse Distance Weighted (IDW) algorithm. The
potability of the water was also analysed using the Water Quality Index. The calculated Water
Quality Index and depth of the groundwater were subjected to Correlation. The result shows
that the concentration of the heavy metals (Fe2+, Mn, Cd and Cr) had value above the
reference level with depth exceeded 60m.The calculated Water Quality Index based on
Standard Water Quality Classification Schemefor all the sampled groundwater shows that
27.27% of the groundwater sampled were excellent water and they were all hand-dug wells
with depth ranged between 3m – 8m. For the borehole alone, 50% were good water with
depth ranged from 35m to 50m while 50% of the sampled boreholes were very poor to unfit
for drinking with depth between 60m and 100m which shows that water quality in the study
area decreases as the depth increases to 100m. The regression analysis carried out shows that
there is a strong positive relationship betweenWater Quality Index and depth of the
groundwater. It shows that the value of Water Quality Index increases as the depth increases
to 100m. The study has revealed that water quality varies with depth in the study area. Hence
water quality in bitumen formation varies with depth.
