The Guam Waterworks Authority (GWA) issued Tier 1 health advisory notices to 1,112 customers in Yigo after detecting dieldrin levels above Guam Environmental Protection Agency’s Interim Action Level. The chemical, once widely used as an insecticide and termiticide until production ceased in 1987, was found at concentrations greater than 0.2 parts per billion at one well serving the area. While dieldrin is not federally regulated, Guam EPA established action levels earlier this year to address potential long-term health risks.
The advisory, issued on Sept. 12, applied only to specific households supplied by the affected well. Of GWA’s 43,780 accounts, less than 3 percent were impacted. Officials emphasized that this was not an island-wide notification. Since 2007, GWA has reported water quality test results in its annual reports, and beginning in 2023, dieldrin-specific findings were highlighted following Guam EPA’s review of potential risks.
In response, Upi Elementary School was equipped with NSF-certified water filtration systems on all fountains and cafeteria sinks. GWA also deployed water fill stations and tankers at several Yigo locations, including the mayor’s office, the Yigo gym and the Route 1 pump station, ensuring residents had access to safe water sources not impacted by dieldrin contamination. Construction of a $6.4 million granular activated carbon treatment system at the affected well is slated for completion by summer 2026.
The exact source of the contamination remains under investigation. Officials suggest that soil disturbance during demolition or construction may have released residual dieldrin into groundwater supplies. Guam EPA established its Interim Action Level for dieldrin under authority granted by Public Law 35-115, setting limits of 0.2 ppb for long-term exposure and 0.5 ppb for short-term concerns. Residents seeking more information are urged to contact Guam EPA or visit GWA’s website for updates.