Résumé
This study looked at the effect of depth on the microbial pollution of shallow wells in the three floodplains of Makurdi metropolis of Benue State, Nigeria. Water samples from the wells were collected and analyzed monthly for seven months from February to August (covering both wet and dry seasons) using the pour plate technique. The assessment was for the presence coliform bacteria. The species isolated were Salmonella typhilis, Escherichia coli, Streptococcus faecalis, Proteus spp. and total coliform. The pollution of wells was found to increase with decrease in depth and decrease with increase in depth. The water table varied from 4.3m (in wet season) to 6.4m (in dry season). Generally pollution level in the floodplains was between 17cfu/ml and 297cfu/ml of bacterial population. No well studied met the limit by World Health organization (WHO) for drinking water which is 0cfu/ml and 10cfu/ml by the National Agency Food and Drugs Administration and Control, Nigeria (NAFDAC). This shows that wells must be up to 15m deep so as to be free from pollution. Screening the wells to the depth of 15m and treatment by disinfection before drinking were the recommendations made.