Impact of flooding on water contamination, Tennessee and Kentucky, 2010–2011

Background: Floods are the most common natural disaster in the U.S. In addition to posing the immediate risk of drowning, floods can increase exposure to toxic chemicals and pathogens by flushing contaminants from industrial, agricultural, and waste facilities into rivers and residential areas, and potentially contaminating drinking wells. Despite these concerns, limited information exists on flood water contaminants. Objective: We characterized contaminants in flood water during two flood events and assessed the impact of flooding on well water contamination. Methods: In 2010, we collected flood water (n=10), post-flood river water (n=3), and post-flood well water (n=19) samples in Tennessee. In 2011, we collected flood water (n=15) and post-flood river water (n=8) samples in Kentucky. We collected grab samples and filtered water via dead-end ultrafiltration. We analyzed water samples for microbial indicators (total coliforms, E. coli, and enterococci), human pathogens (including Salmonella, E. coli O157:H7, Campylobacter, Cryptosporidium, Giardia, enterovirus, and adenovirus), nitrates, and atrazine. Additionally, we tested metals in 2011. We compared flood and post-flood concentrations from similar geographic locations using t-tests. Results: E. coli, enterococci, and Salmonella were present in all flood water samples tested for microbial indicators (n=23). In Kentucky, these contaminants were more concentrated in flood water compared to river water sampled three months post-flood (p<0.05). Arsenic and lead were also more concentrated in Kentucky flood water compared to post-flood river water (p<0.05). In Tennessee, one inundated drinking well disinfected prior to the flood contained E. coli, enterococci, Salmonella, and Campylobacter when tested post-flood. Discussion: Our results suggest that flood water contains higher concentrations of some microbial, pathogenic, and chemical contaminants than river water, and also suggest that flood water may cause well water contamination. These findings reinforce commonly recommended guidelines to limit flood water exposure and sanitize potentially contaminated drinking wells prior to use.