Water quality assessment of shallow and deep boreholes in Ekpan community, Effurun, Delta State, Nigeria

Twelve (12) groundwater samples (six from shallow and six from deep boreholes) were randomly collected in Ekpan community and environs, Delta State, Nigeria, for water quality/safety assessment. All samples were collected in replicates and transferred to the laboratory within 24 h of collection. Soil samples were collected in well-labelled sterilised polythene bags. The samples were subjected to laboratory analysis. Descriptive statistics was used to explore data, while Pearson correlation (r) was used to determine the relationships of the physicochemical and microbial parameters. The test of homogeneity in mean variance of the parameters (with the single-factor analysis of variance ANOVA) was used to determine possible differences between the shallow and deep groundwater sources. pH, temperature and biological oxygen demand (BOD) varied from 6.00 to 6.66 (6.22 +/- 0.04), 24.00 to 25.10 (24.50 +/- 0.09) mg/l and 2.50 to 5.82 (4.15 +/- 0.21) mg/l, respectively. Salinity and total hardness varied from 3.00 to 79.40 (32.24 +/- 5.74) % and 4.50 to 97.69 (37.84 +/- 7.20) mg/l, while NO3- and SO42- varied from 0.03 to 1.35 (0.67 +/- 0.11) and 1.80 to 71.35 (13.97 +/- 4.03) mg/l. The heavy metals Pb, Cd, Cr, Mn and Hg ranged from 0.01 to 0.15 (0.07 +/- 0.01), 0.01 to 0.64 (0.25 +/- 0.05), 0.02 to 0.11 (0.08 +/- 0.01), 0.04 to 0.16 (0.10 +/- 0.01) and 0.0001 to 0.00039 (0.0002 +/- 0.00001) mg/l, respectively, while total coliform counts ranged from 1.90 x 10(5) to 4.90 x 10(5) cfu/ml. pH correlated significantly with Cd, Ni, Mn and As, with Pearson correlation r >0.43, while total coliform counts were influenced by temperature, electrical conductivity EC, total dissolved solids TDS, BOD, K, Mg, SO42- and NO3-, with Pearson correlation r > 0.7. While Hg is averagely at contaminant level, Pb, Cd, Mn, Cr, BOD and total coliform values exceeded the recommended values of World Health Organization WHO guidelines for drinking water quality, and thus constitute pollutants. Relative water quality (and hence water safety) averagely increases with depth of the boreholes (and by implication, the depth to the aquiferous units). The major contributors to heavy metal load are essentially surface/near-surface-based geologic and anthropogenic activities. The predominant effect of natural filtration (during infiltration/recharge through precipitation) is evident and is most likely enhanced by appreciable presence of fines (clay and silt) at variable horizons.