GROUNDWATER QUALITY ASSESSMENT AND MAPPING IN UYO CAPITAL CITY, NIGERIA: A GIS-BASED APPROACH

Background: Groundwater from commercial boreholes is a major source of drinking water in urban areas, yet its quality is often compromised by poor siting and inadequate treatment. This study assessed the physicochemical and microbial quality of water from commercial boreholes in Uyo Capital City, Nigeria. Methodology: Water samples were collected from seven commercial boreholes and analyzed for 17 parameters including pH, conductivity, turbidity, TSS, TDS, chloride, bicarbonate, total hardness, calcium, magnesium, sulphate, total iron, nitrate, sodium, lead, total coliforms, and faecal contamination. Results were compared with WHO and Federal Ministry of Environment standards. Inverse Distance Weighting (IDW) spatial interpolation in ArcGIS 10.7 was applied to generate continuous surface maps of key contaminants. Results: The findings revealed widespread non-compliance with drinking water standards. pH ranged from 4.5 to 6.61, with most samples below the acceptable limit of 6.5-8.5. Total coliform counts (30-40 CFU/100ml) exceeded the 20 CFU/100ml standard, and faecal contamination (20-40 CFU/100ml) was detected at all sites, violating the required 0 CFU/100ml. Other parameters such as conductivity, TDS, chloride, and sulphate fell within acceptable ranges. IDW interpolation successfully visualized contamination hotspots, particularly for microbial parameters and pH, indicating influence from proximate septic tanks and soakaways. Conclusion: Commercial boreholes in Uyo do not fully comply with drinking water standards and pose potential health risks. GIS-based IDW interpolation proved to be a valuable tool for groundwater quality monitoring and public health protection. Recommendations: The study recommends enhanced regulatory enforcement, regular monitoring programmes, improved borehole siting regulations with adequate separation distances from contamination sources, appropriate water treatment such as disinfection and pH adjustment, and public awareness campaigns on the health risks of consuming untreated borehole water.