At a Guam Legislature oversight hearing, officials from the Guam Water Works Authority (GWA), Guam EPA and the Department of Public Health told senators that the pesticide dieldrin has been detected in multiple groundwater production wells and that efforts are underway to isolate affected distribution zones, increase testing and deploy point-of-entry and permanent treatment systems.

GWA operations staff said the authority’s distribution system “is a combined, distribution system where the wells pump directly into the piping that goes to domestic supply,” and that water from multiple wells is blended in the pipes, which makes tracing the path of water to individual customers complex. GWA said it used valve closures and a booster pump to isolate part of the Santa Rosa pressure zone and move water not affected by the Y‑15 well into the southern portion of the zone, temporarily taking some customers off Y‑15.

The hearing focused on how far dieldrin-contaminated water may travel in the distribution system, GWA sampling results, and health risks. GWA reported that of 124 tested locations, 32 were non-detect for dieldrin; about 83 locations had detections at or below 50% of the interim action level (IAL); and nine locations tested above 50% of the IAL. Officials identified three wells highlighted in the briefing as Y‑15, D‑17 and M‑4. GWA said Y‑15 typically produces about 600 gallons per minute and that the authority has installed temporary treatment at Y‑15; treated effluent from Y‑15 is now testing non-detect for dieldrin.

Evangeline Nuhan, identified in the hearing as a senior regulatory analyst, corrected a scheduling point about testing frequency: “It just depends on the constituent that we’re testing for. Some of them are required yearly. Some of them are required every 3 years... we do get regular testing for majority of the wells quarterly, but not all of them.” GWA added that, under the IAL, sampling frequencies for dieldrin were increased: Y‑15 is being sampled weekly, the nine wells at or above 50% of the IAL will be sampled monthly, and the remaining entry points will be sampled quarterly.

On health thresholds and toxicology, Sierra Armstrong Bettis (staff member) said the authority set the IAL “right at 0.5 micrograms per liter, and that was to account for the neurotoxic toxicological level, the non cancer, and the cancer levels.” Senator speakers at the hearing contrasted that level with hypothetical lower thresholds tied to cancer-risk benchmarks discussed in previous analyses.

Department of Public Health Chief Medical Officer Dr. Robert Leon Guerrero cautioned that there is no medical antidote: “There is no treatment, for Dieldrin, unfortunately,” he said, describing dieldrin as an organochlorine pesticide historically banned because of neurotoxic effects and later linked in some studies to elevated cancer risks. He and other health officials discussed two possible public-health responses: a full epidemiological study to evaluate cancer risk — which they said could be costly — and more immediate outreach and biomonitoring through mobile clinics and targeted screening. Health staff estimated a smaller community screening program could cost on the order of several million dollars; Dr. Guerrero referenced much larger estimates for comprehensive longitudinal epidemiology studies.

On enforcement and source-tracing, Guam EPA staff said the agency and federal partners are searching for possible contamination sources, including legacy uses in building foundations, demolition, illegal dumping and agricultural application decades earlier. Guam EPA officials told senators the compound is regulated under Clean Water Act authorities for toxic pollutants and that the agency maintains monitoring programs for recreational waters and total maximum daily loads where detections have occurred. Director Lastimosa said Guam EPA had applied for federal emerging-contaminant grant funds and that a five-year, $45 million grant had partially funded capacity-building for the territory’s laboratory services but that the fifth year of the grant would not be awarded.

On testing capacity, GWA laboratory administrator Jennifer Cruz said the authority contracts with a certified external laboratory and that the University of Guam is working to expand local capability: “Eurofins is the largest certified laboratory in the United States, and we have a contract with them,” Cruz said. GWA said most well samples are sent to that contract lab for dieldrin analysis.

Officials also addressed operational measures and timelines. GWA said it has installed temporary point-of-entry treatment at some affected points and expects design and construction work for permanent systems at well sites to take at least a year for design plus construction, with permanent systems targeted to be in place by 2026 for the highest-priority sites. The authority said it would continue monthly confirmation sampling at Y‑15 to support any lifting of a “do not drink without filtration” advisory should treated effluent remain non-detect.

On legal and financial remedies, a GWA legal representative said Guam Water Works Authority has filed claims as a claimant in multi-district litigation against manufacturers and that 3M has confirmed settlement amounts and that GWA had received settlement monies; other defendants (cited in the hearing as DuPont, Tyco and BASF) had approved settlements without confirmed disbursement schedules at the time of the hearing.

The hearing record shows several contested points among officials and senators: whether past annual water‑quality reports provided sufficient public notice of detections, how often individual wells should be retested, the adequacy of the IAL given local exposure factors, the feasibility and cost of epidemiological research, and the time needed to deploy permanent treatment without creating water shortages. Senators asked officials to expand downstream distribution testing in affected pressure zones to clarify which customers are receiving blended water from contaminated sources.

Officials said vending-machine operators and some establishments were allowed to resume using treated water after Guam EPA tested finished water from those vending machines and reported non-detect results for dieldrin. The Department of Public Health said it regulates establishments and that, where vending equipment provides effective filtration (for example, reverse osmosis), finished-water testing can justify reopening.

Senators closed the oversight hearing by scheduling follow-up work. The committees said they would reconvene for continued oversight and would invite additional agencies, including the Department of Agriculture, to future meetings. The record shows the panel asked GWA, Guam EPA and public-health staff to continue sharing sampling data publicly and to consider expanded biomonitoring and community outreach in affected villages.