Improving state-level emergency well disinfection strategies in the United States

After flooding events, well users are encouraged to disinfect their private wells. However, well disinfection strategies are not consistently applied or proven effective. This study examines the science-based evidence that disinfection procedures reduce microbial loading in well water; reviews inclusion of disinfection principles in state-level emergency protocols; and explores research gaps potentially hindering disinfection efficacy. Emergency well disinfection protocols from 34 states were reviewed based on instructions for creating chlorine solutions; circulating chlorine solutions throughout the distribution system; achieving effective CT disinfection (chlorine dose*contact time); and post-disinfection guidance. Many protocols were missing key information about fundamentals of disinfection. Only two protocols instructed well users to verify chlorine residuals and three protocols instructed users to measure water pH. Most protocols recommended that high chlorine doses be introduced into the well, circulated throughout the system, and stagnated for several hours. A CT value estimated to inactivate at least 99.9% (3-log removal) of Cryptosporidium (255 mg-hr/L) was predicted to be achieved by 72.7% of protocols, and estimated CT values ranged from 35 to 16,327 mg-hr/L. Two research gaps identified were determining whether chlorine doses should differ based on well water chemistries and evaluating the appropriate chlorine dose that should be recommended for inactivating pathogens. This effort underscores a need for consistent, evidence-based messaging in emergency well disinfection protocols.