The Guam Waterworks Authority says the work continues to address the presence of dieldrin in parts of the island’s water system. At this week’s Consolidate Commission on Utilities meeting, GWA officials shared updates on testing results, treatment progress, and next steps in the ongoing mitigation process.

At Tuesday’s CCU work session, GWA presented its formal report on dieldrin – a pesticide banned in the United States since the late 1980s, but recently detected at high levels in Guam’s northern wells.  GWA general manager Miguel Bordallo outlined the timeline on the issue, noting that while dieldrin had been detected in Guam’s groundwater as far back as 2012, the US Environmental Protection Agency required no corrective action at the time.

However, that changed as Guam EPA established its own interim action levels in 2024. "In September we issued the ‘Do Not Drink Water Without Treatment’ advisory”," confirmed Bordallo.

Following that advisory, GWA began installing granular activated carbon (GAC) treatment systems designed to remove dieldrin from affected wells. The first of those systems went online this month at Well Y-15 in Yigo, which remains the only affected well currently in operation. 

“The initial samples that we pulled prior to placing it online did confirm that the treatment is effective with no dieldrin detected in water after the GAC treatment vessels," said Bordallo.

Though Well Y-15 has been cleared, the utility agency says it will continue regular testing at the site and within the distribution system. Two other wells, D-17 in Dededo and M-4 in Mangilao, have also been taken off line and are included in a project for permanent treatment systems expected to be completed by summer 2026.

“We will continue this type of weekly sampling for four weeks and we anticipate at that time that would be sufficient," he said.

Bordallo hoping that after the four weeks of treatment, GWA will be able to request Guam EPA to lift the advisory for each of the affected areas.  GWA has also launched guamwatersafety.com, a microsite containing updates, advisories, and applications for residents seeking reimbursement or assistance with home filtration systems. Approximately 80 of 1,200 affected households have applied for installations of point-of-entry filters, as well as reimbursement for point-of-use systems.

For now, GWA says interim treatment will remain in place until permanent systems are operational and regulatory requirements are met. 

At this time, residents are advised to follow current guidelines and use treated or filtered water until the advisory is lifted.