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Friday’s joint oversight hearing on GovGuam’s response to the dieldrin contamination and detection raised more questions, including why it took several days to weeks for the Guam Waterworks Authority to say when exactly it shut off the Dededo and Mangilao water wells, which both had dieldrin levels over the 0.2 parts per billion cutoff for local “acceptable risk range” for increased cancer risk. Delaying response to a simple question about the banned pesticide in water wells does not inspire confidence, when customers are already wary about the safety of water coming from their tap since the Yigo notice came out on Sept. 12. GWA and the Guam Environmental Protection Agency since September indicated that the Dededo and Mangilao wells were turned off. But it was only on Friday that the shutoff dates were publicly disclosed. GWA also has not responded to inquiries on whether any notice will go out to customers served by Dededo water well D-17 or Mangilao water well M-4, considering that the wells were just recently turned off. And how soon can GWA test other water wells again, outside of Yigo, Dededo and Mangilao? Consider the information so far been disclosed. Dededo D-17 well, near the Northern Community Health Center: 0.3247 ppb average in samples from 2022 to 2023.0.2425 ppb average in samples taken between July 2024 and May 2025.Well was shut off on July 31, 2025, per GWA.But it was only on Oct. 24, 2025 that GWA told the public, during the oversight hearing, when the well was shut off.Guam EPA started requiring on Aug. 1, 2025 public notification when dieldrin is detected above the interim action level of 0.2 ppb. The Dededo well shut off was just the day prior to that requirement going into effect.Long-term consumption of water with over 0.2 ppb of dieldrin has “unacceptable” risk of developing cancer, Guam EPA said.0.47 ppb in November 2022At concentrations higher than 0.5 ppb, liver damage and other health concerns begin to present.0.279 ppb in June 2021. Why didn’t GWA inform Dededo residents that well D-17 also had over 0.2 ppb of dieldrin based on samples taken up to May 2025, at the same time it notified impacted Yigo residents for samples taken up to July 2025? Mangilao M-4 well, in the Adacao area near Marbo Cave: 0.17 ppb in samples taken between July 2024 and May 2025.This well was shut off this month, but GWA couldn’t recall when exactly.This information was publicly shared only on Friday.0.2278 ppb average in samples taken from 2022 to 2023.0.41 ppb in October 2013. Guam EPA has yet to decide when the “do not drink without treatment” advisory can be lifted for Yigo water well Y-15, where contamination is the highest at 1.76 ppp. While this advisory is still in effect, impacted Yigo residents are not supposed to drink, cook, or brush their teeth with water coming out of their taps in September. Test results for treated water at Y-15 are clear for dieldrin but Guam EPA said it is still conferring with the U.S. Environmental Protection Agency and other jurisdictions about when the advisory can lift. How did other areas successfully deal with dieldrin contamination? We look forward to the permanent treatment for the Yigo, Dededo and Mangilao wells. Once again, local agencies knew from federal regulators since at least 2008 and again in 2012 about dieldrin in Guam water but no clear communication to the public about what it meant then. GWA said it’s because there was no “significant deficiency” identified then, and dieldrin is still not a federally regulated drinking water contaminant. It’s only on Aug. 1, 2025 that Guam EPA started requiring GWA to notify customers when dieldrin is detected above the interim action level requirements of 0.2 ppb. But even then, as Sen. Chris Barnett stated during the Friday oversight hearing, GWA and Guam EPA should have informed the public more clearly about dieldrin. “Hawaii chose to inform its people as far back as 2015 even though this dieldrin wasn’t, isn’t regulated by the federal government,” he said at the hearing. “Erring on the side of caution, being prudent, absolutely, the people of Guam should have been told, informed.” We also look forward to updates from GovGuam about its planned investigation into the source of the still ongoing contamination of Guam’s groundwater, decades after the cancer-causing dieldrin was banned in the U.S. in 1987.
