Hurricane Floyd (September 1999) caused extensive flooding in North Carolina and adjacent Atlantic coastal areas. In the flooding, thousands of homes were made uninhabitable and 48 people died. Potential fecal and pathogenic bacterial contamination of wells due to their immersion by flood waters was identified by state authorities as a significant health risk, consistent with other flooding events. To restore many of the 12,000 affected wells, over 2000 of which showed total coliform positive (potentially unsafe) results, wells were disinfected in the affected areas. However, a significant fraction of wells were still not providing coliform-free water after multiple treatments. Disinfection methods developed for preventive use, or to inactivate bacteria introduced during service or other small-scale contamination may be inadequate in response to flood water inundation. Flood waters contain very high loads of sediment, debris, and chemical and biological contaminants. Significant depth of immersion can force contaminants into the aquifer formation.
To improve response to such large-scale flooding events in the future, the U.S. Federal Emergency Management Agency (FEMA) identified the need to develop procedures and protocols for emergency well disinfection that it can recommend to state and local emergency management agencies.
FEMA commissioned the National Ground Water Association to conduct a study and provide recommendations for improved practices to respond to such mass flooding-immersion events. NGWA chose Ground Water Science to conduct the work, which we completed on a rapid schedule in 2002 with the help of EGIS PA, Chapel Hill, NC. The report was duly prepared, submitted to and accepted by FEMA, then never seen again. Some derivations were published and the work formed a basis for recommendations by NGWA after other big flooding events such as Hurricane Katrina. However, we thought we should (with NGWA's permission) publish the full report.
The last chapter has a series of recommendations for emergency management preparation for and rapid response to a mass flooding event that inundates large numbers of wells. We hope you find this useful and look forward to your feedback.
The full report is attached below.