Spatial Variation of Borehole Water Quality with Depth in Uyo Municipality, Nigeria

Abstract

The objective of the study was to evaluate the spatial variation of borehole water quality with depth, and compatibility with Nigerian Water Quality Standard in Uyo Municipality, Uyo. The State Capital of Akwa Ibom is in the coastal plain sand formation of Nigeria. Four functioning boreholes located at representative zones of the municipality were selected, and their water samples collected by pumping monthly and for one year and analyzed by standard procedures at the technology laboratory of the State Water Board for physico-chemical and heavy metal properties. Two sampling methods, grab and composite methods, were useful for this study. Heavy metals were oxidized with nitric acid digestion and analyzed by Atomic Absorption Spectrometry (Unicam Model). The pollution status of the overlying soil surface and rainfall supply was observed from their chemical properties. The borehole quality was evaluated against Nigerian Standard for Drinking Water Quality (NSDWQ) and the degree or percent compatibility was computed. Using SPSS ver 17 package, descriptive statistics, paired sample t-statistics, ANOVA for significant differences, correlating coefficient of percent compatibility with depth were evaluated. Significant spatial differences (p< 0.01 and p< 0.05) were observed in water quality especially for ammonia, calcium hardness magnesium, barium, DO and SS, which concentrations were generally above NSDWQ and particularly the borehole with 54.54m and 45.45m. The percentage compatibility varied with depth as follows: 63, 64, 71, and 87% for 45.45, 54.54, 60.60 and 106.06 m depths respectively giving a strong correlation (r = 98%) between depths of borehole and their water quality; and water quality compatibility varied with different borehole depths in the corners of Uyo Urban, Akwa Ibom State, Nigeria. Depth must be considered if quality compatibility has to be guaranteed in the coastal plan sands formation and water quality authority should set baseline depth for compatibility quality assurance in Uyo Municipality considering groundwater dynamics and seepage of polluted runoff in the largely flat terrain of the territory.