Bacteriological Assessment of Groundwater from Hand-Dug Wells in Flooding-Prone Communities of Bayelsa State

Annual flooding in Bayelsa State, South South Nigeria, threatens groundwater quality by facilitating faecal contamination of shallow hand-dug wells that serve as the primary water source for many riverine communities. This study conducts a bacteriological assessment of groundwater from hand-dug wells in flood-prone communities of Bayelsa State, comparing pre-flood and post-flood contamination levels. Water samples were collected from 40 wells in Yenagoa and Sagbama local government areas during dry and peak flood seasons. Multiple tube fermentation for most probable number determination and membrane filtration for faecal coliform counts were applied following standard methods. Results showed a statistically significant increase in faecal coliform counts during the flood season, with post-flood samples showing mean contamination levels 4.7 times higher than pre-flood baseline values. Escherichia coli was confirmed in 72 percent of post-flood samples, compared to 31 percent pre-flood. Vibrio cholerae was isolated from two post-flood samples from communities proximate to river overflow channels, highlighting cholera risk. Well construction depth and proximity to flood channels were the strongest predictors of contamination severity. The study recommends elevation of well casing above flood levels, promotion of sealed borehole adoption, and emergency water treatment tablet distribution by the Bayelsa State Emergency Management Agency during flood seasons. Keywords: groundwater contamination, flooding, Bayelsa State, faecal coliform, cholera risk