PHYSICOCHEMICAL STUDIES OF BOREHOLE WATER IN ENUGU NORTH SENATORIAL DISTRICT, ENUGU STATE, NIGERIA
The groundwater quality indices of 12 randomly selected boreholes in Enugu North Senatorial District in Enugu State, south-east Nigeria have been studied. Using standard methods by American Public Health Association, American Water Works Association; World Environmental Federation (APHA-AWWA-WEF) and the Association of Official Analytical Chemists (AOAC), 22 physicochemical parameters were determined in triplicates at monthly intervals for three months in dry season and then repeated in rainy season. The parameters and the range of values obtained during dry season include: BOD5(3.14–6.37 mg/L), COD(5.8–10.51 mg/L), temperature(29.0-31.9 ͦ C), phosphate(0.12-0.87 mg/L), nitrate(1.24-8.72 mg/L), sulphate(20.10-24.34 mg/L), pH(4.900-7.500), E.C(10.0–410.0 μS/cm), total acidity(0.06 – 1.24 mg/L), total alkalinity(28.0–22.10 mg/L), total hardness ( 100.0 – 140.1 mg/L), TSS(70.0–270.0 mg/L), TDS(0.00–210.0 mg/L), TS(70.0–390.0 mg/L), turbidity(3.4 –50.0 mg/L), Na(0.0–21.28 mg/L), K(0.0–12.03 mg/L), Cu(0.0–23.01 mg/L), Fe(0.0–11.03 mg/L), and Zn(0.01–3.00 mg/L). During rainy season, the parameters in the 12 samples revealed the following ranges: BOD5(2.88 – 6.10 mg/L), COD(3.49–7.45 mg/L), temperature(29.0-31.9 ͦ C), phosphate(0.30–10.60 mg/L), nitrate(1.20–120.0 mg/L), sulphate(0.0–100.0 mg/L), pH(4.900-7.500), E.C(10.0- 360.0 μS/cm), total acidity(0.10-10.5 mg/L), total alkalinity(10.0-52.1 mg/L), total hardness(100-130 mg/L), TSS(100.0-280.0 mg/L), TDS(0.0-260.0 mg/L), TS(110.0- 560.0 mg/L), turbidity(3.80-56.0 mg/L), Na(0.0-21.28 mg/L), K(1.32-15.11 mg/L), Cu (0.03-28.37 mg/L), Fe(0.0-12.29 mg/L), and Zn(0.02-3.61 mg/L). The mean values of the parameters were compared with standard guideline values recommended by World Health Organisation (W.H.O.), Nigerian Standard for Drinking Water Quality (NSDWQ), National Agency forr Food and Drug Administration and Control (NAFDAC) and the European Union (EU) for drinking water. Seasonal variations of the parameters in the samples were observed. The mean values of BOD5 and temperature in all the samples were above the standard values. The rainy season nitrate values in some samples and phosphate mean values were higher than recommended values. There was a drop in pH during rainy season with the range generally acidic in both seasons. Turbidity in some samples was above the guideline value. A rainy season increase in total acidity (with a corresponding rainy season drop in total alkalinity), total hardness; sulphate and Zn values was observed. Cd and Pb were not detected in all the samples studied. The mean values of Cu and Fe increased in rainy season and were above the recommended guideline values in both seasons. K mean value increased in rainy season slightly above the standard guideline value. Recovery analyses were performed for the metals to validate the accuracy of the methods and instruments as well as the reliability of the results obtained. A two-way analysis of variance (ANOVA; using SPSS Windows Version 20) performed on the data obtained showed statistically significant variations between the 12 borehole water physicochemical parameters in dry season as well as in rainy season. Post hoc tests of multiple comparisons were conducted to specify the patterns of variability between the samples. An overall physicochemical Water Quality Index (WQI) for each borehole was computed and used in the groundwater rating. Levene’s T3 test revealed no significance difference between the dry season overall physicochemical WQI and rainy season overall physicochemical WQI t (18.67) = – 1.27, p = .22. Pearson correlation coefficient showed linear relationships in some of the physicochemical parameters studied.