HAGTAN, Guam — Guam lawmakers pressed local and federal partners on Dec. 11 over Dieldrin contamination in parts of the island's drinking water, while regulators said treatment and monitoring have reduced immediate risks and set out next steps for a wider investigation.

The joint oversight hearing, convened by committees that include transportation, land use and health lawmakers, followed an Oct. 24 session and focused on recent detections and what agencies are doing to protect residents. "Is the water safe to drink?" the chair asked at the start of the hearing, framing the central question that has driven the inquiry.

Guam Waterworks Authority General Manager Miguel Cverdario described operational responses at the highest-risk production well, known as Y-15. "As of December 9, we have 305 applications" for point-of-entry treatment systems for affected households, Cverdario said, and he told lawmakers that interim treatment at Y-15 produced four consecutive weekly non-detect samples in treated water. GWA also distributed 35,116 cases of bottled water to affected residents between Oct. 2 and Nov. 12 at a reported cost of about $250,000.

Guam EPA Administrator Michelle Lastimosa and senior science adviser Captain Elizabeth DeGrange said the agency formally concurred to rescind the do-not-drink-without-treatment advisory for Y-15 on Nov. 13 after the non-detect results and the utility's mitigation plan. DeGrange said the rescission was coupled with conditions: monthly monitoring for at least a year, documented mitigation and trigger-based reentry procedures for wells that had been taken offline, and a waste-management plan for spent granular activated carbon (GAC).

"We required GWA to test 4 consecutive weekly samples so that we could be certain that the system that was installed is successfully pulling out the Dieldrin from their water," DeGrange said, adding that Guam EPA has added procedures to its risk-assessment document clarifying how advisories may be lifted.

Agencies said work to install permanent treatment systems is underway. Cverdario said the major components for the permanent system arrived on-island and were being staged for seismic retrofit before installation at Y-15; GWA estimated completion of key early elements before the first quarter of next year and said it is accelerating scheduled work at other flagged wells.

Regulators and public-health officials also outlined broader investigative steps. DeGrange said Guam EPA and the Department of Public Health and Social Services plan to submit a joint request to the Agency for Toxic Substances and Disease Registry (ATSDR) for a population-level public-health assessment in early January. "If we're able to secure an assessment under CERCLA, there's the potential for federal funding" to identify, investigate and clean up contaminated sites, she said, and ATSDR's review could take 18 to 24 months.

The agencies described efforts to collect historic monitoring data from military installations and other records to search for possible sources. Peter Bautista, Guam EPA's chief engineer, said military installation projects are subject to pesticide management plans and hydrogeological assessments when ground-disturbing activities occur, but he also noted limited staff capacity and reliance on contracted engineering help.

Department of Agriculture Director Chelsea Munia urged attention to soil and food-safety questions. "Crops that show the highest levels of Dieldrin uptake are cucurbits like cucumbers, melons, and squash," Munia said, and she noted the difficulty of on-island produce testing. DPHSS's environmental public-health officer, Leilani Navarro, told lawmakers that all 11 regulated food establishments in the affected area had been cleared to resume operations after the advisory was lifted.

Lawmakers raised federal involvement, arguing the Department of Defense and other federal partners should help finance investigation and remediation because military activities and legacy pesticide use may be linked to contamination. A community representative also urged that cleanup costs not be borne by local water ratepayers.

Agencies described specific operational details: several wells (M2, D18, EX11) currently have running annual averages below the action level; some wells (M3) are used intermittently and others (M4, D17) remain offline while treatment systems are constructed. GWA said it has transmitted procurement records for POE systems to the attorney general and expects deliveries within four to six weeks after clearance so installations can begin.

Officials also addressed treatment-media disposal: GAC vessels used at production wells will be containerized and shipped off-island for hazardous-waste disposal, and Guam EPA has requested a storage and mitigation plan from GWA for spent media. GWA estimated the in-field lifespan of the GAC vessels for the Y-15 application at roughly six months to a year depending on flow and contaminant levels.

While agencies said the interim system at Y-15 is producing water that meets Guam EPA's conditions, they emphasized that Dieldrin is a legacy pesticide used widely in past decades and that finding a single "smoking gun" source may not be possible. DeGrange said the island-wide pattern suggests legacy contamination in multiple areas and that disturbance of soils during demolition or construction could mobilize bound contaminants.

The committee recessed the hearing until Jan. 7, 2026, at 2 p.m., and agencies pledged continued coordination with federal partners and follow-up reporting to the legislature.

What's next: agencies will prepare the ATSDR request, continue monthly monitoring at previously impacted wells, progress permanent-treatment construction, finalize POE procurement and installations, and provide lawmakers with cost estimates and schedules at the next oversight session.