Abstract

Hydrogeochemical assessment of surface water Resources of Orlu and its environs was carried out in order to evaluate the chemical composition and quality profile with respect to the environmental setting of the study area. A total of six samples were collected, from different rivers and streams traversing different communities in the area, and analyzed for major cations and anions as well as trace elements like Fe, Mn, Zn, Pb and As. The major cation concentrations determined were in the order of Ca²⁺> Na⁺> K⁺> Mg²⁺ with mean values of 4.14, 3.78, 1.60 and 1.19 mg/L respectively and that of the major anion concentration of the surface water is of the order HCO₃^2-> Cl^-> SO₄^2-> NO₃^- with mean values of 19.83, 11.67, 3.45 and 0.24 mg/L respectively. Two major water groups were identified based on characterization on the Piper Trilinear diagram. They include Ca-(Mg)-Na-HCO₃ and Ca-Mg-(SO₄)-HCO₃. This reflects diverse effects of bedrock lithologies, base exchange processes, precipitation and weathering. The pollution index (PI) value of 9.10 (which is greater than the critical value of unity) shows that the surface water bodies in the area are slightly polluted by the trace elements and as such not fit for domestic use as those parameters exceeded the maximum permissible level set by the Nigerian Industrial Standard (2007) and the World Health Organization (2006) Standard. Finally the electrical conductivity (EC) values of 13.0 to 97.0 µs/cm and total dissolved solids (TDS) values of 8.0 to 66.0 mg/L, alongside the estimated sodium absorption ratio (SAR) of 1.74 revealed a fresh water grade that is fairly suitable for agricultural purposes.

Key words: Hydrogeochemistry, pollution index, water facies, water quality.