Hydrogeochemical evaluation of groundwater resources of the Ishan Plateau, southern Nigeria

A total of thirty-four (34) water samples were collected randomly from thirty-four (34) boreholes within the Ishan Plateau for groundwater quality evaluation. Physio-chemical parameters such as pH, temperature, total dissolved solids (TDS) and electrical conductivity (EC) and other constituents of the sampled borehole water were measured in-situ. The samples were analyzed for their major cations, anions and heavy metals concentrations using the AAS and Titration method. Result of cations showed that Ca range from 0.8 – 16.03 mg/L, Mg ranged from 0.48 – 4.86 mg/L, Fe ranged from 0.01 – 1.39 mg/L, Mn ranged from 0.01 – 0.21 mg/L, while the result of the anions showed; NO 3 ranged from 0.01 – 7.11 mg/L, Cl ranged from 7.06 – 23.2 mg/L, SO 4 ranged from 0.17 – 29 mg/L, and P ranged from 0.09 – 3.1 mg/L. Heavy metal such as Pb and Cd were not detected in the water samples but Zn recorded 0.01 – 0.51 mg/L. Comparing the results with WHO and NSDWQ standard revealed that all the anions analysed in the groundwater were within the permissible limit. pH of groundwater samples in the study area is slightly acidic with and only representing 8.8% of the water samples falls within WHO standard of 6.5 – 8.5 for potable water. Total solids, bicarbonate, phosphate, calcium and potassium have values less than 100 mg/L, 25 mg/L, 3.5 mg/L, 16 mg/L and 7 mg/L respectively. Turbidity range from Low – high and have strong correlation with colour. The groundwater is soft and fresh and values of high iron recorded in the norther section of the area and deeper wells exceeded the standard limit of 0.3 mg/L. Schoeller, Piper trilinear diagram show dominant dissolved ions and mixed water type, while the Gibb’s plots showed clearly precipitation / rock dominance water type. Water samples are slightly acidic, other parameters fall within the WHO standard and the groundwater is excellent for irrigation